Is anybody else using the PE Woofertester? - Home Theater Forum and Systems -

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post #1 of 8 Old 02-05-08, 01:55 PM Thread Starter
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Is anybody else using the PE Woofertester?

I've been playing with this lately and it is a great and inexpensive product. I just wanted to see if anyone else has it and if there are any tips to using it. There are a few things that I have noticed about it.

1. some of the parameters will change depending on how the driver is oriented.
2. Some parameters will also change depending on how the VC's are wired.
3. Manufacturer's specs can be way off.

I use the added mass method of calculating VAS. I use nickels placed on the cone(5 grams each). Does anyone else use a different technique?

The calculated VAS may or may not be very accurate because it asks you to input the driver piston diameter as part of the calculation. Most of the time you may just have to guess, or hope that the mfg's
spec is correct.
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post #2 of 8 Old 02-05-08, 02:40 PM
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Re: Is anybody else using the PE Woofertester?

I own the WT3 and haven't had any issues with it. Slight irregularity (within ten percent) with the T/S retrieved are of no concern to me as their effect on final outcome of the design is minimal.

I always test my drivers in the same way. First be sure to allow the unit to stabilize by leaving it plugged in for at least a minute. After this I always calibrate it with the supplied resistor and then test away. I have always tests with the drivers magnet laying flat on the ground like this.

I also use the added mass method using various coins of known weight. It is the simplest way I have found to do this.

As far as driver piston diameter I generally use the supplied information after measuring it myself. With a ruler/measuring tape and you can get a close approximation of the piston diameter.

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post #3 of 8 Old 02-05-08, 03:36 PM Thread Starter
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Re: Is anybody else using the PE Woofertester?

Thats how I test my drivers too. The other day I was thinking about suspension sag, and wondering how this would impact the measured parameters, especially since most drivers will be mounted normally and not firing up into the ceiling. I tested a big 18" and the parameters changed when I measured horizontally. Enough to model slightly differently. Not hugely different, but maybe with a different driver...Who knows? I think that from now on I will test them in whatever orientation they are going to be mounted in.

As far as the different VC wirings measuring differently, I believe this may be partly due to the differences in the actual amount of speaker wiring used?
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post #4 of 8 Old 02-05-08, 11:16 PM
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Re: Is anybody else using the PE Woofertester?

Audiojunkies did a pretty nice little review when the new version came out.
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post #5 of 8 Old 02-06-08, 12:33 PM Thread Starter
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Re: Is anybody else using the PE Woofertester?

Nice link. I hadn't seen that review before. Basically it outlines the strengths and weaknesses that I've found with it. It's still a great product though. If you are into DIYing your speakers or subs I think it's a must have.
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post #6 of 8 Old 02-06-08, 03:43 PM
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Re: Is anybody else using the PE Woofertester?

Hi Josh,

As you saw on AudioJunkies, I found some positives and some negatives to it. I feel that the WT3 is a good entry level product and the price reflects that. It does require a little requisite knowledge of speakers to identify where variances in measurements occur.

The differences you cited are completely normal with any measurement system. Most notably the difference in measurements when using different wiring configurations. Many manufacturers specify whether the specifications were measured with the voice coils in parallel or in series.

If you're wondering why this is, I suggest reading a book like D'Appolito's Testing Loudspeakers. As a cursory understanding from a mathematical standpoint, check out this article from Wikipedia. The mathematics are clearly laid out and, as you will see, changes in the DC resistance of the voice coil (listed as Re in thiele/small parameters) will cause a change in parameters like Qts and Qes. Overall, there are only a handful of measured parameters from which all others are derived. They are BL, Cms, Re, Sd, and Mms. There are, of course, the other one-off type of parameters like Xmax and Le as well.

The WT3 will fit the needs for many.

Last edited by DevilDriver; 02-06-08 at 10:28 PM.
post #7 of 8 Old 02-08-08, 12:28 PM Thread Starter
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Re: Is anybody else using the PE Woofertester?

That is a good read. Thanks for posting it Neil. As with modeling programs and TSP's themselves, the WFT3 is a solid tool to get you in the ballpark it seems.
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post #8 of 8 Old 02-08-08, 01:22 PM
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Re: Is anybody else using the PE Woofertester?

The suspension compliance is a huge variable and how you measure it varies your results significantly.

Things like Re, Le, Mms, Sd & BL are pretty tightly controlled. Its easy to wind a VC with the same gauge wire and the same amount of windings unit to unit and get tight tolerances. BL is usually within 5% because its easy to machine the parts to a tight tolerance. If your magnatizer is set-up right it will work the same unit to unit. The Mms is easy to keep tight too. The parts don't vary that much in mass.

The spider is the biggest variable in the entire process. Even the best quality spiders are +/- 15% so you get a wide range in Cms based just upon production tolerances. Also... measurement technique has a huge effect on measured Cms. Break-in the driver over a couple days and it the compliance drops. Measure at a higher signal level, and the compliance drops. Measure in a colder environment and the suspension will be stiffer. It changes with time also, measure right after working the suspension for awhile the the compliance may be softer. Measure after the driver has sit for days and it can trend to a stiffer compliance.

Luckily the in-box alignments are not highly effected by Cms change. Also... consider that even if the measured low-signal level Cms was EXACT the high signal level in actual use is stiffer in both directions of cone movement. The Cms curve is just that, a curve so don't get too wound up when the measured T/S parameters drift a little from the published ones.
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