Setting up a PC based loudspeaker measurement system
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.
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.
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.
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.
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:
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.
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
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
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.
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.
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
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]