Acoustic (Air) Suspension

[Zilch]

It's been a very long time since I've worked with or listened to small closed-box speakers, a design approach pioneered by "East Coast Sound" proponents of the '60's - AR, Advent, KLH, etc.. Building DIY Minis recently led me to trying that approach with JBL drivers, with good result.

A little research in Dickason's Loudspeaker Design Cookbook serves as a refresher on the essentials:

1) A good starting DIY project - easy to build and easy to succeed; the alignments are not critical.

2) Excellent extended bass, as the rolloff is just 12 dB/octave.


3) Driver parameters:
EBP = Fs/Qes < 50
Qts > .3
Low Fs
High Xmax
High MMS

High Vas



4) Box size - for true air suspension, < 1/3 Vas.

5) Easy to measure (test) and understand.

There's not many JBL drivers that qualify, but BB6P EBP meter identifies these potential candidates:

116A, H, H-1
123A
125A
127A, H
2145A
2213

Another group, more intermediate between closed and vented designs includes:

2245
508G
LE10A
LE8T-8
Sub1500



[Lists subject to change without notice.... ;) ]


I have been using a $15 yard sale pair of AR4x as test boxes (18.45 l, 0.652 cuft gross internal volume,) but recently discovered that the OASR "Dr. Seuss" horn would just fit. Ut-oh:

3" hole saw and small Sawzall make the "clover-leaf" cutout for the OASR horn with 2407H neodymium tweeter.

708G-1 8" woofer fits perfectly. I'm trying others, too.

Control 128W crossover (2.5 kHz) plus notch filter on the woofer and L-pad + compensation cap on the tweeter gives immediately satisfying results, bottom.

Off to critical listening tests, soon.... :thmbsup:

[Hoerninger]

Zilch,

be so kind and explain the difference between the orange and green graphs.
___________
Peter

[moldyoldy]

Glad you feel the 2245 (sorta) qualifies Zilch, as I'm playing with some in A-S mode.

Another characteristic;

Excursion at resonance is minimized. Therefore, unlike BR designs, you don't have to quit at Fs (yay). Naturally, there's a catch, small boxes raise the system resonance and introduce a parameter not used in BR design, Fb. Suddenly, your 20Hz Fs driver has an effective resonance of 40Hz or more (boo). No problem, just apply 12dB-sloped EQ, and take it back down, way down (yay), as long as you can supply enough juice and your driver can take it (boo). You also no longer have a port to integrate with its' chuffing, one-note bass (yay). Critical damping via stuffing density can be tricky to achieve, but when you get it, it's smooth as a baby's butt.

My favorite A-S design was Roger Russell's (McIntosh) ML SYSTEM. I emphasized system, because it needed the active EQ unit to work as intended, something many owners never understood, so they didn't buy the EQ with the speakers (big mistake). The EQ gave 3, 6, or 12dB boost at 20Hz, which allowed one to compensate for placement and room gain, and run flat to 20Hz without blinking.

Great thread topic, and something new to DIY. I know you had a big grin taking the sawzall to an AR box.

And don't worry, we won't make you move to Boston.

[johnaec]

Zilch - that's got to be the ultimate "bookshelf" system. ;)

John

[Zilch]

Zilch, be so kind and explain the difference between the orange and green graphs.Hi, Peter.

The orange is the nearfield response of the woofer at 1" or less, running through the filter, showing what's happening at the very lowest frequencies, particularly the rolloff. I don't even bother turning off the tweeter for that measurement; you can see it still playing down 30 dB there. You can also see I've notched down ~400 - 1 kHz in the woofer response (perhaps too much for this one, actually,) to get rid of the hump in response common to several 8" drivers in this alignment.

The green is the full system response at ~1 M. I've shown both RTA and non-windowed MLS, separately. There's boundary and room response effects inculded in those, of course. A purist would stitch groundplane or nearfield LF and windowed MLS HF response together to show a composite pseudo-anechoic response curve instead, but these separate curves pretty much show what's going on.


Great thread topic, and something new to DIY. I know you had a big grin taking the sawzall to an AR box.Heh, heh. I jus' KNEW there were others out there, tho some members might desire I show less of the gore. :p

I sure wish Giskard were here to participate. He likely knows the full skinny on this inside and out.

A/S bass certainly has a different character from that of the vented systems we're used to, as much different as bass horns, I would imagine, though in an other way. Transients have something to do with it, and the tonality seems more "natural." Anyone running Sub1500 in a small closed box, for example, knows what it's like.

I'm thinking there's a way to match the inherent power compression and system "Q" to equal loudness contours for an expanded SPL range without EQ. It's certainly easy to get sweet-sounding bass at moderate levels in a modest-size package with this.


Zilch - that's got to be the ultimate "bookshelf" system. ;)Well, there's precedents. :D

In addition to the entire "other" industry, JBL themselves makes a couple of products configured this way:

http://www.jblpro.com/pub/cspels/CSP18.pdf

http://www.jblpro.com/ae/am4200_95.html

Those're both vented, tho.

Performance Series is closed box.

I'm starting to consider more what the cone material is and how well it plays the mids, too. The woofer does the lion's share of the musical content work in these....

[Chas]

Cool idea Zilch. Even though the idea of a 2235H in a sealed box may not seem to make sense, I tried it with a 5cu.ft (4505 box) with medium fill and with EQ it was pretty darned good, somewhat along the lines of the old McIntosh ML/MQ systems from the 70's, someone mentioned above.

The MAC's were damned good in their day if correctly set up.

Even without EQ, the 2235H was impressive.:)

[duaneage]

My favorite box of all time is the sealed bandpass. I have built quite a few of them and always enjoyed the performance of any driver in this configuration. The transient response of a sealed system will usually be superior and accurate than a vented box because of the gradual rolloff and better phase characteristics. Amplifiers also prefer the impedance curve of a sealed system over a vented one.

A/S bass certainly has a different character from that of the vented systems we're used to, as much different as bass horns, I would imagine, though in an other way. Transients have something to do with it, and the tonality seems more "natural." Anyone running Sub1500 in a small closed box, for example, knows what it's like.

