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Resonances from the room can turn the great sound from our expensive speakers into a drone that covers any subtleties of the music. Or the reverberations make it impossible to clearly hear percussive elements or vocals - or your instructions. The above picture is of the most challenging room I ever taught in. It had the amazing charm of a cathedral, but put on Guem et Zaka and all you hear is noise.

Here are some tips from my experience on how to get your precious music to your group with the best possible sound quality. 

1.  Dealing with Reverberation

Unless we teach Gregorian Singing, we want the room to have a “dry” sound, which means, we do not want the echoes of whatever has come from our speakers to cover the ongoing music. To check it out, clap your hands and listen to the room’s reply. Technically the echoes should decay within less than a second. One way of dealing with reverberation is to dampen the reflection of sound from the walls, ceiling and floor using sound absorbing materials. There are lots of materials for the professional treatment of rooms in that way, like perforated panels on the ceiling or bass traps on the walls, but if that is not an option, you can try heavy textile curtains on windows or walls, large cushions in corners or a large sheet of thick textile below the ceiling. (Filling the room to capacity with people also improves the acoustic properties of the room and warms the heart of the teacher.)
The other approach to dealing with reverberation is to bring the original sound as close as possible to the people. If you are not using the whole room as a dance space, bring your speakers as close to the limits of the dance space as you can. If you have, increase the number of speakers and spread them out along the dance space.

You might also try using speakers on the floor pointing upwards like stage monitors to get an immersive Sounds From the Ground experience and make the speakers  less dominant in their appearance yet close to the dancers. The closer to the speaker you are, the less will the sound heard be contaminated with echoes from the room. This also means, you might be better off with four (or more) speakers of reasonable quality than with one or two high end speakers.

2.  Dealing with Resonance

A bass sound of 100 Hz from your speaker has a wavelength of roughly 3,5 meters or 10 feet. Frequencies that “match” the dimensions of your room kind of get caught (technically speaking: form standing waves), and will be grossly amplified or cancelled. You will notice either a kind of drone at that frequency or a lack of warmth in the sound. A good speaker reproduces all frequencies at the same level, but even an average room can easily distort the spectrum by 20 db, which means fluctuation in the energy level by a factor of 100!
The simplest way of mitigating such effects is by not placing your speakers close to the wall, in corners of the room or standing directly on the floor. Although there are room simulation programs available to calculate the best placement of your speakers to mitigate resonance, I suggest experimenting. Sometimes moving a speaker just for an armlength can make a difference.
The next step is to use an equalizer to selectively reduce or boost frequencies that are distorted due to resonance. The usual bass-mid-treble controls that we have in our mixers are better than nothing but too coarse to effectively control the sharp resonance peaks or valleys. You do not want to turn down the whole bass part in your music just because you have a drone at 40 Hz. 

A better solution is a parametric equalizer. I am using a Behringer Ultra Curve Pro, but there are other manufacturers as well.

With that tool, you can attend to every frequency with precision. By connecting a microphone to it, it will even automatically determine which corrections to apply to the room. While it is true that the effects of resonance vary for different locations in the room and cannot be completely compensated by an equalizer, I am impressed by the tangible improvement of sound quality that I got from the Ultra Curve. It can also effectively block microphone feedback. At 230 € (less on Ebay) it was an investment that made me very happy.

Do you feel like diving deeper?

If you do not mind a little science, numbers and diagrams, REW is a free software that can run on your computer.

Plug in a microphone and it will analyse the acoustic properties of your room and tell you which frequencies need compensation and how effective your measures to reduce resonance and reverberation have been: https://www.roomeqwizard.com

Michael Kuehn, 5Rhythms teacher from Germany