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Old 30th November 2019, 03:42 PM   #21
Pallas is offline Pallas  Pakistan
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Quote:
Originally Posted by Patrick Bateman View Post
Oh, that phase plug will only work on a ring radiator.

Ah. I presume the nose of an XT19 or XT25 would get in the way?
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Old 1st December 2019, 07:32 PM   #22
Patrick Bateman is offline Patrick Bateman  United States
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No, the XT19 or XT25 should work fine.

I personally prefer using 3/4" domes because they have more displacement, allowing for a lower crossover.

A one inch ring radiator might be worth a look; it would probably be competitive with a 3/4" dome.

But I'm getting killer results from the $25 NE19 dome, stay tuned...
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Old 1st December 2019, 08:14 PM   #23
Patrick Bateman is offline Patrick Bateman  United States
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After designing and building five different phase plugs, I think this one is the best:

Click the image to open in full size.

Click the image to open in full size.

I made it this way, because I found that *increasing* the number of channels in the tangerine phase plug made things worse. (See page 2 of this thread for details)

Based on that, I cut the channels from six to three.

Click the image to open in full size.

Here's the frequency response and distortion of the NE19 with the three channel phase plug.

Click the image to open in full size.

Click the image to open in full size.

Here's the polar response of the three channel phase plug on this waveguide.

Click the image to open in full size.

Just to show off a bit, here's the polars at zero and eleven degrees. These curves illustrate that if you're listening at a distance of two meters, the sound doesn't vary at ALL if you're in a window that's about a meter wide, all the way to 24khz.

Click the image to open in full size.

For comparison's sake, here's the polar response of a Scan Speak D3004 Illuminator.

Click the image to open in full size.

Normally I publish curves using 12th octave smoothing, but this design is so smooth, I thought I'd show the unsmoothed curves too.
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Old 1st December 2019, 08:21 PM   #24
Patrick Bateman is offline Patrick Bateman  United States
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Click the image to open in full size.

Of the five phase plug designs, these were the four best. In clockwise order, from the top left:

1) a two channel phase plug, from two days ago

2) a six channel tangerine phase plug, from two days ago

3) a clone of Celestion's phase plug design, from yesterday

4) a three channel phase plug, basically the same as #2 but with half the channels.

If you look at these four, an argument could be made for the six channel tangerine phase plug. In particular, it performs better below 5000Hz. But this improved performance is due to the *length* of the phase plug; it's a quarter of an inch longer than the three channel phase plug.

IE, you could get better performance from the three channel phase plug by simply using a larger waveguide. Basically an undersized waveguide will start to beam on it's low end, and that's what we're seeing at 4500Hz in the measurement above. One could improve on that by simply using a larger waveguide, along with the three channel phase plug.
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Old 1st December 2019, 08:50 PM   #25
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.

The fourth of the five phase plugs is a straight-up copy of the phase plug used by Celestion in the CDX1-1425. The size has been reduced by 25%, because the Celestion diaphragm is larger than the Vifa NE19.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Of the five phase plugs, it's the most complex. There are two annular channels and a conical phase plug that masks off the center of the dome. Basically the idea is to create two "rings" of sound, similar to what B&C does in the DE250:

Click the image to open in full size.

My phase plug is more "open" because I'm not sure if a soft dome can withstand the high compression that a mylar or titanium can.

Click the image to open in full size.

Here's the frequency response and distortion of this phase plug, tweeter and waveguide.

Click the image to open in full size.

Here's the polar response, with EQ and highpass.

These polars are really quite good, I think. But they're not quite as epic as phase plug number five, from post #23.

The performance of phase plug four and five is so good, it makes me wonder if I might be able to get good performance out of a one inch tweeter. I've generally stopped using them, because they work terrible on horns, but they might work well with a phase plug...
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Old 1st December 2019, 08:56 PM   #26
Patrick Bateman is offline Patrick Bateman  United States
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I don't have any way to do a one-to-one comparison of the Vifa NE19 on the Celestion "style" of phase plug, because the throat is smaller.

But I *do* have a measurement of the Celestion, on a different waveguide:

Click the image to open in full size.

Click the image to open in full size.

The "real" Celestion has smooth response and good extension. But it's also four times as expensive.

Another "neat" thing about my design, is that it plays all the way out to 20khz. The CDX1-1425, even with 9db of EQ, is rolling off at 16khz.

Last edited by Patrick Bateman; 1st December 2019 at 09:00 PM.
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Old 1st December 2019, 09:31 PM   #27
Patrick Bateman is offline Patrick Bateman  United States
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Click the image to open in full size.

This is a BMS 4526HE, a ring radiator with a 16mm exit. It sells for $90, or nearly four times as much as the Vifa.

