Use of subwoofers for older JBL studio monitors

[Bill Shenefelt]

I have two home built L-200's and two home built 4343 monitors. Speakers and crossovers are jbl design and components but boxes are home built. I am using the L-200 types for front channels on my video system. I also have an 18 inch JBL woofer in an 8 cu ft cabinet at the opposite end of my 28 ft room from the front channels sitting between my 4343 stereo system speakers. I tried using it with the 4343's using a 6th order electronic crossover but found it did nothing positive for music so I use it as a stand alone with only a tuned port on a single channel of my 200 w/ch heat amp for the video system. Is there a good design for a sub for use with L-200's for video? Would a sealed box sub design fight with or compliment the ported L-200 front channels? What would be a good way to integrate the 18" sub with the L-200 front channels or would it be better just to buy something like the current jbl amped 12 inch subs?

[Aaron]

What kind of crossover are you using? Does it give you options like how many db/oct your filters are?
6th order is very steep and could cause group delay issues.
Are the subs further from the listening position than the mains by more than a few feet?

[Bill Shenefelt]

What kind of crossover are you using? Does it give you options like how many db/oct your filters are?
6th order is very steep and could cause group delay issues.
Are the subs further from the listening position than the mains by more than a few feet?

Initially I had a Heathkit crossover and built a 6th order to use the big sub with my 4343 speakers. The 6th order I mentioned was the box tuning, not a crossover filter. I used 6 db/octave slope at 40 cps for low pass to the 18 inch driver with no highpass crossover at all on the 4343 woofers. The 6th order was not a crossover slope but an equalization to boost port output at a box frequency below a normal reflex tuning with and a faster cutoff (6th order) than provided by a port loading to quickly grab the woofer at a lower frequency to prevent speaker destruction. I think I had the box tuned to about 24 cps with a 5 or 6 db boost and a quick 6th order cutoff at about 18 cps. The 4343 speakers were on each side of the 8 cu ft sub box at the one end of the room. The listening position was about 10 ft in front of the front of those speakers. The 4343's were bi-amped. I think I set the hf to 300 and the low to 280 cps using a heathkit crossover. It had selectable 6 or 12 dB/octave crossover filters switchable and variable crossover frequencies. Inside I set up a 6th order box tuning for the 18 inch subwoofer to put it on a 200w/ch bridged using the heath crossover. Never sounded right so later I substituted a Marchand crossover and just bi-amped the 4343 without any sub. I tried triamp to move the compression drivers to a McIntosh 24 w/channel tube amp but it was a real waste. Just too many interconnects to keep working well. Went back to bi-amping. I settled on the passive JBL components and a 100 w/channel Amber amp for the 10 inch, horn and slot radiators with the 15 inch bass speakers went on a 250 w/channel Heathkit amp with the Marchand crossover for the bi-amp setup. I then moved the sub to try to avoid a null at the listening position and just use it with the L-200 tv front channels. No real music seemed down there anyway but movie sound effects sure are. I am considering getting a Klipsch RC-64 II Reference series center channel speaker (horn tweeter and 4 four 6 1/2 inch bass speakers) between the L-200's, and a pair of klipsch RS-62's (Each has two sets of 6 1/2 inch bass and horn tweeters angled toward front and toward rear) for side surrounds.
I should not need a second sub to get bass back into the listening position.
I moved the sub to a position closer to the TV end and away from the music system 4343's. A good visual layout is the listening position half way down the 28 ft living room and the sub is halfway between the listening position and the tv. It seems to prevent the big null that had been at the listening position when the sub was at the end of the room. I set it up for use with my home built L200's for the movie system on one channel of a 200 w/channel heathkit amp fed by the sub out of the Yamaha av receiver. The L-200's and surround and center front are on amps inside the yamaha but I may move the L-200s to an Audire 100 w/channel rather than the yamaha to possibly get a little better punch with the L-200s. The Yamaha internal amps should suffice for the surround system.

[Aaron]

Hmm...I've never heard the L-200s or 4343s but from what I've read, they are capable of playing very low (high 20s, low 30s).
I can see why you want extra lows for movies and how the subs might get in the way of music.

I'll tell you what my set up is, it works very well for me, maybe it will give you some ideas:
For main speakers I have JBL L96s. The L96s are set atop 3.5cuft boxes with JBL sub1500s and 18" passive radiators tuned to 17Hz iirc.
I'm bi-amping the whole works through a DBX 223XL crossover and into a single Yamaha MX-55 four channel amp. In the low frequency chain I have a Behringer feedback destroyer pro. I tuned the Behringer with data from room EQ wizard (REW) and a microphone.

