Basotect is not outrageous expensive. You can buy it in really huge blocks. If it's big enough it might be helpful in controlling the polar response at frequencies lower than 1khz.
Best, Markus
Best, Markus
After learning about the benefits of controlled directivity it prompted me to experiment with some things.
I tried something like this with rockwool. Using a 4" thick, 8# density, 2' by 4' sized panel, each placed alongside both sides of the speaker in a roughly 45 deg angle. -just as Markus shows in that pic. I was experimenting with using this as an alternative to controlling the sidewall reflections with panels along the walls. It resulted in a noticable increase in treble & midrange resolution. However, I felt it threw the tonal balance off, distinctly, in the bass and wasn't something that I could live with.
I think you would find the same result with the foam used this way.
I had considered cutting it down into smaller pieces and mounting it on some kind of stand so that it was only adjacent to the mtm section of the speaker... but then I decided just to buy the Abbeys...
😎
-Tony
I tried something like this with rockwool. Using a 4" thick, 8# density, 2' by 4' sized panel, each placed alongside both sides of the speaker in a roughly 45 deg angle. -just as Markus shows in that pic. I was experimenting with using this as an alternative to controlling the sidewall reflections with panels along the walls. It resulted in a noticable increase in treble & midrange resolution. However, I felt it threw the tonal balance off, distinctly, in the bass and wasn't something that I could live with.
I think you would find the same result with the foam used this way.
I had considered cutting it down into smaller pieces and mounting it on some kind of stand so that it was only adjacent to the mtm section of the speaker... but then I decided just to buy the Abbeys...
😎
-Tony
http://www.plasticsportal.net/wa/plasticsEU~en_GB/portal/show/content/products/foams/basotect
By the way, I have 4 cornerblocks of Basotect (each 110cm x 42cm x 42cm) that I need to get rid of. So if anybody is interested, send me a message.
Best, Markus
By the way, I have 4 cornerblocks of Basotect (each 110cm x 42cm x 42cm) that I need to get rid of. So if anybody is interested, send me a message.
Best, Markus
Earl,
What about having this kind of foam on the ceiling in order to absorb the ceiling first reflection?
Or do you prefer diffusion there? (I had a omnidirectional schroeder device in mind)
Regards,
Etienne
What about having this kind of foam on the ceiling in order to absorb the ceiling first reflection?
Or do you prefer diffusion there? (I had a omnidirectional schroeder device in mind)
Regards,
Etienne
gedlee said:
Why not? If you want to control the energy a speaker radiates to the back and sides, absorption could help.
Etienne88 said:
Yes, this would work well on the ceiling. I use diffusion and prefer it but absorption is better than nothing, which is what is usually done.
markus76 said:
Markus, then I don't understand what you are saying. I thought that your idea was to wrap the speaker in foam, including the signal path. Or do you just intend to put the foam at the sides and back? Kind of like building the speaker into a foam soffit? Sure that would likely be OK. Kind of impractical and I'm not sure how much benefit it would be, but I don't see a problem with it.
You might be surprised to learn that I actually do something quite similar. I stor the foam behind my speakers and so the area behind the speakers is filled with foam. Can't say it that it makes a huge difference because this area has always been well damped and the extra foam just adds some more damping, particularly at LFs.
gedlee said:
That's exactly what I was thinking about. An enclosure for the enclosure that doubles as a speaker stand. Would love to do some experiments on that but I can't do any low frequency freefield measurements.
gedlee said:
No, I'm not surprised as I do the same 😉
gedlee said:
I am glad you prefer diffusion since it will not absorb valuable sound energy that will later become reflections.
What kind of diffuser you recommend? Classic or omnidirectional?
Over what frequency band should the diffuser be effective? My (uneducated) guess says between around 1 kHz to 10 kHz…
Thank for your answer so far,
Etienne
Etienne
Ideally the diffuser should work over all frequencies, but at least above 500-1000. I prefer "omnidirectional" (not exactly sure what "classical" is), but there should not be any specular reflection to the seats.
