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How to Calculate New Speakers?

Discussion in 'Archived Threads 2001-2004' started by Brad_Shifflett, Feb 13, 2001.

  1. Brad_Shifflett

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    Got a quick question, I hear about people measuring the SPL on there speakers and all this stuff. I have a Radio Shack SPL meter and have calibrated my speakers. I recently built a pair of Kit81 speakers from Adire and would like to test them with a SPL meter. How would I do this? Is there a special way of testing the SPL of the speakers? According to the plans, it says this "Maximum in-room SPL (driven with 100W) will be in excess of 105 dB SPL (at 1 meter) from 28 Hz and up, which makes this system well suited for wide-band audio applications". Can anyone explain that to me a little more clearly for someone who is just getting into this stuff?
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    "To Buy or Not To Buy, that is the question"
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  2. Greg Monfort

    Greg Monfort Supporting Actor

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    >Got a quick question, I hear about people measuring the SPL on there speakers and all this stuff. I have a Radio Shack SPL meter and have calibrated my speakers.
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    Please elaborate.
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    > I recently built a pair of Kit81 speakers from Adire and would like to test them with a SPL meter. How would I do this? Is there a special way of testing the SPL of the speakers?
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    There are a number of ways to do this, whether in-room, or semi-aneochoic. Is the SPL meter all you've got for testing?
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    >According to the plans, it says this "Maximum in-room SPL (driven with 100W) will be in excess of 105 dB SPL (at 1 meter) from 28 Hz and up, which makes this system well suited for wide-band audio applications". Can anyone explain that to me a little more clearly for someone who is just getting into this stuff?
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    It just means that with a 100W amp, the speaker is capable of >105dB transient peaks at frequencies >28Hz/1m in a typical room. A transient peak is a high Q (very narrow bandwidth (BW)) spike. The average SPL/1m will vary depending on frequency, but overall will be limited to ~75dB/1m average to keep from clipping the amp in the lower mids. Since SPL attenuates at up to the square of the distance depending on the room, this equates to an overall minimum SPL of 69dB/2m, 63dB/4m, etc..
    IOW, if you want loud, this isn't the speaker to use unless you're sitting
     
  3. Brad_Shifflett

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    Well I hear about people testing there speakers with the SPL meter (which is all I got), they say they measure from 1M. How do you recommend to do this? Do you do the test at with a certain tone? CD? etc...
    Ok, so what is semi-anechoic and in-room difference mean?
    I find these speakers seem to get loud. I have a hard time turning it up to loud. The room is pretty small. When I put it in the other room, open vaulted ceilings and large, it does not get near as loud, the amp is also only 80 watts in the front room. My amp/receiver in the den is 100watts per channel which is where I normally listen to them. What exactly does Wide Band Audio Applications mean?
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  4. Greg Monfort

    Greg Monfort Supporting Actor

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    >Well I hear about people testing there speakers with the SPL meter (which is all I got), they say they measure from 1M. How do you recommend to do this? Do you do the test at with a certain tone? CD? etc...
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    Measuring at 1m in a typical room is as much about measuring the room as it is the speaker due to all the reflections, room modes. For just a speaker measurement, an auditorium sized room or outdoors is needed to keep reflections from affecting the frequency response (FR).
    At minimum you'll also need a test CD that has either 1/3 octave BW pink noise, or sine waves, and a digital MM.
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    >Ok, so what is semi-anechoic
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    In a ~reflection free area.
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    > and in-room difference mean?
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    In a room, usually at the listening position.
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    >I find these speakers seem to get loud. I have a hard time turning it up to loud. The room is pretty small. When I put it in the other room, open vaulted ceilings and large, it does not get near as loud, the amp is also only 80 watts in the front room. My amp/receiver in the den is 100watts per channel which is where I normally listen to them. What exactly does Wide Band Audio Applications mean?
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    For music/HT, the frequency bandwidth (BW) is from ~16Hz-20kHz, though as I noted, many find the LF acceptable if it just goes down to between 25-30Hz.
    But to answer your question, if you want to measure it at 1m in your room, which really doesn't tell you much IMO, then:
    Set the SPL meter on a stand, such as a camera pod, oriented and with the switches set per the instructions at the speaker's vertical centerline, and on center with the tweeter horizontally. Using the test CD at 1kHz, and with the MM set on VAC and attached to the speaker terminals, turn the volume up until it reads 2.83V for 8ohm, or 2.0V if 4ohm, and record the SPL. Now go up and down the BW, recording the SPL at each frequency or 1/3 octave BW. Plot it on log paper. This is its 1W/1M in-room response.
    For 100W/1m, add 20dB to each reading. This won't be 100% correct, but I don't think you want to do the testing at loud levels.
    BTW, I suggest you do this when alone, and wear ear plugs, as test tones are quite irritating to listen to.
    If you want to do this with a computer program, then scan the archives for what others have used.
    GM
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