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L-pad primer--please?

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I have homemade speakers made from TAD 2001 (109 dB/W) drivers and 15" woofers (95 dB/W), and I have horns for the TADs on order, and I'm trying to prepare to make a crossover to equalize output from the two drivers. I am sorry to report that I don't know what the heck I'm doing. I plan to put in L-pads, then check the resistance through the L-pad when the system sounds good, and replace the L-pad with a fixed component system (high wattage resistors). However, as I think about this I understand that I need some HELP in understanding L-pads. I have done a search, but most of what is posted presupposes a basic knowledge of how they work, and I don't have that basic knowledge. The little bits of basic stuff I've found suggest that L-pads can be used to lower signal levels to a driver without changing the overall resistance seen by the amp, and since they do not change resistance they do not change crossover frequency. Is that right? It seems bizarre to me, but I don't claim to to understand electricity. A related question: does an 8 Ohm L-pad add 8 Ohms of resistance to the circuit, so that the new total resistance is 16 Ohms, or is total resistance somehow maintained at 8 Ohms? (This again gets to the question of calculating correct values for crossover at a given frequency.) And lastly--for now anyway--can I measure the summed resistance through the L-pad to get the value I want in order to make a fixed system, or do I need to measure it through the internal series and parallel resistors separately?
Thanks to all you kind people for your help.

Follow Ups:

Re: L-pad primer--please? pkell44 19:35:01 05/22/01 (0)
You're on the right track. After you have "voiced" the speakers for your listening room replace the L-Pad with Caddock non-inductive R's of about 20 - 30 watt size.
The best way to 'voice' your speakers is to connnect only one speaker i.e.LC or RC, If your system allows it, set the output to Mono so that you're getting both channels thru each speaker. Turn the MR & T L-Pads down all the way and play something that has a fairly well balanced tonal spectrum. Slowly turn up the MR L-Pad until its' output is equal in volume to the woofer when you are listening with your head close to the speaker enclosure (known as "The near field method"). Then repeat the process with the tweeter until its' output is equal to the Woofer & MR. This should be a slow and relaxed process.
Disconnect the voiced speaker and connect the other speaker and repeat the process. Check the results of these setting at the norma; listening position and adjust as necessary. You have now voiced both speakers to your room. Listen to them for several listening sessions, during which you will tweak both speakers' settings. After you are sure that they are voiced to your satisfaction disconnect each L-pad in turn and use a DVM to read the resistance of each L-Pad's legs and record your readings. These are the values of the Caddock R's you will need to replace the inductive wirewound L-pads with solid-state non-inductive L-Pads. You should notice a significant improvement in resolution of fine detail, transient attack & decay, etc.
Happy Listening !
Here's a site to calculate one. Walnut 16:00:07 05/21/01 (3)
http://www.lalena.com/audio/calculator/lpad/
- Thanks a lot, but I guess I wasn't clear... Twistnshout 17:15:07 05/21/01 (2)
  I mean to use a variable L-pad to get a subjectively pleasing setting, then substitute with fixed resistors. Also, my main problem is just understanding the basic way they work and how to go about determining the proper values of fixed resistance from a given setting of a variable L-pad.
  - Re: Thanks a lot, but I guess I wasn't clear... Jon Risch 01:02:15 05/22/01 (1)
    An L-pad consists of a series resistive elemetyn, and a shunt resistive element. You would have to measure both to arrive at the fixed pad equivalent.
    AN 8 ohm L-pad will maitain a nominal 8 ohms as it is adjusted, and not add to the speaker impedance already there.
    
    As an example:
    0 dB attenuation is 0 ohm series, open shunt.
    -3 dB atten is 2.34 ohms, and shunt of 19.4 ohms
    -6 dB atten. is 4 ohm series, 8 ohm shunt
    -9 dB is 5.16 and 4.4
    -12 dB is 6.0 and 2.7
    All of these assume an 8 ohm resistive load, as do almost all commercially available L-pads.
    If you know what the sensitivity difference between the two drivers is, then you should be able to judge the amount of tweeter atenuation needed, and try a few fixed L-pad values and see which one sounds the most balanced. This eliminates any potential errors when measuring the l-pad for values.
    In any case, given the drivers you state, your tweeeter atenuation will probably be on the order of about 12 dB, rather the the 14 that the straight sensitivity ratings would tend to indicate. If you do use the L-pad method, and measure the series and shunt resistances, they should come out very close to what I posted for the -12 dB case.
    Jon Risch
    - Hugely helpful--thanks so much! (nt) Twistnshout 06:33:43 05/22/01 (0)
      nt

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