The difference is in the low end rolloff. As a transient signal, such as a bass drum, decays it's fundamentals are very low. The vented box cuts them off while the sealed box responds to the note. The vent in a ported system is a strict component in how it operates while the air in a sealed box offers variable damping in both frequency and amplitude. With big enough drivers and large boxes sealed systems are truly spectacular. The only drawbacks are lower efficiency ( -3 db less) and greater cone movement ( higher distortion compared to a vented box operating at the port frequency) although Qtc has a LOT to do with the cone movement, distortion and ringing performance. I prefer .707, others like .5 or even 1.2

I have built more sealed systems than vented, although it was with non-jbl drivers that I worked with. JBL has always been a ported box company it seems.

[Zilch]

How about the "Plenty available from L100 partouts" 123A-1?

How high do they play well? Clearly not 2 kHz, e.g., in L88, but if 1 kHz, that would open up a bunch of good DIY options for HF, maybe....

Edit: L100 woofer only 1" nearfield, port closed. Fc = 56.19 Hz, Qtc (as Qts) 1.25. Still a boomer, just a little less so:

[1 kHz looks "workable," at least insofar as it BEING there is concerned.... :p ]

[Zilch]

Take NO prisoners!

Two-way @ 1.2 kHz.

[Windowed HF, cyan, bottom.]

[Zilch]

I'm not about to take the SawZall to this L100, of course, but since it's on the test stand, here's a look at performance of this one in comparison to the experimental two-way above.

I'm providing RTA and unwindowed MLS results for the same 4 conditions:

1) Presence and Brilliance controls at "0", red.

2) My best attempt at dialing it flat, LE5-2 (Presence) virtually off, and LE20-1 (Brilliance) at -2, green.

3) Same, but LE20-1 full on, to see VHF response, orange.

4) Two-way with PT-F95 waveguide from above, Presence and Brilliance full off, external crossover, cyan.

The "problems" with this L100, if I may call them that, are:

A) Boomy bass.

B) Brilliance and Presence both operate in the HF ~10 kHz. It's not possible to adjust mids and highs independently to achieve good balance.

C) LE20-1 dies at ~12 kHz.

D) Sounds terrible - can't mitigate the "forward" rising midrange successfully.

Anyone else have L100s they can measure similarly? It'd be interesting to see if it's just mine behaves like this....

[Zilch]

From the start, this L88 is certainly better balanced (orchid) than my L100, above. If this is chacteristic of the genre, I think I'd forgo the "plus" process and just do the factory recommended replacement of the tweeter with 035TiA to fix the VHF.

http://manuals.harman.com/JBL/HOM/Technical%20Sheet/L88%20Nova%20ts.pdf

However, I do also hear the midrange muddiness rotormotor speaks of:

http://audioheritage.org/vbulletin/showthread.php?t=12077

Upgrading the HF to a mylar-diaphragm re-entrant annular-ring compression driver on a progressive transition waveguide with a lower (~1.2 kHz) crossover frequency improves the situation substantially (cyan). Getting a low-pass filter on the woofer is part of this, also (nearfield LF, orange). Stock, it runs full range.

Still a bit "boxy" sounding, I'll adjust the damping with more fill.

Note port closed for acoustic suspension bass using Zilch's proprietary box tuning device. :p

Fc = 60.94 Hz, Qtc (as Qts) = 1.24

[Hoerninger]

Note port closed for acoustic suspension bass using Zilch's proprietary box tuning device. :p

Great tool. ;) :applaud: ;)
___________
Peter

[Zilch]

Re: #10, above:

In fairness to L100, per Mr. Widget:

http://audioheritage.org/vbulletin/showpost.php?p=42004&postcount=3

I measured on tweeter axis. See his observations with respect to this there.

So, "Blown Away" orientation is correct, then.

[Or, lying in bed.... :p ]

[Zilch]

An interesting case, L88.

I was puzzled by the bass response measurements I was getting, closed box versus ported.

BB6P tells the story (below).

Ported L88 LF rolloff is already ~12 dB/octave (red) in this alignment.

Closing the port apparently gets rid of the 85 Hz bump very nicely, but only slightly extends the bass response. Typical fill (grey) vs. heavy fill (black).

Group delay is substantially improved with port closed (bottom).

[Where's GISKARD, dammit! :banghead: ]

[allen mueller]

I use 2 121a's in separate sealed enclosures as stereo subs. I absolutely love the way they sound.

Allen

[SETriode]

So Zilch I was just wondering how much the tone of you l100's in that picture changed because blocking the port seems like a very easy thing to do and I am bored enough to try it. I know I'll lose some efficiency but it shouldn't be that big of a deal. I think it would from what has been described change the bass from a thump to more of a roll. Also I won't damage my midrange by putting all that pressure on it will I?

[Robh3606]

Also I won't damage my midrange by putting all that pressure on it will I?

No the midrange is in a subenclosure.

Rob:)

[SETriode]

Now I just need to figure out how plug the port. I wonder if that metal thingy Zilch has would work for the intake of the port inside of the cabinet? If not I can always stick it on the outside and call it a "boutique" tweeter.

[Zilch]

I know I'll lose some efficiency but it shouldn't be that big of a deal.If what's shown in the BB6P simulation (and my measurements) is correct, what you lose is not bass efficiency, but rather, the entirety of the anomalous "bump" from 50 - 400 Hz, to which L100's boominess is largely attributable.

Many L100 lovers would miss that artificial bass coloration initially, but with time, perhaps, appreciate the more natural bass and improved transient response. You can see that the low bass frequency response remains essentially the same, which is my experience listening to the L88s nearfield. I suspect I could actually put them next to a wall now, to extend the bass response via boundary effect, without them booming me to death.

What's stunning is the difference in behavior of the cone. It's loose and floppy with the port open. Once you plug the port, the effect of the enclosed air "cushion" is immediately apparent in the stiffness of the suspension.

The port in my L100s is 2.75", and the 3" plug type shown required a bit of filing of the rear metal disk to get it to fit, so a little effort may be required. It's a $3.49 plumbers' test plug from the hardware store. The L88 ports are 3", so no problem there, just pop it in and tighten. You'll be listening to the difference in a matter of minutes, in either case....

[Zilch]

Now I just need to figure out how plug the port. I wonder if that metal thingy Zilch has would work for the intake of the port inside of the cabinet? If not I can always stick it on the outside and call it a "boutique" tweeter.With proper handling, you can enjoy the benefit of MANY six-packs from your pals as they try to induce you to disclose the secret of your new L100 tuning.

Occasionally go over and tweak the wingnut while they're listening.

