advertisement


Quad 63 - sound absorption/diffusion/scattering panels?

R

RichardA

pfm Member
Starting a separate thread on a narrower topic than the other ESL 63 thread running at the moment, to avoid confusion.

I have been using the 63's for a while now and am very happy with them but I continue to ponder various improvements. I have set aside thoughts of super tweeters but have started to wonder about the various acoustic panels that you can buy from Auraflex and GIK. (I have tried Auraflex foam stands under my sub woofers and have been very pleased with the results.)

in particular I wonder whether putting some of these panels close behind the 63s might cancel some of the rear reflections. If so would that be beneficial (or might it lose something valuable)? Also I do not properly understand the difference between absorption/diffusion/scattering and whether these effects in fact overlap and apply to different frequencies. I would say that I like the overall balance of the sound I have now though I am wondering whether the backward firing output is creating cancelling effects that are slightly spoiling the forward output.

Has anyone experimented along these lines with Electrostatics who can offer first hand experience of results/benefits?

[Background - My 63s are on GFD strands firing long ways down the room with their outside edges close to the side walls. They are roughly 2 metres from the back wall (though there are bits of shelving and furniture behind them). I already have bookshelves and racks down each side of the room which I understand might help to break up reflection points etc. I use Gradient subs below 110hz on aura flex stands with the 63s.]
 
I’m very interested in any input on this myself. I’ve settled with mine just under a meter from the wall, and have pushed the listening chair back accordingly leaving my head around 90cm from the wall behind.

Richard, do you use any EQ? I’ve applied mode correction, and a little overall bass roll-off which has tidied things up.
 
I have no idea about these speakers, but I’m surprised by how much people spend on their hifi and do nothing to treat the room. I think room treatment is probably the most important thing one could do. I use Vicoustic panels as diffusers and absorbers. The most important are the first reflections off the side walls and the ceiling, but in reality, the whole room should be treated, including front and rear walls. Rarely does a couple of panels do any thing significant.
 
Whaleblue said:
I’m very interested in any input on this myself. I’ve settled with mine just under a meter from the wall, and have pushed the listening chair back accordingly leaving my head around 90cm from the wall behind.

Richard, do you use any EQ? I’ve applied mode correction, and a little overall bass roll-off which has tidied things up.
Click to expand...

Re EQ - not really. I use the gradient integrated power amp/electronic crossover which allows for some adjustment to the bass output but I have decided to leave it alone else I will constantly be fiddling with it. Instead I have played with the positioning of the quads and the 2 separate gradients to tweak the overall sound.
 
tvheadhunter said:
I have no idea about these speakers, but I’m surprised by how much people spend on their hifi and do nothing to treat the room. I think room treatment is probably the most important thing one could do. I use Vicoustic panels as diffusers and absorbers. The most important are the first reflections off the side walls and the ceiling, but in reality, the whole room should be treated, including front and rear walls. Rarely does a couple of panels do any thing significant.
Click to expand...

I am sure you have a valid point re the balance of spending money on room treatment versus audio equipment. Sadly, many of us want to preserve some amount of marital harmony and domestic decor! I have occupied one half of two connected receptions but I still need to store books, records, CDs etc and I don't fancy too many panels potentially spoiling a traditional victorian space. Your warning that too little treatment might be ineffectual is also a good point. Thanks.
 
I could see the challenge of maintaining a Victorian look with absorbers dotted around the room. Vicoustic does have some very nice stuff, but more on the modern side of design. I have just put some pics of my room, which is dedicated, in the system pics thread if you want to take a look. For a more dead room you use absorbers but for a more lively room, you need a mix of both diffusers and absorbers. My projector screen is also acoustically transparent so that the entire wall behind the screen is treated as well.
 
tvheadhunter said:
I could see the challenge of maintaining a Victorian look with absorbers dotted around the room. Vicoustic does have some very nice stuff, but more on the modern side of design. I have just put some pics of my room, which is dedicated, in the system pics thread if you want to take a look. For a more dead room you use absorbers but for a more lively room, you need a mix of both diffusers and absorbers. My projector screen is also acoustically transparent so that the entire wall behind the screen is treated as well.
Click to expand...

