Setting up a PC based loudspeaker measurement system

[npdang]

Setting up a PC based loudspeaker measurement system

Introduction.

Setting up a PC based loudspeaker measurement system is a very easy, accurate, and cost effective alternative to the days of using unreliable “Rat shack” spl meters, or expensive and cumbersome RTA’s as an aid for tuning your car. It also makes tuning and set up of your next car audio system a breeze. You no longer have to play guessing games with where and how to set your equalizer, crossover, or time alignment. It’s also an extremely useful tool for finding problem areas in your car, so you can know why your bass isn’t tight, your midrange sounds muddy, or how to fix that harsh sounding tweeter.

Equipment.

Probably the first thing you’re wondering is, what kind of gear do I need to make this all happen and how much is this going to cost me? Well, to get started you’re going to need the following basic items :

A. Full duplex (meaning it can record and play simultaneously) soundcard with a stereo line input and output. In fact, simpler is often better. Soundcards with all kinds of funny 3d or special effects processing can interfere with your measurements if they can’t be reliably turned off. Oftentimes, the integrated soundcard that comes with your computer is perfect and there is no need to purchase an aftermarket sound card.

However, if you must buy an add-on card for one reason or another, my recommendation is M-Audio’s usb transit. It’s cheap, portable, and very reliable. Expect to pay around $80 for a new unit.



http://www.m-audio.com/products/en_us/Transit-main.html

B. Next you will need a microphone, and a power supply or “pre-amp” for the mic. A very popular, low budget choice that yields fairly consistent and accurate results is the Behringer ecm8000 mic, combined with the M-audio Audio Buddy pre-amp. Just like with the soundcard, you want to avoid using any preamp that feature distortion or special effects generators (such as tube pre-amps). This combo has been tested against laboratory grade equipment, and should guarantee great results for a very small cash investment.


http://www.behringer.com/ECM8000/index.cfm?lang=ENG



http://www.m-audio.com/products/en_u...uddy-main.html

And for those with a little more money looking for an all in one sound card and mic preamp, you can check out the M-Audio MobilePre USB for $180 msrp.



http://www.m-audio.com/products/en_u...SB-main-1.html


C. Measurement software. Probably the most important and yet least understood. The first question to ask is, what do I want to do with this setup? Price, and ease of use is also important. And lastly, do you want to use a RTA or MLS based measurement software.

Generally speaking, a RTA is more convenient because all you need to do is burn a “pink noise test cd”, and play that on your headunit. Then you turn on your mic, and you are given a 1/3 octave frequency response graph to look at. It’s as simple as that.

A MLS based system can give you a FAR greater amount of information and flexibility (especially time domain info and not just frequency response), but it will require you to connect your soundcard’s line output to the input of your audio system before any crossovers, eq, or processing is used. The way it works is that the software generates the test signal, sends it out through your soundcard, and into your stereo.

Here is a list of some commonly used software packages, their general capabilities, and pricing:

LspLab v3.01

My personal favorite. It does nearly everything you could want, and is fairly straightforward and simple to use. Includes box, crossover, and measurement software. Unfortunately, the demo doesn't give you very good frequency resolution.

http://www.lsp-lab.com/

WinMLS 2000 – The standard personal license is just $79. A great MLS package for the beginner. Easy to setup, and use. The interface is fast and quick to learn. This will allow you to:

- take frequency response measurements
- measure distortion
- see what the frequency response of your setup looks like without reflections
- configure time alignment by measuring the arrival time of each speaker
- create waterfall plots
- oscilloscope

http://www.winmls.com

Sample Champion – Student license $149 euro. Home license $199 euro. Not quite as easy to learn as WinMLS, but with far more options. Same features as WinMLS plus the following:

- t/s parameter calculation
- option for mic and soundcard calibration which allow you to take more accurate frequency response measurements
- RTA capability
- easier to use, built-in distortion analyser

http://www.purebits.com

TrueRTA - $40 license fee for the basic software. Very simple to use. Your basic RTA right here, but not much else. Other than taking 1/3 octave frequency response measurements, there’s not much else to do with it.

http://www.trueaudio.com

SpectraPlus – A software very similar to TrueRta, but with a few more features such as a spectrum/fft analyzer, and distortion analyzer. A spectrum analyzer is a little different from a RTA. Where a RTA shows you frequency response in 1/3rd octave increments, a spectrum analyzer shows you frequency response in set increments, such as 10hz, or 1hz.

http://www.telebyte.com/pioneer/

Speaker Workshop – A free program. It will allow you to take frequency response measurements, calculate t/s parameters, and perform distortion analysis. Clunky and non-intuitive interface, but the price can’t be beat. You can read the manual here: http://www.audiodiycentral.com/resou...nual%201.0.zip

http://www.speakerworkshop.com

D. Last but not least, you will need cables to wire this whole thing up.

- A cable to connect the mic to the mic pre-amp
- A cable to connect the mic pre-amp to your soundcard input
- A cable to connect the soundcard output to your amplifier/processor (not required if you’re using an RTA and test cd w/pink noise)
- A mic stand to hold your mic while taking measurements (optional)[/i]

[Hobbes26]

WinMLS doesn't give you an MLS excitation signal in the $99 version - you have to get the 4th level Pro to get that.

