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Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Alex1M6 wrote ...
Why would this BTL chip show speaker polarity in its datasheet if it doesn't matter?
Confused(.com)
@ConKbot of Doom Just from looking at the speaker cone when I touch the audio input, it does move in or out slightly depending on which way I have it connected.
I measured the voltage between the output pins and there is about 100mV DC between pins 17-15 and 14-12, with the non-inverting sides being the more positive pins.
Its not polarity. Don't think of it that way. Its PHASING!
If you have two stereo speakers, and the phasing is backwards, you are going to get some strange audio effects and the stereo imaging is going to way out of whack.
Its to ensure that you get the proper phasing when you hooking up multiple speakers.
Imagine you are in a pool in the water.
Each hand represents a speaker.
Now move your hands towards you and then away from you (both at the same distance). This represents a single AC cycle. When you do that, the water ripples / waves will hit you at the same exact time. This is what you want with a stereo pair of speakers. Each audio wave to hit your ears at the same time)
Now move one hand towards you in the water, and the other away from you. You will now get a delay between when each ripple / wave hits you.
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
EasternVoltageResearch wrote ...
Alex1M6 wrote ...
Why would this BTL chip show speaker polarity in its datasheet if it doesn't matter?
Confused(.com)
@ConKbot of Doom Just from looking at the speaker cone when I touch the audio input, it does move in or out slightly depending on which way I have it connected.
I measured the voltage between the output pins and there is about 100mV DC between pins 17-15 and 14-12, with the non-inverting sides being the more positive pins.
Its not polarity. Don't think of it that way. Its PHASING!
If you have two stereo speakers, and the phasing is backwards, you are going to get some strange audio effects and the stereo imaging is going to way out of whack.
Its to ensure that you get the proper phasing when you hooking up multiple speakers.
Imagine you are in a pool in the water.
Each hand represents a speaker.
Now move your hands towards you and then away from you (both at the same distance). This represents a single AC cycle. When you do that, the water ripples / waves will hit you at the same exact time. This is what you want with a stereo pair of speakers. Each audio wave to hit your ears at the same time)
Now move one hand towards you in the water, and the other away from you. You will now get a delay between when each ripple / wave hits you.
Get the idea?
Yes thanks, got it.
However now it seems I have other problems with this circuit. I can actually pick up radio stations by touching an audio input pin and waving my arms around in the air to tune it!
I take it this means I have a poor layout or something like that? Should I be using ferrite beads anywhere to filter this out?
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Add in a 10k resistor from your audio input to ground, should solve your problem. Alternatively, you can use a variable resistor and it will double as a volume control (one end of the resistor to ground, other end to audio source, the middle to the amplifier input pins).
as per the speaker situation, I can see a situation if one were listening to actual music (as opposed to sine waves...) where, for example, there is a drum beat which has a large positive spike which quickly falls back down to 0v, well before the low pass filters have a chance to do anything. The end result would be the speaker cone sharply shooting out or in depending on the phasing. That said, it shouldn't really make much of a difference.
I would connect the non-inverting output to the + end of the speaker, it is how normal amps are wired.
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
... wrote ...
Add in a 10k resistor from your audio input to ground, should solve your problem. Alternatively, you can use a variable resistor and it will double as a volume control (one end of the resistor to ground, other end to audio source, the middle to the amplifier input pins).
as per the speaker situation, I can see a situation if one were listening to actual music (as opposed to sine waves...) where, for example, there is a drum beat which has a large positive spike which quickly falls back down to 0v, well before the low pass filters have a chance to do anything. The end result would be the speaker cone sharply shooting out or in depending on the phasing. That said, it shouldn't really make much of a difference.
I would connect the non-inverting output to the + end of the speaker, it is how normal amps are wired.
Thanks for this information, I really appreciate it!
Also I am sorry if any of my previous replies came across as aggressive or anything like that. I was having a bad day yesterday but that is no excuse.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
since there may be 6 'speakers' in a 5.1 audio system it is important that the relative 'polarity' of each speaker is correct, and a public/performance sound system may have many 'speakers' so by convention a positive signal at the amplifier input produces a positive sound pressure. So a 'speaker' drive unit moves the cone outwards when its + terminal is positive with respect to its - terminal and similarly an amplifier is non-inverting. The same convention also applies to microphones etc.
If ALL amplifiers are inverting instead of non-inverting and/or all speakers are 'reversed' polarity there will be no problem.
(some 'Golden Ears' Hi-Fi reporters say they can tell the difference but I never could)
So, for a single speaker (mono-phonic) system it doesn't matter, with multiple speakers stick to the convention and all speakers should end up with the correct phase relationship to each other.
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Inverting and non inverting outputs on an audio amplifier chip
