L-pad for tweeter level control?

[pzannucci]

4 hours ago, wdecho said:

Adding more resistance than 1 ohm is going to upset what Klipsch designed in the crossover but then you may like the result. Not so with an L-pad whether discrete resistors or pots, simple ohms law. In a L-pad circuit the resistor in series attenuates the signal and the one in parallel is there to retain the correct impedance with the driver the crossover sees. Research resistors in parallel for a better understanding of how the resistor in parallel with the driver lowers the impedance the crossover sees. With the resistance the same using the parallel resistor with the driver using the resistor in series from the crossover  to attenuate the signal the crossover network circuit designed by Klisch is not going to be changed. What you are doing is designing a different crossover by adding resistance in the crossover circuit. Think of the L-pad circuit, whether discrete or with a pot, as being part of the driver and not part of the crossover. With the resistance changed by the resistor in parallel with the driver when you add the resistance of the series resistor with the new resistance of the driver and parallel resistor the nominal impedance of the driver the crossover sees is not changed. Adding just a resistor in series without adding the resistor in parallel with the driver increases the resistance the crossover sees. Instead of say 8 ohms you will be adding more resistance if you add say 4 ohms for total 12 ohms the crossover is seeing. The crossover was designed to see 8 ohms not 12. 

 

Nothing wrong with playing but understand what you are doing in the process. Who knows you may like the result. 

To do a real l-pad configuration, you need to know the impedance of the driver that the network was created for at a particular frequency.  Not the impedance of the spec "4 ohm or 8 ohm" since as you will see from the schematic, isn't a by the book 8 ohm crossover.  So all bets are off on using an l-pad but none the less, always fun to try different things.

 

Dial l-pads present a compromise since they are not as perfect (series / parallel resistance) as being presented.  They need to be measured and created using proper resistance for the target frequency and impedance to match upstream crossover components.  Not really as easy as just sticking a dial type l-pad in front of the driver.  It can be 100% off for what you want to do.

 

If you want to do it correctly, do a frequency sweep of the high frequency component to figure out what the matching parallel/series components are needed to keep the impedance seen by the caps and chokes exactly the same as the impedance of the driver.  Then you can maintain the same slope/q as the original.  Remember as you drop the output of the tweeter, you will raise the crossover point.

[Guest wdecho]

I just like to keep things simple for the majority of members on this social media forum. Technically you are probably correct but most on this forum do not have the equipment or electronic knowledge to delve that deep into crossover and attenuation design. L-pads are the solution for the masses and they work pretty darn well. Close enough for most. 

[rjp]

I need black tissue paper 

 

[Deang]

I think you need a pair of these!

 

https://www.madisoundspeakerstore.com/l-pads-attenuators/fostex-r100t-transformer-type-attenuator/

[rjp]

Wow, that's fancy!  Too rich for me though. I think I'll stick with the cheap L-pad

 

What is the advantage of a transformer over a resistor as far as preserving fidelity?

[Guest wdecho]

14 hours ago, rjp said:

What is the advantage of a transformer over a resistor as far as preserving fidelity?

 Resistors are the least offensive component in any circuit. Any and all components have side effects. Transformers are considered attractive for many applications but I do not believe there would be any advantage of using a transformer vs resistors, L-pads are variable resistors, for attenuation.Transformers have capacitance between the two winding's to account for as well as some inductance in the windings. Resistors are just resistance unless a wire wound one is used. Wire wound resistors do have some inductance to account for. 

[Guest wdecho]

19 hours ago, pzannucci said:

To do a real l-pad configuration, you need to know the impedance of the driver that the network was created for at a particular frequency.  Not the impedance of the spec "4 ohm or 8 ohm" since as you will see from the schematic, isn't a by the book 8 ohm crossover.  So all bets are off on using an l-pad but none the less, always fun to try different things.