Otherwise, I guess you use pink noise to get FR?

[npdang]

I guess prices have gone up? I paid $79 for my full copy of WinMLS 2000.

[Hobbes26]

Ah... I wonder how much better WinMLS 2004 is, compared to 2000, considering it's quite the jump in price - to get MLS capability at least.

[npdang]

Originally Posted by Hobbes26

Ah... I wonder how much better WinMLS 2004 is, compared to 2000.

As far as I can tell, it doesn't really do anything new that I would be interested in. Sine sweep excitation takes forever compared to MLS. Distortion is kind of nice, but that's only if you're too lazy to compute it yourself from the FFT. Uhm... other than that a very high price increase and really nothing else I would use.

Also, you can still buy the old WinMLS 2000 standard personal for $79. Honestly, the only thing I like about WinMLS is how easy it is to stack and format multiple measurements onto one display. Like if you're taking multiple frequency response measurements, you can shift one up +5db the other down -5db, normalize them all to 0, stack them on top of each other or only display one at a time, etc.

Value wise, though I think Sample Champion or Sound Easy gives you the most for your money. Sound Easy interface just sucks... not alot of customization with respect to displaying output either, but it's a very powerful and comprehensive package. Sample Champ is pretty good, but no xover stuff, and it's a lil harder than WinMLS to overlay graphs and edit their appearance. If I had money, I'd just buy LMS and be done with it

[Hobbes26]

LMS?!? Full length ISA card based? Swept sine wave measurement? I'm partial to using the MLS methods - and rather have it NOT on an ISA card. We've had enough problems with our MLSSA measurement card (actually, problems with the OLD computers we've had it installed in).

You actually bought all of those programs? I haven't heard much about SoundEasy... SampleChampion looks decent.

Know how much a Praxis setup costs?

Found a 'full' Clio setup for $700 at audioxpress.com (ClioWIn Lite? Wonder how up to date it is.). It's also sold at e-speakers.com (~$2k for hardware and software). Have you used Clio? Seems like a good package for everything you need to do a measurement.

[npdang]

Originally Posted by Hobbes26

LMS?!? Full length ISA card based? Swept sine wave measurement? I'm partial to using the MLS methods - and rather have it NOT on an ISA card. We've had enough problems with our MLSSA measurement card (actually, problems with the OLD computers we've had it installed in).

You actually bought all of those programs? I haven't heard much about SoundEasy... SampleChampion looks decent.

Know how much a Praxis setup costs?

Found a 'full' Clio setup for $700 at audioxpress.com (ClioWIn Lite? Wonder how up to date it is.). It's also sold at e-speakers.com (~$2k for hardware and software). Have you used Clio? Seems like a good package for everything you need to do a measurement.

Praxis I think is $800 with the audpod? That would be my second choice after LMS.

I didn't like Clio because I thought it was a bit pricey, but it does come with a calibrated mic/pre and the spl measurements are absolute. Doesn't support the variety of post processing and stimulus that Praxis does though IIRC.

[Hobbes26]

Originally Posted by npdang

Praxis I think is $800 with the audpod? That would be my second choice after LMS.

I didn't like Clio because I thought it was a bit pricey, but it does come with a calibrated mic/pre and the spl measurements are absolute. Doesn't support the variety of post processing and stimulus that Praxis does though IIRC.

What makes LMS so good?

[npdang]

Originally Posted by Hobbes26

What makes LMS so good?

I don't like swept sine measurements since they take so long, but supposedly they have higher noise immunity than MLS. But the biggest feature of LMS is all the post processing features you get... especially the non-linear measurements. Interface is pretty straightforward as well. But yeah that ISA card is a big pain.

For most people that just want something to use in the car I"d probably just learn Speakerworkshop since it's free and it does actually do quite a bit.

[Hobbes26]

Originally Posted by npdang

I don't like swept sine measurements since they take so long, but supposedly they have higher noise immunity than MLS. But the biggest feature of LMS is all the post processing features you get... especially the non-linear measurements. Interface is pretty straightforward as well. But yeah that ISA card is a big pain.

