Cardioid sub array - semi diy

[Luvchampagne]

Hi
Currently have Revel Salon2s in challenging room with 25 foot ceilings. 22x 25x25 opening to kitchen and hallways. 6 sided room facing west and opening east. Also opens to loft.


PLAN
Components
4 x GSG Audio BTS 18-21 boxes
4 B&C 18DS115 drivers
4 Crown XLS2502 amps
Minidsp HTX

Goal was cardioid specifically 25hz to 80hz but due to irregularity of room and setup it is more of a boundary reinforcement sub array crossed over at 80hz.
Salon2 HP 80hz
Subs HP at 80 hz and LP at 20hz to minimize floor vibrations.

Trying to improve reflections and nulls.
Have used MSO and REW on 3 smaller subs and better than just Salon2 full range but I think there's lots of room for improvement.

Are the B&C drivers appropriate or overkill?
Already own the 4x Crown XLS2502
Looking to buy the Minidsp HTX.
Currently using Minidsp 2x4hd only for the subs and using Salon2s full range.

Thoughts?

 

[Keith_W]

I don't think anybody can predict whether that is going to be a good setup or not based on the information you provided. Four 18" subwoofers certainly sounds like enough, but it is a VERY LARGE ROOM and who knows what your SPL preference is. I would say it's a good start, but nobody knows for sure until it's in your room and some measurements are taken.

FYI I thought that 4x 12" subs were enough for my room (6m x 7m x 2.7m). It's not quite enough, I get audible flapping (subs hitting excursion limits) when the volume is turned up. But at normal listening volume it's fine.

 

[Tell]

Why would one use cardiod subs at home? Boundary gain is a good thing (equalized of course).

 

[Ktacos]

I don't think anybody can predict whether that is going to be a good setup or not based on the information you provided. Four 18" subwoofers certainly sounds like enough, but it is a VERY LARGE ROOM and who knows what your SPL preference is. I would say it's a good start, but nobody knows for sure until it's in your room and some measurements are taken.

FYI I thought that 4x 12" subs were enough for my room (6m x 7m x 2.7m). It's not quite enough, I get audible flapping (subs hitting excursion limits) when the volume is turned up. But at normal listening volume it's fine.

Wow, I have a similar sized room, I wouldn't really call that very large at all, at times this space feels cramped. Four 18's is nuts, I get gut wrenching whole house shaking bass from two 12's. Frankly four 18's IS plenty for your space, I mean we bring less than that for bigger live shows. Are you aiming for hearing damage spl's or something?

 

[NTK]

Since in a cardioid implementation the purpose of the back driver is to cancel the energy from the front driver radiated backward, it is not really "contributing" to the total sound energy radiating into the room.

In the example shown in the link below, the on-axis (front) SPL with the additional sub is increased by only 1 dB, not the 6 dB normally from the coherent summing of 2 stacked identical subs. The back SPL is also reduced by 20 dB and will severely reduce the room boundary gain one would normally get from a typical omni sub sitting next to a wall. You may actually get less total effective output energy from 2 subs in a cardioid config than 1 sub in a normal config.

Cardioid Subwoofer Setups | FOH | Front of House Magazine

Managing low frequencies is one of live audio’s constant challenges. We deal with room nodes, architectural resonances, uneven coverage and unwanted spill. ...

fohonline.com

 

[Luvchampagne]

Wow, I have a similar sized room, I wouldn't really call that very large at all, at times this space feels cramped. Four 18's is nuts, I get gut wrenching whole house shaking bass from two 12's. Frankly four 18's IS plenty for your space, I mean we bring less than that for bigger live shows. Are you aiming for hearing damage spl's or something?

No. Not done for SPL at all.
Done solely to minimize nulls and other room effects.
Now looking at 4 x 21" in a cardioid setup. Each with a Crown XLS2502 and run through a minidsp Htx.
HP Salon2 at 80hz.

1 rear facing and 1 front facing 6 inches apart on the South end of the room. Same setup on the North end of the room.
All somewhat hidden from view.

 

[Geert]

A cardioid sub setup isn't going to be cardioid when placed close to a wall. In a 22 x 25 x 25 room, everything is close to the wall considering the wave length of very low audio frequencies. Just saying that I'm not sure the whole idea is going to work. I have a lot of experience with cardio subs for PA work, but then we're talking other dimensions.

