Maker Pro
Maker Pro

Volume control at the speaker?

D

DaveC

In a distributed audio system in a residence, how can volume control in each
room be accomplished.

I realize that it's more complex than just putting a potentiometer in the
speaker leads.

Is this accomplished via 70v distribution system (ie, high-impedance
amplifier output)?

Or is some kind of acceptable variable attenuation possible in each room?

Google turns up L-pads. If I understand, an L-pad keeps 8-ohm impedance on
the line from the amplifier, while providing an attenuated signal to the
speaker.

As long as it is properly chosen, are there any cautions I should know about
installing an L-pad for each pair of speakers in a room?

Are L-pads reliable (no noise, etc.)? Brands to recommend? Or avoid?

Other ideas? Speak your peace.

Thanks,
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
[email protected]
This is an invalid return address
Please reply in the news group
 
B

Beachcomber

In a distributed audio system in a residence, how can volume control in each
room be accomplished.

I realize that it's more complex than just putting a potentiometer in the
speaker leads.

Is this accomplished via 70v distribution system (ie, high-impedance
amplifier output)?

Or is some kind of acceptable variable attenuation possible in each room?

Google turns up L-pads. If I understand, an L-pad keeps 8-ohm impedance on
the line from the amplifier, while providing an attenuated signal to the
speaker.

As long as it is properly chosen, are there any cautions I should know about
installing an L-pad for each pair of speakers in a room?

Are L-pads reliable (no noise, etc.)? Brands to recommend? Or avoid?

Other ideas? Speak your peace.

Strictly speaking, L- Pads are fixed attentuators that match different
impedances.

What you want is a variable attenuator pad that will keep the
impedance (as seen by your amp) constant (commonly 8 ohms but it can
vary) as you vary the volume. Additionally, the controller has to be
able to handle the power being applied to your speaker and may be
ganged together for a stereo application.

No affiliation, but here is a link to one such product.

http://www.hometech.com/audio/volume.html

70 V distribution systems are used for PA systems (music and paging)
where there are particularly long runs with multiple speakers.

With a home audio 8 ohm speaker system, you can't just keep putting
parallel speakers on the line as each unit will lower the load
impedance and you will very quickly get to the point where you are
overloading your amplifier.

Beachcomber
 
T

Trevor Wilson

DaveC said:
In a distributed audio system in a residence, how can volume control in
each
room be accomplished.

**There are a bunch of methods. The best is to distribute the music, via
line level (balanced) cables and amplifiy in each room. There are many more
methods, which are generally inferior.
I realize that it's more complex than just putting a potentiometer in the
speaker leads.

**Not necessarily. It depends on how much quality you are prepared to
sacrifice.
Is this accomplished via 70v distribution system (ie, high-impedance
amplifier output)?

**It can be. If you want to increase cost and throw away any chance at good
sound quality.
Or is some kind of acceptable variable attenuation possible in each room?

**That is one way to do it. Quality will be sacrificed, however.
Google turns up L-pads. If I understand, an L-pad keeps 8-ohm impedance on
the line from the amplifier, while providing an attenuated signal to the
speaker.

As long as it is properly chosen, are there any cautions I should know
about
installing an L-pad for each pair of speakers in a room?

**Not really. Just be aware that the L-pad needs to be able to cope with the
maximum output of your amplifier. They can get very hot.
Are L-pads reliable (no noise, etc.)?

**If the power is kept to reasonable levels (say: around 10-15 Watts
AVERAGE), they can last a few years.
Brands to recommend? Or avoid?

**They all come out of Asia and porbably from the same factory. Just look
for the biggest, heaviest one you can find. That would probably be around
70-80mm diameter.
Other ideas? Speak your peace.

**Many surround sound receivers employ a second zone system, which has power
amps dedicated for this purpose. That would be a good, economical choice.
 
A

Arfa Daily

It can also depend on whether the driving amp is a tube or semiconductor
type. The general rule of thumb is that tube amps don't like open circuits
( or anything in between ) across their outputs whilst semiconductor types
don't like shorts ( or anything in between ). By this, I mean that if a tube
amp is designed to deliver its rated power into say 16 ohms, then it won't
like having 50 ohms across it when you wind the wick up. Likewise, a
semiconductor amp ( transistors, ICs or STK hybrids ) won't like 2 ohms
across it, if it's designed to run into an 8 ohm load.

