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Re: Acoustic polarity, again

Hi Klaus

Time-alignment normally refers to the driver to driver relationship at crossover, it is not referring to how much spread in time a broad band signal is reproduced with.

Conceptually reproducing the input wave is something a speaker should do, feed in something with a complex waveshape like a square wave or music and that is what should come out right?
In reality the vast majority of loudspeakers spread out a signal so much in time that they cannot reproduce the waveshape. VERY few multi-way speakers do it at all.

The subject of “absolute” polarity gets even more fuzzy when you consider that over much of its band, a direct radiating woofer has an acoustic phase which lags about –90 degrees but also swings to a positive values above and below that mid area.
So, while it is easy to see what phase a cone would produce when a battery is applied, for radiated sound in the mid band, the system is lagging ¼ cycle, half way between + and – absolute.
How about a full range speaker multi-way that has thousands of degrees of excess phase across its band, where would ”zero” be anyway? The problem is loudspeakers tend to have a time of origin that is frequency dependant.

For more on the rarely discussed “time” aspect of loudspeakers, look up Richard Heyser’s landmark paper on “determination of loudspeaker arrival times”.

Preserving waveshape is something that has been a concern for me, here is one design which passes / reproduces a square wave (or music) from about 220Hz to about 2600Hz.
The first thread covers some of what needs to be done, the second explains how it works.


http://www.danleysoundlabs.com/forum/forums/thread-view.asp?tid=407&posts=3&start=1

http://www.danleysoundlabs.com/pdf/danley_tapped.pdf

Frankly, there is little actual science applied to “home” speakers, most of the focus is on looks and things imagined to be important as opposed to research dwelling on the radiated sound.
Where the highest quality sound must be produced in a large space, one faces the same acoustical problems one has in a home except they are all larger, including the sound level that must be produced.
Best,

Tom Danley


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