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Sealed DIY subwoofer + EQ + amplifier questions

post #1 of 6
Thread Starter 
I've been running WinISD simulations for a few weeks now, intending to build a pair of decent sealed, flanked stereo subwoofers in the size 15" or 18".

What has remained a mystery during my extensive product research is amplification. Stereo Integrity HT 15" reaches F3 @ 20Hz in a 75 liter sealed enclosure, when 22Hz is amplified +9dB Q2.00. In this particular sealed enclosure, the mentioned subwoofer without EQ can handle 500W before reaching -10% Xmax, and exceeds it by a few percent at 600W which is still not fatal as it has way bigger Xmech. However I want to stay completely inside linear excursion for the sake of higher fidelity and less THD.

Reading the WinISD page, I need to divide maximum amplifier output level by a factor of 7.9 if I EQ +9dB. This would result in the 500W amplifier putting out slightly above 60W, limiting maximum SPL to 105dB. Is that enough for a small scale HT/music listening room? (Room gain not included)

Now here's what I don't get. With this EQ, actual output level for the rest of the range is 63W (-9dBFS at 500W output), while the 500W peak is situated at 22Hz (0dBFS at 500W output)? I suppose I still have to set my amplifier at maximum output, given that my DSP unit (Behringer DCX2496) is set at overall gain -9dB, and the EQ point at +9dB so that I don't clip signal and the peak sits comfortably at 0dBFS. Does this make any sense to you or is my trail of thought considering the gain structure completely wrong?

If I do what I mentioned above (negative gain to counter positive gain in the DSP unit/DAC), do I need to do anything to my amplifier to not overload the driver?

EDIT: Nevermind, I seem to have answered my own question by simulating filters further in WinISD.
500W -9dB gain is 63W, +9dB from 63W at 22Hz results in a 500W peak output at 22Hz while keeping the rest of the bandwidth at 63W. +9dB relative to 63W is 500W which of course would be impossible for the amp to handle because of 9dB worth of nothing but clipping. To keep the signal pure I should just apply global gain of -9dB into all channels and make sure it never goes beyond that. I'm not really worried about original source material's integrity as I only listen to 16-bit music and there is no benefit in 24-bit recordings.

Below the dark orange line is the sealed enclosure without EQ, and the orange one is two identical lines overlaying, other 63W +9dB EQ, other 500W with 0dB EQ and -9dB gain elsewhere.


Edited by seepra - 10/9/13 at 4:14am
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post #2 of 6
22hz @ 105db is impressive. What's the rest of the system going to be?
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post #3 of 6
Thread Starter 
Thank you. However, I will hold my amazement until the system has been assembled some months from now, as the T/S parameters fed into WinISD are manufacturer given. Even though Data-Bass has confirmed they're accurate, and room acoustics help even further but I have never built a subwoofer system before so there's no knowing what all can go wrong. It's sealed though, so I've eliminated most of the bad what-if scenarios (port air velocity, overexcursion, bad group delay and phase issues..).. Here's some measurements on a sealed unit someone else built, it seems to outdo one of the very respected HT subs, SVS PB-13 Ultra!

For mains I've got several options, of which highest quality would be Genelec 8030A or 8020A. They have very little distortion, very even frequency response, minimal self-noise, are incredibly well built and durable, and they reach -3dB around 50Hz so they integrate fairly easily even with a shallow crossover. I've heard them in several situations in both home and studio environments, and compared them both (as well as 6010A) against Behringer, M-Audio and KRK Rokit offerings of similar size and price, and I have to say they've so far been the best overall representation. For more bass extension, Behringer B3031A have done well too but I sold them because at the time I insisted going full-range with the monitors and they had some port noise issues, might have been a build QC issue too as my friend reported no port noise on his pair. They're big and ugly though, and I'd rather minimize the clutter around my desk.

As a DSP/DAC unit I was contemplating on the Behringer DCX2496. It's a six-way crossover and DSP rack unit. I was intending to use it for mains (high-pass), stereo subs (low-pass), and a full-range copy for a possible future headphone amplifier. It also acts as a DAC when fed AES/EBU or S/PDIF. I'm not sure does the processor capacity allow me to do more than the 9dB peak and -9dB static gain into two channels, but if so I will also look into room correction and phase correction with it.
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post #4 of 6
So, you're into that "Pro" stuff.

Have you been here?: AudiogoN
Edited by billbartuska - 10/9/13 at 8:47am
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post #5 of 6
I can tell you now that manufacturer T/S parameters can be so completely wrong it isn't funny. Best bet is to measure your drivers yourself (if possible of course) and run your sims with your own data. Even each driver itself may be off from the other, so build each enclosure to it specifically. Or just hope for the best with the data they present.
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post #6 of 6
Thread Starter 
Quote:
Originally Posted by SwishaMane View Post

I can tell you now that manufacturer T/S parameters can be so completely wrong it isn't funny. Best bet is to measure your drivers yourself (if possible of course) and run your sims with your own data. Even each driver itself may be off from the other, so build each enclosure to it specifically. Or just hope for the best with the data they present.
Yeah, this is particularly true in the low end segment where QC is an issue. At least a third party has measured the parameters from one sample, and many people have amazing results with these drivers, but of course there is some leeway in the individual drivers.

I'll try running my own measurements just to be sure, thanks for the headsup!

As far as AudiogoN goes, I've heard them mentioned but never looked at the site. Not really convinced with the lack of professionalism that devoting a section for cables represents. Overall "high-end" is a nonsense term used to sell over expensive gadgets that are not measurably better. I'll stick to DIYaudio and HydrogenAudio. I'll take a look anyway.

And yes I've come the full circle, started as a kid with studio gear, converted to silver cables and Wharfedales and Naims, heard Focal Scala Utopias once and when the salesperson blamed silver cables for the painfully sibilant sound I asked about , I read up a bit on marketing nonsense and converted back into measurable performance and pro gear (having worked as a part time audio technician played it's part in choosing tried and proven pro gear I could easily compare)
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