High Frequency Compression Driver Evaluation

Re: High Frequency Compression Driver Evaluation

Greg Cameron said:
That's interesting. One of my biggest complaints about a lot of audio codecs is how much distortion in the higher frequencies I actually do hear. Granted it has much improved over the original mp3 format. But I do hear it even with AAC at the lower to mid bit rates. I suppose many folks don't notice it but I do, namely on cymbals and high hats. That phasey-swishy sound. Nowadays I use lossless AAC when encoding my own stuff. If you buy from the iTunes store, you're stuck with 256k AAC which is adequate for a lot of stuff but not always. It depends on the musical content as far as how bad the artifacts are.
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Yep, I agree. I do too. One of the problems of the switch to digital perceptual compression schemes has been allowing users to choose datarates. Unlike analog systems like FM radio or NTSC TV where the quality or "datarate" is fixed; ignoring interference and fading with distance. And even for a given compression scheme (MP3, MPEG2-AAC...) there are better and worse encoders. Encoder tuning takes a lot of time - multiple listening tests on critical test pieces for all allowable datarates.
 
Re: High Frequency Compression Driver Evaluation

Art Welter said:
Interesting.

The recordings were all made using an Alesis Masterlink, which makes standard Redbook CDs.

The distortion in the MP3 "bounce" recordings seems as apparent to me as listening to the original.

When you compare the DRPA (which did not go through a horn /driver) recording to the others, especially the high drive level ones, don't you hear the difference?

Art
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Sorry Art. I wasn't at all implying any problems with your MP3 files. (At high enough datarates, I'd expect to be able to heard the differences in the source content. But I haven't yet listened to any of your files.) I was just more broadly talking about the masking effects in the ear (that we exploit in perceptual codecs), and that I'm curious how this masking may, or may not, be reflected in designer's choice of the HF drivers.

Regards distortion in compression drivers, JBL's new D2 drivers (in the VTX series) claim a "dramatic" reduction in HF distortion when compared to single diaphragm drivers. I'm very interested to see them compared in the way you did, but I understand JBL don't sell these outside of the cabinets, and in general are moving away from individual drivers sales.
 
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Re: High Frequency Compression Driver Evaluation

Michael Smithers said:
Yep, I agree. I do too. One of the problems of the switch to digital perceptual compression schemes has been allowing users to choose datarates. Unlike analog systems like FM radio or NTSC TV where the quality or "datarate" is fixed; ignoring interference and fading with distance. And even for a given compression scheme (MP3, MPEG2-AAC...) there are better and worse encoders. Encoder tuning takes a lot of time - multiple listening tests on critical test pieces for all allowable datarates.
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When I had DirectTV, they had so many damn channels packed into their satellite feed they were compressing the hell out of the audio to stuff all the streams in there. It was unlistenable much of the time depending what channels you were watching. It seemed the bigger networks got more stream bandwidth and therefore less compression of their audio (and video). Switching to cable seemed to help quite a bit. I don't know how people can put up with it. "Digital Quality" was the catch phrase in Direct's advertising. What the heck does that mean? Nothing.
 
Re: High Frequency Compression Driver Evaluation

Michael Smithers said:
Regards distortion in compression drivers, JBL's new D2 drivers (in the VTX series) claim a "dramatic" reduction in HF distortion when compared to single diaphragm drivers. I'm very interested to see them compared in the way you did, but I understand JBL don't sell these outside of the cabinets, and in general are moving away from individual drivers sales.
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Michael,

The “revolutionary” JBL D2 utilizes two voice coils, each with its own polymer annular diaphragm, the same arrangement as the BMS 4592 driver has used for many years.

I have found no published distortion specifications for the JBL D2, but the BMS 4592 published distortion specs, though decent, are not as good as the EVDH1A. That, and the driver's cost, is why I did not request one from Jack Arnott for comparison.
I would not expect the JBL D2 to be much different than the BMS 4592, the designs are quite similar, it is even rumored that BMS makes these drivers for JBL.

The triple D2 VTX cabinet uses a long, almost non-expanding wave-guide coupler. Although the D2 may have “significantly lower levels of nonlinear distortion” (than what, a K-Mart megaphone?) the long non-expanding air column insures plenty of nonlinear distortion to go around.

John Meyers was quite proud about their line array driver to horn coupler length being the shortest of any such coupler, reducing nonlinear distortion.

