Apogee Group LLC Blog

Trials and Tribulations of Business & Healthcare

High quality multi-zone commercial audio system on a budget

Posted by Alexander Komarov • Jan 23, 2011 • Category: IT

Author
Alexander Komarov
Most commercial spaces I've been in have mediocre sound - at least so it would seem, their system may simply be improperly used. This is of course untrue of Bose showrooms and movie theaters, but I'm talking primarily about businesses that don't focus on sound - like gyms, restaurants, grocery stores. The typical setup consists of a bunch of ceiling speakers and some amplifiers in the closet, perhaps a CD changer or radio. Sometimes this setup produces fairly decent sound, but most of the time some of the frequencies just aren't there.

Surprisingly, these mediocre systems often cost tremendous amounts of money - but there are certainly ways of getting more value out of the audio investment. This is what this project attempts to achieve.

First, let's look at the decision process surrounding the possible options.

Decisions Decisions

Ceiling Speakers

Ceiling speakers are tricky simply because of what they are - a driver in the ceiling. A quality driver is matched to its cabinet, which is responsible for reinforcing the lower frequencies, proper resonation, etc. Ceiling speakers, then, have some disadvantages:
  • A ceiling speaker (most of the time) has no cabinet at all, making the open plenum space its (unpredictable) resonator. Some come with fitted cabinets (plastic buckets), at increased cost.
  • Another issue with ceiling speakers is that in a typical commercial setting the ceilings are fairly high. This is both bad and good as a distant speaker creates more even coverage (no extra-loud spots), but it needs to be more powerful to reach the people below.
  • A ceiling surface is also probably a considerable area to cover for even distribution, which means a large number of speakers.
  • Good ceiling speakers exist (in fact, even good impedance-matched speakers exist) but cost a substantial amount. If you are going for the inconspicuous look and ceiling (or in-wall) speakers are your only option, then the extra expense may be justified. Some examples are shown.


Wiring

Then there is the wiring. A typical speaker has 8 ohm impedance, and impedance drops if you wire speakers in parallel (or increases when wired in series). The reason this is bad is that a regular amplifier cannot tolerate a significant impedance deviation from its normal design target (typically 4,8 or 16 ohms). Lower impedance means that your amplifier is working too hard (likely to the point of a meltdown), higher impedance means that it can't drive your speakers at sufficient volume. Hence there are only a few wiring options that produce a working multi-speaker setup:
  1. Get a lot of amplifiers. For example, if a small(ish) amp drives two speakers and you have 20 speakers, set yourself up with a nice rack of 10 units, and run 20 wires to the rack. Of course in a hacky set-up you might buy a few low-cost 7.1 home receivers, set them to "All-Channel-Stereo" or similar mode, and drive 7 speakers at a time with each amp, but the idea here is that you drive only one speaker per amplifier channel

  2. Series-Parallel
    Wire them in series+parallel. For example, a string of five 8 ohm speakers wired in parallel is 1.6 ohms ( 1/(1/8 * 5) ). Hook 5 of those strings in series and you're back at 8 ohms (25 total speakers). This is great while it works, but a single blown/shorted/miswired/disconnected speaker can destabilize the whole setup, potentially damaging the amplifier or causing unexpected volume changes, even creating different volumes in different strings. The other concern is that the total wattage being fed to this configuration is probably fairly high, at low voltage, meaning high current. In other words, the wire connecting the strings to each other and to the amplifier must be able to carry this much current, and ideally have very little voltage-drop over the distance required in your configuration. In other words, you need really thick wire!

  3. Use impedance-matching transformers. This is the principle of operation in 70V and 100V systems. The idea is that the amplifier puts out a high-voltage signal, but because the voltage is high, the current can be low (and the speaker wire can be thin and cheap).
    70V wiring
    Each speaker is then connected in parallel through a matching transformer, which makes the signal appear to be 8 ohm to the speaker. The transformer will typically have several taps (coils) that allow a configuration that all adds up to about the right load, and even permits specific speakers to be louder/quieter than the rest. Each speaker gets a fraction of the ampifier power, and a certain amount of quality degradation occurs as well (more for low quality components). A common 70V ceiling speaker configuration may drive each speaker at 4 watts - enough to be heard but not enough for full-range sound, as low frequencies require more power. The principle of operation here is very similar to high-voltage power lines: Send high voltage over great distance to minimize wire gauge and power loss, then convert it to the voltage you need at the destination (eg to 250v/120v for household use).