For most people that just want something to use in the car I"d probably just learn Speakerworkshop since it's free and it does actually do quite a bit.

Ah, nearly forgot this was a diyMOBILEaudio site... . In-car measurements are kinda tricky. I was speaking in terms of more general applications of speaker measurement.

I should try out Speaker Workshop - have you used it extensively?

[npdang]

Originally Posted by Hobbes26

Ah, nearly forgot this was a diyMOBILEaudio site... . In-car measurements are kinda tricky. I was speaking in terms of more general applications of speaker measurement.

I should try out Speaker Workshop - have you used it extensively?

I did play with it for like 15 mins... but I didn't like the interface. Other than that, AFAIK it's accurate and does a buncha stuff like xover etc.

[blackreplica]

hobbes> Based on cheapboy's recommendation
via email i decided to give speakerworkshop a try. Cheap is right, the thing is damned hard to use. Very non-intuitive interface. BUT its free. And recently, i managed to get a hold of the unofficial speakerworkshop manual (try searching for it on the web, its a 10mb word doc compiled by an enthusiast). The manual is EXTREMELY detailed, but its over 200 pages long so lets just say the learning curve on this software is very steep. I just spent last night reading about 10 pages at the beginning and i think i have figured out how to to mls speaker measurements on it. i didnt have an mic or speaker(to measure) connected to my laptop but when i hit the measure-frequency-response button the thing made a short pink noise burst for less than half a second or something(if that is an mls signal then i suppose i am on the right track) and spit out an FR chart for me. It was a horribly jagged response, but i presume its my laptop soundcard FR which is probably crap anyway since there was no mic hooked up. But hey, i think it works, and if it can take Fr measurements, then i guess its good enough for in-car tuning. of course the functionality is far more advanced than that. You can do pretty much everything from passive cicuit design, enclosure design, impedance/ T/S measurements, distortion, a whole lot of other stuff. of course, i have no idea how to measure those yet. have to finish reading the manual which will probably take me another 5 years or so LOL but hey at least its free. hope this helps

[npdang]

Performing a mls measurement should just be (more or less) a one click process.

You really don't have to read through the entire manual... alot of it is just good misc. background info. Just skip straight to the part about taking frequency response measurements.

If you have a loopback cable you can plug the output of your soundcard into the line input and take a fr measurement of your card

[blackreplica]

Yea thankfully the MLS measurement was a one click process, but there was some work to be done beforehand. You have to actually create a speaker file in the project tree, then do a bit of setup then finally the MLS itself.

The interface is really clunky though, and the thing i dont like also is the difficulty in joining different chart measurements together. So far the software is just ok for me, so i think i may actually go for WinMLS 2000 instead. the price is not that expensive anyway. Software packages like Soundeasy at more than 200+ is definitely out of the question for me

[blackreplica]

OK i managed to mess around with a trial version of winmls 2000 personal just now. I couldnt do much besides clicking buttons though since i havent got the unlock code for the trial version yet but at first glance things look a LOT more intuitive. not only does the layout make sense, but the help file is really well organised and detailed as well. Once winmls sends me the unlock code i'll be able to know more.

BTW cheap, do you typically use pre-emphasis when doing mls measurements? Also, would you need to calibrate anything in the software if all you were using it for was mls, impulse, and maybe THD/waterfall measurements? or is calibration just to obtain accurate spl readings?

[npdang]

Originally Posted by blackreplica

OK i managed to mess around with a trial version of winmls 2000 personal just now. I couldnt do much besides clicking buttons though since i havent got the unlock code for the trial version yet but at first glance things look a LOT more intuitive. not only does the layout make sense, but the help file is really well organised and detailed as well. Once winmls sends me the unlock code i'll be able to know more.

BTW cheap, do you typically use pre-emphasis when doing mls measurements? Also, would you need to calibrate anything in the software if all you were using it for was mls, impulse, and maybe THD/waterfall measurements? or is calibration just to obtain accurate spl readings?

Also give lsplab a try. The free version actually offers quite alot of functionality.

The only thing I would worry about is the time latency calibration... and only if your sound card doesn't have a fixed time delay between when it starts playing a signal, and when it begins to record.

It's really easy to test this with a loopback cable. The impulse response should be at exactly the same position everytime you take a measurement. If it moves, then you would need to use a loopback cable on the left or right channel to "calibrate" the time delay of your soundcard.

[blackreplica]

I'll probably give that a try later with speakerworkshop. I never thought of trying the loopback method up till you recommended it(i've got an earphone cable with 2 male ends somewhere at home). I'll measure the latency but i presume this wont become an issue once you use an external sound card like the m-audio usb transit? Cos i was planning on getting one anyway. i seriously dont trust the quality of the built in sound card on my laptop.