Help with figuring port sizes.

[Hamilton]

Hey guys,

I'm half way through building my center speaker and I'm ready to cut the two 4" ports.

The cab will house two 2118s, a 2426 w/2370A horn, a 4430 crossover, plenty of bracing with 3/4" baffle. Dimensions are 11"h | 56.5"w | 16"d with 3" insulation.

Also, how many walls should receive insulation?

I'm very grateful,
Hamilton

[Zilch]

Your box is 5.75 cuft. gross. After deducting dual 2118 volume and .25 cuft for the 2370A and 2226 (a guess), your net volume is 5.41 cuft., about 5 to 10 times what those drivers want.

BassBox6 Pro suggests 0.53 cuft. net tuned to 89 Hz for "High Fidelity" (black), or 0.917 cuft. net tuned to 78 Hz for "Extended Bass" (violet). In both cases, you're displacement limited to 100 Watts at 60 Hz.

Perhaps I've got it wrong, but where'd you get the idea to build such a big box for these?

Lemme work up 4612 specs here and see what JBL did with paired 2118's....

[Later tonight, maybe....]

[Hamilton]

Hey, Zilch.

I didn't *purposely* build that size box for the speakers, it was built because the plasma is going to sit on it.

It is no problem for me to "minimize" the cabinet by bringing the back farther inside. I'm all ears, just tell me what to do. http://audioheritage.org/vbulletin/images/smilies/smile.gif

Thanks again,
Hamilton

[johnaec]

BassBox6 Pro suggests 0.53 cuft. net tuned to 89 Hz for "High Fidelity" (black), or 0.917 cuft. net tuned to 78 Hz for "Extended Bass" (violet).Zilch - is that recommended size for two speakers in a single cabinet, or is that the volume if using two individual cabinets?

BTW - 'stopped by your house Thursday on the way back from visiting my friend's studio, but no one home... :dont-know

John

[GordonW]

A 4612, to a close approximation, was about 1.35 cubic feet total (or .675 cubic feet per 2118J), tuned to around 68 Hz (two 2" holes bored into the front of the cabinet, for an effective vent length of .75").

I'd probably go a bit smaller volume than that, after doing the calculations again. Maybe 1.2 cubic feet (.6 cubic feet per 2118J), tuned to right about 68 Hz. That'd give an f3 of around 72 Hz, before the contribution of series inductance in the crossover was considered (which would lower the effective f3, probably, to something in the high-60s). To do this, I'd use one 3" diameter vent per woofer (two vents total, in a cabinet with two 2118Js), each vent being about 4" long. Use just enough fiberglass insulation, to cover the walls (every wall except the baffle, but only 1 or 2 inches thick, max). My calculations also indicate, in this box, that the woofer will not be significantly volume-displacement-limited, until about 60 Hz. With a standard 80 Hz "small speaker" setting on a HT receiver/processor-amplifier, it should be just fine, to play as loud as you want (within reason :D )...

Regards,
Gordon.

[Zilch]

Zilch - is that recommended size for two speakers in a single cabinet....Yup, two 2118's. Sorry I missed you Thursday; at a seminar in Stockton.... :(


I'm all ears, just tell me what to do. http://audioheritage.org/vbulletin/images/smilies/smile.gifHang on a bit for other forum members to confirm my results. In the meantime, I'll take a closer look at 4612 here. I think the answer is to block the box internal size down with a second set of side walls closer to the center.

I'll run the 4430 crossover on 2370A and post the results for you here; I don't think that's gonna work well. You need a 2344A, probably, but that's too tall for your 11" box height. 2342 might work (it's smaller, and will fit), but I've never played one on a 2426 with 4430 crossover. That'll take a little more effort, but I can try that, too....

[Zilch]

Regarding the box and ports, it looks like Gordon and I are honing in on the same design. :)

Here's the story so far on various horns with the N3134 (4430) crossover:

1) With 2344A, the 4430 horn, controls at "0". It's about the 10th time I've independently measured and posted it on the forums; always the same, so I'm confident it's a reliable reference here.

