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L-pad for tweeter level control?


rjp

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Greetings fellow Klipsch owners.

I would like to experiment with controlling the output level of the tweeter in my RP-260F speakers. Can this be accomplished by inserting a simple 8-Ohm L-Pad between the crossover and the tweeter? I've seen some fancy level adjustment circuits in other threads involving adjustable tap transformers and I was wondering why a purely resistive approach like an L-Pad wouldn't work as well.

 

Thanks for any info,

 

Rich

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Take off the straps and put it on the high frequency connectors.  You could also just use a high quality resistor 1-a few ohms to do some minor changes in output.

Autoformers keep the driver impedance variations constant though changing the impedance of the whole section of the network, requiring modifications to the cap and coil portions (whatever are before the autoformer).  In theory if you used an lpad, the impedance stays constant 8 ohms or whatever.  Not really true since it is tied to the impedance of the driver but if you are not too far out of whack, should not hurt too much.

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Guest wdecho

L-pads work fine for what you want to do. Not really hard to hook up if you just remember the center lug goes to the driver. If the outside ones are inverted and not  hooked correctly the pot will be reversed. Not really that big a deal. Outside lug input, output lug ground, center to driver. Using just a resistor will change the frequency of the X-over point of the tweeter, the reason for L-pad. 

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Get a schiit loki 4 band eq. It will not only work great on the 260 it will work on any speaker you use in the future! I use it on the rp280f speakers and it tames the highs and adds to the mids. Truly a great little item. It gives lots of control but not more than I want or need.

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40 minutes ago, wdecho said:

 Using just a resistor will change the frequency of the X-over point of the tweeter, the reason for L-pad. 

You must use 2pcs resistors to avoid frequency offset. 

IMG_20180501_125153.png

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Guest wdecho

Using two resistors is the way I do it but for most an L-pad is the better solution and is adjustable. With two resistors you have to spend a lot of time trying different combinations of resistors for the attenuation you eventually think is best. With an L-pad you just turn a knob to reach the right balance that you prefer. I spent many days experimenting with attenuation using just 2 resistors changing and listening to the effects. It can be a long process but admittedly probably best but you are splitting hairs for the most part. L-pads are used by many speaker manufacturer's.  

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11 hours ago, rjp said:

I would like to experiment with controlling the output level of the tweeter in my RP-260F speakers. Can this be accomplished by inserting a simple 8-Ohm L-Pad between the crossover and the tweeter?

Welcome to the Klipsch forums with your Post #1.

 

Back in the bad old days people needed an L-pad because it was cheap and buying an 8 or 16 band equalizer was expensive.  Fast forward to the present, the new good old days.

 

Use the EQ built into your AVR.  If you are running through a computer every sound card comes with an EQ software program.  Or pick up a physical EQ and plug it in, they are available used everywhere and they are cheap because nobody uses them anymore.

 

You might think an L-pad will attenuate the highs in your tweeter, but what if the problem is not enough mid-bass that needs boosted? An L-pad will not help you experiment with that, an EQ would.

 

Nobody uses L-pads these days.  There's just no need for it.

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30 minutes ago, wdecho said:

Using two resistors is the way I do it but for most an L-pad is the better solution and is adjustable.

 

I just saw your old posts in a similar thread from April 29, 2016.  You haven't changed a bit!  :lol:  :P

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20 minutes ago, wvu80 said:

Nobody uses L-pads these days.

I just got a set in the mail yesterday and will be using them soon.  Mids are way too hot on a pair of KP-2500's and this is the easiest and cheapest solution.

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2 hours ago, mr clean said:

Get a schiit loki 4 band eq. It will not only work great on the 260 it will work on any speaker you use in the future! I use it on the rp280f speakers and it tames the highs and adds to the mids. Truly a great little item. It gives lots of control but not more than I want or need.

Wow! So many replies! Thank you all so much. I will address a few here and yours is first.

 

Believe it or not, I have tried the Loki 4 band EQ. My son owns one that he uses for his headphone setup. It is a really nice unit, but I don't like being limited to just 4 center frequencies. I have been looking for a parametric version but can't find one. Even a single band full PEQ would be wonderful, but I only seem to find them in guitar stomp boxes. It would be great to have one in a small box like the Loki.

 

 

 

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3 hours ago, pzannucci said:

Take off the straps and put it on the high frequency connectors.  You could also just use a high quality resistor 1-a few ohms to do some minor changes in output.

Autoformers keep the driver impedance variations constant though changing the impedance of the whole section of the network, requiring modifications to the cap and coil portions (whatever are before the autoformer).  In theory if you used an lpad, the impedance stays constant 8 ohms or whatever.  Not really true since it is tied to the impedance of the driver but if you are not too far out of whack, should not hurt too much.

