Help me improve the acoustics of my Prodigies

[18000rpm]

I live in an apartment and my home theater is in my living room (Prodigies in front, Summits in the rear, with Descent subwoofer). My placement is far from ideal due to size constraints and the fact I have a wife. My Prodigies are almost against the wall, with the back around 4 inches from the wall and the panels a little over two feet from the back wall.

Here are my REW measurements (green is Left, red is right):

What acoustic treatments can I do to improve the sound? They actually sound great to me despite the poor placement and measurements, but I like to tweak and improve what I can. I have tried some foam panels in the corners and behind the rear-facing woofers but they didn't make much difference both by ear and by measurements so I removed them (and left the hideous tape stains which I have been unable to remove...ugh).

So do I need big acoustic panels behind my speaker panels, and do I need absorption or reflection etc? Any advice will be appreciated!

 

[Rehan Azim Hashmi]

I do not know much about room treatment. But however little I know I now share with you.

In any room goal is to only listen to direct forward radiation of loudspeakers. And not reflections of walls of the room that reach the best listening position. Reflections spoil by interfering with the original aural image created by speaker.

If I am not mistaken best panels to place in corner behind speaker and center behind speakers are abfusers. Abfusers absorb the sound wave and what part they do not absorb they diffuse. Abfusers need to be placed alongside side walls and on wall in front of loudspeaker.

After viewing the image of your living room. You can move the prodigy forward by two feet. Back panel of speaker should be in line with the front of your equipment cabinet. Moving them two feet forward may improve the sonics from Prodigy. Experiment with moving them forward. Try and see if you are satisfied with the result.

 

[18000rpm]

Thanks for the advice Rah. I don't know if I can afford to move them forward 2 feet but will see what I can do. And I have them on spikes and they're a b*tch to move.

Will look into abfusers, never heard of them before thanks.

 

[RDC]

Hi 18000rpm,

I took a different approach from what RAH suggested. I use diffuser panels on the wall behind the speakers to diffuse the rear-soundwave. Directly on the main reflection point behind the speakers. Around 80cm (~33") behind the panels. I did try absorption first. I started of with the same type you showed, but they didn't do anything for me either. Some 5cm (2") thick rockwool DIY absorption panels did work far better, but I found that this took away too much energy and the music felt enclosed between the speakers.

I already had bought some polystyreen 1D diffusion panels and experimented a lot with them in different positions and orientation till I found my preferred sound. I already had 10cm thick DIY absorption panels and a row of the same diffusion panels on the wall behind the listening position. So I already knew they probably would have some kind of impact on the sound.

The result was that I got a wider soundstage, a sense of a lager room, but with the level of energy that I like. Instruments and voices sounded clearer and more natural. and with the right 'size' and separation in the room.

I briefly turned back to absorption, but just to test that there actually was a difference. A kind of double-check. And I lost again what I gained with the diffusion. So I'm still using diffusion panels behind the speakers. Just two of them, one above the other and both panels in horizontal position, attached behind each speaker. Excellent value for money. But I decided they aren't really nice to look at. So I build a wooden casing around them with light gray speaker cloth at the front to hide them from sight. I'm very happy with the end-result in looks and effect.

 

[JonFo]

I've done extensive research on acoustic treatments and how they interact with MLs, using REW metrics, and listening.
My conclusion is the most accurate, clean sound is to seriously mitigate the rear wave, so you are primarily listing to the direct sound from the front of the panels, and very little of the delayed (6 to 10ms) and bounced (arriving from the side walls) rear wave.

For setups like yours, where space and aesthetic constraint force a location really close to the wall behind the speakers, the one and only type of treatment I'd recommend is absorption. And a specific product: Real Traps MiniTrap HF; the HF is important, as that means full high-frequency absorption due to no 'limp-mass' elements, which are reflective.
Hang then offset from the wall by 2" to maximize low-freq absorption.

Since you placement is asymmetrical relative to the room (right side seems to be open in the pic, and the REW graphs show a clear skew from the left with a boost in the bass, and cancellations in the mid-bass), you can re-balance a bit with another Mini-Trap HF along the left side-wall and the front wall. So from the curtains all the way to the front wall, an absorber at panel height.
Since the corner is boosting the low-end a ton, a 2x2' absorber on the floor, straddling the corner would also help.

If you want further advice, please post or PM-me the REW measurement file, and I'll take a look at the impulse response, bode, waterfall and group-dealy for further insights and recommendations.

