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Multi-Way Conventional loudspeakers with crossovers

"Unitized" Image Control Waveguide
"Unitized" Image Control Waveguide
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Old 10th April 2019, 02:21 AM   #41
Patrick Bateman is offline Patrick Bateman  United States
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Oh, one more thing that you guys might enjoy:

Take a look at the polar response of both waveguides above 10khz. See how the beamwidth starts to narrow? For instance, the beamwidth of the SMALL waveguide shrinks by about half beginning at 10khz.

Click the image to open in full size.

When people talk about the amazing treble of ribbons, I think a lot of it is simply that the diaphragm is super narrow. By using a narrow diaphragm and a powerful motor, you end up with a tweeter that has wide beamwidth and high efficiency, all the way to 20khz. These RAAL ribbons sell for $1960 a pair. Raal Lazy Ribbon 9" Ribbon Tweeter

In the measurements of my waveguides, you can see that both dome tweeters and compression drivers suffer from very narrow beamwidth above 10khz. I think this can contribute to a lack of 'sparkle.'

Click the image to open in full size.

If you look at JBL's newest compression drivers, they're freakishly consistent, all the way to 20khz. Basically you can walk around the entire room and the high frequency response barely changes at all. Really, really consistent response. I think that JBL has figured this out; that high frequency 'sparkle' has a lot to do with using a very small tweeter. In the case of the JBL compression drivers, they're using a throat that's just 0.7" in diameter now. Not coincidentally, 20khz is (you guessed it) 0.7" in length.

Last edited by Patrick Bateman; 10th April 2019 at 02:24 AM.
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Old 16th April 2019, 02:47 PM   #42
spalmgre is offline spalmgre  Finland
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Quote:
Originally Posted by Patrick Bateman View Post
If you look at JBL's newest compression drivers,
Pleace be specific on witch drivers you are refering to. We are reading your writing very cearfully.
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Old 17th April 2019, 01:55 PM   #43
Patrick Bateman is offline Patrick Bateman  United States
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Quote:
Originally Posted by spalmgre View Post
Pleace be specific on witch drivers you are refering to. We are reading your writing very cearfully.
I hope people don't take me too seriously, my posts are mostly the ramblings of a lunatic, hence my pseudonym.

To answer your questions:

About 5-10 years ago, JBL hired Alexander Voishvillo. Voishvillo has the patents on most of the ring radiators. He used to work for Cerwin Vega.

As time has progressed, Voishvillo has refined his ring radiators. In particular, there have been three refinements:

1) Voishvillo has implemented a phase plug design that randomizes the pathlengths. You can see this phase plug in the JBL 2408H-2, the JBL D2430K, and the JBL D2415k.

2) JBL has been shrinking the diameter of their waveguides. JBL's newest speakers use a waveguide with a throat that measures 3/4". This diameter controls directivity up to 18khz.
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Old 17th April 2019, 07:32 PM   #44
kipman725 is online now kipman725  United Kingdom
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There seem to be various opinions about the exit of the drivers effect on the maximum frequency directivity is controlled by the wave guide. Certainly if the exit dictates this quite a lot of drivers have a small section of horn in front of their actual exit (quite often the same driver is offered with 1.4" and 2" exit).

I took this screen shot from Gedlees polar map software, it shows that this speaker (Abbey 12ca) which has a 1" exit driver has constant directivity to 17kHz whereupon the on and off axis response is diminishing (plot is not normalized). If the directivity was dictated only by the exit you would expect it to narrow beyond 13kHz.

One of the normal critiques of small exits is that the high pressures at the exit cause harmonic distortion. Is anyone aware of a paper where this is quantified? I.E. if you aim for a certain SPL at 1m with a certain coverage angle what exit size will you need.
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File Type: png PolarMap.png (190.7 KB, 490 views)
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Old 17th April 2019, 07:56 PM   #45
3eepoint is offline 3eepoint
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Originally Posted by kipman725 View Post
One of the normal critiques of small exits is that the high pressures at the exit cause harmonic distortion. Is anyone aware of a paper where this is quantified?

Well, yes and no.



I am almost certain that there was/is a paper by JBL where they measure it and derive some equations from it and I even have a Matlab script that replicates that Graph. Only Problem: I cant for the life of me remember which axis stands for what value....so it is relative useless without the Paper or til I remember.
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Old 21st April 2019, 06:59 AM   #46
Patrick Bateman is offline Patrick Bateman  United States
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Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

It's starting to look like an acutal speaker. Pepsi can is included to show the size of the speaker. The complete volume is a bit over one cubic feet, the width is about 12" and the height is about 16".

As horns go, it is very small.
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Old 21st April 2019, 09:24 PM   #47
Patrick Bateman is offline Patrick Bateman  United States
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Click the image to open in full size.

Here's the response of the midrange array and the tweeter. Should be easy to come up with a working crossover.

I measured this at 22.5 off-axis, as the speaker is designed to be listened to off axis, a la Geddes: http://www.gedlee.com/Papers/Philosophy.pdf

Attached are the FRD and ZMA files for the midrange array and the tweeter, respectively.

I'll be working on the xover today.

I'm doing the crossover in Bill Waslo's XSIM. If you load these files up in XSIM, be sure to remove the "txt" extension. I had to rename them to upload them to the forum.

Right now, here's my goal for the speaker:

1500hz - 20khz covered by a single SB19 tweeter (3.5 octaves)

600hz - 1500hz covered by an array of Gento 2" midranges (1.5 octaves)

100hz - 600hz covered by an array of MCM 55-1870 midbasses (2.5 octaves)

Click the image to open in full size.
The reason that the midbasses are on the top is that this increases the pathlength between the midranges and the midbasses. It's basically a sneaky way of controlling directivity without resorting to a huge box. One of the challenges with using the MCM midbasses was that the power handling suffered if the box was too BIG. So I had a big incentive to use a small box. It doesn't just look better, it also handles significantly more power, like double.

I stole the idea from forum member "Follgott":

Click the image to open in full size.
Attached Files
File Type: txt sb19-on-april-unity.frd.txt (11.9 KB, 3 views)
File Type: txt sb19-on-april-unity.zma.txt (11.6 KB, 2 views)
File Type: txt midranges-on-april-unity.frd.txt (12.0 KB, 2 views)
File Type: txt midranges-on-april-unity.zma.txt (11.6 KB, 2 views)

Last edited by Patrick Bateman; 21st April 2019 at 09:31 PM.
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Old 22nd April 2019, 02:08 AM   #48
bwaslo is offline bwaslo  United States
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"Unitized" Image Control Waveguide
Patrick,

The good souls at diyaudio recently made Xsim's ".dxo" file format attachable here. So, for those reading this in windows and having Xsim already installed, a double click here should load it all up with your files (a quick shot at a crossover included).
Attached Files
File Type: dxo PBs_Unitized_IC_Waveguide.dxo (52.4 KB, 19 views)
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Crossover design Xsim; Depot diffusor super-easy diffusors
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Old 22nd April 2019, 04:15 AM   #49
ErnieM is offline ErnieM  United States
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Looks good! Look forward to off-axis curves.
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Old 22nd April 2019, 05:58 AM   #50
Audiodidakt is offline Audiodidakt  Norway
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Quote:
It's basically a sneaky way of controlling directivity without resorting to a huge box.
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
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