Quality drivers

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This is a rather basic question (I assume).

When looking through drivers for speaker builds, aside from just the stated specs of the drivers, how does one determine what a "good quality" driver is.

I don't like the idea of judging an item's value just based on price.

So all specs being the same, what would make one driver "better" than another for a speaker build?

Unfortunately there's no hard rule for this when using manufacturers datasheets alone. Often all they will contain is a frequency response graph, impedance curve and the T/S parameters.

It goes without saying that most people want a driver to have a flat frequency response over the range of frequencies they would wish to use it. Then the T/S parameters will allow you to see if the driver will work in the enclosure size you have in mind but the fine details are almost always missing.

Lots of manufacturers will smooth their frequency response plots to hide anomalies and crush the resolution on the impedance to hide any potential resonances too.

If the T/S parameters fit and the frequency response looks good then if the driver mentions the use of shorting rings, copper caps or inductance linearisation etc you can usually be assured of the thing having decent harmonic distortion performance but this is all conjecture.

I've seen some drivers that appear good on paper to perform far worse than their spec sheet would indicate and then the opposite happens too.

This is one of the reasons why John K, now retired, started Zaph.com to perform detailed measurements of drivers to really sort the men from the boys. Hificompass has now pretty much assumed this role and for that we will all be forever grateful.

In an ideal world the manufacturers would all measure their drivers with some industry set of standards so we'd know exactly what it was we were getting. Sadly it's a bit of a gamble were it not for those who have taken the time to measure before us.
I believe weight is a good sign of quality.
Take a 1.5 Kg 400W 12" woofer from a cheap speaker and compare it with an 8Kg speaker from a reputable manufacturer. Yes I know Neodymium drivers exist...
Stamped steel cast or molded Alu are also different in quality, but on my DXR15 1000W Yamaha's they use stamped Celestion (I believe) drivers and they sound fine.
It's not easy to tell, but cheap speakers usually are crap for sure.
Another issue is the variability between units, a function of build-quality and automation and QC used. Clearly the cone uniformity is very important, with some materials being inherently harder to make uniform, but spiders and physical alignment are also crucial to getting datasheet performance out of a unit.

The good manufacturers test every unit's FR and output level against a template and do analysis for voice-coil rubbing and other spurious noises in the sound and reject any bad units. There are some nice YT videos from factory tours out there that give a great insight into manufacturing quality for various companies, as well as being strangly fascinating if you're like me(!)
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