Two horns would be ugly. There has top be a way to do this.

Capt. Jeff

There are a couple of ways to do this.

1. Use resistive pads at the outputs of the two radios and a resistive
summation circuit to feed a separate amplifier which then feeds the
single speaker.

2. Use a stereo-to-monaural isolation transformer backwards. Each radio
feeds one stereo input and the monaural winding feeds your single speaker.

I am certain #1 will work, but it obviously requires purchase of an
amplifier and some soldering. Amps are not particularly expensive, but
this is probably not a job the average boater would undertake unassisted.

The second solution is more elegant, but I have no personal experience
with those transformers. Power rating would be an important
consideration, of course. It is my understanding that they provide on
the order of 20 dB of isolation, which should be more than adequate to
protect the two radios.

Good luck.

Chuck

Tamaroak wrote:
Two horns would be ugly. There has top be a way to do this.

Capt. Jeff

As a follow-up, the easiest solution, by far, and perhaps the least
expensive one, is to purchase a dual voice coil speaker. Each voice coil
is completely (as they say) independent of the other so there is no
damage to equipment. I have no idea whether you can find a dual voice
coil horn, but you can search for one.

Good luck.

Chuck

chuck wrote:
There are a couple of ways to do this.

1. Use resistive pads at the outputs of the two radios and a resistive
summation circuit to feed a separate amplifier which then feeds the
single speaker.

2. Use a stereo-to-monaural isolation transformer backwards. Each radio
feeds one stereo input and the monaural winding feeds your single speaker.

I am certain #1 will work, but it obviously requires purchase of an
amplifier and some soldering. Amps are not particularly expensive, but
this is probably not a job the average boater would undertake unassisted.

The second solution is more elegant, but I have no personal experience
with those transformers. Power rating would be an important
consideration, of course. It is my understanding that they provide on
the order of 20 dB of isolation, which should be more than adequate to
protect the two radios.

Good luck.

Chuck

Tamaroak wrote:

Two horns would be ugly. There has top be a way to do this.

Capt. Jeff

In article k.net,
chuck wrote:

As a follow-up, the easiest solution, by far, and perhaps the least
expensive one, is to purchase a dual voice coil speaker. Each voice coil
is completely (as they say) independent of the other so there is no
damage to equipment. I have no idea whether you can find a dual voice
coil horn, but you can search for one.

Good luck.

Chuck



Motorola used some really nice dual voicecoil Speakers in their
Bridge to Bridge version Modar Vhf Radios. These were designed in just
for this specific purpose, to combine audio from both the main
Receiver, and the Ch 13 Monitor receiver, that was grafted on the top
of the main radio. I always liked the simplicity of this design.
Maybe Motorola still has some of these in the supply system......


Bruce in alaska
--
add a 2 before @

On Fri, 21 Oct 2005 14:37:54 GMT, chuck wrote:

There are a couple of ways to do this.

1. Use resistive pads at the outputs of the two radios and a resistive
summation circuit to feed a separate amplifier which then feeds the
single speaker.

Not a great idea in that you'll want to be putting something like a 3-4 ohm pad
in there. AND if you have a 20 watt output (not likely into 8 ohms) you'll want
to use a 20 watt resistors. (atually 20watt resistors will get pretty damn hot!)
Not to mention you'll be loosing most your output power in heat. Pretty poor
solution. - If you don't care about the loss then use some like 3 ohms for the
resistors. Assuming the amps are rated to drive no less than 4 ohms this will
keep you safe if the horn is 4 or 8. Seems like a rather silly solution with
this much power loss. Best you'll ever get is less than 3 watts to the speaker
at full amp output.


2. Use a stereo-to-monaural isolation transformer backwards. Each radio
feeds one stereo input and the monaural winding feeds your single speaker.

Except for the DC component this is no different than just tying the leads
together. The transformer provides DC isolation not AC isolation. The outputs
from the two radios are likely ALREADY isolated in terms of the DC. This is not
a option.

wrote:
On Fri, 21 Oct 2005 14:37:54 GMT, chuck wrote:


There are a couple of ways to do this.

