# Room treatment and bass traps



## dean70

I am after some advice on room treatment and where to place bass traps (and how many). Should I focus more on the front of the room or equal front/rear treatment?

The room dimensions are 16'1"L x 14'1"W x 7'10"H. There is a double sliding glass door at the back of the room covered by heavy curtains. The left side wall is insulated with brick behind the drywall and right an internal wall. Heavy curtains cover from the front corners to 1/3 away along each side wall (the entrance is on one side near the front behind the right curtain).

The system is 7.1 channel with sub on the left side in line with the fronts (each towed inward towards center) to make an SW-L-C-R arc. The surrounds are Dipole's - side surrounds front firing (at 60deg) and back surrounds firing inwards towards listener. The seating position is about 3'7" from back wall.

I have divided the room into 1/6 segments and taken 6 x measurements with REW along the center from front to rear for both SPL and Waterfall 

From 3/6 (which is the most perfect response), there are some progressively big nulls/peaks that form. Can this be correctly with bass traps?

The other issue I have is mainly with the side surrounds is major slap echo. It is most noticeable when running Audyssey measurements and you can hear the echo when the chirps finish (same with rear surrounds but to a lesser extent). 

Is it a matter of placing absorbent panels somewhere on the side walls? I don't want to make the room sound too "dead".


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## Prof.

Hi Dean and welcome to HTS..



dean70 said:


> I am after some advice on room treatment and where to place bass traps (and how many). Should I focus more on the front of the room or equal front/rear treatment?


Ideally you should have bass traps in the front and back corners of the room..



> The room dimensions are 16'1"L x 14'1"W x 7'10"H. There is a double sliding glass door at the back of the room covered by heavy curtains. The left side wall is insulated with brick behind the drywall and right an internal wall. Heavy curtains cover from the front corners to 1/3 away along each side wall (the entrance is on one side near the front behind the right curtain).


Sounds very similar to my original set up before I put in acoustic treatments..
I don't have siding glass doors at the back of the room, but I have a very large window in that position..and I used to have heavy curtains down the side walls!..

To tame the peaks and nulls, this is what I did in my room.

Cover the entire front wall with 2" acoustic insulation..I do have a screen wall so you don't see the insulation..
Put in floor to ceiling bass traps in the front corners..
Removed the side wall curtains and fitted first and second reflection point acoustic wall panels..
Covered the entire back window with an acoustic panel, fitted into the window to stop all light leaks..
Put in 4' high bass traps in the rear corners..

I also have a suspended light tray covering 2/3 of the ceiling, which is also acoustically treated..
All of the above provided a well dampened room (not to excess) that gives me quite a flat response through the frequency range.. 




> The other issue I have is mainly with the side surrounds is major slap echo. It is most noticeable when running Audyssey measurements and you can hear the echo when the chirps finish (same with rear surrounds but to a lesser extent).


All of the above treatments will help considerably in controlling slap echo..
Do you have wall to wall carpet, or is it bare boards?


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## dean70

thanks for the info. Thats alot of panels!

The room is carpeted with thick underlay. Ceiling has thick insulation bats.
Curtains cover the open entry-way at the front right corner (1'11" from front) and "fake" curtain on right to match.

With the slap echo, if I do a clap test from front 1/2 of the room it is fairly controlled (from "dead" at front to mild echo). As I move towards the back, it gets progressively worse till about 5/6 of the way to the back of the room and at the back it improves somewhat. I did a quick test of putting one of the kids soft couches against the right wall about 12" infront of the Dipole side surround and it improved somewhat (not very scientific, but seemed to help things).


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## dean70

I am thinking along the lines of 2" thick panels on the front wall up to 47" from floor to cover behind the mains and 12" panels under the projector screen (100") and same along the top of the screen. This would cover behind the center speaker to under the entertainment cabinet that the center sits on. Also an additional 24" row of 2" thick panels in line with the surrounds height. which would cover most of the front wall.

