Attenuating HF with Adjustable Wirewound Resistors

[Dave A]

Has anyone used wirewound adjustable resistors to dial in their HF? Reading about these and wondering if for experimentation purposes these might be the way to go to find correct values without having to buy tons of wire wound resistors instead. Yes I know those online calculators exist but not thrilled with them.

[Curious_George]

You can use an L Pad, dial it in, then measure the values and use two discrete resistors.

[Dave A]

Yes I know that but my question is as posted. I want to hear from those who have tried these and what they found.

[Curious_George]

So in other words, you want to use two discrete wire wound adjustable resistors and dial them in to attenuate the HF driver?

[Dave A]

Yes that is what I am thinking. I have tried some L-Pads but they seem to drift a bit.

[Curious_George]

Quote

 

Unless you do the math for the resistor ratio, you need to use the online calculator(s). When you start adjusting your two discrete adjustable wire wound resistors, if you don’t keep the ratio correct, the impedance seen by the crossover network will change, thus changing your crossover frequency, then you will be changing the level and the crossover frequency. 
 

 

[Dave A]

I have some resistors on order using that method too.  My problem is attenuating a 109db 150 watt hf driver to a set of 99.9db woofers.

[HiFi Heaven]

Hello Dave -

Any 50W L-pad will do the job for home listening.  You are only dropping 9dB, at a few watts max.

Your 150W HF driver (?) is made for ballpark PA systems which are tri-amped, not for passive systems.

If you insist on using it consider electronic crossovers where you can play with levels by spinning a knob

instead of endless experimenting with resistors, capacitors, driver phasing & time-correction.  You can do

in 10 minutes

[HiFi Heaven]

... what might take months.  Use AUDIOTOOL on your phone or tablet to see the audio spectrum w/ 12 bands per octave.

Have a blast, tell us what you learn in the process!

 

[Dave A]

Sigh, I have two Xilicas and a Mini DSP HD and use a Xilica 3060 on my Super MWM's. I know all about electronic crossovers. What my question is though, and still is, has anyone used adjustable wire wound resistors to attenuate a passive crossover on the HF side.

 

  Please refrain from answering this very specific question by suggesting it is not optimal or there are better ways etc. I want to talk to someone who has tried this and yes I have my reasons for doing so.

[carlthess40]

Dave A. It’s so funny that people question your questions. Lol
This is why I’ve pretty much stopped asking questions on the forums, people can’t give a straight answer ( like our politicians)
Wish I could help you out but it’s over my level of knowledge

[henry4841]

Dave I doubt anyone on this forum has tried the experiment you are talking about. The way I would go about it though would be to use an adjustable L-pad and measure the amount of resistance you need then set the adjustable wire wound resistors to the same value. Calculate the parallel resistor using an L-pad calculator. A multimeter will help dialing in the adjustable wire wound resistors. I do not understand the reasoning behind what you are trying but look forward to the results. I have always done it like Curious George describes when I was experimenting with crossovers. In my present main system I found I need to use discrete resistors along with an adjustable L-pad to fine tune and have enough attenuation for the high efficiency drivers I am using. I could take out the adjustable L-pad and put in higher value discrete resistors but I honestly see no reason to. Nelson Pass designed a crossover for a pair of JBL L200's and used adjustable L-pads so I figure he does not consider them to drift enough to be a problem. Good enough for him then good enough for me. There are many laymen on this forum with no experience in the electronic field that will say how terrible L-pads are. I just ignore them. There is always going to be critics on most every posting on a social media forum. 

[Curious_George]

5 hours ago, carlthess40 said:

Dave A. It’s so funny that people question your questions. Lol
This is why I’ve pretty much stopped asking questions on the forums, people can’t give a straight answer ( like our politicians)
Wish I could help you out but it’s over my level of knowledge

A question about a questions usually infers clarification. This is how humans communicate effectively.

[Dave A]

6 hours ago, henry4841 said:

Dave I doubt anyone on this forum has tried the experiment you are talking about. The way I would go about it though would be to use an adjustable L-pad and measure the amount of resistance you need then set the adjustable wire wound resistors to the same value. Calculate the parallel resistor using an L-pad calculator. A multimeter will help dialing in the adjustable wire wound resistors. I do not understand the reasoning behind what you are trying but look forward to the results. I have always done it like Curious George describes when I was experimenting with crossovers. In my present main system I found I need to use discrete resistors along with an adjustable L-pad to fine tune and have enough attenuation for the high efficiency drivers I am using. I could take out the adjustable L-pad and put in higher value discrete resistors but I honestly see no reason to. Nelson Pass designed a crossover for a pair of JBL L200's and used adjustable L-pads so I figure he does not consider them to drift enough to be a problem. Good enough for him then good enough for me. There are many laymen on this forum with no experience in the electronic field that will say how terrible L-pads are. I just ignore them. There is always going to be critics on most every posting on a social media forum. 

My thought was to use crossover L-Pad calculators to get a value to start with. Then I could set the adjustable resistors to those values and tweak from there without having a drawer full of resistors of fixed value. Calculators are a place to start not finish unless you get real lucky.

 

6 hours ago, Curious_George said:

A question about a questions usually infers clarification. This is how humans communicate effectively.

Or they are attempts to answer questions that were not asked. Well he really meant to ask ------- so I will help him out by asking the correct question he meant to ask.

[Curious_George]

56 minutes ago, Dave A said:

Or they are attempts to answer questions that were not asked. Well he really meant to ask ------- so I will help him out by asking the correct question he meant to ask.

Exactly. Sounds like a suitable time for a Forrest Gump idiom, but I will refrain since I promised the moderators I would be on my best behavior. 

[Dave A]

7 hours ago, Curious_George said:

Exactly. Sounds like a suitable time for a Forrest Gump idiom, but I will refrain since I promised the moderators I would be on my best behavior. 

You are a true forum paragon of steely resolve and diligence, a bulwark against negativity plus you did not need to google your answer.