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First reflection points on the floor

64.103.142.138

Hi,

Typically first reflection points on the floor are covered using a carpet.

Are there any other alternatives ? I am thinking of keeping fabric covered ottomans ( size 2 or 3 sqft ) at those two points on the floor, instead of carpet... Will that work ?

Thanks,
Hifisound

Follow Ups:

RE: First reflection points on the floor - Hifisound 07:43:27 01/06/11 (6)
One question on flooring options...

Are there tile based alternatives for flooring for listening rooms ?
typically complete floor carpets can be used but it can be tough to maintain in countries like India. Was wondering if there options with ease of maintenance as a tile and acoustic absorption as well...

Thanks.
- RE: First reflection points on the floor - David Aiken 12:11:51 01/06/11 (5)
  By "carpet" do you mean "rug"? I think most people refer to "carpet" when talking of wall to wall carpeting and to "rugs" when talking about smaller areas of carpet placed somewhere on the floor within a room.
  
  Any floor material I know�timber, concrete�is reflective. Some floor coverings such as stone and ceramic tiles are definitely reflective. Others such as vinyl and lino are probably going to be less reflective than hard tiles but still wouldn't be recommended for absorption.
  
  Basically I think the usual option for an absorptive floor covering is carpet (natural fibre such as wool, not synthetic) in the form of wall to wall carpeting or rugs. You could use carpet tiles to cover a small area but that's effectively using them for what you would normally use a rug for and I would expect a rug to work better acoustically than carpet tiles which have the carpet fabric embedded in a rubber/synthetic layer unless the actual carpet layer of the tile was as thick as the rug you're comparing it to. Most carpet tiles I've seen have only very thin carpet layers.
  
  The only other approach I've seen is used by a person with marble tiled floors which are normally left bare. When he settles in for a serious listening session he spreads a quilt over the floor between the listening position and the speakers and takes it up again at the end of the listening session.
  
  If ease of maintenance is a big problem, my recommendation would be to get a good quality thick woolen rug of a size that fits between the speakers and your listening position and to place it in position when listening and roll it up and store it elsewhere when not listening. That way it will get little foot traffic and need minimal care and maintenance. Carpet tiles have the advantage that you can remove individual tiles for cleaning or replacement, and you can also swap tiles from areas that get heavy foot traffic with ones from other areas of the tiled area in order to spread the wear and tear more evenly over the whole surface, but they will still need more maintenance than a tiled floor.
  
  That's about all I can think of.
  
  David Aiken
  - http://. (Open in New Window)
  - RE: First reflection points on the floor - Hifisound 20:37:50 01/06/11 (4)
    Thanks David,
    
    I was thinking on similar lines. That is to use a rug during listening session and removing it, but thought of asking if there are other permanent alternatives
    
    Also one more thing I have gathered is, that nobody recommends synthetic rugs.... Almost the recommended material is wool... ( how would cotton be ? )
    
    I was almost about to buy synthetic rug but have dropped the idea now...
    will look out for a thick woolen rug...
    
    Thanks a lot for all your suggestions.
    
    Rgds,
    Hifisound
    - Absorption coefficients of building materials - KlausR. 01:26:00 01/07/11 (2)
      Porous absorbers are 100% efficient at frequencies where their thickness is equal to or greater than 1/4 of the wavelength. A 1 inch carpet will efficiently absorb frequencies above about 4 kHz, below that efficiency will drop, to levels close to zero in the bass region. This means that carpet or rug will not remove the reflection. What carpet or rug will do is remove the high frequency content of the reflection, which is the equivalent of turning the level of the tweeter down. Just keep that in mind.
      
      Klaus
      
      Absorption coefficients (Open in New Window)
      - RE: Absorption coefficients of building materials - Hifisound 09:02:17 01/07/11 (1)
        
        In Reply to: RE: Absorption coefficients of building materials posted by KlausR. on January 07, 2011 at 01:26:00
        
        Hi Klaus,
        
        So what would be the alternative ??
        
        RE: Absorption coefficients of building materials - KlausR. 10:45:43 01/07/11 (0)
        
        In Reply to: RE: Absorption coefficients of building materials posted by Hifisound on January 07, 2011 at 09:02:17
        
        The problem with reflections is that if you want to get rid of them, or at least lower their level to below perception threshold, you need broadband absorbers. Floyd Toole advises to use stuff that goes down to 150-200 Hz, which in the case of porous absorbers means 42-57 cm thickness for total absorption.
        
        But the question is: are reflections in general and the floor reflection in particular a problem? You did not mention anything, why do you want to tame the floor reflection, is there any particular reason? There is no scientific evidence that reflections are a problem as a matter of principle. They may be in individual cases.
        
