75 degree waveguide, any good reason?

[dantheman]

If you using a 75 degree waveguide tweeter with a direct radiating Mid driver, won't you have to crossover above the pistonic range if you want matching directivity? In other words you'll have midrange cone breakup in you response.

Does that seem correct?

Is there any reason you'd want this directivity pattern?

Thanks,

Dan

[gedlee]

Originally Posted by dantheman

If you using a 75 degree waveguide tweeter with a direct radiating Mid driver, won't you have to crossover above the pistonic range if you want matching directivity? In other words you'll have midrange cone breakup in you response.

Does that seem correct?

Is there any reason you'd want this directivity pattern?

Thanks,

Dan

Dan

There is not enough information to answer this question.

[dantheman]

a 90 degree WG tweeter can be crossed to a woofer approximately at the wavelength of the woofer's diameter to match directivity at the crossover point. Both would then be essentially 6dbs down at 45 degrees off axis correct?

Dan

[gedlee]

Originally Posted by dantheman

a 90 degree WG tweeter can be crossed to a woofer approximately at the wavelength of the woofer's diameter to match directivity at the crossover point. Both would then be essentially 6dbs down at 45 degrees off axis correct?

Dan

Basically that is correct, yes. Why? In detail, it might differ somewhat.

[dantheman]

Originally Posted by gedlee

Basically that is correct, yes. Why? In detail, it might differ somewhat.

Exactly what I was thinking.

So why does Parts Express build a 75 degree waveguide which in my measurements are down 9 dBs at 45 degrees. My ten inch woofers then have to be crossed higher into their break-up region in order to match them. About 2.5 kHz instead of 1.5kHz for a 90 degree WG. It seems a 75degree WG would only make it harder for the DIY community to get their design right by doing this--there's a good chance the woofer's response will be rippled and have an erratic decay plus the center to center spacing at the crossover frequency will be further apart. So I figure there must be a good reason to build such a device. My guess is that it will work better in larger rooms b/c it can minimize early reflection problems. It seems that the benefit wouldn't outweigh the advantages in anything but a large have or gymnasium or if you are concerned with mastering your own score. Any other input?

Thanks,

Dan

[dantheman]

Oh one other question someone smarter than me might be able to answer: is there an equation that would accurately predict a driver's beaming behavior if pistonic behavior is assumed at all frequencies(even though I know this does not actually exist)?

Thanks again,

Dan

[LineSource]

From Altec literature...

Variable ka is the ratio of the circumference of the speaker, or baffle, to a wavelength. High ka numbers indicate high frequency. A loudspeaker will be omnidirectional starting at ka=1 and the beamwidth will halve for each octave increase in frequency. A baffle will act as a half-space baffle until it reaches about ka=2, where it makes a transistion (45 degrees on log/log graph) to 360 degrees at ka=1. Half space radiation is about 160 degrees (-6db) in real world situations instead of the 180 degrees predicted theoretically. Any loudspeaker in a large baffle is not affected by that baffle at high frequencies where the free-air beamwidth is smaller than 160 degrees or so.

[gedlee]

Originally Posted by dantheman

So I figure there must be a good reason to build such a device.
Dan

Hi Dan

This is audio, logic need not apply.

[Key]

Well my guess would be feedback rejection in live sound applications.

[dantheman]

Originally Posted by gedlee

Hi Dan

This is audio, logic need not apply.

That's funny. I've debated audio nuts and gurus that claim just that point with me--even a manufacturer! Yet they have literature and/or design criteria proclaiming their products' and/or builds' superiority. "Just don't make sense."--Ross Perot

LineSource, thank you for that information! It is useful. I think I actually understand it. hahaha

Dan