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 Multi-Way Conventional loudspeakers with crossovers

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Patrick Bateman
diyAudio Member

Join Date: Oct 2006
Location: San Diego
Quote:
 Originally Posted by bwaslo Except the dimensions needed also depend on the coverage angle. To make a narrower beam, the horn has to bigger. Per Keele's (http://www.xlrtechs.com/dbkeele.com/...xp%20Horns.pdf, see figure 18) empirically derived formula, the dimension goes inversely as the angle, also inversely as the 'intercept frequency').
I know that Bill and Jack understand how all these variables relate, but I threw together a few pictures to illustrate what's going on.

Here's a speaker with the QSC waveguide, which is basically oblate spheroidal. That's very close to conical. The idea being that the angles of the waveguide walls define the horizontal and vertical coverage.

Here's a 3D model of 60x40 conical horn. This is straightforward stuff, the horizontal walls form a sixty degree angle and the vertical is forty.

THIS IS THE EXACT SAME HORN, except I've "chopped off" part of the horn to form a diffraction slot. By doing so, I've kept the vertical beam exactly the same.

This is super important, because it illustrates what Bill Waslo is saying. Basically there's no free lunch in engineering, if you want a narrow beam you're going to need a big deep waveguide. The only "real" ways to get around this are to do geometric tricks by folding the wave over, like in a DOSC or a Paraline.

Also, note that the horizontal beam has widened by 30%.

More pics of said device.

Once all that makes sense, you can fire up the 3D software and come up with all kinds of strange waveguides. For instance, you could have a 40x40 waveguide with a symmetrical mouth, then 'slice' off a chunk of the waveguide to create a 90x40 beam using a diffraction slot. So the overall volume of the horn is smaller, the mouth size stays the same, but the beamwidth becomes 90x40.

Another "neat" thing about diffraction slots is that it allows you to have a beamwidth similar to a conical waveguide, but a response shape that's closer to a conventional horn. The "loading" of a horn depends on the horn's expansion rate. A slowly expanding horn like an exponential horn loads differently than a conical horn. The "conventional" way to achieve horn loading was by using a symmetrical horn. But if you juggle the variables in a diffraction horn, you can use the slot to reduce the expansion rate of the horn near the throat.

All the old horn guys knew about this. They did things like using flat horizontal walls for directivity control and exponential vertical walls for loading. But in 2018, in a world of 3D printing and BEM simulations, we can go nuts with it.

Last edited by Patrick Bateman; 28th July 2018 at 10:54 PM.

bwaslo
Old guy with soldering iron
diyAudio Member

Join Date: May 2006
Location: Portland, Oregon!
Quote:
 The Keele Electrovoice horns from 43 years ago use an expanding flare at the mouth to prevent beamwidth narrowing as the horn directivity collapses The Danley horns do likewise
In Danley's pattents, he references the Keele 'what's so sacred' paper as I recall.

Diffraction slots are good(?) for widening coverage, but usually in homes the challenge is narrowing it. So larger (or tricks like arraying) is needed.

Another difference between Lambda Unity and SH50 is that the Lambda is just a 2-way!
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Crossover design Xsim; Depot diffusor super-easy diffusors

 29th July 2018, 02:13 AM #53 AllenB   diyAudio Member   Join Date: Oct 2008 A quarter radial horn can be made without a diffraction slot, except that it asks for a quarter radial source.
Patrick Bateman
diyAudio Member

Join Date: Oct 2006
Location: San Diego
Quote:
 Originally Posted by bwaslo Diffraction slots are good(?) for widening coverage, but usually in homes the challenge is narrowing it. So larger (or tricks like arraying) is needed.
One 'neat' trick you can do with a diffraction slot is to rotate the waveguide 90 degrees, while still maintaining a symmetrical pattern.

Here's what I mean by that:

If you took this QSC waveguide, and you rotated it ninety degrees, you'd have a beamwidth of about 70 degrees by 100 degrees.

Now if you add a diffraction slot, you can get the beamwidth to be about 100 degrees by 100 degrees - even though the mouth is taller than it is wide.