Tom Danley’s Paraline driver to horn coupler path length is shorter than Meyers’ line array horn coupler, and also has a faster expansion rate.
I use his design in my small format line array.
In side by side comparisons of my line array using EV DH1AMT to a JBL 4889 line array, many hearing it commented that the Paraline HF was more “clear”.
My system was using only 10) DH1AMT, compared to 48) JBL 2435H, 3 inch diameter beryllium diaphragms used in the 16 box 4889 system.

The EV drivers were also crossed over much lower than the JBL, which should increase distortion. The 90 degree conical waveguides in each system are similar, the primary difference being the driver to wave-guide coupler.

John Meyers quoted from Beranek's book “Acoustics” , which describes the nonlinear distortion mechanism:
"If the horn were simply a long cylindrical pipe, the distortion would increase the farther the wave progressed..."

Doubling the distance doubles the second harmonic distortion in a pipe.
The nonlinear distortion increases linearly with distance traveled in the tube, or the length of the horn.

"in the case of an exponential horn, the amplitude of the fundamental decreases as the wave travels away from the throat, so that the second-harmonic distortion does not increase linearly with distance."

John Meyer’s) interpretation of Beranek basically says that in a long, narrow driver to wave-guide adapter like JBL (and many other line arrays) uses, while SPL is falling at roughly the inverse distance law, the nonlinear (air) distortion increases with distance.

My ears agree with Beranek and John Meyers.

It would be very interesting to see actual distortion measurements of the HF sections employed in various line arrays compared at actual usage levels and see if my ears are “telling the truth”.

Art Welter
 
Re: High Frequency Compression Driver Evaluation

Art Welter said:
Michael,

The “revolutionary” JBL D2 utilizes two voice coils, each with its own polymer annular diaphragm, the same arrangement as the BMS 4592 driver has used for many years.

I have found no published distortion specifications for the JBL D2, but the BMS 4592 published distortion specs, though decent, are not as good as the EVDH1A. That, and the driver's cost, is why I did not request one from Jack Arnott for comparison.
I would not expect the JBL D2 to be much different than the BMS 4592, the designs are quite similar, it is even rumored that BMS makes these drivers for JBL.
Art Welter
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Hi Art,

Once again, thank you very much for all the info.

Re the 4592, BMS describe it as a coaxial arrangement with two different size voice coils and requiring a crossover - passive crossover or active. (We updated the horns in our screening room with coaxial BMS units and BMS supplied passive crossovers.)

From the literature I've seen, the JBL D2 uses two same size annual diaphragms that operate on the same frequency range. The diaphragms push/pull towards/against each other and feed a slotting waveguide with tunnels towards the center and then outward, along the centre axis and out a single exit.

Cheers,
Michael
 
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Re: High Frequency Compression Driver Evaluation

Michael Smithers said:
Hi Art,

Once again, thank you very much for all the info.

Re the 4592, BMS describe it as a coaxial arrangement with two different size voice coils and requiring a crossover - passive crossover or active. (We updated the horns in our screening room with coaxial BMS units and BMS supplied passive crossovers.)

From the literature I've seen, the JBL D2 uses two same size annual diaphragms that operate on the same frequency range. The diaphragms push/pull towards/against each other and feed a slotting waveguide with tunnels towards the center and then outward, along the centre axis and out a single exit.

Cheers,
Michael
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The BMS as you say uses a larger annular ring for the LF portion of the range, reducing IM distortion.
Last night got a chance to see an annular eclipse here (south of Albuquerque), a "ring of fire" version of the BMS arrangement!

The JBL D2's two annular polymer diaphragms cover the same range and have the same radiating area as a "conventional single dome", evidently a rather small dome.
 
Re: High Frequency Compression Driver Evaluation

Michael Smithers said:
Hi Art,

Once again, thank you very much for all the info.

Re the 4592, BMS describe it as a coaxial arrangement with two different size voice coils and requiring a crossover - passive crossover or active. (We updated the horns in our screening room with coaxial BMS units and BMS supplied passive crossovers.)

From the literature I've seen, the JBL D2 uses two same size annual diaphragms that operate on the same frequency range. The diaphragms push/pull towards/against each other and feed a slotting waveguide with tunnels towards the center and then outward, along the centre axis and out a single exit.

