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Frequently
Asked Questions (FAQ)
You will find most
of the information you need to get the best out of Turbosound products
from either the engineering data sheets or user manuals for that product.
However here are some of the most frequently asked questions about Turbosound
products that may not be covered. If you do not find an answer here to
your specific question or audio problem, please email us (click the email
button at the top right of this page) and we will endeavour to give you
an answer.
Turbosound
Power Ratings Explained
Our loudspeaker ratings
are deduced as follows:
RMS - i.e. rated as the power handling of the loudspeaker using a predefined
signal which is applied for 100 hours (we only do 8 hours), after the
test there should be no physical or performance change in the loudspeaker
(IEC-268-5). The signal is heavily clipped (2:1 peak to RMS) pink noise,
shaped with a defined IEC filter broadly imitating the frequency content
of an average music signal.
The reason the signal is clipped so heavily is so that the test really
only indicates the long term heat dissipation capabilities of the loudspeaker,
and is not effected by any spurious huge instantaneous impulses (which
do occur in true pink noise). This provides a very useful indication of
how the loudspeaker will perform in real applications over long periods
of heavy abuse.
As a side note we have started to test our floor monitors to the same
method but with unclipped pink noise, because monitors are much more likely
to encounter occasional huge impulses from dropped mics and feedback etc.
The 'program' rating
can then be explained as follows:
The loudspeaker test signal used has a crest factor (peak to RMS ratio)
of 6dB (2:1), but in reality full range music has a much higher crest
factor of over 9dB.
Amplifier power ratings however use sinewave signals (calculated on maximum
power delivered into a load using a before the onset of distortion). However
sine waves only have a crest factor of 3dB.
By using an amplifier which has a RMS rating twice that of the loudspeaker,
the system can run at the maximum rating of the loudspeaker and also cleanly
reproduce signals with a crest factor of 9dB (3dB amp headroom and 6dB
from the doubled RMS rating). i.e. the peaks in the reproduced music can
be 9dB higher than the average.
Well designed loudspeakers
are easily able to handle these peaks and more without mechanical destruction
(that's what suspensions are for !) and also high quality amplifiers are
generally capable of providing slightly more power when necessary for
the occasional peak impulse. The end result is that dynamic music, with
a high crest factor, can be reproduced on a well matched sound system
which is running 'hot'.
Therefore we recommend
amplifiers with power ratings twice that of the loudspeaker which is shown
as our ‘Program’ rating.
Q: What is the
correct angle between cabinets in order to get even coverage?
A: A good rule of
thumb is to calculate 60% of the nominal horizontal dispersion angle of
the cabinet at the -6dB points, and splay adjacent cabinets at that angle
(50° x 0.6 = 30°) as your starting point. Then walk across the
front of the PA using familiar program material as your music source and
listen for peaks and troughs in the frequency response as you move between
cabinets. Fine-tune the angle until you achieve the desired result.
Q: What is the optimum size
of power amplifier for my speaker set-up?
A: You should use
an amplifier that whose broadband r.m.s. power rating is equal to twice
the stated r.m.s. power handling of the loudspeaker at its nominal impedance.
For example the power handling of the TSW-718 is 800 watts r.m.s., and the
nominal impedance is 4 ohms. Therefore you should use a good quality power
amplifier capable of delivering 1600 watts per channel into a 4 ohm load.
Q: How can I calculate the
sound pressure level at a known distance from the PA?
A: Sound intensity
reduces rapidly in intensity at a distance from the source according to
the inverse square law, which predicts that a doubling of distance will
result in a reduction of ¼ the original, equal to a drop of 6dB,
providing there are no reflections or reverberation. For example, in an
open space where the front seats are 6 meters (20 ft) from the sound source
and the back seats are 60 m (200 ft) from the sound source, you would
expect the sound pressure to drop by a factor of 100 (=20 decibels) between
the front seats and the back seats. In a real world auditorium, this reduction
is partially mitigated by the effects of reverberation in the distant
field, and in the near field because the speaker looks more like a wall
source than a point source. However in a real-world situation like an
auditorium, this reduction is partially mitigated by the effects of reverberation
in the distant field, and in the near field because the speaker looks
more like a wall source than a point source. Therefore the sound field
in a room only behaves according the inverse square law in relatively
narrow distanced range.
Q: What does a Loudspeaker
Management System actually do?
A: The concept
of an Loudspeaker Management System is to provide all the electronics
you might need in front of an amplifier in one box.
