L-Pad Confusion

[Oozure]

Many AKers may be familiar with the Zenith Allegro 3000 speakers. I recently purchased a pair and quite enjoy them for non critical listening.

I would like to add an adjustable L-pad for the Foster horn tweeter. I am having a hard time choosing the proper one to use. I will be getting one from Parts Express. I know that I will use one rated for 50 watts. I just don't know if it should be an L-pad designed to maintain an 8 OHM load or 16 OHM load. It is a 2 way 16 ohm speaker and each driver is 8 ohms. I don't know if I am supposed to match the impedance of the tweeter (8 ohms) to the l-pad, or to match the impedance of the entire speaker system (16 ohms) to the l-pad.

Hope that made some kind of sense. So L-pad rated to maintain 8 ohms or 16 ohms?

Any help will be greatly appreciated.

 

[donprice]

Can you get to the crossover to see if it has any other resistors in there? A pair of them on the tweeter would be a fixed L-pad. Not sure if that will really help answer your question but it won't hurt to know....and might as well think about replacing the caps while you are in there.

You probably don't need the 50 watt L-pad since the tweeter (and L-pad) sees much less power than the woofer so one rated for 10 or 15 watts will be fine for home use.

 

[Oozure]

Thanks for the answer Don. I thought about the 15 watt l-pad but was going to err on the side of caution and us a 50 watt unless it is detrimental to overall sound quality. I believe there is a resistor but I have yet to figure its impedance. It is an older color banded resistor and I have yet to figure out it's value. I also wanted to use a variable L-pad for versatility in different listening environments. I attached a picture of the resistor if anyone can help.

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[Oozure]

Forgot to mention that a re-cap is happening soon. One crossover has a wax and paper cap and the other has an electrolytic.

 

[ken kantor]

Many AKers may be familiar with the Zenith Allegro 3000 speakers. I recently purchased a pair and quite enjoy them for non critical listening.

I would like to add an adjustable L-pad for the Foster horn tweeter. I am having a hard time choosing the proper one to use. I will be getting one from Parts Express. I know that I will use one rated for 50 watts. I just don't know if it should be an L-pad designed to maintain an 8 OHM load or 16 OHM load. It is a 2 way 16 ohm speaker and each driver is 8 ohms. I don't know if I am supposed to match the impedance of the tweeter (8 ohms) to the l-pad, or to match the impedance of the entire speaker system (16 ohms) to the l-pad.

Hope that made some kind of sense. So L-pad rated to maintain 8 ohms or 16 ohms?

Any help will be greatly appreciated.

Unfortunately, L-Pads don't work nearly as well as many seem to think. But, they do attenuate the signal, and most people don't notice the big response errors they introduce. So, you can use either 8 or 16 Ohms, with no real difference in SQ.

-k

BTW- L-Pads only work semi-correctly on "Constant Voltage Distribution" systems, such as a "70 Volt" PA circuit in a venue. They simply were never meant to be used on the kind of circuits typically used in the home, despite their presence on some crossover networks.

 

[Oozure]

Thanks Ken. Between what you and Don have said, I may just go ahead do a fixed l-pad. I appreciate the help guys!

 

[Zonker92]

Unfortunately, L-Pads don't work nearly as well as many seem to think. But, they do attenuate the signal, and most people don't notice the big response errors they introduce. So, you can use either 8 or 16 Ohms, with no real difference in SQ.

-k

BTW- L-Pads only work semi-correctly on "Constant Voltage Distribution" systems, such as a "70 Volt" PA circuit in a venue. They simply were never meant to be used on the kind of circuits typically used in the home, despite their presence on some crossover networks.

Interesting; thanks. What about setting them to preference, testing the resulting DCR, then substituting a resistor of that value?

Hmmm.

 

[ken kantor]

Interesting; thanks. What about setting them to preference, testing the resulting DCR, then substituting a resistor of that value?

Hmmm.

Variable or fixed doesn't make any difference. The problem is that an "L" attenuator introduces a series resistance between the source and the load, one that neither the source, nor the load was meant to see. Often, the introduction of an L-Pad lowers the crossover frequency by up to 30%, and introduces bumps in the frequency response of the driver on the order of 3 or 4 dB.

They are handy for providing a course adjustment for level or tonal balance, but they in no way preserve the original response while doing that.

-k

 

[donprice]

Ken - I've only used the adjustable L-pads in the ewave crossovers. I assume using them is not detrimental (ignoring audiophool hearing abilities) if the crossover was designed to use them in the first place. Is that a reasonable assumption?

