Hi,

I want to build a portable device that will help public school teachers in teaching. The system i was thinking will incorporate a "lapel" or a small microphone and a loudspeaker that can be heard over a small classroom of about 40-50 people. The system must be battery operated and somewhat handheld (or can be worn on the waist).

Since I'm new to audio, i don't know what speaker and speaker driver to be used. I saw one, the TDA2002 which is an 8W car speaker amplifier but i don't know if its going to be an overkill.

Can anyone help me with what speaker and amplifiers to be used?

Thanks a lot.

 

Hi,

I want to build a portable device that will help public school teachers in teaching. The system i was thinking will incorporate a "lapel" or a small microphone and a loudspeaker that can be heard over a small classroom of about 40-50 people. The system must be battery operated and somewhat handheld (or can be worn on the waist).

Since I'm new to audio, i don't know what speaker and speaker driver to be used. I saw one, the TDA2002 which is an 8W car speaker amplifier but i don't know if its going to be an overkill.

Can anyone help me with what speaker and amplifiers to be used?

Thanks a lot.

I think most teachers would be best helped by an old fashioned bullhorn.

 

If the microphone can hear the speaker (it will if they are close together) then there will be acoustical feedback howling.

 

If the microphone can hear the speaker (it will if they are close together) then there will be acoustical feedback howling.

microphone can hear speaker all the time. anyways, that doesn't answer my question...

 

There are a lot of off the shelf stuff that will do this. As Audio Guru suggested, you will have problems with squeal (feedback). Are you wanting to build something or find out where to buy it?

 

i want to build something. i actually have one (purchased one for around $45), and it doesn't suffer from feedback if the speaker is placed at the back of the speaker. Will an 8W amplifier going to be an overkill? I don't have an idea how loud an 8W is..

 

Hello,

Here is a table of sound intensities:
http://www.sengpielaudio.com/TableOfSoundPressureLevels.htm

They are talking about watts / square meter.

Greetings,
Bertus

 

I found a 4-ohm 0.5W speaker (the one inside a standard pc speakers). So i'm gonna be using a 1.5W audio amplifier. Would that be ok?

 

I found a 4-ohm 0.5W speaker (the one inside a standard pc speakers). So i'm gonna be using a 1.5W audio amplifier. Would that be ok?

No.

Use a speaker that is rated for more power than the amplifier.

Alternatively, use an amplifier that is rated for less power than the speaker.

However, a 1/2 Watt system won't be of any help.

 

What system could be good? Is 1.5W ok? I'll just find a speaker with higher rating.

Use a speaker that is rated for more power than the amplifier.
Alternatively, use an amplifier that is rated for less power than the speaker.

Thanks for the info.

 

It is not the number of people in the audience that will make the difference, but the size of the room. The more wattage the more the clarity. Volume is independent of wattage. You can turn up any audio amplifier and produce the same volume no matter what the wattage.
You will want any amplifier capable of 15 - 30 watts driving an 8 ohm,
8 inch speaker. Any musical instrument store will have cheap vocal range microphones with a wireless sender/reciever. Then just build the amplifier.
I hope this helps.
Dan

 

having been a touring sound engineer for...all my life, I would say that this seems kinda impractical. There are too many consumer based mics, amps and audio mixers available to support small meeting rooms of 50-60. If yur inclined to build it then make sure you take gain structure and headroom into account. Otherwise you will have one squealing unintelligible mess.

 

Volume is independent of wattage. You can turn up any audio amplifier and produce the same volume no matter what the wattage.

No.
A powerful amplifier will be able to be much louder than a low power amplifier.

People near the back of a room will be far from the speaker so the speaker must be loud enough for them to hear it. But the clarity will be bad if the reverberating sounds are the same loudness or louder than the direct sound from the speaker.