Tweeter power capability - how do you determine this?

[RadShak1251]

You see general/approximate power ratings for tweeters, but they never seem to be stated along with a specific crossover frequency and cut-off slope.

So for the tweeter & crossover gurus out there, any opinions on how to figure out a tweeter's maximum (clean) power input limit?

Build the crossover, connect it to the tweeter in question and keep increasing the volume until the tweeter generates audible distortion? Or until fries itself? :sigh:

I am wondering about this since I am seriously considering building a "casual use"* 2-way system using a 10" - yes ten inch - woofer operating in an acoustic-suspension enclosure and one tweeter (soft dome or phenolic-ring cone, not sure which yet). And since such a system's tweeter probably needs a lower-than-average xover point, I guess around 2000Hz at least, I figured I would need to be quite careful about the xover frequency and its cutoff slope.

FYI: I'm not trying to build a speaker to use at gut-pounding party volume levels, but do like to turn up my music to say around 40-50 undistorted watts per channel with much of my music, and don't want to do this & have to be constantly worrying about burning out the tweeters.

Thanks for any advice. :thmbsp:


* in other words this won't be for critical listening; plus I'm experiencing a really tight financial situation and simply cannot afford even mid-quality components for this planned project i.e. I am looking at tweeters in the $15-$20 range; lastly, this will also serve as a learning project - especially crossover design - for later projects I have in mind.

 

[BinaryMike]

I'm no expert on this topic, but I imagine you could get a pretty good estimate of a tweeter's true power handling capability by driving it at a known safe level long enough to establish thermal equilibrium, say 2~3 minutes, then measuring voice coil resistance and comparing it with the cold resistance. Copper resistance increases by 0.393% per degree C, so it's easy to calculate VC temperature rise. If implied VC temperature reaches 100C at some drive level, then that's a good point to call the limit.

 

[RadShak1251]

I'm no expert on this topic, but I imagine you could get a pretty good estimate of a tweeter's true power handling capability by driving it at a known safe level long enough to establish thermal equilibrium, say 2~3 minutes, then measuring voice coil resistance and comparing it with the cold resistance. Copper resistance increases by 0.393% per degree C, so it's easy to calculate VC temperature rise. If implied VC temperature reaches 100C at some drive level, then that's a good point to call the limit.

Thanks Mike.

I realized after writing my post that manufacturers may not want to print real-world power limits because of liability reasons, rather than technical ones e.g. I've sold enough audio gear to know that many people never bother to read manuals, except maybe the bold-print portion. Though I would think a few "probablies" and "approximates" liberally sprinkled into their spec sheets should(?) cover them, because not everyone is sue-happy.

 

[SaSi]

I'm no expert on this topic, but I imagine you could get a pretty good estimate of a tweeter's true power handling capability by driving it at a known safe level long enough to establish thermal equilibrium, say 2~3 minutes, then measuring voice coil resistance and comparing it with the cold resistance. Copper resistance increases by 0.393% per degree C, so it's easy to calculate VC temperature rise. If implied VC temperature reaches 100C at some drive level, then that's a good point to call the limit.

This is sound advice. Provided the voice coil is made of copper. Some are made of aluminium. And there's the former that needs to be considered. There are plastic formers and aluminium ones, with the latter being able to dissipate more thermal power hence allowing a higher power handling.

I glanced at the KEF spec sheets for T27A, T33A and T52 and they specify max continuous service temperature between 120 and 130 degrees (30min) and Max intermittent temperature (5sec) of 200~220 degrees Celcius.

KEF also specifies temperature rise / Watt, with a value of 4degrees /W for T52 and 19.6 degrees/W for the T27.

Verifying the "programme power handling" of 100W for the T27, that makes 5W to reach 125 degrees (25 ambient + 5x19.6/W).

For the T52, that is again rated for "100 W Programme", the 4degrees/W gives 25W to reach 125 degrees (25 ambient +25x5/W).

Attacking the matter from a different angle, the T27 is rated for 8VRMS while the T52 rated for 10VRMS, a 20% increase. That is totally inconsistent with the thermal rise figures that reach 5 times more power for the T52.

 

[RadShak1251]

Thanks SaSi.