Speaker Asylum General speaker questions for audio and home theater.

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RE: Speakers specs question

Posted by tomservo (M) on December 23, 2023 at 05:48:03

In Reply to: Speakers specs question posted by tube524 on December 22, 2023 at 15:22:24:

There are several answers.

The spec + - 3dB means that the acoustic power varies by a factor of 2 greater (+3dB) and lesser by a factor of 2 (-3dB) so within that frequency band (38Hz to 30KHz) the output varies from twice to one half the average level. Perfectly flat means it has the same output over that same frequency range (and generally only possible using dsp)

Normally, one specifies a loudspeaker response in an anechoic condition (where the room has no impact so that might be outside or using a Klipple machine like we use at work). For the purpose of being able to predict level at larger distances, 1 meter is normally the specified measurement distance although for large loudspeakers, it is better to measure at 10 meters (-20dB re 1 Meter). The reason is rooms are all different and so "in room" are close to meaningless so far as specifying what a loudspeaker does. A comparison of different speakers all in the same location in the same room would be a valid comparative case.

So that leaves the 38Hz (just below low E on a bass guitar) and 30KHz (about an octave above what an average adult person can detect without other sounds present). IF you remember picture tube TV's, most made a pretty loud 15,575 Hz pitch from the flyback transformer.
That 30k is a VERY high audio frequency near an octave higher than the flyback pitch and about a half octave above what can be captured on a CD (~22Khz).

What you get at the listening position is "Different" and what you hear changes from mostly direct sound up close to mostly reflected sound far away.
That reflected sound profoundly changes the stereo image as all of it is added to and not part of the recording, an "effect" you can't turn off.

Just as directivity helps voice intelligibility in a room (by reducing reflected sound at the ear),extending the "near field" where the direct sound dominates also helps the stereo image.

If you want to hear what your speakers actually do, set them up outside where there is no room or horizontal reflections -or- set them up in the middle of a room and sit very close.

What you will hear outside immediately is a loss of bass, the most obvious room effect is the progressive containment of the low end, resulting in the "preferred listening position response" which is not flat.
Hope that helps
Tom Danley
Danley Sound Labs

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