Took a look. Very different space to mine. Total flexibility!!
 
It's a really unfriendly thing to try to deal with.

I got GIK, who make bass traps etc., to do a plan for how to treat my room, it's a free service on their website, they have a questionnaire where you describe your room and system. They were very quick to respond.

They suggested a huge number of panels and traps, with a huge aesthetic impact at a significant cost. The consultant I dealt with had no specific understanding of ESLs in particular or bidirectional speakers in general, which didn't inspire confidence.

You can't try before you commit, and they all say this:

tvheadhunter said:
Rarely does a couple of panels do any thing significant.
Click to expand...

So it's an all or nothing kind of thing.

It wasn't even easy to see the panels in a showroom -- it may have been possible if I went 20 miles from SW to NE London, and even then it wasn't clear whether the dealer had any on display or in stock even.

I gave up -- too difficult.
 
Like I said, the best starting point are the first reflections, so that would be a couple on each wall next to the speakers, and then if possible three on the ceiling. Start with that and have a listen. Use velcro so you can remove them easily when necessary. You may want to try absorbers on the walls and diffusers on the ceiling. Of course a study by GIK or Vicoustic would be ideal. It is like a drug, because once you begin to hear their impact on the aound, it’s hard to stop. I would say this is an even more crucial step with bi-directional speakers or open baffle speakers than traditional ones. I have come to beleive that room and speakers are the most important thing in the audio chain. Source is up there as well.
 
I made some sound absorbers,roughly the same size as my 989's placed them behind my speakers and all they did was suck the life out.
Next I attached some ply sheets as 'wings' to the inner sides of the panels, no significant improvement.
 
What I think is needed is to pay someone to come and listen to your speakers and see your room, take proper sound measurements, and make recommendations for a fee, and then install the stuff on approval. I would be very happy to pay for that.
 
My QUAD 2805's are about a metre from the back wall, which is hard plaster over brick - very reflective. Without room treatment, the sound lacked clarity and images were somewhat diffuse. I improvised some absorption with duvet quilts on drying racks behind the speakers and these gave decent results but were domestically unacceptable. I then installed a GIK large diffuser/absorber on the wall behind each ESL and for me this did the trick - great clarity and very firm images - they worked better than the quilts and have better appearance.

I noticed that just unpacking the GIK's in the listening room led to a change in its sound - just talking sound different. I certainly wouldn't want to introduce any more of them in to the room - they are powerful devices and could easily lead to an over-damped room, lacking in life.

I too tried GIK's advisory service but clearly the consultant didn't understand the characteristics of bi-pole loudspeakers and so the advice was rather generic. It's unlikely that treating the side walls and ceiling should be the first priority with ESL's.

Chris
 
I have diffusor panels behind my Martin Logans. They are GIK Versifusors, which are polystyrene panels -- so they are lightweight and easy to pin to the wall and can be painted to match your décor. I have two Versifusor panels stacked vertically behind each speaker.

30709404544_859c0d4dd8.jpg


I’ve found the improvement to be very significant. The diffusors help to mitigate rear-wave cancellation in the mid-range. They do this by (obviously) causing the reflected waves to bounce off the wall behind the speaker at different times, which means that the cancellation, rather than having an acute effect on a relatively narrow frequency range and so causing a nasty mid-range suck-out, is spread across a wider band and made less acute.

They also cause spatial diffusion of the waves – i.e. the reflection of the waves is scattered directionally as well as temporally. Again, a good thing.

What they don’t do is absorb the reflections – and this is a good thing. Retaining the reflections keeps the feeling of space and ‘airiness’, without which the room acoustic would be deader.
 
These look like interesting and valuable posts, but unfortunately they are contradictory.

Chris Shorter says that using a panel to absorb reflections resulted in "great clarity and very firm images."

