measurements of nude ribbons and a dome-dipole

[CharlieLaub]

Even though there is another recent thread devoted to the new GRS ribbons, I thought I would start this new thread that compares the frequency response and distortion for the following:

• GRS PT2522-4 (Neo3 copy)
• B&G Neo3PDRW
• Radian LM8K
• Unbranded Asian copy of Neo8
• GRS PT5010-8 (Neo10 copy)
• back-to-back dome tweeters as a dipole

My primary interest for all of these drivers is in dipole or open baffle systems with little to no baffle (e.g. nude) so I measured all of them "in the nude". To do this, I used the following:

• All drivers were suspended by wires about 4-5 feet off of the ground
• Measurements were taken in a room with 7 foot ceiling, about 15 feet wide and 40 feet long
• ARTA and STEPS were used to perform the measurements, running on a Windows laptop
• The mic was an Earthworks M30BX, placed at 20in (~0.5m) from the driver
• Audio interface was a Focusrite Clarett 2Pre USB
• Amplifier was a Parasound Zamp v3
• SPL meter was the Galaxy Audio CM-130

Prior to starting the measurements for any driver, the SPL was measured at the mic tip using the SPL meter, and the level was adjusted to be 96dB using bandlimited (>200Hz) pink noise as a stimulus. This output is equivalent to 90dB at 1m distance. Levels remained identical during all subsequent tests on the driver.

Below, please find a pic of the drivers used. Starting from the two dome dipole and moving clockwise are the PT5010, PT2522, LM8K, and the Asian Neo8 copy at bottom left. Not shown: Neo3PDRW. All drivers were used right out of the box, without break-in. No series capacitor was used for these tests. I did not perform any impedance measurements.


.

[CharlieLaub]

First up are the frequency responses.

[CharlieLaub]

Next is the distortion for each driver measured in ARTA (I like to call this a "quick distortion measurement").

[CharlieLaub]

Finally, distortion measured using STEPS.

NOTES:
I did not perform a STEPS measurement for the Asian Neo8 copy so I don't have the data for it.
I accidentally overwrote the Neo3PDRW STEPS datafile with the STEPS measurement for the two-dome dipole. I will remeasure the Neo3PDRW and repost it later.

[CharlieLaub]

While performing the STEPS re-measurement of the Neo3PDRW it died and there was a "smell". I noticed that it, and the GRSPT2522, had become warm during the tests - the GRS was slightly less warm than the B&G from what I recall. I didn't think much about it at the time. The signals used in STEPS are essentially high power constant sine waves. In hindsight, the STEPS test is probably delivering more power than these two drivers can dissipate. Oh well, lesson learned. I got the two Neo3s off of Ebay as new last year and while they did look new you never know.

I re-tested the other Neo3PDRW and the resulting STEPS data is shown below.

[Matty]

Thank you very much for your measurements.

I have been very interested especially in the distorsion measurements of the LM8K. But now I'm honestly a little bit disappointed. I hoped to be able to use it as a single naked midrange driver down to about 600Hz.
But your measurement show me, that you should not use it this way below 800Hz or even a little bit more.
However it is still worth trying them with a good midwoofer.

A direct comparison with the Neo8s will be very interesting.

[bentoronto]

Yes, thanks much for posting. A lot of work but important to see comparisons. What were the domes and if anonymous brand, a word about their design?

Post #80, linked below, shows my FR and THD plots for an ESL cell, a bit bigger than the ribbons. Not easy to compare the two test set-ups, but in my biased opinion, the ribbons sure look lousy next the the ESL plots.

New planar drivers at Parts Express

B.

[CharlieLaub]

Originally Posted by Matty

Thank you very much for your measurements.

I have been very interested especially in the distorsion measurements of the LM8K. But now I'm honestly a little bit disappointed. I hoped to be able to use it as a single naked midrange driver down to about 600Hz.
But your measurement show me, that you should not use it this way below 800Hz or even a little bit more.
However it is still worth trying them with a good midwoofer.

A direct comparison with the Neo8s will be very interesting.

Yes, based on distortion I think that 800Hz would be a good choice for crossover point. It depends a bit on the order of the crossover - lower orders like LR2 will be rolling off the power above the crossover point, so you MIGHT be OK going a little lower in frequency. It would be a good idea to measure the driver on the final speaker and see how low you can get away with.

[CharlieLaub]

Originally Posted by bentoronto

Yes, thanks much for posting. A lot of work but important to see comparisons. What were the domes and if anonymous brand, a word about their design?

Post #80, linked below, shows my FR and THD plots for an ESL cell, a bit bigger than the ribbons. Not easy to compare the two test set-ups, but in my biased opinion, the ribbons sure look lousy next the the ESL plots.

New planar drivers at Parts Express

B.

I saw that - why aren't there any modern versions of that? Looks pretty good!

The domes I used are Dayton ND25FW-4. It's a 25mm dome in a waveguide with a neo motor. I have crossed these over as low as 1.6kHz. The drivers are not expensive, but sticking two of them back-to-back is tricky. They can just about nest that way if the mounting holes are used and the drivers are offset a bit. For this particular prototype I cut away some of the waveguide so that the motor of one driver could rest up against the motor of the other. This keeps the side-to-side and front-to-back offsets of the acoustic centers to a minimum. I have to do off axis measurements to see how the pattern holds up but even with a slightly larger spacing, an un-altered pair actually has a very good dipole pattern.

[CharlieLaub]

I tracked down a link for the "Asian Neo8 clone" that I included in the measurements. You can find it here:
2 PCS/LOT Diy monitor audio flat monitor HiFi speaker high power ribbon tweeter planar transducer AMT Neo8|Combination Speakers| - AliExpress