One of my hobbies is hi-fi audio reproduction. I have even built the occasional subwoofer, so I’m not into the high-end quack stuff where you pay thousands of bucks for a couple of meters of wire.
This hobby of mine has been rather dormant for years, but recently, I visited a friend of mine, only to find that his stereo system sounded like shit. Quite unlike what I remembered. So I helped him out, placing his speakers in a more optimal position in the room, and fixing some other problems, particularily placing his speakers on low concrete slabs.
One of the things I needed was a test CD, to find out if there were any particular problem areas with the reproduction in his living room, so I created a simple test CD, containing 63 tracks, containing sine waves at various frequencies.
“Download the test CD”:http://virtuelvis.com/download/201/testcd.7z. You will need “7-Zip”:http://www.7-zip.org/ or another program that understands the 7-Zip compression format to decompress the file. Please note that while the archive is only 218KB compressed, it will expand to 106MB when decompressed.
Make sure you read the instructions for use, either in this entry or in the readme file contained within the archive.
The audio CD contains 63, tracks each being 10 seconds, containing a pure sinewave at frequencies from 20Hz to 22000 Hz (recorded at 0dB).
h3. CD Creation
Use the bin and cue files to create an Audio CD. How this is done, will vary from program to program. In general, if your program supports bin and cue files, there will be some option in the program with the words “Burn image”, or similar. What is important is that you do not try to burn the files directly, as that will not create an audio CD. For specific instructions, please consult the manual of your CD burner’s software.
A free Windows application that should be able to burn these files is “InfraRecorder”:http://infrarecorder.sourceforge.net/.
When playing the Audio CD in a CD/DVD player, caution with the volume setting is highly encouraged. The CD contains frequencies your system might not be able to reproduce properly. These frequencies, while not subsonic, may cause damages to your system if the volume setting is to high.
Caution is also encouraged with regard to your hearing: Loud noises, like the ones on this CD may cause hearing damage.
If you skip between tracks, you may hear popping noises from the speakers. This is quite normal, and not anything to be worried about. Caution is still encouraged with the volume setting.
h3. How to listen
When you listen to the CD, you may/will discover that some frequencies sound noticeably louder than the previous or next frequency. This may be an indication that either your loudspeakers have an anomaly in its frequency response, or that you have hit some resonance frequency of your room.
If the latter is the case, try to put the particular track on repeat, and walk around your listening room. If there is a considerable difference in loudness depending on where in the room you are, this might be an indication that your loudspeakers are suboptimally placed. This will typically only occur with the lower frequencies, where the wavelengths are longer.
Please note that some variation in your loudspeakers frequency response is entirely normal, and that certain frequencies will sound louder than others, because your ears have a different sensitivity at different frequencies.
h3. Speaker placement
The quick and dirty rule for placing loudspeakers is this: Make sure that your speakers are placed at a distance of 1/3, 1/5, 1/7, 1/9 … 1/n (where n is an odd number) from any wall.
Example: Let’s say that your room is 6 x 4 metres, and you want to place the speakers along the short wall. This will provide you with the following “acceptable” distances for you to place your speakers:
|Ratio||From side wall||From back wall|
Placing your speakers symmetrically is encouraged, if that is not possible, you should still take care that both speakers are placed at one of the suggested ratios, meaning it you may for instance place the left speaker 1/3 from the side wall, and the right speaker 1/5 from the side wall. With regard to the back wall, loudspeakers _should_ be placed at an equal distance from this wall, or you may experience noticeable loudness differences from the speakers.
Whether you should place your speakers far from or close to the back wall are highly dependent on the speakers you use: Small stand mounted speakers (often called bookshelf speakers) typically needs to be closer to the back wall than large floor standing speakers. Your loudspeakers’ instruction manual may contain information on the optimal placement of the speakers.
This speaker placement guide can also be used to determine the optimal placement for the center and rear speakers in a Home Theatre setup.
h3. Bookshelf speakers
With regard to so-called bookshelf speakers, if you at all care about sound quality, never ever place any kind of loudspeaker in a bookshelf. A bookshelf typically resonates when you play music, becoming a “musical instrument” of it’s own, making anything from Verdi to Slipknot sound awful. Even the cheapest of loudspeaker stands are better. Make sure that the loudspeaker stands are tall enough to bring the elements level with ear height when sitting down. Your speakers, when placed on the stands, should roughly be in the 85-105cm height range.
h3. Midrange and treble
The midrange and treble frequencies on the CD are typically more suited to finding problematic furniture that resonates: Picture frames, windows, tables and such. The best way to remedy such problems might be moving the offending piece of furniture, or in the case of windows resonating: Use your curtains when listening seriously.