"THERE, that's MUCH better now, don't you think?" :p

[moldyoldy]

Zilch, you could up the wager from 6'ers to cases by using an inflatable test plug instead of compression (found only at wholesale suppliers). An added bonus is the much wider range of ports a single plug will cover (balloons also work in a pinch as temps). No need for a compressor, an old football pump and adapter, or a bicycle pump, works fine. The reaction from observers is....what you'd expect.

The reduced excursions you note can have a big effect on driver longevity, not to mention reduced distortion by keeping things within their range of linear response. Excursion becomes less of a factor for max response, as coil burnout takes its place as the limiting factor.

[Hoerninger]

The reduced excursions you note can have a big effect on driver longevity, not to mention reduced distortion by keeping things within their range of linear response. Excursion becomes less of a factor for max response, as coil burnout takes its place as the limiting factor. At another place in this forum Steve mentioned Tom Danleys recording of July 4th fireworks:

http://audioheritage.org/vbulletin/showpost.php?p=122314&postcount=18
It's unbelievable! :thmbsup:
And a great task for closed boxes.
:thmbsup:
____________
Peter

[SETriode]

Ahh that is a drain plug! I recognized it vaguely but was drawing a bit of blank. Later tonight I think I'll pull one of my woofers out and measure the opening to the port on the inside so i can keep my l100s lookin pretty especially once my 104h-2 midranges arrive:bouncy::applaud::bouncy:. Should i also go out and grab some acoustistuff for the cabinet? I think last time i looked in there it was pretty spartan.

Ooooo this weekend is gonna be sweet with my new amp and "new" l100's!!!

[Zilch]

Later tonight I think I'll pull one of my woofers out and measure the opening to the port on the inside so i can keep my l100s lookin pretty especially once my 104h-2 midranges arrive:bouncy::applaud::bouncy:Closing the port at the front recovers the duct volume into the box, even though it stays in place. This will provide a bit more bass extension than plugging it inside the box.


Should i also go out and grab some acoustistuff for the cabinet?I haven't completed my damping determinations, but they're sounding a bit "boxy" with just the stock insulation in there.

Maybe you try different fills and help us out with that part. :thmbsup:

[If they sound like poo, remember it'll take four to six weeks for them to break in.... :p ]

[Phil H]

Zilch,
I was curious if the black woofer in the L88 has a folical with a model number. Was there a 123A without the -1 or -3?

[Zilch]

Was there a 123A without the -1 or -3?Well, I don't remember now, but I'll be opening it up again to change the damping in the next day or so, and will make a point of documenting that; it's important.

The nearfield bass response of the two woofers is a bit different, so I'm thinking of measuring a bunch of them in the same box, too. I have four 123As and two 2213s here somewhere, I think. Also want to measure some D123s.

That's more like something for the weekend. It'll be interesting to see what WT2 says about all of them. Gotta take out all the insulation and measure the interior dimensions precisely to get it right.

[It's tough pullin' them outta L100s.... :p ]

[duaneage]

A friend of mine showed me his L88Plus speakers and thought they were the best thing he ever heard. I shoved a rubber ball into each port and he remarked that the bass was " all gone".

After a few songs and a little more volume he began to agree that they sounded better. Repositioning them against a wall increased the low bass output a little and they did handle more power that way. The rubber balls remained.

Zilch has proven that using a driver different than what it's T/S parameters suggest may be a good marketing trick but in the end it's better to do it right. I wonder if the world wide supply of drain plugs will be affected by this. Might be a good time to stock up.

[SETriode]

Well i didn't make it to the hardware store tonight, so i decided to stuff a rolled up towel into the port on my l100 and wow it is sooooooooooooooooooooooooooooooooooooooooooooooooo oooooo much better. these things are actually listenable now!

[SETriode]

Think i might have found an alternative to the towels, rubber balls or metal drain stoppers. Think it would stay in there or get shot out at listener level?:blink:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=230005969101&ssPageName=STRK:MESE:IT&ih=013
More (http://www.audioheritage.org/vbulletin/newreply.php?do=newreply&noquote=1&p=123734#)

[Zilch]

The plumbers' test plug is rubber, actually. The metal plates squeeze a thick rubber washer when the wingnut is tightened to make a secure seal.

Wingnut in the way? Replace with a hexnut and a shorter carriage bolt.

[Cheaper than that stopper, too.... ;) ]

[Zilch]

By coincidence, Audivex had a 2213 recone on the bench today illustrating a failure mode from overexcursion. I snagged the old cone from the trash.

Theory: flexure occurs in the cone itself where it "rounds over" to meet the accordian surround, which creates an annular weak spot over time:

[Zilch]

Zilch has proven that using a driver different than what it's T/S parameters suggest may be a good marketing trick but in the end it's better to do it right.It's been mentioned several times in the past in these forums; I can't claim credit for anything other than not ignoring the good advice previously posted here.

[And maybe having an "easy fix" available.... :p ]

Calculation update: 2213 (123A-1) in L88. Blk = port closed, heavy fill (yet to be determined). F3 = 48 Hz, Qtc = 0.838. Usable bass (-10 dB) to 30.41 Hz (cursor).

[SETriode]

I know the plumbers plug would probly work better, but I was looking at the other plug on ebay for its aesthetic quality of being black versus the look of shiny metal. While I could paint the fancy one up all pretty and throw an acorn nut on it instead of the wing nut I think the black plug might just dissappear better. That and I don't want to have to prep prime and paint something........

Oh and Zilch even though you may not be able to take credit for coming up with the idea to use a driver as it is intended, plugging the ports with a plumbers test plug will from this day forward be known as the "Zilch mod" :applaud:. Congratulations on your new legacy!:cheers:

[ngccglp]

Hi Zilch,

Great thread. I'm getting too much bass from my L222 in my small room. For a while, I've been thinking of removing the passive radiator and sealing up the opening to make the L222 into a A-S design. Is that recommended for the L14A?

Thanks

[Zilch]

LE14A isn't on the "closed box" list, but you might explore what would happen with WinISD.

I think I'd try tuning the passive radiator per L220 first. There's info in some threads here. L222 has the boomy "Disco" tuning, as I recall.... :p

[edgewound]

LE14A isn't on the "closed box" list, but you might explore what would happen with WinISD.

