Started working in a golf course pro shop recently and found a
disaster of a sound system. Every time we wanted to announce a group
to tee off the sound system would just cut out. We had to really
speak softly into the mic to get it to work. Apparently the staff
just got used to this. Yuk !

Not being one to just sit back and accept the status quo I started
digging around and found a Mackie Industries AM 4120 P.A. Amplifier.
I noticed that when the sound did cut out that the Overload light came
on the amp. It was wired up using the 100v output and I found it was
going to an 8ohm outdoor radio shack speaker and other various
speakers thorughout the club house. I changed the output to a 4ohm
output and the overload was gone and the speaker worked ok. I further
poked around the basement area and found wires going to speakers that
were cut and multiple wiring attempts and other hacks.

It appears that the Amp is working fine and I'll have to go back in to
discover what other speakers are disconnected/unusable and start
replacing them and the wiring. The Amp has 25v, 70v, 100v, and 4ohm
output.

I'm not an audio pro but I can sure see why this system doesn't work
right !


RR

"Ron Richardson" wrote in message
om...
Started working in a golf course pro shop recently and found a
disaster of a sound system. Every time we wanted to announce a group
to tee off the sound system would just cut out. We had to really
speak softly into the mic to get it to work. Apparently the staff
just got used to this. Yuk !

Not being one to just sit back and accept the status quo I started
digging around and found a Mackie Industries AM 4120 P.A. Amplifier.
I noticed that when the sound did cut out that the Overload light came
on the amp. It was wired up using the 100v output and I found it was
going to an 8ohm outdoor radio shack speaker and other various
speakers thorughout the club house. I changed the output to a 4ohm
output and the overload was gone and the speaker worked ok. I further
poked around the basement area and found wires going to speakers that
were cut and multiple wiring attempts and other hacks.

It appears that the Amp is working fine and I'll have to go back in to
discover what other speakers are disconnected/unusable and start
replacing them and the wiring. The Amp has 25v, 70v, 100v, and 4ohm
output.

I'm not an audio pro but I can sure see why this system doesn't work
right !


RR

It sounds like someone that didn't know what they were doing hooked up a
speaker to a PA system.

PA amplifiers for this kind of application often use 25, 75 or 100 volt
outputs. These are for (relatively) high-impedance transmission lines for
bridging a lot of speakers onto a single amplifier. Each speaker on the line
should be connected through a PA transformer to match the speaker impedance
to the transmission line. PA transformers typically have 4, 8 and 16-ohm
taps on the speaker side, and 25, 75 and 100 volt taps on the other side.
Just hook up the correct taps, and you're good to go. The amplifier manual
can tell you how many speakers you can safely run on a particular tap.

If you just have one or two speakers, you can hook them up to one of the
low-impedance outputs (e.g., 4-ohms) without transformers, but it's probably
better to use the transformers if you can; it will be easier to add or
remove speakers in the future without having to re-configure the whole
system.

In , on 08/21/04
at 12:15 PM, (Ron Richardson) said:

Started working in a golf course pro shop recently and found a
disaster of a sound system.

[ ... ]

It was wired up using the 100v output and I found it was
going to an 8ohm outdoor radio shack speaker and other various
speakers thorughout the club house. I changed the output to a 4ohm
output and the overload was gone and the speaker worked ok. I further
poked around the basement area and found wires going to speakers that
were cut and multiple wiring attempts and other hacks.

The 4 Ohm output is for home applications, the others are for
professional jobs. For home jobs one attaches speakers, wired in
parallel, until the total impedance falls to the amplifier limit. If
all the speakers are identical, calculating the final impedance is
easy. If they are different, the formula is a bit more complex. If the
speakers are identical, then all will present the same acoustic output.

For voltage distribution, things are much easier. Each speaker includes
a transformer that is designed for 25, 70, or 100 Volt systems. The
speaker side of the transformer is appropriately 4, 8, or 16 Ohms. The
primary (amplifier) side is marked in Watts (power). Typically, there
are several "taps" on the primary side for various powers. Use the high
power taps for larger spaces. The beauty of the system is that you can
keep adding speakers until the sum of the individual powers equals the
amplifier power and it is relatively easy to accommodate varying room
requirements.

It appears that the Amp is working fine and I'll have to go back in to
discover what other speakers are disconnected/unusable and start
replacing them and the wiring. The Amp has 25v, 70v, 100v, and 4ohm
output.

My recommendation is to find all of the junctions and make sure all of
the connections are tight and that there are no shorts. I'm not a fan
of wire nuts for audio wiring applications. You can use a standard
flashlight or 9V battery to check a speaker. At the instant the battery
is connected the speaker will "thump". Any decent Ohmmeter can help
diagnose other problems. You will find that each of the transformer
taps will measure a different resistance. If you map out one
transformer you can measure speaker lines running out into the woods
and get a feel for which tap is used (if any). For very long speaker
wire runs, don't forget to add a few Ohms for the wire.

If transformers are not being used, buy some. They are not expensive.

When I'm faced with similar situations, I make an effort to track down
and check every wire and every connection. I'll also pull down or climb
up to every speaker and find out how it is wired. What the box says
outside may not be what is inside.

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Thanks for the help. Looks like the hardest part to this will be
tracing wires through a musty basement and dusty ceiling...

Ron