Dispersion and crossover points

How low does the crossover frequency between woofer and a horn/waveguide need to be in order to lower the importance of dispersion matching at the crossover frequency?

Any input on this? :)
Larger diameter woofers "beam" at higher frequencies than small woofers.
Waveguides can be made in a variety of dispersion patterns.
The lower the crossover frequency, the larger a waveguide needs to be to have pattern control.

A small diameter driver can cross at a fairly high frequency to a small waveguide and match dispersion.

As a rough rule, a 90 degree waveguide needs to be approximately the diameter of the driver to match dispersion .
 
Isn't that the other way around?
I meant to say "larger diameter woofers "beam" more at higher frequencies than small woofers".

The larger the piston diameter, the lower the frequency that the speaker beams at.

A 15” has a -6 dB 90 degree dispersion at about 1200 Hz.
Dispersion varies with frequency, a 15” speaker is about -6 dB at 60 degree at about 1.8K, a 12” at 2.2K, a 10” at 2.8K.

A 12” speaker is around 180 degree at 900 Hz, 90 degree at 1200 Hz, 50 at 2400 Hz, and 30 degrees at 4000 Hz.

A 15” has a 180 degree -6 dB beam width at around 600 HZ, a 12” at about 800, and a 10” at about 1200 HZ.
 

Defo

Member
2008-11-06 9:15 pm
I appreciate the reply, but that wasnt the answer for my question.

How low does the crossover frequency between woofer and a horn/waveguide need to be in order to lower the importance of dispersion matching at the crossover frequency?

In other words, how low must one cross in order for dispersion matching between horn and woofer to be irrelevant?
 

AllenB

Moderator
Paid Member
2008-10-18 11:31 am
I think Defo is asking more like: would it be better to cross two 90 degree patterns properly at 2k or to bluntly cross 90 to 180 at 1k, for example. How does a person answer that? The transition may be more smooth with a slow crossover, haven't tried that for this purpose but the less successful that is, the lower the better. After all, doing it properly isn't actually perfect either. It still means crossing between two sources, and a dispersion transition of seemingly arbitrary (merely practical although tested and workable) transition bandwidth.
 

Defo

Member
2008-11-06 9:15 pm
The background for my question is;

As of today, I cross a 90 degree waveguide to a 10 inch woofer at 1600 Hz to roughly match dispersion.

But I'm considering trying a much larger horn and driver with a crossover point at 350-500 Hz. But that will mean the dispersion patterns at the crossover frequency no longer will match between horn and woofer.

How relevant will it be when crossing that low? When does it start to become less relevant?

By the way, I'm crossing digital at 48 db/octave.
 
As of today, I cross a 90 degree waveguide to a 10 inch woofer at 1600 Hz to roughly match dispersion.

But I'm considering trying a much larger horn and driver with a crossover point at 350-500 Hz.
In the first case, matching makes sense, the pattern will just gradually widen from 90 degrees below 1600Hz.
Same will happen in the second case, only in a more narrow frequency range since you have chosen a 48 dB per octave xover.

A "bad" dispersion result would be crossing from a small waveguide that was more than 90 degree at 1600 to a larger woofer that was less than 90 degrees at the crossover point.