4x B&C 18DS115 with a capable amp should be sufficient to cause structural damage to your room

 

[Exprymer]

Unfortunately a cardoid low frequency radiator is not enough to suppress the modal behavior of a room. It can however suppress the phenomena called SBIR (Speaker Boundary Interference Response) which is a local cancelation at a given position and frequency.

One would still see the peaks and dips caused by the modal behavior.

 

[levimax]

GSG kits are great, I didn't know what to expect and they exceeded my expectations. I have played around setting up a DBA like system to cancel modes with out much luck... most successful set ups seem to have 8 or more subs. I decided to wait for DIRAC ART and if you read and look at the graphs posted on the ART threads they look impressive and most report it works well with 4 or even one sub.

 

[kemmler3D]

I think your heart is in the right place, but if you are planning on deploying 4 18"s, plus a good bit of time and money, you should look into a DBA (double bass array) instead of cardioid. It will work (maybe quite a lot) better for your goal (cancelling modes / nulls) with the drawback that you lose flexibility on placement.

It works on the same principle (one sub cancels out the unwanted reflections from another) but will work better for low frequencies inside a room.

 

[Arindal]

One would still see the peaks and dips caused by the modal behavior.

I agree. But in many cases a cardioid sub is attenuating the excitement of room modes at least to a degree taming prolonged decay and subjective booming, which allows for applying simple EQ to counter the problem.

you should look into a DBA (double bass array) instead of cardioid. It will work (maybe quite a lot) better for your goal (cancelling modes / nulls) with the drawback that you lose flexibility on placement.

There is another downside of a DBA: If you have only 2 woofers or speakers per side, you cannot create anything resembling of an even wavefront at shorter wavelengths (which is a necessary condition to make the rear woofers cancel out exactly what the front ones have produced some t=d/v ago). Have heard examples of such DBA working perfectly below 60Hz, but poorly at higher frequencies, which is subjectively emphasizing the mode-induced decay and nulls in what is supposed to give some ´kick bass´.

 

[Exprymer]

I agree. But in many cases a cardioid sub is attenuating the excitement of room modes at least to a degree taming prolonged decay and subjective booming, which allows for applying simple EQ to counter the problem.

Unfortunately I have to disagree. The cardioid configuration is described as a simple double monopole setup inside a closed box, and when applied the integral formalism together with the Green's functions, the result is simply the superposition of both monopoles individually. The problem is that for a monopole enclosed by any volume, the Green's functions states that the pressure response for a given position (x,y,z) is a function only of the room position and the loudspeaker location. Thefore adding another monopole cannot cause artificial damping into the room. The simulations shows nothing but a mild decrease of efficiency, as part of the energy created by one monopole is canceled by the second. The directivity profile of the cardioid however helps to balance the excitation of the modes, which might help creating a flatter frequency response, but still with the same time constant as a simple monopole. The RT60 has absolutely no reason to decrease with a cardioid monitor as no artificial damping was created anywhere to dissipate the acoustic energy.

Please have a look on this nice contribution on the forum:

Visualizing How Different Loudspeaker LF Directivity Patterns Couple to Room Modes

This opening post is to demonstrate how different loudspeaker low frequency directvity patterns couple to our room modes. If you are unfamiliar with what room modes are, please refer to @DonH56's excellent thread for an in-depth introduction...

www.audiosciencereview.com

 

[Arindal]

the Green's functions states that the pressure response for a given position (x,y,z) is a function only of the room position and the loudspeaker location.

The simulation you have linked seems to contradict that. It would be applicable to a hypothetical perfect dipole source as well. But practice and simulations show that dipoles have kind of the opposite behavior as omnis when it comes to positioning relative to the room modes.

A cardioid can be seen basically as a dipole plus delay (or allpass) between the two monopoles. The net sum of sound power into the room is in theory -4.8dB lower than with a perfect monopole. So why should the pressure function at listening position be the same, when taking into consideration that the on-axis SPL is the very same?

Thefore adding another monopole cannot cause artificial damping into the room.

I am not speaking about damping. We can agree on this statement, a cardioid does not dampen the room mode and it will not automatically mean a flat FR at listening position. With the help of cancellation, it does radiate attenuated sound power in the direction of the room mode´s pressure maximum, that alone helps a lot to excite the mode to a lesser degree.

Which true cardioid woofers did you use for experimental confirmation? I did this experiment with two Basis 14k by MEG, admittingly a long time ago.