 

Dial l-pads present a compromise since they are not as perfect (series / parallel resistance) as being presented.  They need to be measured and created using proper resistance for the target frequency and impedance to match upstream crossover components.  Not really as easy as just sticking a dial type l-pad in front of the driver.  It can be 100% off for what you want to do.

 

If you want to do it correctly, do a frequency sweep of the high frequency component to figure out what the matching parallel/series components are needed to keep the impedance seen by the caps and chokes exactly the same as the impedance of the driver.  Then you can maintain the same slope/q as the original.  Remember as you drop the output of the tweeter, you will raise the crossover point.

Pzannucci, I want to apologize for flying of the handle on a previous post. It is one of my faults I am working to correct. Admittedly my social skills need improvement. I can understand your post as probably correct if one want to dissect a circuit down to the last mite but most on this forum just want a simple solution to solve their issue they want corrected. I just try to keep things as simple as possible on a social media forum. I have edited my offensive post and again I apologize for flying off the handle.  

[pzannucci]

46 minutes ago, wdecho said:

Pzannucci, I want to apologize for flying of the handle on a previous post. It is one of my faults I am working to correct. Admittedly my social skills need improvement. I can understand your post as probably correct if one want to dissect a circuit down to the last mite but most on this forum just want a simple solution to solve their issue they want corrected. I just try to keep things as simple as possible on a social media forum. I have edited my offensive post and again I apologize for flying off the handle.  

Same here if perceived that way.  I was trying to give the most simple way to make small amounts of change which is a resistor with minor variance.  Large variances require an lpad or autoformer.  When using an lpad, the best way is with high quality resistors and not using a pot.  I've measured several pots and not super accurate.

There is a plus side to using an autoformer and that is the variance in impedance of the driver is passed through though magnified via the the autoformer.  Drop via resistors will change with the changing impedance of the driver modifying the frequency response.  Using an autoformer, depending on the amp, it will see the changes in impedance which could be good or bad on the sound.  Hence a swamping resistor.  That's why crossovers are an art and I stated choose your poison.

[Guest wdecho]

37 minutes ago, pzannucci said:

  When using an lpad, the best way is with high quality resistors and not using pots. 

 

I can agree with that statement but it will take and a lot of trial and error along with hours of listening to find the right combination. I know from experience. I chose the resistor method for attenuation of my drivers on my LaScala's after ditching the autotransformer. For most purchasing a L-pad will be good enough. Below is a calculator for those wanting to attenuate their driver using just a couple of resistors. 

 

https://www.diyaudioandvideo.com/Calculator/DriverAttenuationLPadCircuit/

 

I suggest starting with 3 db attenuation and use 10 watt resistors. Ten watts is plenty for the watt field because one is talking a steady 10 watts and not just peaks which Klipsch speakers will never need. But even Nelson Pass says there is not a lot of difference sound wise using a L-pad vs. just 2 resistors in his rebuild of the JBL L300 speakers. He shows a network of resistors for those choosing that route as an example if one wants to go that route as well. He is very thorough in any project he undertakes before publishing an article. 

[pzannucci]

9 minutes ago, wdecho said:

I can agree with that statement but it will take and a lot of trial and error along with hours of listening to find the right combination. I know from experience. I chose the resistor method for attenuation of my drivers on my LaScala's after ditching the autotransformer. For most purchasing a L-pad will be good enough. Below is a calculator for those wanting to attenuate their driver using just a couple of resistors. 

 

https://www.diyaudioandvideo.com/Calculator/DriverAttenuationLPadCircuit/

 

 

I guess that's why I have boxes of caps, resistors, and chokes.  When you are striving for something much better than stock, you should do it the right way.  Otherwise why do it?

 

If you are just looking for a minor tweak than a pot l-pad may work.  You have to have the crossover designed correctly for the end impedance of the l-pad / driver circuit which again, isn't textbook in Klipsch speakers.  End results will vary but you will never call your babies ugly .  I do remember some things I did when I was learning that did border on ugly.