2) With 2370A, same settings. How I'd expect your design to play on axis. 2370A narrows the vertical dispersion, so it's concentrating HF energy. JBL lit on that horn states that it requires no compensation when used with 2425/6. That's stretching it, but the compensation provided by 4430 crossover is clearly wrong for it.

http://www.jblpro.com/pages/pub/components/2370a.pdf

The vertical beamwith AND frequency response both collapse in the VHF region. :(

3) Adjust the N3134 crossover controls to try to flatten the response with 2370A, and you lose the HF extension because you have to raise the mids and lower the HF to make it happen.

4) Same with $38 OASR horn. (I'll find a suitable application for these ultimately. :p )

5) With $10 PTF95 Progressive Transition waveguide. Retains the HF extension, but hardly "flat". Would probably sound the best of the "wrong" horns illustrated here. Been a while since I played program material through this combination; I recall it being pretty good, but overly "crisp" from the 10 kHz peak there.

I'll access a 2342 for you tomorrow.

The red thingies are reflections from an LED on the front of the camera. There's a way to turn it off, but I'd have to RTFM.... ;)

[Hamilton]

Thanks for the reply, Zilch.

Hmmm....what to do. http://audioheritage.org/vbulletin/images/smilies/frown.gif I own a horn that doesn't work well....... http://audioheritage.org/vbulletin/images/smilies/frown.gif I decided on that horn because of the SR4725Xs, and because of space requirements.

http://www.jblproservice.com/pdf/SR-X%20Series/SR4725X.pdf

Well, at least I can finish the cab. http://audioheritage.org/vbulletin/images/smilies/smile.gif Each 2118 will have its own box, what would you shoot for in cubic feet, around .6?

Thanks again.

[Lancer]

Each 2118 will have its own box, what would you shoot for in cubic feet, around .6?


If you don't have software or the AES papers containing the formulas to play around with this stuff then the next best thing is to read the Product Sheets...

http://www.jblpro.com/pub/obsolete/2118.pdf

Review Gordon's post above.

[Zilch]

Each 2118 will have its own box....Hang on, now.

We're still working on this for you based upon the 4612 model, which has both drivers in a common chamber.

http://www.jblpro.com/pub/obsolete/4612ok.pdf

I should have something neato for you by the end of today according to your original design.

Actually, a forum member built something similar. I recall the biradial horn being rotated 90°....

[Zilch]

Small 2342 horn (right), shown here in comparison to 2344A, still available from JBL Pro Parts, I believe, is 8-3/4" wide x 8-15/16" high.

I can't read the part number: http://www.jblproservice.com/pdf/Studio%20Monitor%20Series/4425LR.pdf

The complete assembly with 2426H using the treaded "snoot" is just 6" deep to horn mounting surface. This suggests good potential for use in shallow box designs. With 241x drivers, the depth might be further minimized, even.

It plays very nicely on 4430 crossover, here shown at about 1 dB boost setting on both MF and HF controls. Compare to curves for other horns above. I'd use it.

Note for future use: Bottom pic shows technique used to remove horn from 4425 - a utility knife blade gently tapped in the edge wedged it loose with gasket intact.... :D

Horn mounting hole in 4425 is 6" wide by 7.25" high. Somebody asked about that a couple of months ago. :p

[johnaec]

Small 2342 horn ... still available from JBL Pro Parts,

I can't read the part number:HORN 2342 is part number 65820 and currently listed on JBL's site at $156.

John

[Zilch]

Actual speaker compartment interior dimensions 36" x 7" x 10" nets the ~1.20 cuft. volume Gordon recommends. Use extra volumes at sides and rear for "stashes." ;)

"Woofers" spaced per D'Appolito 2 X crossover wavelength for 3/2 geometry. They're far enough apart I would have no concern about the horn's projecting "cheeks." It's not necessary to rotate the horn.

Ports are 3" diameter, 3.25" deep tuning to 68 Hz, also per Gordon's spec. Use four 2" diameter ones of the same length if symmetry matters.... :p

Members desiring a thin profile wall-mount biradial center channel could modify this design down to maybe 6" deep or less (exterior) using 2418H-1 and L200t3 crossover. Make it 42" wide, perhaps. Robh is working with that combo....

