This week I have been having a great time playing with speaker stuff. About a week ago I bought Woofer Tester 2 from the US, and I’ve since been blown away by what you can achieve with it.

But first, a step back.

If you’re into sound systems (either car or home), you’ll be well aware of the famed Thiele Small speaker parameters that are especially important when designing woofers and subwoofers. These parameters are the speaker specs that you plug into software (or an on-line calculator) to allow you to design the speaker box. That box design includes aspects such as internal volume, length and diameter of any ports, and so on.

Without the Thiele Small (abbreviated to TS) specs of the driver, you’re just guessing the box design – and the chances are overwhelming that your guess will be less than optimal!

So to design a good speaker enclosure, the TS specs are needed. Which is fine if you’re buying a new driver or one that is second-hand but still has specs available on it.

But what if you’ve sourced a speaker that is literally an unknown? For example, a quality driver from a late model car being sold off cheaply? Or even the speaker from a salvaged TV or surround sound system? (Don’t laugh: some of these consumer goods speakers are small and high quality – perfect for enclosures built into car doors or under seats. And people just throw these speakers away…)

In those cases, the driver’s specs need to be measured.

And, if you do a search online, you’ll find plenty of DIY techniques for measuring TS parameters. You’ll need a precision resistor, an AC multimeter that measures over a wide frequency range, and a frequency generator. And a lot of time spent doing very finicky measurements and plugging numbers into lots of equations. It’s certainly possible, but who wants to spend the time and effort doing all that? Especially if you’re sorting through a whole bunch of drivers to find one suitable for an application?

Well, now you now longer need to do so – just use Woofer Tester 2.

Woofer Tester 2 is a complete speaker test unit. This incredible piece of hardware plugs into the USB port of a PC or laptop and connects straight to the speaker under test. Open the software, press a button and within literally seconds many of the TS specs are measured. Do some more testing (eg by weighting the cone by a known amount) and the rest of the important specs are there in front of you – it’s that easy!

You can then import those specs into the provided Thiele Small program that will allow you to model sealed, ported and band-pass enclosures.

Build the enclosure, and then you can use Woofer Tester 2 to test it to see if it matches the predicted response. (Woofer Tester doesn’t include a microphone, so you cannot directly measure frequency response – but, indirectly [eg by impedance plots] you can get a good idea of what is happening.)

So does the system work? Does it ever!

So far, I have measured about 15 pairs of salvaged speakers. Picking the best of these, I have built two different types of enclosures to suit.

In one case, using just an 8 litre ported enclosure and a 5-inch woofer, I have clearly audible (and smooth) response down to 50Hz. In the real world, that’s a stunning result from such a small driver in a very small enclosure. Especially when the woofer (bought as a pair of second-hand speakers) cost $5!

In another case, I had some ex-Sony home surround sound drivers that were originally mounted in tiny (200cc!) boxes. For these drivers, I modelled and then built 2 litre ported enclosures, made from short lengths of 125mm heavy-wall plastic pipe, with MDF ends cut to suit. The drivers are just 3 inches in diameter (and have an effective piston diameter of only 2.4 inches) and yet in these easily built enclosures, sound very good indeed. I am thinking of using them as outdoor speakers for a BBQ area – they’d fit nicely under the house eaves.

Using Woofer Tester 2 hardware and software, you can now measure all those speakers for which proper TS specs are not available (and that’s almost all car sound speakers) and then model enclosures to suit. You can even build enclosures that work for individual drivers (useful, because even apparently identical drivers can have different measured specs).

I think that this approach represents a revolution in how bass / midrange speakers can be installed in cars, and how speakers can be sourced.

I paid US$160 for Woofer Tester 2 – and think it’s incredible value for money.

We’ll be covering in much more detail in AutoSpeed how to use the Woofer Tester 2 hardware and software, and what it can achieve in DIY speaker design and installation. But to say I am impressed is a vast understatement….

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