[[email protected]]

Hi All,

I'm hoping I can get some help from you guys. I'm an electrical
contractor, however, I'm not an audio tech. I am pretty versed in
home audio, however, commercial audio is kind of foreign to me. Here
the deal:

I have a commercial installation where there are 3 speakers (15ohm).
Each speaker has a multitap of 30, 15, 7.5, and 3.75 watts. The
amplifier has outputs of 4 ohm, 25V (21 ohm) and 70V (163 ohm). Also,
on the back of the speakers, they say 70.7V. My question is, do I
connect these in series or parallel ? If connected in parallel, I
believe the total impedance would be 1/15 + 1/15 + 1/15 = .2 = 1/.2 =
5 ohms.

Do I need to be above the impedance on the amplifier to be safe ? If
so, I can use a combination of series parallel circuitry. I assume
having 2 speakers in series and 1 speaker in parallel to the other
speakers would make the single speaker louder and that's where having
the adjustable tap comes into play to balance the sound ?

Also, which tap do I use ? Do I have to use the 70 V tap ? What
would the effect be on the system if I used the 25V tap ? or the 4
ohm tap ?

Also, can a speakers impedance be measured by an ohmmeter over the
speakers terminals, or is this just resistance ?

Any help or guidance would be greatly appreciated. Thanks.

joe

[Peter Larsen]

wrote:

Hi All,

I'm hoping I can get some help from you guys.

Some, but wait for other follow-ups.

I'm an electrical contractor, however, I'm not an audio tech.
I am pretty versed in home audio, however, commercial audio
is kind of foreign to me. Here the deal:

I have a commercial installation where there are 3 speakers (15ohm).

How did you determine that impedance?

Each speaker has a multitap of 30, 15, 7.5, and 3.75 watts.

They then have an input transformer with different secondary taps.

The amplifier has outputs of 4 ohm,

IF it is a solid state amp, and IF the 4 Ohm setting bypasses the output
transformer THEN the 4 Ohm output is just like the output of a home
audio amplifier. It probably sounds better like that, but distributing
low voltage high amperage electricity is as problematic from an
amplifier as from a power plant.

25V (21 ohm) and 70V (163 ohm). Also, on the back of the
speakers, they say 70.7V.

70 volt lines - ie. max amplifier output power is obtained at an output
voltage of 70 volts - are used to distribute audio over large wiring
distances because the higher voltage allows lower amperage and thus
lower resistance losses, ie. the use of thinner or longer wires or a
combination thereof. Copper is costly ...

My question is, do I connect these in series or parallel?

It is my understanding - notice the inbuilt disclaimer - that a 70 volt
distribution system is designed for connecting all speakers in parallel,
it is exactly the same concept as mains distribution, ie. that each
receiving apparatus matches its power-uptake by having a suitable
impedance.

If connected in parallel, I believe the total impedance would be
1/15 + 1/15 + 1/15 = .2 = 1/.2 = 5 ohms.

Well, if you either measured the input resistance of the transformer or
go by the stated impedance of the loudspeaker units neglecting the
outcome of feeding them via the transformer it appears must be in the
boxes they are in then you could be right. However for a 70 volt
distribution syste the maximum power delivered in 5 Ohms would be quite
large.

Do I need to be above the impedance on the amplifier to be safe?

The beauty of a 70 volt distribution system is that each loudspeaker
matches its power updake by adapting its apparent impendance via a
change of the transformer setting. Because of this the voltage that each
loudspeaker units sees - and thus its power uptake - is matched to is
power handling capability and to the intended loudness of it in the
system.

If so, I can use a combination of series parallel circuitry.

In the sense of the question: no, a 70 volt setup is a power grid just
like the mains grid, with all loads effecticely in parallel and
impedance matched to the intended power uptake.

I assume having 2 speakers in series and 1 speaker in parallel
to the other speakers would make the single speaker louder and
that's where having the adjustable tap comes into play to balance
the sound ?

The transformer in the loudspeaker boxes matches their input voltage
sensitivity to the voltage on the sysdtem.

Also, which tap do I use?

About here it will help those that really are "in the know" if you
mention the actual products that are involved and their specs.

Do I have to use the 70 V tap?

From your description it is a system that is capable of being a 70 volt
system. There must be literature on that technology available.

