Multiple Small Subs - Geddes Approach

[camplo]

1) You've said the source type does not matter, then why didnt you like ported Summa? You could have ported it very low at 25Hz and got a shallow sloped response to blend with other bass sources.

From my experience asking questions, the port just creates one more complexity in phase. If LF extension is challenging excursion then add more woofers. Don't forget also, fixing Group Delay with DSP, adds more delay to the whole signal.

 

[wonderfulaudio]

Hi Earl (@gedlee),

Please help me understand below questions:-

1) You've said the source type does not matter, then why didnt you like ported Summa? You could have ported it very low at 25Hz and got a shallow sloped response to blend with other bass sources.
2) Why did you like dipole? if we ignore the SPL loss for a moment.
3) How important is it to raise one of the subwoofers amongst the three subs?
4) Can we sum the subs below the first room modes in phase with other subs?
5) In a bass reflex sub, at the tuning frequency there is 180 degrees phase shift. With modern DSPs the phase at the tuning frequency can be reversed back to make more like the phase of a sealed sub. Do you think, it is worth a try to mimic a sealed sub using a bass reflex one?

Thanks and Regards,
WonderfulAudio

I would appreciate if somebody could answer point by point for better understanding.
Thanks and Regards,
WonderfulAudio

 

[AllenB]

3) How important is it to raise one of the subwoofers amongst the three subs?

Having spatial diversity in that dimension is what gives you control over those modes. People speak of leaving certain things to chance. Who knows, you might get lucky. Go ahead anyway, do some measuring and see how it goes.

 

[gedlee]

Hi Earl (@gedlee),

Please help me understand below questions:-

1) You've said the source type does not matter, then why didnt you like ported Summa? You could have ported it very low at 25Hz and got a shallow sloped response to blend with other bass sources.

The original Summa had ports. But after I went with multiple subs I realized that at best porting was not necessary and it could also be detrimental because of the total lack of cone control below tuning. So I just deleted them. All my subs are closed box.

2) Why did you like dipole? if we ignore the SPL loss for a moment.

The bass was clean, cleaner than most monopoles, but still not as good as multiple subs.

3) How important is it to raise one of the subwoofers amongst the three subs?

I think that it should be advantageous, but not critical. Only one of my subs is a few feet off the floor.

4) Can we sum the subs below the first room modes in phase with other subs?

We can, but I am not sure why one would want to do that. In my room, the first mode is at about 22 Hz. Not much point in trying to go lower than that.

5) In a bass reflex sub, at the tuning frequency there is 180 degrees phase shift. With modern DSPs the phase at the tuning frequency can be reversed back to make more like the phase of a sealed sub. Do you think, it is worth a try to mimic a sealed sub using a bass reflex one?

You could never do that. One cannot control the phase difference (180 degrees) between the cone and the port with DSP so below tuning the two are just cancelling each other out - no sound to EQ - and trying to do so would just add a lot of excursion with no gain in output.

 

[wonderfulaudio]

I think that it should be advantageous, but not critical. Only one of my subs is a few feet off the floor.

Hi Earl (@gedlee)
1)Can the corner sub be the one that is lifted? It could be aesthetically more acceptable, the other two subs not so.
2)The multi sub article at https://mehlau.net/audio/multisub_geddes/ recommends adding delay, but you have told delay is not a good idea, am I understanding right?
Thank you,
Warm Regards,
WonderfulAudio