Cheers,
Michael
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Hi Michael,

Do you like the sound of coaxial BMS drivers, I have been looking at them to replace some 18sound NSD1480N’s.
http://www.eighteensound.com/index.aspx?mainMenu=view_product_simple&pid=182

I love thesound of 1480’s but I want to crossover lower, around the 700-800 Hz - a bit low for the 1480. The other option maybe their new ND4015BE.
ND4015BE - HF Neodymium Driver

Regards

Peter
 
Re: High Frequency Compression Driver Evaluation

Peter Morris said:
I love thesound of 1480’s but I want to crossover lower, around the 700-800 Hz - a bit low for the 1480. The other option maybe their new ND4015BE.
Regards

Peter
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Peter,

On a horn with a low Fc, the 1480 would have no problem with a crossover at 700 Hz.

To keep up with a 2x15" horn loaded bass section at 500 Hz, a 4" diaphragm would be a good idea.
A 4" diaphragm is capable of more output in the 500-800 Hz range than a 3", but a 3" on a proper horn can still put out more clean output in that range than most any single 15" speaker.

Art
 
Re: High Frequency Compression Driver Evaluation

Peter Morris said:
Hi Michael,

Do you like the sound of coaxial BMS drivers, I have been looking at them to replace some 18sound NSD1480N’s.
http://www.eighteensound.com/index.aspx?mainMenu=view_product_simple&pid=182

I love thesound of 1480’s but I want to crossover lower, around the 700-800 Hz - a bit low for the 1480. The other option maybe their new ND4015BE.
ND4015BE - HF Neodymium Driver

Regards

Peter
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From photos, the BMS drivers appear to be 4590's or 4590P's. I personally wasn't involved in comparisons or procurement but colleagues who were, said that they are a clear and obvious improvement on what used to be in place. Subjectively, one colleague said that they've helped overcome some of the typical horn sound of the cinema screen channels.
 
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Re: High Frequency Compression Driver Evaluation

Art Welter said:
Bennett,

Sensitivity and frequency response of drivers on different horns and AES power ratings unfortunately only give a limited amount of comparative data.

BMS includes distortion specifications on their single page spec sheet, which is more concise than JBL and EV spec sheets in general.
Comparing the EV DH1A and the BMS 4550 and 4552 distortion specs it was obvious that the DH1A was going to smoke them in the lower response, less obvious that it would also surpass their HF output in terms of low distortion at high level.
I still was interested in how they sound, Jack Arnott graciously let me test the BMS drivers with the understanding they would most likely not result in a sale.

The failure of any manufacturer to provide distortion specifications at anything near rated AES power and lack of any readily available distortion data from B&C was the reason I felt the need to conduct a driver comparison myself.
Even though the tests took an enormous amount of time, I felt they would have been worth it had I found a driver that performed better than the 20 year old EV drivers I currently use.

Could you please provide distortion specifications for whatever the lowest distortion 3" diaphragm, 1.4"/1.5"/2" exit driver B&C currently has in their lineup.

I would like to compare them to the DE82 and DE82TN, the distortion spec sheet you sent was at conducted using 8 volts, 8 watts for 8 ohm drivers rated at 80 and 110 watts AES.
The amplitude response was missing in those tests, it would be helpful.

Do you have any distortion data for the drivers at their rated AES power?

Thanks,

Art
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Art, I am very sorry that it has taken me so long to respond to your question. I asked our technical support manager in Italy what he thought, and here is the answer:

The AES standard (1984, r.2003) specifies that distortion measurements should be taken at 1/10 of the rated power handling value. This is the reason why we use 8 watts as power level for distortion measurement on compression drivers with 80W AES power handling.

When you have to compare two or more different drivers, to make the comparison meaningful, they should give almost the same SPL level or, at least, they should be driven with the same voltage. For compression drivers we use the same driving voltage ( which is about 1/10 of the rated power handling for 8 ohms drivers) so to make a sort of standardization for our lab THD measurements.
We don't make THD measurements at full AES power, simply because it is not considered in the AES standard procedure.


