Alternative current

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Baptiste
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Alternative current

Post by Baptiste » Jan 13, 2018 8:13 pm

Hi
How can I mesure the power(max) of an audio signal which I guess is an alternative current?

I am asking this because I bought an amplifier of 50w and a speaker of 12w. Eventullay, if I supply the speaker with a power 50w it would be broken but I can regulate the power delivered by the amplifier with a little potentiometer but I don t know "how far I can turn it" so I need to know how to mesure the power of a (alternative) current with a multimeter.

Instead of limiting in output power of the amplifier, I think it might use a resistance but I what kind of resistance I should use.

Regards

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Re: Alternative current

Post by Dauntless » Jan 13, 2018 11:00 pm

Been awhile since I've even looked at consumer audio. It used to be that an amp would give continuous power in watts while a speaker would give peak, so you definitely needed the bigger number on the speaker if you were going to crank the amp up. Then the speakers were usually 8 ohm but sometimes they were 4 and sometimes 16.

Don't have a clue of your use, but now you see speakers with their own amps, comes with a match, right?

https://www.amazon.com/gp/aw/d/B01C6P0Y ... ref=plSrch
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Punx0r
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Re: Alternative current

Post by Punx0r » Jan 15, 2018 5:17 am

The amplifier already has a potentiometer to limit the output - it's called the volume control...

It's a myth that using a powerful amp you will end up unintentionally destroying your speakers - the reverse is more likely. As long as you don't use a powerful amp to deliberately drive your speakers into obvious distortion they will be fine.

Also, ignore any "peak" ratings like PMP or PMPO, they are near-meaningless marketing garbage. Only the RMS rating is accurate and means anything.

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Re: Alternative current

Post by Baptiste » Jan 15, 2018 3:19 pm

Ya but smth is quite strange. When I rise the volume the amplifier there is a moment when the speakers do like a big "boom" and stop playing music. I believe that this is because they are receiving more than 12w. Have you got an explanation to this?

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Re: Alternative current

Post by Addy » Jan 15, 2018 3:26 pm

Baptiste wrote:
Jan 15, 2018 3:19 pm
Ya but smth is quite strange. When I rise the volume the amplifier there is a moment when the speakers do like a big "boom" and stop playing music. I believe that this is because they are receiving more than 12w. Have you got an explanation to this?
That could be the amplifier detecting a problem and shutting down to protect the system. Some amps that I use do that sort of thing - if too much current is drawn on the output they shut down to prevent damage.

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Re: Alternative current

Post by Baptiste » Jan 15, 2018 3:47 pm

If this can help, here are the links of the speakers and the amplifier.
https://m.aliexpress.com/item/326067949 ... 2606794975
https://m.banggood.com/TPA3116D2-Digita ... m-alsolike

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Re: Alternative current

Post by Addy » Jan 15, 2018 4:06 pm

Wow, that board uses the TPA3116 amplifier IC, which is the same with my amp. That's the one I had which shuts down to protect from damage.

From the datasheet:
"The TPA31xxD2 devices are fully protected against faults with short-circuit protection and thermal protection as well as overvoltage, undervoltage, and DC protection."

So one of these protections is kicking in if you turn the volume up too high. You might want to limit the amp's power to prevent that kind of situation. There are a few ways you could do this. You could lower the supply voltage. Also, that amp's gain can be configured by changing some resistors, you could lower the gain which would make it quieter. It even has some other resistors which can limit the voltage of the amp output to limit the power.

Check the datasheet for the details about gain setting and power limiting: http://www.ti.com/lit/ds/symlink/tpa3116d2.pdf
However, these options would require some reverse engineering of the amplifier board you bought.

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Re: Alternative current

Post by Chalo » Jan 15, 2018 4:51 pm

A simple way to limit the power would be to use a power supply that doesn't produce more than the amp and speakers consume at their maximum rating. I made a nominally 40W portable amp and ran it with ten AA NiMH batteries. They probably could have produced more than 40W into a resistive load, but in the case of the amp, a higher peak demand would have resulted in voltage sag and power attenuation.

