Dayton Audio WT3 Woofer Tester

Dayton Audio WT3 Woofer Tester

Postby crawdaddy » Fri Apr 18, 2008 4:34 pm

Hi,

New to the forum. Nice, knowledgeable group!

I was wondering if anyone had purchased and tried, or heard any feedback(pardon the pun) on the Dayton Audio WT3 Woofer Tester availble at Parts Express.

It appears to do a lot for the current $99 price tag.

Any thoughts appreciated.

KC
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Re: Dayton Audio WT3 Woofer Tester

Postby Klaus Stock » Sat Apr 19, 2008 1:53 pm

crawdaddy wrote:I was wondering if anyone had purchased and tried, or heard any feedback(pardon the pun) on the Dayton Audio WT3 Woofer Tester availble at Parts Express.

No, haven't even heard of it until now.

crawdaddy wrote:It appears to do a lot for the current $99 price tag.

Actually, as far as I can see, it only assists a computer in measuring a driver's parameters. It may be a modified USB soundcard inside, but I don't really know.

I think it would be really cool if it was a complete hand-held device (not requiring a computer nearby).

If you already own a computer with an even half-decent sound card, you might as well try Speaker Workshop, available for free at http://www.speakerworkshop.com/, together with an impedance jig. The impedance jig (described in the help file of Speaker Workshop) consists of a few connectors, a bit of wire and a resistor. T/S parameters can conviniently be measureb via the "added mass" method.

Cables, connectors and the resistor should be very well below $5. It might make sense to add a cheap plastic enclosure as well...but I suspect that the cables and the resistor can also be conviniently be hidden inside some heat shrinkable tubing.

Best regards, Klaus
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Re: Dayton Audio WT3 Woofer Tester

Postby Klaus Stock » Sun Apr 20, 2008 12:06 pm

:shock:
Klaus Stock wrote:I think it would be really cool if it was a complete hand-held device (not requiring a computer nearby).

Yes, well...I actually did spend some thought about designing a self-contained DIY "parameter gadget".

I thought about using an Atmel AVR microcontroller, which generates signals via PWM and measures the current (voltage drop across the resistor, actually) with one of it's internal ADCs (another ADC channel would be used for self-calibration)). The use of PWM limits measurements to the bass frequencies, but allows for a simple single-chip design. Other components would be a quartz, a few capacitors and resistors, aligator clamps, a power switch and a power supply (9V battery based).

Yup, no buttons, no display! What, the gadget measures the parameters and then it keeps them secret!? Well, not quite. The idea was to use the connected speaker to have the device talk to the operator when it has completed it's measurement cycle: "Q E S Zero Point Seven Four Q M S Five Point Two Four" and so on.

However, without the help of the operator, only Re, Fs, Qes, Qms and Qts can be calculated. And there's the problem. To calculate Vas, either the "equivalent air compliance" or "added mass" method has to be used. The gadget could, of course, simple communicate the altered Fs when the operator measures the driver in the box or with added mass, enabling the operator to calculate Vas with the aid of a few forumals and a pocket calculator. The reason why the gadget cannot perform the calculation on it's won is that it does not know the box volume (for the "equivalent air compliance" method) or the area of the diaphragm and the added mass (for the "added mass" method).

So, for Vas, the gadget would't be really self-contained any more - in fact, the benefit over using a function generator or a test CD and a voltage meter would be insignificant! The option of adding some sort of user interface would make the device more expensive and complicated to build (like, an LCD and pushbuttons) or cumbersome to operator (like, pushbuttons but no display, relying entirely on stupid voice prompts...). Yup, it could be done even without any buttons, reading the operator's input via the voice coil ("slap the driver once if the diameter is larger than 200 millimeters"). Visualizing that was enough for me to ditch the idea of the self-contained "measurement gadget".

A PC-based measurement system also gives a plot of the impedance curve over it's useable range, which is very valuable for passive crossover design, I believe.

Best regards, Klaus
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Re: Dayton Audio WT3 Woofer Tester

Postby crawdaddy » Mon Apr 21, 2008 3:55 pm

Klaus,

Thanks for the tip on the speakerworkshop software. I like the "free" part, plus a few dollars parts and such.

Great stuff!

Thanks,

Keith
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Re: Dayton Audio WT3 Woofer Tester

Postby john_l_murphy » Wed Apr 30, 2008 2:19 pm

I thought I'd give a bit more info for those interested in checking out the WT3 Woofer Tester I designed for Dayton Audio. I hope this does not come across as too commercial for the Bass List.

Here is a link to basic product information:
http://daytonaudio.com/wt3

Here is where you can buy it and see user reviews:
http://www.partsexpress.com/pe/showdetl ... er=390-804

Here is a detailed product review at Audioholics:
http://www.audioholics.com/education/lo ... -audio-wt3


More about WT3:

The WT3 hardware unit is a small USB unit you connect to the PC and which has a pair of alligator leads to clip onto the driver (component/system) to be tested. The stimulus for the test is a swept sine wave chirp which is captured and processed to achieve a high resolution (32k data points) measurement of the impedance response down to 1 Hz. An impedance measurement only takes about 2 seconds. No additional jig is required. V(AS) can be measured using a test box, added mass or just by specifying the 1W/1m SPL (for "quick and dirty" V(AS) estimates). Impedance measurements are very accurate and highly repeatable.

Because driver parameters are extracted from the impedance response, the parameters can only be as accurate as the measured impedance. And this is exactly where WT3 excells. To achieve a more accutrate impedance response would require a (really big $$) labortory grade bench top impedance analyzer. Just look at the impedance measurement of a 1k Ohm resistor compared to another product in the audioholics review (link above). You'll see that WT3 nails the measurement from 1 Hz to 20 kHz while the competitive product exhibits considerable error in the impedance measurement along with a number of measurement "glitches". There is no question which measurement is more accurate...the WT3! (at 1/10th the price of the other product!)

Cheers!

John
John L. Murphy
Physicist/Audio Engineer
True Audio
http://www.trueaudio.com
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Re: Dayton Audio WT3 Woofer Tester

Postby Brian Steele » Fri Jun 27, 2008 2:40 am

Hi John:

I just received my own WT3 from P.E. (via a friend, as P.E. don't want to ship to me directly). I'm quite impressed so far. Using it to measure T/S parameters and impedance is quite simply, a breeze. Just an idea for WT4 - make the calibration resistor part of the meter package, instead of something separate, e.g. two metal tabs on the sides that the leads can hooked to, and bridge the tabs internally with the 1K resistor. Presto-zappo - no little resistor that's likely to get lost if I don't keep my eyes on it :-).

Nice job.
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