So, to run several sets of speakers, each adjustable, from one amp, it is
not a problem to put a wirewound pot in series with each speaker, assuming
that you are running a semiconductor amp. You can calculate the total load
easily by series addition, and ohms law. It's not quite right, as the '
ohmage ' quoted for a speaker, is its impedance at a particular frequency,
not its DC resistance, but near enough.

I would suggest using series resistors as well, to balance up the levels in
each room, and still leave a good adjustment range, as well as making sure
that the whole network cannot drop below the minimum load impedance before
the amp is being overloaded.

So let's say you are going to feed out to 5 rooms and use some 8 ohm
speakers that you've already got. The quoted minimum load impedance for your
semiconductor amp, is 8 ohms. If you just hook them all up in parallel, the
impedance presented to the amp will be 8/5 or 1.6 ohms - clearly an
overload.

Now change things so that at each speaker, you have a 22 ohm wirewound
resistor, in series with a 22 ohm w/w pot, hooked as a variable resistor, in
series with the 8 ohms of the speaker. With the pot at minimum resistance
( maximum audio ), each speaker will represent 30 ohms. So with all 5 rooms
set like this, the total paralleled load presented to the amp, would be 30/5
or 6 ohms. Unless you're going to play drum and bass at full volume, then by
the time you've added in a bit of cable resistance, your amp is not going to
mind this slight reduction in the minimum presented impedance.

Now turn each speaker to minimum vol ( maximum pot resistance ) Each speaker
will now be 22 ohms + 22 ohms + 8 ohms = 52 ohms. Parallel all these up, and
the impedance presented to the amp will be 52/5 or about 10 ohms.

You would set all this up by setting each pot to about half way, then
setting the amp volume control to get the desired level in the ' loudest '
room. The other rooms can then be adjusted down to the desired levels, but
could also still be adjusted above the loudest room if that became a
requirement. If the quieter rooms are still too loud with the pots at max
resistance, then just go for a higher value resistor until you reach the
level you want, bearing in mind that the higher you go with the resistor,
the less range the pot will have if you keep with the same value.

The best thing is to try it in the garage or wherever first. A few different
values of resistor and pot to play with, bought from your local Radio Shack
store, will be a lot cheaper and easier than getting special pads. The
values I've used are just to make the math easy to understand. If you follow
the principle, you should be able to adapt it. 22 ohms is probably a good
starting point though. It's hard to calculate a definitive power rating for
the pots and R's because it depends on many factors, but 3 watt wirewound or
cermet pots would probably be ok, with 3 or 5 watt resistors. Just try it
out and see if they get more than ' 3 watts hot '. Assuming that they don't,
then they will last for ever, not just a few years.

Finally, by presenting something other than the design impedance to the
driving amp's output, audio enthusiasts will tell you that you are
compromising the audio quality. Whilst this is strictly true if you start
looking at damping factors and other such esoteric quantities, I defy Joe
Average-Listner to hear anything untoward.

Geoff
 
A

Adrian Tuddenham

DaveC said:
In a distributed audio system in a residence, how can volume control in each
room be accomplished.

In the days when amplifiers were expensive, there would have been one
central amplifier, for economy of scale, with its output at 70v (US) or
100v (UK) fed around the building by a line.

Each loudspeaker unit would have a transformer built-in to reduce the
line voltage to whatever was required for the speaker. A
multiple-tapped primary (or sometimes secondary)was used with a rotary
switch as a volume control.

Unlike a potentiometer, this method wasted no power at intermediate
settings and reduced the loading on the amplifier when loudspeakers were
set to low levels.

Nowadays, you may find it better/cheaper in a small building to
distribute the signal at a lower line level or just from the loudspeaker
terminals of your source and use individual amplifier-speaker units in
each room.
 
Arfa said:
It can also depend on whether the driving amp is a tube or semiconductor
type. The general rule of thumb is that tube amps don't like open circuits
( or anything in between ) across their outputs whilst semiconductor types
don't like shorts ( or anything in between ). By this, I mean that if a tube
amp is designed to deliver its rated power into say 16 ohms, then it won't
like having 50 ohms across it when you wind the wick up.

That's an interesting set of assertions, considering the fact that
it's not at all unusual for a speaker's impedance to rise to 50 ohms
and above within its operating frequency range.
Likewise, a semiconductor amp ( transistors, ICs or STK hybrids )
won't like 2 ohms across it, if it's designed to run into an 8
ohm load.