[Zilch]

HORN 2342 is part number 65820 and currently listed on JBL's site at $156.We'll lean on Don to tell us how he got his for $70. :p

http://audioheritage.org/vbulletin/showthread.php?t=5418&highlight=2342+Horn

[boputnam]

Also, how many walls should receive insulation?Hey...

This question appears to have been overlooked. SOP is to line the cabinet but not put batting on the baffle. There some discussion of this throughout the Forum - try some searches...

[Hamilton]

Gosh, that's fantastic, Zilch! I appreciate your efforts. I can't believe how far out of spec I was going to build it. http://audioheritage.org/vbulletin/images/smilies/banghead.gif This will be easy to shorten the boxes.

If a 2342 can be had for $70 then I'll have no problem making another baffle board and putting the 2370A on the shelf. A big thanks to all who have helped. http://audioheritage.org/vbulletin/images/smilies/applaud.gif

Hamilton

[Zilch]

Well, we can have an academic debate here about the applicability of D'Appolito alignments to this biradial case, but I'd just build it and see how it sounds. :p

Those are 16-Ohm 2118J's and you're gonna just run them in parallel, we presume....

Look here for inspiration: http://audioheritage.org/vbulletin/showthread.php?t=3774

[Robh3606]

Just some food for thought. The compensation and networks used in both the 4430/35 and L200T3 won't work well with a pair of 2118's. The 4435 might but with a single driver. Coming in at 100Db you won't be able to balance to top end off using a 2418/2426 and a 2342. Figure those networks work with drivers that are 91dB 93dB and 96dB. If your sensitivity goes above say 96dB what happens is you don't/can't trim enough level off on the lower 1K-2k areas to balance off the top of the curve. What you end up with is a level matched midrange but it rolls of above 10K or so. Just remember what the system sensitivites are when using the networks when you swap drivers.

Rob:)

[Zilch]

Thanks, Rob!

So, L-Pad on the 2118's to set the balance right?

I think we'd prefer not to modify the 4430 crossover here.

Looks like N200t3 LP is easily adjusted to provide the requisite attenuation.

Me, I just biamp everything, so I'm apt to forget about that part.... ;)

[johnaec]

Personally, I'd just look for a 2404H instead of the 2342/2425/6 option and use the 4612B network...

John

[Zilch]

At 4612B's 3 kHz crossover frequency, there's not enough room between the woofers for a 2404 using D'Appolito geometry, if it applies. Centers would only be 9" apart. :(

4612B also lets one of the 2118's play full range, so there's potential major overlap and concomitant phase cancellations....

[Lancer]

Personally, I'd just look for a 2404H instead of the 2342/2425/6 option and use the 4612B network...Personally, I'd just take up golf and not worry about any of this goofy nonsense...

[Zilch]

Personally, I'd just take up golf and not worry about any of this goofy nonsense...Sure, but that'd only be AFTER our diaphragms were dusted with Aquaplas....

:p

[Lancer]

I just dusted a dozen new golf balls with aquaplas...

[Robh3606]

"I just dusted a dozen new golf balls with aquaplas..."

How do they sound at the range?? A nice sharp crack or a slightly resonant whomp??

Rob:p

[Lancer]

When I hit them with the iron they have a nice damped tone to them, yeah, like a whomp! When they hit the people standing around watching, they exhibit a decidely "heavier" thunking sound followed by a higher pitched yelp.

[Robh3606]

How many points if you beem the driver on the tractor cleaning up the balls??

Rob:D

[Lancer]

It's 10,000 points for hitting the guy driving the tractor. He has some kind of nitrous injection rigged up that automatically kicks in when his onboard radar picks up incoming golf balls so he's pretty damn hard to hit. He's into customizing his equipment. He's pretty confident, there isn't a cage around him.