Mattgbell uses a diffuser, which does not absorb reflections, but rather scatters them directionally. He argues that absorption is to be avoided because it deadens the room acoustic and so is detrimental to " the feeling of space and ‘airiness’"
 
Here is a copy of an email which GIK sent me

Thank you for reaching out to GIK Acoustics, my name is David Shevyn and I will be working with you on setting up your room.
I will be addressing your frequency response, decay time, early reflections, and SBIR (speaker boundary interference) which can be improved with proper speaker placement, and room treatment. You may also wish to watch the video at the end of this email. It is a lecture I delivered at the Munich High End Show this year and it goes through everything we discuss here in more detail.

This will significantly improve the acoustical performance of your listening environment. The following is broken down into the areas that we need to address.


Set Up
There are four concepts to really consider here. For clarity, I am defining the orientation as the front wall being the wall you are facing when seated at the mix and the rear/back wall as the wall behind you.

a) Facing the short wall – A lot of room mode issues are created by the back wall so ideally we would get the back wall as far away from us as possible
b) looking to be sat at 38% off the front wall (this is a good starting point as this is where the nulls and peaks effected by the length modes are the weakest)
c) SBIR (Speaker Boundary Interference Response). This is how the speakers respond to the environment around them. Often the advice is pull them put into the room but often closer to the walls can work better if there is going to be interference anyway - http://gikacoustics.co.uk/speaker-boundary-interference-response-sbir/

d) Symmetry – In an ideal scenario we would have symmetry in the listening position, you will notice as we recommend treatment this is one of the concepts we will continue to keep in mind.

Obviously in your scenario I do only have the one photograph to look at. I am also going to presume, as this is clearly your living room, that you are unable to change the room around at this stage.
Of the four points above that you can certainly control however is always worth experimenting with is speaker position. Just moving them back and forth a few inches can make a massive difference. However, sometimes moving them closer to the work can make a difference in the low end but in your case with alcoves this is rarely the case


Keeping this set up in mind I would then suggest the following
treatment:


Corner Bass Treatment

Bass builds up at any boundary such as a wall, a floor, or a ceiling. Corners are efficient because they are the ends of 2 or 3 boundaries. Placing bass traps in as many corners as possible will improve low end decay times, frequency response, and Imaging.

Some information about bass trapping:

http://gikacoustics.co.uk/video_bass-traps/
http://gikacoustics.co.uk/how-bass-traps-work/

Ideally, we would get some bass traps in the corners in any free corners that we have. Obviously again I only have the one photograph you do have the front two corners free. Putting in something like the tri trap floor to ceiling or alternatively the alpha panel would make a big difference to the low end -
http://gikacoustics.co.uk/product/gik-acoustics-tri-trap/
http://gikacoustics.co.uk/product/corner-ct-alpha-bass-trap/


Back Wall Bass Treatment
The back wall can be responsible for large peaks and nulls, not only in the low end but in the mid and upper frequency range. Unlike corners, the back wall is a single boundary and requires different types of treatment.

You mention in the form you could treat here. What we are looking for is thick treatment (at least 6 inches) as we need to cover all the frequency ranges. If you could them, you would benefit a lot form 2 X the rectangle panels (2 foot by 4 foot). Aesthetically there are a few options and all would be a good choice -
http://gikacoustics.co.uk/product/gik-acoustics-monster-bass-trap-flexrange-technology/
http://gikacoustics.co.uk/product/6a-alpha-panel-diffusor-absorber/
http://gikacoustics.co.uk/product/impression-150mm-bass-trap-diffusor-absorber/
http://gikacoustics.co.uk/product/gik-artpanel-acoustic-panels/



Early & First Reflection Points

These are essential to treat to avoid issues with stereo imaging and comb filtering. Basically any reflections reaching your ears very shortly after the direct sound can generally create an inaccurate listening environment. These are located along side walls and ceiling.