In an active system
the crossover comes before the amplifier. This means you need more amplifier
channels to deal with the split up frequency bands but gives massive advantages.
In low voltage electronics
it is much easier (and more efficient) to manipulate audio than in passive
crossover networks. For example a single power amplifier powering a passive
crossover which splits the frequency range into two drivers has lots of
problems:
1. You lose a lot
of energy (amplifier watts) as heat in the components of the crossover.
2. It is not possible
to design steep roll-offs so a broad band of frequencies are covered by
both components, which causes smearing between the drivers and potentially
raises the distortion from the individual components. An obvious example
is an HF compression driver run at low frequencies, being forced to produce
bigger mechanical excursion and hence more distortion.
3. When you get near
the limit of the amplifier you will often hear the HF component “pumping”
as large amounts of energy are consumed by the low frequency transients.
Additionally the
distance between the components and your ear is different due to the horn
length of the HF, and therefore the arrival times of 50Hz and 18kHz audio
signals is not the same.
Moving the crossover
outside the cabinet and before the amplifiers solves these problems:
1. All of the electronics
are low power and therefore little energy is lost to heat
2. It is easier to
design steep roll offs (upto 52dB per octave) with digital processing.
This also enables more output from the speakers as they are individually
handling smaller bandwidths
3. By having 2 separate
amplifiers the LF performance has no effect on the HF performance.
By adding delay it
is possible to delay the LF to match the arrival of the HF, again helping
to make the image more intelligible.
The rest of the system:
In addition to the
passive system components you are likely to use some kind of graphic EQ,
and perhaps a compressor/limiter in front of the amplifier and passive
speakers in order to get them to sound the way you want and compensate
for any bad reverberations in any particular room.
All Turbosound LMS
series units are digital processors. This means it is possible for us
to put everything in one box.
So we have EQ both
for the room and the drivers. We have delay to align the drivers within
the box. We also have limiters which are set for each individual component
and can be set to ensure you do not damage the long term reliability of
your drivers. These can also be set optimally for your amplifiers.
You can also use
them to divide and run totally separate systems, perhaps as delays or as
a separate zone of an installation.
Q: Why does Turbosound
often use 1" HF compression drivers in preference to 2" drivers?
A: Generally we prefer
the cone-type mid range drivers (12's, 10's and 6.5's) to do most of the
work in three-way and four-way systems to cover the vocal frequency range,
and not allow a break in the middle of this range between two unlike driver
types. This is why Turbosound speakers have that characteristic 'forward'
nature, very often referred to as being 'in your face'. So the compression
driver is normally designed to handle only high frequencies above 3 or 4kHz,
and in some cases as high as 8kHz, where it is under minimal mechanical
stress and therefore far less prone to failure than a 2" driver handling
a wider frequency band. We have also found that 1" compression drivers have
a far sweeter sound than 2" drivers, which can be harsh.
IP Ratings Explained
IP (Ingress Protection)
Rating for Equipment and Enclosures is a three-digit number and is used
to provide a definition a piece of equipment's suitability to different
forms of environmental influence:
The first digit represents
protection against ingress of solid objects
The second digit
represents protection against ingress of liquids
The third digit represents
protection against mechanical impact damage.
The third digit is
often omitted, resulting in a 2-digit IP Rating covering ingress against
solid objects and liquids only.
The larger the value
of each digit, the greater the protection from that influence. As an example,
a product rated as IP54 would be better protected against environmental
factors than another similar product that was only rated as IP43. For
example, TCS Compact Loudspeakers are rated at IP54 (protected against
dust and protected against sprays of water from all directions).
| Value |
First
digit (Protection against solid objects) |
Second
digit (Protection against liquids) |
| 0 |
No
Protection |
No
protection |
| 1 |
Protected
against solids objects over 50mm (e.g. accidental touch by hands |
Protected
against vertically falling drops of water |
| 2 |
Protected
against solids objects over 12mm (e.g. fingers) |
Protected
against direct sprays up to 15° from the vertical |
| 3 |
Protected
against solids objects over 2.5mm (e.g. tools and wires) |
Protected
against direct sprays up to 60° from the vertical |
| 4 |
Protected
against solids objects over 1mm (e.g. tools, wires and small wires |
Protected
against sprays from all directions - limited ingress permitted |
| 5 |
Protected
against dust - limited ingress (no harmful deposit) |
Protected
against low pressure jets if water from all directions - limited
ingress permitted |
| 6 |
Totally
protected against dust |
Protected
against strong jets of water e.g. for use on shipdecks - limited
ingress permitted |
| 7 |
|
Protected
against the effects of temporary immersion between 15cm and 1m.
