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Downloads - Loudspeaker / Room Measurement
Test Tones, all 44.1kHz, 16 bit .wav files	pink noise wav file for RTA testing white noise wav file for use with spectrum analyzers mls test tone for impulse testing bong file for speaker testing CD1 1/3 octave modulated tones zip file. Use for testing without a pc.
Software Links, mostly free / open source W=Windows, M=Mac, L=Linux or BSD	Audacity Open Source Sound Editor / recorder, (W,M,L). It has a built in spectrum analyzer. http://audacity.sourceforge.net TrueRTA, excellent Real Time Analyzer (not free but only US$39 for 1/3 octave version) (W) http://www.trueaudio.com Praxis from Liberty Audio. Excellent, free RTA (W) http://www.libinst.com/praxis_downloads.htm
Low cost Test Microphones / sound meters	Behringer ECM8000, requires phantom power, see microphone amplifiers below. Full audio frequency range. http://www.behringer.com/EN/Products/ECM8000.aspx Radioshack Analogue Sound Meter, Catalog #: 33-4050. Battery powered, self contained, response 50Hz - 10kHz, phono output. http://www.radioshack.com
Microphone Amplifiers. Required if your sound card does not have a phantom supply.	Behringer MIC100 http://www.behringer.com/EN/Products/MIC100.aspx ART Tube MP http://www.artproaudio.com/products.asp?id=1&cat=1&type=79
Low cost but flexible Analogue Equalizers. May be used for basic room equalization.	Behringer T1951 (now discontinued) http://www.behringer.com/T1951/index.cfm?lang=eng TL Audio 5013 http://www.tlaudio.co.uk/docs_07/product_07/5013.shtml
Audio Testing Notes
Audacity for beginners	1. Set sample rate and sample format in "Edit / Preferences" to 44100 and 16 bit 2. Create a new audio file with "File / New". Click record and the track should appear as a recording is made. 3. Stop the recording process after 3 to 4 seconds and drag the cursor over approximately 1 second of the recording. Select "Analyze / Plot Spectrum" 4. Here is a screenshot of the result so far. That's all we need to know at this point!
Measurement Methods	1. Test signals should be from one speaker only 2. I would suggest 3 speaker to microphone distances 1 - 1.5m for general measurements near field, a few cm from a particular driver. This will significantly reduce any room effects and driver interactions and leave the pure driver / cabinet response. Your listening position 3. When doing an actual recording of white or pink noise, aim for a recording level of -6 to -10db below peak.
Using the Spectrum Analyzer	Use Log Frequency scale and the Hamming Window. There is one parameter that needs to be changed and that is the sample size. Adjust this to the lowest value that gives the sharpest spectrum. For example, a 100ms selection at 44100 Hz requires a sample size of 8192.
Interpreting Results	1. Assume your speakers are flat in anechoic conditions and within the manufacturers specification. Many listeners tend to blame their speakers for any problems, not the room ! 2. Remember with a microphone distance >1.5m, what you are measuring, up to around 2kHz, is the the room response coloured by room effects. Room gain will increase bass output below 100Hz and room modes will give severe peaks and troughs in the same region. Floor reflections will probably give a major dip in the response in the lower midrange and crossover notches may also be present. 3. Mid Range and Tweeters Room effects in this range can best be explained with reference to the level of room absorption present. Remember, typical thicknesses of materials used means that absorption falls off rapidly below 500Hz and is low below 100Hz. To a varying degree, tweeters behave differently in rooms due to directivity effects. The more directional tweeters may maintain a flatter response but this will not match an omnidirectional midrange. Its response will suffer in a room with a fair amount of absorption as the reverberent field will be less and will collapse quicker. To summarise: Normal / bright room - poor bass, possible roll off above 2kHz Some extra room absorption - maybe more bass, tweeter response could go either way High room absorption (not in bass region) - poor bass, possible suck out in the mid range See this article for typical problem responses.
Speaker Impulse Testing	Impulse testing is particularly useful as it enables frequency responses at higher frequencies to be measured in non anechoic conditions thus eliminating the effects of the environment. We have included an mls test tone in the download section. This can be reproduced through your speakers and recorded in the same way as pink or white noise. The entire file has to be recorded with a small amount of silence at the start and finish. Unfortunately, deriving the impulse from the recorded tone requires specialised processing. The Audiophile Recordings Trust will process and return emailed files, for non commercial users, by special arrangement . A good quality speaker impulse and its spectrum is shown here.
Room Impulse Testing	A room impulse can easily be measured by recording a balloon bursting. Hold the balloon above your head while bursting in order to get omnidirectional results. The Audiophile Recordings Trust will process and return emailed impulse files, for non commercial users, by special arrangement . This will give reverberation times over a range of frequencies. Here is a typical example recorded in a church hall with good acoustics for recording.
Making Improvements	Now that we are able to make measurements, more options are available. Room treatment in the form of absorption, diffusers or both is easy to install at frequencies above a few hundred Hz and this should be considered first. Unfortunately, room effects in the bass region are difficult to treat in a domestic environment. However, room bass gain and other effects outlined in the "Interpreting Results" section, should be corrected by using an appropriately designed analogue equalizer. The nearest commercially available products I have found so far are mentioned in the links section above. They are for studio use and so are not ideal for use with typical unbalanced domestic equipment. Parametric equalizers like these examples will not introduce colouration if the filters are limited to a Q less than 1.

Last modified 2010-12-03