Finding out the power an unknown speaker can handle

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Hello. I found a couple of good-looking old Philips speakers in my parent's home, and I was thinking about using them in an amplifier I want to build. But I would like first to be sure that the speakers would be able to handle the power.

Is there any way to discover the maximum power a speaker can handle by making simple measurements in it? Any theory or rule-of-thumb?

They are 8 ohms and have something like 15cm diameter...
 
I would compare it to what is commercially available in a 15cm or 6" size. Try to get an approximation of the VC size.
Personally, unless this was something other than a typical 6" ( not a high end 6" ). I would limit it to 60 watts or less.

I consider Max power ratings to be functionally irrelevant. It is what is done with the wattage from -10 to -3db ( 1/10 - 1/2 ) power that is most significant.
Thermal/Power Compression:
Within 30sec of play a voice coil heats rapidly. This changes the electrical characteristics of the driver. So as more power is supplied more get wasted as heat, so it becomes a matter of diminishing returns - Power in gets no louder - just hotter. Depending on the materials, the heat will start to damage/melt/burn the voice coil.
I know someone who has devised a means of calculating VC temp, but that won't tell you how much abuse it will take, short of destructive testing.
With a volt meter and an SPL meter you can plot the SPL out vs Vin and you will see it start to plateau, that gives you an indication of thermal effects.
 
There are two components to power handling, thermal and mechanical. At bass frequencies the limitation is usually mechanical - the coil or spider will hit some sort of hard limits - usually this is the coil hitting the back plate of the magnet or the VC leads fatiguing or tearing off, or the spider hitting the front plate and tearing off the coil, etc...

The other element is thermal power handling. As a very rough rule of thumb, it would vary with diameter, say a modern driver with a 1" voice coil can handle ~50W, A 2" voice coil similarly constructed could handle 100W and a 4" voice coil 200W - a half inch would handle 25W. Thi s is just an example and the real power handling would vary a lot based on how the coil is constructed and what the coil insulation is made out of, etc... Things you can't necessarily know....

If the driver has a paper coil former or was built before 1980, it probably won't handle much more than 10W. The advent of quality car audio and dB drag races, etc have led to an increase in power handling and reliability over the last ~20 years. The major manufacturers have ironed out many of the more typical failure modes.

Usually you can avoid damage to a speaker, no matter how much power you are feeding it, by listening to what it is telling you - drivers usually complain before breaking, with distortion or nonmusical noises. But not always...

I remember trying to hear 20kHz with some cheap bookshelf speakers when I was about 25, turning up the volume slowly. I heard nothing but amplifier hiss from about 10 feet away until the right tweeter made a nice spark and cut out. It handled almost 60W RMS at the point of failure, which is fairly impressive even today.

I agree that the most "average power" you would want to feed a driver is typically 1/10 or 1/20 it's peak rating. Nothing wrong with having an amp too large, as long as you know to listen for teh signs...
 
Another consideration:
How would you use this 6"?.
If you feed it sub 100Hz signal, it will handle a LOT less power, If you filter out the lower octaves it's more likely to be thermal limited than mechanically. For every octave drop - excursion demand goes up 4x.

Ron E observation about age vs power handling mirrors my experience: A Rectilinear speaker I used around 1972 used a Phillips 5" full range speaker as a midrange. It blew during a period of "youthful exuberance".
 
Thanks so much for the great reply, guys!...

I thought some pictures of the speakers in question could be interesting, here is the front.
 

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...and finally the inside of the speaker.

The application I have in mind is a stereo amp capable of at most 14+14W to use with a computer. For now I am not much concerned with getting low frequencies for example, but just finding out the most I can get from these speakers without much headaches.

Let me try to summarize the limits. We must take care of the maximum distance the cone can move safely, what implies a maximum current, and also the maximum temperature the coil can get to before starting to distort the signal, or melting. Right?

Should I just throw in a 1kHz sine wave and increase the current until I start to hear distortions then? Let's just be empiricists, isn't it? :)

Thanks again for all the great info. If I do any more interesting tests with these speakers I'll let you know. And it would be great to hear if anyone has ever used this exact model before.
 