I think I'd try tuning the passive radiator per L220 first. There's info in some threads here. L222 has the boomy "Disco" tuning, as I recall.... :p

That's an easy one. The PR300 has a number of mass-loading discs that are attached to the backside under the dustcap via a 10-32 machine screw. Simply take out the PR300 and remove one disc at a time, remount and listen. The factory did that by design so the user could adjust the bass response.....pretty cool feature. Just make sure the screw isn't too long to break through the dust cap when only one disc is used. Some versions used paper discs, some used metal discs.

[grumpy]

While you're experimenting...

might also consider -adding- weight.
(swap fiber disc out, metal disc in, if bolt-length limited)

-grumpy

[edgewound]

It's been mentioned several times in the past in these forums; I can't claim credit for anything other than not ignoring the good advice previously posted here.

[And maybe having an "easy fix" available.... :p ]

Calculation update: 2213 (123A-1) in L88. Blk = port closed, heavy fill (yet to be determined). F3 = 48 Hz, Qtc = 0.838. Usable bass (-10 dB) to 30.41 Hz (cursor).

Just to keep the facts straight and not embarrass anyone...the 2213 is the same a 123A-3

123A-1 is the same as 2212.

....and as grumpy pointed out...adding a little mass could also be a cure for boominess...depends on your room.

[SETriode]

Stuck some poly fill inside my l100 cabinet today after installing my 104hs and I wasn't too impressed. Perhaps I'll have to start experimenting later, but in this application (where the woofer half of the midrange) i think you've got to pick either blocking the port or stuffin the box with insulation. Polyfill was just too much and all i had left was HF and upper MF, so for right now I'm gonna leave em be and enjoy my new amplifier and midranges. Which if you have an l100 i strongly advise and upgrade to 104h's

[Zilch]

123A-1 is the same as 2212.Well, HELL.

Now I gotta make more plots.... :D

[edgewound]

Well, HELL.

Now I gotta make more plots.... :D

Just wanted to keep you off the streets Zilchster!:D

[ngccglp]

Hi Edgewound and Grumpy,

Can I clarify - more heavy weights equal less bass? or vice versa?

Thanks

[Rudy Kleimann]

The reduced excursions you note can have a big effect on driver longevity, not to mention reduced distortion by keeping things within their range of linear response. Excursion becomes less of a factor for max response, as coil burnout takes its place as the limiting factor.

In defense of A-S designs, the nicest thing about sealed boxes is the lack of delay in output near resonance, not to mention the lack of wild swings in output delay depending on what frequency the sealed box woofer is reproducing. It is, simply put, "faster" and more integrated time-wise with the other frequencies being produced at the same instant. "Time aligned" comes to mind right now...:hmm:

However...

Don't forget the AlNiCo's are bad about suffering demagnetization from over powering... so watch it with your vintage AlNiCo woofers, or you'll end up with a driver that needs reconing so it can first be re-magnetized. :( Output goes down across the board from box resonance all the way up to where the midrange or HF finally takes over. All the while you're thinking how "safe" your drivers are in their new sealed box home.
Add to this the loss of LF output of an A-S system compared to a ported driver system, and you'll be wanting to put more power to them automatically. We all know JBL coils can handle power... pretty soon you could be asking yourself "what happened to the lows and mids?":dont-know

Regarding distortion vs. excursion, any ported system should be rolled off sharply below the tuned frequency of the ported box anyway. I never run a ported system without a steep cut-off high-pass filter set about 7% below tuned frequency of the box. See the user manuals on the BX63 bass filter or the dipswitch settings inside the 5234,5235 crossovers for more info. While you're at it, note that you can tune a ported box 1/2 octave lower than normal and add a 6 dB narrow-band peak at the new frequency and extend the output of the ported system 1/2-octave lower if you have the power and the speaker can handle it... that is the purpose of the BX63 and the other dipswitch settings in the 523x crossovers.

Notice also that most of the DBX PRO (another Harman brand) crossovers, EQ's and signal processors are equipped with switchable 40Hz high-pass filters to protect the 40Hz tuned JBL PRO cabinets (virtually all JBL PRO cabs are tune to 40Hz). Other electronics MFG.s also provide this function in their gear. Makes a world of difference in the sound quality, whether it's on a 25,000 watt FOH stack, a 500-watt stage monitor system, or a 100-watt amp at home.

If you don't eliminate the signals below box frequency, you'll:

A: beat the woofer to death, since the ported box basically "unloads", letting the woofer flop uncontrollably while at the same time the port delivers out-of-phase output that cancels the woofer output and even helps push the woofer even farther. Suspension components get stretched out of shape permanently. Even with a modest amount of power, the coil can bottom out in the magnet, quickly destroying the coil.:eek:

B:waste a lot of Amplifier power, to the point of creating amplifier clipping while it delivers signal that the speaker system can't even reproduce.

C: create a lot of harmonic and intermodulation distortion from extreme cone travel. And power compression from heated-up voice coils...

If you do roll off these frequencies, all of these "disadvantages" relative to a sealed box are virtually eliminated. In a ported cabinet, there are a narrow range of frequencies somewhat above the box tuned frequency that excursion is slightly higher (for the same SPL level produced) than would be in a closed box, but not by much. OTOH, the increased loading by and acoustic output generated by the port in a tuned box system dramatically lowers cone movement (and distortion generated by long excursions) is a benefit over a broad range of frequencies. As the frequency goes down near resonance in a ported cabinet, cone motion reduces to the point that the woofer barely moves at all near resonance, where the A-S woofer moves farther and farther as you go down in frequency toward resonance.

[Rudy Kleimann]

Hi Edgewound and Grumpy,

Can I clarify - more heavy weights equal less bass? or vice versa?

Thanks

More weight lowers the tuning frequency which also lowers the output above the tuned frequency. If there is a peak in output above resonance before adding weight, the peak will be reduced while at the same time the heavier weight will yield deeper bass.

The same is true of ported cabinets with a port longer than stock, a la L100...

The problem with the L88/L100 is the cabinet is too small for flat, deep response anyway, esp.for ported use with that 123A woofer...

[Zilch]

However...

Don't forget the AlNiCo's are bad about suffering demagnetization from over powering... so watch it with your vintage AlNiCo woofers, or you'll end up with a driver that needs reconing so it can first be re-magnetized. :( Output goes down across the board from box resonance all the way up to where the midrange or HF finally takes over. All the while you're thinking how "safe" your drivers are in their new sealed box home.