What would the effect be on the system if I used the 25V tap?

Well, it would probably sound better because the higher the
transformation ratio the larger the sonic influence of the transformers,
but that is not your question.

or the 4 ohm tap?

About here you have to tell us whether it is a valve amp or a transistor
amp, there are still some valve amps around. 70 volt systems go well
with valve amps, because the required output transformer is smaller and
cheaper, also in terms of sonic cost; they just require less downward
transformation than they otherwise would. A solid state amp usually
requires upward transformation to match its output voltage maximum to 70
volts, but some large amps don't ...

Also, can a speakers impedance be measured by an ohmmeter over the
speakers terminals,

No. An Ohmmeter measures resistance. You say you are an electrical
contractor, surely you ARE an electrician? - anyway, audio distribution
is different, and it is good that you ask when in doubt.

or is this just resistance ?

You need an AC source to determine impendance at that frequency. About
here is where things really are different: mains power distribution is
single frequency AC, sound distribution is about three full decades, and
circuit impedance will vary greatly over that range.

Any help or guidance would be greatly appreciated. Thanks.

By my way of thinking the power setting on the loudspeakers would be
about how much power they take up from a 70 volt grid rather than being
about their max power handling. If so, then the voltage over the units
will be lower the lower the setting.

The two main differences between audio and mains power is that audio
contains three full decades of frequencies, ie. impedance becomes
unsimple and that audio peak voltage level hardly ever will (should,
ought to) reach the nominal 70 volts the distribution system is designed
for. It appears to me that the amplifier should be set to 70 volts, and
that all loads should be in parallel and loudness of each loudspeaker
matched via its transformer setting, but I may be wrong or what I write
may be inapplicable on the actual system. Equipment data, or a link to
web based images of the equipment, will help those that really really
know this give you a more precise answer.

joe


Regards

Peter Larsen

[Don Pearce]

On 24 Feb 2007 18:13:06 -0800, wrote:

Hi All,

I'm hoping I can get some help from you guys. I'm an electrical
contractor, however, I'm not an audio tech. I am pretty versed in
home audio, however, commercial audio is kind of foreign to me. Here
the deal:

I have a commercial installation where there are 3 speakers (15ohm).
Each speaker has a multitap of 30, 15, 7.5, and 3.75 watts. The
amplifier has outputs of 4 ohm, 25V (21 ohm) and 70V (163 ohm). Also,
on the back of the speakers, they say 70.7V. My question is, do I
connect these in series or parallel ? If connected in parallel, I
believe the total impedance would be 1/15 + 1/15 + 1/15 = .2 = 1/.2 =
5 ohms.

Do I need to be above the impedance on the amplifier to be safe ? If
so, I can use a combination of series parallel circuitry. I assume
having 2 speakers in series and 1 speaker in parallel to the other
speakers would make the single speaker louder and that's where having
the adjustable tap comes into play to balance the sound ?

Also, which tap do I use ? Do I have to use the 70 V tap ? What
would the effect be on the system if I used the 25V tap ? or the 4
ohm tap ?

Also, can a speakers impedance be measured by an ohmmeter over the
speakers terminals, or is this just resistance ?

Any help or guidance would be greatly appreciated. Thanks.

joe

Just read this - all is explained very nicely.

http://www.rane.com/note136.html

d

--
Pearce Consulting
http://www.pearce.uk.com

[Laurence Payne]

On 24 Feb 2007 18:13:06 -0800, wrote:


I have a commercial installation where there are 3 speakers (15ohm).
Each speaker has a multitap of 30, 15, 7.5, and 3.75 watts. The
amplifier has outputs of 4 ohm, 25V (21 ohm) and 70V (163 ohm). Also,
on the back of the speakers, they say 70.7V. My question is, do I
connect these in series or parallel ? If connected in parallel, I
believe the total impedance would be 1/15 + 1/15 + 1/15 = .2 = 1/.2 =
5 ohms.

The speakers themselves may be 15ohm, but each appears to be connected
through a transformer designed to interface with a 70v distribution
system. The amplifier sees the transformer's impendence, not the
speaker's.

Use the 70v amplifier output. Connect in parallel. Chose a
transformer tapping on each speaker to give an appropriate relative
volume.

