Physically determine speaker wattage?

[Axtman]

Is there a way to physically look at a speaker and roughly determine the wattage capability?

[catalin gramada]

The "wattage" is expression of power and is related by the heat dissipated by the speaker coil in You instance. You have to determine this as maximum admissible condition. Maybe some guys know how can be done
..

[olddawg]

Not really.. with old speakers you could ballpark it by the size of the magnet sometimes with with lower wattage speakers.

[Mick Bailey]

Not without removing the voice coil and carrying out measurements on the wire gauge and construction. A few years ago I had a 6" speaker rated at 600W RMS that had failed. Massively inefficient and designed to run hot to get the 'Numbers' that car audio space-cadets want. So, very misleading.

You could run a speaker up to where it begins to distort and measure the input power. At this point X-max (maximum cone excursion) is reached and then any more power cannot be converted to mechanical energy and has to be dissipated as excess heat in the voice coil. This assumes that the speaker is designed such that the voice coil is capable of operating safely up to X-max. If not, the coil could fail before the mechanical excursion is reached. You also have to consider the damping effects of the enclosure and input frequency. Manufacturers give and enclosure size on which parameters are based.

Some speakers are tolerant of being run up to distorting, others not. For example, I find that Neodymium speakers have a much higher failure rate than other types and they have a knife-edge failure characteristic when pushed hard.

[jmaf]

Unfortunately there is no non-destructive way that I know of.

Most pros will ID the speaker based on models they've known before, magnet size, cone type and so on.

[Chuck H]

Doing a strictly visual evaluation of the Rola speaker in your Bantam Bass I discovered that the basket used on that speaker was typical of the early 60's. Mostly for their old school alnico models as I didn't see it used with any ceramic magnet speakers. The magnet assembly on your speaker looks very much like the ceramics used on Celestion speakers from the mid 60's. I'd guess that your speakers wattage is similar to a Celestion of similar appearance from the early to mid 60's. So, twenty five or thirty watts.?.

The histories of Rola and Celestion are quite complex and the two have been incidentally linked since 1947! (so what exactly is a pre Rola Celestion ) More research to locate a similar speaker (to yours) made by one of the other holding companies for these two brands might be possible. Though I don't think it's necessary. Like many "similar looking" speakers of that era I'd say it's probably rated at 25 or 30 watts but will handily manage 50W.

[J M Fahey]

Not by just "looking" at it.
In general we are talking thermal limits, and you simply don't have the voice coil in your hands to determine it.

The thermal limit means either adhesive softens and voice coil disassembles irreversibly , or voice coil former melts/burns or in rare cases wire enamel fails and voice coil shorts, and all this depends *heavily* on adhesives, former material and dissipation helpers.

I make my own speakers and the exact same mechanical structure (frame an magnet system) can be built with:
roundwire copper:
* short winding - paper former - nitro lacquer adhesive : 12W RMS *Alnico sound* , think Jensen P/C 12Q
yes, so called "alnico sound" comes from voice coil, not from magnet. Ultralight moving parts for sparkle, low damping and highest efficiency.
* normal winding, same as above, 15W RMS
* normal winding, Nomex former, epoxy: 25W RMS.
Curiously, failure mode here is not burning, both epoxy and Nomex stand a lot, but damn Nomex bubbles, literally , and bubbles scratch .
* normal winding, epoxy, Kapton former, 40/50W RMS , think MOD12-50 and similar.
* normal winding, epoxy, kapton, somewhat larger diameter voice coil, 70W RMS , think cheap Eminence, typical Fender speaker found on Performer 70, M80 and a thousand other models from different brands.
* normal winding, epoxy, aluminum former (excellent dissipation and never melts), 80W RMS
* same as above , but larger diameter: 100W RMS
* maximum VC diameter which fits in magnet, thick plates, vented pole, black anodized aluminum former, ventilation holes all around, long heavy wire winding : 150W RMS

So itīs clear that looking at it from outside does not shed much light on the subject.

If you have a batch of speakers, say you bought "mystery speakers" at auction, you can sacrifice one in the interest of Science.

