Welcome! Need support, you got it. Or share your ideas and experiences.
In Reply to: RE: felt or yarn? THE DEBATE BEGINS posted by BDP24 on September 21, 2020 at 16:57:19
Owned COSMOSTATICS : AN ELECTROSTATIC OMNI-DIRECTIONAL HYBRID. The multiple woofers were suffused with lambs wool which helped the transition to the stat portion. Each speaker weighed 175 lbs- have the hernia to prove it. Soft materials are an important part of speaker design or should be so your question is pertinent but absent in most discussion. It matters
The QUAD ESL (aka "57") has a layer of felt on the backside of the center tweeter strip, the rest of the rear grille a scratchy sort of rough material. Peter Walker did not intend the ESL to be a dipole!
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 Jäger 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.
Felt is used to minimize diffraction.
Curiously, Roger's Tympani IVA's have felt on the baffle, while my later IVA's don't.
I have seen a comment by Jim Winey about some problems in early production causing diffraction around the ribbon tweeter. The response from front and back of the tweeter is different, maybe even more so in the later models with its cavity around the tweeter and the double cloth in front of it.
Where did the rest of my post go??? Only 1/3 of it is there!
Science doesn't care what you believe.
Vandersteen has been using felt on his "baffles" for ever.
Here is an article on AudioEPress.
"... This is, of course, the naturally derived felt taken from sheep. It has many uses that I won't go into, but it is used in combination with various synthetic materials to produce the numerous types available.
The acoustic quality of these compositions varies, primarily as a function of the percentage of real wool in the felt and its density.
Synthetic felt just doesn't work. It is more reflective than it is absorptive. Don't even consider using anything that is purely or even largely synthetic. ..."
Just need to narrow down the region, type, color, age and gender of sheep next and we should be good to go !!! =)
Post a Message!
This post is made possible by the generous support of people like you and our sponsors: