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Multi-Way Conventional loudspeakers with crossovers

"Unitized" Image Control Waveguide
"Unitized" Image Control Waveguide
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Old 23rd April 2019, 01:50 AM   #51
Patrick Bateman is offline Patrick Bateman  United States
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Quote:
Originally Posted by Audiodidakt View Post
Superb work! Could you please elaborate on the directivity-issue, i.e. how does this allow you to change the speakers directivity in a controlled fashion?

Best regards

Gisle
Click the image to open in full size.

If you have a pair of drivers and you slooowly move them further and further apart, their beamwidth will become narrower and narrower. There's a point where the beamwidth becomes a huge mess, where you wind up with off-axis lobes that are louder than the ON axis lobes.

The animation above shows the beamwidth as the frequency goes up. But the exact same thing happens if you keep the frequency the same, and increase the center-to-center spacing.

Click the image to open in full size.

All of that is fairly basic, and well documented by Joe D'Appolito in 1983: forum.vegalab.ru/attachment.php?attachmentid=285268&d=1485366742

One way to shrink the footprint of the box is to simply put the woofers on the TOP and the BOTTOM of the box, or on the sides. It allows you to leverage the beamwidth control of a D'Appolito array, without building a huge box. For instance, the D'Appolito "Thor" speaker could be reduced by about 33% by putting the woofers on the top and the bottom of the enclosure.

Of course, in order to do this, the woofers have to be operating at a frequency where their radiation is omnipolar. For instance, I am using MCM 55-1870 woofers. They're 5" in diameter, but the cone is about 4". That means that it will be omnipolar below 3375Hz. (13500 / 4" = 3375Hz.)

Last edited by Patrick Bateman; 23rd April 2019 at 01:53 AM.
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Old 24th April 2019, 03:38 PM   #52
spalmgre is offline spalmgre  Finland
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Quote:
Originally Posted by Patrick Bateman View Post

One way to shrink the footprint of the box is to simply put the woofers on the TOP and the BOTTOM of the box, or on the sides.
I can understand if you have a pair of midbass drivers. But does it work as you show on the pictures to just have one driver on top?

This I very interesting as I have plans to build a new box for my present 4way setup. I use it to learn how to design filters and how to measure. I have Najda DSP which can store 8 setups that I can switch between. So it is also possible to do 2, 3, 4 way and all kind of filter and crossover frequency listening evaluation.

My idea is to build the box such that the baffle can be changed and with it also the horns and drivers. Now if I also make the top so that it can be changed then I can try the top-mounted midbass.
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Old 24th April 2019, 05:02 PM   #53
Patrick Bateman is offline Patrick Bateman  United States
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Oh, I should've explained that:

With a crossover point of approximately 500hz between the Unity Waveguide and the midbasses, we'll want a center-to-center spacing of approximately 18.9"

Here's the math:

( speed of sound / xover frequency ) x 0.7 =
(13500 / 500hz ) x 0.7 =
18.9"

With a conventional D'Appolito, you would need a box that's something like 27" tall. (Because the midbasses are nineteen inches apart, and then you need about six additional inches to accomodate the top and the bottom of the midbasses, and then a couple of inches above and below the midbasses.)

But my plan is to put the midbasses on the top AND the bottom.

Click the image to open in full size.

And then put the boxes on stands that look similar to this.
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Old 25th April 2019, 04:17 AM   #54
Audiodidakt is offline Audiodidakt  Norway
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Thank you very much, Patrick!
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Old 25th April 2019, 04:44 AM   #55
Patrick Bateman is offline Patrick Bateman  United States
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No prob!

If anyone wants to jump on the Unity bandwagon, I have six waveguides sitting here, ready to go.
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Old 25th April 2019, 11:08 AM   #56
arcgotic is offline arcgotic  Romania
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Thanks for the math example. So this formula will cover the vertical lobe, right?
What about the horizontal one? How do you do the math for enclosure width, related to crossover point?
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Old 25th April 2019, 05:13 PM   #57
1hiep0 is offline 1hiep0  United States
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Default Dimension

Hey Patrick,
What is the overall dimension? Is it more like 90X60 horn? Thanks,
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Old 26th April 2019, 10:12 PM   #58
Patrick Bateman is offline Patrick Bateman  United States
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Quote:
Originally Posted by arcgotic View Post
Thanks for the math example. So this formula will cover the vertical lobe, right?
What about the horizontal one? How do you do the math for enclosure width, related to crossover point?
From 1500Hz until 10khz the beamwidth is about 80 degrees horizontally. I haven't done vertical polars yet, they should come in around 55 degrees.

One of the interesting things about Unity horns is that the polars aren't exactly the same as the waveguide, because the location of the midrange taps, the crossover slope, and the crossover point will impact beamwidth in the range of about 1500hz to 3khz, because both mids and tweeters are active.

TLDR: if you use the crossover that I'm going to post shortly, along with this waveguide, you'll get a beamwidth of approximately 80 degrees by 55 degrees.
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Old 28th April 2019, 08:05 AM   #59
Quip is offline Quip
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Given that the Homepod uses a multiple-entry waveguide for its MF/HF array, thought you guys might like to see the Harman-style spinoramas (accurate down to 500Hz) that Sausalito Audio Works took of the Apple Homepod as another datapoint of a multiple-entry implementation:

Click the image to open in full size.

Here's their full report.
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Old 30th April 2019, 06:34 AM   #60
Patrick Bateman is offline Patrick Bateman  United States
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Fun fact:

The first person to build a DIY Unity Horn is also the same person who worked on Apple's Homepod speaker. I posted a thread about it a year ago.
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