Re: [PSUBS-MAILIST] I NEED A SPEAKER!

[Gregc02@ibm.net]

From:           	"Captain Nemo" <vulcania@interpac.net>
To:             	<personal_submersibles@psubs.org>
Subject:        	Re: [PSUBS-MAILIST] I NEED A SPEAKER!
Date sent:      	Thu, 30 Nov 2000 00:17:05 -0000
Send reply to:  	personal_submersibles@psubs.org
Pat,

I wouldn't think that you'd get much volume out of it in the air, although it might be OK for talking 
to your divers within a few feet. I think that if you switch it into use as a microphone, like an 
intercom, that you should be able to use it to receive sound from outside (submerged) as well. 
With a matching rig on the surface boat you'd have two way communication. If I remember 
rightly, the underwater telephones we had on the navy subs (UQC) used single side band shifted 
up to about 6 or 8 kc for better range (it sounded like high pitched Donald Duck on a regular 
sonar) but for short range use regular audio should be fine. 
If you use a regular car stereo amps, voltage shouldn't be a problem. Most regular speakers are 
8 ohm impedance and when they're being driven to full output there isn't more than, at the most, 
10 or 20 volts involved.  Commercial PA systems use 25 or 70 volt line levels at full output but 
that is for longer output lines and multiple speakers, each with their own matching transformer; 
sort of like the power distribution system, with a stepdown tranformer in the alley feeding your 
house. "Single ended" amps at 12 volts can't put out more than a few watts, so the higher 
powered car stereo stuff uses a voltage converter in the amp to get a bit higher voltage for the 
outputs, but I don't think it'd be any kind of safety problem. I don't think you'd need much power; 
5 watts should do it just fine.
The driver that I'm going to use to put some "ping" in the water is rated at 100 watts but I don't 
think I'd want unprotected divers in the water near it.
I'll be out of town all of next week but I'm going to try the proof of concept "Radio Shack" special 
the week after, I'll keep you posted.

Hope this helps.

Greg
> Hi Greg,
> 
> Sounds like it could work underwater.  How well might such a speaker project
> sound in the air?  (I'd also like to broadcast while surfaced).  Sounds to
> me like it would at least be muffled when used in the atmosphere; but do you
> think it would be (almost) totally muted?
> 
> Thanks for the info; I think I'll experiment with this one myself.  I, too,
> thought about pool speakers; can't find one around here so far; and I'm not
> sure what the voltage might be.  Know anything about them?
> 
> VBR,
> 
> Pat
> 
> 
> 
> 


> 
> ----- Original Message -----
> From: <Gregc02@ibm.net>
> To: <personal_submersibles@psubs.org>
> Sent: Wednesday, November 29, 2000 11:31 PM
> Subject: Re: [PSUBS-MAILIST] I NEED A SPEAKER!
> 
> 
> > Pat,
> > My plan "A" is to put a cheap Radio Shack speaker horn into a plastic jar
> and fill it with mineral
> > oil or something similar and seal the top on and just let the plastic flex
> a little for compensation.
> > The oil should transmit the sound real well into the water and with the
> sealed horn all the sound
> > will come out of the front of the horn (with a cone type speaker, the
> sound off of the front and
> > back tend to cancel out).
> 
> > Greg
> > ex STS 3 (SS)
>