Ideally the diffuser should work over all frequencies, but at least above 500-1000. I prefer "omnidirectional" (not exactly sure what "classical" is), but there should not be any specular reflection to the seats.
You know I've seen very little discussion over DIY diffusion and would love some discussion on the topic. Manufactured acoustic products often cost quite a bit, and many of them are of questionable usability. There are very few tuned bass traps, which it seems many consider far more effective, and those that do exist are very expensive. There used to be a few good websites on how to calculate and design these yourself, but I've noticed many of those sites have gone missing. It's also very difficult for me to wade through all misleading or bad information as compared with the good.
Also, why do those plastic or foam diffusers cost so much. It seems like making the mold, pouring in the expanding foam, and painting should create a product, especially if made in a country like China, should cost no more than say 50 dollars for each one, yet 300+ seems to be the going rate for many of these. Then there is the whole looks thing, most of these things are quite ugly and are very difficult to pass through the WAF. I've seen attractive ones, but they seem to mostly come out of Europe, are of limited availability, and/or are marketed to the modern architectural commercial interior designer.
Hey Dr. Geddes, any recommendation on the best way to mount an acoustically transparent screen the correct distance from the rear wall to mount your speakers behind them, in a non-dedicated theater. My long term plans here include repainting the living room a darker color (though likely not that dark). Moving the majority of the equipment to a side wall, and running the speaker wire through conduit tracks. I'm undecided on the speaker mounting, I was initially thinking stands, and I still like that idea, but may go with strong wall shelves. The problem with wall shelves is making sure they can support the weight, making stands a better options.
I'm not sure the size of your screen or the spacing of your speakers, or what you prefer. Using the often cited models, the distance between the left and right most speakers should be less than the distance to the listener. I then see various ratios as to how much less, with a common one being 2/3 or 3/4's the distance. If I stick with a 100" screen, placing all three speakers within the screen area places the Left and Right speaker a little too close, about 50" apart, which would be closer to 1/3 the distance to my listening position. I could go larger, or even utilize a wider 1.78:1 screen with masking. Another option I thought of was to use something like black acoustically transparent material for the left and right speakers, on the outside edge of the screen, so all are hidden, but only the center is actually behind the screen. I would really need to get into a 120" 16:9 screen or larger, and that large of a screen would require a much brighter projector with better contrast than what I have or can afford. Especially given my 14 foot projector to screen distance.
I have brackets for hanging a normal motorized screen, and I had considered buying two more of these (I can get them for around 20 dollars a pair) and using hooks and bungees to suspend the screen between the brackets. How big of a screen can be made with a king sized sheet? I know you don't like commercial acoustically transparent screens, but there are a couple of brands that charge more reasonable rates, such as 7-10 dollars a yard, making a 100" screen somewhat reasonable. No it's not as cheap as a sheet, but it requires no stretching or tension to keep wrinkles out, and has slightly higher grain. I've found out that the majority of the current preferred materials are actually white or gray solar shade material.
Also, why do those plastic or foam diffusers cost so much. It seems like making the mold, pouring in the expanding foam, and painting should create a product, especially if made in a country like China, should cost no more than say 50 dollars for each one, yet 300+ seems to be the going rate for many of these. Then there is the whole looks thing, most of these things are quite ugly and are very difficult to pass through the WAF. I've seen attractive ones, but they seem to mostly come out of Europe, are of limited availability, and/or are marketed to the modern architectural commercial interior designer.
Hey Dr. Geddes, any recommendation on the best way to mount an acoustically transparent screen the correct distance from the rear wall to mount your speakers behind them, in a non-dedicated theater. My long term plans here include repainting the living room a darker color (though likely not that dark). Moving the majority of the equipment to a side wall, and running the speaker wire through conduit tracks. I'm undecided on the speaker mounting, I was initially thinking stands, and I still like that idea, but may go with strong wall shelves. The problem with wall shelves is making sure they can support the weight, making stands a better options.
