# Acoustic treatment advice



## stevekale (Jan 19, 2013)

Howdy all. Now that I seem to have REW finally sorted, I would like to get some thoughts on room treatment. Here is my basic room setup (the equipment rack is in the gap behind the front right speaker). (See "my system" profile.)










I intend to widen the speakers so the gap between them is in line with Egglestonworks's recommendation of 8 feet for the Andra IIIs and also reduce the toe-in. For now, though, here is my SPL measurements for the front Andra III speakers running full range without the sub (with room modes noted along the bottom):










And the rather awful RT60:










Clearly the first thing that needs to be tamed is the room modes boosting 35Hz and the 70-100Hz area. I was chatting with an acoustic retailer/consultant in the UK and he recommended fitting two RPG Modex Plates up front. Given their dimensions of 1m x 1.5m, these would have to fit on the side walls rather than the front wall. I was then thinking of adding a set of Skyline or similar panels (3x2 for a 6" x 4" section) on the rear wall. I would then take a look at first reflection points on the left side wall (there's a window and curtain on the right wall; tests with and without the screen didn't appear any different so that will likely go). I can't do much with the ceiling as I don't own the property but I am going to get a larger, thicker carpet (3.5m x 3.5m) for the floor. 

Has anyone had any experience with the Modex Plates? I understand that they work on a pressure-based system which is ideal unless I really want to fill the corners with copious amounts of foam. 

With regards to the sub, I have run tests crossing the front speaker LF to the sub and it doesn't add much, if anything, so I am thinking of using the sub for LFE in 5.1 and for the low frequency of the rear Eggworks Rosas. Perhaps it would be better placed mid-way along the rear wall. The seating position is really just 2 seats (or me alone sitting in the middle). The other thing I can do for 2-channel listening, if it is recommended, is to run the front speakers on full range AND crossover LF from them to the sub. While I could only control the relative volume of the rear sub, I would effectively have LF emission from 3 speakers. I'm not sure this is necessary though for such a simple listening setup.

Any thoughts appreciated.

Steve

PS: any products recommended would have to be readily available in the UK/Europe


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## morca (Aug 26, 2011)

Could you post a fullrange waterfall diagram.

The sub would have more gain in the low freq placed behind the L or R front i think.

Regards,
Marco


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## stevekale (Jan 19, 2013)

Hi, sorry for the delay. I saw your message but was travelling with work and so could not access the file.








Here is the REW data file:

https://dl.dropbox.com/u/70685392/REW/SPDIF tests 7 March.mdat


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## AudiocRaver (Jun 6, 2012)

A few thoughts...

The modes at 35 Hz, 70 Hz, 105 Hz, 140 Hz, and 175 Hz are all attributable to your room length, and are all strong contributors to your frequency response curves. They seem like the most important ones to go after with room treatment.

Your room width modes are at 42 Hz, 83 Hz, 125 Hz, and 166 Hz, but are not as strong. For instance the one at 83 Hz should be causing a null at the center listening position, and you can only see a hint of that tendency. Curious. 

I am not certain, but what looks like a null a 50 Hz may just be the "normal" level between big peaks due to reinforcing modes above and below. At least I couldn't figure out any obvious null modes that would account for it.

What is you ceiling height, by the way?

I am not a room treatment expert like some around HTS, but it seems like placing bass traps anywhere but on the end wall(s) would be less than effective given the strength of those room length modes. Someone else please correct me if that is wrong. Understood you have limited space options to work with.

Would love to hear those speakers!

Keep us updated.:sn:


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## stevekale (Jan 19, 2013)

Hi. Thanks very much for the reply. The ceiling height is 2.3m. 

What is the colour coding for the REW room mode indicators? 

At this stage I have placed an order for 2 "Type 2" RPG Modex plates to have a first crack at the low end. It was a bit of a debate between the Type 1 and the Type 2 and just my luck that the Type 2 were a bit more expensive (although they're no where near as expensive in the UK as the US which really is a shock). I have also ordered a new, thicker and wider rug for the room (albeit still a flat weave). It will be interesting to see what effect that has on the higher frequencies. 

The other thing I was thinking of doing sooner rather than later was to add 6 Skyline panels on the rear wall. Is it worth getting the deeper ones?

Unfortunately the Modex Plates won't fit in the gaps on the bottom of the front wall corners but will fit on the side walls in the front corners. Presumably pressures will be pretty dispersed in the corners? I may try them on the rear wall's corners before fixing them down.

The Andra IIIs are rather nice. I bought the original Andras in '98 and had them upgraded last year. I have the centre speaker in getting upgraded at the moment to 'match' the front pair. I can't wait to get this decay down to hear them closer to their best. (I also want to get the Rosas upgraded as well.)


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## AudiocRaver (Jun 6, 2012)

stevekale said:


> What is the colour coding for the REW room mode indicators?


Same height and same color all apply to the same room dimension. The five tall dark red modes are all for the length of your room, the dark green at the next height all apply to the width of your room, etc.



> At this stage I have placed an order for 2 "Type 2" RPG Modex plates to have a first crack at the low end. It was a bit of a debate between the Type 1 and the Type 2 and just my luck that the Type 2 were a bit more expensive (although they're no where near as expensive in the UK as the US which really is a shock). I have also ordered a new, thicker and wider rug for the room (albeit still a flat weave). It will be interesting to see what effect that has on the higher frequencies.
> 
> The other thing I was thinking of doing sooner rather than later was to add 6 Skyline panels on the rear wall. Is it worth getting the deeper ones?
> 
> Unfortunately the Modex Plates won't fit in the gaps on the bottom of the front wall corners but will fit on the side walls in the front corners. Presumably pressures will be pretty dispersed in the corners? I may try them on the rear wall's corners before fixing them down.


This all sounds like a good approach. When you get plates and panels in hand, do not be afraid to experiment with them temporarily in positions that seem acoustically ideal but are ultimately unusable/impractical, just for the sake of your own understanding of what works best. If possible, I would favor deeper panels for the rear wall, since those room length modes are the worst offenders. Again, I am not the greatest acoustics treatment expert around Home Theater Shack, if someone has better advice, please chime in.

Best of luck.


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