While this might be true of some units, as a generalization,
it's not.
So, to run several sets of speakers, each adjustable, from one amp, it is
not a problem to put a wirewound pot in series with each speaker, assuming
that you are running a semiconductor amp. You can calculate the total load
easily by series addition, and ohms law. It's not quite right, as the '
ohmage ' quoted for a speaker, is its impedance at a particular frequency,
not its DC resistance, but near enough.

I would suggest using series resistors as well, to balance up the levels in
each room, and still leave a good adjustment range, as well as making sure
that the whole network cannot drop below the minimum load impedance before
the amp is being overloaded.

Series resistors and series pots may not be the worst way to
accomplish this, but until someone suggests something worse,
this will stand as the likely candidate.

Given that the impednace of the vast majority of speakers is
a frequency dependent function and can easily vary by as much
as a factor of 1 to 10, any substantial series resistance WILL
result in fairly gross frequency response errors. Let's take
your suggestion below and see what happens.
So let's say you are going to feed out to 5 rooms and use some 8 ohm
speakers that you've already got. The quoted minimum load impedance for your
semiconductor amp, is 8 ohms. If you just hook them all up in parallel, the
impedance presented to the amp will be 8/5 or 1.6 ohms - clearly an
overload.

Now change things so that at each speaker, you have a 22 ohm wirewound
resistor, in series with a 22 ohm w/w pot, hooked as a variable resistor, in
series with the 8 ohms of the speaker. With the pot at minimum resistance
( maximum audio ), each speaker will represent 30 ohms. So with all 5 rooms
set like this, the total paralleled load presented to the amp, would be 30/5
or 6 ohms. Unless you're going to play drum and bass at full volume, then by
the time you've added in a bit of cable resistance, your amp is not going to
mind this slight reduction in the minimum presented impedance.

Now turn each speaker to minimum vol ( maximum pot resistance ) Each speaker
will now be 22 ohms + 22 ohms + 8 ohms = 52 ohms. Parallel all these up, and
the impedance presented to the amp will be 52/5 or about 10 ohms.

In such a scenario, each "nominally 8 ohm" speaker will be looking at
44 ohms in series with it. Let's reasonably assume that the speaker's
impedance varies from a low of about 7 ohms in the midband to say 40
ohms at resonance. With 44 ohms in series, the attenuation at the
high point of the impedance will be:

G = 40/(40+44)
= 40/84
= 0.48

which is equal to -6.4 dB. At the minimum impedance of 7 ohms,
the result will be:

G = 7/(7+44)
= 7/51
= 0.14

or about 17.3 dB.

Thus, the scheme suggested will introduce a frequency response error
or nearly 11 dB on such a speaker. Hardly subtle.

Second issue, since all these resistors are in series and thus
the same current must pass through both the speakers and the
series resistors, and since the power dissipated goes as the
resistance times the square of the current, it becomes quickly
apparent that MOST of the amplifier's power will be used to
heat up the series resistors. Let's assume that the amplifier used
can produce 100 watts into a nominal 8 ohm load. Since:

P = E^2/R

thus

E = sqrt(P*R)

then such an amplifier can produce about 28 volts RMS across the
load. By Ohm's law:

E = I * R

thus

I = E/R

so

I = 28/52

or about half an amp. That half amp into the speaker will produce:

P = I^2 R
= 0.5^2 8
= 2 watts

while the series reistor and pot will dissipate:

P = 0.5^2 * 44
= 11 watts

Fully 85% of the amplifier's output will be devoted to heating
up those resistors, only 15% will find its way to the speakers.
now consider the very likely possibility that the speakers used
You would set all this up by setting each pot to about half way, then
setting the amp volume control to get the desired level in the ' loudest '
room.

GIven that the total series impedance can vary from 22 to 44 ohms,
and assume, for the purpose of simplicity, that the speakers DO
represent a resistive 8 ohm load, the minimum and maximum gain
of the proposed arrangement will be:

Gmin = 8/(22+22+8)
= 8/52
= 0.15
= -16.3 dB

Gmax = 8/(22+8)
= 8/30
= 0.27
= -11.5 dB

A range of 4.8 dB, or only +- 2.4 dB from the "midpoint" setting.
That's completely insufficient for compensating for differences
in speakers, differences in room acoustics and positioning,
differences in the amount of level desired or, for that matter,
to make a substantial audible difference.
The best thing is to try it in the garage or wherever first. A few different
values of resistor and pot to play with, bought from your local Radio Shack
store, will be a lot cheaper and easier than getting special pads.