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While it's tempting to re-use old components, for the large part old speakers are not so good, and are prized more for their characteristic distortion in vintage applications although this is not always the case.

These speakers have a perforated hardboard back, and are instantly identifiable as LoFi. They are not 'good-looking'.

If you are going to put the effort into building something you would probably be better to use new components.

You also need get more experience of looking at equipment critically, cause if you were buying a car, I could sell you a clunker.

w
 
wakibaki said:
These speakers have a perforated hardboard back, and are instantly identifiable as LoFi. They are not 'good-looking'.

Well, I'm a bit of a lo-fier myself... I could definitely buy a clunk, provided it comes with a nice discount. :D

I just think they look good because they are brown and made in Holland, and I'm so sick of the gray-metal-and-black-plastic looks from the eighties... But I do have a couple of more modern speakers lying around, perhaps I should build my amp for them and use these just to fit in the small computer room.
 
Considering how little material actually went into them, Phillips made some remarkably nice sounding portable record players back in the sixties.

If these speakers are used for your computing station with a few clean watts they will probably sound OK as long as you don't try to run them really loud.

But as someone mentioned, they're not really hifi. They probably will sound pleasant because the perforated back effectively makes them open baffle with damping for the back wave.

Have you played them?
 
I would call those ~5-10W speakers. They should be fine with a 14W amp. with 14w you should clip your amp well before you damage the speakers. The cabinets will probably have nasty vibration issues as well...

Don't play a 1kHz test tone and see how loud they will go, play music and be gentle with the volume control. Why do you care if they will handle 14W - do you run your amps at full tilt all the time? If you are playing normal music with an amp rated at 14W, and the music sounds OK, you are probably putting less than a couple watts into the speakers.
 
Ron E said:
The cabinets will probably have nasty vibration issues as well...
Yes, they are so thin, that might turn out to be a problem.

Don't play a 1kHz test tone and see how loud they will go, play music and be gentle with the volume control.
In my experience sines are better to hear the onset of distortion, specially because in my kind of music the distortion can often be perceived as an improvement to the sound. :) But I would certainly test with "real" signals also... Empiricism has the last word!

Why do you care if they will handle 14W - do you run your amps at full tilt all the time? If you are playing normal music with an amp rated at 14W, and the music sounds OK, you are probably putting less than a couple watts into the speakers.

Well, that's exactly the issue. I want to build an amp with the right power not to have a very large circuit for speakers that can't handle it. I do prefer to be wrong by making a larger amp than by "wasting" the speakers, but if it turns out that 14W is way too much, I'll just move to either 10 or 6W (I'm going to build a TDA chip amp).

I haven't tested them yet because I have no large amplifiers available here at my parent's home. :rolleyes:
 
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I'm in with the other guys. Not really Hi-Fi, but they could be a lot of fun. Where's P10 Dave? He would know for sure.

14W seems just about right to me. Lower than that and you will run into amp clipping - and that will be bad for the speakers.

I have set small speakers on fire with too much power, but it was much more than 14W. :hot:
 
Almost correct, bjorno, it's a AD8080 X8 speaker which differs from the M8 with an fs of 95 Hz and max frequency range to 10 KHz but otherwise the same.

It was not considered a good speaker by any means at the time, and certainly now almost 40 years later they probably wouldn't hold their own against $2 bargain bin speakers.

I suggest throwing them out and not waste more time on them.

Known specifications:

Xmax/Xdam: 3mm
Fs: 95 Hz
Frequency range: Fs - 10 KHz
Impedance: 4 Ohm
Rated Power: max. 6 Watts (or 10 Watts depending on production month but most where 6 Watts)
 
I suggest throwing them out and not waste more time on them.

Agree.

Thank you Saturnus for correcting me, I just glanced at the pictures and drew a too fast conclusion, I also took a look in my old drivers collection but didn’t find anyone.

At that time (late sixties) you could find those drivers in Radios, TV-sets and you are right, they are/were lousy drivers even for DIY’rs and I remember both types had huge peaks between 2-5 kHz, the 8080M more than 10 dB and 8080X around 15 dB.

b
 
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