Speaker Power Handling

[69stingray]

Hello everyone, I am having a brain-cramp figuring out power handling. For the sake of conversation, let’s say I have a speaker that has a power rating of 10-Volts. At 10-Volts, it is fine, at 11-volts, it blows up.

If I connect two of these drivers in series, what is the maximum input voltage before they blow up?

If I connect two of these drivers in parallel, which is the maximum input voltage before they blow up?

[Ron E]

20V series
10V parallel

[69stingray]

See, I thought it was opposite for some reason. In series, the maximum input voltage would be the same and in parallel it would be double...

[Original Burnedfingers]

Speaker handling ratings are a joke.

I seen and experienced many instances where it means absolutely nothing. It is a means to sell the product or move you toward a higher model up the line.

Example:

A model 9 Altec book shelf speaker is rated to handle amplifiers in the 18-250 watt range. Another specification by Altec on the same speaker says long term power handling capacity 60 watts pink noise.

The same speaker was lunched by a 40 watt amplifier. The same speakers were rebuilt and driven by a higher powered amplifier which exceeded the manufacturers specifications. The result was no further damage was suffered by that pair of speakers.

Conclusions I have drawn over the years are that more damage can and will result from a smaller amplifier being over driven/driven into clipping thus over heating the voice coil of the driver causing severe damage which will require rebuilding the speaker. Speakers in most cases will withstand an amplifier that is larger than their ratings given that some care is given.

I drove Klipsch Heresy speakers which are rated at 100 watts with Altec Lansing model 9440's in bridge mode capable of delivering in excess of 800 watts per channel.

So, what do ratings really mean anyway? Maybe not too much after all. Common sense might be a better indicator. In other words don't put in 18db of gain at the 40 HZ band in your EQ and expect your speaker to live because it just might not make it.

Oh, there is no magic number such a 10 volts and the speaker lives and 11 and its toast.

[joe carrow]

Nope, Ron's got it.

Power is voltage times current, and if the speaker is a resistor, you have to see that the voltage across it comes from the current passing through it. It's Ohm's law: Voltage = Current x Resistance

If the speakers are in parallel, the voltage of the two speakers is equal- regardless of their resistance. This means that more current (and thus power, since voltage is equal) will flow through whichever has a lower resistance.

If the speakers are in series, the current through each is equal since if it goes through one, it has to go through the other to complete the circuit. The voltage across each resistor is determined by its resistance and ohm's law. The voltage from current flowing through each adds up to the total voltage across the two of them. Only if the resistances are equal will a 20 volt input give 10 volts on each speaker.

Power is found from Power = Current x Voltage, so if two speakers are in series, whichever has the higher resistance will receive the most power.

Power handling in speakers is a bit more complicated than this. A lot of the time a speaker will run out of excursion (the cone will be moving too far, distorting the sound and causing noise) at low frequencies. Many speakers will do this without even using much amplifier power. We say that these speakers are excursion limited. You can increase this speaker's power handling by cutting down on the low frequency signal sent to it.

Thermal power handling is when a speaker heats up too much. A light bulb is basically a resistor, and you know how hot those get. 100 watts can really cook if there's nowhere for the heat to go. If a driver starts to get too hot, its resistance increases- and this causes all sorts of problems that you don't want to have happen. This isn't a matter of frequency, so the only way to get more output is to sit closer to the speakers or add more speakers in series/parallel- which I think was really the root of your question.

[69stingray]

Thanks everyone, I just needed to be re-aligned. I agree the actual rating are somewhat of a joke, but I couldn't remember which one doubled and which one stayed the same.

heating the voice coil of the driver causing severe damage which will require rebuilding the speaker.

The primary purpose of the RMS power rating would be to avoid this and I agree, you usually hit excursion limits long before the rating of most drivers.