        Alternatives? If you do need to treat the floor reflection, then I would first calculate what thickness is necessary for porous absorbers to get the level of the reflection below perception threshold, so you'd need psychacoustic data. For music the threshold is, depending on music motive, between about 10 and 18 dB below the level of direct sound. Everest should provide equations to calculate what thickness of what material you need to lower the reflection level by say 15 dB.
        
        You mentioned blocking the reflection by using furniture. Sound waves have the tendency to move around obstacles so I'm afraid that will not work either. You could re-direct the reflection by using angled panels, but again, for low frequencies the panels will have to be large.
        
        Klaus
    - RE: First reflection points on the floor - David Aiken 23:19:02 01/06/11 (0)
      Haven't seen any documented comparisons of wool rugs vs cotton rugs for absorption. Cotton is a finer fibre and cotton fabric tends to be a tighter weave than wool. That would make it less absorptive at all frequencies than wool, and I would guess that a cotton rug would be less absorptive than a wool one.
      
      David Aiken
An eye-opener on room acoustics... - KlausR. 03:28:59 01/05/11 (1)
is the linked paper by Floyd Toole, an extensive version of which is his book:

http://www.amazon.com/Sound-Reproduction-Acoustics-Psychoacoustics-Loudspeakers/dp/0240520092

There is acoustics/room acoustics (what we measure) and there is psychoacoustics (what we hear) and you have to consider both. For instance, there is no need to battle with reflection induced comb filter coloration when you don't perceive it as such.

Klaus
- Toole AES paper (Open in New Window)
- RE: An eye-opener on room acoustics... - Hifisound 07:46:29 01/06/11 (0)
  Hi Klaus,
  
  Thanks for the AES paper link.
RE: First reflection points on the floor - David Aiken 00:26:43 01/03/11 (2)
Any sound absorbing object will work.

How well the ottomans will work will depend on what is under the fabric�you'll get better results with something like foam rather than something hard, and thickness helps.

The other issue is one of surface area of the uncovered floor and what the floor is made of. If you've got a large uncovered floor surface area and the surface is something like tiles, concrete, or even hardboard, it will be more reflective at mid to high frequencies than a floor that is carpeted or largely covered with a rug. Some later reflections contribute to tonal character as well as first reflections so even though you're dealing with the first reflection points, that large uncovered area may still make the room a little on the hard, bright sounding side. That can be compensated for with other absorptive areas in the room such as curtains/drapes and even other absorptive furniture.

David Aiken
- RE: First reflection points on the floor - Hifisound 00:45:24 01/03/11 (1)
  Hi David,
  
  My flooring is vitrified tiles and the living room area is 26' x 14'
  Even if were to put a rug it would either 6' x 4' or 8' x 6' around the first reflection points ( Other area has sofa etc).
  So I was wondering if blocking just the first reflections is optimal. Though more the cover in the room the better it will be.
  
  I was also thinking that more furniture pieces like ottomans,etc will help overall absorption in the room.
  
  As recommended by you I have bought the "Master Handbook of Acoustics" and I am going through it... :)
  
  Thanks,
  Hifisound
  - RE: First reflection points on the floor - David Aiken 11:46:46 01/03/11 (0)
    With a large vitrified tile area, covering more than just the first reflection points would probably help but I have to admit that I live with probably a similar sized room with ceramic tiles for my open plan living/dining/kitchen area which is where I have my TV and the floor has no coverings anywhere. The sound can get a bit on the bright and hard side of things at some times. My stereo listening room is carpeted and treated with RealTraps products and sounds quite different.
    
    Evidence suggests that we tolerate the floor first reflection reasonably well, after all we always have a surface under our feet so we're adapted to hearing a reflection from that source, but there is a difference between hearing a reflection and hearing a bright reflection.
    
    More furniture may help. A lot depends on how absorptive the furniture is but at the very least it will help break up reflection patterns which is usually beneficial. Of course there's a point where you can add too much furniture and I'm not talking acoustically here. You've got to live in and with the room and at some point adding things ends up in either too much clutter or getting in the way of movement and causing problems other than acoustical. I'd just set the room up the way I liked it, try and consider the acoustical impact of the things I was adding and go for absorptive choices when I could, and then work out how I felt about the sound when that was done. You can then decide whether you want/need to do anything more and consider your options in relation to more standard acoustic treatment of the room.
    
    The book should help you a lot in terms of understanding. You'll probably have to reread some parts several times but it will be worth it.
    
    David Aiken

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