Did Google AI get this correct?

[2Sunny]

I am moving to Florida on September 28th and planning one room in the new house to be a dedicated home theater, but I am keeping everything as simple as possible so I can revert the room to normal if necessary. In any case, I have been discussing various issues with Google.ai in hopes of learning something, and I think it's working. As part of a recent conversation regarding room treatment for bass correction I told the AI server that I planned on using a DIRAC ART to tame the bass and it came back with a recommendation for putting an acoustic panel behind the front L & R speaker to prevent SBIR. Here is exactly what was said:

". . . you now have to look out for Speaker Boundary Interference Response (SBIR). When a speaker is 12 inches from the front wall, the distance from the front of the speaker's cabinet (the baffle) to the wall creates a cancellation reflection notch. [1, 2]

• At 12 inches from the wall, the cabinet thickness plus the gap places the speaker baffle roughly 24 inches from the wall.
• A 24-inch distance causes a severe SBIR cancellation dip at around 140 Hz.
• Because 140 Hz is above your 80 Hz crossover, this dip will happen directly on your towers, taking away the "chest thump" or upper-bass punch of drums and male vocals."

Did Google's AI get this one correct?

Does it make sense to put an acoustic panel behind my speakers?

Unfortunately I do not have any pictures of the room to share and I'm not sure what other info folks here need to make an educated answer, but I will say the room is 465 cm long by 353 cm wide by 365 cm tall (11' 7x15'3x12') and will have a 9x12 wool area rug with a 1/2 pad under and a single 3 seat cloth couch and be a 7.4.6 system and the towers are Ascend Acoustic ELXs and the receiver is a Denon AVR-A10H.

 

[Redacted]

First, put your kit in the room and see how it sounds.
Then try changing main speaker positions to see what happens, if it's not fine. Repeat.
If you get resonances or suckouts at your listening position, no matter where you position the speakers, then try EQ as mentioned a lot on ASR.
If after that, the sound is still odd, and you can't put more furniture/big soft things/rugs/rugs on walls etc, then look at acoustic treatments.
Don't spend money on extra stuff unless you can hear that you actually need it, and do the easy stuff first.

 

[ElJaimito]

you now have to look out for Speaker Boundary Interference Response (SBIR).

Yep this is real, not hallucinated. There's a reason studios use flush monitors. Cf:

How to place your monitors? - Genelec.com

To create the ideal listening experience, several aspects need to be taken into account when placing the monitors within the listening space. First, you need to identify the listening area within the space and consider where the listener will be placed in relation to the space as well as the...

www.genelec.com

 

[Keith_W]

In theory the answer is correct, but in the real world it's not practical.

SBIR cancellation wavelength = quarter wavelength = 4x distance of front baffle to front wall.
- I looked up the dimension of your speakers (Ascend ELX) and found that the depth is 26.7cm
- If your speakers are 30cm (12") from the front wall, the combined distance is 56.7cm. So the SBIR cancellation wavelength is (4x 56.7) = 226.8cm
- f = c/lamda = 343/2.268 = 151.23Hz

Thickness for foam absorbers to be effective = 1/4 of the longest wavelength you want to absorb.
- Example: Vicoustic Mega Bass Trap VMT XXL (thickness = 682mm / 26.9")
- In theory this should absorb 682 * 4 = 2.728m wavelength = 125Hz
- Look at its acoustic performance chart:

Notice how its absorption drops off below about 150Hz whilst remaining high up to 5kHz and beyond.

Now take a good look at that Vicoustic Bass trap and ask yourself whether you want something that big in your listening room.

Alternatives:
1. Flush mount the speakers. You won't have to worry about SBIR any more.
2. Pull your speakers even further into the listening room. This lowers the SBIR frequency into the subwoofer range. You then let the subs do the work filling in the dip for you. For 80Hz, the speakers need to be 1.1m away from the front wall.
3. Don't worry about it. There is a price to be paid for chasing perfection. Too much focus on one problem can lead to problems elsewhere. Like, installing a massive bass trap can lead to over-absorption of high frequencies and eats into your living space.

 

[kemmler3D]

If you put a bass trap behind the mains use something tuned for the SBIR frequency and not foam / rockwool. I think GIK has tuned absorbers.

 

[2Sunny]

Thanks everyone. Love the acoustic knowledge on here!

I just asked it a second question: Can DIRAC ART with bass control be used to counteract SBIR?

"Within 20 Hz – 150 Hz (Highly Effective): Dirac ART's co-op MIMO processing strictly operates in the 20 Hz to 150 Hz frequency band. If your speakers are positioned such that the SBIR null falls under 150 Hz, ART can effectively use nearby subwoofers or other capable speakers to neutralize the boundary reflection."

Since I plan on placing the speakers 30 cm from the front wall and SBIR at that distance is in the 130 Hz range it looks like I needn't bother wasting money on GIK panels. Ah well, they do look cool and I was willing to try

 

[HalSF]

Thanks everyone. Love the acoustic knowledge on here!

Good luck with the room treatment. But I would have just started by asking the questions here, and carried on talking with the actual knowledgeable embodied human beings here, and skipped the Google AI velveeta entirely.

But that’s just me, who hates adult suckling on infantilizing consumer LLMs with the burning heat of a thousand suns (coincidentally, the same amount of energy your prompts wasted at some godforsaken data center somewhere).

Yeah, I’m that guy!

 

[2Sunny]

Happily even Luddites get to speak their mind in the good ole U.S. of A. Keeps 'merica great. Thanks for the helpful and thoughtful input!!

 

[amirm]

Ah well, they do look cool and I was willing to try

Nothing useful comes out of deploying such a thin panel. It will act as an EQ at higher frequencies and that is it. And that is assuming you deploy a bunch of them.