Matching dispersion characteristic at the crossover point (400hz). - AVS Forum
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post #1 of 17 Old 02-04-2013, 09:38 PM - Thread Starter
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Back story: I have a big space to fill with sound, 11,000 ft^3 or so. I also have a collection of large horns and compression drivers that I would like to use, if possible, for the surround speakers.

They will be active 3 ways. The mid-range horns are the big Altec Mantarays. I have two with a 60x40 dispersion and two with a 90x40 dispersion.

I can provide the time alignment easily enough since these are active. The c2c spacing is going to be less than 1/2 a wavelength but greater than 1/4 wavelength @ 400hz - acceptable?? How do I determine what drivers/alignments will have matching dispersion characteristics? Or to be more specific, I want to mate these horns to a simple sealed cab with a pair of 15" pro drivers. Is comb filtering even audible at 400hz?
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post #2 of 17 Old 02-05-2013, 02:07 AM
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most horns and many woofers have some sort of off axis measurement in the spec sheet. if your woofers don't, just use an average of similar woofers.

15" drivers are going to be radiating more or less omnidirectionally up to around 500hz or so. i don't know how low your horns hold pattern control, but if they are very large horns, you may end up with a mismatch. however, you can cheat by putting the speaker in a corner. that essentially turn the room into a 90 degree horn for your woofers, so you get much closer to a directivity match even if not perfect.

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post #3 of 17 Old 02-05-2013, 11:35 AM
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simple rule of thumb is that the width of the woofer array should be close to the width of the horn

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post #4 of 17 Old 02-05-2013, 12:00 PM - Thread Starter
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Thanks guys, that info is of great help!

Since these are going to be surrounds, they will be along the back and side walls, not in the corners. Nothing can be that easy smile.gif
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post #5 of 17 Old 02-09-2013, 01:15 PM - Thread Starter
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Quote:
Originally Posted by noah katz View Post

simple rule of thumb is that the width of the woofer array should be close to the width of the horn

I've have a little more time to think about this and... If I were to build a 2x15" array the drivers would be at least 16" apart. But when crossing at crossed 400hz (1/4 wavelength would be 8.1") so there would be comb filtering between the two 15" drivers AND between the 15's and the mid horn.

Is this a big concern or something you can file under compromise? The Onken w (two driver array) is often matched to altec mid horns, but it's obviously going to suffer comb filtering as I just described.
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post #6 of 17 Old 02-09-2013, 02:13 PM
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if you don't care about vertical directivity, one option is to mount the two 15" drivers vertically with the horn on top like a jbl 4722n.

that is a 90 degree horn on there and it is a directivity mismatch at its crossover point to the woofers, but it doesn't seem to matter.


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post #7 of 17 Old 02-09-2013, 02:39 PM - Thread Starter
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Originally Posted by LTD02 View Post

if you don't care about vertical directivity, one option is to mount the two 15" drivers vertically with the horn on top like a jbl 4722n.

that is a 90 degree horn on there and it is a directivity mismatch at its crossover point to the woofers, but it doesn't seem to matter.

What's the advantage of stacking them vertical, vs horizontally? The Altec mid horns are wide enough to accommodate a side by side configuration.

It's bad enough that there are so many rules (as dictated by physics) to speaker building, but the real killer is that there is no consensus on what you can get away with, because you pretty much have to break a few rules. Even Danley's synergy horn doesn't have a smooth mouth termination and as such should cause reflections back into the mouth, right?

Buy, build, measure/audition rinse and repeat can get pretty expensive.

I think I'm going re-visit the idea of a FLH. I like what I already have (80hz FLH) but want a f3 at 60hz this time around.

Building and bracing six, 60hz front loaded horns is going to take awhile... (makes me think of the quote in your signature)
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post #8 of 17 Old 02-09-2013, 03:11 PM
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Originally Posted by steve71 View Post

What's the advantage of stacking them vertical, vs horizontally? The Altec mid horns are wide enough to accommodate a side by side configuration.
Read this:
http://www.gtaust.com/filter/05/07.shtml

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post #9 of 17 Old 02-09-2013, 03:29 PM - Thread Starter
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Originally Posted by Bill Fitzmaurice View Post

Read this:
http://www.gtaust.com/filter/05/07.shtml

Thanks Bill. I will read it, and more importantly attempt understand it all. Thanks for the link. smile.gif
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post #10 of 17 Old 02-09-2013, 04:52 PM
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the advantage of the vertical stack is the nulls from the two drivers are aimed at the floor and the ceiling vs. the left and right seating positions.

it is why most speakers use a vertical orientation.