You mount it in a generic box, say a 2 cu ft plywood cube so it is acoustically loaded, and apply pink noise to it, going up in 5W steps and staying at each level at least 15 minutes until it dies.
If it self destroyed at, say, 65W RMS, then itīs safe to use with 40/50W Guitar amps or up to 80W if Voice/Music/Keyboards duty, where it will never be heavily overdriven.

Although no manufacturer (except EV) mentions it, speakers stand more power in open cabinets than in sealed and fiberglass stuffed cabinets.
Voice coil transmits heat to magnet parts which in due time dissipate it into air.

A BIG problem in NEO magnet speakers is that they are *tiny*, negligible mass, so they can not take heat away from voice coil.

Notice many have finned heatsinks attached, now you know why.

That said, you can make an educated guess based on where were they pulled from:
* alnico era (up to mid 60īs) (paper former) : 15/20W RMS , read description above.
* early ceramic, think C12N, Greenback, G12H (Nomex + better adhesives): 25/30W RMS
* generic ceramics from 70s on, think generic Eminence/Celestion : 50/60W RMS . Whatever you find in a generic Fender/Crate/Randall/Laney/Acoustic/Kustom/Ampeg/etc. cabinet.
* premium Ceramics, think FANE, they invented the fiberglass epoxy former, first true 100W RMS speaker.

EDIT:

I'd say it's probably rated at 25 or 30 watts but will handily manage 50W.

Exactly.
Itīs the typical 70īs "Twin Reverb" speaker.

as everybody knows, such Twins could be played "clean" (Fender clean that is) for years, but *cooked* their speakers if played full blast, overdriven or with long pedal distortion driven solos, etc.
Of course, Leo never expected his amps would be used ***dirty***

I reconed truckloads of them, always the same problem: scorched voice coils.

I had a custom batch of coils made, they never came back.

[Mick Bailey]

Even when run within their rated power I find that many modern speakers will fail through thermal problems. I've just taken a load of the manufacturer-fitted low-end Chinese Celestions for scrap. I pulled the voice coil on every one and they've all suffered from overheating with either a distorted voice coil rubbing in the gap or shorted coils as a result of rubbing. That's maybe 30 or more speakers taken from Marshall combos. I have four as-new 10" alnico blue Eminence speakers that are wound on paper coils. All rubbing and distorting but too good to throw away and too expensive to recone. Maybe I'll turn them into light fittings, but that's a shame. A few months later they changed the former material and no longer had problems. So that's 4x25W rated speakers from a 60W combo that had an early bath. But in reality maybe they would have held up fine in a 40W amp.

[Chuck H]

I distinctly DON'T hate to be "that guy" in this instance... The Chinese can make anything. And well too. But there's sometimes problems with spec on raw materials. Like which copper alloy, temperature spec glue, steel grade and it's heat treatment, etc. that can and does fall short. This is definitely my main gripe about the quality of imports from Asia. If, for example, it's a part that goes on your car's brakes and it's supposed to have a certain grade and temper for the steel, but it's wrong because the reclaimed and untreated steel part, maybe a spring steel butterfly that holds the pads in place or something, isn't considered the main enchilada so it gets past inspection. But now your doing 50MPH and your car won't stop!?!

[HaroldBrooks]

I don't think you can tell precisely just by looking at it as others have mentioned, but you could make a fair guess based on the visual size of the magnet and voice coil, as Chuck H indicated. I always run all my speakers with the intended amp for about a half hour of flat out playing, and then measure the temperature of the magnet with an infrared gauge.

The magnet generally shouldn't be any hotter than around 110F to 120F - (perhaps a bit hotter on a very hot day), If you play for a couple of hours continuously it could get even hotter as in 130F. The Jensen's and Rola speakers I've run like that have all lived happy and long lives, provided they were in good shape at the beginning.

While that's not an accurate or definitive test, bear in mind that the whole magnetic assembly acts as a type of heat sink, so if it's getting real hot, as in over 130F, or it get's hot quickly, then your voice coil is probably very, very hot and is handling too many watts for the design.

I have a Valco amp that I run two 30 Watt greenbacks in it. The amp is about 20 watts clean, and perhaps 30 watts in full overdrive. Both Celestion speakers have never gotten over 105F, even after a couple of hours of cranked playing, but that's what you would expect based on the reserve capacity of the two speakers combined, so you might want to use this as a very safe baseline, IMHO.

