Home Tweakers' Asylum

Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

Re: I understand your view on the reference 0 dB, my reference was this...

Ah, so you've referenced the readings to the level you got for 126 Hz. I wondered what was going on.

Well, if the level you got for 126 Hz is comparable to the level you would get if there was, say, a 1000Hz tone on the disc, then it would make a good level. If 126 Hz happens to be the frequency of a standing wave in your room and the reading actually represents a peak in the room's response at that frequency, your string of lower readings from 35 to 70 Hz or so might actually look desirable. If the 126 Hz reading represents a trough in the room's response, you would have a very bad string of readings over the 35 to 70 Hz range. As I said, however, we don't know how your reference level of 0 dB at 126 Hz relates to what's happening above that range. Whatever frequency you use for a reference should be well up above the frequency range where the room's dimensions strongly affect the response you get and 126 Hz isn't high enough in the audible range to serve as a useful reference point.

Even though the test tones are one third octave apart, it would be worth while getting a hold of a copy of something like one of the Stereophile test discs which have tones ranging from 20 to 20 kHz. That would give you a much better idea of the room's overall response and a reference tone at 1000 Hz as well.

You could then replay the JBL disc using one of the tones on that disc which matches the frequency of one of the test tones on the Stereophile disc as the reference tone. Ideally you would adjust the volume when playing the JBL disc so that the reading you get with your meter is exactly the same as the reading you got for the identical frequency test tone on the Stereophile disc (note that the reading for that frequency on the Stereophile disc is almost certainly going to be + or - something in relation to the reference 1000 Hz tone). If you then overlay the readings from the JBL disc on the readings for the Stereophile or other test disc, you will have a bit more information on what's happening than the Stereophile or other disc gives. You may well find some of the Stereophile or other disc's reading's in the 35 to 70 Hz range elevated in comparison to JBL disc readings at other frequencies in the same range, and you will have a much better idea of where the sound you're getting over that range compares to the rest of the audible frequency range. That should also give you a reference point for what you want to achieve over the 20 to 126 Hz range of the JBL disc.

David Aiken


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  • Re: I understand your view on the reference 0 dB, my reference was this... - David Aiken 00:18:42 03/19/07 (0)


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