You end up with a waveguide that produces a symmetrical beam, while still being relatively narrow.

Obviously, this is a bit of an 'edge' case, but it's kinda handy if you're trying to make a loudspeaker with good WAF. (Since wives love speakers that are tall and narrow.)

Quote:
 Originally Posted by bwaslo Another difference between Lambda Unity and SH50 is that the Lambda is just a 2-way!
As I understand it, the Lambda Unity Horn was basically a 'scaled down' version of the Sound Physics Labs TD-1. The tweeter is the same and the midranges are the same. The Lambda Unity Horn uses a horn that's about half the diameter, and the woofers are Lambda instead of whatever is used in the SPL TD-1.

 15th August 2018, 08:07 AM #55 Patrick Bateman   diyAudio Member     Join Date: Oct 2006 Location: San Diego Follgott's new speaker has a baffle that's 31cm wide. With a baffle that wide, you'd expect to see the directivity collapse around 1100hz. (1100hz is 31cm long.) But it doesn't. Here's the polars. You can see that the beamwidth grows wider, but it widens slooooooowly. Obviously, those woofers on the side are doing SOMETHING but I wasn't entirely sure WHAT. There's some clues in the crossover. The midranges and the woofers are playing at an equal level at 580Hz. Here's my theory on what's going on. In a speaker with one midrange, the sound will start to wrap around the enclosure below 1100Hz, because the wavelengths are longer than the baffle. (illustration on the top left.) If you put TWO midranges on the same baffle, the pattern narrows. This is because the midranges combine constructively in front of the baffle. (In the illustration on the top right, you can see how the drivers combine.) If you put TWO midranges on the same baffle, along with two woofers on the side, it looks like you can approximate the performance of an array that is physically larger. (illustration at the bottom.) The speed of sound is constant, so by juggling the delay and the geometry of the woofers, you can produce a wavefront that's shaped as if the woofers were actually spaced further apart. In other words - To control directivity down to 580Hz, you need an array that's 59cm wide. FollGott's array is 31cm wide. The speed of sound is constant. So you can use DSP delay, or physically delay the woofers, to create a wavefront that mimics having the woofers physically spaced 59cm apart. Obviously, this would require some trial and error, but I imagine that's why FollGott made a BEM model. (Pseudo-coaxial with narrow directivity (and Horbach-Keele filters))
FoLLgoTT
diyAudio Member

Join Date: Oct 2006
Location: Hannover, Germany
I think you are right. The trick is the overlapping of the woofers and midranges. In this range they form some sort of array.

Only front woofers:

Only side woofers:

All woofers (front drivers delayed):

As you can see the front woofers alone widen faster below 1 kHz and much faster below 500 Hz.

The side woofers alone narrow directivity in front hemisphere, but significantly radiate in the back hemisphere and produce side lobes at 800 Hz.

With all woofers enabled and the front woofers delayed most of the problems in the back hemisphere are attenuated and still the directivity is narrowed in the front hemisphere.
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 16th August 2018, 10:04 PM #57 bwaslo   Old guy with soldering iron diyAudio Member     Join Date: May 2006 Location: Portland, Oregon! that's pretty neat __________________ [W9MJE] Horn spreadsheet SynergyCalc/; SmallSyns SmallSyns; Crossover design Xsim; Depot diffusor super-easy diffusors
 17th August 2018, 12:43 PM #58 ErnieM   diyAudio Member   Join Date: Dec 2009 Location: Fresno, CA Thanks for sharing. I've been planning a 3-way project with 4 channels of dsp. Front and side woofers sharing the range below 300hz with separate channels. Looks to work well.
Ro808
diyAudio Member

Join Date: Mar 2010
This is an interesting and often marginalized subject in horn related discussions.

A few months ago, I was tempted to buy a pair of Renkus-Heinz Complex Conic Horns that were offered on a local ebay marketplace.

For a number of reasons I let them pass, but I did save the images.
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Ro808
diyAudio Member

Join Date: Mar 2010
At the time I wasn't convinced these horns would work with my 2" drivers, or even work at all without the compression woofers, as shown below.
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