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post #11 of 17 Old 02-09-2013, 05:36 PM - Thread Starter
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Originally Posted by LTD02 View Post

the advantage of the vertical stack is the nulls from the two drivers are aimed at the floor and the ceiling vs. the left and right seating positions.

it is why most speakers use a vertical orientation.

Ah, got it. So in something like the JBL Everest (side by side configuration) they are crossing to the mid horn low enough that they avoid lobbing between the drivers?

So if vertical orientation avoids horizontal lobbing, then with something like my current setup (single driver front loaded horn crossed to the altec 1003 horn at 300hz) I shouldn't get any lobbing/comb filtering on the horizontal axis, correct? With the right floor and ceiling diffusion/absorption the lobes will have a pretty minimal impact... hmmm interesting.

So the Onken W is only horizontal because it would be too tall to stack the drivers vertically?
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post #12 of 17 Old 02-10-2013, 11:37 AM
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Even Danley's synergy horn doesn't have a smooth mouth termination and as such should cause reflections back into the mouth, right?

True, but there's nothing to stop you from adding a termination to a Synergy. The horn is simply a conical.
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post #13 of 17 Old 02-10-2013, 11:42 AM
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Originally Posted by steve71 View Post

Ah, got it. So in something like the JBL Everest (side by side configuration) they are crossing to the mid horn low enough that they avoid lobbing between the drivers?
Yes. Where you run into problems is with high frequencies and large format horns, which you can't get close enough together, be it in one cab or in multiple cabs horizontally arrayed.

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post #14 of 17 Old 02-10-2013, 03:00 PM
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"Ah, got it. So in something like the JBL Everest (side by side configuration) they are crossing to the mid horn low enough that they avoid lobbing between the drivers?"

the everest is a .5 way. the second woofer rolls in around 150hz or so iirc in order to enhance the bass.

at that low of frequency, the wavelength is about 8 feet long, so 1/4 wavelength is 2 feet. if the driver centers are within 1/4 wavelength the amount of comb filtering will be negligable.

i'm not familiar with the onken w.

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post #15 of 17 Old 02-10-2013, 06:16 PM - Thread Starter
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Originally Posted by bwaslo View Post


True, but there's nothing to stop you from adding a termination to a Synergy. The horn is simply a conical.

Yep, good point, but I wonder why Tom didn't bother with it. Maybe it's not that audible at certain frequency's? Your avatar looks like a DIY synergy horn. Got any details on it, I would love to learn more!

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Originally Posted by Bill Fitzmaurice View Post

Yes. Where you run into problems is with high frequencies and large format horns, which you can't get close enough together, be it in one cab or in multiple cabs horizontally arrayed.

Exactly, I understand the limitations. But is it a worth while trade off for having 300-5Khz (or 500-7Khz) on a single horn/compression driver.

There is approx 56cm c2c between my bass horn and Altec1003's horns. That would require a crossover at 147hz to satisfy the 1/4 wavelength rule.

I can cross the 1003 as low as 300hz. So that would allow a max c2c of 27.5cm or 10.8". The bass horn would have to be very squashed to achieve that kind of spacing.

This is looking more and more like mission impossible. Looks like I either have to live with it or move away from large format horns. At least with my single driver bass horn & 1003 mid horn (see avatar), the lobes will be directed at the floor ceiling, correct?
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post #16 of 17 Old 02-10-2013, 06:17 PM - Thread Starter
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Originally Posted by LTD02 View Post

"Ah, got it. So in something like the JBL Everest (side by side configuration) they are crossing to the mid horn low enough that they avoid lobbing between the drivers?"

the everest is a .5 way. the second woofer rolls in around 150hz or so iirc in order to enhance the bass.

at that low of frequency, the wavelength is about 8 feet long, so 1/4 wavelength is 2 feet. if the driver centers are within 1/4 wavelength the amount of comb filtering will be negligable.

i'm not familiar with the onken w.

Ah, I didn't know that the 15's had different crossovers points.
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post #17 of 17 Old 02-11-2013, 12:24 PM
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Originally Posted by steve71 View Post

... when crossing at crossed 400hz (1/4 wavelength would be 8.1") so there would be comb filtering between the two 15" drivers AND between the 15's and the mid horn.

This isn't comb filtering, though the basic mechanism is the same one of interference, and is necessary to achieve directivity.

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