I agree with Punx0r; if the sound is reasonably good, the speakers will be fine. They'll sound like they're self-destructing before they actually self-destruct.
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Re: Alternative current

Post by Dauntless » Jan 15, 2018 5:23 pm

So this boom and bust in the speaker, that is what my now dead car stereo used to do, until maybe last summer. Now it does NOTHING!

My real concern with an undersize speaker is sound quality. Inevitably bad, right? So as a teenager I got my first stereo receiver/amplifier by fixing someone's junk with a bad transport resister. Those of modest knowledge at the time passed on the thought that the speaker would cause that, dont know how true thag was but it was sounded similar to an inadequate motor/contoller match. It was old even then, now they make things differently so I can't compare.

If you get an answer to your off and on problem I'd be curious to hear about it.
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Re: Alternative current

Post by Punx0r » Jan 15, 2018 6:16 pm

Baptiste wrote:
Jan 15, 2018 3:19 pm
Ya but smth is quite strange. When I rise the volume the amplifier there is a moment when the speakers do like a big "boom" and stop playing music. I believe that this is because they are receiving more than 12w. Have you got an explanation to this?
Are you sure the 12V power supply for the amp isn't dropping in voltage due to the load, and causing the amp to cut out?

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Re: Alternative current

Post by Baptiste » Jan 16, 2018 12:39 pm

Punx0r wrote:
Jan 15, 2018 6:16 pm
Baptiste wrote:
Jan 15, 2018 3:19 pm
Ya but smth is quite strange. When I rise the volume the amplifier there is a moment when the speakers do like a big "boom" and stop playing music. I believe that this is because they are receiving more than 12w. Have you got an explanation to this?
Are you sure the 12V power supply for the amp isn't dropping in voltage due to the load, and causing the amp to cut out?
Thank you.
I found a way to avoid this problem but I don t know why it is working. I connected the two speakers in series instead of in parallel. I tought that this would make the speakers less vulnerable.

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Re: Alternative current

Post by amberwolf » Jan 16, 2018 1:47 pm

If they're in series, using both amps, you're cutting the power they use in half or less because nothing is ground referenced anymore; you're just getting the difference between left and right channel. So it's not stereo, either: if you feed the same signal into both channels you won't get any sound at all.


If they're in series, using just one amp (which also isn't stereo, because you are only using half the sound information), seriesing from that channel's output to ground, you're probably cutting the power down to around 1/4 of what it was--first it's cut in half because you're only using one side of the amp, and then that is cut in half because you're doubling the resistance with two speakers in series.


Basically you're just reducing the total power used, so reducing voltage sag on the power supply.

Did you try testing as others suggested?

What were the results?

I notice that the repair to the battery you were using to power this amp here
https://endless-sphere.com/forums/viewt ... 2#p1339503
was never finished; so whatever problem you had there is probably still there and could be causing your present issue.

If you did fix that problem you didn't come back to that thread to report what it was and that it was fixed, so we have to assume it's still broken.

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Re: Alternative current

Post by Dauntless » Jan 16, 2018 2:12 pm

Baptiste wrote:
Jan 16, 2018 12:39 pm
I connected the two speakers in series instead of in parallel. I thought that this would make the speakers less vulnerable.
Assuming your speakers are identical, you cut the impedance in half by connecting them in parallel. Meaning that they were probably 8 ohms and you cut it to 4 ohms.

But here we go. Yes I was in a band as a teenager, yes I was a party DJ for 3 years in college with the sound system, yes I worked as a soundman at the same time with a staging company. But after college when I was done with that, it was out of my life. I think when you lower and raise impedance there's this 60% increase or 40% drop thing, I don't remember exactly but it seems obvious that decreasing resistance would increase output. So the 50 watt amplifier would effectively be at 8 ohms but capable of 30 or 80 depending on 4 or 16 ohm impedance. But you want the lower impedance with higher power amplifiers, so I remember running the V35 with the additional V30 in parallel with the big system. But is your amplifier up to running the low impedance? As you turn the sound up it's like the motor that's too big for the controller and it just sucks what it wants from the amp that can't handle it. It'll go off for a moment, maybe eventually blow the modern equivalent to a transport resistor, (Or they might still call it that) and maybe my car stereo is dead because my speakers weren't right even though I didn't turn it up at all. I think cars are normally 4 ohms, but if they set mine up at 2. . . .

