Too small sealed box-nasty peak, and too high Qts-can EQ solve this??

Hi Guys...
Please see the attached image.

Im trying to put a 15" midbass driver in a ridiculously small box.
Driver needs 180L for flat responce, but im trying to fit in 30L box !!!

I have two problems
1. Nasty peak between 200-100Hz
2. Qts (sealed) is too high 1.3 !!!!

Can a Minidsp EQ solve this to get a flat response???
What problem is this very high Qts going to create??
Any issues with amp power requirements ??

Thanks & Regards
AudfrkNaveen
 

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Crashpc

Member
2008-11-26 4:28 pm
Heya.

3dB peak is not really "really big", and not a fatal problem by itself. EQ will solve that. Only thing is that you will not get much bass from that, and that's it. Also carefully with power input, as the speaker will not have the chance to cool down its coil.
 
In other places here at DIYAudio they talk of an amplifier with a low output Z as being able to tame down a high Qts -versus something like a tube amp. I think theoretically you could have an amplifier with negative output impedance (lessthanzero) which may tame it further. Unsure if such an amplifier even exists.

You can increase the box size virtually by stuffing it full of damping material, but that only goes so far and certainly not 30 --> 180... More like 30 --> 33...

You could drill an array of holes and make a dispersed resistive port of sorts, that plus the stuffing could turn it from sealed into an aperiodic - that might reduce the Qts. No idea of what it'd do to the frequency response, maybe tames the hump but falls off even faster.

You can force the driver (if it and the amp can take it) by using the trick the OB woofer assist designs do - put in a line level filter with a reversed rising response. That could be done using MiniDSP or op-amps. That might extend the flat frequency range lower, but for sure at the expense of how loud you can play it.

You can only defy physics so far. Hope this helps,
 
Heya.

3dB peak is not really "really big", and not a fatal problem by itself. EQ will solve that. Only thing is that you will not get much bass from that, and that's it. Also carefully with power input, as the speaker will not have the chance to cool down its coil.
Thanks a lot for highlighting the coil heat issue!! I will see what i can do for that !!
 
In other places here at DIYAudio they talk of an amplifier with a low output Z as being able to tame down a high Qts -versus something like a tube amp. I think theoretically you could have an amplifier with negative output impedance (lessthanzero) which may tame it further. Unsure if such an amplifier even exists.

You can increase the box size virtually by stuffing it full of damping material, but that only goes so far and certainly not 30 --> 180... More like 30 --> 33...

You could drill an array of holes and make a dispersed resistive port of sorts, that plus the stuffing could turn it from sealed into an aperiodic - that might reduce the Qts. No idea of what it'd do to the frequency response, maybe tames the hump but falls off even faster.

You can force the driver (if it and the amp can take it) by using the trick the OB woofer assist designs do - put in a line level filter with a reversed rising response. That could be done using MiniDSP or op-amps. That might extend the flat frequency range lower, but for sure at the expense of how loud you can play it.

You can only defy physics so far. Hope this helps,

This is exactly what I'm thinking too !!! Aperiodic box!!
In fact the graph i posted includes Damping material. Since the box is too small, it still shows the peak. Will check how it turns out.
 
A common way to deal with this issue is a Linkwitz transform which the miniDSP can do. You need more power and more excursion for it to work.

But as a midrange i tend to like low pressure midBoxes (like aperiodic TLs. You can get some aperiodic releif of theat bump by drilling a series of holes on the back and damping the inside of that panel heavily (you will have to tune). It is surprising how much that can clean up the mids. You might not get quite as much extension but it should be better behaved.

dave