Add to this the loss of LF output of an A-S system compared to a ported driver system, and you'll be wanting to put more power to them automatically. We all know JBL coils can handle power... pretty soon you could be asking yourself "what happened to the lows and mids?":dont-know .Speaking specifically of the L88/L100 alignment, I was surprised to discover that the 123Ax is already operating with quasi-2nd-order rolloff ported in that too-small box.

If the BB6P analyses are correct (and I do wish some others would run them to be certain,) closing off the port merely strips off the LF bump (e.g., #32, above,) the overall efficiency throughout the range remaining the same, while a bit of LF extension is picked up concurrently.

I'm hearing "too much bass" as the primary complaint, so "wanting to put more power to them" doesn't seem to be concomitant with removal of the "boom" in this case.

For my own part, working with L88, there's still too much bloom, even freefield, which I'm addressing with additional damping to further lower the Qtc. BB6P says heavy vs. typical fill should lower it by 0.1, i.e., from 0.948 to 0.838, with one driver variant in particular, a substantial improvement.

I'm not getting those kinds of numbers here in my own measurements, but just now pursuing it more precisely in a controlled manner to report here....

[Rudy Kleimann]

Most people who own L100's (or other AlNiCo systems like the L26 and L36) and plug the port will notice LESS bass, and will have an urge to turn up the bass before they realize what the truth is, response-wise. And, with no flopping of the cone and all the focus on the cone control afforded by the A-S design, some may want to see how much they can get out of the woofer in this "new" box. Wouldn't want to see or hear about any "long faces" when they realize it is too late, since demagnetization is only reversible by ripping the cone out to recharge the magnet. That's all I was getting at. Moldyoldy had al;ready brought up the coil burnout issue...


It is well known that the box size was chosen for suitability as a near-field monitor. JBL figured that any bigger cabinet would knock it out of the running. How large would be tolerated sitting atop one of the two most important -and expensive- components of a studio? (cabinet crashes onto the control surface). It was also designed to emulate the sound of the old Altec/Urei duplex monitors that were the industry standard then, while sitting out in the middle of the room with no boundary reinforcement. Hence the boomy bass.

I find it surprising that BBPRO says the 123A in the cab is a good alignment. We all know it is not just by listening to them. Sure you didn't miss on your measurements or your math? On a box that size, a little means a lot re: percentage of volume change.

The A-S "Q" is too high, as you can see and probably hear. That is why I said the box is too small for either, really, IMHO.

[Rudy Kleimann]

Stuck some poly fill inside my l100 cabinet today after installing my 104hs and I wasn't too impressed. Perhaps I'll have to start experimenting later, but in this application (where the woofer half of the midrange) i think you've got to pick either blocking the port or stuffin the box with insulation. Polyfill was just too much and all i had left was HF and upper MF, so for right now I'm gonna leave em be and enjoy my new amplifier and midranges. Which if you have an l100 i strongly advise and upgrade to 104h's

If you're trying to run it as a ported system, you have to make sure the airflow through the port on the inside of the cabinet is unrestricted. Allow 3"-4" minimum clear space all 'round the inside end of the port. Same goes for getting up against any of the moving parts of the woofer, including the tinsel leads. Use cheescloth stapled back as appropriate to hold the insulation.

Also, try fiberglass inside of polyfill. It just plain works better. And use only long-strand fiberglass -the short stuff can get into places it shouldn't, like the voice-coil gap-

Filling or stuffing the box adds virtual volume -up to 30-40%, which will tame the peak and lower the cabinet tuning -which helps in either case, ported or A-S.

[Zilch]

I find it surprising that BBPRO says the 123A in the cab is a good alignment. We all know it is not just by listening to them. Sure you didn't miss on your measurements or your math? On a box that size, a little means a lot re: percentage of volume change.

The A-S "Q" is too high, as you can see and probably hear. That is why I said the box is too small for either, really, IMHO.BB6P wants bigger for Q = 0.707, yes.

I'm just exploring, given the box size of L88 and/or L100, which alignment is "better." I outlined elsewhere here how one might build an improved closed-box version using 123Ax per BB6P suggested volumes.

Part of this also comes from wondering what's being done with all those 123Ax woofers dumped on the market by chop shops over the last couple of years. :dont-know

[Zilch]

R21 is high-density fiberglass insulation, 6" thick. It's what I had on hand here, purportedly better than normal density for this. Added benefit is I now have two densities in the box, each presumably optimal over a different frequency range.

Impedance, phase, and nearfield (~1/4") frequency response, before and after installation of fill augmentation.

Black cone 123A woofer:

[Zilch]

White cone 123A woofer and both overlaid, bottom.

Tamed 'em both 1.5 dB @ 80 Hz. :thmbsup:

Lowered Qtc 0.07 and 0.13. :thmbsup:

Qs now matched within 0.05. :thmbsup:

Lowered Fc of both ~3 Hz. :thmbsup:

Fcs now matched within 0.09 Hz. :thmbsup:

Leveled notch @ 240 Hz. :thmbsup:

MF unaltered, looks like. :thmbsup:

[clmrt]

Right now, this is my favorite thread on the intraweb.:applaud:

Call me when we get into Aperiodic vents.;)

[Zilch]

Call me when we get into Aperiodic vents.;)Empiricism is the path to enlightenment. Get to WORK! :thmbsup:


Stuck some poly fill inside my l100 cabinet today after installing my 104hs and I wasn't too impressed.Isolate the variables. Measure. Learn. RTA's a good start.

Just look at what that woofer's putting out in the upper midrange:

[Zilch]

Zilch,
I was curious if the black woofer in the L88 has a folical with a model number. Was there a 123A without the -1 or -3?Nope, identical to rotormotor's. Surprisingly, the white one's the same, no foilcal or serial number. Only ID is the part number stamped on the cone. Both have intact red wax seals:

[SEAWOLF97]

Note port closed for acoustic suspension bass using Zilch's proprietary box tuning device.


I am getting to know the Ed May designed Marantz speakers (having bought 2 pairs in the last month)..Marantz addressed the port issue with a "Vari-Q" foam plug. The instruction was to plug the port on lower powered receivers. It has a metal rod thru it with 2 larger end caps. You tighten them to expand the foam for tight fit. It rots away just like L100 grills.:bouncy: Maybe a pair of rolled socks (white) would work as well....:blink:

[Zilch]

The genesis of a PRODUCT concept, perhaps? :hmm:

[SEAWOLF97]

The seed of a PRODUCT concept? :hmm:

Darn, you are good Zilch , gotta go foto some of my socks for eBay auctions before you all do.....