Duration of test 30 minutes |
| 8 |
|
Protected
against long periods of immersion under pressure |
| |
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Q: What gauge speaker cable
should I use?
A: The recommended
wire size for the majority of applications is 2.5 square mm, which is
perfectly acceptable under normal conditions. The following table illustrates
losses in speaker cables over increasing distances.
| Cable
run in metres |
Cross
sectional area
of conductor
in square mm |
Cable
Resistance
in Ohms |
Percentage
Power Loss
at 4 Ohms (%) |
|
|
| 2.5 |
1.0 |
0.066 |
2.2 |
| |
1.5 |
0.058 |
1.5 |
| |
2.0 |
0.043 |
1.1 |
| |
2.5 |
0.035 |
0.9 |
| |
4.0 |
0.021 |
0.55 |
|
|
| 5 |
1.0 |
0.173 |
4.3 |
| |
1.5 |
0.115 |
2.9 |
| |
2.0 |
0.086 |
2.2 |
| |
2.5 |
0.069 |
1.7 |
| |
4.0 |
0.043 |
1.1 |
|
|
| 10 |
1.5 |
0.230 |
5.8 |
| |
2.0 |
0.173 |
4.3 |
| |
2.5 |
0.138 |
3.5 |
| |
4.0 |
0.086 |
2.2 |
| |
6.0 |
0.058 |
1.5 |
|
|
| 25 |
1.5 |
0.575 |
14.0 |
| |
2.0 |
0.431 |
11.0 |
| |
2.5 |
0.345 |
8.6 |
| |
4.0 |
0.216 |
5.4 |
| |
6.0 |
0.144 |
3.6 |
|
|
| 50 |
2.0 |
0.863 |
22 |
| |
2.5 |
0.690 |
17.0 |
| |
4.0 |
0.431 |
11.0 |
| |
6.0 |
0.288 |
7.2 |
| |
10.0 |
0.173 |
4.3 |
|
|
| 100 |
2.0 |
1.173 |
43.0 |
| |
2.5 |
1.38 |
35.0 |
| |
4.0 |
0.863 |
22.0 |
| |
6.0 |
0.575 |
14.0 |
| |
10.0 |
0.345 |
8.6 |
Q: What are the pin connections
on cabinets equipped with EP6 connectors?
A: The convention
is from low to high frequency with increasing pin number, starting with
the negative. So on a 3-way system such as a Floodlight mid-high the EP6
is wired pin 1: LMF -ve, pin 2: LMF +ve, pin 3: HMF -ve, pin 4: HMF +ve,
pin 5: HF -ve, pin 6: HF +ve. Active wedges like the TFM-230 and TFM-330
also use the same convention i.e. pin 1: LF -ve, pin 2: LF +ve, pin 3: HF
-ve, pin 4: HF +ve, pins 5 and 6 not connected. EP6 connectors are being
phased out in favour of Speakon NL4 and NL8 connectors where appropriate.
Q: What are
the pin connections on cabinets equipped with Speakon NL4 connectors?
A: Passive speakers
which use Speakon NL4MP connectors are wired pin 1+: positive, pin 1-: negative.
Pins 2+ and 2- are not connected. Bi-amped speakers are wired pin1+: LF
positive, pin1-: LF negative, pin2+: HF positive, pin2-: HF negative.
Q: What are the pin connections
on cabinets equipped with Speakon NL8 connectors?
A: Three-way active
speakers are configured as follows: pin 1+: not connected, pin 1-: not connected,
pin 2+: LMF positive, pin 2-: LMF negative, pin 3+: HMF positive, pin 3-:
HMF negative, pin 4+: HF positive, pin 4-: HF negative.
Q: What is a virtual point
source array?
A: The primary objective
of a flown loudspeaker array is to provide all seats in the auditorium
with an even and equal sound coverage. The best way of doing this is to
position the loudspeaker enclosures in such a way so that no two enclosures
point in the same direction. If you draw lines parallel to the way
the drivers are pointing, back behind the loudspeaker array, they should
intersect at the Virtual Point Source. The effect is like listening
to only two sources, one left and one right, which stands a heck
of a lot better chance of sounding coherent than a bunch of boxes coming
at you from different locations and distances.
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