At the very high end of the frequency spectrum on this CD (Tracks 55-63), you should not feel too worried if you cannot hear anything:
* Many cheaper stereo setups are not able to reproduce these frequencies, despite what the specifications say.
* Some degradation of hearing with age is to be expected.
* At lower volume settings, these sounds might be below your hearing threshold at that particular frequency.
This CD should never be used for medical purposes, diagnostic or otherwise: If you are at all worried about your hearing you should consult a physician/audiologist, and get properly tested, and have your ears cleaned by a professional. _Never ever_ use Q-Tips or similar to clean your ears. Do not let objects smaller than your elbow near your ear.
h3. Spikes and slabs
Make sure that your loudspeakers never stand directly on to the floor. The direct coupling with the floor usually makes the floor an instrument on it’s own: The bass will sound mushy in the listening room, and your downstairs neighbours (if you have any), will probably want to kill you whenever you turn the volume up to normal listening levels, since they’ll hear a constant “Boom boom boom” from the drums and bass from your music.
Buy some simple spikes/cones to place your speakers/stands on. They will effectively decouple your speakers from the floor, leaving your neighbours happy. If you are worried about the cones damaging your floor, you can place coins or similar under the spikes, or you can buy spikes with integrated floor protectors, like the “Soundcare superspikes”:http://www.soundcare.no/
If your floors are very uneven, you might also consider placing an additional concrete slab under the speakers, so that your speaker, or you can use three spikes instead of four.
Uhm. Well. Don’t bother, as long as the cables have acceptable electrical and mechanical parameters there really isn’t much of an audible difference.
This test CD can also, with some care, be used when determining the optimum sound level setting for a subwoofer.
When placing a subwoofer, consult the manual: Some subwoofers may benefit from being placed in the corner of a room, others might benefit from a free-standing position.
When you’re setting the sound level and crossover frequencies for a subwoofer, ensure that you _cannot hear where the subwoofer is placed_ and also _make sure your subwoofer doesn’t sound louder than your ordninary speakers_.
While it might be fun setting your subwoofer at a level that causes seismic monitoring equipment to register it: for sound quality, it is a horrible idea.
h3. Final words
Have fun listening to and tuning your audio equipment. Remember that following this guide probably is a lot cheaper (and more fun) than buying new, expensive equipment from the local hi-fi quack.
h3. (Update) “Tracklisting”
Some people have requested the frequencies used. Here they are:
# Tone: 20 Hz
# Tone: 25 Hz
# Tone: 30 Hz
# Tone: 35 Hz
# Tone: 40 Hz
# Tone: 45 Hz
# Tone: 50 Hz
# Tone: 55 Hz
# Tone: 60 Hz
# Tone: 65 Hz
# Tone: 70 Hz
# Tone: 75 Hz
# Tone: 80 Hz
# Tone: 85 Hz
# Tone: 90 Hz
# Tone: 95 Hz
# Tone: 100 Hz
# Tone: 120 Hz
# Tone: 140 Hz
# Tone: 160 Hz
# Tone: 180 Hz
# Tone: 200 Hz
# Tone: 240 Hz
# Tone: 280 Hz
# Tone: 320 Hz
# Tone: 360 Hz
# Tone: 400 Hz
# Tone: 500 Hz
# Tone: 600 Hz
# Tone: 700 Hz
# Tone: 800 Hz
# Tone: 900 Hz
# Tone: 1000 Hz
# Tone: 1200 Hz
# Tone: 1400 Hz
# Tone: 1600 Hz
# Tone: 1800 Hz
# Tone: 2000 Hz
# Tone: 2400 Hz
# Tone: 2800 Hz
# Tone: 3200 Hz
# Tone: 3600 Hz
# Tone: 4000 Hz
# Tone: 4500 Hz
# Tone: 5000 Hz
# Tone: 5500 Hz
# Tone: 6000 Hz
# Tone: 6500 Hz
# Tone: 7000 Hz
# Tone: 7500 Hz
# Tone: 8000 Hz
# Tone: 10000 Hz
# Tone: 12000 Hz
# Tone: 14000 Hz
# Tone: 16000 Hz
# Tone: 18000 Hz
# Tone: 19000 Hz
# Tone: 19500 Hz
# Tone: 20000 Hz
# Tone: 20500 Hz
# Tone: 21000 Hz
# Tone: 21500 Hz
# Tone: 22000 Hz