Please also note that THD on compression drivers is also strongly affect by the acoustic loading they see, that is the horn. The same driver measured at the same level with different horns gives different THD results.
This makes, for example, void the comparison between 2" and 1.4" throat drivers, because we have to change the horn.
So, as you can see, all this stuff is very tricky and, what it is worst, can lead to misleading results.
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Re: High Frequency Compression Driver Evaluation

Peter,

its me again :)~:-)~:smile:
I do own 4592 and 1050,
bought the 4592 first and now use them only for Disco
the 4592 ( the HF part ) is very picky about the horn, and because you are picky about the IR, you might imagine, what happens if you cross over around 6k with IIR

And for Art Welter,
in the beginning you were looking for some serious HF output.
The DE920 has 3 dB more than the DE82
and regarding sound, the beyma CP 755ND is worth a look also

Uwe
 
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Re: High Frequency Compression Driver Evaluation

Uwe Riemer said:
And for Art Welter,
in the beginning you were looking for some serious HF output.
The DE920 has 3 dB more than the DE82
and regarding sound, the beyma CP 755ND is worth a look also

Uwe
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Uwe,

The 20 year old EV DH1A/ DH1AMT drivers I have now have more than 3 dB more clean HF output than the DE82.
 
Re: High Frequency Compression Driver Evaluation

Bennett Prescott said:
Art, I am very sorry that it has taken me so long to respond to your question. I asked our technical support manager in Italy what he thought, and here is the answer:
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Bennett,

Though I had hoped for more information, his answer is what I expected, no answers to my questions.

Glad I did my own tests, distortion measurements taken at 1/10 of the rated power handling value are useless other than for home users.


Art
 
Re: High Frequency Compression Driver Evaluation

Art Welter said:
Bennett,

Though I had hoped for more information, his answer is what I expected, no answers to my questions.

Glad I did my own tests, distortion measurements taken at 1/10 of the rated power handling value are useless other than for home users.


Art
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Art,
the German Production Partner mag performs distortion tests on complete speakers, now if you know or can guess, what the manufacturer is using, some conclusions are possible.
Yet they perform the distortion test a little different, the raise level until 3% and 10% THD is reached and plot a 3% and 10% Frequency Response ( maybe you get, what I want to express ), of course this does not include IMD,
and I would be glad to read about you comparing the 920 and the 755 to your driver.

Uwe
 
Re: High Frequency Compression Driver Evaluation

Art,

You might look at reviews in Voice Coil magazine. There have been many published of our drivers, the latest this month of the DE120. I always post these on our Facebook page (B&C Speakers - Company - Bagno a Ripoli, Italy | Facebook) when they come out. Vance Dickason has a lot of experience measuring woofers and drivers from all manufacturers and seems to set the bar in that regard.
 
Re: High Frequency Compression Driver Evaluation

Bennett Prescott said:
Art,

You might look at reviews in Voice Coil magazine. There have been many published of our drivers, the latest this month of the DE120. I always post these on our Facebook page (B&C Speakers - Company - Bagno a Ripoli, Italy | Facebook) when they come out. Vance Dickason has a lot of experience measuring woofers and drivers from all manufacturers and seems to set the bar in that regard.
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Bennett,

I like Vance's reviews, but they are done at home stereo listening levels:

"For the distortion measurement, the DE120/XR1064 combination was mounted on the same baffle that was used to generate the on- and off-axis frequency response measurements,and the SPL set to 104 dB at 1 m (2.05 V) ..."

Although it is interesting to see distortion levels already above 3% at 1000 Hz at this moderate drive level, my tests were done to see and hear what the distortion levels were at the AES rated levels that the drivers reach in PA use, not at 1/10th (or 1/50th) rated power.

Art
 
Re: High Frequency Compression Driver Evaluation

Uwe Riemer said:
Art,
the German Production Partner mag performs distortion tests on complete speakers, now if you know or can guess, what the manufacturer is using, some conclusions are possible.
Yet they perform the distortion test a little different, the raise level until 3% and 10% THD is reached and plot a 3% and 10% Frequency Response ( maybe you get, what I want to express ), of course this does not include IMD,
and I would be glad to read about you comparing the 920 and the 755 to your driver.

Uwe
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Uwe,

What drive levels resulted in 10% distortion on HF drivers in an active (not pasive crossover) HF driver in the Production Partner magazine ?

I would have liked to compare the 920 and the 755 to the EVDH1A, but from what I can see (and hear) from the comparative results of the DE82, looks like they would still be no better in terms of ouput/vs distortion.

Art
 
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