Need a catchy name...maybe "The ZilchWolfMaster 2000 Precision Port Adjuster" ?? ,,,,,,,,,,welll, maybe not. :blink:

Geeze we could get them in different colors to match grills and maybe make enough $ for those Everests with your name on them ??

(we can even advirtise the propriatory folding technique , and how you void the warranty if unrolled to steal the trade secret)

[Zilch]

125A and 127A play nicely acoustic suspension in L40's 1.6 cuft box, below.

Measurements (middle):

Nearfield driver only orange.
Nearfield with 3120A filter red.
Full range orchid.

BB6P indicates usable bass (-10 dB) available down to ~32.75 Hz, bottom.

These alignments can take advantage of boundary reinforcement for noticebly better extended bass. I don't know about everybody else, but that's how I typically use bookshelf speakers anyway.

Footnote: Pooched tweeter dome doesn't affect the sound.

[It ain't connected.... :p ]

[Zilch]

C36 Viscounts assembled in another thread using two different L100 woofers:

http://audioheritage.org/vbulletin/showthread.php?p=131814#post131814

More info this thread:

http://audioheritage.org/vbulletin/showthread.php?p=126371#post126371

These 3 cuft. box plans are here:

http://www.lansingheritage.org/images/jbl/plans/c35-c39/page2.jpg

[Merely neglect to put in any port.... ;) ]

[Zilch]

A second 2213 over-excursion. I'm not doing this, folks.

In fact, I think closed-box alignment affords some protection against woofer damage like this.

Voice coil jumped out of the gap, either coincident with, or after the cone failed (bottom).

Of interest, perhaps, it's flatwound.... :dont-know

[Fred Sanford]

Hi Zilch- not sure if there's enough info available to you to simulate this situation & come up with any opinion, but I've got six L46s slated for my 5.1 surround setup, and since I was at the Depot yesterday purchasing plugs for my L100s, I picked up two 2" plugs as well that would fit a test pair of my L46s.

My thought was that, in an HT environment (where there's some serious dynamics, but a dedicated sub for 80Hz & under), the L46s might have a happier, longer life (suspended animation :D ?) with the ports plugged.

Driver is a 117H-1, not sure of the interior volume of the cab, I'll poke around or take some rough measurements if this intrigues you in the least.

Thanks in advance,

je

[Zilch]

http://manuals.harman.com/JBL/HOM/Technical%20Sheet/L46%20Sigma%20ts.pdf

We'd have to hunt up 117H-1 T/S parameters to model it, but I'd say there's no harm in continuing with your plan to try it.

I recall Giskard recommending port closure of JBL bookshelves when incorporating into HT with subs, but I doubt he meant that to be universally applicable.

Clearly, the T/S parameters have to fall within a prescribed range for it to operate in true acoustic suspension, but the objective here may be different, i.e., to roll off the bass response and let the sub do its job, while also improving the dynamics and power-handling by operating the woofer closed-box.

*****

Please report your "findings" with closing the ports of L100s here, also, so it's all in one place for interested readers. :thmbsup:

[duaneage]

Like the 115, 116 and 118 woofers they are probably High Qts drivers. I would add more fiberglass as well to tame the impedance peak a bit. Another more drastic way to do this is to stretch fabric across the rear of the driver. The blanket trick will lower the Qts a bit but also lower efficiency a little.

[Fred Sanford]

We'd have to hunt up 117H-1 T/S parameters to model it, but I'd say there's no harm in continuing with your plan to try it.

Yeah, that's been a dead end so far for me. Replacement recommended driver is 116H-3 with slight acoustic difference from the 117H-1. All I've found so far is the 116A's T/S parameters (see below).


I recall Giskard recommending port closure of JBL bookshelves when incorporating into HT with subs, but I doubt he meant that to be universally applicable.

Yep, and without ever testing the L46s, I don't know if there is anything to gain sonically by plugging the port (ie: taming the L100s @ 80Hz). And, seeing as they're all stacked in my giant "pile of potential" for now, I also saw that the 3" plug fit into the L110's port, and I have used them with an M&K sub as well...they sound great already, though.


Clearly, the T/S parameters have to fall within a prescribed range for it to operate in true acoustic suspension, but the objective here may be different, i.e., to roll off the bass response and let the sub do its job, while also improving the dynamics and power-handling by operating the woofer closed-box.

Exactly, the surround processor can be 'told' to roll off below 80Hz, but I guess I'm looking toward attempting to preserve their longevity in a situation that they were never really designed to work in (plus, seeing if there's any accompanying sonic advantage).


Please report your "findings" with closing the ports of L100s here, also, so it's all in one place for interested readers. :thmbsup:

Didn't get to fire 'em up today as planned, my wife had a job fair here in our new town, and so of course she fell last night & broke her foot. We spent the night dosing her with Sam Adams Brown Lager & tweaking her resume'. I then had to drive her to & from the job fair today, so I lost my window of window-shaking opportunity. She's a trooper, I must say, so I'm not punishing her with any audio experiments today. When my new set of L100s arrive there will have to be a welcoming party, and we'll break out the port plugs then. The new ones are also supposedly original, so I can compare to the assembled-from-seven-sources L100s I already have to see if there's an audible difference. Not 100% sure yet that they're the same exact series & x-over.

Thanks,

je

[DaCarlson]

Most people who own L100's (or other AlNiCo systems like the L26 and L36) and plug the port will notice LESS bass, and will have an urge to turn up the bass before they realize what the truth is, response-wise. And, with no flopping of the cone and all the focus on the cone control afforded by the A-S design, some may want to see how much they can get out of the woofer in this "new" box. Wouldn't want to see or hear about any "long faces" when they realize it is too late, since demagnetization is only reversible by ripping the cone out to recharge the magnet. That's all I was getting at. Moldyoldy had al;ready brought up the coil burnout issue...


It is well known that the box size was chosen for suitability as a near-field monitor. JBL figured that any bigger cabinet would knock it out of the running. How large would be tolerated sitting atop one of the two most important -and expensive- components of a studio? (cabinet crashes onto the control surface). It was also designed to emulate the sound of the old Altec/Urei duplex monitors that were the industry standard then, while sitting out in the middle of the room with no boundary reinforcement. Hence the boomy bass.

