Baffle Diffraction and Full Range

[stephenmarklay]

I am new to all of this so I have a basic diffraction question as it pertains to full range drivers.

Playing with Jeff Bagby's Diffraction simulator I started wondering if for diffraction purpose it is better to not use a tweeter. I am not sure however if this is too simplistic a model however.

I am sure that coaxial Full range drivers won't behave any better and maybe worse as the tweeter section by design is nearer the center of the baffle.

What about a Jordan or the like?

[planet10]

The newest Mark Audios, and the Fostex FF85k definitely go into HF territory previously reserved for tweeters.

dave

[stephenmarklay]

I think in a round about way you answered my question. Playing with the software (new fun for me) the smaller the the cone area the more problematic baffle diffraction (best I can tell anyway).

I think what you are saying is the smaller the wavelength the more baffle diffraction to deal with. I am speaking about the smaller 1-3 db undulations not the 6db rise/loss.

I guess I was wondering if you get away from some of this problem by not using a small cone?

[InclinedPlane]

Someone please combine the F120A or F200A with the FF85K and report back! I'm really wanting to try it.

[planet10]

Originally Posted by stephenmarklay

the smaller the the cone area the more problematic baffle diffraction

It should not be related to driver size, only baffle size

dave

[stephenmarklay]

Thanks Dave! I was just about to agree with you when I thought of this.

Think if a circular baffle. Put a point source in the middle. Bad. equidistant to all sides. Now think of the limit the point source grows to the size of the baffle.
No more diffraction.

[planet10]

You still have diffraction. The bafflestep diffraction is the same. Edge diffraction will likely differ with the driver's dispersion characteristics.

dave

[R-Carpenter]

It's all a set of trade offs and benefits. All or most (you ask about Jordan and the answer is yes) Full range drivers go all the way up to 20 000 or sometimes higher territory. The question is how well they get up there and with what level of linear and non linear distortions. How good or bad is the off axis response of the driver? Adding a tweeter allows to get a much better off axis response and lower distortions and because full range driver gives you a wide window where to cross, you don't necessarily need a $$$ tweeter to play clean low. But it adds up the crossover and it's own drawbacks. Coax drivers appear to resolve off axis problems at the crossover frequency. I have come across a couple of older Tannoy coaxial drivers and measured them. Quite honestly I was blown away by how low the THD were.
Diffraction depends on the size and the shape of the cabinet. You can lower it somewhat by applying fabric to a front panel as well.

[stephenmarklay]

Thanks Guys! I had been wondering why people don't apply some sort of damping to the baffle... I guess no matter there will be a freq at which the damping is not useful.

Again thank you guys - Dave.

[just a guy]

Originally Posted by planet10

It should not be related to driver size, only baffle size

dave

IIRC from playing with The Edge, smaller drivers exhibited more diffraction than larger drivers, centered at the same place on the same baffle. Maybe not dramatic enough to make a big deal about but I think I remember seeing a difference. I'd try it again to confirm but it's pretty busy with the holidays and all.