Access 902 User Manual - page 11
10
Equal Volume Comparisons (902 Only)
The Equal Volume Comparison, or EVC Section of the Control Panel, provides a variety of advanced features
to enhance your demonstration capabilities. Generally, these features are:
1) Automatically adjusting for equal volume levels among speakers when performing A/B-type
comparisons.
2) 2 levels of audio Muting to instantly lower the demo volume by a preset amount when you need
to talk over the music.
3) Digitally display in decibels the current Sound Pressure Level (SPL) in the demo area.
The concept and need for equal volume product comparisons is based on two facts. First, a limitation of
human hearing is that our sensitivity to low, middle, and high frequency sounds varies with the volume level.
As the volume level decreases, our sensitivity to low and high pitched sound becomes progressively worse.
Conversely, as the volume, or SPL, increases our hearing steadily improves to provide a more even response
across the full audio spectrum. For this reason, in any A/B-type product comparison, the products being
auditioned must be played at exactly the same loudness to negate this deficiency in our hearing.
The second factor is that audio components vary randomly in their electrical sensitivity, or efficiency – that is,
with the exact same input signal, two different components will likely produce differing amounts of output.
This characteristic is most pronounced in loudspeakers, but is also found in amplifiers. However, a product’s
efficiency is not necessarily a measure of quality or accuracy.
These two factors combined mean that in any A/B-type product comparison it is imperative that the demon-
stration system provide a convenient and accurate method to eliminate any volume differences between the
products being auditioned. Otherwise, the listener will almost always hear the louder product as sounding
better, even when its reproduction quality may actually be inferior. For valid product comparisons, all
products must be playing at exactly the same sound pressure level. That is what EVC is all about.
Despite its importance and benefits, providing equal volume demonstrations in a showroom setting usually
requires additional education, training, time and effort for salespersons. However, with the Model 902, this
critically important aspect of your product presentation can happen automatically! The 902’s EVC Section is
able to sample the relative efficiency of each component within a Product Group and store its relative effi-
ciency. When EVC is ON, selecting a product automatically recalls its relative efficiency, adjusts its loudness,
and allows the 902 to play each product at exactly the same volume level.
Equal volume adjustments are performed by the Model 987 Audio Level Module, which is included with the
902 Control Panel. This 987 Module is inserted in the system’s signal path just prior to the input bus of each
amplifier group (see diagram). Each 987 has 4 channels (two stereo pairs) available. Additional 987 Modules
can be used to adjust more than 4 channels. The 902 also includes a precision calibration microphone (typi-
cally hung from the ceiling) which allows the 902 to measure the SPL in the demo area, and in turn control the
987 Audio Level Module.
EVC can only be applied to corresponding speaker and amplifier Product Groups, that is, electronics and
speaker Product Groups with matching Group numbers. When a valid Product Group is selected, the EVC
window will display two dashes (– –) if EVC is OFF, or the selected product’s relative efficiency (an attenua-
tion value between 0.0 and 30.0 dB) if EVC is ON.
The EVC section’s control keys and multipurpose display window are associated only with the currently
SELECTED product in the ACTIVE Product Group (the one with its red LED ON). When EVC is ON, that
product’s relative efficiency in decibels is shown in the display. The least efficient product in the Group will
display a value of 0.0 dB, or no attenuation. More efficient products will display the number of decibels of
attenuation necessary to achieve equal volume.