OP - apologies for going off on a tangent

 

[dc270]

If I understand correctly an ideal speaker set, with a passive network would be designed around the how the driver(s) interact, balance with L/C components, to avoid having to use L-pad, resistors.
Regarding the fact that passive x-overs are a necessary evil-just how wicked do you want them to be..........
DC

 

[Zonker92]

Variable or fixed doesn't make any difference. The problem is that an "L" attenuator introduces a series resistance between the source and the load, one that neither the source, nor the load was meant to see. Often, the introduction of an L-Pad lowers the crossover frequency by up to 30%, and introduces bumps in the frequency response of the driver on the order of 3 or 4 dB.

They are handy for providing a course adjustment for level or tonal balance, but they in no way preserve the original response while doing that.

-k

Cool; thanks.

 

[fred soop]

Be careful if using L Pads to replace rheostats in vintage AR speakers (other brands could be similar). The original rheostats at maximum remained as a resistance in parallel with the driver. The L Pad actually goes open circuit at max and may overload the driver. When rebuilding my AR crossovers, where the rheostats had been replaced with L Pads by the original owner years earlier, I added 30 ohm 12 watt resistors across the midrange and tweeter.

 

[ken kantor]

Ken - I've only used the adjustable L-pads in the ewave crossovers. I assume using them is not detrimental (ignoring audiophool hearing abilities) if the crossover was designed to use them in the first place. Is that a reasonable assumption?

OP - apologies for going off on a tangent

It's a very reasonable assumption.... if the L-Pad was designed in, it has a much better chance of working well.

Just a note, though: Back when AR was using pots as driver level controls, we found it pretty much impossible to get the correct response at all settings. So, standard procedure was to design some point, often full up, as the correct response, and not to worry about any other setting. The logic was, set it the way it was designed, in the "flat" position, or you are on your own, caveat emptor. When it was necessary to maintain correct response at different settings, both L-Pads and potentiometers were dispensed with, in favor of the complex autotransformer circuit that can be found in the LST and 10pi.

Of course, like so much in audio, this comes down to the essential question of "doing it the way you think it sounds best" vs. "doing it the way that is supposed to be most accurate." (I have generally favored the latter, since it forces recordings to improve. But, the former method is usually the most rewarding for the audiophile hobbyist.)

-k

 

[toxcrusadr]

Just wanted to point out: The original post said this was a 16 ohm speaker with two 8-ohm drivers. If the drivers are each 8 ohms, you have an 8-ohm speaker. Only way for that to make 16 is for them to be in series, which they are not in a speaker. They essentially run in parallel, but since the signal is divided by the xover, the portion sent to each driver 'sees' an 8-ohm load. Just thought we should clear that up.

 

[Brian]

Thanks for the answer Don. I thought about the 15 watt l-pad but was going to err on the side of caution and us a 50 watt unless it is detrimental to overall sound quality. I believe there is a resistor but I have yet to figure its impedance. It is an older color banded resistor and I have yet to figure out it's value. I also wanted to use a variable L-pad for versatility in different listening environments. I attached a picture of the resistor if anyone can help.

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red, violet, gold, silver

let's see: bbroygbvgw so, 278ohm. The 4th band is tolerance and I remember silver is 10%. Not sure of the wattage as it is related to its size. I preferred wirewwound on crossovers to carbon comp as they were more stable as to frequency shifts. Not sure what is out there today that may do as well. WWs generally start at 5 watts whereas cc usually max at 1 watt. As long as you go higher, wattage is not a significant factor.

 

[HTHMAN]

red, violet, gold, silver

let's see: bbroygbvgw so, 278ohm. The 4th band is tolerance and I remember silver is 10%. Not sure of the wattage as it is related to its size. I preferred wirewwound on crossovers to carbon comp as they were more stable as to frequency shifts. Not sure what is out there today that may do as well. WWs generally start at 5 watts whereas cc usually max at 1 watt. As long as you go higher, wattage is not a significant factor.

That is 2.7 Ohms which also seems like a more reasonable value in a speaker crossover.

 

[Oozure]

Just wanted to point out: The original post said this was a 16 ohm speaker with two 8-ohm drivers. If the drivers are each 8 ohms, you have an 8-ohm speaker. Only way for that to make 16 is for them to be in series, which they are not in a speaker. They essentially run in parallel, but since the signal is divided by the xover, the portion sent to each driver 'sees' an 8-ohm load. Just thought we should clear that up.

Hey Toxi, I believe that the drivers in my Allegro 3000's are wired in series each of the two drivers are rated 8 ohm and the information on the back of the speaker cabinets States a 16 ohm load.

 

[Oozure]

Thanks Brian and HTHMAN. I found an online capacitor calculator that seems to confirm the 2.7 ohm resistor. Who knew the internet was for more posting selfies?