Matching a new tweeter to existing drivers

[Dr.H]

Hello all,

A newbie question:

I have a ported loudspeaker rated at 89dB sensitivity and using a first order x-over network. I recently decided to replace the tweeter (Vifa, 89dB) with something of better quality. Problem is that the new tweeter is rated at 91dB.

Is there a formula to calculate the value of the series resistor required to match the loudness/sensitivity of the new tweeter to that of the old tweeter?

Thanks for nay help
Ryan

[Gregm]

You'll need two resistors, one series & one across.
For a quick view take a look at attenuation here http://www.mhsoft.nl/spk_calc.asp Cheers

[brady]

Hi Dr. H,

The 2 db advantage of your new tweeter will probably be offset by our ear's lesser sensitivity to higher freq. I have a 96-97db main speaker and a 105db tweet. Second point : the new tweet may have a different operating range than the old one. So check x-over.

HOWEVER, for maximum flexibility, get an L-pad.

Hope this helps.

[Dr.H]

Thanks guys,

I have used the tweeter without any adjustments and found it to be too "loud/bright". Greg, the website you suggested is great, thanks, I was able to calculate that I needed a 1.65R series and 30.9R parallel resistor.

Do both of these have to be at least 5W?

Also, can someone explain why the parallel resisitor is needed, I would've thought that the series R would be enough to achieve the desired 2dB attenuation?

[Dave Jones]

Originally posted by Dr.H
Also, can someone explain why the parallel resisitor is needed, I would've thought that the series R would be enough to achieve the desired 2dB attenuation?

Folks are assuming that the impedance characteristics of the two tweeters are similar, and that you want to salvage your old x-over. You can pad down the tweeter while leaving its impedance more or less unchanged by using an "L-pad", which is what a circuit comprizing a series and parallel resistor is called. If you used only a series resistor, you would significantly increase the tweeter's impedance, which would in turn affect the characteristics of the crossover. You may not be home free even with the L-pad. If you would name the original and replacement tweeters, one of the crossover gurus might be willing to tell you if the swap is feasible.