Help choosing measurement and modelling setup

[SimontY]

Hello!

I've searched around the forums quite a bit and just couldn't find any useful guide on what I need...

What I'm looking for is a speaker measurement setup (acoustics and even better impedance too). I'm prepared to pay a reasonable amount for it if it will match the following criteria:

- easy to use, intuitive front end.

- includes everything in one box (mic, software, any dongles etc.)

- only requires a computer with a "normal" soundcard to work correctly

- can enable me to achieve great speaker designs!

The reason for this is two-fold. Firstly, some time ago I bought a speaker kit (Intertechnik/Audiocom Seas Pontus) and wasn't entirely happy with the sound, so I changed the crossover, by guesswork. The sound is better, but I would like to take it even further by measuring the drivers' individual outputs and total output to optimise the crossover as far as possible.

Secondly, quite a few people have asked if I could design and build speakers for them. They know I don't have the measurement setup but ask anyway! One good friend has gone as far as offering payment and suggested I could use that to buy software and get the job done really well. He's right of course, this is the way forward.

So I need some help in deciding what to buy or put together. A name I've seen used a lot is Speaker Workshop, and I notice that it's freeware, which is nice!

It probably doesn't help because I don't have a calibration chart for it but I have a general purpose microphone and preamp. I have an ageing but adequate pc: 2.3ghz Athlon, 1gb RAM, Soundblaster Live Player 1024 sound card.

I'm not sure where to start with this, hence this thread! I just need a push-off in the right direction.

Thanks for any help you can offer me.

Simon

[MJL21193]

I use speaker workshop(free) and built the jigs, mic, cables myself. It takes a while to learn SW but it work great, and you can't beat the price.
I've heard good things about CLIO but it is fairly expensive.

[joe carrow]

I've also just downloaded Arta, http://www.fesb.hr/~mateljan/arta/index.htm, which has a free demo that seems to be very useful.

I just used it to measure my laptop's sound card, and I found that I have about 0.15% THD+noise, and a frequency response that's fairly flat between 80 hz and 10 khz, but down 3db at 40 hz and 20 khz.

I would say that my sound card is probably good enough to design speakers if I don't worry about competing with super high-dollar speakers. It would fall short if I wanted to very accurately measure the distortion of a driver, since the very best drivers have distortion components that are even lower than the noise floor of my sound card. The THD of the laptop is actually much better- about 0.015%, but with the noise floor so high there's really nothing I can do to get better measurements.

A quick and cheap thing to see if your present sound card is good enough for your purposes is to get a patch cable to connect your sound card's input and outputs to perform the same tests I did.

Also, I have a Behringer ECM8000 measurement microphone. They are available now for around $40. It is definitely the right tool for the job, and operates at a much higher level of performance than my laptop. You should be able to pick one up cheaply if you don't purchase a package that's all inclusive. Just be aware that it requires phantom power.

[SimontY]

Originally posted by MJL21193
I use speaker workshop(free) and built the jigs, mic, cables myself. It takes a while to learn SW but it work great, and you can't beat the price.
I've heard good things about CLIO but it is fairly expensive.

Thanks, I will have more of a look at Speaker Workshop. No point spending money if I don't need to.

Simon

[SimontY]

Originally posted by joe carrow
I've also just downloaded Arta, http://www.fesb.hr/~mateljan/arta/index.htm, which has a free demo that seems to be very useful....

Thanks for the tips. ARTA looks like it could be handy, lots of help guides there. I'm not interested in going as far as THD tests right away, so I probably needn't worry about my sound card yet.

If you've used both of these software tools, which would you recommend I spend more time trying to get my head round?

As for the mic., something like your Behringer ECM8000 sounds ideal. A quick look on Ebay UK reveals they're about twice what you paid, annoyingly, but affordable.

Do you think my cheap mic. preamp will provide phantom power? I will have a look when I remember and I'm at home. Does the Behringer connect via xlr?

Thanks for the replies so far.

Simon

[richie00boy]

I have a Thiele-Small measurement toolkit in development on my website. Probably not as press-and-go as Speaker Workshop, but it's there if you want to take a look.

Ultimately I want to develop the toolkit into a single user-friendly spreadsheet.

[SimontY]

Thanks Richie,

That calculator works nicely, well, with randomish numbers put in it seems to make sense! But I need the physical setup to actually measure driver impedance too. I tried something from a textbook before and got vaguely believable numbers but my method was criticised and so I really need to know how to do this properly but as easily and cheaply as possible!

Simon

[richie00boy]

Did you not read my white paper? It should have been obvious how to do an impedance plot...

[SimontY]

Originally posted by richie00boy
Did you not read my white paper? It should have been obvious how to do an impedance plot...

Err, I'm a numpty sometimes.... Reading it now!!

[SimontY]

Fantastic guide there Rich, thanks. There are a few bits I don't understand, such as why we want Fb and a port on the test box. Is this the way to work out the tuning frequency of your finished speaker? Or is it a part of measuring drive unit params?

I think when I had a go at measuring a driver I used the voltage source method and it seemd as though my multimeter wasn't accurate enough to give great results (very rough I thought). To calculate Vas I did the added mass method, which again, perhaps wasn't too accurate. Building a test box is a mega-pain though! How strongly do you recommend this?

Thanks,
Simon