1. Use resistive pads at the outputs of the two radios and a resistive
summation circuit to feed a separate amplifier which then feeds the
single speaker.


Not a great idea in that you'll want to be putting something like a 3-4 ohm pad
in there. AND if you have a 20 watt output (not likely into 8 ohms) you'll want
to use a 20 watt resistors. (atually 20watt resistors will get pretty damn hot!)
Not to mention you'll be loosing most your output power in heat. Pretty poor
solution. - If you don't care about the loss then use some like 3 ohms for the
resistors. Assuming the amps are rated to drive no less than 4 ohms this will
keep you safe if the horn is 4 or 8. Seems like a rather silly solution with
this much power loss. Best you'll ever get is less than 3 watts to the speaker
at full amp output.


Which of us is confused here? I offered as one solution the use of
resistive pads "... to feed a separate amplifier which then feeds the
single speaker". There is really nothing to limit the power that the
separate amplifier could produce. Use a 20 watt amplifier and get 20
watts out. Pretty simple concept.

I certainly agree it's not a "great" idea. But it is not nearly as bad
as what you imagined I said. If there are volume controls on the units
being combined, then power into the pad could be as small as you'd like
and there would be no power loss to speak of. But if the full outputs
were being fed into the pad, then some power dissipation would have to
occur. Still, it is unlikely that anything like 20 watts rms would be
continuously fed into a speaker on a cruising yacht so the resistors
would not have to be rated for such high power.

This is basically an alternative version of the auto stereo booster amp
you suggested. Probably cheaper, but not certainly not simpler.


2. Use a stereo-to-monaural isolation transformer backwards. Each radio
feeds one stereo input and the monaural winding feeds your single speaker.


Except for the DC component this is no different than just tying the leads
together. The transformer provides DC isolation not AC isolation. The outputs
from the two radios are likely ALREADY isolated in terms of the DC. This is not
a option.

I think you misunderstood what I suggested and how such an isolation
transformer would work. RF power combiners are routinely used for this
exact purpose (at RF, of course) and easily provide on the order of 30
dB of isolation. Although I have never worked with a hybrid or combiner
at audio frequencies, one can easily be designed. You can find passive,
transformer-type audio combiner circuits on the Internet. although these
are generally for low-level signals. They can provide up to 55 dB of
isolation. It is my understanding that power-level hybrids are
manufactured but I have been unable to locate any on the web. A very
simple solution if a power hybrid can be found.

The dual voice-coil speaker, as I mentioned in my subsequent post, is
undoubtedly the best solution in my opinion.

Regards,

Chuck

On Sun, 13 Nov 2005 15:53:09 GMT, chuck wrote:

wrote:
On Fri, 21 Oct 2005 14:37:54 GMT, chuck wrote:

Which of us is confused here? I offered as one solution the use of
resistive pads "... to feed a separate amplifier which then feeds the
single speaker". There is really nothing to limit the power that the
separate amplifier could produce. Use a 20 watt amplifier and get 20
watts out. Pretty simple concept.


You're right.. Missed the additional AMP included. Same as the 'off the shelf'
car amp. Doesn't seem like the fella is likely to be capable of rolling is his
own here.


I think you misunderstood what I suggested and how such an isolation
transformer would work. RF power combiners are routinely used for this
exact purpose (at RF, of course) and easily provide on the order of 30
dB of isolation. Although I have never worked with a hybrid or combiner
at audio frequencies, one can easily be designed. You can find passive,
transformer-type audio combiner circuits on the Internet. although these
are generally for low-level signals. They can provide up to 55 dB of
isolation. It is my understanding that power-level hybrids are
manufactured but I have been unable to locate any on the web. A very
simple solution if a power hybrid can be found.

The dual voice-coil speaker, as I mentioned in my subsequent post, is
undoubtedly the best solution in my opinion.


Never heard of a audio combin at high power levels. Plenty of stuff around for
low or line level combining. Never heard of anything handling 20watts. Doesn't
seem like a particularly useful thing.