 

2 hours ago, wdecho said:

L-pads work fine for what you want to do. Not really hard to hook up if you just remember the center lug goes to the driver. If the outside ones are inverted and not  hooked correctly the pot will be reversed. Not really that big a deal. Outside lug input, output lug ground, center to driver. Using just a resistor will change the frequency of the X-over point of the tweeter, the reason for L-pad. 

 

Great. I am going to install the L-pads right now and will post back with my results.  Though the two fixed-resistor solution is probably more pure, I do like the option of adjusting the level anytime I like. I suppose if I find I am keeping the L-pads at one particular setting all the time I could take them out and measure the two resistances and swap in fixed resistors of the same values.

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Guest wdecho
48 minutes ago, wvu80 said:

 

Welcome to the Klipsch forums with your Post #1.

 

Back in the bad old days people needed an L-pad because it was cheap and buying an 8 or 16 band equalizer was expensive.  Fast forward to the present, the new good old days.

 

Use the EQ built into your AVR.  If you are running through a computer every sound card comes with an EQ software program.  Or pick up a physical EQ and plug it in, they are available used everywhere and they are cheap because nobody uses them anymore.

 

You might think an L-pad will attenuate the highs in your tweeter, but what if the problem is not enough mid-bass that needs boosted? An L-pad will not help you experiment with that, an EQ would.

 

Nobody uses L-pads these days.  There's just no need for it.

I am a proponent of less is better especially when one goes to the trouble of purchasing expensive class A amplifiers. Why would want to throw an equalizer into the mix with all those op-amps twisting and twisting the sound. Defeats the purpose. I do not want any type of device including bass and treble controls on my preamplifier for the very same reason. And you are wrong about manufacturers using L-pads. Simple easy cheap solution for increasing or decreasing attenuation without effecting the basic simple circuit. Equalizers are for Bose 901's in playback.  

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2 hours ago, raeggis said:

You must use 2pcs resistors to avoid frequency offset. 

IMG_20180501_125153.png

 

Wow! Truly amazing. Thanks for this diagram. This brings up another question I have but didn't want to cram into my first post. Maybe I should start another thread?

The question is regarding the Zobel network in this schematic. I have been reading so much about them. I understand how they cancel the imaginary component of the complex impedance of the speaker so the pair looks purely resistive, but I'm not sure if I should add one to my tweeter or not.

 

How important are these? Since Klipsch has been working on refining the horn tweeter for 70 years I would think they must have tried this and would have included it in my current speaker for the cost of one resistor and a capacitor if it made a difference, right?

 

I'm going to take a closer look at my crossovers soon. I seem to recall the HP filter was 4th order, which surprised me since I'v never seen a 4th order filter used, but maybe the last leg was a Zobel?  I'll post back with the circuit after I inspect it.

 

 

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Guest wdecho

Leave in the zobel. It has nothing to do with the crossover frequency. It tames a too hot driver or horn. Commonly used in quality speakers to refine the sound. Too much is not a good thing though. For instance someone went entirely crazy when designing the AL crossover using zobel networks in all the drivers for a more flat frequency response. Being more flat is not always best but I expect Klipsch has learned from their mistakes of the past and the zobel is needed with your speakers. If you want to experiment then certainly take it out and judge for yourself. Below is a calculator I use to determine the proper attenuation instead of a chart. Either one works just fine.

 

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

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15 minutes ago, rjp said:

I am going to install the L-pads right now and will post back with my results. 

Be sure you have the correct Ohm rated L-pad.  I just sent back a pair of 8 Ohm pads as I should have ordered the 16 Ohm version.

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1 minute ago, wdecho said:

I am a proponent of less is better especially when one goes to the trouble of purchasing expensive class A amplifiers. Why would want to throw an equalizer into the mix with all those op-amps twisting and twisting the sound. Defeats the purpose.

Oh, I agree.  (with the whole post)  My post referenced two other solutions before we got to the third option, a physical Equalizer.

 

Our new friend @rjb said he wanted to experiment with the tweeter section of his RP-260F's.  Now it's possible that he is running those with "an expensive Class A amplifiers" such as a tube amp but not likely since tube amps and Class A only amps are only used by a very small minority, and then not usually used with mid-tier Klipsch speakers where AVR's rule the roost.  I was going with the higher percentage AVR/speaker combination to offer some advice. 

 

It's true that more than a quarter of a century ago back in the 70's there were some manufacturers that used L-pads but those have largely gone by the way of the dodo bird thanks in large part to the to built-in EQ of any modern AVR.  The exception is not the rule.

 

Just my view. B)

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55 minutes ago, wvu80 said:

 

Welcome to the Klipsch forums with your Post #1.