Click the image to open in full size.

Here's the equalized response of the Vifa and the BMS, on the same waveguide. The BMS is getting approximately 20dB LESS power.

Click the image to open in full size.

Click the image to open in full size.

Here's the published curves of the two drivers. The BMS is about 15-20dB more efficient than the Vifa.

For $150, the BMS would be a great compression driver, but at $90, it's a steal. Due to the small throat and small size overall, it barely needs any EQ at all to play out to 24khz.

But despite it's great performance, the $25 Vifa still outperforms it, for hi-fi, IMHO. This is for two reasons:

1) The Vifa has significantly wider bandwidth. This is due to higher displacement and a dramatically larger back chamber. The back chamber on the BMS is almost non existent.

2) The Vifa is smoother.

But the BMS is really REALLY nice, nonetheless, especially at this price point.

Click the image to open in full size.

Normally, I do my measurements at about 100dB. Out of morbid curiosity, I cranked up the SPL on the BMS to intolerable levels and dropped the crossover down to 1200Hz. I did this because I was curious if it might be possible to get the BMS to play down lower by leveraging it's ridiculous efficiency. IE, the BMS is rolling off at 2khz, but it might be able to squeeze some bandwidth out of it by taking advantage of the fact that it has efficiency to burn. I didn't measure the SPL on this sweep, but I'd guess it was around 110-115dB. Even at this ridiculous SPL, distortion is "just" 1.59% and it's mostly 2nd harmonic.

One thing that was puzzling about the BMS, is that even when equalized, it sounds MUCH different than the Vifa. Subjectively, the Vifa sounds a bit sweeter and duller. If I didn't see the measurements with my own two eyes, I would think that the Vifa rolls off sooner, but it doesn't. I wonder if I might be hearing HOMs from the BMS; it has a very hard 90 degree turn in it's phase plug. The JBL ring radiator phase plugs, from Voishvillo, have a much more gentle transition from ring to throat.

Click the image to open in full size.

Here's the BMS 4526HE polars on the same waveguide as the Vifa.

Click the image to open in full size.

Here's the frequency response and distortion of the BMS at a level comparable to where I measured the Vifa. The BMS just *crushes* the VIfa in the distortion department.

For $90, the BMS is killer, but I like the Vifa better because of:

1) better polars

2) smoother response

3) a fraction of the price

But if low distortion is important to you, and you don't need a low xover point, the 4526HE is REALLY nice.

Last edited by Patrick Bateman; 1st December 2019 at 09:33 PM.
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Old 2nd December 2019, 12:59 AM   #28
BradH is offline BradH
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On the 0 and 11 polars - How much should amplitude decrease over intervals like this to allow for the balance of distance vs axis when crossfiring CD speakers.
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Old 2nd December 2019, 09:41 AM   #29
tmuikku is offline tmuikku  Finland
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BradH, one would probably want constant amplitude variation within a desired listening window. Outside of the listening window one would possibly want less sound depending on your system design goals. Chosen waveguide and physics dictate how much amplitude decreases between any two axis (interval).

Gedlee has papers on the subject, check for example http://www.gedlee.com/Papers/directivity.pdf

On the sweet spot (listening window), a sofa for three for example, one would want to hear same frequency response (amplitude) from both speakers on all the seats. Sitting at the center is easy, both speakers are equidistant and the frequency response is optimum from both speakers. But person sitting to the side is now closer to the other speaker than the other. To compensate the amplitude difference the speakers are toed in, closer speaker is now "attenuated" because the listener is off axis to it. If the speakers are constant directivity, both still sound the same (same frequency response) if stereo triangle setup correctly* and there is three (or more) happy people on the sofa

*Amplitude variation to an angle is related to this, one would want amplitude to decrease just right amount to an angle. I think constant directivity waveguides advertised to have 90 degree horizontal beam width are most suitable for the recommended stereo triangle of equal length sides. With such waveguide use 45 degree toe in on the speakers and design ~20 degree to be the main axis (main listening position).

In general the idea is to toe in the speakers so that the amplitude of both speakers is roughly the same given the difference in distance and difference in listening axis to both speakers from any seat on the sofa (within the sweet spot). Inversed thinking: if speakers are not constant directivity, and/or stereo triangle is not set up correctly to take advantage of the costant directivity, the sweet spot becomes smaller and the speakers + room system sounds worse than it could ps. yes, 95% of hifi setup images you see on google search are not optimal in this regard, but almost all of them are not constant directivity and taste vary.

Last edited by tmuikku; 2nd December 2019 at 10:03 AM.
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Old 2nd December 2019, 02:17 PM   #30
BradH is offline BradH
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Thank you, well explained.

Last edited by BradH; 2nd December 2019 at 02:24 PM.
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