The difference being, of course, that "special pads" have at least
a chance of working.
The
values I've used are just to make the math easy to understand. If you follow
the principle, you should be able to adapt it. 22 ohms is probably a good
starting point though.

Okay, using that math, I think it can be shown that the scheme is
uworkable.
It's hard to calculate a definitive power rating for
the pots and R's because it depends on many factors, but 3 watt wirewound or
cermet pots would probably be ok, with 3 or 5 watt resistors.

Actually, no, as shown above the math is VERY straightforward. To
generalize it even further, the amount of power dissipated in
each serires resistance is directly proportional to the ratio of
that resistance to the total serires resistance. Take that ratio,
multiply it by the total power output of the amplifier, and that's
your power requirement.
Finally, by presenting something other than the design impedance to the
driving amp's output, audio enthusiasts will tell you that you are
compromising the audio quality.

I might suggest that such "audio enthusiast" are unaware of the
fact that almost EVERY speaker on the market presents an impedance
which varies rather substantially from the "design impedance" of
amplifiers. From your assertion above, it follows that almost
every speaker on the market "compromises the audio quality."

In fact, all audio amplifier MUST cope with the fact that the
load impedance is LIKELY to vary widely. And since most amplifiers,
even most tube amplifiers (with some notable pathological
exceptions) behave essentially as low output impedance voltage
sources, this is not an issue.
Whilst this is strictly true if you start
looking at damping factors and other such esoteric quantities, I defy Joe
Average-Listner to hear anything untoward.

I might posit that an 11 dB error on the frequency response is
likely to be detectable by Mr. Average Listener. That's equivalent
to adjusting an equalizer to have an 11 dB boost in the bass, about
a 3 dB boost in the midrange, and a 3-4 dB boost at high frequencies.
Are you asserting that such is NOT audible?

If the system is used for primarily background listeing and not
the utmost in fidelity, then a 70V distribution system with
levels taps on the speaker transformers is the most reasonable
way to achieve moderate quality, adjustability, safety and
reliability with an existing system at moderate cost. However,
the best way, as suggested by another poster, is to distribute
the audio signal at some low level and then use local amplification
at the listening point. The distribution could be low-level analog
signals over appropriately shielded, twisted pair or preferably,
via either multi-drop digital or even via networking. This would
orovide the maximum quality, efficiency and versatility, but
at the highest cost.
 
D

Dave Plowman (News)

In a distributed audio system in a residence, how can volume control in
each room be accomplished.
I realize that it's more complex than just putting a potentiometer in
the speaker leads.
Is this accomplished via 70v distribution system (ie, high-impedance
amplifier output)?

You can often cludge together a system using 100 volt line transformers on
a normal amp, and use the power output taps via a switch to give some
control of level. Not ideal, but any form of resistive system will sound
worse.

But a far better way is to have an amp per pair of speakers, and feed that
at line level.
 
B

BoborAnn

I did this in my home using NXG Impedance matching volume controls ( part
number NX-VCM80) which you can get on EBay for under $20 each this device
allows up to 8 sets of speakers to be connected to a receiver.It has taps
based on how many you are using which allow too to present a constant
impedance to the receiver. They have 12 steps of attenuation which is plenty
for me
hope this helps
Bob
 
A

Arny Krueger

In a distributed audio system in a residence, how can
volume control in each room be accomplished.

(1) Separate amp at each location, not totally impractical
in these days when you can get a pertty fair 100 wpc amp for
under $80 if you look around.

(2) Transformer-type stepped volume controls. Ironically
they are around $30 each, so you're talking a bit less than
half the price of the receiver.

http://www.hometech.com/audio/volume.html
 
D

DaveC

Thus spake Dave Plowman (News):
You can often cludge together a system using 100 volt line transformers on
a normal amp, and use the power output taps via a switch to give some
control of level. Not ideal, but any form of resistive system will sound
worse.

You being in the UK, I presume you mean 240:100v line transformers, yes? In
the USofA this would be half that: 120:50v transformers, yes?

Thanks,
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
[email protected]
This is an invalid return address
Please reply in the news group
 
D

DaveC

Thus spake Arny Krueger:
(1) Separate amp at each location, not totally impractical
in these days when you can get a pertty fair 100 wpc amp for
under $80 if you look around.