So a mic is well under 1 volt, a line signal is 1 volt, I think a speaker signal is nominally 30 volts but of course varies up and down. (Don't want to try to look this up online, it'll probably confuse me more.) To get 30 volts, you multiply the impedance by the current, so divide the 30 by I assume 4 and you have 7.5, while by 8 is 3.75. Oh darn, this was stuff I sort of knew but didn't really understand when I was working with it, so how that really applies I'm not sure. The only guy at the company that knew more than I did back then was an electrical engineering major who has patents now but he was struggling along too.
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Re: Alternative current

Post by Dauntless » Jan 16, 2018 2:23 pm

Oh darn, is Amberwolf right that yours is stereo? Leaving a channel without a speaker will eventually blow it up, the more you turn it up the sooner. But that would be the channel you're not using. Did you mean you have two speakers EACH? I'm not sure what he's saying about cutting the power to a quarter, that doesn't jibe with my understanding.

In the time I'm writing these posts I'm STILL waiting for the pages of your equipment to open. AT&T is the worst.
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Re: Alternative current

Post by amberwolf » Jan 16, 2018 2:29 pm

Dauntless wrote:
Jan 16, 2018 2:23 pm
I'm not sure what he's saying about cutting the power to a quarter, that doesn't jibe with my understanding.
The side with no speaker doesnt' use significant power--no load means no current flow.

So if you used just one speaker on one side, it'd use half the power it would if you had a speaker on each side wired normally.

If you then put both speakers in series on that single side, it doubles the impedance, which cuts current flow in half, which cuts power usage in half.

Since that power usage is already half of what it was with two speakers wired normally, it means the total power usage would be only 1/4 of what it had been.


BTW, I don't know if his actual amp is stereo or not, but the chip is (I've seen them in stuff before).

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Re: Alternative current

Post by Baptiste » Jan 16, 2018 3:14 pm

I don t mean to supply the two speakers with a great power. They are tweeters. It is also not a big deal if the sound is not stereo.
Here below is a photo of my work.
The big speaker is a 25w one, I added a bass filter to it. The component at the bottom right is a voltage regulator. Nevertheless, I feel that the 25w speaker is not at 100% of its capacity. So I am now going to add a transitor to the audio signal to have a higher output audio signal ( when rising the supply of the amp, the music is not getting louder). I think that by doing this, an extra resistor will be needed on the tweeter circuit.
Attachments
_IMG_000000_000000.jpg

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Re: Alternative current

Post by Punx0r » Jan 16, 2018 5:58 pm

It looks like you have both the smaller speakers (which are 4ohm) connected to the left channel of the amp and the right channel is connected to a crossover to the large speaker?

if so, that isn't right.

For a start, two 4ohm speakers in parallel is a 2ohm load and your amp is rated for 4-8ohm. The 2ohm will overload it and *might* be what was causing the amp to cut out (overload protection circuit).

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Re: Alternative current

Post by dustNbone » Jan 16, 2018 7:01 pm

Sounds like an impedance mismatch to me. Putting the speakers in series doubles impedance. If the amp was expecting 8-16 ohms for example (quite common) and you connected a single 4 ohm speaker to it, that might trip a protection (overcurrent maybe). Put 2 in series and it's an 8 ohm load, and so is within the impedance spec.

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Re: Alternative current

Post by Dauntless » Jan 17, 2018 12:28 am

amberwolf wrote:
Jan 16, 2018 2:29 pm
If you then put both speakers in series on that single side, it doubles the impedance, which cuts current flow in half, which cuts power usage in half.
I thought he meant he had switched from series to parallel. Sounds likePunx0r does too. (Is this just getting more and more confusing?)

