Acoustic Treatment Advice Needed

[Kruppy]

I’m looking for some acoustic treatments advice from the experts:

Room: Finished basement
Use: 40% HT 60% 2 Channel
Speakers: Martin Logan SL3s
Budget: As usual, not much.

Please see the attached diagrams of my room.

Issues: I’m not happy with the lack bass response. I understand and can accept that SL3s are bass shy (I plan on adding a sub in the not so near future). When I optimize speaker location for low frequencies, the imaging/soundstage gets very exaggerated. Cymbals sound like they’re 8 feet from the drum set. When I optimize for soundstage bass response is limited. The upper frequencies can also be a bit harsh at times.

I’m currently looking at GIK treatments. Other suggestions are welcome.

The bass issue, I know treatments will not improve output, but tighten up/flatten the response. I think I know what to do here, add corner traps. I think the most cost effective panel here is to put a 244 bass trap in both front corners. I like the Tri-Trap but it’s a bit more expensive. The ceiling height at the front wall is only about 80 inches high. Is it necessary to go all the way to the ceiling with a corner trap?

The imaging/harshness issues I believe are due to side and front wall reflections. The first side wall reflection points I’m planning on using 242 panels. Behind the speakers is where I’m not sure what to do. Absorbsion, more 242 panels? Diffusion? I’m also going to have limited room behind each speaker do to any corner trap and my projection screen.

I can post REW freq curves if needed.

Can some one help a brother out?

 

[bpape]

Hi Kruppy.

Can you be a bit more specific about where you end up for best bass and where you end up for best imaging? Also, what do you consider proper imaging? I'm just trying to get a handle on what you're shooting for.

Do you already have some of our products - if so please post what so I can see what we have to work with.

The side reflections are important but the ML's aren't as wide dispersion as some other speakers - and certainly not wide at all in the vertical dimension.

I'll be happy to work through this with you.

Bryan

 

[Kruppy]

Can you be a bit more specific about where you end up for best bass and where you end up for best imaging? Also, what do you consider proper imaging? I'm just trying to get a handle on what you're shooting for.

Do you already have some of our products - if so please post what so I can see what we have to work with.

The side reflections are important but the ML's aren't as wide dispersion as some other speakers - and certainly not wide at all in the vertical dimension.

Bryan,
Thanks for the response and I'd be happy to take your help.

In terms of imaging, I'm looking for the correct sound stage proportions, whether its large or small. Drums and cymbals are the best example that I have. When listening to a drumer, at times the cymbal crashes are located way out of proportion of the drum set, like the drummer has to reach over 10 feet to the guitarist or bass player to hit them. Hi-hats can sometimes be in the same situation, they seem out of place. I just want imaging/soundstage that is in correct proportions for all of the instruments, reguardless of whether it's a big or small sounding recording. Sorry, I'm not sure how to explain this better.

Speaker location: To be honest, I have not be as diligent with keeping track of what specific location is the best for imaging vs. bass. Here's what I do know. I'm getting pretty good bass and imaging from a position that is 1 foot foward and 6 inches out (or closer to the side walls) in respect to the speaker position on the diagram on my first post. Relative to the diagram position, if I back the speakers up roughly a foot and move them in towards each other imaging gets more in line, but the bass suffers. Again from the position in the diagram if I move them towards the outside walls, bass improves but I had imaging issues, from what I recall.

No, I do not have any acoustic treatments.

I understand about MLs side reflections from sound emitting from the front of the panel not being so important, what I'm more concerned about are rear emitted front wall to side wall reflections as my speakers are slightly toed in.

Bob

 

[bpape]

Well, there are a couple of things at play here.

Being close to the front wall will foreshorten the soundstage DEPTH but add some bass reinforcement - but not evenly. It will change the sawtooth response caused by SBIR.

Moving them toward the side wall will expand the soundstage WIDTH (sounds like too much for your taste) but also cause more SBIR and reinforcement from the side walls.

If it was me and based on what you're trying to accomplish (I think), I'd put them back closer together and pus them closer to the wall behind them. That might complement things nicely.

Now, with all of that said, once you treat the bass in the room with something like Tri Traps or 244's, you're likely to get MORE apparent bass to the point that you may want to pull them back out again.

If I can post a pic to a different forum (not sure if this is a no-no here or not) here is a setup a customer of ours did with Maggies using a combination of absorbtion and diffusion that he absolutely loves.

Something like that takes the boom away but tightens and extends the bottom end while diffusing the backwave in the mids and highs to allow for a cleaner soundstage.

Thoughts?

Bryan

 

[Kruppy]

Being close to the front wall will foreshorten the soundstage DEPTH but add some bass reinforcement - but not evenly. It will change the sawtooth response caused by SBIR.

Please excuse my ignorance here but I do not know what the acronym SBIR stands for.

Moving them toward the side wall will expand the soundstage WIDTH (sounds like too much for your taste) but also cause more SBIR and reinforcement from the side walls.

If it was me and based on what you're trying to accomplish (I think), I'd put them back closer together and put them closer to the wall behind them. That might complement things nicely.

I can try moving them back towards the front wall, however, everything that I've read and have been advised about ML positioning is that they need 3 or more feet behind them (of course this is room dependent). I'll be happy to try moving them back.

Now, with all of that said, once you treat the bass in the room with something like Tri Traps or 244's, you're likely to get MORE apparent bass to the point that you may want to pull them back out again.

Something like that takes the boom away but tightens and extends the bottom end while diffusing the backwave in the mids and highs to allow for a cleaner soundstage.

Thoughts?

Looks nice. Is there any way of identifying whether I would be better off with diffusion vs. absorbtion behind my panels?

Here's some room response measurements that I've taken from the 1 foot forward and 6in out to the side position (relative to the diagram position).

I'm using REW with a Radioshack SPL meter.

 

[Kruppy]

Bryan,
Before I forget, what are the dimensions of the GIK Tri-Trap? I know the website says 2ft x 4ft, but is the 2ft dimension the length of the hypotenuse of the tri-angular cross section or the sides? I'm looking at size constraints in my room, 244 vs. Tri-Trap.

 

[Glenn Kuras]

Bryan,
Before I forget, what are the dimensions of the GIK Tri-Trap? I know the website says 2ft x 4ft, but is the 2ft dimension the length of the hypotenuse of the tri-angular cross section or the sides? I'm looking at size constraints in my room, 244 vs. Tri-Trap.

The Tri Trap is 17'x17'x24'... From the face of the Tri Trap to the back of the corner is 12'. The 244, when straddling a corner takes up about 22' on the side walls. From the front of the panel to the corner is about 17'. So YES the Tri Trap takes up far less room and absorbs lower. Nothing wrong though with the 244 as it does have a nice peak at 80 to 85 hz.

Glenn

 

[bpape]

Sorry - was in a hurry. SBIR stands for Speaker Boundary Interference Response.

It's a term used to describe the effect of the portion of the spherical bass wavefront that comes off the rear wall and bounces off to mix with the front wave. Some blends in phase and creates a peak. Some blends out of phase and causes a dip in response.

Yes - the MLs do like more room behind them but then we can't get your bass response by 'cheating' and using the wall to reinforce things a bit. Using the side walls as you found out will help some but then makes your soundstage larger than you like.

With those speakers, most likely a combination of absorbtion and diffusion is best as I showed in the pic I attached. Corners are dead, between speakers is dead, behind speakers is diffusive to minimize comb filtering by being closer to the wall than desired but not totally killing the backwave.

Bryan