What is the best tweeter

Discussion in 'Speakers' started by Matthew J Poes, Jan 9, 2019.

  1. Kerry Armes

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    Which 18sound model is this? I've never seen a compression driver measure like that before. Even the very good ones usually have high second order (above 1%) and low third order but not that low.
     
  2. Matthew J Poes

    Matthew J Poes Staff Writer
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    https://www.audioxpress.com/article/test-bench-eighteen-sound-nd3st-1-4-compression-driver

    ND3ST. It’s excellent.

    When you say this, are you referring to your own measurements or those from Vance? He and I had a chat about this and tested a Dome tweeter at the same level as a CD is tested at. The Domes distortion was much higher.
     
  3. Kerry Armes

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    Measurements from both. If you look at most other CDs he tests they have much higher second order distortion.
     
  4. Matthew J Poes

    Matthew J Poes Staff Writer
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    They are being played back at 10dbs higher and it’s based on a full band pink noise level. A dome won’t be any better at 104dB (and many of those CD’s are actually 120dB in their operating bandwidth. I’ve actually asked Vance to explain why. I think I know but want confirmation.
     
  5. Matthew J Poes

    Matthew J Poes Staff Writer
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    I currently have speakers with domes, ribbons, and CD. I can test later at different safe volume levels and see what I get. That will make direct comparison possible.

    I can’t test Planars or such as I don’t have any to test at the moment. Maybe we can get some sent to me later to add to the comparison data.

    I was thinking of testing at 75dB, 85dB, and 90dB. The 90 is probably the highest level I’d be comfortable testing a speaker I don’t own with $500+ worth of tweeter.
     
  6. tesseract

    tesseract Senior Admin
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    Matt, the Chane 5.0 A2rx-c set I owned prompted me to add a 3 channel amp to my AVR. Those planars love power.
     
  7. Matthew J Poes

    Matthew J Poes Staff Writer
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    I have very little experience with finished product Planar speakers. I wouldn’t know. I’ve tested raw B&G drivers or cheap crap speakers with leaf tweeters (as they call it). I may have had one or those Dayton planars once, can’t recall for sure anymore.

    I’ve mostly played with domes, ribbons, and CD’s. Pretty much only CD’s the last 5-6 years.
     
  8. tesseract

    tesseract Senior Admin
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    Planars exhibit the same dispersion properties as ribbons, wide to the sides, with vertical nulls. The main difference is that the voice coil is also the driver with ribbons, necessitating a transformer to give the amp something other than a dead short to see. Lighter, quicker is the gain.
     
  9. Kerry Armes

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    Hi Matt,

    I just want to clarify a couple of things. First, you cannot test distortion with pink noise because all of the frequency band is being played at the same time and therefore you would never be able to accurately measure the harmonics. Vance uses pink noise to set the SPL level and then tests distortion in the same way as everyone else would, which is a long wave sign sweep.

    Second, one of the issues I have with the way Vance measures is that he is not consistent from driver to driver, which makes them impossible to legitimately compare. There are two ways to test distortion that provides consistency and both have benefits and downsides. You could either match SPL and distance between all measurements or you could test everything at 2.83V (or some other consistent voltage) and keep distance the same. If distance changes, the measurements are not directly comparable. If input level or SPL are not kept constant, measurements are not directly comparable. Vance even sometimes changes the scale of the graph to show a different frequency band.

    To me, this is a little frustrating because he does a great job of getting accurate measurements, it's just that they aren't necessarily comparable. Now, Vance does have to be somewhat careful because he is working for a magazine that is trying to sell publications and advertising to the people who are getting their drivers tested, so it doesn't surprise me that this might occur.

    But all I was really referring to is that every other compression driver I've seen him test has much higher second order distortion. I wasn't comparing to a dome but to those other compression drivers he tests, which are usually in a somewhat similar manner.

    Here are some links to show you what I am talking about with differences in testing format. All of these were tested differently.

    Two compression driver:
    Measured at 2.83V/1M equivalent
    https://www.audioxpress.com/article/test-bench-b-c-speakers-de780tn-8-compression-driver

    Measured at 2.37V/1M equivalent
    https://www.audioxpress.com/article...pression-driver-from-radian-audio-engineering

    Two dome tweeters:
    Measured at 4.82V/1M equivalent
    https://www.audioxpress.com/article...s-from-dayton-audio-rst28a-4-and-the-rst28f-4

    Measured at 4.82V/1M equivalent but graph only goes to 3 kHz as opposed to 2 kHz like the previous
    https://www.audioxpress.com/article...on-1-inch-aluminum-and-magnesium-dome-tweeter
     
  10. Matthew J Poes

    Matthew J Poes Staff Writer
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    Thanks Kerry.

    I think you misunderstood my post. I didn’t mean to imply he tested distortion with punk noise, it was that he set the levels that way.

    I emailed him to get specifics. He measures with bandwidth limited pink noise at 1 meter but measures distortion at 10cm. He indicates that it is appropriate and accepted that pro drivers are measured at a higher level. They aren’t meant to be compared. That the higher levels and variation in the fundamentals isndue to difference in the response and sensitivity. I’m not totally sure why sensitivity matters but that’s what he said.

    You are absolitely right about that CD being unusually low in distortion. I’m not totally sure why, it’s Lowe than others he’s tested.

    But some things I’ve cobsidered. First, it is an unusual Cd so that’s may be part of it. second, it’s a large optimally designed waveguide that was developed recently and does not use diffraction. All things considered, it is possible that it contributes less distortion than other waveguides.

    You may already know this but a waveguide itself develops specifically 2nd harmonic distortion. How much and where depends on the design and size of the waveguide. Nearly every CD Vance tests is in a different waveguide, as such it’s unclear how much the waveguide contributes. Vance indicates that the CD is going to be the dominant source of distortion. However Geddes disagrees and a review of some articles examining this also seem to suggest that isn’t true. It seems that the waveguide is often either a dominant or equal source of 2nd harmonic distortion.

    I decided to test this myself last night. I was curious how a CD would compare to a dome tweeter under otherwise similar conditions. I have a ton of data from the experiment to go through still, including compression data. Basically the test involved raising the level of the speaker in 3dB increments until such time that compression was reached (level wouldn’t increase at 3dB anymore).

    25BC4AA2-6F70-4832-BC11-3148D3ECCCC5.jpeg

    This goes from 88dB to 105dB. It was labeled but the label is cut off.

    The CD is the one with higher distortion above 3khz. That is a DE250 on a Geddes OS waveguide. Dome was a Dayton silk dome. The spike in distortion was caused by the location of the mic causing a cancelation in the response of the waveguide. Just ignore it.
     
  11. Kerry Armes

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    Oh, ok. Got ya. I thought you were saying he tested at with pink noise. I think we are on the same page then.

    I would agree with Vance that the compression driver is going to be the dominant source. This should be testable by taking a distortion measurement with and without the horn. The horn does reduce relative distortion at the low end of the driver though, so you'd probably have to EQ to flat to make a comparison.

    Thanks for posting the data. Were these both tested at the same initial SPL and was there any crossover in place on the low end?
     
  12. Matthew J Poes

    Matthew J Poes Staff Writer
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    Oops I meant he measures the spl level with bandwidth limited pink noise. Did it again.
     
  13. Matthew J Poes

    Matthew J Poes Staff Writer
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    Both tested at the same levels and yes there is a highpass crossover on both. They both had a roughly flat response. I was trying to compare on similar grounds.
     

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