L-pad for tweeter level control?

[Guest wdecho]

1 hour ago, pzannucci said:

????  

What??????????? no common sense. Understandable from some of your post. 

[Guest wdecho]

1 hour ago, richieb said:

 

--- although I have zero interest or knowledge of this topic I do glance at most of what happens around here. I propose the mods treat all future L-pad topics as they do with politics. Lock ''em down! I mean Jeez, 7+ pages on L-pads and half of those are arguments. Even the political threads are less toxic than this --- .  

And about just basic common electronics and common sense. But then many just will never admit they are wrong but will go to extremes with false info on social media forums. These kind of arguments never appear on diyaudio forums where more adult topics are addressed and everyone understands the basic electronic components and their functions without rambling and rambling on. An electronic genius, Nelson Pass, has stated there is no appreciable difference in a discrete L-pad and a rotary one and there is no way they would argue with him but since I do belong on this forum they will argue and argue with me. And then there are those that do not understand the simple resistor, capacitor and inductor functions and use. I will agree that this silly thread has went long enough on this subject. Since these kind of clowns love the last word I will not respond to this thread any longer. 

 

 https://www.electronics-tutorials.ws/pdf/basic-electronics-tutorials.pdf

[pzannucci]

43 minutes ago, wdecho said:

What??????????? no common sense. Understandable from some of your post. 

I hope you aren't referencing my common sense as I have none.    I'm still in this thread (that answers that question) though not arguing but trying to understand point / counter point.  You're right there is some bull being thrown.

 

Really though, you do need to go back and read about damping, q, and impacts of resistance in a electro-mechanical circuit known as a loudspeaker.  Also I can't believe the idea of 30 degree phase shift when using 3 way horns with passive crossovers.  30 degrees of an autoformer may have some issue when you are getting into time aligned speakers but we are quite a way from it with a k-55 w/40x horn and k-77xxx.  Even with an dual woofer configuration with a high cut off unless in an MTM configuration.

 

It would be a much more genuine argument if it wasn't rationalized why autoformers are not liked over resistors.  I really doubt the phase shift has anything to do with it.  Just say "I don't like it"

[Khornukopia]

On ‎5‎/‎3‎/‎2018 at 12:24 PM, Deang said:

I think you need a pair of these!

 

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

 

 

I like it, a rotary knob adjustable transformer, and with an added resistor option at the flick of a switch. 

[Deang]

I think the switch just gives you the other range of numbers.

 

I think that thing is just an autotransformer with swamping resistors, and a nice attenuator. I laughed when I saw the price. BEC taught me how to build one those a decade ago. If I would have known I could charge that kind of money for it,  I would have built it.  

[Deang]

2 hours ago, wdecho said:

An electronic genius, Nelson Pass, has stated there is no appreciable difference in a discrete L-pad and a rotary one and there is no way they would argue with him but since I do belong on this forum they will argue and argue with me. And then there are those that do not understand the simple resistor, capacitor and inductor functions and use. I will agree that this silly thread has went long enough on this subject. Since these kind of clowns love the last word I will not respond to this thread any longer. 

I read that thread, that's not what Pass said. What he said was that a careful listener could hear the difference. Also, the folks over there also struggle sometimes, and I've read plenty of threads where things got somewhat heated. However, the one thing you won't see over there is someone calling someone else a clown.

 

One thing we have learned over the last couple of years is that the Engineers at Klipsch do not like swamping resistors, and you won't find L-pads in any of their networks (they use resistors in series).

[pzannucci]

30 minutes ago, Deang said:

I think the switch just gives you the other range of numbers.

 

I think that thing is just an autotransformer with swamping resistors, and a nice attenuator. I laughed when I saw the price. BEC taught me how to build one these a decade ago. If I would have know I could charge that kind of money for it,  I would have built it.  

You missed the boat 

[Guest wdecho]

12 hours ago, Deang said:

 

One thing we have learned over the last couple of years is that the Engineers at Klipsch do not like swamping resistors, and you won't find L-pads in any of their networks (they use resistors in series).

Quickly, I could explain how an engineer designs a new crossover saving a resistor but you posted as a statement not a question so I will not go into detail on how to do it that way. Not easy to do for a hobbyist designing a new crossover without a lot of trial and error or a thorough electronic background but if one lacked a thorough electronic background they would not be designing crossovers for Klipsch. Using just 1 resistor for attenuation in an existing crossover is not doable without upsetting the crossover hence the need for a L-pad of some sort. It is a moot point being that resistance is now used for attenuation by Klipsch vs using an autotransformer. Certainly those favoring an autotransformer as best could design a new crossover using one for their newer model speakers if they think they can improve upon the engineers at Klipsch.  I think of PWK as a giant in the audio field and the autotransformer served his purpose in his time designing his amazing speakers. 

