I'm going to build a crossover and add a tweeter to my full range speakers. The tweeters will need attenuating so I was going to make a simple L-Pad with 2 resistors for my 8ohm tweeters.
I then thought that if the tweeter was over or under powering the music, it would mean I would need to change the resistors again. I've seen rotary L-Pad attenuators on eBay and they all say that they are 8ohm. Does this mean each winding is 8ohm?
When using various online L-Pad calculators, a 3dB attenuation requires 2.33ohm series and 19.33ohm parallel resistance. A 1dB attenuation requires 0.87ohm series and 65.7ohm parallel! What is the actual resistance of the windings of these attenuators?
I then thought that if the tweeter was over or under powering the music, it would mean I would need to change the resistors again. I've seen rotary L-Pad attenuators on eBay and they all say that they are 8ohm. Does this mean each winding is 8ohm?
When using various online L-Pad calculators, a 3dB attenuation requires 2.33ohm series and 19.33ohm parallel resistance. A 1dB attenuation requires 0.87ohm series and 65.7ohm parallel! What is the actual resistance of the windings of these attenuators?
It means that the amp/crossover will see 8 ohms. Calculaors will get you in +/- 20% of actual values, I have tested suggested L-pads and they deviate from reality. L-pad is a voltage divider, also, the shunt resistor will reduce the impedance peak at Fs for the driver thus changing the slope and phase of your crossover.
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It has different series/parallel resistance values, so no. Why not build an L-pad with resistors? Do some calculations on how much you need to pad, get a bunch of cheap wirewound resistors around these values and build your L-pads.
In another thread I see you`re looking at the XT25SC as a possible option - shunt resistor will decrease the resonance of this tweeter to some extent. The XT25 is around 3ohms DC, get L-pads/resistors after you have the tweeter.
adjustable L-pads tend to oxidize over time, and become scratchy & unreliable. If you do this a lot, it's a good idea to buy just one, solder crocodile clips to it, & use it while setting up the xover. Measure the value of each arm, & replace with fixed resistors.
(although it's not much hassle to tweak a fixed resistor L-pad, you can usually get it pretty good after one or two series resistor changes. I usually use cheap 1/2 or 1 w resistors until I've found the final values, & you don't need to be too precious about the values, e.g. the 3dB example you give above, I'd use 2.2 ohms & 18 ohms, susbtitute the 2.2 with a 2.7 to see how that sounds, & tweak from there)
(although it's not much hassle to tweak a fixed resistor L-pad, you can usually get it pretty good after one or two series resistor changes. I usually use cheap 1/2 or 1 w resistors until I've found the final values, & you don't need to be too precious about the values, e.g. the 3dB example you give above, I'd use 2.2 ohms & 18 ohms, susbtitute the 2.2 with a 2.7 to see how that sounds, & tweak from there)
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