I find it surprising that BBPRO says the 123A in the cab is a good alignment. We all know it is not just by listening to them. Sure you didn't miss on your measurements or your math? On a box that size, a little means a lot re: percentage of volume change.

The A-S "Q" is too high, as you can see and probably hear. That is why I said the box is too small for either, really, IMHO.


What causes the decrease in bass when the ports are plugged? Could you great some kind of passive woofer around the port to create more bass?

[Zilch]

What causes the decrease in bass when the ports are plugged? Could you great some kind of passive woofer around the port to create more bass?In vented alignments, port resonance is a source of bass output in the region of the system tuning. Close the port, and the burden of reproducing those frequencies shifts to the driver alone.

See post #14:

http://audioheritage.org/vbulletin/showthread.php?p=123449#post123449

In the instance of L100 and similars, there's no less bass when the port is closed, rather merely a perception of same, as the artificial peak of the original design, intended as compensation in their use as nearfield monitors wherein there is no boundary reinforcement of low frequencies, is stripped away.

It may certainly be argued that removing the peak comprises less bass output, but from the perspective of accurate reproduction, it's only less fake "boom," and the true bass extension actually increases, as is illustrated in the simulation curves.... :yes:

[Don C]

Has anyone tried an LE14 in a sealed box?

[Joe Alesi]

It's been a very long time since I've worked with or listened to small closed-box speakers, a design approach pioneered by "East Coast Sound" proponents of the '60's - AR, Advent, KLH, etc.. Building DIY Minis recently led me to trying that approach with JBL drivers, with good result.

Hello Zilch,

I have always liked sealed boxes, and although JBL is a true love I cant really suggest anything specific other than selecting one with good excursion and using low end eq and more juice to make up for some of the bass in going for a sealed over a ported box.

I suppose one could try to doctor the driver by adding mass, damping (around the driver- as already suggested) or even electrically modifying its parameters by adding resistors to increase the effective Re of the driver and hence Qes and Qts. But I see this as wasteful and would prefer to choose one (probably and unfortunately non-JBL) for sealed box sub bass use.

I can thoroughly recommend the NHT 1259 + eq. in this role. I have built subs with these (well the 4 Ohm version- not available any more) and I am very pleased with the results. That is not to say I dont love the 2245 subs I have waiting in the wings:D. Some info:

http://www.madisound.com/nht1259.html

[Zilch]

Has anyone tried an LE14 in a sealed box?Yes, briefly, in S99. I wasn't paying much attention to the bass, and didn't do nearfield:

http://audioheritage.org/vbulletin/showthread.php?p=74311#post74311

http://audioheritage.org/vbulletin/showthread.php?p=74410#post74410

Ported, shortly thereafter:

http://audioheritage.org/vbulletin/showthread.php?p=75210#post75210

http://audioheritage.org/vbulletin/showthread.php?p=75790#post75790

Not terribly helpful. Run the sims....

[Joe Alesi]

Hello Zilch,

I suppose one could try to doctor the driver by adding mass, damping (around the driver- as already suggested) or even electrically modifying its parameters by adding resistors to increase the effective Re of the driver and hence Qes and Qts.

As for modifying existing drivers- here is some info and an example which shows the way:

http://www.birotechnology.com/articles/mass.html

[speakerdave]

The LE15A was initially presented by JBL as a sealed box driver. Does anyone have any experience with it in that type of enclosure? I've read quite a lot about disappointing bass from this driver in bass reflex enclosures, but no one seems to look at the more gradual roll off of low bass in a sealed box which results sometimes in actual greater extension. That coupled with careful use of room rise might get a good result with this driver in a livingroom sized space. Since this driver was first offered for either closed box or bass reflex, I should think it would be an option to try sealed. I would think also that the big magnet would be an advantage for that.

I think the real price of going sealed over bass reflex with that driver (and others) would be either remembering to stay within the decibel level it can produce safely that way (not a problem most of the time) or adding more cone area. The added cone area dictates a low crossover point for me. I find that even crossing over in the mid-hundreds there is definitely a sense of multiple sources that I don't care for (at my listening distance--10-12 feet). Even drivers side-by-side, following the most conservative view on when acoustic coupling occurs (acoustic centers a quarter wave length apart), pairs of 15 inch drivers must be crossed over at under 200 Hz.

David

[Robh3606]

The main issue I see with either one sealed Le-14 or 15 is the xmax. You may very well be able to get a good in room response but you will be SPL limited and won't really be able to add any significant boost if you are not happy with the inroom response with room gain. I will model them for you and post them. I am running a pair of 121A'a now in my second system in sealed enclosures and they sound really good. With room gain they are very nice. You have to watch the SPL though. I rarely ring the bell on the mass rings but it can happen depending on content. The LE-15 would give several db SPL advantage over the 121's.

Rob:)

[Zilch]

In 6 cuft Olympus, BB6P says LE15A closed-box F3 = 80.99 Hz, and F10 = 34.21 Hz. It'll handle 2.91 W down there, for 100.9 dB output.

Vented looks like a WAY superior alignment with Fb = 27.86 Hz, F3 = 48.2 Hz, and F10 = 25.65 Hz, 15.7W, 108.3 dB output:

[secondslc]

What's stunning is the difference in behavior of the cone. It's loose and floppy with the port open. Once you plug the port, the effect of the enclosed air "cushion" is immediately apparent in the stiffness of the suspension.



The 122-A in my L166 seems stiff even with the port open. Did JBL try to eliminate some of the loose boom with this woofer? Dare I plug the horizon?

Also, the 044 tweeter, has a higher extension than that in the l100, before I go ahead and re-cap this thing, should I think about giving it a new crossover?

[toddbailey]

what tools did you use to take these measurements?

If possible, I'd be interested in testing my L36's, a couple of advents, the system I installed in the cars, rv and a home built no name pair.

[Zilch]

Me?

CLIO.

[badman]

Hi Zilch:

Halfway down the page below we see some measures of the 123A. Looks like you may have been picking up baffle diffraction artifacts, compare the smooth response on the curved baffle to the nasty jaggeds from the terrible diffraction of the stock box.

http://www.troelsgravesen.dk/JBL_L100.htm

Also, this is a beast of a woofer and deserves a beast of a box, the L100 are painfully undersized. The driver is made with subwoofer optimized thiele smalles, but happens to avoid the most serious misbehavior up until the kHz range. It's much more efficient than most subs, with a .5 Qts (or so) and a 25Hz Fs with a 90-91dB ref. efficiency. One could easily get a lot of output with 50W in a 6 ft. sealed box.

