Hi, I've seen a similar thread where someone asked whether to rely on DATS measurements or the factory specs. I bought a SEAS coaxial driver and measured it with DATS v3.0. I was very careful in testing/calibration etc and broke the drivers in for several hours at 30Hz beforehand. The T/S values came out very different than the specs and I know that this happens a lot. When I simmed it, the box size and the f3 were different as well. So I contacted SEAS and asked them for guidance. The SEAS engineer assured me that their measurements are correct and insisted that I should use their measurements. So I made the boxes using the factory data. Somewhere else in the forum, I read that the DATS "guesses" the Qms, Qes and Qts values based on the impedance graph. So now I'm wondering how reliable measuring is. How can I make sure I'm using the right T/S values in my sims?
That’s a great question. I have the datz2 and have had a hard time with getting it to work with my laptop.
why would dats do guessings, that sounds absurd! from the driver impedance curve one calculate a lot of parameters and with some additional info one can calculate a full set of parameters. on sb acoustics website and their tech notes there is a paper you can download how to do your own calculations from driver impedance curves. basically you want to plot the shape of the impedance curve at resonance very precisly, but the curve will change shape with drive level and drive method, some drivers change a lot and other not at all.
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I mean estimate when I say "guess". 🙂 The engineer at SEAS sounded very convincing that their specs were correct and that their manufacturing is very controlled such that the products don't deviate from factory specs. The engineers at the factory can actually measure electro-mechanical parameters like compliance and Q factors directly I presume, while DATS needs to derive a whole set of parameters from a graph. This still leaves me with the question, who's data should I use and in which case, especially when they lead to widely different box sizes, tuning and f3?
Some drivers are known to have inaccurate factory specs like MCM's. And for some Tang-Band drivers, I read similar stories on the forum. But for a SEAS, after speaking to the engineer I'm doubtful that the derived T/S values from an impedance graph are accurate. I'm lost.
Some drivers are known to have inaccurate factory specs like MCM's. And for some Tang-Band drivers, I read similar stories on the forum. But for a SEAS, after speaking to the engineer I'm doubtful that the derived T/S values from an impedance graph are accurate. I'm lost.
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Can you post a textual file of the impedance of the drive unit if dats can export such or at least post an image of it and we can derive T/S parameters from it. For a full set of parameters, 2 of the impedance measurements are needed. Everything done properly, one should take dats measurement over factory one for further design.
You said that they are a coaxial speaker. Did you unhook the tweeters? You need to only Measure the woofers or you may get the wrong numbers.
T/S are curves not scalars. The scalar numbers you see publish, or measure collapse the curves at a certain point. The typical diy measure kit we diyers typically use tend to collapse the curves at a different place than teh expensive factory software so the numbers are typically different. If you get numbers close it is more likely an indication that those T/S curves are linear.
Further, according to the authour of the DATs software, it measures the impedance and then estimate the T/S parameters. This is very quick but less accurate. More useful numbers ar ehad with a method (SW like WooferTester 2, or manually) where one measures Fs (ie phase is zero), F1, F2(phase is minimum or maximum) and then directly calculate the parameters directly.
Having successfully designed many, many speakers, and having built many of those, i always start with the factory numbers as they have proven more useful. As long as the manufacturer is reputable (SEAS is) i would just use the numbers published.
dave
Further, according to the authour of the DATs software, it measures the impedance and then estimate the T/S parameters. This is very quick but less accurate. More useful numbers ar ehad with a method (SW like WooferTester 2, or manually) where one measures Fs (ie phase is zero), F1, F2(phase is minimum or maximum) and then directly calculate the parameters directly.
Having successfully designed many, many speakers, and having built many of those, i always start with the factory numbers as they have proven more useful. As long as the manufacturer is reputable (SEAS is) i would just use the numbers published.
dave
so, you have two sets of t/s.
fit the driver to a test box to make a closed/sealed setup, and run your software to get the Fs and Qts values in this known size sealed box.
then see which of two sets of t/s predicts the above Fs and Qts for that box size.
fit the driver to a test box to make a closed/sealed setup, and run your software to get the Fs and Qts values in this known size sealed box.
then see which of two sets of t/s predicts the above Fs and Qts for that box size.
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Here's another example: I have a pair of TB W5-2143's that I'm measuring. I've flexed the diaphragm by hand a few times on both, and ran them both at 70Hz close or at xmax for an hour. Factory spec says fs: 55Hz. One driver measures 69Hz, the other measures 81Hz. Q values are way off too. One of the drivers diaphragm feels stiffer than the other's when I flex them too. Should I rely on factory data here too? I don't think DATS will be wrong about the fs.
Here is an example of a driver i measured (at the time using sw that used the same technique as DATS), then sent to Hong Kong to Mark Audio where Mark measured it using his factory kit.
I have measured thousands of drivers. I use it to get a match. To truly compare drivers they have to be measured at the same time in the same jig, as the parameters will change based on the weather (mostly pressure/temp). And it is hard to compare drivers measured on different systems due to drive level and other factors.
To get T/S parameters a reputable manufacturer takes a random sampling of production drivers (say 50 out of 2000), measure them under identical conditions and publish the average. Even reputable factories will have production spread of ∓15%, really good <10% (samples of 20 drivers typically).
dave
I have measured thousands of drivers. I use it to get a match. To truly compare drivers they have to be measured at the same time in the same jig, as the parameters will change based on the weather (mostly pressure/temp). And it is hard to compare drivers measured on different systems due to drive level and other factors.
To get T/S parameters a reputable manufacturer takes a random sampling of production drivers (say 50 out of 2000), measure them under identical conditions and publish the average. Even reputable factories will have production spread of ∓15%, really good <10% (samples of 20 drivers typically).
dave
Let me see if I understood you correctly, so after I fit the speaker to a sealed box with a known volume, I run DATS and get the Fs and Qts for that specific box. Then I run a sim on, say WinISD, with both the factory data and the free-air DATS measured data and see which of the sims give me the Fs and Qts I measured with the closed box.
Did I understand you correctly?
Aha, that explains it. So unless the driver is from a totally unknown manufacturer, has no published specs or is from a not reputable company/factory, the DATS type of measurement software is somewhat pointless. I suppose now I have to figure out which driver maker's data to trust. And/or use the technique @ctrlx described.
Indeed! Plus T/S theory peters out at the driver's effective upper [Fhm], lower [Flc] mass corners, so any bandwidth response plot beyond these points are strictly due to [inputted] inductance [mH] and/or mass roll off, with on-line freeware generally just flatlining it:
Fhm = 2*Fs/Qts'
Flc = Fs*Qts'/2 [normally never used]
Qts' = 2*Fs/Fhm
Qts' = Qts + any added series resistance [Rs]: HiFi Loudspeaker Design
[Rs] = 0.5 ohm minimum for wiring, so may be higher if a super small gauge is used as a series resistor
GM
No clue about nowadays, but of the manufacturers I had knowledge of; at least until the 2000s, quality assurance [QA] just measured efficiency [n0] as a quick way to check, so specs can be surprisingly far off, yet the published specs will be fine for designing a box alignment as they will shift to closer to T/S spec with break in over time, so in your example the [n0] apparently isn't 'close enough' the same [~ +/-10% IIRC].
Scroll down to : n0 and SPL rating – Efficiency
Thiele Small parameters equations - How each one affects the others
GM