Ice Rink Sound
Most skaters are aware of how bad ice rink sound typically is. Why is this? Is there something inherent about ice rinks? Are there any remedies?
Although I don't consider myself an acoustics expert, I have had some experience in sound, and I have skated in many rinks, most of which have terrible sound. I have also skated at a couple that have excellent sound. The ones that I have skated at that were good have used a common strategy: control the acoustics of the room, then install a decent speaker array, centrally mounted.
Acoustics
Envision a typical rink. Hard surface floor, concrete walls, metal ceiling. There is virtually nothing in it that absorbs sound. The net effect is a room that is in essence an echo chamber, with reverberation time of 5 or 6 seconds. Possibly OK for a medieval cathedral, but bad if any sort of intelligible sound (especially voice announcements) is required. Because the room is inefficient at absorbing sound energy, the listener is bombarded with delayed versions of any sound that is produced (including skater and equipment noise), resulting in an unintelligible muddle. To make matters worse, rinks commonly have parallel walls, leading to large numbers of resonant modes: it will strongly reinforce certain frequencies, leading to extremely uneven frequency response. The sound from any noise sources such as compressors, dehumidifiers, Zambonis, and skaters bounces around instead of being absorbed, so it is heard many times and is hence unnaturally loud.
Typical recommendations for the reverberation time of a room of this volume (A typical rink might have 750,000 cubic feet) would be 1 - 2 seconds. What would it take to bring our rink of 5 sec reverberation time into a reasonable range? It would take a bunch of sound absorbing material.
How much? Well, a commonly used equation for the reverberation time of a room of volume V (in cubic feet) is:
T = 0.049 x V / A
where A is the total absorptance of the room, in Sabins (a Sabin, named after the acoustician who came up with the formula, corresonds to one square foot of area that absorbs all sound that hits it). Assuming that the room initially has a reverberation time of 6 sec (you could also guess at the acoustical properties of all of the exposed surfaces), you could calculate that a 750,000 cubic foot rink has a total absorptance of about 6150 Sabins.
Supposing you want to get reverberation time down to 1.5 sec, What do you have to do? The equation would tell you that you need to have a total absorptance in the room of .049 x 750,000 / 1.5 = 24,500 Sabins. Subtracting the 6150 Sabins that are already there, you would want to add 18350 Sabins of absorptance to the room. This is quite alot, of course!
One possible solution would be to mount sound absorbing panels on the walls. Given a rink room that is 110 x 230 feet, with 30 foot walls, the total surface area of the walls is only 20,400 square feet, so you would have to completely cover the walls with sound absorbing material.
An alternative would be to hang sound absorbing panels from the ceiling. An adventage is that both sides of a hanging panel capture the sound, so less material can be used. Assuming 4 x 8 foot panels, 10,000 square feet of material would require 312 panels. Given that 28 panels would fit lengthwise in the length of the room, you could get close to your goal with 10 rows of panels. Given creativity in installing it, some appealing visual effects might be obtained.
An Example
I recently skated at the Skating Club of Boston, and was surprised at the
changes to the ceiling. The new radiant barrier (to reduce refrigeration
costs) is augmented by 600 2 by 4 foot fiberglass panels (hanging edge down)
covered in thin plastic. The total exposed surface area is 9600 square feet. Compared
to my impressions from the last time I skated there, the quality of sound is dramatically
improved. The following photo shows this installation.
Speakers
It is tempting to believe that rink sound problems can be solved by installing more hardware (more speakers, bigger amplifiers). If the objective is lots of noise, then this is a good approach. If it is good sound (and, despite some opinions to the contrary, there IS an objective definition of this), the acoustics problem first MUST be addressed first.
Assuming a reasonable acoustic environment, what speaker arrangement would be good? I will state flat out that the best systems that I have heard had a single, center-mounted array. Visit any large facility designed for public events, and you will find this type of speaker installation. There are good acoustical reasons for this: If multiple sound sources are used in a large room, you hear all of them, but the arrival time from the different speakers is different. If the speakers are widely separated, the different arrival times will amount to artificial echos, which muddle the sound.
Consider a rink with speakers at both ends (I have experienced this!). If you are at one end, you can hear sound from both speakers. The sound from the ther end is delayed by 0.18 second. This is confusing in Ice Dance music, where the duration of a beat might be only 0.5 second (not to mention what it does to intelligibility of speech!).
Summary
Successful sound can be achieved in ice rinks. It is never achieved without addressing room acoustics, unless the room just happens to have lots of insulation stuck on the walls (a case of good luck). Properly addressing the acoustics is expensive, but given a better room, a surprisingly inexpensive sound system can suffice. This must be weighed against the marginally effective attempts at achieving success by adding speakers and amplifiers, which can also be very expensive.
Finally, I would point out the obvious fact that people who sell sound equipment are usually interested in selling sound equipment. They are unlikely to even consider alternatives to selling more equipment. Don't make the mistake of thinking you are going to cheat physics by paying more money for sound equipment, when the real problem is bad acoustics.