Line Array Subwoofer

[Mike Dubay]

I was itching for winter time audio project, and I had wanted to upgrade the bass response of my 2 channel system I use when I exercise.

As usual I set down some goals and parameters to stay within.

Subwoofer system goals:

Be able to provide bass at a system with at the very most 115 peak dB, but normal listening levels of 95 dB.

Be able to provide tight slam with low distortion.

Will give up low frequency extension to provide a solid tight sounding system.

Frequency response at a maximum of -5 db down at 30 hz. Does not have to dig to 20Hz.

Be cost effective in driver selection; want to keep the budget to less than $300 for drivers, but no foam surrounds allowed.

Have cross over frequency and driver balance be easily adjustable.

Be able to apply what I learn for the next upgrade of my Cornscala system’s subwoofer.

Parameters

First and foremost is to do something different. I have done 3 sub woofer systems. Each was single drivers with a plate amplifier.

Per above, the system will have multiple drivers.

Will also use light a duty PA grade stereo amplifier instead of a plate amplifier.

The amplifier should be in the 500 WPC into 4 ohm class, the exact number here in not set in stone.

Want to try an inexpensive active cross over to provide easy cross over frequency and driver balance.

[Mike Dubay]

Here is the current system, a pair of KG4’s on stands

The KG4’s are a homely looking pair. Lots of scratches and nicks and the driver surrounds have been repaired, but the surround repair does not seem to affect the sound. Boy, the price was right, a 45 minute drive was the only investment, and got to listen to a great pair of K-horns to boot.

[Mike Dubay]

Current amplification.

A pair of Bogen M60As. Got the first one at a flea market, $12. Never thought I would find another, but later that summer another comes up on e-bay, $70 later it is on my door step. Spending $41 dollars per channel for 60 watts of tube amplification was quite a good deal. A winter was spent off and on rebuilding them. Replaced all of the coupling and electrolytic caps, replace the dioes, removed all of the PA inputs down the just the line level (tape) input, removed all of the balance and tone adjustments, installed a span/gain bias adjustment, did a slight re-bias of the input stage. Broke the bank and had to buy a pair of 8417 output tubes. In the future will rebias the system for KT-88. But these do provide a very sweet midrange with the KG4s.

[Mike Dubay]

From the white papers I have been reading a line array subwoofer system could provide benefits over a single driver sub woofer system.

With multiple drivers each driver has to work less hard to produce the same over all dB.

Each doubling of the number of drivers gives a 6 dB increase relative to a single unit.

An array will beam the sound to a directionally centered beam, reducing sound reverberation off side walls. Almost like a horn loaded drivers, sending the sound where we need it and less to where we don’t.

I remember these bad boys from the 80’s, way outside of the buget for a poor college student.

[Mike Dubay]

Boy, looks impressive, but the problem is that the cost of 12 drivers over 2 channels can run up the cost of this project quickly. You can easily find nice sounding subwoofer drivers in the $150 range, but $1,800 for the drivers is not going to fly. So I sat tight and scoured the clearance sections at some of the one and retailers and came up with this driver:

Eminence produced 10 inch DVC subwoofer: It features dual 8 ohm voice coils, poly cone with rubber surround, *Power handling: 150 watts RMS/300 watts max *Impedance: 4 ohms *Frequency response: 27-1,000 Hz *Fs: 27 Hz *SPL: 86.5 dB 1W/1m *Vas: 3.15 cu. ft.

Sealed vol cu/ft: 2.94 cu ft And in quantities of 4 or more, is just under $20.

[Mike Dubay]

To round out the system a Behringer CX2310 crossover and a passive preamplifier. Dave Harris modified a Behringer crossover to a valve output stage, and I have done a similar converion to a CD player. So will take the Behringer for what it is for now, but in the future...

[Mike Dubay]

And finally a QSC GX3 amplifier, 300 watts into 8 ohms, 425 into 4 ohms.

[Mike Dubay]

Here is one of the 3 x 10 cabs.

[Mike Dubay]

With the KG4 on top, no grill.

[Mike Dubay]

Over all view. This is my view while I ride my stationary bike. Not small singe driver cabinet used for initial testing of the driver.

