Speaker Selection.

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premkumar9

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Hi,
In a hospital there is a requirement to install a speaker near the bed of each patient to listen the audio of the TV mounted on the wall. The volume of the speakers will be kept very low (audible to that patient with out disturbing others) and at the same time audio quality should be good. Can anybody give me some guidance on the selection of speaker and speaker box?
 
Use headphones, you can't get good quality at quiet levels (check for loudness compensation).
 
A cheap small speaker has a resonance at a fairly high frequency. When it is enclosed in a speaker box then its resonant frequency is increased which creates a "boomy" sound.
 
Boston Acoustics don't make that nice little radio anymore. They make a similar Solo mono radio and a Duo stereo radio both with 3.5" little speakers.
They probably use bass-boost because they have a Bass-trac system that reduces the bass boost when the volume is turned up.

My computer speakers use a 3" speaker with the biggest magnet I have ever seen on a little speaker. They sound pretty good for a little speaker and have an output of 4W RMS each.
 
Use a parabolic sound reflector. They use them in the music sections of large stores so the person standing directly underneath can listen to CD selections without disturbing anyone, even the person 5 feet away at the next listening booth. Very effective and adequate fidelity for TV.

Here is a link to one. I am sure there are cheaper versions, the ones at my local store don't look near as nice.

SoundTube FP6020 SoundTube Parabolic Speaker | Full Compass
 
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I don't think a granny in the hospital would want a dome like that over her head.
 
I think all the sick grannies should each have their own chamber (room?) so they can blast the TV sound and the others won't hear it.

I haven't been to a hospital for about 26 years (my son was born) so I don't know if the rooms are not private anymore. Maybe on the other side of the world they have millions of sick grannies in one room.
 
Hi,
A 3" ordinary speakerbox with a 3" 2W fullrange speaker will do the trick. If more than one patient is there in a single room you can connect them serially or parallely to get the required load resistance. Use a commercially available low rms cheap audio amplifier for this purpose.
 
The problem is that the sick grannies each watch a different TV show and some grannies are trying to sleep.
 
We can provide a switch for each speakerbox. When it is switched of insert the corresponding speaker resistance into the circuit!
 

Some of the speakers will be in rooms. But most of them will be in wards where so many beds will be there in the same hall. So another requirement is that the audio from the speaker near one bed should not cause much disturbance to adjacent patients if they don't want sound. I plan to mount the speaker on the wall with a bent clamp to avoid hindrance to the other movements.
Any advice?
 
I think the "wards" in India are like the "wards" in North America a few hundred years ago. India is in a completely different world or planet.
 
premkumar9 said:
Around 30.
Click to expand...

So you need maximum 30 speakerboxes in a ward

See the attached picture for connecting multiple speakers for a load resistance of 8Ω in effective assuming each one has 8Ω impedance.
In series connection, total resistance = R1+R2 where R1 and R2 are speaker resistance.
In parallel connection, total resistance = R1*R2/(R1+R2)

Suppose you are using a 2*20W stereo amplifier for this purpose for 8Ω load.
Each channel can hold 4 speakers of 8Ω in this way, so a total of 8 speakers you can connect.
For 30 speakers you need 4 stereo amps in this way. This is just an example you can connect more than 8 speakers if you have a higher power amplifier as the power will be equally distributed to each speakers. Got it?

Use a two way push type ON/OFF switch for each speaker. When it is swithched off switch over to a corresponding resistance connected, for example an 8.2Ω
 

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transistor495 said:
So you need maximum 30 speakerboxes in a ward


Use a two way push type ON/OFF switch for each speaker. When it is swithched off switch over to a corresponding resistance connected, for example an 8.2Ω
Click to expand...

What will happen if the speaker is simply disconnected with out connecting to another load resistance?
 
premkumar9 said:
What will happen if the speaker is simply disconnected with out connecting to another load resistance?
Click to expand...

That you can understand by looking on to the picture I have attached. Disconnecting one from a series connected speakers will disconnect the others also.
The amplifier will have certain load impedance. Simply disconnecting will affect the effective load. Adding resistance in place of that is not a good method because a speaker is not actually a resistance, but an inductive load.
If you really want a switch for each speaker, there's no other way I think unless otherwise you have separate channel for each speaker!
 
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