DSP Filter To Extend Bass Response

Hi guys,

Quick question I haven't found much information on.

What are peoples thoughts on increasing the bass response of a multi way ported speaker by using an appropriate DSP filter?

It would be as below, where the first image is the natural gradual roll off down to the tuning frequency of 30hz and the second image has had a DSP filter applied to flatten the bass response down to the 30hz tuning frequency.

I don't plan on doing this as the gradual roll off of my speakers compliments room gain nicely but It is just something I wondered if its applicable in practice or if there would be any negative effects such as reducing bass accuracy and transient response etc.

The above assumes the amp is capable of driving the load and that the xmax of the drivers in question would be sufficient.




Thanks,

Andy.
 

eriksquires

Member
2013-05-10 4:11 pm
Hi Andy!

Equalization to extend bass in general is a common thing. However, with a ported speaker, you end up increasing the cone excursion dramatically vs. a sealed speaker, so you should be more careful. Several tools can help you visualize this, but WinISD is one. Design a box with a sealed and ported version and compare the excursion at various output levels.

Perceived bass is often better improved by using bass traps and equalization above the port (if any) tuning frequency.
 
Thanks eriksquires,

My thoughts on using a filter to do this would be to flatten the bass response down to the tuning frequency but never in an attempt to extend the response beyond this for obvious reasons with excursion etc as you mention. So in the above images, a gradual filter has been applied to raise the bass response in order to counter the natural roll off from 200hz down to 30hz to flatten the response.

I suppose this could be a useful technique in very large rooms where room gain is not significant. Thanks for the tips with the bass traps as well, I may give that a go to try and get the bass response more even throughout the room.
 

eriksquires

Member
2013-05-10 4:11 pm
Thanks eriksquires,

My thoughts on using a filter to do this would be to flatten the bass response down to the tuning frequency but never in an attempt to extend the response beyond this for obvious reasons with excursion etc as you mention. So in the above images, a gradual filter has been applied to raise the bass response in order to counter the natural roll off from 200hz down to 30hz to flatten the response.

I suppose this could be a useful technique in very large rooms where room gain is not significant. Thanks for the tips with the bass traps as well, I may give that a go to try and get the bass response more even throughout the room.

Of course, another way to extend the bass is to limit the midrange and treble. :) I usually like to follow the B&K curve in room, so +3 around 70 Hz, and -3 at 20 kHz. You are not very far from that at all.
 
Semantics = not helpful.

I meant, design a speaker cabinet, a good simulator will include excursion calculations at various levels and frequencies, which can help determine the best application of bass equalization.

Erik

Thanks for this, I have used unibox to get an idea of excursion at various power levels in my cabinets. All so far are within limits, both with and without the dsp filter applied.

Of course, another way to extend the bass is to limit the midrange and treble. I usually like to follow the B&K curve in room, so +3 around 70 Hz, and -3 at 20 kHz. You are not very far from that at all.

With regards to cutting the mid and treble, this is exactly what I do when using a boost filter on the bass region.. Ie. I apply the boost, but then reduce the line input level of the driver to ensure the maximum peak is always at or below 0dB then adjust the input levels of the mid and tweeter to suit the new woofer level as required.

Thanks for the tips. It is something I have wondered about for a while, even if I'm not going to apply this to my current speakers.