[[email protected]]

Thanks to all who replied. Here's the specs:

Amp: TOA BG-130
Speakers: Tannoy i5TAW
SPeaker wi 16/2 unshielded; max run 70'

Also, I got the 15 ohms by measuring with an ohmmeter. Doing some
research, I think the speakers may be 6ohm rated, however, the cut
sheet was missing with the details and I don't see an impedance rating
on the speakers themselves. All components were sent as a sytem for
the "playnetwork". However, they don't give actual instructions for
installation.

Thanks.

[[email protected]]

joe

Just read this - all is explained very nicely.

http://www.rane.com/note136.html

d

--
Pearce Consultinghttp://www.pearce.uk.com- Hide quoted text -

- Show quoted text -

That was great information ! It makes understanding it much easier.
Thanks so much.

[Peter Larsen]

wrote:

Thanks to all who replied. Here's the specs:

Amp: TOA BG-130

http://www.toaelectronics.com/amp0006.asp

Speakers: Tannoy i5TAW

http://www.tannoy.com/media/i5%20AW_manual.pdf

Thanks

And thank you for the feedback!


Regards

Peter Larsen

[Richard Crowley]

wrote ...
Thanks to all who replied. Here's the specs:

Amp: TOA BG-130

Use the 70V output since you have 70V speakers.

Speakers: Tannoy i5TAW

According to the info on the Tannoy website, those speakers
have a transformer inside for use with 70V

SPeaker wi 16/2 unshielded; max run 70'

Likely sufficient. Doesn't need to be shielded.

Also, I got the 15 ohms by measuring with an ohmmeter.

You can't measure speaker or transformer *impedance*
with an ohm meter. You are measuing only DC resistance
which doesn't have any real application here. Impedance
is an AC measurement and typically varies with frequency.

Doing some
research, I think the speakers may be 6ohm rated,

It doesn't matter what the speakers are rated since they
have a 70v transformer between them and the amp.

however, the cut
sheet was missing with the details and I don't see an impedance rating
on the speakers themselves.

The Tannoy website has the cut-sheet. It says that model
has an internal transformer for 70V line use.

All components were sent as a sytem for
the "playnetwork". However, they don't give actual instructions for
installation.

Connect all the speakers in parallel to the 70V output of the
amplifier. This is how the 70V line was intended to be used.
How many speakers are in the system? (i.e. what is the total
of the power numbers?)

[[email protected]]

3 speakers total. I assume as long as the total power is under 30
watts (amp), all should be OK. Probably use the 7.5W tap on each.
Total wattage is 22.5. Am I correct ? If I use a combination of taps
on different speakers, the higher the power tap, the louder the
independant speaker ?

Thanks !

[Richard Crowley]

wrote ...
3 speakers total. I assume as long as the total power is under 30
watts (amp), all should be OK. Probably use the 7.5W tap on each.
Total wattage is 22.5. Am I correct ? If I use a combination of taps
on different speakers, the higher the power tap, the louder the
independant speaker ?

Exactly right. You've got it.

[Geoff]

wrote:
Thanks to all who replied. Here's the specs:

Amp: TOA BG-130
Speakers: Tannoy i5TAW
SPeaker wi 16/2 unshielded; max run 70'

Also, I got the 15 ohms by measuring with an ohmmeter. Doing some
research, I think the speakers may be 6ohm rated, however, the cut
sheet was missing with the details and I don't see an impedance rating
on the speakers themselves. All components were sent as a sytem for
the "playnetwork". However, they don't give actual instructions for
installation.


NO ! Ohmeter means nothing.

If you have multiple speakers ona 70V Line system, you add them in parallel.
To determine the maximum loading simply add the wattages of all the
connected speakers (or the wattage 'tap' they are set to) and do not exceed
the amp's max output power rating..

Or to get it exact, buy an impedence meter designed for that purpose.. Toa
do one.

geoff

[Geoff]

wrote:
3 speakers total. I assume as long as the total power is under 30
watts (amp), all should be OK. Probably use the 7.5W tap on each.
Total wattage is 22.5. Am I correct ? If I use a combination of taps
on different speakers, the higher the power tap, the louder the
independant speaker ?

Yep !

geoff

[[email protected]]

THANK YOU ALL FOR YOUR HELP !