# Simulation Overview of the 'Double Bass Array' Configuration.

OP

#### René - Acculution.com

##### Senior Member
Technical Expert
I am not trying to argue that this response shape can be predicted from the radiation of a piston in an infinite baffle into half-space. My question was about the nature of the stimulus used in the simulation itself.

So why should I care about "radiation of a piston in an infinite baffle into half-space" then? Because that's how the on-axis pressure at a point at distance d from the piston is calculated using the Thiele/Small theory. For an ideal sealed or infinite-baffle subwoofer with zero voice-coil inductance, in the T/S theory the passband is the frequency region for which the acceleration amplitude is constant with frequency.

For such a sub, with an applied voltage having a constant amplitude vs. frequency:
• The displacement amplitude vs. frequency has a low-pass characteristic
• The velocity amplitude vs. frequency has a bandpass characteristic
• The acceleration amplitude vs. frequency has a high-pass characteristic (same as the pressure response of the sub itself)
This nature then becomes relevant when such a sub is placed in multiples in a DBA. One might rightly wonder how the subs' response according to the T/S theory is modified by the DBA. I would argue that, to determine such an effect, such a simulation would best be done with a stimulus having a constant acceleration amplitude with frequency.
I believe I used constant acceleration without any filter on it. You then need to look up the pressure in a tube with one end having acceleration and the other end perfect absorption.

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#### tmuikku

##### Senior Member
You could argue that they should be placed halfway up now, but I am going with this setup, since you probably have to place them near the floor in most situations anyway. In general, as you stray more and more away from the ‘walls moving’ situation, the response curves will naturally take a hit.
Cool sims, thanks!

What do you think how far one push it to still be useful arrangement? I mean, if the idea and implementation was simplified to just two subs and vertical dimension would it still work? one sub below the main listening position seat and one above would make easiest / cheapest / smallest practical implementation only if it worked. If it works, then shape of the room would not matter that much.

##### Major Contributor
Is this the reason of different delays?))
View attachment 238577

:
View attachment 238580

I agree; this will help to adjust the subs in reality

Notice that you have the rear subs pointed toward the wall. Right-clicking on them rotates the driver. Clicking on the individual sub to highlight it will allow you move the sub with the arrow keys for more accurate positioning. The spinbox for the delays only accepts whole numbers, so distance only moves in roughly one foot increments, therefore, 'inch' or sub-millisecond precision is not possible.

OCA

#### Flaesh

##### Senior Member
you have the rear subs pointed toward the wall.
I had rear subs pointed toward the wall in my second DBA with IB front subs)).
In real processors\software delay and gain increments is small enough; for roomsim modeling you may adjust size and absorption respectively

OP

#### René - Acculution.com

##### Senior Member
Technical Expert
Cool sims, thanks!

What do you think how far one push it to still be useful arrangement? I mean, if the idea and implementation was simplified to just two subs and vertical dimension would it still work? one sub below the main listening position seat and one above would make easiest / cheapest / smallest practical implementation only if it worked. If it works, then shape of the room would not matter that much.
It all depends. But perhaps it is the best way if two subs are to be used.

#### ppataki

##### Major Contributor
I have created a digital filter acting like a virtual bass array in REW. I never had a double bass array system so I cannot compare with the real thing but the digital version works nicely. Here's a link to the tutorial video if anyone is interested:

This is pretty cool @Serkan, thank you for sharing, much appreciated!

I don't want to play the devil's advocate here but just one point that came to my mind: one of the advantages of a real-life DBA is to get rid of the freq. dips too (DBA would create a wave plain that should fill the dips pretty much everywhere in the room)
With this digital solution I don't see that really happening
It indeed cut the peaks and somewhat filled the dips too but what is the added value vs doing the same with traditional EQ filters?
Thank you

#### OCA

##### Addicted to Fun and Learning
Forum Donor
This is pretty cool @Serkan, thank you for sharing, much appreciated!

I don't want to play the devil's advocate here but just one point that came to my mind: one of the advantages of a real-life DBA is to get rid of the freq. dips too (DBA would create a wave plain that should fill the dips pretty much everywhere in the room)
With this digital solution I don't see that really happening
It indeed cut the peaks and somewhat filled the dips too but what is the added value vs doing the same with traditional EQ filters?
Thank you
Your welcome! You're absolutely right that this is not a true replacement for a physical double bass array but more like a quick and easy to implement digital prefilter before you start correcting your speaker response.

Edited: As per the added value compared to EQ filters, I guess you can expect less overall deterioration in clarity as the counter signal is based on a Dirac delta which will not lower the impulse magnitude of the final response as an IIR filter does.

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#### ppataki

##### Major Contributor
Your welcome! You're absolutely right that this is not a true replacement for a physical double bass array but more like a quick and easy to implement digital prefilter before you start correcting your speaker response.

Edited: As per the added value compared to EQ filters, I guess you can expect less overall deterioration in clarity as the counter signal is based on a Dirac delta which will not lower the impulse magnitude of the final response as an IIR filter does.
Sounds good, next week I will have time to try it
Will report back with my measurements

Can you please elaborate what you mean by lowering the impulse magnitude
Thank you

#### OCA

##### Addicted to Fun and Learning
Forum Donor
Sounds good, next week I will have time to try it
Will report back with my measurements

Can you please elaborate what you mean by lowering the impulse magnitude
Thank you
You can see the difference better in step response (un-normalized) comparison which is sort of integral of the impulse response:

red is 100Hz xo VBA filter, blue is 20-100Hz 6 band REW auto min phase EQ

sorry for off topic!

Forum Donor

#### ppataki

##### Major Contributor
I made a huge mistake by posting under this topic. I didn't use to consider a double bass array in my system but these graphs are obliterating my digital correction works in every way and it seems I will have to cough up some cash for new subs soon

Beware @Serkan that DBA will work only in a regular-shaped room with at least 4 subs - if you have an irregular shaped room most likely it won't work
I tried it in my irregular shaped room and unfortunately it did not work........

#### Flaesh

##### Senior Member
I made a huge mistake by posting under this topic
I think not! VPDBA (sometimes and somwhere wrong called SBA) deserves fair criticism and exposure))
To be honest ever arbitrary placed VPDBA (APVPDBA ) "kills" first lenght mode:

to cough up some cash for new subs soon
More or less suitable room is desirable for simple 2channel DBA, while some unperfections may be compensated by EQing subs individually.
Can you show your room drawing?

#### OCA

##### Addicted to Fun and Learning
Forum Donor
Beware @Serkan that DBA will work only in a regular-shaped room with at least 4 subs - if you have an irregular shaped room most likely it won't work
I tried it in my irregular shaped room and unfortunately it did not work........
My room has a descent rectangular shape (5.35m x 3.75m x 2.65m) but there's a door opening in the middle of the rear wall and there's no door. So there's a door sized hole at the back. Would that be a problem?

#### OCA

##### Addicted to Fun and Learning
Forum Donor
I think not! VPDBA (sometimes and somwhere wrong called SBA) deserves fair criticism and exposure))
To be honest ever arbitrary placed VPDBA (APVPDBA ) "kills" first lenght mode:
View attachment 250615

More or less suitable room is desirable for simple 2channel DBA, while some unperfections may be compensated by EQing subs individually.
Can you show your room drawing?

The red line is an opening to dining room with no door (old German flat). I have two Focal Air subs at opposite corners but I don't use them in the hifi system. The speakers placement and LP are accurate in the drawing.

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