One last thing, large excursions caused by a big 60 cycle signal, or some other too low bass or big DC voltage can destroy many speakers, even when the wattage rating was deemed OK. It's a good idea to introduce some type of fast-roll-off high pass filter (nock down everything below 80Hz or so) in most amps to protect the speakers from electro-mechanical damage like I just described.

[J M Fahey]

Even when run within their rated power I find that many modern speakers will fail through thermal problems. I've just taken a load of the manufacturer-fitted low-end Chinese Celestions for scrap. I pulled the voice coil on every one and they've all suffered from overheating with either a distorted voice coil rubbing in the gap or shorted coils as a result of rubbing. That's maybe 30 or more speakers taken from Marshall combos.

Just curious, what model speakers and combos?
So I add them to my informal database about who-stands-what in the Real World.
I alwaysb take published ratings with a grain (or a pound) of salt.
Manufacturers often get away with it because when replaying Music most Humans canīt stand too much distortion, itīs ugly, Bass heavily intermodulates voice, etc. , so such speakers tend to be used at not more than, say, 20% of 30% of amp RMS power (where they already sound ugly).

Now guitar players LOVE power amp clipping and that puts out 200% higher than RMS .

I have four as-new 10" alnico blue Eminence speakers that are wound on paper coils. All rubbing and distorting but too good to throw away and too expensive to recone. Maybe I'll turn them into light fittings, but that's a shame. A few months later they changed the former material and no longer had problems. So that's 4x25W rated speakers from a 60W combo that had an early bath. But in reality maybe they would have held up fine in a 40W amp.

Maybe you should learn reconing?
Not kidding.

[Mick Bailey]

Actually I was doing Marshall a disservice as there were a good few from Blackstar amps. Speakers mainly G12T and 70/80. Some "MG" labelled - certainly two taken from fairly late Marshall MG combo amps and a quad taken from an MG series 4x12 cab. Amps - Blackstar HT 40&60 series, Marshall DSL40, MG 100, MG30.

Some of the amps still under warranty, but the owners almost happy to pay for a different speaker.

As to re-coning, here in the UK supplies seem to be really difficult to find. I've re-coned in the past with excellent results and saved up speakers over the years to re-cone. I had a shed full until a few months ago when I just ran out of storage for them. I would have to take a different approach to the guys in the US where there's an abundance of components and materials. I'd intended to expand into reconing but got fed up with chasing suppliers who didn't want to deal with me. Speaker replacement seems to have eased off recently - few years ago I was ordering speakers pretty much every week. I've sent speakers off for reconing and only had bad results that backfired on me so though it may be a good idea to do them myself and be in control of the quality.

[J M Fahey]

Thanks.
Surprised at G12T75 and 70/80 because those are "real" speakers and can take at least 60W RMS routinely.
In fact G12T75 was the standard speaker in VS8080 and in general worked well.
Unless amp shorts and applies DC that is.

Now MG speakers are a joke, cheapest of the cheap, only to allow kids to have a "Marshall 4 x 12" using speakers barely acceptable in a 15W practice amp.

[HaroldBrooks]

Now MG speakers are a joke, cheapest of the cheap, only to allow kids to have a "Marshall 4 x 12" using speakers barely acceptable in a 15W practice amp.

You Are 100% Correct.

Seeing how I'm not a kid anymore, when I got back into playing and buying equipment, I spotted those cheap MG speakers from a mile away. I've seen a lot 100watt Marshalls blow big brawny real 30 watt Celestion speakers on occasion, so I wasn't going to start with junk paired my real JCM 800 head.

There's something about the MG frame stampings alone that looks very cheap. After a while you can just look at equipment and tell if it's going to last or not, in many cases and regardless if you are a design engineer or not, as life teaches you what to look out for.

You DO get what you pay for, more or less, and Marshall couldn't pull off that trick for $299, not while the real 4 x 12 cabinets are still commanding big bucks, there has to be good reasons why.

[Mick Bailey]

I've also replaced a fair number of speakers with the same frame stamping as the MG series, though not branded MG. Identical construction in every other respect and branded Celestion. Maybe these are knock-offs. Or maybe Celestion has decided that putting their name on a cheap speaker does the brand a favour. Like Daewoo cars that are sold in the UK badged as Chevrolet.