IPB

Welcome Guest ( Log In | Register )

 
Reply to this topicStart new topic
Amplifiers: Questions., Couple of questions!
krafty
post Jun 26 2012, 00:43
Post #1





Group: Members
Posts: 274
Joined: 20-March 10
Member No.: 79175



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
Go to the top of the page
+Quote Post
Glenn Gundlach
post Jun 26 2012, 04:23
Post #2





Group: Members
Posts: 364
Joined: 19-April 08
From: LA
Member No.: 52914



I'm sure many (most?) here could listen to it and give a reasonable evaluation of the shortcomings. When I see the word 'piezo' I cringe. Condenser, electret and dymanic are usually better choices for microphones. The TDA2005 is a 20 Watt bridge amplifier for cars. You may simply be overloading the daylights out of that little amplifier.

There isn't an easy answer to your power question. Is the room 'live' or damped? A reverberant room is difficult because of all the reflections / echos. A damped room will absorb a lot of the power but be more intelligible for speech and not so good for music. How efficient are the speakers? How are they connected to the amplifier? Series, parallel, combination?

Need a lot more information.

G
Go to the top of the page
+Quote Post
Speedskater
post Jun 26 2012, 13:06
Post #3





Group: Members
Posts: 137
Joined: 12-December 07
From: Cleveland, OH
Member No.: 49500



That's a very large room in terms of home hi-fi equipment. What is really needed is a small PA (Public Address) system. With that many speakers a 70 Volt output PA system would be appropriate. A 25 Volt or a 100 Volt unit would also be OK.


--------------------
Kevin
Go to the top of the page
+Quote Post
Arnold B. Kruege...
post Jun 27 2012, 12:31
Post #4





Group: Members
Posts: 3646
Joined: 29-October 08
From: USA, 48236
Member No.: 61311



QUOTE (krafty @ Jun 25 2012, 19:43) *
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).


These days a "small cheap speaker" could anything. Offhand, I'd figure that you're not going to risk driver burnout until you get above 20 watts per speaker.

How you have the speakers hooked up could be very important. If they are hooked in parallel, each amplifier could be seeing as low as 1 ohm load, which is very bad, on top of the obviously too-little power from the amps if they were seeing an ideal load.
Go to the top of the page
+Quote Post
krafty
post Jul 4 2012, 01:53
Post #5





Group: Members
Posts: 274
Joined: 20-March 10
Member No.: 79175



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
Go to the top of the page
+Quote Post
uart
post Jul 4 2012, 09:41
Post #6





Group: Members
Posts: 782
Joined: 23-November 04
Member No.: 18295



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
Go to the top of the page
+Quote Post

Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



RSS Lo-Fi Version Time is now: 23rd July 2014 - 20:41