Are both speakers accounted for in his links? (Which I still can't open.) Are they both the same impedance? They are different in what ways besides being 12w and 25w? What is the crossover for on the other speaker output if there's no speaker?

A stereo 50w output means what for a single channel? Would your 12w and 25w total more or less than that single channel? I can't answer those questions because it matters if they are in series or in parallel. But it is indeed possible you're not using the full capacity of the 25w, but why would that matter?

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Re: Alternative current

Post by amberwolf » Jan 17, 2018 12:47 am

We could help him a lot better if he'd actually answer the questions being asked, with clear answers.

Without the answers, we can't know what's really going on, leading to just more confusion on both sides.

We don't even know that he has a working power supply for it, because it still wasnt' working the last time he posted to the thread about it, and never came back to answer the other questions there to help him fix it.

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Re: Alternative current

Post by Baptiste » Jan 17, 2018 2:49 pm

I have to apologise because I do not understand you quite well. In fact my knowledges in electricty are terribly low and so I kindly ask you to post less sophisticated answers because I often don t know what to do to answer your questions. :/
Here is a little scheme of the circuit. I hope that it would help.
The speakers are all 4ohm
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_IMG_000000_000000.jpg

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Re: Alternative current

Post by Dauntless » Jan 17, 2018 4:51 pm

You asked a question that is sophisticated, requiring a sophisticated answer.

But there might be a simpler thing for you to look for. Only part of your picture loads for me, I'm still working blindly. Get a second identical 25w speaker to hook to the other side, do not use the 12w at all. What MIGHT have been happening is you were lowering your impedance below where it wanted to work, OR you might have overloaded the one side by having no speaker at all and that is what shut it down. You need a match to both sides. A pair of 25w 4 ohm speakers might work just fine on this, whatever it is. But I'm still not sure what it is.
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Re: Alternative current

Post by liveforphysics » Jan 18, 2018 5:35 am

Thank goodness Amberwolf was on this thread.

Balancing channels stopped mattering after the days of tubes and output transformers.

The right side of that modern chip amps has no idea if the left side is on the same planet with it or not, let alone if it's connected to a speaker.

Your popping sound is from the step-wave function of connecting or disconnecting an input source, you can fix it by adding a resistor typically if you care, but it's not going to be related to over-powering your speaker or putting excessive heat into the voice coils of the drivers.

The amp only puts as much power into the speakers as you request of it by turning up the volume knob, and it's always better to have more amp than speaker for sound quality reasons if it's something you care about, but either way with any amp, just turning it down until the speaker isn't mechanically clipping or overheating it's voice coil is the solution (or throw the voice coil pair in series if for some reason you can't control yourself on the volume knob after it starts sounding awful).
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Re: Alternative current

Post by Baptiste » Jan 18, 2018 11:32 am

I unfortunately do not have an extra 25w speaker. While by the speakers I bought a 25w to release bass the bass frequences and two 12w speakers to release the trebel frequences. I used to connect the two 12w speakers two the "bass filter" (on my scheme) because it also a trebel filter. By doing this the music quality was quite good ( but I found that there was has too much trebel frenquences) but and that was a major issue, not loud.

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Re: Alternative current

Post by Baptiste » Jan 18, 2018 11:45 am

In a nutshell
I have a 2x50w amplifier, a bass and trebel filter, a 25w 4ohm speaker and two 12w 4ohm speakers. According to you, how should connect those component to have the best sound quality and/or the loudest sound? And should I by other componants to improve the quality/loudness of the sound?
Here are the links o the componants
Filter
https://m.banggood.com/2-Way-Audio-Freq ... s=myorders
25w speaker
https://m.banggood.com/3inch-4Ohm-25W-F ... s=myorders
12w speakers
https://m.aliexpress.com/item/326067949 ... 4cdb63rqY4
Amp
https://m.banggood.com/TPA3116D2-Digita ... s=myorders

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