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  1. #1
    Ears too big for wallet
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    wavelength of sub-30 Hz sounds

    I am in the process of auditioning a new sub for my room to get as low bass as possible. i measured the frequency response of my 8" mains using a SPL meter and a tone generator, and they have a flat response until 40 Hz and a rapid dropoff after that. i want any new sub i buy to be able to go significantly below that, at least a little below 30 Hz. i am a physics student, and we are learning about wave theory in class...i realized that the wavelength for a 30 Hz sound is over 38 feet long, and my room is only 12'x13'. does this mean that i am losing large parts of sounds at this frequency? is it possible to have extremely low bass in a small room?

  2. #2
    a hell of an engineer
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    Quote Originally Posted by lazyhaze
    I am in the process of auditioning a new sub for my room to get as low bass as possible. i measured the frequency response of my 8" mains using a SPL meter and a tone generator, and they have a flat response until 40 Hz and a rapid dropoff after that. i want any new sub i buy to be able to go significantly below that, at least a little below 30 Hz. i am a physics student, and we are learning about wave theory in class...i realized that the wavelength for a 30 Hz sound is over 38 feet long, and my room is only 12'x13'. does this mean that i am losing large parts of sounds at this frequency? is it possible to have extremely low bass in a small room?
    Yes, it is possible to have extremely low bass in a small room. What is difficult to achieve is accurate low bass frequency response in a small room. At low frequencies, standing waves between parallel surfaces become a factor and some frequencies become reinforced by in-phase reflections while other frequencies become diminished by out-of-phase reflections. Very low frequencies, with long wavelegths relative to room dimensions, are reinforced because the reflections are only slightly out-of-phase from the original waves. The net result is to increase the loudness of the lower bass overall, but the effect varies by frequency. Therefore, subwoofer placement becomes an important factor and an equalizer is often required to achieve accurate bass frequency response.
    Last edited by bargainseeker; 01-14-2005 at 06:47 AM.

  3. #3
    Forum Regular
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    Nov 2003
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    883
    Quote Originally Posted by lazyhaze
    I am in the process of auditioning a new sub for my room to get as low bass as possible. i measured the frequency response of my 8" mains using a SPL meter and a tone generator, and they have a flat response until 40 Hz and a rapid dropoff after that. i want any new sub i buy to be able to go significantly below that, at least a little below 30 Hz. i am a physics student, and we are learning about wave theory in class...i realized that the wavelength for a 30 Hz sound is over 38 feet long, and my room is only 12'x13'. does this mean that i am losing large parts of sounds at this frequency? is it possible to have extremely low bass in a small room?
    1130 ft. sec./30 Hz = 37.6 ft. I presume this is at sea level.

    Ask yourself whether you can get deep bass in a really small space like a car. The sub pressurizes the room below its fundamental resonance.

    Find the primary room resonances by dividing 565 by the room dimensions in feet. 565/13 = 43.5 Hz and 565/12 = 47 Hz. Ooh, nasty that! Two resonances quite close to each other. Assuming an 8 foot ceiling, we get 565/8 = 71 Hz for the third primary resonance. Below the fundamental resonance of the room of 43.5 Hz, the bass is boosted by 12 dB per octave, as I recall.
    "Opposition brings concord. Out of discord comes the fairest harmony."
    ------Heraclitus of Ephesis (fl. 504-500 BC), trans. Wheelwright.

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