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How do I make a frequency plot/curve

Discussion in 'Home Cinema Speakers' started by Brogan, Sep 28, 2004.

  1. Brogan

    Brogan
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    I did a search on this topic but to be honest, most of it didn’t make a lot of sense to me. :blush:

    What I'd like to know is, in words of one syllable, how I can make a frequency plot/curve of each of my speakers, including my sub?
    I have a Radio Shack SPL, a compensation chart for the SPL meter, and a DVE disc.

    The problem I see with the DVE disc is that it only does a discrete Frequency Sweep (15Hz - 20KHz) for left, centre and right speakers.
    This means I can’t plot the surrounds.
    There is however a Bass Management Test (15Hz – 150Hz) for all 6 speakers so at least I can get that part of the frequency band covered.

    Should I even be using these test tones?
    What about White or Pink noise tones? Or are they just for setting the reference 75dB level?

    The main problem though is the sweep happens fairly quickly and it’s obviously impossible to manually record the meter readings for every single Hz.
    I suppose this is where the OUTPUT jack on the meter comes in?
    What do I need to connect this to? The AUX input on the PC soundcard?
    That’s going to require a fairly long Phono-Mini Jack cable so is not very practical.
    And what application would I use to record the resulting data?

    As you can see, I have almost no idea what to do so can anyone summarise what equipment (hardware and software) I need and explain very simply what I need to do?
    Or alternatively point me in the direction of a site that covers this in detail?
     
  2. owain_thomas

    owain_thomas
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    Sorry, brogan, don't have a full answer myself but I'd be very interested in a definitive one. I think that to do the job with the SPL meter you (& I) have you have to run individual frequencies separately and record with a pen and paper the SPL reading. As I understand it the sweep needs a calibrated mic plugged into a PC. I may well be wrong on this though!

    Owain
     
  3. Brogan

    Brogan
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    That would be one way of doing it but you would need a CD/DVD with all of the tones recorded and even if you only did say 20 test tones per speaker (from 20Hz to 20Khz), that would be 20*7 = 140 separate values and would take quite a while.
    I'm willing to try this as a last resort however so if you know where I can download some reference tones, let me know.

    I though the SPL meter OUTPUT jack and the compensation chart would be capable of doing the same job?
    I'm just not sure how to use it and what software I would need to decode the output of the SPL meter.
     
  4. Brogan

    Brogan
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    Just found this site which has some tones (mainly bass frequencies) available for download: http://hometheaterhifi.com/down/

    I haven't yet worked out the best way of testing each speaker individually; I suppose it will mean physically disconnecting them...

    It also states they've been recorded at -10dB so I'm trying to work out whether that means they will read 65, 75, 85 or 95dB on a meter compared to a reference signal of 75dB or not?
    I say this because I understand the amp internal test tone to be at -20dB when the volume is set to 0? But it could be -30dB which is what DVE is supposed to be, except for the sub tone which has been recorded 10dB louder for some reason?
    Confused? You will be :confused:
     
  5. Ian J

    Ian J
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    There are loads of tones for downloading on the snapbug site and the normal way is to play one tone at a time and note down the reading.

    The site also has sweeps too but as you say they only give you a quick overview

    http://www.snapbug.ws/sinewaves/
     
  6. Brogan

    Brogan
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    Thanks Ian, I didn't know of the snapbug site.

    Just out of interest, if the file is named SIN030.mp3 does that mean it is 30Hz?
    If so, the highest frequency tone on that site is 1000Hz.
    Do people generally not plot above 1KHz?

    Also, what level are these tones recorded at?
    If the receiver volume is set to 0dB, what should I be reading on the meter; 75dB?
     

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