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Amplifiers: Questions., Couple of questions!
krafty
post Jun 26 2012, 00:43
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1) For a small auditorium about 30 meters long, 20 meters wide and 4 to 6 meters tall, equipped with 12 small cheap loudspeakers (6 each side) along the hall, what is THE BEST WATTAGE amplifier for speeches? We have setup two TDA2005 circuits plus one small "workaround" for a preamplifier (actually a weaker amp before the power amp).... but it doesn't seem to deliver good sound. Was it because we needed a piezoelectric microphone? Is it best to be equipped with a real preamplifier?

2) When someone talks over the microphone, and the speakers "distorts" according to some tonal sylabs, what sign is that... bad amplifier, weak speakers or lack of a hardlimiter circuit?

3) Going around the previous problem, what kind of circuit must one have to "control" voice pitches so that one won't "shout" over the mic or not be clearly listened by the crowd (because his voice may be too low).


THANKS FOR ANY REPLIES

This post has been edited by krafty: Jun 26 2012, 00:46
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krafty
post Jul 4 2012, 01:53
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Well, this is a university project that consists in disassembling sized slot machines and take the parts to construct simple amplifiers systems. So basically we have 10W 8ohms speakers boxes with many TDA2005 stereo amp boards. We are not to "buy" anything, we have to "make" it out of those guts. The power is delivered from PC power-supply so we are short in options for systems above 12V. I think the room is a mix of damp and live since there are components which absorb sound but the roof is quite "bare", not having a proper ceiling.

We did set up 2 amps for each side. One amp takes care of microphone and it is setup as 3 speakers each side. Other amp takes care of audio from notebooks and it is set just as the mics. As for serial or parallel or combined I am not sure, all of them are connected to just one wire for each channel/amp. Being M for Mic and A for Audio, there is M1W1+A1W2+M2W1+A2W2+M3W2+A3W2 on one side and M1W3+A1W4+M2W3+A2W4+M3W3+A3W4. So wires W1 and W3 are one stereo amp and W2 and W4 are the other stereo amp.

The results were "OK". We had this poor microphone which was not "dynamic", so I believe that if someone buys a better mic, a dynamic one, we will have better results. But nevermind really, we have been told that a professional system is being purchased for that auditorium. However we will move those to classrooms, and I believe it will be just fine because they are much smaller.

This post has been edited by krafty: Jul 4 2012, 01:58
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uart
post Jul 4 2012, 09:41
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QUOTE (krafty @ Jul 3 2012, 16:53) *
Well, this is a university project that consists in disassembling sized slot machines and take the parts to construct simple amplifiers systems. So basically we have 10W 8ohms speakers boxes with many TDA2005 stereo amp boards. We are not to "buy" anything, we have to "make" it out of those guts. The power is delivered from PC power-supply so we are short in options for systems above 12V. I think the room is a mix of damp and live since there are components which absorb sound but the roof is quite "bare", not having a proper ceiling.

We did set up 2 amps for each side. One amp takes care of microphone and it is setup as 3 speakers each side. Other amp takes care of audio from notebooks and it is set just as the mics. As for serial or parallel or combined I am not sure, all of them are connected to just one wire for each channel/amp. Being M for Mic and A for Audio, there is M1W1+A1W2+M2W1+A2W2+M3W2+A3W2 on one side and M1W3+A1W4+M2W3+A2W4+M3W3+A3W4. So wires W1 and W3 are one stereo amp and W2 and W4 are the other stereo amp.

The results were "OK". We had this poor microphone which was not "dynamic", so I believe that if someone buys a better mic, a dynamic one, we will have better results. But nevermind really, we have been told that a professional system is being purchased for that auditorium. However we will move those to classrooms, and I believe it will be just fine because they are much smaller.


Hi krafty. The trick to debugging this is to temporarily replace some components/sub-systems with known good (consumer) parts to find the true "weak link". Forget about your mic and the tricked up pre-amp for now, just get a good pre-amp and feed a known good audio source (from digital player for example) and use this to test the sound of your power_amps/speakers. Vary the preamp output level until you get the best results. This experiment will tell you straight away which part of the system needs re-jigging.

This post has been edited by uart: Jul 4 2012, 09:42
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