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Old 5th January 2005, 08:19 PM   #1
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Default dual driver sealed sub <40Hz only

I think a sub project is in order to match my KLF-30's for music only. Sound quality is top priority. The 30's are 102dB sensitive and can reach down to 36Hz themselves. I'd like to cross the sub over about 40Hz or so with a steep slope just to add on the very last octave down to the ~20Hz region.

I'm having somewhat of a problem finding a suitable driver for this project. As always, I am trying to get the most for the least. I already have one DPL12 and am very seriously considering buying only one more DPL12 to serve as my extra woofer. Each KLF-30 has dual 12's in it anyway, so I doubt one 12" sub would be able to keep up. Heck, two still might not. But, buying all new 15" or larger drivers will exceed my budget a tad....

When listening loud, I don't think I hit more than 100-105dB peaks. Usually, the level is a lot lower (currently listening at about 70dB with peaks). I want something that is flat to 20Hz (or a little lower), though, and can play at a high enough level to match my 30's when I am listening loud. So, in other words, at least 105dB sustained at 20Hz.

I have chosen sealed for musical purposes... I am not a big fan of ported designs. Dual driver is a must. Volume of enclosure required cannot exceed 2.5 cubic feet.

Are there any other drivers I should consider besides the DPL12 for this app? Keeping cost at a minimum...

Oh, and while I am thinking about it... I really wish I could end up with net load of 4-ohms, but using two DPL12's (or most other subwoofers, for that matter) will leave me with 8-ohms. Won't this hurt my efficiency and basically negate the benefits of using two drivers? But are there actually any 8-ohm subwoofer driver out there?

Sorry for the tons of questions... Any help is appreciated.
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Old 5th January 2005, 09:30 PM   #2
simon5 is offline simon5  Canada
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A single DPL12 can probably reach 105 dB at 20 Hz with room gain in a sealed box big enough. The problem is that you want it all, small box for 20 Hz @ 105 dB... It's feasible, but pricey.

Maybe you could try isobaric to bring your box smaller and achieve your goal, I hope you have a very powerful amplifier lying around...!
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Old 5th January 2005, 09:53 PM   #3
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105db in a sleaed box is easily probable, it wont even be that big!(coming from the guy who thinks anything shy of 180l is small). Mind you youll need alot of power to get full excursion in a tiny box. Dpl is pretty close to shiva though, and since its in a slealed box you could prob get a shiva which would sound quite musical as well.
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Old 6th January 2005, 12:08 AM   #4
RHosch is offline RHosch  United States
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Are the KLF-30's ported? If not, you won't want a steep crossover at 40 Hz. Shoot for 2nd order at ~40Hz if the mains are sealed, or filter the mains 12dB/oct at 40Hz and the sub 24dB/oct at 40Hz. Or, you could go for the more conventional approach and use symmetric 24dB/oct filtering on mains and sub somewhere around 80Hz. That would greatly relieve the stress on the KLF-30 low frequency drivers and allow them to produce less distortion on midbass and lower midrange signals.

As for drivers, since dual driver is a must, I'd recommend a second DPL12 as you won't find a pair of drivers for anywhere near the price of a single DPL12 that will offer anywhere near the performance of two DPL12's. A bonus is that they work very well in smallish sealed boxes. As for impedance, I'm a bit confused as I thought the requirement for dual drivers was to maintain stereo integrity. In that case, 4 ohm per channel is perfect for a typical prosound amplifier. If you are talking about a single enclosure, what's wrong with a single Tempest or other quality 15" driver?
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Old 6th January 2005, 01:32 AM   #5
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I saw an ascendant audio driver called Atlas that looks like its a pretty good value. XBL^2 15" sub 18mm one way excrusion 300watts $185. It has a smidge more displacement than 2 of the DPL's, but not enoug for more than a fraction of a DB more down in the low region. Its a good driver for a sealed enclosure also.

I'd personally go ported myself. You only want the lowest frequencys which takes the group delay factor out of the picture mostly. The only comprimise is enclsoure size. If you ask me taking up a little more space is a good trade off for higher efficiency. Its basically free. Flat response without EQ is something I like. Mostly because I'm cheap and I dont want to buy an EQ, but also due to all of the other effects it has on performance.
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Old 7th January 2005, 12:26 AM   #6
simon5 is offline simon5  Canada
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You could achieve close to your goals with a isobaric pair of DPL12 in a 153 liters closed box, I estimate about 103 dB at 20 Hz with a steep rumble filter, or you'll run in overexcursion. You'll need 200W per driver at 4 ohms or a 400W 8 ohms or 2 ohms amplifier.

Then you could go ported to workaround this problem. Then the port length is high, but passive radiator could work around this problem. Box size is great, about 70 liters tuned to 18 Hz would be perfect and you could achieve your 105 dB easily. About 112 dB with a 800W amplifier in 2 ohms or 8 ohms.
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Old 7th January 2005, 01:13 AM   #7
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I think I have a box type/size worked out... but powering it is my biggest worry. Which sub plate amps out there actually can run 2-ohms safely? And wiring for 8-ohms will cost me a fortune in amp power... I'd have to buy the 1000W, 4-ohm amp just to get 500W into 8-ohms. Not exactly cost effective...
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Old 7th January 2005, 02:48 AM   #8
RHosch is offline RHosch  United States
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Instead of building a plate amplifier into the enclosure, use an outboard stereo prosound amp. One channel per sub, 4 ohms nominal impedance, cheap prices, plenty of clean power... a good match. The only real need for a plate amp is if you require the crossover functions most have integrated.
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Old 7th January 2005, 06:55 AM   #9
simon5 is offline simon5  Canada
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Quote:
Originally posted by needtubes
I think I have a box type/size worked out... but powering it is my biggest worry. Which sub plate amps out there actually can run 2-ohms safely? And wiring for 8-ohms will cost me a fortune in amp power... I'd have to buy the 1000W, 4-ohm amp just to get 500W into 8-ohms. Not exactly cost effective...
You could get a QSC RMX 850 amplifier at 300$, 430W RMS in 2 ohms.

To achieve your goal, you'll need a isobaric pair of DPL12, this 430W amplifier and a passive radiator.
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Old 7th January 2005, 09:56 AM   #10
mike.e is offline mike.e  New Zealand
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I wouldnt go isobaric because efficiency is -3db,and the sensitivity of the DPL12 is already ~84db/1watt

70litres sealed per DPL12 Will do 'something' if its just music-I wouldnt run HT through them. Avoiding a ported box doubles your cost on woofers in this case. With a little room gain you should reach 108db at 20hz.

Bear in mind that the woofers arent exactly linear near their xmax [read: nonlinear distortion being horrible by then too]rating so you might want to limit the LF content slightly or give in to ports.

edit: also i forgot,if you run your DPL12s as high as perhaps 50 or 60hz then distortion from the main 12" speakers will be reduced[which,being commercial speakers and not subwoofers will have limited displacement]
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