Terminology and Concepts
If you are a performer new to managing your own sound, some of
the terminology you encounter here in the forum may be unfamiliar.
Here are some terms that come up fairly often when discussing
the Bose Personalized Amplification System™ family of
products. I've added some quick explanations and references.
Most of these are terms that sent me searching for definitions within the first
few months of owning my System. I hope you find this helpful.
If you have suggestions, additions, or corrections please
me a private message.
amplifiers that musicians typically have on stage (behind them) to amplify the
sound of their instruments. Examples: Guitar amps, Bass amps, Keyboard amps.
Comb filtering occurs when two identical (or nearly identical) signals, one
delayed in time relative to the other, are added. Depending on the delay time,
the resulting summed signal can sound hollow or “boingy”, and is usually
considered an undesirable sound.. Comb filtering occurs most commonly when
signals are combined electronically, such as in a hard disc based recording
system, but can also occur acoustically, such as a talker located slightly off
axis of two identical microphones spaces inches apart.
Ken-at-Bose for this information).
Please see: Nulls and Phase
a DI when you want to connect two devices and you have any of these issues:
- impedance mismatch
- line level mismatch
- differences in wiring or connectors
(e.g. Balanced XLR to
Unbalanced 1/4" Tip-Sleeve)
- noise - especially "hum" (ground loop)
A DI unit or DI box is an electronic device designed for connecting a
piece of equipment with an electronic audio output to a standard microphone or
line level input. It performs both level and impedance matching to minimise
noise and distortion. DI is variously claimed to stand for direct input, direct
injection or direct interface. DI units are extensively used with professional
and semi-professional PA systems and in sound recording studios.
You will also see the term DI used to refer to devices used to modify the
tone as well as other properties of a signal. This is often in the context of
Acoustic Guitar and Electric Bass. In the picture above the first
two are passive DIs used for solving problems. The others are
as DIs that also shape the sound.
This is amplifying the same sound source through two separate loudspeakers.
vs. Mono in a Live Setting
mono is usually not a good idea ...
Can I use
it as a PA? (Cliff-at-Bose talks about Dual Mono)
Equal Loudness Curves
(also known as Fletcher Munson curves)
"You will see lots of references to equal loudness curves or equal loudness
contours- these are based on the work of Fletcher and Munson at Bell labs in
30s, or perhaps refinements made more recently by Robinson and Dadson. These
were made by asking people to judge when pure tones of two different
were the same loudness. This is a very difficult judgment to make, and the
curves are the average results from many subjects, so they should be considered
general indicators rather than a prescription as to what a single individual
and Initials of Acoustics
Fletcher Munson Curves
See Equal Loudness Curve (above)
Gain Before Feedback
Gain before feedback refers to the maximum sound pressure level that can be
attained before the sound from a speaker enters the microphone and is amplified
a second time, creating a loop that only builds on itself: feedback.
An often not very scientific measure of how loud a sound reinforcement
system can be turned up before any open microphone(s) will feed back. The point
at which feedback occurs is effected by numerous variables, including
atmospheric conditions (temperature, humidity, etc.) so it's not something that
anyone considers an objective measure of performance. Instead the phrase is
to state relative differences: "By adjusting the EQ I was able to get 'more'
gain before feedback."
Inverse Square Law
Doubling the distance drops the intensity by about 6 dB and that 10 times the
distance drops the intensity by 20 dB. Click the image to the right to see the
page in which it originally appeared.
Localization, Spaciousness and
Originally posted by Hilmar-at-Bose:
There may be some confusion about “localization” and “spaciousness”. Both are
perceptual attributes, which have been intensively studied especially in the
context of concert hall acoustics.
“Localization” refers to your ability to detect the direction of a specific
sound source. Let’s say you have your eyes closed but you can immediately tell
where the guitar is (as opposed to the bass or the violin).
