Lowell PA250A Installation Sheet And Operators Manual Download Page 7

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Instruction Sheet

IS-PA250A

Issued: 1-18-19

Lowell Manufacturing Company

100 Integram Drive

Pacific, Missouri 63069 U.S.A.

Call: 800-325-9660

Fax: 636-257-6606

Click: www.lowellmfg.com

70 volt and 25 volt

“Constant Voltage Distribution Systems” have been a source of confusion for people for a long

time.    Our  Series/Parallel  speaker  wiring  discussion  on  page  6,  illustrates  why  industry  engineers  developed  the
“Constant Voltage” concept. Series/Parallel configurations are manageable for small localized systems using up to
4  to  8  speakers  and  when  no  expansion  is  anticipated.    Even  with  only  4  to  8  speakers,  wiring  a  Series/Parallel
configuration can be confusing.  Nobody would ever want to attempt Series/Parallel wiring for 8000 speakers spread
over an  entire office  complex. The 70V and 25V speaker systems (and  the 100V system which is used  in  Europe)
rely  on inexpensive  line  matching transformers to simplify  the

“impedance matching” and “amplifier loading” issues.

The line matching transformers allow all of the speakers in a 70V or 25V speaker system to be wired in parallel
regardless if there are 8 speakers or 8000 speakers in the system, as long

as the total of all transformer taps

used does not exceed the power rating of the amplifier.

Parallel connections make field wiring easy and it

makes it possible to add speakers anywhere along the speaker string without any concern about Series/Parallel
load impedance. The term

“Constant Voltage” can be misleading. “Constant Voltage” means whether you have a

10W 70V amplifier, 100W 70V amplifier, or a 1000W 70V amplifier, the output will  be  at 70.7V when the amplifier is
turned  all  the  way  up.   When  a  70V  amplifier  is turned  down, it  will  be  running  at  less that 70V.   The  key thing  to
remember is that  the transformer power  tap values are calculated for when the amplifier is running  at a full 70V. A
70V speaker transformer tapped at 5 watts, will only draw a full 5 watts, when the amplifier is at it

’s full 70V output.

70V / 25V Speaker System Wiring

Individual Speaker Transformer Tap Settings:

A 70V or 25V speaker that is chosen  by the  system designer, has  a matching transformer
with a maximum power rating .  For example, the Lowell R1810-72 (shown to the right) has
a Lowell TLM-572 5-watt 70V/25V dual voltage transformer. That means that this speaker
can  be  used  on  both  70V  systems  and  25V  systems.    The  8

secondary of the

transformer is connected directly to the 8

input terminals on the 810 speaker. The

primary  has  transformer  taps  for  either  70V  or  25V  at  0.25W,  0.5W,  1W,  2W,  and  5W.
When  a  designer  is  mapping  out  the  coverage  of  these  ceiling  speakers,  he/she  will
determined  how  many  speakers  are  required  and  in  what  locations,  and  what  power  tap
will be  used for the speakers to  be  loud enough  for this application. Let

’s say for example

that the designer has determined that 100 speakers will be required tapped at  1W each at
70 volts. That means that our total speaker  load is 100 watts. The speakers will be wired
in  the  field  in  parallel  as  shown  below  making  sure  the  connections  are  made  with  the
proper polarity to keep all of the speakers operating in phase with each other.

A 70V or 25V speaker system is easy  to  design and easy  to wire in the field because all speakers  can  be wired in
parallel.   The  higher transmission  voltages used  greatly  reduce  the power lost  in  the  speaker lines so  smaller  less
expensive speaker wiring can be used. The volume of a single speaker on the line can be adjusted louder or softer
by  adjusting  the  power  tap  used  on  that  speaker

’s matching transformer. That adjustment does not affect the

volume of the other  speakers  in the system. The volume  adjustment  of a single speaker on  the  line  or the volume
adjustment  of groups  of speakers  in  a  zone  can  be made accessible  to the user  by way  of inexpensive wall-mount
autoformer-based  volume  controls.    The  settings  on  wall-mount  volume  controls  can  be  easily  bypassed  during
pages  or during  emergency announcements.   (See Lowell

“priority attenuator” volume controls that include a “-PA”

in  the  model  number).    It  is  easy  to  add  speakers  to  the  system in  the  future  without  having  to  change  any  of  the
existing wiring. If adding additional speakers in the future will require a more powerful amplifier at the head -end, an
amplifier  with  a  higher  output  power  capability  can  replace  the  existing  unit  without  changing  any  of  the  existing
speaker  wiring  or  any  of  the  existing  speaker  transformer  tap  settings.    For  example:    A  Lowell  MA60  could  be
replaced with a Lowell MA125 so that more speakers could be added to the system, with no other changes required
to the existing speaker wiring or transformer taps.

70V / 25V Constant Voltage Speaker System Advantages:

Lowell R1810-72

Note: Always insulate the

transformer taps that are

not being used so they

don

’t short together.

.5W

.25W

COM

.5W

.25W