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Thread: Reducing low end output.

  1. #31
    Join Date: Aug 2009

    Location: Staffordshire, England

    Posts: 25,663
    I'm Martin.

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    Quote Originally Posted by Pharos View Post
    "Sound vibrates the molecules in the wall the same as it des the molecules in the air - is my understanding anyway. So airborne and structure borne transmission are essentially the same thing. "

    Yes Martin, but we are discussing which route the leakage may be through, and the curative treatment is appropriate to that route.
    The curative treatment is the same either way - you need a very thick, very dense boundary between the source of the sound and the person you don't want to be hearing it! Or a vacuum. But that's even harder to achieve.

    These modern apartment buildings have pretty thick concrete walls and floors between the flats though so I'm guessing that is working well in this particular situation. I had the same experience years ago living in an end terrace, saw the neighbour out front and asked her if the music was a bother, she said she had never heard me play any music. After that it was party time!
    Martin



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  2. #32
    Join Date: Mar 2017

    Location: Seaford UK

    Posts: 905
    I'm Dennis.

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    I disagree. If the sound is travelling through air, (compression and rarification of that air), it will be prevented from exiting the source room by sealing, and constraining that process from reaching and entering the receiving room.

    If it is travelling through the subststrate, this substrate must either be restrained from movement, (bracing in the case of a cabinet), or more realistically, absorbed somehow from that substrate. In the case of speaker cabinets heavy absorbing layers are applied to the internal surfaces, but it is difficult to see how this could be done with a wall, a 6" thick rubber 'sheet' glued to the walls perhaps.

  3. #33
    Join Date: Nov 2011

    Location: Seaton, Devon, UK

    Posts: 1,849
    I'm Adrian.

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    Quote Originally Posted by Pharos View Post
    I disagree. If the sound is travelling through air, (compression and rarification of that air), it will be prevented from exiting the source room by sealing, and constraining that process from reaching and entering the receiving room.

    If it is travelling through the subststrate, this substrate must either be restrained from movement, (bracing in the case of a cabinet), or more realistically, absorbed somehow from that substrate. In the case of speaker cabinets heavy absorbing layers are applied to the internal surfaces, but it is difficult to see how this could be done with a wall, a 6" thick rubber 'sheet' glued to the walls perhaps.
    Sorry you are not quite right as concrete is a pretty solid and inert medium, yes it will vibrate but will need significant force to do so. I used to work in a sound and vibration lab at Southampton University. The two anechoic chambers (echo boxes) where about 25' by 25' by 25' and the walls, ceiling and floors were about 18' thick re-enforced concrete, they had huge steel doors which were filled with serious sound deadening material and had a latching mechanism to seal them shut them air tight to very efficient triple seals all around the edges. I remember we tested several ships horns and these were putting out in the region of 130dB at full blast, measured inside the chamber with a wired up microphones. Outside the chamber even with 130dB running the maximum level we read to check on safety was around 75dB, so the concrete walls had a significant deadening effect. You have to remember that 130dB is an extremely loud noise, and if you were subjected to it then it would be end of your hearing pretty quickly. So for the concrete soak up that much energy and to lower the sound pressure level by nearly 50% is a huge change.
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  4. #34
    Join Date: Mar 2017

    Location: Seaford UK

    Posts: 905
    I'm Dennis.

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    Please can you show me my error in thinking Adrian?

    This may seem arrogant, but I think that in principle, I'm right.
    I of course bow to your superior experience and knowledge, and am surprised that the sound was not attenuated more then 55dB.
    How did that sound get out? Yes "the concrete walls had a significant deadening effect" but were not 100% rigid, and hence non vibrating, and 'conducted' some sound. The doors and seals also were not perfect seals, the doors will also flex to some extent, and some air will also pass through the non perfect seals; transmission through air.
    If the walls do not move at all, then surely any transmitted sound must be via air.

    I know about high spls, because I have just won a legal case against BT for them subjecting me, amongst others to headphones producing up to 131.5dB.
    Last edited by Pharos; 17-04-2019 at 08:23.

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