I'm not sure the size of your screen or the spacing of your speakers, or what you prefer. Using the often cited models, the distance between the left and right most speakers should be less than the distance to the listener. I then see various ratios as to how much less, with a common one being 2/3 or 3/4's the distance. If I stick with a 100" screen, placing all three speakers within the screen area places the Left and Right speaker a little too close, about 50" apart, which would be closer to 1/3 the distance to my listening position. I could go larger, or even utilize a wider 1.78:1 screen with masking. Another option I thought of was to use something like black acoustically transparent material for the left and right speakers, on the outside edge of the screen, so all are hidden, but only the center is actually behind the screen. I would really need to get into a 120" 16:9 screen or larger, and that large of a screen would require a much brighter projector with better contrast than what I have or can afford. Especially given my 14 foot projector to screen distance.
I have brackets for hanging a normal motorized screen, and I had considered buying two more of these (I can get them for around 20 dollars a pair) and using hooks and bungees to suspend the screen between the brackets. How big of a screen can be made with a king sized sheet? I know you don't like commercial acoustically transparent screens, but there are a couple of brands that charge more reasonable rates, such as 7-10 dollars a yard, making a 100" screen somewhat reasonable. No it's not as cheap as a sheet, but it requires no stretching or tension to keep wrinkles out, and has slightly higher grain. I've found out that the majority of the current preferred materials are actually white or gray solar shade material.
gedlee said:
Yea, I've found room treatment to be very useful. I took some measurements when I did my room - you can see the difference of adding ceiling absorption here: http://spikyfish.com/acoustics/
I've since moved everything round, and the speakers are now at the other end of the room, which is a couple of feet wider. This really improved things, as it allows a bit more space between the speakers and the side walls. I don't use the side panels (mainly because it's not practical at that end of the room), however, I think the greater speaker-wall distance has more than offset the loss of the side absorption.
I was at a very interesting talk at the AES by Siegfried Linkwitz a while back, and he put forward reasons to not use absorption at the first reflection points. Part of it was that it's pretty much impossible to have a broadband affect, hence you merely change the spectrum of the reflected sound. I did point out that this may be the only option (compromise) for small rooms, though he felt that an omni-directional design would be less affected, and therefore more suitable for a small room. I'd be interested in Dr Geddes' views on this subject.
A massively complex subject, not well suited to simple posts and probably better done in its own post.
I think that there is general agreement that it is better not to have first reflections than to try and absorb them. Thats a big reason why I toe-in my speakers as this accomplishes that goal - but only if the speakers are directional. Thus no absorption is required and I, in my room, use none on the side walls.
But ceilings and floors are different and I have found a big effect from difusing the ceiling and absorbing the floor. The floor (and then only a small spot in the center where there is a thick rug) and the wall behind the speakers are the only places where absorption is used. If there is a screen a dark color rough surface heavy fabric works to absorb sound and transmitted light when hung behind the screen - both good things behind the screen.
As to the screen, mine is slightly less than the speakers are set appart so that "most" of the speakers lie outside of the screen and, as Matt suggested, the screen is surrounded by very sheer black fabric that covers the speakers and frames the screen in black. To do this the screen frame needs to be round and as thin as possible (the frame is nearly in front of the LR mains). Two options - tubing, like copper soldered together to make the frame and then painted or patina black, or make the frame from good pine or oak and route all the edges round. I did the later as its then easy to fasten the screen material on the back with staples (but routing can be a pain). Now support the top at the center and sides with bunge cords (I actually use rubber bands on the sides), the sides ones going out at an angle. I find a single cord on the bottom to a weight or into the floor maintains a good tension on the screen. The weight is nice because it can be used to vary the tension. More than one weight can be used. Getting a prefectly flat screen is very easy with this technique. If the frame is square and tensioned correctly there won't be any problems with the surface.
Only three small eyelets would need to be put into the ceiling as the screen weighs next to nothing.
My speakers are about 2/3 the distance between them as the distance to the seats.
I think that there is general agreement that it is better not to have first reflections than to try and absorb them. Thats a big reason why I toe-in my speakers as this accomplishes that goal - but only if the speakers are directional. Thus no absorption is required and I, in my room, use none on the side walls.
