OT: is there a way to test speaker wattage?

[smoguzbenjamin]

Hey all

I have an anonymous speaker lying around. It's oval, and the sticker's been peeled off, I can make out that it's frequency range is from 20 - 30 000Hz and that it is 8 ohms. That's it, no wattage. I might pop this in a bridged ruby practice amp, but don't want to kill it because it was only rated at 1W. How can I go about testing how much power it can handle? :?

[Tubebass]

Easy....just keep jacking up the input power till it blows, then back it down a watt or two..... :wink:

[smoguzbenjamin]

And I wont permanantly damage the speaker?

[puretube]

I wanted to tell about that test too: needs only exact one test-run !

[Tubebass]

That was borrowed from the model airplane guys who want to know how many turns they can put into their rubber band "motors". Just wind it till the rubber breaks, then back off a few turns.
     You can probably get a rough idea of a drivers' power handling by looking at the magnet size of your speaker and comparing it to a speaker whose ratings you know. Not a very helpful answer really but unless you can figure out who made the speaker and get the straight dope from the manufacturer, it may be the best you can do.

[Mike Burgundy]

Guessing is one way, actually measuring voice coil temperature while slowly increasing power is another. Rather hard to do, though.

[Boofhead]

There's two limits to speakers.  The electrically limited  power (not cooking the speaker coil) and the displacement limited power (not making the cone more than it was intended to do). These are quite difficult to estimate with out risking damage.

Even if you set-up a scheme to measure the coil temperature you don' tknow how hot it is allowed to get - this can depend on the coil construction and adhesives used which you have no information.  You also have to allow for the speaker to heat-up to a stable temperature and this could take some time.

The displacement limited power can be estimate from loew frequency distortion measurements, but again you don't know exactly what the intended limit is - you do have some leeway here but pushing it too hard can reduce the life.

The easiest way is to track down the numbers on the driver or back engineering it from the equipment it came out of.

[Nasse]

:roll: Maybe you could post a pic of it, front and back pic and something in the pic one can see how big it is. Diameter, weight, magnet size, etc.

Some common small oval speakers used in TV and old small power stereo or powered recco players are perhaps five watts or less, 6"x9" car speakers usually more

[Paul Perry (Frostwave)]

I now this is just 'rough' advice, but in my experience you can hear that a speaker is in trouble, before it blows. So I'd try connecting it up to something & sneaking the volume up carefully until it 'sounds' stressed.
That should indicate what it can take, if you are able to get a handle on the voltage across the coil.

[petemoore]

All these speakers have a sweet band / volume level area at which they sound good.
 I like to have a small enough speaker so that it is moving somewhere in a good percentage of it's travel...or being 'pushed' a bit.
 Very low volume [for 'x' speaker] doesn't usually sounds as good.
 When I want to know what a speaker can handle I [in very small incraments once past 'mid-high' volume] slowly increase settings [all settings should be tested for this ie if you have a big bass boost it could easily push the speaker past its ceiling of safety] anyway you should begin to hear the difference in 'as loud as it really gets' and so loud it is distortion undesirably [some ppl desire this and blow speakers].
 The best time to test the limits of amps and speakers is alone, with the setupS as you would be using them.
 There's a field of Blues players  who swear by the Blow your speaker up for kicks technique and use say Fender Champ with 15w 'lightly suspended specialty speakers and  replace them because of damage/half bakedness on the average of every six months....so I read.
 So there is different MOJO to blowing speakers. I used to do it,
 It sounds so kool for a while [taking a great old stereo speaker and trying to push it out of it's sockets] till the coil starts breaking off and skidding on the magnet...even still...but that turns to 3/4s, thenfull bake in no time.
 Oh yeah the do heat up the coil...takes along time for that to dissipate through to where you can feel the magnet getting warm or hot...basically you'd have to push it hard for a half hour, feel it, push it a little harder for 20 minutes, feel it, push it real hard for 20 min., feel it etc.
 The coild itself can heat up real quick/

[smoguzbenjamin]

Problem is, a buddy gave it to me because he wasn't using it, and he doesn't know where it came from either. Hang on a sec I'll measure it up: (inches are approximate, my ruler measures in centimeters)

Magnet: 6cm (2.4")
Widest diameter: 12cm (4.8")
Smallest diameter: 7.5cm (3.0")

:? I'll set up a test soon and see if it sounds stressed anyplace... Thanks for the help

[Boofhead]

Probably in the 3 to 5W region - again it's impossible to tell with any precision.

I'll set up a test soon and see if it sounds stressed anyplace... Thanks for the help

That can depend on what you use as the signal.  If you use bassy signals and an open back cabinet it will could out earier than the quoted (in this case unquoted) rating.

[smoguzbenjamin]

That can depend on what you use as the signal. If you use bassy signals and an open back cabinet it will could out earier than the quoted (in this case unquoted) rating.

I was thinking a 5kHz sinewave :?

[Nasse]

It smells like small power general purpose hi-fi or small car stereo speaker. And yes, because it is not instrument speaker, it is very easy to blow it out of its surroundings. But quess LM386 type amp or even bridged one may let it live for some time, if you dont punish it full tilt long time. Bigger the power the more easily you burn the voice coil.

I made not the only mistake in my life but once found *killer* sounding few watts 10" alnico magnet speaker from old tube radio. I connected it to 50 watts Marshall head. Smoke come out and it never worked any more. Maybe it would have been even worth reconing, but did not know then and trhow it out...

Traded a brand new EH Mike Matthews Freedom amp for that Marshall, well that was just a helluwa portable amp! Not like new ones which are battery powered, but powerful transistor amp and a 12" speaker in very small closed cabinet. It was so airtight cabinet that you could fell sharp air blow half metres above input jack hole! (it was not airtight there) If anybody knows where to find any info about it´s preamp section schemo im interested. Quess that closed cab helped more defined bass response and power handling.

[petemoore]

Closed back will prevent a speaker from travelling outside of it's socket more than open back...the volume of the enclosure dictating when the 'backpressure' also 'frontpressure' excalates...the farther the cone moves from idle position the more vaccum or pressure it encouters from the differential of air pressures outside Vs inside the enclosure...
 We did an experiment...staple chicken wire to the sound board that covers the back of the speaker frame...stuff insulation in the enclosure...expecially useful to reduce bass 'Wwhommphh', [tightens the bass response considerably if it's loose], this too will act as a 'cone retainer'...but in a different way than an enclosure filled with air.

[smoguzbenjamin]

Hmm now I'll have to build a cabinet for it. Doesn't matter, I'll have to make a mini cab for it anyway but I'll need to go get some wood

[Boofhead]

I was thinking a 5kHz sinewave

Unfortunately high frequencies just heat up the coil without much audible effect (within reason).  Perhaps a dual tone signal 200Hz + 250Hz.  Honestly, with a 1W amp I don't think you will have a problem - the distortion will be coming from the amp clipping most of the time anyway.

[Ge_Whiz]

Just remember that if you ain't gonna try it because you're afraid of blowing it up - then it ain't no use anyway!

[smoguzbenjamin]

Yes, you are right! OK let's get testing!

[Boofhead]

then it ain't no use anyway!

Very true, I suppose it's more a matter of how hard you intend on driving it in the application vs what you think it can take.   If things are kept to realistic levels then you don't have to cringe every time you hit a power chord .