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Some time ago Henk from Audioselectief offered me to borrow his Shure room equaliser/analyser (type M615-2e). When I visited his shop in Sneek a while later I took the "briefcase" with the equipment home. At home I discovered that the contents of the box contained a room equilisation system. The analyzer system was manufactured in the 70-80's so it was not one of those modern digital room correction systems.
The box contained a analyser box, a matching microphone, some hookup wire and a user manual. Several times I promised myself to do some analysis in the living room, but when reading the manual I suspected that it would take more effort than a simple connect-'n'-go.
Some weeks ago we had our wooden floor sanded and the walls painted. And since we rearranged the furniture I had to find the best place for speakers and hifi set. As a result I found the time to experiment with the analyzer as an aid in determining my optimum speaker placement. On this page you find my not so scientific description of the process. The reason for not being too academic about this process is that I discovered that curtains, furniture arrangement etc. all have their effect on the equalisation and I found out that a few dB difference is nothing to worry about.
Most difference from the ideal curve may be corrected by means of the tone control on the amplifier (oh boy, a forbidden word for audiophiles), but most of the times I did not find this necessary.
About 30 years ago, every amplifier had a tone control facility built-in. Treble and bass response could be adjusted from flat to +12dB range. In the last years using equalisers (and therefore tone control) became less fashionable. For stereo music reproduction this may sound logical to most audiophiles, after all there is a movement to minimalistic designs, tubes and analog music. But for multi-channel reproduction (and digital stereo) things are different.
At least in Holland it is difficult to find living rooms where multichannel/DVD and home entertainment equipment can be setup in an ideal fasion (all speakers on the theoritical best position) which would not require any setup of the amplifier or receiver system. And most AV receivers contain very sophisticated means of calibrating speaker positions to the listener. The latest equipment of B&O and some others contain logic to perform auto-calibration according to the specific room/furniture/position conditions.
It may therefore be useless for me to defend a position where I do not want to do any room correction in my combined analog/digital Hifi set. Modern homes, made of concrete floors and walls and wooden floors, interiors with designer leather couches, glass tables etc. make a less than ideal listening room for uncalibrated audio equipment. Initial simulations with Cara made me suspect that I may have a little too much bass and too little treble, but strangly enough it may be within "acceptable" limits (according to Cara).
Anyway, it explains my motivation for further work in this area. I might just end up with turning these good old tone-control knobs again.
The Shure equaliser is easy to setup; The pink noise generator output is connected
to an input of my amp and the microphone is connected (with a long cable) to
the input of the analyser. Then the fun begins: turn up the volume on the amp
and on the pink noise generator. As the mic is very sensitive, there is no need
for excessive sound levels as long as the noise level is 10dB above the room
noise. The pink noise generator generates an equal noise sound level for all
frequencies (by definition for pink noise).
Turn the hi-lo envelope (treshhold) to 12, the highest value, so that there is a +/- 6dB frequency band for low and hi measurements. If all is right all LED's indicate "low" sound levels for their corresponding frequency.
Then the input sensitivity is slowly increased until most of the LED's go out. In a reasonable damped room it should be possible to get all LED's out. Some might blink on "low"of "high" but in general it should be possible to get all frequencies withing the +/- 6 dB band.
After that, I tried to reduce the treshold bandwith from +/- 6dB to +/- 2dB
or even lower and maintain the same LED reading. In general I succeeded for
the +/- 1.5dB setting to get most LED's to be out with only the 16kHz LED being
"low". However, curtains and furniture position determine whether
the highest frequencies are reproduced correctly.
My Elac Dolce Vita speakers are equipped with a 360 degree supertweeter (aka
Calimeros) and therefore it relies upon room reflection to get a flat frequency
curve. This also means that aiming the microphone too strong to the speaker
will not give the correct reading.
I could even get a better reading when making small adjustments with the tone controls on my amplifier. But all-in-all I was already quite satisfied with the results.
Late on a saturday I started the experiment again and input all values into my notebook computer. I discovered I needed several "experiments" in order to be able to see a trend and reliably interpret the results (as far as I can trust the Analyzer to produce results).
First, it is not easy to get all the LEDs out; With the envelope set to 12 (treshold is -6dB to +6dB for LEDs to turn on), bass is above avarage and treble of 8kHz and 16kHz is lower than the 1kHz reference point.
The low-frequency fall-off of the microphone is calibrated for by the analyzer, and as a result both low and high frequencies are perfectly flat as far as the analyzer is concerned. On the front bezel there is a switch to select "roll-off"which results in a filtering above 1kHz of 3dB per octave. The manual recommends this setting, especially when using the Shure for live performances, as the flat setting might result in an overly bright music reproduction.
Of course I wondered whether I should use this setting as well, but initially I decided to do my experiments with a flat setting since after all it is the normal behaviour for music reproduction I assume.
And as the Dolce Vitas with their 360° supertweeter do have a natural fall-off built in (see the test in the German Audio Magazines about this speaker), and rely on some reflection of the room to get a flat treble reproduction I do think I don't need this setting. It was however no surprise that with the roll-off switch "on" the reproduction curve for treble was becoming even better.
What can you do to limit the effect of excessive bass? The on-lin Cara program promotes audio absorbers (apparently a sponsored link) and it even allows you to simulate your room with these absorbers placed in the corners of your room (preferrable behind your speakers).
For me, having one of these modern homes, I see no joy in making a mess of my living room again by putting all kind of absorbers in the corners of my room. Maybe it'll come to that but for the moment the WAF factor of such things is just not acceptable.
Now, by playing with the analyzer I did find out that closed curtains and a little rearranging of furniture can have a positive effect on the frequency response curve.
I probably need to redo this session with a digital room correction system, that will do these tests and more without me having to do anything. Moreover, it will make the necessary changes to equalisation, timing or phase response of frequencies (in stereo or multi-channel even).
The Shure equializer analyzer is focussing only on the frequency response of the listening room, and not on any of the other things that keep me from reaching the absolute audio nirvana.
But even so, I did get a good feel for the frequency resonse of my living room. As expected for a modern house (concrete ceiling, floor and walls) the bass reponse was a tid too high. But it was within acceptable limits. One could say that the readings of this test confirmed what I had already simulated with Audio Cara, but I'm glad I got the chance to confirm this myself.
I would like to recommend everybody to at least once verify their Hifi setup by means of a room analyzer. Your favourite HiFi shop might have one available for a weekend or so, and it will change the way you think of your listening room (it not being a recording studio that's for sure).
The following links and references are of interest for room analyzers
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