The Great experiment! Acoustics

Discussion in 'Home Cinema Speakers' started by Phil Hinton, Oct 29, 2002.

  1. Phil Hinton

    Phil Hinton
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    Well My room is very odd in its layout. The fact it has solid stone walls on three sides and a false wall on one, And it has three alcoves make getting good acoustics and bass response is a problem. The ceiling is pretty high as well.
    So I went armed with £20 to Focus diy and have bought some polisterene wall tiles and 4 x90% coving also polisterene(sp).
    The idea is to try and tame the high end reflections,and create bass traps in the corners(this idea came from Uncle eric).
    I have put the coving in the corners up to a height of 48" (and sorted the skirting board as well) and tiled around the Subwoofer wall. I have also tiled around the side walls up to 48" for the first 1/4 of the room. (this is a dedicated cinema room and i have no missus to worry about).
    Whilst in Focus I also noticed underlay blocks that are 1" thick and made from material that will be fantastic at sound absorbsion, I intend to put this on the screen wall and then cover with Black material, that will allow sound to travel through it,and be absorbed. But at the moment i am just experimenting with things(last thing i want to do is actually make the room too dead.)

    I am hoping to kill all standing waves from the sub, and get a more even response from it, as well as tighten up the top end and get a better focus to the channels.

    I have yet to fire up the system, shop below still open, but will report back with some findings soon. Its good fun though.
     
  2. James45

    James45
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    Network Guy posted a link earlier today about a look at Jonathan Ross' HC office over in General Hardware.
    The muppet spent £330,000 on his room... most of which must have been spent on padded suede cushion tiles that cover the entire room!! The result?? A completely acoustically dead room. Apparently he came up with the idea himself (although for aesthetic reasons rather than thinking acoustically) and his HC installer was amazed at the result. Oh and where the skirting board should be... he has something like 100plus plug sockets.

    The link is in the plug sockets thread at the top.
     
  3. The Nightfly

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    Phil,

    Spooky coincidence, yesterday I ordered a load of RPG acoustics profoam panels. My HC is in quite a small room and the spaekers are close to smooth unbroken walls. I'm probably hearing as much reflected sound as direct sound. The idea of the profoam panels is to absorb and diffract most of whats hitting the walls and effectively make the room acoustically bigger.

    The stuff should have arrived today but for some reason it didn't turn up. Hopefully here tomorrrow, then the fun begins.

    Here's a link to the product I'll be using.

    studio in a box

    BTW, trying to tame bass is difficult. For a start you're dealing with wavelengths in the 10 to 20ft region. Generally you need mass (heavy soft furniture) and/or bass traps to deal with it.

    Allan
     
  4. CarlB

    CarlB
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    Allan,

    I was also looking at the Studio in a Box stuff when I ordered some accoustic foam last week. Let us all know how you get on with it and your impressions, I'd be keen to know if you are pleased with the results.
     
  5. Grimley

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    I heard rockwool slabs (Available in Wickes) are pretty good for soundproofing a room.
     
  6. Ramius

    Ramius
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  7. Chris Bellamy

    Chris Bellamy
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    Hi, THX, please keep us posted ? this is of great interest.

    You may have already done this but, may I suggest you try and do some detailed measurements of the acoustic responses of your room at your usual listening/viewing position, and again at (any) other seating positions in the room, to best define your problem where it matters most. There are 2 issues: achieving equality of acoustic responses between the various seating positions, and achieving a balenced acoustic response over the audible frequency range. I?m no expert but these are not at all the same problem.

    For taming bass (ie: <100Hz) problems, I have begun to believe that resistive ?Bass traps? are overhyped. To most effectively damp standing waves you need to put the potential absorber where the air particle velocity is maximum, ie: ¼ of your problem frequency?s wavelength from the room boundary. For 50Hx this is over 5ft, and about 10ft for 25Hz! The only way to realistically get close to achieving this is with a dropped suspended acoustic ceiling, because of the large airspace volume above the resistive surface. Otherwise, these resistive materials are really only practical and effective with frequencies more than 200Hz or so.

    Apparently, you could try a ?membrane? (resonating) absorber to deplete the standing waves? energy, of which a great example is a thin (ie compliant) plasterboard panel overlying a damped volume, containing, say rockwool/fibreglass or similar (but not touching the panel) to further deplete energy from your standing waves. Again, the deeper the volume behind the panel, the lower the frequencies attacked. I would envisage blocking over the corners of the room with something like that, as there is good depth for relatively little ingress into your room space.

    Moving your sub and/or your seats and/or using 2 subs may do a lot to solve deep bass inequalities, without resorting to an equaliser to tame a really fierce resonance, but you?d need to do the measurements to define the problems.

    I?m afraid this is all gleaned from reading ? no practical experience, so I?d appreciate any opinions to the contrary. Without wanting to appear negative, there does seem to be a lot of rubbish on this subject, and a lot of not necessarily related information more concerned with soundproofing than achieving acoustic balance in your room.

    I?m going to be doing up a room in a steading for HC (4 stone walls, concrete floor, no ceiling yet) so will be very pleased to hear about your experiences,

    Good luck!