Maybe this week or the weekend will have some measurements and more listening impressions. Steel head season is upon us here in the Midwest, which can take up my spare time.

[Guest " "]

Keeps us posted on your impressions.....measurements would be cool too.

[CECAA850]

Did you wire them for 6 Ohms/channel?

Any problem with vibration or walking?

[Mike Dubay]

Each DVC driver was wired as 16 ohm, the three drivers where then wired in parrallel, to give 5.3 ohms per cabinet.

I use speaker spikes, which kind of take a set in the concrete floor, provide isolation, and prevent vibrations. Due to the top heavy nature of these I have each of them bolted to a wall using an "L" bracket. Just in case a young niece or nephew decides to pull or tug on on them. I can lean on them and they don't move.

They are vibration free.

[colterphoto1]

look up cardiod sub array if you want to get fancy with low end.

[Mike Dubay]

Initial testing was done with a single driver in a 3.3 cu ft box. At low levels the driver sounded nice, low distortion, tight bass. When pushed to higher volume this is where the driver began to have problems, less controlled sound at higher levels,more distortion, and could not keep up with the KG4 volume wise. Would go into oscillations and a few times would hit its mechnical stops with a loud knock. Well enough of that, on to a multidriver system.

[Mike Dubay]

With the 3 drivers in each of two cabs at 3.3 cu ft the sub takes on an entirely different sound. The bass now sounds that it envolopes the entire room.

The system can deliver much higher volume levels, it readily keeps up with the KG4s to the point when the KG4 sound a bit stressed and at volumes not normally used. Even a moderate volume levels there is a visceral slam that was not present with the single drivers.

The frequency plots attached were generated with a test tone CD and a RS SPL meter.

The single driver is plotted againt the response to the 3x10 left, 3x10 right, and both 3x10 cabs at the same gain setting on the system. The point of measurement was 9 feet from each speaker at the midpoint beteen the speakers, at ear level. You can see the dramatic increase in gain as you add more drivers, so you get more volume with the same power, or same volume at lower power. So you are running the drivers in the more linear lower extension range at the same volume levels.

The multidriver does help with some of the frequency problems with the room. The 100 to 300 Hz range appears much more smoother with both towers compared to a single driver. But the dip at 80 Hz and the peak at 60 Hz remain, with the ample head room some equilization might be in order to help even this out. Use of multidrivers does not appear to be able to lower the -5 db Fz of 35 hz.

[Mike Dubay]

So how did we do against our stated goals:

Be able to provide bass at a system with at the very most 115 peak dB, but normal listening levels of 95 dB. Exceded, can keep with the th KG4s to very high volume levels.

Be able to provide tight slam with low distortion. Strong visceral slam with the multidrivers, exceeded expectations.

Will give up low frequency extension to provide a solid tight sounding system. Sealed enclosure gave tight bass, met.

Frequency response at a maximum of -5 db down at 30 hz. Does not have to dig to 20Hz. No, had a -5 db of around 35 hz, will use larger drivers next time or a ported design, not met.

Be cost effective in driver selection; want to keep the budget to less than $300 for drivers, but no foam surrounds allowed. For a total driver cost of only $120 we are well below budget. The use of multidrivers at $20 each greatly exceedes the performance of subwoofers with single driver cost in the $150 to $200 range, by far exceeded expectations.

Have cross over frequency and driver balance be easily adjustable. Met, the low cost crossover provide easy adjustment, just not the most transparent cross over, the KG4s sounded more solid state like.

Be able to apply what I learn for the next upgrade of my Cornscala system’s subwoofer. Yes, now I'm confident to move to a multidriver system for my Cornscalas, just need to have larger drivers. Could investigate the use of lower powered woofers (instead of subwoofers) in a multidriver configuration. Running multiple 12's ported, or 15's sealed. Also want to provide full floor to ceiling coverage. 5 12's each side with 4 inches between drivers is about 7 feet tall. 4 12's with 4 inches between drivers is about 5 feet tall.

[Linkster]

Mike - I also have some (4) of these 10" DVCs and was wondering what to do with them. I am interested in knowing more about the design you came up with. From what I can tell, the cabinet is 3.3 cu ft and sealed. What dimensions did you use, what type of bracing, etc.?