High quality 16-ohm L-pad and/or alternatives?

[Alidore]

I need a very high quality variable (at least 0 to -6 dB range) attenuator for a 16-ohm driver. It can be an L-pad or a transformer, or perhaps a six-click (rotary?) switch allowing changes in 1 dB increments. I'd like 100 watts power handling, but will admit that's probably overkill.

The only such products I know of at this time are the six dollar, 16-ohm, 100-watt L-pads sold by Parts Express (and others), but having tried it, I want something that sounds better even if it's significantly more expensive.

Anyone know of a source for very high quality pro-sound L-pads? That would probably be ideal.

One possibility is to use a high-quality 8-ohm L-pad such as a Fostex unit, but I'd rather stick with 16 ohms because the idea is to build an OTL-friendly loudspeaker.

Any and all suggestions appreciated.

Thanks!

Alidore

 

[catapult]

I need a very high quality variable (at least 0 to -6 dB range) attenuator for a 16-ohm driver.

You may be asking for the impossible. The problem is "16-ohm drivers" are only nominally 16 ohms. They may vary from 10 ohms to 50 ohms across their frequency range. So your passive attenuator is going to change the frequency response depending on where it is set.

 

[Alidore]

Thanks for responding, catapult.

I understand your point that "16 ohms" is only a nominal figure, but so is "8 ohms".

I see people using 8-ohm L-pads quite often. The frequency response with L-pad attenuation is not nearly as susceptible to variations in driver impedance as it would be with a simple series resistor, as Dickason demonstrates in "The Loudspeaker Design Cookbook", 6th edition.

Also, it is fairly simple (even routine) to compensate for the driver's voice coil inductance and flatten out the impedance curve. The impedance peak at resonance is more complicated to cancel out but that can be done as well, though it really isn't necessary unless the driver's resonance is near the crossover point (how near depends on the steepness of the net acoustic rolloff).

So assuming I can deal with the real-world impedance curve of a 16-ohm driver (as many of you deal with the real-world impedance curves of 8-ohm drivers), any suggestions on where I might look for a high quality attenuator?

Thanks!

 

[Bill Fitzpatrick]

Re: Thanks for responding, catapult.

Also, it is fairly simple (even routine) to compensate for the driver's voice coil inductance and flatten out the impedance curve. The impedance peak at resonance is more complicated to cancel out but that can be done as well, though it really isn't necessary unless the driver's resonance is near the crossover point (how near depends on the steepness of the net acoustic rolloff).

Flattening out the impedance curve will not help compensate for the change in response due to the curve. In any event, for quality you will want to go for the switched resistors.

 

[sreten]

Make your own proper L-pad using resistors.

Or simply experiment with series and parallel resistors.

Regarding a previous point, an L-pad effectively flattens
the impedance curve of the driver malking the crossovers
job easier, but it does have some effect on driver response.

🙂 sreten.