    Chris
     
  8. Phil Hinton

    Phil Hinton
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    Chris,

    I have been concentrating on the higher frequencies so far, with some success, but i have just started my next working shift pattern(7days on) and won't have the time to do anything to much for the next week. It does start to get very complicated though when you look towards the bass end of things.

    I will update when i have some spare time.

    A little off topic Chris, but where abouts in the Borders are you? I am originally from Hawick.
     
  9. The Nightfly

    The Nightfly
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    Today I've installed a total of eight 4ft x 2ft RPG panels down the side-walls. The difference is nothing short of stunning. For the first time in this room I can actually hear a real and tangible acoustic space created soley by the soundtrack. Dialog clarity has jumped to another level. If I had to estimate the cost of acheiving these kind of improvements through box upgrades I would have to put it in the £4k to £5k region.

    I was initially contemplating installing velvet curtains for this purpose but when I got an estimate they were actually slightly more expensive (per square meter) than the RPG Profoam. I decided to go for the Profoam as a) its designed specifically for this exact purpose and b) I'm not particularly keen on the 'baronial' look, I far prefer the functional, industrial look of the Profoam. Now I've started installing the Profoam I'm positive that I've made the right decision. I'd rate it as my number one value for money investment in Home Cinema.

    Bear in mind though that I had specific problems relating to a small dedicated room, ie proximity of speakers (and listener) to walls and lack of breakup and dispersion of the sound that you would normally get in a regular living space caused by furniture, shelves, bookcases, etc.

    Chris, what you say makes a lot of sense. I also have a dedictated HiFi room and have spent probably two years tweaking the acoustics in that room. I could probably write a book on the practical knowledge I've gained. Suffice it to say that high quality two-channel music reproduction suffers badly when a room has too much absorption. Heavy duty bass traps (tube-traps) in particular quickly render a room incapable of holding a tune. I learnt that in this case best results were obtained using as much diffusion and as little absorption as possible. Where I had to absorb some mid-bass, the most effective and unobtrusive way was to fold a large heavy rug in half over a sturdy 2"x1" length of wood and suspend the rug between two bookcases with an air-gap of about six inches trapped at the back. For very low bass, I avoided the problem and downsized the speakers.

    I think the main problem with absorption with two-channel stereo is that unnatural lack of 'ambiance' approching the ears from a multitude of directions. Home Cinema doesn't seem to have this problem due to the re-created ambiance from 5, 6, 7 or more speakers and hence absorption works really well and killing the rooms ambiance to allow the recorded ambiance to be created.

    Allan
     
  10. Phil Hinton

    Phil Hinton
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    Allan,

    Sounds excellent(excuse pun) so what do you get in the Studio in a box set? How long did it take you to find the best places for the boards? And how much did it cost?

    Cheers
    Phil.
     
  11. Apocalypse

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    I too would be interested in trying out these profoam thingies, atm I'm temporarily using plasterboard with 1" of foam attached to it but unless you stack it one in front of the other it doesn't really stop standing waves. To say it's unsightly in this fasion is an understatement the like of which has never before been uttered by a human being :eek: :D
     
  12. Chris Bellamy

    Chris Bellamy
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    Hi, THX: I?m some way from Hawick, up on the Biggar side of Peebles. Funnily enough, I?m only 40 mins drive from a certain Gordon Fraser?

    Allan, great to hear how good the RPG Profoam has been. I?d looked at the website after seeing Charlie Whitehouse?s HC page, but hadn?t seen any other customer feedback, so this is very encouraging. Did you get the whole studio in a box set or a set of panels alone? What colour are the panels, and do you just glue them to the wall?

    Chris
     
  13. The Nightfly

    The Nightfly
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    Phil,

    The complete studio in a box was more than I needed so to start with I've bought twelve 4ft x 2ft panels. Thats enough to cover just under 2/3rds of the side walls (from screen wall towards listener) with four panels left over to cut up into 1ft x 1ft panels to make a start on the checkerboard pattern in the rear section of the room. The sound is so dramatically better already that I may not even bother with checkerboarding the untreated areas.

    I knew just based on how close the speakers are to the side walls (< 6" away) that this was going to be the primary source of reflected sound.

    I've bought the unfinished dark gray panels. They look almost black and to my eyes look perfect for home cinema. They can be bought in unfinished dark purple foam or with a variety of fabric finishes. Having them finished in fabric does add significantly to the cost though.

    I bought the panels from custom audio designs . A box of 12 panels starts of at a very reasonable £144 but when you add £20 for delivery and then VAT on all of that the total cost is about £195. But compared to any other £195 home cinema upgrade, I guarantee this one is the best.

    Chris, I made a mistake when I first put the panels on the walls by trying to use solvite wallpaper adhesive. For some reason it wouldn't dry. Embarrisingly, when we were watching a film last night the panels, one-by-one over the course of the evening started peeling off. My wife who would normally scoff at such a blunder felt genuinely sorry for my embarresment. Probably because she herself had been privvy to the genuine and significant improvement the panels made.

    This morning I popped out to B&Q to get some 'liquid-nails' type adhesive. Right now B&Q have a two-for-one offer on tubes of UniBond - "No More Nails" so duly bought four tubes. You need to allow for three 4ft x 2ft panels per tube.

    Can I join the Borders club ? I lived in Gattonside, near Melrose (near Galashiels) for about four years. We loved it and often talk about living there again.

    Allan
     

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