Also, in commercial environments where wires are pulled through the plenum, all wire typically has to be plenum-rated to meet code. Plenum-rated low-gauge speaker wire is not cheap! Anything plenum-rated is more expensive, and it becomes significant when you need a large quantity - for example, a 1000' spool of 14/2 speaker wire is $300, 16/2 is $200. If you choose to use powered speakers (as I did, see below), 22AWG shielded balanced audio is only about $90 (Markertek) at this time. This is even cheaper than plenum-rated CAT5e.

Amplifiers! Then there are amplifiers. Option 1 requires a lot of weak(er) amplifiers, Option 2 requires fewer (or just one) powerful amp (and thick wire), Option 3 requires one or more 70V (or 100V) amplifier and 70v speakers (and less wire). Either way, can't forget the cost of amplifiers

Cabinet Speakers

Cabinet Speaker
Or, shall we say, visible speakers.
The pro's of this type are obvious:
  • Matched to cabinet for better sound
  • Can be larger as they aren't designed to fit in tight spaces
  • Can be optimally positioned (closer to the listener, perhaps)
  • A powered speaker is an option which simplifies the amplifier configuration (no amplifier needed)

Of course, these speakers are large(r), visible, and hard to integrate into decor if you're going after a particular look. They will often require wall mounting, or proper mounting from ceilings (flying) which has some liability considerations and should not be done carelessly.

Music Sources

As we were looking for continuous music in all the zones, we needed a source of music that would ideally be non-repetitive and flexible in genre. We also wanted to avoid copyright issues, naturally. Since in our setup music is largely sourced from the servers, pirated MP3's were not a good choice. For that matter, public playback of a CD is probably questionable as well. The choices boiled down to:
  • CD player.
    This could work, but you need to research copyright issues. You'd probably need a changer, and there is only so much variety that you can get from even 6 CD's
  • MP3s on hard drive
    Same issues as above, except variety is easier to achieve. Legal issues are likely more problematic.
  • Personal IPods (that come and go)
    Legally speaking, this somehow feels safer because of their nomadic nature, though I'm not a lawyer. Practically speaking, this is a human-reliant configuration that's prone to failure - someone forgets their IPod, forgets to plug it in and turn it on, they have some inappropriate content that gets into the playlist, etc.
  • Internet Streams (free, eg Shoutcast).
    While I cannot speak on the legality of this option, the transient nature of streamed data certainly feels better than possession of copyrighted material. RIAA has gone after stream publishers, if I recall, but you'd have research the current state of affairs. As these are free, a lot of publishers include advertising in the broadcasts, and some of the ads may conflict with your business offerings
  • Internet Streams (paid, eg Sky FM)
    Same as above, minus the ads, and at better quality. Typical bandwidth requirements are 256kbit for pretty good sound (per zone).
  • Paid ISP-provided music Streams (eg Comcast, Cablevision, Verizon, etc)
    Same as above but without bandwidth requirements. Typically fewer channels. Requires hardware (eg cable boxes) per channel.
  • Good old radio
    FM or XM is of course an option. For XM, same issues as Paid ISP hardware above.

The Case At Hand

My challenge was to design and put together a low cost (relatively speaking) system that would impress people with quality (not by loudness), providing that "beyond expectations" experience. These were my requirements, give or take:

Design Goals

  • Quality Sound
  • Non-exorbitant pricing
  • Multiple Zones. The space is 21,000 sq ft, with the main audio areas being:
    1. Fitness Floor (7000 sq ft) - must be able to adjust volume of each speaker individually
    2. Group Exercise (2000 sq ft) - potentially louder than Fitness floor. Some walls are glass, so watch out for flutter echo
    3. Lobby/Cafe (Tazi's Cafe, incidentally) (2000 sq ft). This area is also to become a mini movie theater in the future. This means that we would have a surround sound setup driven by the projector screen location, and use part of it for everyday music (probably only two speakers).
    4. Bath/Shower/Changing Rooms - no specific design goals other than having some sort of music in there, more or less evenly covering the space
  • Ability to play background music (different channels) in each zone. Channels should be easy to change.
  • Ability to plug in microphones, IPod's, etc to any zone temporarily for events
  • Ability to send sound from any zone to any zone
  • Speakers do not have to be hidden, but should not be ostentatious.
  • Set up should be able to support or at least integrate with live performances as needed
  • Integration with the (Asterisk-based) phone system (Public Address) would be nice

With this in mind, I made the following decisions:

Design Decisions

  • Speakers will be powered wall-mounted cabinets (Behringer B215D). These are PA speakers but they fit the bill very well - plenty of power, plenty of clarity, and wall-mount brackets are available (and they are half the price of comparable Mackie speakers). These are not flyable, but are vertically wall-mountable. As they are powered, we needed 120V outlets (switched, ideally) near each one. As we were still in mid build-out this was easily accomplished (We turn the speakers off at night from wall switches in the audio closet).
  • All audio wiring would be balanced. (Meaning 3 wires per channel, not "balanced" as in stereo - Wikipedia explains this well). This allows for no signal loss over very long runs (We have runs that are over 300 feet). Something like this audio wire is an example, though I got my wire from Markertek. Most wiring is terminated with XLR connectors (on patch panels when appropriate). We wound up pulling 4-6 runs of this wire between the audio closets and the server room, only to realize sometime later that multi-cable "snake wire" would have simplified pulling a lot.
  • As I was sending balanced audio signals everywhere, each zone would have an audio closet (or a semblance of a closet) with an audio mixer (used musical gear is often affordable if you don't care how scratched up it is). I was able to find some old editions of the Alesis Studio 12R on Ebay for about $100 each - they are completely overkill, but why not?
  • The fitness floor has 5 speakers, and is not a good candidate for stereo sound. In fact, even the other rooms may not be, but here we would like control of individual areas, in other words - control of individual speakers. This is done by a 5-zone mixer, I found a used ART-405 at Music Go Round
  • Background Music would be provided from a server PC. Servers are already on, so why not? Each zone gets a $9 USB sound card, an instance of mpd (linux media player), and all of this is controlled with MMPD (PHP app I wrote). This way the employees can change what's playing where, and send the output to any zone. We use internet streams (some premium) for the music. This also means that music can be controlled from any PC on the local network
  • Because cheap USB sound cards do not output balanced level audio (and they aren't in the same room as the mixers), I use a DI (Direct Interface) to balance the signals (see above) so that they reach the professional equipment intact.
  • Bathrooms will be served by a 70V ceiling speaker system (leftover from prior location), these are low quality speakers but are good enough for the bathrooms. We ran 16 AWG wire in parallel, installed the speakers, and rack mounted our old TOA 60 watt amplifier next to the mixers that serve the rest of the space - bathroom is done. It doesn't have its own zone per se, but it can play what's being played in either the Fitness Floor or the Lobby
  • The Lobby (Cafe) only has two speakers at this time, with provisions for 5 (5.1 Surround for future Movie Theater). Only the "rears" are installed as they provide the best locations for the background music. The 'Audio Closet' is a wall-mount IStarUSA cabinet housing a DI, the future receiver, and one Behringer Ultralink (a flexible rack-mounted mixer-like creature)
  • Asterisk (the phone system) can output to the audio system for PA (Public Address) - this is done by simply running audio from the sound card on the PC to one of the mixers (via the DI). Also, the phone system can control the music (you can play/stop/etc from any phone), in addition to contols via Web interface (see above). I wrote details of this in another blog
  • Future movie theater is expected to be set up using a conventional 5.1 (or 7.1) surround sound receiver + the DI I mentioned earlier. This is much cheaper than buying a receiver or decoder with XLR outputs
The following is a high-level wiring layout of this system:

What this picture doesn't tell you:


Apparently it's a little tricky to share your powered speakers between two sources. Normally you would use a mixer but in this case it would create loops that I need to avoid. The problem is that I want to drive the speakers with our surround-sound receiver (my speakers are rears in this setup) while watching movies, but when not watching movies they should be driven by the mixer for background music or live performances. (The two blue arrows going to the same speaker on the Lobby diagram). You could fix this by having someone raise/lower volumes or switching plugs as needed, but the potential for human error is too great.

As I didn't want to keep the receiver on all the time when it's really only used occasionally, I wound up building a relay-based auto-transfer switch - when the receiver is on, it switches the XLR connections to the Receiver/DI combination. When it's off, the XLR cabling is connected to the mixer for background music. If anyone wants the diagram, ask and I'll post it here.

Result


The result: while this setup was a lot of work (and a lot of soldering), the sound is excellent, sound routing is very flexible, and when we host concerts in our space the performers typically do not need to bring speakers. Total cost of the system so far (11 550-watt speakers, 5 mixers, 2 8-channel DI's, wireless mic, handheld mic's and stands, all wiring, every single connector/cable/patch panel, rack, cabinet, sound cards, etc) is about $6K. The cost was lower because of opportunistic used equipment harvesting (Ebay and Music-Go-Round, primarily), and inheriting a TOA 60w 70V amp and some speakers for the bathroom. Servers are not included in the total as they are multi-purpose machines and playing music is only a secondary occupation.

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  1. Great article very very helpful. Thank you!
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