Electrovoice 205-4t Manuel D’Utilisation

such as speaker placement, boundary loading (are speakers placed close to a wall or in a 
corner?), size of the room, coupling of multiple speakers/subwoofers, reverberance of the room, 
the type of music, the type of activity and the expectations of the listeners all come into play.  

Hanging a subwoofer in the middle of a room results in the lowest possible output from the 
subwoofer. Placing a subwoofer at the ceiling, wall or floor increases its output. Placing it within a 
few feet of a 2-boundary junction (like a ceiling/wall junction or a wall/wall junction) increases its 
output further. Placement within 3 feet of a corner increases its output still more. In these cases, 
there is both an increase in sensitivity (output per watt of input) and in maximum total SPL 
capability. This can help in getting as much sound as possible from a few subwoofers. However, 
there is a potential pitfall in placing a subwoofer in a corner: You can wind up with uneven bass 
coverage in the room. 

Because there are often so few subwoofers, you can have a problem getting even coverage of 
the space. People sitting or standing very close to the subwoofer are going to hear excessive 
lows while people who are father away might not be getting enough.  

To resolve this problem keep in mind that  as you move farther from the sub, the volume drops 
off, typically at 6 dB per doubling of distance. Then, when you reach a certain distance, the 
subwoofer level stops dropping off at such a high rate. This is called the critical distance, which is 
where the reverberant field within the room equals the direct sound from the subwoofer.  The 
critical distance depends on how reverberant the room is. As you get farther past critical distance, 
even though the level of the subwoofer doesn't drop off nearly as quickly, the quality of the 
subwoofer sound might not be as good. But even though this may happen, it's sometimes 
acceptable for subwoofers in business music applications. 

One way to make the subwoofer coverage as even as possible is to use more than one.  In many 
places, it's a good idea to add a second subwoofer, or more. Even if you don't need additional 
subwoofers for volume reasons, you might want to consider them just for evenness of subwoofer 
coverage. Generally, if you have to use just one subwoofer,  it is best to sacrifice the sensitivity 
increase and place the subwoofer for most even coverage, as long as you can achieve the SPL 
goals. 

Practical distributed sound system installations almost always require the ability to handle 
multiple signal inputs. Pages may originate from two or more sources, the telephone system and 
a hand-held microphone, for example. Background music from two selectable sources, with 
muting keyed to the paging input(s), may also be required. There may even be a need for a low-
level noise-masking signal mixed in with the other signals at a consistent, adjustable level. 

For these reasons, combined mixer/amplifiers are commonplace in sound contracting. Designed 
to handle several audio inputs at different signal levels and source impedances, such units 
incorporate mixing and automatic muting along with amplification. By efficiently consolidating 
often-used functions in a single enclosure, they greatly simplify routine installations, reducing 
costs and increasing reliability. 

In this article, we examine the criteria for selecting mixer/amplifiers, describe the range of alterna-
tives offered by ElectroVoice Sound, and suggest applications for each. Our aim is to encourage 
appropriate equipment choices to maximize both profitability and customer satisfaction. 

The first step in selecting a mixer/amplifier is to examine the demands of the application. What 
are the intended uses for the system? Will background or foreground music be required in 
addition to paging? If so, from what type of source: FM/AM radio, tape, or both? Where will pages 

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