“Spaciousness” refers to the perceived size of the sound source and how much
you feel enveloped with sound. Most researchers believe that a “good” concert
hall provides both: accurate and easy localization and a sufficient amount of
spaciousness. The main contributing factors for spaciousness are “early lateral
reflections”. These are reflections from the sidewalls. Reflections from the
side help quite a bit with creating a sense of space and envelopment.
from the floor and ceiling are less desirable since they don’t enhance
spaciousness but can negatively impact clarity and spectral balance. There are
very interesting physiological reasons of why lateral reflections are perceived
so much differently than vertical ones. I could drone on for hours on this
topic, but I’ll save that for later. Anyway, it’s not too much of a surprise
that most renowned concert halls (e.g. Musikvereinssaal in Vienna, Concertgebow
in Amsterdam, or Boston Symphony Hall) have a “shoebox” shape that is long,
narrow and tall. This shape provides good lateral reflections pretty much
everywhere in the audience. Ironically, it’s not very popular with architects
since the sight lines are terrible. Visually oriented architects prefer the
“shell” shape, which provides great viewing but (unfortunately) no lateral
reflections whatsoever. But I’m digressing again… The L1 does (in my humble
opinion) the best thing. It radiates very wide horizontally but very little
towards the ceiling. Thus it provides enough energy for lateral reflections but
keeps interfering ceiling reflections at bay. Since it’s a single source, it
provides very easy and accurate localization, but in most venues the image will
also be pleasantly spacious. That’s at least my own experience. -
it in context -
Originally posted by Ken-at-Bose (later in the same discussion):
What we perceive as "reverberance" is caused physically almost entirely by
the persistence in time of an acoustic event.
Spaciousness -- the feeling of envelopment and room size is different.
Localization -- where we perceive the sound to be coming from -- is different
again. Localization is almost entirely determined by the direction of the first
arrival of sound (almost always the direct sound from the speaker in this case)
and thus is almost entirely immune from the effects of reflections.
is heavily determined by lateral reflections, which are produced in relative
abundance by the L1 because it's so wide in its pattern.
High reverberance is caused by lots of reflections in rooms with little
absorption. The L1 is particularly good at NOT producing as much reverberance
because it sends little sound to the upper walls and ceiling where many
detrimental reflections originate and are perpetuated. -
it in context -
Dead spots or areas of a room where there is a significant drop in
When your sound is hollow, diffuse, and thin, you may be experiencing nulls
or comb filtering. This is usually the result of a single sound source be
amplified from several loudspeakers. Phase
Out of Phase (for Drum mics)
Originally posted by Hilmar-at-Bose: Here's the nerds view :) Wiring the the
two mics out of phase creates essentially a "dipole". Everything that is in the
middle (i.e. equal distance) between the two microphones will get equally but
out-of-phase so it cancels when the two microphone signals are summed together.
In essence it creates a "blind spot" for the microphones for whatever is right
in the middle plane. For the drums, that's mainly the kick (as Larry pointed
out) and also the drummer (when he/she is hemming and hawing, squeaking with
chair, yelling about or in general having a grand old time). Another nice trick
is to place the L1 that gets the mic signal somewhere the middle plane of the
microphones. This drastically reduces potential for feedback and unwanted
regeneration. Sound sources that are significantly closer to any one of the
microphones are not much affected by the whole procedure.
See the entire discussion in context:
Wiring two SM 75s with a Y cord
Phase (cancellation, interference)
Phase cancellation occurs when two signals of the same frequency are out
of phase with each other resulting in either a boost or cut in the overall
of the combined signal.
Phase at the Zen Audio
If you are suffering from some or all of these, you could be experiencing
- "Hot" and "cold" spots in the audience area
- Tonal coloration
- Poor speech intelligibility
- Lack of music clarity
- Poor gain-before-feedback
- Poor imaging
Realities of Phase Interference
On the PS1 power stand, there are selectable presets for Channels 1 and 2.
Bose has created optimized settings for specific microphones, instruments and
applications. For more about how to work with them see the
section in the Unofficial Users' Guide.
devices are often placed between an instrument and an amplification system to
modify the tone and other aspects of the sound of the instrument. Some
are using these in place of backline amplifiers and running their processors
directly into their Bose System. Typically these can be run into Channels 3 or
of the PS1 powerstand. They can also be run to Channels 1 or 2 with preset #00.
The bass response of all directional microphones is increased as the signal source
- your voice - comes closer to the mic capsule. This is called Proximity Effect
and it becomes apparent at a range of one foot and increases as the distance of
mouth to mic decreases.
For speakers or singers with high or thin voices, proximity effect can boost the
bass, filling out the sound.
- source Shure Notes