I might be able to offer better assistance if I know the details regarding the subs:
Driver model:
Box internal volume:
Port length:
Total port cross section area:

[Bill Shenefelt]

I found the jbl sub that was using the 18 inch driver It was a B460. The driver is apparently a 2245. I cannot see the label on mine as it is in the box and I refuse to pull it just to look! ha ha. It was the one they used in that box since I was looking for one and found a dealer that had one laying in the back room!. Someone put money on it to have it ordered in and never picked it up. The dealer gave it to me for $150 which is what he had in it above and beyond the deposit from the prospective buyer. They used a 5th order alignment on it to provide some LF boost and faster cutoff than std ported box. I tried a "Speaker Builder" magazine alignment design to make a the 6th order one but it really does not buy much. I have it currently tuned around 25 cps in the box and it is pretty good to around 21 cps then drops at 12dB/octave. Remember this thing really pumps! It has a 1 inch excursion at full power and extremely tight Qt. The 6 inch port will flutter your pantlegs at 6 ft away! No uncontrolled flopping this guy like a car boom box. I have hit it with a 250 watt per chanel Heathkit amp BRIDGED which claims to have 3db headroom! I lit the amp overload lights, and knocked a few pictures off the walls in the room. I moved it to one channel of a 200 watt/channel Heathkit amp with no bridge, just one channel driving it.

The 4343 is pictured a lot on the internet. There is a whole forum here on homebuilt 4343. Try google for JBL 4343 and check out some of the youtube hits. The real one has a rectangular baffle but I sort of played with that dividing it between two separate boxes (one for the 10 inch midrange and one for the 15 inch bass driver. On the box for the midrange I extended the baffle face up to hold the horns sort of naked. (I kind of like seeing the horns and magnets!)
The L-200 pair I have are really drivers for an JBL L-300 with the slot radiator tweeter robbed for the 4343's. I built all enclosures and started with the drivres for the L-300 (136A 15 inch alniclo magnet bass, le 85 horn, and o77 slot radiator. When I got the 2121 midrange to upgrade the system to a 4343, I had to get two shorter horns since the midrange crossed ovber higher. Thus I had two extra horns. I then found a pr of 136 A the ferrite pro not the older alnico version) and grabbed them Then I found a couple of compression drivers with blown diaphragms, bought jbl replacement diaphragms and built the L-200's. Since I have not found any 077 slot radiators around for less than about $700 a pr, I forgo the HF above about 16k which I cannot hear anyway. Info and photos of any of these can be easily found with a google search.
Just out of curiosity, why the 18 inch passives? Did you find it easier to weight them to get the box frequency you wanted but did not have the needed length and room available for a big port? I started with an L shaped port using a 6 inch pvc elbow to achieve the length needed for a 6 inch diameter port. .

[JeffW]

See if you can find the JBL/Harman paper on Distributed Bass. It's not so much that the big monitor drivers can't produce fairly low bass, it's more along the lines of multiple subs smoothing the room response and making the bass seem cleaner.

Ah, Here it is

[audiomagnate]

Hmm...I've never heard the L-200s or 4343s but from what I've read, they are capable of playing very low (high 20s, low 30s)...

They don't go that low. I use a simple 50Hz, 2nd Order (12 dB/8ve) electronic crossover between my subs and my L300s. The L300s sound better with the deep bass filtered out and the port moderately stuffed. I have a swarm of three sealed subs that go very deep. Good modern subs do wonders for vintage speakers, which sacrificed deep bass for increased sensitivity. The rolloff is great for protecting those expensive woofers as well.

[ivica]

See if you can find the JBL/Harman paper on Distributed Bass. It's not so much that the big monitor drivers can't produce fairly low bass, it's more along the lines of multiple subs smoothing the room response and making the bass seem cleaner. Ah, Here it is

Hi JeffW,
Thank You for the very informative reading about Bass driver optimal placing in the room.
From that it seems that almost all suggested is not too practical for home placement.

regards
ivica

[Bill Shenefelt]

Hmm...I've never heard the L-200s or 4343s but from what I've read, they are capable of playing very low (high 20s, low 30s).
I can see why you want extra lows for movies and how the subs might get in the way of music.

I'll tell you what my set up is, it works very well for me, maybe it will give you some ideas:
For main speakers I have JBL L96s. The L96s are set atop 3.5cuft boxes with JBL sub1500s and 18" passive radiators tuned to 17Hz iirc.
I'm bi-amping the whole works through a DBX 223XL crossover and into a single Yamaha MX-55 four channel amp. In the low frequency chain I have a Behringer feedback destroyer pro. I tuned the Behringer with data from room EQ wizard (REW) and a microphone.

I might be able to offer better assistance if I know the details regarding the subs:
Driver model:
Box internal volume:
Port length:
Total port cross section area:

http://www.audioheritage.org/vbullet...4-way-For-Sale

See the above for info on a look alike for the 4343