 

Back in the bad old days people needed an L-pad because it was cheap and buying an 8 or 16 band equalizer was expensive.  Fast forward to the present, the new good old days.

 

Use the EQ built into your AVR.  If you are running through a computer every sound card comes with an EQ software program.  Or pick up a physical EQ and plug it in, they are available used everywhere and they are cheap because nobody uses them anymore.

 

You might think an L-pad will attenuate the highs in your tweeter, but what if the problem is not enough mid-bass that needs boosted? An L-pad will not help you experiment with that, an EQ would.

 

Nobody uses L-pads these days.  There's just no need for it.

 

Thank you! In the "old days" when I was a teenager, we all used cheap graphic EQ's, but along the years since then the consensus I was hearing from more sophisticated audiophiles was that tone controls were bad, but to really screw things up required an equalizer. :)

 

I guess I've kind of subscribed to the thinking that the less tone control in the signal path the better, but maybe I should re-evaluate this. Are modern equalizers much better now? Are the still analog or do they convert to digital for the processing and then back to analog for output?

 

I am currently using a home made tube amplifier and plugging in my iphone directly. Signal source is Spotify on highest bitrate. The amp is a customized EL84 push-pull similar to a Dynaco ST-35. There are presently no tone controls. I did experiment with treble and bass controls and a single tube preamp in this box but they seemed to make the sound better in some places but worse in others so I took them out. It did sound pretty good with the Loki though as mentioned above.

 

The only digital EQ I have access to at present is the iPhone app called SpotEQ. It is a 31 band graphic EQ that is designed to work with Spotify. It seems to work great but is not easy to adjust on the little iPhone screen. I was wondering if digital filtering was a good thing. Is throwing math at the signal better than analog circuits (pots, caps, and resistors, etc)?

 

Again, it would be so great if I could find a parametric version. The freq I want to attenuate most seems to be close to 3KHz according to this app.

 

I'm not sure how accurate all these iPhone apps are, but it is a lot of fun to use the white noise generator and spectrum analyzer to listen to the room. No idea how well they've compensated for the mic, but at least it's fun to play with. :)

 

Whoa! I see three more posts have come in.

 

 

 

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14 minutes ago, CECAA850 said:

Be sure you have the correct Ohm rated L-pad.  I just sent back a pair of 8 Ohm pads as I should have ordered the 16 Ohm version.

Interesting you should mention this. I just measured the horns and I get 16 ohms at 1KHz and 8 ohms at 10KHz. There are no other frequency options in between on my LCR meter.

The pads I have are 8 Ohm.

 

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1 minute ago, rjp said:

I'm not sure how accurate all these iPhone apps are, but it is a lot of fun to use the white noise generator and spectrum analyzer to listen to the room. No idea how well they've compensated for the mic, but at least it's fun to play with. :)

 

Whoa! I see three more posts have come in.

Yep.  You have raised an interesting topic.  :)

 

You answered my question, "what amp do you have?"  Tube amp it is.

 

There are so many variables in the audio chain and it all starts with the source.  Who knows why the tweeter may be a little hot to your ears?  It might be the Iphone, it might be Spotify, it might be your tube amp, it might be the speakers.  I fully agree you should be able to tame it to where it sounds good to you.

 

As far as modern Equalizers are concerned I just don't see them any more.  I just suggested one because I think it is an easier solution to installing an L-pad for $50.

 

If you have the Iphone 31 band Equalizer app, why not try that?  It's quick, easy and you already own it.  It may provide some answers.

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6 minutes ago, wvu80 said:

Oh, I agree.  (with the whole post)  My post referenced two other solutions before we got to the third option, a physical Equalizer.

 

Our new friend @rjb said he wanted to experiment with the tweeter section of his RP-260F's.  Now it's possible that he is running those with "an expensive Class A amplifiers" such as a tube amp but not likely since tube amps and Class A only amps are only used by a very small minority, and then not usually used with mid-tier Klipsch speakers where AVR's rule the roost.  I was going with the higher percentage AVR/speaker combination to offer some advice. 

 

It's true that more than a quarter of a century ago back in the 70's there were some manufacturers that used L-pads but those have largely gone by the way of the dodo bird thanks in large part to the to built-in EQ of any modern AVR.  The exception is not the rule.

 

Just my view. B)

 

I am using a simple EL84 PP tube amp. It is Class AB and is running in pentode mode currently. There are no tone controls. The preamp and PI sections are just a couple 6EU7 tubes and negative feedback is set to keep things as flat as possible. I am getting 15 watts RMS per channel on the 8 ohm taps of the output transformers. It sounds amazing with the RP-260's, it's just that the room is a little bright. More carpet might help. Also, every once in a while I get a song that is not so well recorded and come across harsh. These speakers are very revealing. Truly and amazing listening experience!

 

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