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East 17th February 2006 09:13 PM

impulse response vs. enclosure size
 
Hi guys,

I am new here and want to build an active subwoofer with a sealed
enclosure. Going to use a Hypex UCD400 and Mivoc HCM 12 T.

Trying to get the best possible result I am not sure if there is a big
difference between Qtc=0,579(75l) and Qtc=0675(45l) for the impulse
response in regard to suitable enclosure sizes?

Has the sound, the perfect accuracy if I would have the “perfect”
impulse response, however I can achieve that?

Thank you in advance for any help!

Peace, Andy

Simulation with WinISD:
http://www.djeast.de/misc/Simulation.jpg

Volenti 17th February 2006 10:48 PM

Well you are going to hurt your impulse response more with the subsonic filter, the eq boost (which natural room gain will do some of the work there) and the native Le of the subs voicecoil, which I'm guessing is around 2.5mH+ by the graph then any minor enclosure volume changes.

I would personally choose a middle ground of ~60L and experiment with with fill.

Also the in-room response will vary wildly with location, room treatments/lack there of and phase relitave to the mains.

Ron E 17th February 2006 10:49 PM

You will notice very little difference between the two alignments.
The first thing you would notice is the box size difference, and you will naturally think the larger one goes deeper, even if it doesn't ;) The mind is a crazy thing.

People often think they can tell, but even the difference between impulse/frequency response for Qtc=0.5 and 0.7 is very small. 1.0 starts to get a little tubby, but even 1.3 sounds OK with most music.

Modeled Impulse response isn't necessarily what corresponds with tight or accurate bass, anyway. Low distortion and having a response that matches the room well is arguably much more important.

East 18th February 2006 10:01 AM

Thanks for your help! :)

I guess I have a bettter understanding for the problem now.

ChristianThomas 21st February 2006 05:38 PM

Hi,

I would go for the Qt = 0.58 without hesitation. This is almost exactly a Bessel alignment (I presume this is why you chose it). My experience with subwoofers is that they tend to carry a single characteristic to their sound irrespective of the filtering you use. That's not to say that some filtering isn't better than others, only that this signature pervades every alignment. The other thing is that the lower you can get the resonance, the less sensitive the ear is, and the less the effect of any stored energy will be. That means it is less likely to be heard.

In terms of impulse response, the optimum is a Q of 0.5 so you will get marginally more ringing than none. But the Bessel has the advantage of zero group delay over a wider area; to a higher frequency. To some extent one might be able to say that the transient response is better because a group (or burst) of frequencies all get their reactions at the same time.

Though the truth is that it is the integration into the rest of your system that will be the major factor in determining the impulse response, a Bessel is not a bad place to start. Since you say you are a beginner, I would suggest carrying this simplicity to the low pass filtering too and use a second order bessel there also. This is a good, practical, filiter shape. I like symmetry in filter sections.

If the drive unit breaks up badly higher up, then add another section of filters. A good idea for this is to do it at the same frequency as the bass unit you are combining with - if you have a 3 way loudspeaker. For a two way speaker this frequency would be too high and it forces the design back into your court as to what you would chose to use to get rid of this mess. Because you don't have an ideal, or near ideal, to aim for, my recommendation would be to follow old fashioned filter theory and get rid of it as quickly as possible; one of the less extreme Chebyshevs might be where I would start. The aim here would be to keep things as they were as far as possible, and then switch it off.

Hope this helps

Kind regards

Christian

Artmaster 23rd February 2006 01:53 PM

I think it's absolutely different drivers, that's why it should sound different either.
even the same model a few pcs has differens.
and you can force ones working for choosing box, but any has optimal for your room, another optimum for your opinion, for your favorite phonation.
I think all of DIY'ers looking for something personally - design, sounding.
should you get absolutely same responce from 10" in 50 liters and 12" in 70 litres - anyone will be able to catch sight of sound.
it's seems like - "ideal system" is impossible :) looks like true.


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