Tweeter dispersion

[jmar]

On a typical soft dome tweeter (I have the Vifa D27) what are the dispersion characteristics (generally) like?

I mean like the angle of the radiated sound.

Is it fairly constant across the entire surface area (probably is, I'm guessing) or does it behave in a non linear fashion?

Like an LED lamp for example would have equal output "up to" a 120 degree viewing angle. (with zero being on axis, I guess and (2) 60 degree angles for each side.

I really like the way my tweeter sounds mounted BEHIND my baffle but concerned about the size of the hole to use.

THANKS.

[badman]

There's been a lot of discussion around directivity. Generally tweeter domes are near omnidirectional until about 5k where their beamwidth tends to slowly taper. You want to smooth the baffle cutout as much as possible and create a shallow, flared, 3/4" deep waveguide or the like, to minimize negative influence of mounting behind the baffle. Look up "Basslines waveguide" here and on parts express techtalk- you can find some experimentation with baffle-thick waveguiding.

[jmar]

Ok great.

A real difference with this mounted behind the baffle -- using a Pioneer B20 full range for woofer and no doubt that has something to do with it.

Just enough time delay in the Vifa highs to balance things well.

I'll check out that info -- thanks.

Bottom line though -- the damn thing sounds better that way.

[Spatz]

All speakers are radiating omnidirectional at low frequencies und start beaming at higher frequencies. The speakers usually start beaming at a frequency which wavelength is around the circumference of the diaphragm (ka=1; ka=circumference of diaphragm/wavelength of frequency). Dome tweeters tend to beam at higher frequencies (ka=1,5) but they are beaming stronger above ka.

Beaming is further influenced by the baffle (size, shape, edges), horns, other sound sources (dipoles etc.).

Your comparison with a LED is not right, as a LED is beaming in its whole frequency range.

You can have a look at the software "AxiDriver", which can simulate the sound propagation of waveguides ans horns.

Bye,

Spatz

[jmar]

I would think for a 1" dome that a 3" diameter hole is plenty (for 3/4" plywood) even without a flare? I'm not crossing the tweeter till about 8K or so because of the Pioneer full range so that's an advantage also.

It sounds good anyway and from all angles.

[badman]

You're setting up diffractive edges and cavity resonances. There's a reason I mentioned doing a small waveguide...

[tinitus]

Originally Posted by badman

There's a reason I mentioned doing a small waveguide...

right
and thats what Im doing right now

btw, its for "old" Vifa XT19
faceplate been modified

[Inductor]

Originally Posted by jmar

...Like an LED lamp for example would have equal output "up to" a 120 degree viewing angle. (with zero being on axis, I guess and (2) 60 degree angles for each side.

A LED has half the output (or lumens) at the designated angle, so (would) not (have) "equal output", from what I understand.