For bass traps which come in 2'11"x12"x12" wedge, put two of them from the floor up and ceiling down on the front corners with the flat part angled across the corners of the 2 walls. The rear walls will be the same, except the top trap will have to be cut to fit above the surround.

As for the current room response, a large peak forms around 35Hz, followed by a deep null at 55-60hz and again at 114hz from 2/3 to the back of the room, which is where the seating is. (I will post pics once I have 5 posts).


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## bpape

If the bass absorbers you're looking at are foam, they're not going to do a lot and certainly not going to address the low frequencies you're talking about. In any case you need more coverage than just a couple of feet in each corner. Front corners should be floor to ceiling. 

Likely, some of the response anomalies you're running into are a function of seating position and nulls off the back wall. THICK absorption in the middle of the rear wall (think 3 panels that are 2'x4'x6") will help with those and also with the general low frequency decay time in the room.

Just doing the lower portion of the front wall misses half of the design goal. Yes - doing behind the speakers can help with boundary interactions - but you still are trying to stop reflections from the surrounds from coming off the front wall and messing up the front soundstage. Most of those are up higher - certainly higher than 47". Anything coming from the surrounds that will be hit at 47" would likely have bounced down into the carpet anyway for the most part.

Bryan


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## Theresa

ATS Acoustics make some open backed panels that work well in corners.


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## robbo266317

Welcome to HTS Dean.

Cheers,
Bill


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## dean70

I have found a local supplier of 24"x24"x6" bass trap panels that I could staple 3x2 of down the middle of the rear curtain lining between the window and curtains. 

With the resultant air gap between the panel and window, would this improve the LF absorbsion?

This would at least allow me to open the curtains and the sliding door on the odd occasion.


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## dean70

I have also managed to alter the front speaker arrangement so the sub is on the inside between the cabinet and right main speaker, so the fronts are L-C-Sub-R. This will at least move the sub further away from the right side wall. 

I will re-measure the room response and see if it has improved anything.


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## Prof.

I think you'll find that if you place a 4" thick panel/s over your glass doors (they could be made to be removable to access the door) and with fitting the second reflection point panels on the side walls, that are almost floor to ceiling (so your reflections from the fronts are covered as well as the side surrounds) will help considerably to control your peaks and nulls..


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## dean70

I have taken some REW measurements with the sub in the new position for SPL, Waterfall and RT60 at 1/6 intervals down the center of the room.

1/6:
SPL-








Waterfall-








RT60-









2/6:

























3/6:

























4/6:

























5/6:

























6/6:


























Still some nulls in the response, which are not as big as previously, but the peaks are larger.

Is the increase in the midrange that shows up on the RT60 graph the result of slap echo?


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## bpape

What material is the 24x24x6" absorber made out of?


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## dean70

These are the traps I am looking at: http://www.dmcrecords.com.au/article.asp?type=3&id=2179

For the corners: http://www.dmcrecords.com.au/article.asp?type=3&id=2181


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## bpape

Personally, I would steer clear of those. They're foam. They also don't provide any type of measurement data from lab testing to allow you to see what they're really doing. The most they say is that the effective range is 35Hz and up. I'd bet a months pay that they do basically zero at 35Hz and not a below even 100Hz just looking at them.

Look for something with a fiberglass, mineral wool, or cotton core.


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## dean70

Thanks everyone for the advice. :T

I have decided to DIY my own traps and panels using this http://www.tontineinsulation.com.au/images/docs/Tont_Acoustisorb_3_Version%2010s.pdf which seems to be quite popular for room treatments. Looking ath the Acoustisorb 3 100mm+50mm thick for traps and 50mm for panels. It is not an irritant and doesnt require protective clothing to work with.

It has a 0.63 absorbsion at 125hz for 100mm and 0.4 for 50mm.


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## bpape

That looks like a good product to use as a core. 

Bryan


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## dean70

I have decided to remove the curtains on the sides and fit a semi-solid door to the entrance. 

My question is how do you use the mirror technique to find the first reflection points along the sides? By the time I get the mirror positioned to see the fronts from the opposite side seating position, I am more than halfway along the side wall which seems to be too far back.

Some room pics:


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## bpape

That's very possible that some of the points are more than 1/2 way back given how far back in the room you're sitting.

Bryan


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## dean70

I have finished the front corner panels

































They are 150mm thick and 636mm wide


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## bpape

Good job. Enough surface area and enough thickness to have some real benefits down into the lower 1/2 of the subwoofer range.


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## Prof.

Looking good..:T
What are you doing for the glass doors?


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## dean70

I am making up 2 more 1236mm wide to cover most of the glass door. Depending on how much light they block out, I might be able to leave the curtains partially open and fix convex perspex panels over the front to make diffusors.


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## dean70

I have made up the 2 x rear panels total 2472mm wide to cover most of the glass doors - they were heavy suckers and was a 2 person job to carry them. 

I have taken some measurements again and it has definitely improved the RT60 response and tamed some of the room modes, but still have that node at 30-35hz. The spike at 1khz is probably the result of removing the curtains from the front 1/3 of the room. When I get the side panels in hopefully this will tame the mid back down again.

Position 4 at front of seating area:

















Position 5 at back of seating area:

















Could this be back corners? The same response peak builds at the front of the room and disappears by the middle.


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## dean70

I have finally finished the room treatments, re-run the Audyssey XT eq and had a chance to sample some music BluRay material and it has made quite a noticeable difference. 

I tried Rush Moving Pictures which originally sounded harsh in the midrange-top end and lacked bass (which prompted me to look at treatments originally). The first thing I had noticed is how much smoother the vocals and top end were and the bottom end was more pronounced. I have noticed some slight reverberation in the vocals on one of the tracks, which is a level of detail I had never noticed before in all the times I have listened to this previously!

The next sample was Police Certifiable, which always had a strong bass, but sounded a bit muddy. The bass is now clear and powerful (more so than before). 

Certainly has been well worth the effort. Waterfall plots are looking much cleaner. It now tapers down fairly evenly across the spectrum with only a couple of minor points around 70hz and 17.5 hz. The sub LF response is more extended than previously at -6db @ 15hz and -10db @ 13hz. :T

Just waiting on new HT recliners and upgrading Front and Centre speakers. Some pics below of the completed room:


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## bpape

Another treatment believer created! :T

Congrats. 

Bryan


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## dean70

After getting some upgraded LCR mains, the panels no longer cover the 1st reflection points. 

I took all the panels down and ran some ETC measurements and found that the best location is now down low near the floor. 

The question I have is the left side shown in the picture above needs to be about 500mm further back than the right side. It seems unusual given I measured the position of the Left/Right & Center speakers and they are positioned evenly across the front of the room, spaced evenly from the front wall and the LR are towed-in the same angle. 

It is normal to require asymmetric placement of the panels? 


I double checked the position of the left side panel, by moving it back in line with the right, but the ETC measurement showed stronger reflections again (mainly for the right & centre speakers).

Each speaker was measured individually across each of the 3 seating positions.

The other question I have is the ETC chart showed reflections from the floor, which required damping inline with the right side panel (about 600mm wide). I used the kids soft sofa couches temporarily while taking the ETC measurements, but what can you use permanently to put over carpet in that section without going a full false floor? 

It only needs to be 600mm wide x 2600 long to cover across the sound stage. Any ideas?


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## bpape

If the speakers are set up symmetrically left to right, as are the seats, the side wall reflections should be in the same place, as should the panels.

Was the couch in place when you did the side wall assessment? That would certainly skew things.

Bryan


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## dean70

*Side panels MkII*

I decided to reframe the side panels and put them on stands and mounted some roof panels, which have tamed more of the major reflections, but there are still a few dominant spikes in the ETC plots. 

edit: most of the remaining spikes, I have isolated to the back of the couch. Now have tamed the reflections down to ~-15db or lower. Making some Poly's to reduce slap echo from the side surrounds & should also take care of the remaining reflections which affect the side seating positions.


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