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Tuning freq/room mode question

Discussion in 'Archived Threads 2001-2004' started by Scott M, Feb 21, 2001.

  1. Scott M

    Scott M Agent

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    I have an existing(read crappy) 10" ported Cerwin-Vega sub that I believe is tuned rather high. I want to experiment with changing the tuning freq of this sub before I begin building my sonosub. Will lengthening the port always result in a lower tuning freq?
    I ran a frequency sweep the other day and I want to figure out where my room modes are but I think the tuning of the sub is high enough that some of the peaks are tuning related. I have big peaks at 48 and 58 hz. I figure by changing the tune of the sub I can find out if they are room related...is this sound(no pun intended) logic? My room is approx. 18 x 22 x 8.
    Are there any dangers in lowering the tune of a sub that isn't meant to perform down low? I'm not looking for high output just enough to get measurments. I was measuring at about 85db at the sweet spot, peaks were higher, nulls where lower. Should I be measuring at higher or lower volumes? Thanks.
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    -scott
     
  2. Rich Kraus

    Rich Kraus Stunt Coordinator

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    probably room related. your sub is probably tuned higher than you want, but since your building another use your efforts there. additionally 30 and 50 hz are common room induced peaks (as i understand it) in "normal" sized HT rooms. (i had a ~15 dB spike at 37 hz)
    anyone know of en easy way to graph the subs anochaic response withought a chamber? could he haul it into the front yard on a quiet night and run tones measured at 1 meter?
    id play with an eq before i cut up a sellable commercial sub.
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    'Till next time,
    Rich (the kite guy)
     
  3. Greg Monfort

    Greg Monfort Supporting Actor

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    >Will lengthening the port always result in a lower tuning freq?
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    Correct.
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    >Are there any dangers in lowering the tune of a sub that isn't meant to perform down low?
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    None for low power measurements only (use ~2.83V).
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    >anyone know of en easy way to graph the subs anochaic response withought a chamber? could he haul it into the front yard on a quiet night and run tones measured at 1 meter?
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    Assuming it's fairly quiet, set it outdoors >1WL of the lowest frequency (1130ft/xHz) away from any reflective boundary. for example, if sweeping down to 20Hz, then 56.5ft in every direction. Using 2.83V input (1W/8ohms), measure at ground level 2m away so that the driver/vent can combine. Convert back to 1m SPL by adding 6dB to each measurement.
    GM
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    Loud is beautiful, if it's clean
     

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