tweeter operating power

[madinoz]

Not a question this time. Just a note about something I've observed regarding tweeters (especially those from the Vifa stable).
There are a lot of posts which refer to the power handling of a tweeter (and how to calculate it based on a certain crossover point and driver resonance) which mistakingly use the specification supplied by vifa called "operating power".

I used to think that this figure was the amount of full range (IEC) power that the tweeter could handle without a crossover.
If you look at those figures again on a few spec sheets I think you'll find they actually refer to how many watts need to be applied in order to acheive a reference SPL ( about 96db I think but don't quote me on that).

I think the simple answer to power handling is complex!!!!
It relies on many facters and can probably only ever be really tested by distruction testing i.e apply increased voltage until driver reaches a certain amount of distortion or stops working or blows up.
Just my two bob worth. If any one has any thought please feel free to agree, or disagree!

MADINOZ

[sreten]

High frequencies are very dynamic in nature and continuous testing is pointless.

Testing without a crossover is even more pointless.

Vifa's specification is honest and realistic.

Unless you want to try a build a tweeter that can handle 100W
continuous, has response to 20K and has any sort of efficiency.
You'll find you can't.

You need to understand thermal time constants to understand
the differences between transient and continuous power handling.

sreten.

[madinoz]

I wasn't calling into question the honesty of Vifa's power handling figures. You seem to have misunderstood my post.
When Vifa states that its D25-ag-36-06 tweeter can handle 100 watts rms with X crossover, I don't doubt them. In fact I think they would probably put in a margin of error.

I was talking about the erroneous use of the specification
"OPERATING POWER" , not power handling.
Read my post again.
MADINOZ

[sreten]

Read my post again.

Your saying we are all stupid and think operating power
is true RMS continuous power handling, well we are not
and we don't.

sreten.

[madinoz]

Streten,
You are not stupid, everyone else on this forum is not stupid.
I did not say that or imply that.
Read my post again.

I did not say everyone confuses operating power and power handling but I have read posts just this morning which confuse the two.
Read my post again.

I am simply trying to clear up a confusion which I myself have
experienced.
Read my post again.

MADINOZ
If in doubt read the post again.

[HeatMiser]

That's a helpful observation, madinoz. I believe that varying standards for driver measurement and reporting and the use of ambiguous terminology are ongoing problems for DIYers who rely on manufacturer's specs.

I'm sure sreten doesn't speak for all of us (certainly not me) when he pretends to know everything and decides all posts must meet his personal standards of technical sophistication to be worthwhile.

I see questions relating to power ratings all the time; this thread will probably be helpful to someone at some point.

[madinoz]

Heatmiser,
A miser with heat you may be but the icey chill on this post
just suddenly thawed out.
thanks, MADINOZ

[sreten]

Hi guys,

I'm sorry if it seems I got a little short.

I initially just added some points to the
original post, I did not misunderstand it.

I don't pretend to know everything, but one of my
weaknesses is i don't like being told I'm disagreeing
with something when I'm not, hopefully if I disagree
with something I'll plainly state I think its wrong.

sreten.

[EC8010]

Specifying an accurate power rating for a tweeter is difficult. Really difficult.

Statistically, music contains very little energy at high frequencies. To be more specific, when high frequencies are present, they are low amplitude, and they tend not to be present for long. While they are present, they heat the voice coil of the tweeter. When they're not, the voice coil cools down. You can imagine it as being like a frying pan on a gas stove heated by short pulses of gas. Conversely, a bass driver has the gas fully on almost all the time. The formal property that falls out of this argument is known as the thermal time constant of the driver.

The tweeter needs to be able to accelerate and decelerate very quickly, so it needs minimum mass. But a small mass heats up quickly (think frying pans again). If we use a crossover to prevent low frequencies from reaching the tweeter, we reduce the heating effect because most of the energy is in the mid-range. Thus, the higher the crossover frequency, the higher the power rating for any given tweeter.

But! Imagine a perfect crossover (infinite slope) splitting audio between a tweeter and a woofer of equal sensitivity. Just below the crossover frequency, the woofer receives a certain voltage. Just above the crossover frequency, to produce the same loudness, the tweeter must receive the same voltage. This may cause a large movement, or excursion, increasing distortion.

Loudspeaker power ratings are not just about thermal effects, power handling can also be excursion limited.

Reams have been written on the subject of power handling...