[Zilch]

I have noodled around with this a bit in BB6P. Clearly there is more to be investigated as to their utility beyond the original application. I believe they may run out of excursion in large closed boxes, but let's nobody take my word for that without doing the requisite modeling.

Several DIYers have built EconoWaves with them, but nobody's done the heavy lifting with respect to optimizing the lowpass filter for that combination.

At one point, Gordon provided insight into using them in bandpass alignments for subs. All fun stuff, and I believe 2213H, a particular favorite, may still be available new from the factory.... :yes:

[badman]

While the locals are pretty obsessive round these parts, the 123A also makes a superb open-baffle driver. The (relatively) high Qts and low Fs mean there's a solid amount of bass to work with, and the reasonably high xmax means you can do some EQ.

[4313B]

While the locals are pretty obsessive round these parts, the 123A also makes a superb open-baffle driver. The (relatively) high Qts and low Fs mean there's a solid amount of bass to work with, and the reasonably high xmax means you can do some EQ.Yeah, it's too bad we haven't seen anyone run with a project like that. I've never been much of a fan of the pancake twelve but I am glad that some of you guys have found other uses for it. :thmbsup:

It is a part of our history.

[badman]

I'll post some project details at a later date I suppose. It's not really a JBL project, more a project with a JBL, but certainly it's a woofer that doesn't get the love it deserves :)

[mike]

I always thought that the 123a-1 did some things better than the other 12" woofers like the 122a, 126a and 128H. It just seems to transition better to an LE5 series midrange driver. The 2213H with the ceramic magnet does not sound as good as the 123a-1 to me at least. I don't think it has anything to do with the magnet material but rather a design change.

Mike

[badman]

I have the AlNiCo versions of both, and the 2213 has a little higher Qes and lower Le in the examples I have. This appears to be due to a revision of the voicecoil winding, from what I can tell. The 2213H was one of the early ceramics, as far as I know, and lacks some of the features that brought the later ceramics 'up to snuff' like the SFG polepiece shaping and shorting ring. I could be wrong here, though, as I've looked for a datasheet and not found one.

The AlNiCo 2213 is the same as the 123A-3 fwiw. I do prefer the less obstructive frame on the 123A though vs. the 2213/123A-3.

[Mannermusic]

The LE15A was initially presented by JBL as a sealed box driver. Does anyone have any experience with it in that type of enclosure? I've read quite a lot about disappointing bass from this driver in bass reflex enclosures, but no one seems to look at the more gradual roll off of low bass in a sealed box which results sometimes in actual greater extension. That coupled with careful use of room rise might get a good result with this driver in a livingroom sized space. Since this driver was first offered for either closed box or bass reflex, I should think it would be an option to try sealed. I would think also that the big magnet would be an advantage for that.

I think the real price of going sealed over bass reflex with that driver (and others) would be either remembering to stay within the decibel level it can produce safely that way (not a problem most of the time) or adding more cone area. The added cone area dictates a low crossover point for me. I find that even crossing over in the mid-hundreds there is definitely a sense of multiple sources that I don't care for (at my listening distance--10-12 feet). Even drivers side-by-side, following the most conservative view on when acoustic coupling occurs (acoustic centers a quarter wave length apart), pairs of 15 inch drivers must be crossed over at under 200 Hz.

David
Here you go - old fashioned data from a real oscillator (port tuned to 31-32 Hz):

[Loren42]

Here you go - old fashioned data from a real oscillator (port tuned to 31-32 Hz):

Could you elaborate as to how you conducted the test?

[Mannermusic]

Nothing fancy, the response includes the room etc. Gear was an old HP 200 CD oscillator (recently refurbished) and the engineering standard, RadioShack sound level meter :blink: a couple feet back. Tried to stay close to minimize the room effects - not to engineering test standards - but surely shows the Helmholtz effect. Speakers are 30 years old! Owner is much older. MM

[Loren42]

Nothing fancy, the response includes the room etc. Gear was an old HP 200 CD oscillator (recently refurbished) and the engineering standard, RadioShack sound level meter :blink: a couple feet back. Tried to stay close to minimize the room effects - not to engineering test standards - but surely shows the Helmholtz effect. Speakers are 30 years old! Owner is much older. MM

That would explain some of the things I was seeing in the plots. Very good.

[Loren42]

Nothing fancy, the response includes the room etc. Gear was an old HP 200 CD oscillator (recently refurbished) and the engineering standard, RadioShack sound level meter :blink: a couple feet back. Tried to stay close to minimize the room effects - not to engineering test standards - but surely shows the Helmholtz effect. Speakers are 30 years old! Owner is much older. MM

You know, there are some computer programs that act as a sweep generator and then record the output using a condenser mic. Some can compensate for room reverberations and they provide a nice graphical plot.

You need a good electric condenser mic like Behringer ECM8000 (http://www.parts-express.com/pe/showdetl.cfm?Partnumber=248-625&FTR=ecm&CFID=13047254&CFTOKEN=86635953) from Parts Express.

You need a preamp that supports 48 VDC phantom power and a sound card in your computer. Software should be available free on line.

The whole process can be done in under 10 seconds using the PC. I have a similar setup. The Behringer mic is very good and cheap.

[Eaulive]

Take NO prisoners!

Two-way @ 1.2 kHz.

[Windowed HF, cyan, bottom.]

That looks more like a 2213 than a 123A, according to the position of the connections VS the mounting holes.

Did the L-100 ever came with 2213s ?

[Zilch]

Nope. What is is?

The answer is here:

http://www.audioheritage.org/vbulletin/showthread.php?p=132559&&#post132559

[Eaulive]

You know, there are some computer programs that act as a sweep generator and then record the output using a condenser mic. Some can compensate for room reverberations and they provide a nice graphical plot.

You need a good electric condenser mic like Behringer ECM8000 (http://www.parts-express.com/pe/showdetl.cfm?Partnumber=248-625&FTR=ecm&CFID=13047254&CFTOKEN=86635953) from Parts Express.

You need a preamp that supports 48 VDC phantom power and a sound card in your computer. Software should be available free on line.

The whole process can be done in under 10 seconds using the PC. I have a similar setup. The Behringer mic is very good and cheap.

Interesting... any programs in mind?
I already have an Earthworks M30 microphone that I use with my RTA