Before I ask my question, let me first say what a pleasure this site is. No ridiculous flaming, etc., just decent discussions about the hobby. I tip my hat and send my most grateful thank-yous to those who are responsible for developing and maintaining this site.

Now, to the question at hand: I am still fairly new to this hobby, and am still learning. I purchased some time ago a test cd and SPL meter. On the test cd, it has various tones on the frequency band from 20Hz to 20kHz, so that one can test the frequency response of their system. I would like to do this, but wish to make certain that I am employing the correct methodology.

The book with the cd indicates that the meter should be set at ear-level (I assume in the sweetest spot in the listening room). It also states that one should use the 1kHz band as a reference. So, can I assume that I should start by selecting a certain dB level for 1kHz. After doing so, I assume I would then leave the volume control at the same level to do the test, recording the dB level for each tone on the scale (e.g., 20Hz, 16Hz, . . . 12kHz, 16kHz, 20kHz). Is this procedure correct, or am I completely off base? Am I neglecting any procedures?

I also assume I am hoping to find that the dB level stays fairly constant with each tone on the scale. Is this also correct, or should I be looking for something else, or additional?

I would appreciate any help or advice that anyone could provide. Thanks in advance.

Tom

 Thanks Guys . . . - Tom V. 04:24:40 4/02/99 (0)
 Re: Advice on Testing - Clayton Oxendine 19:55:27 3/31/99 (0)
 Re: Advice on Testing - Jon Risch 19:37:04 3/31/99 (0)

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 Thanks Guys . . . - Tom V. 04:24:40 4/02/99 (0)
 Re: Advice on Testing - Clayton Oxendine 19:55:27 3/31/99 (0)
 Re: Advice on Testing - Jon Risch 19:37:04 3/31/99 (0)

First, be sure to stand in the same place, preferably behind the mic of the meter, to take your readings. Not to close, and not directly next to or directly behind, get as much distance between you and the mic as possible.

Are the test tones warble tones? Steady tones can build up and throw the readings off, as the delayed and refelcted room effects will swamp the speakers response. Your ears can distinguish between direct sound and reflections, the meter can not. This will throw the readings of, sometimes by as much as 6-10 dB.

Even warble tones will tend to be influenced by the room, and delayed room energy will affect warble tones by as much as 2-5 dB. With a warbel, set the meter to the slow setting, and eyeball average the resulting reading.

Don't set the 1 kHz tone level to high, OR too low. A good SPL is around 80-85 dB, as long as there is not a lot of extraneous noise. Turn off any fans, blowers, AC, heaters, etc for the duration of the tests. Note the SPL reading withoput any test tones, it should be lower than 12 dB below thew proposed playback SPL of the test tones, or the readings will not be accurate.

Realize that the SPL meter, unless it is a $500 model or better, will probably not be totally accurate, and could itself have several dB of variation. Even good speakers in a decent room can vary by 6 dB or more, in absolute terms, then add in the meter deviations, and the delayed room energy deviations.

To get a better feel for what is going on, plot the same data for several different locations around the room, one a 1M from the front of the speaker, on the tweetrer axis, and one off somewhere to the side. The closer 1M response curve will reduce the room effects for the upper ranges, and the off to the side response will tend to help correlate what the room is doing to the sound.

Do not be tempted to use an equalizer to try and "fix" the response, as there is no such thing as equalizing a room, it is a poor bandaid that does not work very well (sophisticated digital EQ's are an exception, but still are only good at one spot, and have there own problems).

Jon Risch

20HZ =6.2DB 25HZ =4.4DB 31.5HZ =3DB 40HZ =2DB 50 =1.3DB
63HZ =.8DB 80 HZ =.5DB 100HZ =.3DB 125HZ =.2DB 160 =.1DB
200HZ to 1250HZ Flat
1600HZ = .1DB 2000HZ =.2DB 2500HZ =.3DB 3150HZ =.5DB
4KHZ =.8DB 5KHZ =1.3DB 6.3KHZ =2DB 8KHZ =3DB 10KHZ =4.4DB
12.5KHZ =6.2DB 16KHZ =8.5DB 20KHZ =11.2DB

Tom