If you want more background on acoustics for MLs, I have two threads worth visiting and reading in their entirety (they are long). This one is mostly about my custom treatments, but the first post contains a link to the fundamental research and group discussion on acoustic treatments. Room treatments – part 2

But as I said, in your scenario, only one correct (in terms of accuracy) answer: absorption, lots of it.

 

[kach22i]

One more opinion, but please keep an open mind that everything mentioned so far may also work.

Pull speakers 2-feet more into the room, plus place your subwoofer dead center in between them in front of the audio rack.

You may experiment with subwoofer being 180 out of phase with mains.

It is okay if subwoofer sits out further into the room than the speakers, in fact a few inches more is even better.

Nothing on the front wall behind the speakers.

Take care of first/early reflection points on sidewalls and ceiling with any combination of diffusion and absorption that appeals to you. I like the curved stuff like Acoustic Geometry because it is time aligned, but that's me.

Concept here is that you may not need large base traps if subwoofer is away from room boundaries, and if mains are properly located per owners manual.

Treat the front wall behind the speakers only once everything else possible has been done.

The least amount done to the front wall, the better in my opinion. Nothing is the best option unless you have special issues like an open stairway behind the speakers.

 

[spkrdctr]

Your in room measurements actually look pretty good, especially for an apartment. Tweak as much as you want, but just realize your setup is already pretty dog gone good!

 

[18000rpm]

Oh dear now I have one recommendation for abfuser, one for diffuser, one for absorber and one for nothing on the front wall. Will look into it and maybe I'll shoot ML an email for their recommendation as well.

Thanks spkrdctr, it does sound pretty good to me

 

[Brad225]

Absorb behind the panels and try diffusion and absorption in other places.
There is no one size fits all. As you can see by peoples responses, you will need to see what you like based on the sound.

 

[kach22i]

Short video by M/L.



Shows mirror method for finding early sidewall reflection points and treating them.

Also mentions that if closer to front wall than the 2 or 3 feet recommended, drapes or bookcases behind speakers can be useful to break up the rear wave ( but proper distance is preferred over treatment).

Claims ceiling reflection point (usually half the diagonal distance from ears to baffle) is not as important.

I take issue with that last claim and the 30 degree dispersion claim as M/L simply does not count adjacent energy more than 3 dbl or is it 6 decibels lower in intensity than directly in front of the speakers. The sound energy is there laterally and vertically, just not as loud as with conventional box speakers.

Do NOT over treat and dampen the room is advocated in the video.

Follow the video and treat early 1st and 2nd reflections before adding any thing else.

From what I've been reading on the Internet, free acoustic analysis by acoustic panel makers usually pushes more treatment than one needs (and is focused on conventional boxes).

These companies are in the business of selling acoustic panels, it is how they make their money.

 

[JonFo]

Do NOT over treat and dampen the room is advocated in the video.

I hear that George, but no one ever provides actual in-room metrics that support that these recommendations result in improved, or more accurate, results.
All my tests and metrics and experience show that accuracy goes up with treatments. The massive ringing in my room required a ton (literally) of treatments. Now, I admit I'm running a very big (in terms of radiating surface square footage) system. If all I had were a pair ESL9s, then probably would use a lot fewer treatments. But I'd still treat the room.

I find it disingenuous that at 0.33 into the video, they show an animation of the direct-radiator dynamic speaker experiencing comb-filtering from reflections, and describe it as "coloring the sound", but yet make zero mention of the much more severe comb-filtering resulting from a dipole configuration, especially one where the ESL element is 'transparent' to sound reflected right through it. The animation at 1:10 deceptively shows the reflected rear signal decaying and not interfering, which is BS. Also, no mention of the multiple paths of reflected rear energy, there are way more than depicted. Those reflections, if not dampened, are subject to the usual laws of decay over distance, but 5 feet is not far, and the reflected sound is barely down a few dB at best.
Diffusion of the rear wave just means you are sending reflections to more locations, thus spreading the reflections in the time-domain, meaning,comb-filtering lasts longer.
Dampening the rear wave is the only way (short of having the speaker 20' from a surface) to NOT having severe comb-filtering.

 

[kach22i]

Must be an old video if large box CRT tube TV set enclosures are a consideration.

In fact, anything in the front soundstage including audio racks, center channel speakers and subwoofers can compromise 2-channel stereo imaging.

The front wall is highly sensitive, one chap would not allow protruding lap seam trim and or panel joint reveals in his wood paneled listening room - all flush butt joints.

As you can surmise wood expands and contracts with the weather and before long he had blisters and irregular joint cracks, but it was good acoustically with no random front wall diffraction.