Some information about how to identify your first reflection points:
http://gikacoustics.co.uk/video-early-first-reflection-points/

Unless you want some free standing panels I would leave this for now.
http://gikacoustics.co.uk/product/freestand-acoustic-panel-gobo/

Would a ceiling loud be an option, if so I would use the 244’s for this (give a little extra low end absorption) –
http://gikacoustics.co.uk/product/gik-acoustics-244-bass-trap-flexrange-technology/


Front Wall
There are two reasons we may treat this area. A) to combat SBIR (Speaker Boundary Interference Response) and this may become more apparent as we treat the room b) If we are unable to treat the back wall

Due to the limited space here and the fact the back wall will be well treated I would leave this area.


Rear Side Walls
What we finally have to look at are high and mid frequency reflections, which will cause flutter echoes. Flutter echoes are created by any two flat hard parallel surfaces opposite each other. Depending on the size of the room, we can use absorption, diffusion or a combination of both to tame these reflections.

Again we are going to leave this area for now and concentrate on the areas and frequncy ranges you have highlighted
If you want to learn a little more about what I have been highlighting in this email please check out the video form my lecture at Munich high End this May as well, it goes into more detail about all these concepts

Look forward to working with you on your room
Click to expand...
 
mandryka said:
These look like interesting and valuable posts, but unfortunately they are contradictory.

Chris Shorter says that using a panel to absorb reflections resulted in "great clarity and very firm images."

Mattgbell uses a diffuser, which does not absorb reflections, but rather scatters them directionally. He argues that absorption is to be avoided because it deadens the room acoustic and so is detrimental to " the feeling of space and ‘airiness’"
Click to expand...

Not entirely contradictory.

Chris says he uses a panel that both absorbs and diffuses, so it will in fact reflect some of the rear waves. Also the absorption effect of Chris's panels is only one part of a bigger picture -- the general acoustic of his room. In my room, which is acoustically pretty dead (e.g. no first reflections and lots of absorption behind the listening position), absorption of rear reflections would be undesirable -- which is why non-absorbent diffusor panels are a good thing in my room.
 
I have some sheets of polystyrene, I'll give them a try.

I suspect results are based on many variables. Wall construction, distance from listener, height of ceiling etc.
 
mattgbell said:
Not entirely contradictory.

Chris says he uses a panel that both absorbs and diffuses, so it will in fact reflect some of the rear waves. Also the absorption effect of Chris's panels is only one part of a bigger picture -- the general acoustic of his room. In my room, which is acoustically pretty dead (e.g. no first reflections and lots of absorption behind the listening position), absorption of rear reflections would be undesirable -- which is why non-absorbent diffusor panels are a good thing in my room.
Click to expand...

This is correct: the GIK product I'm using is from the 6A Alpha series - the biggest, fattest one - rather taller than the 2805's. This is a combined absorber and diffuser.

I agree that you have to consider room treatment in the context of the sound of the entire room and the constraints on placing the speakers within it. I'd love to be able to get the QUAD's 2 metres away from the wall like the OP but that's not feasible in our room.

Chris
 
chris shorter said:
My QUAD 2805's are about a metre from the back wall, which is hard plaster over brick - very reflective. Without room treatment, the sound lacked clarity and images were somewhat diffuse. I improvised some absorption with duvet quilts on drying racks behind the speakers and these gave decent results but were domestically unacceptable. I then installed a GIK large diffuser/absorber on the wall behind each ESL and for me this did the trick - great clarity and very firm images - they worked better than the quilts and have better appearance.

I noticed that just unpacking the GIK's in the listening room led to a change in its sound - just talking sound different. I certainly wouldn't want to introduce any more of them in to the room - they are powerful devices and could easily lead to an over-damped room, lacking in life.

I too tried GIK's advisory service but clearly the consultant didn't understand the characteristics of bi-pole loudspeakers and so the advice was rather generic. It's unlikely that treating the side walls and ceiling should be the first priority with ESL's.

Chris
Click to expand...

Chris

Exactly which GIK product did you go for?

Richard
 
You must log in or register to reply here.


advertisement


Back
Top