YES, that is all correct, and if the L-pad is used for a driver with excessive output - a 'knob setting' below max. can actually
smooth the impedance of the driver to a degree, thereby further helping crossover design.
Well, the design of an L-pad is a device that is made to present a true flat impedance to anything driving it.
Inside the L-pad are TWO variable resistors behaving in 'harmony' to maintain the constant intended value.
At full clockwise position, the internal resistors actually disconnect thereby directly connecting the tweeter
to the crossover as if the L-pad wasn't even there.
When the L-pad is dialed anticlockwise the internal resistors come into play.
Due to the purely resistive nature of the L-pad internals, any driver impedance variation is proportionally
reduced by the amounts of pure resistance introduced.
Another example is: If you use an 8 ohm L-pad in 'mid position' but connect a 4 ohm driver,
the crossover will see a load closer to 8 ohms than 4. This is how I would describe an L-pad as having a 'smoothing effect'.
Inside the L-pad are TWO variable resistors behaving in 'harmony' to maintain the constant intended value.
At full clockwise position, the internal resistors actually disconnect thereby directly connecting the tweeter
to the crossover as if the L-pad wasn't even there.
When the L-pad is dialed anticlockwise the internal resistors come into play.
Due to the purely resistive nature of the L-pad internals, any driver impedance variation is proportionally
reduced by the amounts of pure resistance introduced.
Another example is: If you use an 8 ohm L-pad in 'mid position' but connect a 4 ohm driver,
the crossover will see a load closer to 8 ohms than 4. This is how I would describe an L-pad as having a 'smoothing effect'.
I've read there is another advantage of using an L-pad, particularly in the case of non-ferrofluid tweeters:
The parallel resistor in the L-pad can reduce the impedance rise (at the tweeter's Fs), helping to control its resonance.
The parallel resistor in the L-pad can reduce the impedance rise (at the tweeter's Fs), helping to control its resonance.
That is true. The series resistor tends to do the same thing since it has the greatest relative effect on the dips.
Thank you - that is what I understood.
As you adjust the control, the two resistances vary reciprocally in combination with the nominal driver impedance so as to maintain a constant load, no matter the setting.
so no go on understanding that an L pad on the secondary side of the filter will result on a shift of frequency....it's know wonder i've been sin binned for my heretic beliefs....
nice boxes....i guess diffraction does not matter or was Geddes wrong????
nice boxes....i guess diffraction does not matter or was Geddes wrong????
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Option/devil's advocacy: What about just a recone for the woofers? There are still plenty of people that like those--go poke-around on the speaker forum at AK. If nothing else, you can find plenty of threads on the CS-77A's. They're cool old cabs, and everybody would do something different. If you are itching to build, there are plenty of ways. If I have this straight, you have the new set of drivers so you could do a standalone project at least partially funded by selling reconed CS-77A's? Or you might like those and can let your new drivers move-on. My only input is to keep it fun.
All changes have some effect, but an L-pad shouldn't be fundamentally changing the crossover frequency.
I agree with AllenB. Though the impedance shift caused by the L-pad looks significant, the affect on frequency response is typically surprisingly small over a practical attenuation range, and the largest differences tend to be at frequency extremes where things are down enough in level that their contribution is lessened when the drivers combine.
Also, my impedance plot above has issues below 100 Hz. My data cut off there, so I'm not sure if XSim did some kind of prediction down there or what, but below 100 Hz is not representative of that driver. The predicted combined effect of the speaker/L-pad should be OK though.
Also, my impedance plot above has issues below 100 Hz. My data cut off there, so I'm not sure if XSim did some kind of prediction down there or what, but below 100 Hz is not representative of that driver. The predicted combined effect of the speaker/L-pad should be OK though.
I'd like to thank all the contributors to Bigdog's crossover journey. As one who follows this forum, I am amazed at how collectively we can elevate the understanding and skill of newbies like Galu and me so efficiently and effectively! This is the beauty of our access to a global community of audio DIY'rs!