Author Topic: speaker hook-up question  (Read 4285 times)

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Offline simpson

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speaker hook-up question
« on: November 21, 2013, 11:29:20 pm »
This is a theoretical question.

Let's say I have a 100-watt audio mono amplifier. I also have 2 speakers that are each rated for 50 watts.

Theoretically, can I use both these speakers together safely with this amp?

If so, should I connect these speakers to the amp in series or parallel?

Or, will neither work and I should just get a 100-watt speaker?
 

Offline tony3d

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Re: speaker hook-up question
« Reply #1 on: November 21, 2013, 11:41:22 pm »
You really need to make sure the total impedance does not fall below 4 ohms. A lot of amps become unstable under four ohms. Are the speakers ratings for RMS wattage? If so you should be ok. If the ratings are for peak wattage, watch your volume settings. Also, keep in mind if this is a solid state amp, and you are at 4 ohms, your output may be considerably higher than 100 watts.
 

Offline AmmoJammo

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Re: speaker hook-up question
« Reply #2 on: November 21, 2013, 11:46:23 pm »
You need to make sure you're not running the amplifier below its minimum rated impedance. (whether than be 1ohm, 2ohm, 4ohm, or higher)

But for a theoretical question, yes, the speakers will each get half the power.

Depending on the impedance of the speakers, you may need to wire them in series, or parallel, to keep the impedance above the amplifiers minimum impedance ;)

If the speakers are 4ohm, and the amplifier is stable at 2ohm, you can wire them in parallel... But if the amp is only 4ohm stable, you'd be better off running them in series (although this would result in less power)
« Last Edit: November 22, 2013, 01:22:51 am by AmmoJammo »
 

Offline simpson

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Re: speaker hook-up question
« Reply #3 on: November 22, 2013, 12:48:32 am »
Thanks for the above replies.

My main question is: should the speakers be hooked up in series or parallel or doesn't it matter?
 

Offline AmmoJammo

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Re: speaker hook-up question
« Reply #4 on: November 22, 2013, 01:23:26 am »
 :o

Depending on the impedance of the speakers, you may need to wire them in series, or parallel, to keep the impedance above the amplifiers minimum impedance ;)

If the speakers are 4ohm, and the amplifier is stable at 2ohm, you can wire them in parallel... But if the amp is only 4ohm stable, you'd be better off running them in series (although this would result in less power)
 

Online IanB

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Re: speaker hook-up question
« Reply #5 on: November 22, 2013, 01:29:57 am »
Thanks for the above replies.

My main question is: should the speakers be hooked up in series or parallel or doesn't it matter?

As long as the speakers are identical I think it's safest to wire them in series (remembering to observe polarity when you do so).

If you get insufficient volume with series wiring, then start investigating whether the amp is able to drive them in parallel.

Wiring in parallel will often be OK if you keep the volume down to moderate levels, and is especially suitable if the two speakers are different (e.g. main speaker in one room and satellite speaker in another).
I'm not an EE--what am I doing here?
 

Offline Six_Shooter

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Re: speaker hook-up question
« Reply #6 on: November 22, 2013, 03:56:32 am »
Ammo Jammo has it.

There is no one catch all wiring configuration that is correct.

All amplifiers have certain rating and specifications they will work in, same goes for the speakers.

Here's something to cook the noodle.

power does NOT kill speakers, at least it's not the cause of 90% of speaker failures.

What usually kills a speaker is driving them with a clipped signal. When a signal clips, it is pushing DC current to the speaker for a long time, while it may only be micro or nano seconds this is a long time to have large amounts of DC current going to a speaker repetitively. With the frequency that these clipped signals occur it does not give sufficient time for the voice coils to cool down. This excessive heat build up causes the voice coil to fail.

Many times you can run a lot more power into a speaker than it's rated for IF the signal NEVER clips. I have done this countless times over the years, both in my own audio systems, usually car audio and other people's systems. I had one car, a 1984 Sunbird, that I left the factory front speakers in, that were already 12 or so years old. These speakers were rated for 5W each. I ran these off a 50W per channel amp for a couple years, without issue.

Now that's looking at the electrical limits, mechanical limits are a very different thing...

I have only had one time that I can recall that power definitely killed a pair of speakers, 15" Memphis Audio LVS subwoofers that were connected to 4000W each. It was power that killed these because it wasn't the electrical limits that were reach, but the mechanical limits. The power came on so quickly (IIRC we were using a 60Hz tone at the time), and so strong, that the voice coils of both subwoofers jumped out of the magnetic gap and folded the cones inside out. I had never seen that before and haven't seen it again since.
 

Offline AmmoJammo

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Re: speaker hook-up question
« Reply #7 on: November 22, 2013, 04:59:02 am »
When a signal clips, it is pushing DC current to the speaker for a long time, while it may only be micro or nano seconds this is a long time to have large amounts of DC current going to a speaker repetitively.