[Hamilton]

Well, we can have an academic debate here about the applicability of D'Appolito alignments to this biradial case, but I'd just build it and see how it sounds. http://audioheritage.org/vbulletin/images/smilies/tongue.gif
Don't...'cause you lost me just on the "how many walls get insulation" question. http://audioheritage.org/vbulletin/images/smilies/tongue.gif



Those are 16-Ohm 2118J's and you're gonna just run them in parallel, we presume....
Yes they are, I bought them from Gordon.

Well, I finished the inner boxes, but....I had to make a change. http://audioheritage.org/vbulletin/images/smilies/redface.gif Because of the length of the horn/driver, 11 inches, I was not able to make a common box, but had to build two separate boxes for each 2118; each measures .6 cu ft with 3" ports per Gordon's specs. But I won't be able to complete the thing for a couple of weeks due to a job I just got. http://audioheritage.org/vbulletin/images/smilies/frown.gif

[Zilch]

1) 4612B stock with HF set at mid. YEOW, HOT!

2) 2404H tweeter disconnected. Two 2118J woofers in parallel. One runs full range and one has 1.2 mH in series for 6 dB/octave rolloff above 2.1 kHz?

3) Woofs with NL200t3 LP filter.

4) Add 2426H on 2342 Biradial Butt-cheek horn.

5) Run woofs full range with 4612B LF.

[Zilch]

Geometry is a bit different from Hamilton's MTM setup.

I'm thinking NL200t3 is fine.

Maybe move the LF rolloff up a bit?

Lettin' the LF play full range will interfere clear up to 10 kHz. Not good, right?

Suggestions, please....

[Hamilton]

Hey Zilch, yep, you are getting a flatter response than I, here are some RTAs (2426/2342/2118J) :

1. Stock nL200t3
2. nL200t3 - LF 2mH, 6uF, reverse polarity on 2426
3. nL200t3 - LF 1mH, 1uF, reverse polarity
4. nL200t3 - LF 1mH, 2uF, standard polarity *

I ran one more test using the nL200t3 with no LF, the RTA was near identical to #4, but sonically it was too bitey in the upper mids.

*sounds best to my ears.

[Zilch]

Your #2 looks best to me, actually. I suspect that notch at 800 Hz is the reversed polarity on the 2426H. Try it with normal polarity.

Listening is the final test, of course, but we want to be selective in terms of the final intended use. This is a HT center channel. It's gotta be voiced properly for dialog. Using music may not be the best test.

I suggest we move the LF rolloff up somewhat as you have done, but keeping the filter slope similar (right curve, below). Use 2.0 mH for L1 and 10 uF for C2. R1 should be 20 Ohms to take the "bite" out of the HF via attenuation. This combination of drivers seems generally well balanced with respect to overall output levels.

I'm opposed to just letting the paired 2118's play full range, no matter how good the RTA looks. This MTM (Mid-Tweet-Mid) already has two drivers (the 2118's) playing the same program material, but the geometry is optimized to use that to advantage, providing a wide sound field at the center with minimal phase conflict. Letting the woofs play well into the 2426H's upper mid- and high-frequency range will generate unwanted phase cancellations up there. Bad practice for home listening, I'd say....

May we see a pic of your cabinet, please?

[johnaec]

I suggest we move the LF rolloff up somewhat as you have done, but keeping the filter slope similar (right curve, below).Sheesh, Zilch - that curve is almost 80 dB down at 100K - what good is that?? :p

John

[Hamilton]

Here's a pic of the unpainted center cab with crossover parts scattered all across the top. The width of it is 60", the internal speaker cab is 1.2 cu ft, 3" ports 4" long.

[Hamilton]

Sheesh, Zilch - that curve is almost 80 dB down at 100K - what good is that?? http://audioheritage.org/vbulletin/images/smilies/tongue.gif

John
http://audioheritage.org/vbulletin/images/smilies/rotfl.gif

[Zilch]

UT, oh!

Izzat a B380 I spy on the left there? :bouncy:

["This ain' no foolin' around...."]

[Zilch]

Sheesh, Zilch - that curve is almost 80 dB down at 100K - what good is that?? :p Well, I DID have the HF shown there, but took it out so's not to surprise you, John.... :D

Actually, that's how I made sure the slopes were ROUGHLY parallel.... ;)