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Discussion Starter #1
I have one 12" Peerless XLS driver, two 12" Peerless XLS passive radiators and one 350watt amp module.

Driver specs:
Nominal impedance 8ohm
Zmin ohm/Hz = 4.7/106
Maximum impedance ohm 64.2
Resonance frequency fs 18.1Hz
Mechanical Q factor 3.70Qms
Electrical Q factor 0.21Qes
Total Q factor 0.20Qts
Xmax (linear one-way) 12.5mm
F (Ratio fs/Qts) F 90Hz
Mechanical resistance Rms 5.12(Kg/s)
Equivalent volume VAS 139.2 (ltres)
Reference voltage sensitivity Re 2.83V 1m at 106Hz (Measured) 90.6db

Amp specs:
Continuos output power: 350 watts RMS into 4 ohms & 240 watts RMS into 8 ohms
- Frequency response: 20 to 160 Hz
- Adjustable crossover: 50Hz to 160Hz
- THD: <0.1% - S/N ratio: >95db
- Bass boost: 6db @ 35Hz
- Input sensitivity @ max vol.: 120mV, Line out: 200mV @ max vol.
- Power: 240V 50Hz
- Module cutout approx 240W x 285mmH
- Remote receiver cutout 125W x 65Hmm.

Following a design I found online, I have just built a 50 litre box but I'm disappointed with the performance (drops off at around 25hz). The sonotube designs look interesting (& obviously I'd ditch the PRs) but I'm looking for a proven design which I can follow, rather than calculating/designing one myself. My room a concrete block garage, 7 X 4.2 metres approx. (L-shaped) in size. Ceiling height 2.4 metres (8').

Any suggestions as to which direction to go in? Are there any ready made plans derived from Steve Callas's approach/recommendations?

Cheers,
Blue.
 

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Chances are that 6db of boost at 35hz isn't doing you any favors. That boost is usually created by a high Q rumble filter. With such a high boost, chances are the rolloff, usually 2nd order, starts pretty close to 35hz so in addition to the natural rolloff of the driver/PRs, you've got the amp working against you as well.

Your design sounds very much like another members Peerless build that was discussed recently. However, your driver T/S parms don't quite match...wondering if you could have used the wrong Peerless XLS driver...from memory, it seems like there were quite a few variations when I trying to find the specs to model the version he was using.

-Brent
 

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Discussion Starter #3
Well it's funny you should mention about tuning...

I have two threads running:

http://www.hometheatershack.com/forums/diy-subwoofers/8181-low-spl-20hz-12-xls-peerless.html
(if you look near the end of the thread I have posted a graph which shows I get a funny squiggly hump at around 24hz - I'm wondering if it's the wrong Fb tuning... could you check the graph & measurement method please!)

http://www.hometheatershack.com/for...blems-tuning-passive-radiators-built-box.html
(this thread explains the mass I have put on the PRs - basically 307-350 extra on each PR [at one stage I had 390]. Initial weight of the PRs is 425gms - good memory!)

The designer claims obtaining readings flat down to 20hz anechoic with extra mass of 365 each. The amp I think is the same as mine (his Jaycar, mine MWave [Australian suppliers] - look the same but who knows?). At present I have 335gms and my box is very slightly smaller. The design is here: http://www.geocities.com/adrian_mack/

I have heard that it is possible to modify these amps to remove the boost but given that the design I followed didn't stipulate doing this, should it be necessary? But it is a very interesting thought - I've always wondered why I can't see any peak at 35hz..

I can't say that I noticed any real difference in output with the different weightings though - but I was mainly concentrating on the graph dip at Fb and not overall SPL. I'm wondering if I have stuffed something up using REW and so getting false readings? I calibrated the soundcard (but that's a different thread here: http://www.hometheatershack.com/for...pdif-vs-analogue-output-receiver-sub-rew.html)

Cheers,
Blue
 

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The designer's claim is actually that it is down 8 dB at 20 Hz compared with 50 Hz and a claim that it is flat to 20 Hz in whatever room he has it in.
 

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Discussion Starter #5
The designer's claim is actually that it is down 8 dB at 20 Hz compared with 50 Hz and a claim that it is flat to 20 Hz in whatever room he has it in.
Yes, good point.

I seem to be getting a drop of about 12db between 50hz and 20hz (at 75db measurement level - don't know if that makes any difference?) 'anechoic' (not really anechoic, just measured away from the walls, close mic at driver and then each PR - readings averaged). I also get a drop of about 12db between 50-20hz with the sub in the corner of the room.

Could these differences between the designer's and my results be due to measurement error (especially on my part!)? Is this the performance I should expect from my sub, given its dimensions and parts used? Is it worth worrying about not obtaining higher SLP at that lower 24-20hz region (is it likely to be noticeable?). Is it worth starting again with a new design? I.e. do you think a sonotube design using the driver and amp I have would give me better performance or do I need a bigger driver & amp?

Cheers,
Blue
 
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