SPL meter versus software?

[Mark25]

All,
I want to build my own 3 way closed box, active speakers. Is it worth me buying an SPL meter, or should I get some speaker measurement software?

I have a scope and signal generator already. The SPL meter I have in mind measures 35-130 dB, over the frequency range 31.5Hz to 8KHz and costs 135 euro. Any advice appreciated.
Mark

[audionut]

I have used the Radio Shack SPL meter and a signal generator and that worked pretty well...but in a room with reflections, you don't get a very true frequency response on the meter. But owning the Radio Shack SPL meter makes it easy to use one of the speaker programs, such as ADUA's Speaker Workshop (free on the internet) which will measure speaker response. The Radio Shack SPL meter doubles as a preamplified Mike which you plug right in to your computer. Also, Old Colony has the Winair program ($50) which measures frequency response and you would use the Radio Shack meter plugged into your sound card here as well.

[audionut]

The Radio Shack meter costs around $60 for the analog model.

[Nappylady]

The SPL meter only goes up to 8 khz??? Yuck! Skip it!

okay, rant over.

[Mark25]

all,
thank's for your replies. i looked at the spec on the realistic unit and could not find a frequecy reponse. This concerns me as there's a model in the Maplin catalogue in the UK, which has a response of 300 Hz to 8KHz, which is not low enogh for my needs.
Mark

[themadhippy]

ive been using the dazyweb tms1 from http://www.dazyweblabs.com/tms1/index.html
seems to do what is says on the tin and best of all its free

[hancock]

There is no question that if you want to design your own crossovers you need the ability to make quasi anechoic measurements, eg. MLS, TDS. You cannot do this with an SPL meter--you end up measureing the room, not the speaker. You also can't measure phase with an SPL meter. Phase is critically important for crossovr design. Get yourself a good measurement program and sound card and a panasonic WM60 mic capsule (cheap). It's not even absolutely critical that you callibrate the capsule as the mic is much flatter than you will ever get your speakers (unless you're doing DSP like I am).

John

[Mark25]

All,
Thank's again for your replies.
John,
The object of this project is to investigate Rod Elliot of ESP's excellent bi-amping article. I also wish to measure how much Q, i prefer in a speakers bass response.

i will be using the ESP p9 electronic L-R crossover 24dB/oct which is phase coherent, so i was under the impression that i could build a pair of speakers using that, just setting them up in the frequency domain. Am i mistaken?

I was going to use peerless or audax drivers and compare the results to my conventional crossover speakers, which use volt and scanspeak drivers. I think DSP and digital amplifiers for the bass units is probably the way ahead in the long run, but i think i will start simple first.

themedhippy,
thanks for the dazyweb link, looks like a good starting point, when i git the mic input on the soundcard working.


Regards all
Mark

[hancock]

Hi Mark,

You wrote:

"i will be using the ESP p9 electronic L-R crossover 24dB/oct which is phase coherent, so i was under the impression that i could build a pair of speakers using that, just setting them up in the frequency domain. Am i mistaken?"

I'm not familiar with that particular crossover, but in general, a crossover that sums flat electrically will not sum flat acoustically. You need to offset the response of the drivers themselves as well as compensate for any physical offset. You could do that by trial and error until you get a flat frequency response, but unless you get lucky that would take billions and billions of years. A much less painful way is to measure the frequency and phase response of the individual drivers and then design a crossover that from the start will give you a good response. If you're going to do any more than a little playing around in this hobby, I really recommend investing in a decent measurement setup. You will be glad you did.

Regarding DSP, it's easier than you think. Assuming you've got a PC and a sound card with enough outputs (I use the M-Audio Delta 1010--highly recommended), all you need is a program called wavewarp (www.soundslogical.com). I could help you out designing some filters, assuming you can find a way to measure your speakers. I will say with absolute confidence that a digital crossover with the Delta 1010 will absolutely blow away any analog crossover--ruler flat magnitude and phase response on axis and much better off-axis response.

John

[Mark25]

Hi John,
OK I’m convinced; I need to think about phase as well as magnitude, so now I have lots of questions for you!

You’ve recommended investing in a “decent measurement setup”, would you like to recommend a particular decent setup and give a ballpark cost if you know it?

If a can now measure phase error, how would I correct for it in my existing setup? Obviously I could alter the physical position of the separate drivers, but how do I correct errors within part of a drivers frequency range.

Also, you’ve mentioned that with a DSP solution, you get a “much better off-axis response”. I was under the impression that the off-axis response was a property off the drivers themselves, not the X-over. Could you please explain what I’ve missed? Sorry for having so many questions!
Regards
Mark