SEAS Excel T25CF001
http://www.seas.no/index.php?option=...d=54&Itemid=78
R = 4.6 Ohm
BL = 3.5 N/A
B = 1.8 T
Note :
Voice coil height : 1.5 mm
Air gap height : 2 mm
Excursion pp : 0.5 mm
This means the entire coil is in the gap (as opposed to a woofer).
With the same formulas as above :
=> L = 1.9 m
=> S = 0.007 mm²
(wire diameter 13 µm, small !)
=> Copper mass 0.12 grams
Moving mass 0.33 g (consistent).
Temperature rise is :
21.5 K/J
(Kelvin per Joule)
ie. If you give it 1 watt during 1 s it will heat 21.5 °K or °C.
If we suppose the voice coil wire is aluminum instead of copper, we get :
16.5 K/J
So, it will heat much more than the woofer, of course. But it should (hopefully) also receive much less power.
If we were to send a 100W transient during 1 ms the temperature would rise 2.15 degrees K (or °C), this corresponds to a 0.8% change in resistance.
It is significant.
However :
- With a 91 dB efficiency, this would correspond to a 110 dB peak (from one tweeter, 116 dB for both).
- According to this excursion calculator,
Piston Excursion calculator
at 2KHz, to create a 110 dB@1m sound, the tweeter would have to move 0.87 mm one-way, which is 3.5 times its specified Xmax.
Using the specified Xmax of 0.25mm one-way (0.5mm pp) we get a peak acoustic power level of 100 dB, therefore 10 times less electric power..
- With the recommended 2K crossover, it would really take a very large amplifier, and extremely loud levels, for this kind of peak power to occur.
- Since this tweeter will most likely be used in audiophile speakers, it will be mated to small woofers, of maximum size 8-10", which means that if an amplifier capable of those power levels was used, and pushed to the limit, the woofers would either explode, or distort so much that the tweeter self-heating doesn't matter anyway.
All these reasons come down to :
Self-heating in this tweeter should not really be a problem, because other sources of distortion will dwarf it before it happens, like xmax, and woofer cones being ejected from speakers, etc.
Also, this tweeter (while probably sounding excellent at normal listening levels) would be totally inadequate for Geddes' headbanging levels.
************
Now consider this compression driver :
http://profesional.beyma.com/ENGLISH...df=CP350Ti.pdf
1W-1m is 104 dB with horn.
It is aluminum this time.
L = 5 m
S = 0.02 mm² (22 µm dia)
mass = 0.266 g
self-heating = 3.74 K/J
Of course this one has a much larger coil, much heavier, it is built to handle some violent abuse.
For instance, then, to produce 111dB @ 1m during 1 ms,
- The SEAS would need 100W and would heat 2.15 °C
(but this is purely academic because it would never reach this power level)
- The Beyma compression driver would need about 5 watts so it would heat by 0.0187 degrees.
Xmax would probably not be a problem since it is rated for 70W ABOVE 1.5k (ie. 70W average power from 1.5K to 7K).
The SEAS is rated for 90W "IEC 268-5, via High Pass Butterworth Filter 2500Hz 12 dB/oct." whatever that means, probably 90W before the crossover.
*** Conclusion :
The whole speaker will fail before self-heating becomes a problem in the SEAS tweeter.
Your ears will bleed before self-heating becomes a problem for the Beyma driver.
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