But ceilings and floors are different and I have found a big effect from difusing the ceiling and absorbing the floor. The floor (and then only a small spot in the center where there is a thick rug) and the wall behind the speakers are the only places where absorption is used. If there is a screen a dark color rough surface heavy fabric works to absorb sound and transmitted light when hung behind the screen - both good things behind the screen.
As to the screen, mine is slightly less than the speakers are set appart so that "most" of the speakers lie outside of the screen and, as Matt suggested, the screen is surrounded by very sheer black fabric that covers the speakers and frames the screen in black. To do this the screen frame needs to be round and as thin as possible (the frame is nearly in front of the LR mains). Two options - tubing, like copper soldered together to make the frame and then painted or patina black, or make the frame from good pine or oak and route all the edges round. I did the later as its then easy to fasten the screen material on the back with staples (but routing can be a pain). Now support the top at the center and sides with bunge cords (I actually use rubber bands on the sides), the sides ones going out at an angle. I find a single cord on the bottom to a weight or into the floor maintains a good tension on the screen. The weight is nice because it can be used to vary the tension. More than one weight can be used. Getting a prefectly flat screen is very easy with this technique. If the frame is square and tensioned correctly there won't be any problems with the surface.
Only three small eyelets would need to be put into the ceiling as the screen weighs next to nothing.
My speakers are about 2/3 the distance between them as the distance to the seats.
Ok so let's say I don't have a a ceiling that would facilitate easy mounting (It's vaulted, so I would need to have a different length cord at each point, and the longest point would require a very tall ladder). Your general guide here seems to suggest that hanging from eye hooks is fine. This seems cheap enough to make, so I'm going to play around when I have some time.
Late to the party on the finishing aspect but, I wonder if anyone has considered using super glue on the radiused edges of the MDF surfaces? It makes an excellent seal for wood (as well as strengthening the wood); and it's sandable. I used Gorilla brand super glue to strengthen knots and cut edges on some wood projects. Just make sure you use gloves (I like nitrile gloves) when applying this stuff. 😉
See this stuff as well:
Hot Stuff
See this stuff as well:
Hot Stuff
pjpoes said:
Post an intermediate pole, or bar from the vaulted ceiling and hang it from rigid strings, like nylon cord. Then spring mount the screen from that.
chlovinka said:
I do reinforce all of my screw holes in MDf with super-glue. Works great. Its a bit expensive for sealing the edges, but I agree would work well. Thined epoxy does just as well and is a lot cheaper. But, honestly, the Bins works fine for me.
gedlee said:
I know many have mentioned the shellac, but I haven't used it myself. I feel Matt's pain though. I built a stand for my center channel from MDF. It looks pretty decent now, but getting an acceptable look took much longer than anticipated. I made the mistake of sanding and then shooting primer.
Man those cut edges...
Anyway, I laughed a bit because I found myself doing everything that many here have written: sand, glazing putty, sand, and so on. 😉
I'll give the Zinnser a try on my next project.
Zinnser works well, just make sure it's on thick enough and has had plenty of time to dry properly. I've found a few places now where the seems have shown through. As I mentioned, I was forced to do a lot of things I normally would not due to the really really cold weather.
Please note, I'm really picky, my gf can not find these seams. The paint looks great even up close. I will repaint them, but I think a lot of people would be happy with this.
Dr. Geddes, what do you do on the plastice waveguide again? Do you use a special plastic primer and paint? I still am having sticking problems. I know weather may be my primary factor, but the zinser does not stick to the plastic, the black spray primer, which claims it can stick to plastic, didn't stick to the plastic. I haven't tried a plastic specific one, but you didn't indicate that you do either.
Please note, I'm really picky, my gf can not find these seams. The paint looks great even up close. I will repaint them, but I think a lot of people would be happy with this.
Dr. Geddes, what do you do on the plastice waveguide again? Do you use a special plastic primer and paint? I still am having sticking problems. I know weather may be my primary factor, but the zinser does not stick to the plastic, the black spray primer, which claims it can stick to plastic, didn't stick to the plastic. I haven't tried a plastic specific one, but you didn't indicate that you do either.