 

Dean, I would like to consider you as community friend and there is nothing wrong with discussing differences of opinions on this forum in a friendly way and but not having the patience I once had I do fly off the handle at times and I apologize if I have offended you. We both have more important issues in life to quibble over trivia matters such as autotransformers and resistors. Your opinion differs from mind which is fine, there are many that agree with you on this forum. I can remember the many heated discussions you and Bob had years ago and members like reading  the drama when others get into in those kind of discussions. Perhaps our discussion has been entertaining for the members.  But I know Bob considers you as a friend and I believe you consider him as one yourself. Being a Christian I hope we can feel the same about each other.

 

Let's just let it go for now and "discuss" some other topic at a later date. Take care brother. 

 

William

[pzannucci]

How about you are both right and wrong.  There is a place for both and here is my take.

 

Autoformer sans resistance if your amp can handle the impedance swings and properly designed to handle phase shift (which with 3 way horns is all over the place anyway) and using resistance.  Swamping resistor w/autoformer or l-pad used in configurations where you could have a high impedance output amp which could introduce wide swings in frequency response due to the varying impedance of the speaker.  In that configuration you can use the l-pad to keep the speaker impedance constant.  l-pads can also work fine when using SS provided you don't mind throwing away the power and don't mind the variations in response that the driver/resistor mating can introduce due to one being constant and the other not.

 

Kind of a religion like zobel networks.  Some say waste of power and if designed properly, not really but allow constant impedance for a passive crossover to use.  

 

It's all an art!!!

[Deang]

+1 on that post. 

 

I’m not opposed to their use on tweeters. I use fixed L-pads for those who request them (though I prefer Al’s autoformer based tweeter attenuator).

 

I also still build a network that uses the swamping resistor on the autoformer, which allows for on the fly midrange adjustment - a useful feature for those who are using different horns and drivers.

 

For stock configurations, I prefer the unadulterated Type AA. 

 

This just seemed like an interesting discussion to participate in. If I’d know it was going to get nasty - I would have drank more Boubon. 

[Schu]

Question... why would someone use an autoformer as opposed to something like a ladder type stepped attenuation?

[rjp]

On 5/5/2018 at 12:08 PM, wdecho said:

Total BS. A resistor does not change it's characteristics  whether it is on the input or output of the signal. If the damping factor and transient response is reduced by a few ohms on the outputs then all the speakers that Klipsch has sold since say 95 and all the other speakers that are being sold by anyone are also suffering and Al is right. There is anywhere between 20K and 300K of resistance on the audio signal before it ever gets to the crossover with no ill effects.

My understanding is that damping factor works a bit differently. The output impedance of a good audio amplifier is frequently less than 1 ohm. It makes no difference how many resistors the signal has passed through on the way through the amp.  An amplifier with a very low output impedance by definition has a very high damping factor, since DF is by definition inversely proportional to the output impedance. High DF is good because it means the amp can make the speaker do exactly what it wants, prevents overshoot, even stop it dead if necessary. If a resistor is added to the speaker line then there can be a voltage drop making it more difficult for the amp to control the speaker. The amp will not be able to "damp" as well, but this is only due to the voltage drop and has nothing to do with the signal being degraded by passing through a resistor.

 

[Guest wdecho]

7 hours ago, rjp said:

The amp will not be able to "damp" as well, but this is only due to the voltage drop and has nothing to do with the signal being degraded by passing through a resistor.

 

A necessary evil by all 2 and 3 way speaker crossovers unless the mid and high speakers have the same efficiency as the woofer. In Klipsch speakers for example the woofer is less efficient than any of the other 1 or 2 other drivers. Sometimes as much as 10 db. If you do not attenuate the other drivers to match the efficiency of the woofer you will have an extremely bright speaker. All speaker manufacturers use resistors for attenuation. If you are against resistors for attenuation you are going to have to buy some of the old used heritage line of speakers that use an autotransformer. I know of no one but Klipsch that has ever used an autotransformer.  Most amplifiers have enough damping factor where a slight insignificant loss will not matter. If you think the damping factor really matters to you and your amplifier has a low damping factor you might want to look at a full range speaker with just one driver and no attenuation. The only thing damping factor effects is the low frequency's and on some of my amplifiers with limited damping factor I have not found it to be much of a problem but I am not a big bass guy. Music lives in the mids and if the mids do not shine best I could care less about how the lows and highs sound. 

 

Some examples of the damping factor of the Firstwatt line can be found here.  http://www.firstwatt.com/prod.html

The f3 was a very popular speaker with a loyal following with only a damping factor of 8. I have clones I have built of the Aleph 30, F3, F4, F5, F6, M2, and F7 along with some of the Zen amplifier variations. I also have built Nelson Pass' V-fet amplifier for diy'ers which is a gem of an amplifier and assisted others on this forum with their builds. None of the Firstwatt line of amplifiers have extremely large damping factors and I have not found the bass to be lacking in any of them using the mean old nasty resistor for attenuation in my crossover I designed. 