[CECAA850]

21 minutes ago, wdecho said:

I can agree with that statement but it will take and a lot of trial and error along with hours of listening to find the right combination. I know from experience. I chose the resistor method for attenuation of my drivers on my LaScala's after ditching the autotransformer. For most purchasing a L-pad will be good enough. Below is a calculator for those wanting to attenuate their driver using just a couple of resistors. 

 

https://www.diyaudioandvideo.com/Calculator/DriverAttenuationLPadCircuit/

 

I suggest starting with 3 db attenuation and use 10 watt resistors. Ten watts is plenty for the watt field because one is talking a steady 10 watts and not just peaks which Klipsch speakers will never need. But even Nelson Pass says there is not a lot of difference sound wise using a L-pad vs. just 2 resistors in his rebuild of the JBL L300 speakers. He shows a network of resistors for those choosing that route as an example if one wants to go that route as well. He is very thorough in any project he undertakes before publishing an article. 

Seems like a lot of work.  I would think that installing L-pads, adjusting to your liking then measuring your settings to get resistor values would be simpler.  That's IF you want to go the resistor route.  OK< who's going to double blind test an L-pad modded speaker and a dual resistor modded speaker??????

[pzannucci]

5 minutes ago, CECAA850 said:

Seems like a lot of work.  I would think that installing L-pads, adjusting to your liking then measuring your settings to get resistor values would be simpler.  That's IF you want to go the resistor route.  OK< who's going to double blind test an L-pad modded speaker and a dual resistor modded speaker??????

You forgot a permutation, add the autoformer in there 

[pzannucci]

As far as a lot of work, just use the math or calculator that @wdecho references.  Specify the driver impedance at crossover and db drop and you will have a more concise l-pad than a pot.

[CECAA850]

4 minutes ago, pzannucci said:

You forgot a permutation, add the autoformer in there 

I'm not one to get mired in the details.

[CECAA850]

Just now, pzannucci said:

As far as a lot of work, just use the math or calculator that @wdecho references.  Specify the driver impedance at crossover and db drop and you will have a more concise l-pad than a pot.

That's IF you already know how much you need to drop the individual driver.  It's easier to turn a knob and listen.

[pzannucci]

OK, I concede  a knob is good if you move you speakers around (room to room) or you have some recordings / TV that are on the iffy side.  OR if you don't know approx. how much drop you need.  Everyone with a home theater owns an SPL meter don't they?

[CECAA850]

1 minute ago, pzannucci said:

OR if you don't know approx. how much drop you need. 

That's my issue.

[rjp]

3 hours ago, wdecho said:

 Resistors are the least offensive component in any circuit.

 

That has been my opinion as well. It seems pretty hard to mess up a resistor.

 

Using a transformer is interesting though. Whereas the resistor dissipates the unwanted signal energy as heat, the transformer changes the voltage and current ratio. It seem that if a driver volume is reduced by a step down transformer then the current flow through the crossover must be reduced. With a resistor the current flow is unchanged. I wonder if changing the current flow through the crossover effects the sound? I would think it must if there is any internal resistance at all.

 

 

 

[CECAA850]

1 hour ago, pzannucci said:

As far as a lot of work, just use the math or calculator that @wdecho references.  Specify the driver impedance at crossover and db drop and you will have a more concise l-pad than a pot.

So if I understand correctly, I can use my L-pad to get the desired sound out of my speakers, remove them then measure one side, then the other and replace the L-pad with resistors of the measured values?

[pzannucci]

Higher frequency is less of an issue with current.  The autoformer will allow for the impedance to not affect the flow / impedance variation at the driver.  Think about a voltage divider when you change the resistance up or down.  That shifts the voltage thus would have to shift the response using pure resistance.  Not to count the fact that the resistor dissipates power.  The autoformer keeps the impedance variation reasonably constant though multiplied or divided (depending how you look at it)