Its not DC, its still AC. Whether is be a sinewave, triangle wave, or a square wave (in the event of severe clipping), its still an AC signal, as its still alternating current, between positive and negative ;)
 

Offline Six_Shooter

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Re: speaker hook-up question
« Reply #8 on: November 22, 2013, 05:15:32 am »
When a signal clips, it is pushing DC current to the speaker for a long time, while it may only be micro or nano seconds this is a long time to have large amounts of DC current going to a speaker repetitively.

Its not DC, its still AC. Whether is be a sinewave, triangle wave, or a square wave (in the event of severe clipping), its still an AC signal, as its still alternating current, between positive and negative ;)

The overall signal is AC, yes, but the peaks, where it's clipped, or when it becomes clipped, becomes a DC signal for brief periods, both at the positive and the negative peaks of the waveform. When there is no change in voltage up or down, that is a DC signal, as I said this may only occur for micro to nanoseconds at each peak of the waveform, it's still considered to be DC at that point. The speaker will actually move to it's peak outward or inward movement, may not be the XMAX of the speaker but the farthest travel based on the power applied, and hang there, just like a DC signal from a battery would do, again, only for a brief period when it's a changing waveform.

Think about it this way, take your square wave, if you only look at a very short time, where the voltage is high, it would look EXACTLY like a DC signal, because you wouldn't see the change in voltage to 0 (or below if the low is below the ground ref), it's the same thing with a clipped music signal from an audio amplifier, for those brief periods it IS a DC voltage being applied to the speaker, there is no change in voltage up or down, which is a major part of the definition of DC current. The fact that the signal changes at a higher frequency than 0Hz is irrelevant at particular period of time.
 

Offline AmmoJammo

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Re: speaker hook-up question
« Reply #9 on: November 22, 2013, 05:40:48 am »
if you only look at a very short time, where the voltage is high, it would look EXACTLY like a DC signal, because you wouldn't see the change in voltage to 0 (or below if the low is below the ground ref),

 

Online IanB

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Re: speaker hook-up question
« Reply #10 on: November 22, 2013, 08:20:58 am »
It's not about whether it is dropping below 0 V, it is a about whether or not the signal is changing with time (whether dV/dt is 0 over the interval of interest).
I'm not an EE--what am I doing here?
 

Offline Anks

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Re: speaker hook-up question
« Reply #11 on: November 22, 2013, 10:51:09 pm »
After working in the audio industry for many years and still do I can tell you that is as nothing to do with DC when a speakers fails unless the transistors in the amp have shorted clamping it's outputs to the dc power rails.

What happens when a square wave is reproduced by a speaker(for instance clipping) is that the mechanical movement of the speaker try's to represent this. So what in essence (taking resonance and many other variables out of the equation) is that while the sound wave is not changing in amplitude the speaker is still but needs to dissipate the amplifiers energy. As the speaker isn't moving it cant produce sound or cool its self with air flow so the energy get turned into heat. Eventually the voice coil breaks down and goes open circuit.

Other failures (such as over excursion) are of a mechanical nature but are best left out of the conversation.
 

Offline Mark Hennessy

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Re: speaker hook-up question
« Reply #12 on: November 23, 2013, 04:27:50 pm »
The problem with a clipping amp is compression.

Music has a high PMR (peak to mean ratio) - perhaps 20dB, in which case, if we turn up the amplifier so that the peaks reach 100 watts, the mean value is only 1 watt. Strange but true.

If you turn the amp up beyond this point, the peaks don't get any louder (because they are already clipped), but the mean (or average) power rises, and this eventually thermally overloads the voice coil with predicable results.

It has very little to do with higher harmonics being produced, or indeed DC content of the signal (as most audio signals are highly symmetrical about 0V, so don't have a DC component). It's mostly compression: http://sound.westhost.com/tweeters.htm

Use Audacity to get an idea of the PMR of your favourite music - on the level meters, the RMS level is shown in light green, while the peak level is shown in bright green. The waveform display also uses two different shades (of blue) to show this.
 

Offline ciccio

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Re: speaker hook-up question
« Reply #13 on: November 23, 2013, 05:50:27 pm »
When you speak of "speakers" you refer to single speaker drivers (eg. a wide range drive, a woofer, a tweeter) or to speaker systems (two or more drivers with a crossover network)?
In the first case, you can wire them in series, but this will result in double the impedance and half power delivered by the amplifier.
In the second case series connection is usually not reccomended: the impedance of one speaker system will interact with the crossover circuit of the other (and vice versa) and the cut-off frequencies will be modified, with risks for the speaker's drivers safety.
As for power handling, I've learnt that a powerful amplifier is usually better for the safety of high frequency drivers: less clipping equals lower high harmonics dissipated in the tweeter's voice coil.
If the parallel impedance is too low, this will lead to an overheated amplifier, to protection circuits' activation or even amplifer failure, but this depends, obviously, on the amplifier's design.
Ciccio

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