 

[Guest wdecho]

With some research I have now found another manufacturer that incorporated an autotransfromer in one of their crossovers. The original crossover on the JBL L300 appears to have used one for 6db attenuation according to the schematic Nelson Pass included in his article.  http://www.firstwatt.com/pdf/art_l300.pdf  page 3. But in the same schematic it uses those nasty old L-pads to enable the user to have some control over the sound for their own personal room in both the mids and highs. The same addition I am recommending for any owner of Klipsch speakers when they find the sound too bright for their taste and room. Nelson discarded the autotransformer when he designed a better more modern schematic for the L300, 

http://www.firstwatt.com/pdf/art_l300.pdf  page 6 but used instead resistance for attenuation in the form of L-pads with an alternate attenuation solution provided for those that do not like the rotary L-pads, page 7. Here is what he found after improving on the original schematic in summary.

 

"The speaker is very forgiving of amplifiers. I was able to drive them well with 600 watt monoblocks with high damping factors and also with little 5 watt amplifiers having damping factors of three or four. Both extremes worked well, even if the sound was not quite identical. I am very happy with the results. The end product doesn't appear to be an improvement based on response curves alone, but they do sound really great. I think I've managed to respect the JBL legacy while tweaking the sound to reflect the tastes of the 21st century. They still have that lively character of the originals, but the bass thumps are a little tighter and the horns a little more subtle and sweet, inviting you to spend hour after hour going through your entire record collection, which is what we're here for."

 

In the article is valuable information for anyone interested in what is involved in designing any crossover for a certain speaker.

 

There is a wealth of knowledge freely published by Nelson on this page and not just on amplifier circuits. http://www.firstwatt.com/articles.html  This page is often referred to by engineers and talented diy'ers with degrees for a starting point for anyone wishing to increase their knowledge of audio in general. 

 

[geoff.]

...not trying to open any old wounds, and it seems this one ended civilly with a wealth of knowledge being shared, but

 

this thread is a very good read for anyone else just trekking along at their own pace and getting to the L-pad phase 

[Nexi]

Good point! Thread was very helpful and useful at least most of the posts. For example I recently purchased pair of older Klipsch Ref IV RF62 125W and the high/tweeter is much more brighter compared to midrange and bass. When listening on higher levels very quicky sound becomes unpleasant and uncomfortable and I'm listening all kinds of music. All the time horn was overpowering everything else and my listening distance is about 3 meters away. 

 

Sense I don't and can't use the equalizer I try remove the back spikes to "angle" the speakers little bit back which help to some degree. In the end I placed a "toilet" paper over the horn and place the cover grill to hold it in the place. Only that I hit the sweet spot so that can enjoy my speakers and not get the horn "in my face" sort to speak. Then I decided to go steep further and I wanted to measure my speakers frequency using with calibrated microphone and I order the microphone(UMIK 1) which will be delivered soon. I start to investigate crossovers and what necessary parts and software I need to create new crossover or mod the tweeter circuit, whatever helps.

 

Then I found this thread and discover L pads which I had no idea that they existed! What a relief. 

 

Immediately I order the 8 ohm one from a online store and I got them today. I took out the crossover and using the alligator clips I quickly connected and test the L pad. I connected it after crossover output and the tweeter. The L-pad worked! I was able to lower the output of the horn almost all the way down and all the way up. Fantastic! 

 

I will install the L-pad on the back speaker panel for easy access/adjusting and sense I'm planing to keep the speakers dring a hole is not a problem but...

 

The only thing that I'm wondering now is: Did my L-pads are powerful enough? As I got the 15W RMS/30W peak ones. 

I took a horn out and the magnet are not that small. It looks quite big actually to my surprise. On other hand 15W RMS only on the higer frequency after the crossover should in theory be enough... 

 

I would like that someone with more knowledge and experience can back me up how many watts the horn can actually pull...

 

Any help or thoughts would be greatly appreciated. 

 

Wish you all great day! 

 

P.S. I have installed the L-pads few days ago and I like them alot. What a difference! Now I'm able to lower the horn pretty much completely down and up. I found that middle position is my preference for now. Now the sound is much more balanced and no more fatigue when listening at higher levels.

 

I highly recommend L-pads from now to anyone. Much easier to tune up your speakers. 

Here is the image of the L-pads.

 

My UMIK-1 microphone show up in Friday. I took some speaker measurements with REW. If someone is interested I can send some screenshots of measurements with L-PAD set to Max, middle and min. 

 

Edited May 9, 2023 by Nexi
More info added.