Sources for small amplifiers? Place in wall? Attic?

Google turns up so many amps, but are stereo system component types.

Thanks,
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
[email protected]
This is an invalid return address
Please reply in the news group
 
DaveC said:
Thus spake Dave Plowman (News):


You being in the UK, I presume you mean 240:100v line transformers, yes? In
the USofA this would be half that: 120:50v transformers, yes?

No, he doesn't mean that. You're talking about AC power. He's talking
about audio signal distribution and matching.

There is a means of distributing high-level audio (speaker level)
using impedance matching transformers. Two different level conventions
exist: 70 volt and 100 volt. Matching transformers are provided at
each speaker and are used to determine how much power that speaker
can get. Some transformers have switchable taps that allow adjusting
level.
 
D

DaveC

Thus spake [email protected]:
There is a means of distributing high-level audio (speaker level)
using impedance matching transformers. Two different level conventions
exist: 70 volt and 100 volt. Matching transformers are provided at
each speaker and are used to determine how much power that speaker
can get. Some transformers have switchable taps that allow adjusting
level.

Ah, yes. I'd known about 70v, hadn't heard of 100v.

Thanks,
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
[email protected]
This is an invalid return address
Please reply in the news group
 
D

Dave Plowman (News)

You being in the UK, I presume you mean 240:100v line transformers, yes?
In the USofA this would be half that: 120:50v transformers, yes?

No - 100 volt line as used in PA systems for long runs to speakers, etc.
You use a transformer to match a normal low impedance speaker to the
'line' and use the turns ratio to set the power going in and therefore the
level. With this method you can hang as many speakers across one amp as
you want - up to its rated output - unlike paralleling low impedance
speakers across a normal amp. Most such transformers will have taps for
several different output settings, so can also be used to control level.
 
D

DaveC

Is there a wireless solution to distributing audio throughout a residence to
8 rooms? Digital?

Something similar to wireless computer networking...

Thanks,
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
[email protected]
This is an invalid return address
Please reply in the news group
 
A

Arny Krueger

J

jclause

Is there a wireless solution to distributing audio throughout a residence to
8 rooms? Digital?

Something similar to wireless computer networking...

Thanks,


Yamaha makes a system called MusicCAST that does this. Has a hard
drive, stores 1,000 CD's in MP3 format or 100 in original format.
My son sells these in his audio store. See Yamaha.com.

JC the elder
 
D

Dave Plowman (News)

Sources for small amplifiers? Place in wall? Attic?

My solution was to make them, as if hidden don't have to look pretty.
Plenty of kits on the market. I used a DC controlled pre-amp for volume
etc, as then the controls take up a tiny space and can easily be fitted on
a face plate of the type used for sockets etc, and there are no safety
implications if used in a wet room.

This was some time ago - a remote control might do as well.

But I've got an easy to wire house. Victorian with a cellar and dry lined
walls. A modern solid concrete one would be a different matter. ;-)
 
P

Pooh Bear

DaveC said:
In a distributed audio system in a residence, how can volume control in each
room be accomplished.

Seperate amplifiers in each room ( or alternatively so-called 'powered speakers'
with inbuilt amplifiers ) is the only solution that preserves audio quality. I
assume you don't want quality trade-offs which is all that any other approach
can offer.

Graham
 
B

Bill & Debbie

DaveC said:
In a distributed audio system in a residence, how can volume control in
each
room be accomplished.

I realize that it's more complex than just putting a potentiometer in the
speaker leads.

Is this accomplished via 70v distribution system (ie, high-impedance
amplifier output)?

Or is some kind of acceptable variable attenuation possible in each room?

Google turns up L-pads. If I understand, an L-pad keeps 8-ohm impedance on
the line from the amplifier, while providing an attenuated signal to the
speaker.

As long as it is properly chosen, are there any cautions I should know
about
installing an L-pad for each pair of speakers in a room?

Are L-pads reliable (no noise, etc.)? Brands to recommend? Or avoid?

Other ideas? Speak your peace.

Thanks,
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
[email protected]
This is an invalid return address
Please reply in the news group
I used the Niles speaker selector and the Niles volume controls. The
selector I chose allows 6 pairs of speakers to be attached. It's kinda
pricy. I think the selector is about $100 and the volume controls are about
$50 each.

I'm using it for sound in 4 rooms and it works very well.
Bill
 
Top