Planar Speaker Asylum

RE: felt or yarn? THE DEBATE BEGINS

73.209.29.251

This Post Has Been Edited by the Author

In Reply to: RE: felt or yarn? THE DEBATE BEGINS posted by BDP24 on September 22, 2020 at 03:01:40

Using felt around tweeters has been done for quite a while. I've often seen a saw-like pattern cut into the inner edge of the surrounding felt, this exposes greater linear area of felt to the radiation from the tweeter and also varies the distance between the felt and the tweeter- to vary the wavelength fractional distance between the tweeter and the felt.

Bottlehead uses a pattern of felt around their J�ger speaker said to be computed using some variation of fractal math to help deal with diffraction. ( see https://bottlehead.com/product/jager-speaker-kit/ )

The idea is to prevent the expanding wavefront from the tweeter encountering a cabinet edge or other disturbing boundary. When an expanding sound wave hits a boundary, reflections off that boundary act like sound sources, like sonic mirror images of the tweeter... at lower amplitude, or course, but still you end up with what is essentially the acoustic equivalent of a whole bunch of tweeters, all at different fractions of wavelengths from the original tweeter, minor additive and subtractive artifacts appear in the amplitude response....

This is also why tweeters are flush-mounted in speaker baffles and speaker cabinet edges rounded- these are attempts to eliminate this effect.

Compare the measured response of a surface-mounted done tweeter to one that is flush mounted- you'll typically see little ripples in the treble response of the one that's just stuck to the baffle compared to the flush mounted one,and it also creates some disturbance in the 3D distribution - both of these can impair stereo imaging in "point source" (i.e., dome, cone or single ribbon) high frequency speakers. Felting is a further measure beyond flush mounting and rounded corners to avoid these diffraction effects.

Planar and line sources don't have quite the same vulnerability, though there are other things to watch out for when designing planar or line array systems.
Science doesn't care what you believe.

Follow Ups: