Hi Everyone,
I just got a bunch of birthday toys. One of which was a Dayton audio Omnimic/Dats measuring system, and the other is a new Scanspeak 7", 4 Ohm Revelator mid-woofer, the 18W/4531G00.
Of course the first thing I did was measure it. I added 3 quarters, which with tape were 16.7 grams according to my coca... er I mean coffee scale.
To my surprise, resonant frequency was measured at 48 Hz vs. 33 spec and Qts measured at 0.6 vs. 0.35.
I'm wondering if anyone can help me figure out which is most likely to be correct? Yes, I have already calibrated with the supplied cap.
Thanks!
Erik
I just got a bunch of birthday toys. One of which was a Dayton audio Omnimic/Dats measuring system, and the other is a new Scanspeak 7", 4 Ohm Revelator mid-woofer, the 18W/4531G00.
Of course the first thing I did was measure it. I added 3 quarters, which with tape were 16.7 grams according to my coca... er I mean coffee scale.
To my surprise, resonant frequency was measured at 48 Hz vs. 33 spec and Qts measured at 0.6 vs. 0.35.
I'm wondering if anyone can help me figure out which is most likely to be correct? Yes, I have already calibrated with the supplied cap.
Thanks!
Erik
I should mention I measured a Janzten air core inductor a moment ago and the numbers were spot on for spec.
Likely could both be (relatively) correct.
1/ T/S parameters are not scalars, you are likely picking the numbers off a different part of the curve than the factory.
2/ the factory numbers are an average of production. A quality brand like ScanSpeak probably have potential variation of +/- <10%
3/ The numbers you get will vary with the weather (mostly temperature and pressure)
4/ some change will occur as a driver breaks in
5/ The DATs is a cheap unit with some likely significant unit-to-unit variation of its own. I have talked to some who's units work fine and some who just put them on the shelves.
dave
1/ T/S parameters are not scalars, you are likely picking the numbers off a different part of the curve than the factory.
2/ the factory numbers are an average of production. A quality brand like ScanSpeak probably have potential variation of +/- <10%
3/ The numbers you get will vary with the weather (mostly temperature and pressure)
4/ some change will occur as a driver breaks in
5/ The DATs is a cheap unit with some likely significant unit-to-unit variation of its own. I have talked to some who's units work fine and some who just put them on the shelves.
dave
I have the DATS V2 and it is very accurate. The Qts and fs measure are independent of the Vas measurement which requires mass added. Try measuring another driver that you have with known Qts. Scanspeak normally measures close to spec but typically Qts always measures higher than quoted. It's like engine manufacturers quoting hp under ideal conditions. But 0.6 is very far from 0.35 and will make the driver not suitable for a bass reflex alignment designed for 0.35. Taped coins can rattle and give noisy measurements. Better is putty like silly putty shaped into a donut and stuck to joint at dustcap and cone. Silly putty leaves no residue and is sticky so it moves with cone.
DATS is a small signal device, SS uses large signal. Break in your drivers and model them with both sets of parameters, the recommendations for both should be similar.
I haven't read any complaints about the V2. It's also worked flawlessly for me as well...unlike both the V1 and WT3.
DATS doesn't have any magic juice that obviates the need to isolate the driver during testing, does it?
I measured two different Scanspeak midbass models and I am very disappointed - their Qts were much higher than quoted.
Good advice.
Thank you, that is exactly the information I was looking for. It explains why I see kits with them with much larger volumes than I would expect, and it seems DATS is working well. I tested a Focal mid/woofer and it was actually pretty close to spec.
Closer to spec is probably only an indication of how horizontal the curves are.
Here are measurements of an FE127eN, with my kit of the time (similar to DATS) and again using the kit used at a typical factory. Both measures are valid.
I use my measured data for matching drivers into pairs and always start with the factory numbers when designing the boxes (rarely have i had to adjust those)
dave
Here are measurements of an FE127eN, with my kit of the time (similar to DATS) and again using the kit used at a typical factory. Both measures are valid.
I use my measured data for matching drivers into pairs and always start with the factory numbers when designing the boxes (rarely have i had to adjust those)
dave
Attachments
Hi Erik,
Here you have T/S measurements on the ScanSpeak 18W/4531G00:
www.audioexcite.com ScanSpeak 18W4531-G00
All ScanSpeak Relevator mid-woofers have higher Qts than the official specs. Try measuring the drivers with slightly higher added mass and you can also massage the suspension a bit by moving the cone 5-10 times just before measurement or even better, burn in the driver for about 12 hours.
Otherwise, your measurement doesn't look to off for a brand new Relevator mid-woofer.
Regards
/Göran
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