determing the power handling capacity of a tweeter at a given crossover frequency

[Steve Racey]

Although I realize that there may be no hard and fast rules to this, I have noticed that horn drivers for example are rated at lower power ratings than their woofer counterparts. For example Great Plain Audios 900 series drivers are rated for only about 20 watts.

I will ask for an example. If a JBL 2225H is
driven at 200 watts program, and is crossed over at 500HZ at 18db per octave, how much of that 200 watts does the horn driver need to handle?

I would assume the higher the cross over frequency is set, the energy supplied to the horn is lower.

Jbl and Altec seemed to traditionally like to cross over woofers and horns at 500 or 800 HZ where as more modern cross over seem to be at around 1.6 KHZ. is a lower cross over prefered as it lies within the speech and vocal range?

Happy thanksgiving to all of you from your friends in Canada!

Steve

[Robh3606]

Hello Steve

One thing you are not accounting for is the difference in efficiency between the 2 driver types. A 2225 is 97dB @ 1 watt. A typical compression driver like a 2426 is 117dB on a plane wave tube and 110dB @ 1 watt on a horn. They may handle less power but they are also much more efficient. In this case there is a 13 Db difference so the compression driver requires 1/20th the power for the same output. So it's watts into the woofer and milliwatts into the compression driver. You also have to remember the power distribution in music has most of it in the woofer on normal program material. You have to be careful with compression drivers and how low you cross them over. A large fromat driver like a 2 inch 2445 might be OK at 500 Hz and a 1 inch like a 2426 at 800Hz. Both will sound better crossed over higher. If you look at the spec sheets the power handling changes and gets lower as you go down in frequency. It is also important that the horn you use has usable extension at least a half octave/octave below your crossover point. The last thing you want to do in run a compression driver at the low end of it's range and have it on a horn that unloads at the crossover point. You risk slamming the diaphram into the phase plug simply not a good idea. You can use steeper crossover points to your advantage to help prevent this but you are always better off being conservative when you use them. You want them in their linear range like any other driver and pushing them hard getting close to their excursion limits by going too low with them is just not good practice.

Rob

[Steve Racey]

Thanks Rob for this very useful information. As JBL and Altec HF drivers are starting to get quite expensive, I am considering a Eminence driver and crossing over at 1.2 or 1.6 KHZ. The JBL specs for the 2225H driver recommends the highest crossover frequency for this driver be 1.2 KHZ. These 1.2 KHZ passive cross overs are harder to find and are more expensive. Can anyone suggest a non JBL or ALtec driver (heaven forbid!) that works well with a 511b horn that will work with 200 watts program, all things considered?

Thanks as always,

Steve

[duaneage]

Program material and dynamics also matter. The wider the dynamic range of the material and the greater the danger to the tweeter. Highly compressed music ( like Heavy Metal) will have more energy per octave than classical or Jazz will. Err on the side of caution and use fuses, they don't cost much and have no effect on the sound for most of us.