T pads vs L pads

[maxserg]

I’ve built long time ago some 3 way passive xovers. I’ve preferred T pads over the other. The advantage is correct impedance match from amp to speakers.

I used a 12 step 2 db attenuator per way. Witch is no easy task at that time.

T pad seem to be used in hi end systems.

I am right or wrong?

[RMC]

Hi maxserg,

It would seem that you're wrong about T-pads. L-Pads are probably more popular in speakers, high and lower cost, since they're easier to do and save the cost of one resistor (2 for L) and (3 for T). In his Handbook of Sound System Design, Eargle mentions the following about T-Pads:

"For most applications, the L-pad is the easiest to implement, and it allows the loudspeaker to look back into a lower resistance than does the T-pad for the same amount of attenuation. The T-pad, shown in Figure 1-13 is best used when both source and load impedances must be carefully matched. This will typically be the case when pads are to be inserted between devices having 600-ohm input and output impedances." (p.15)

So the L is on the crossover board, whereas the T would typically be between two pieces of electronics based on impedance mentioned.

Richard

[maxserg]

Thanks for your explanation.

[RMC]

Note "best use" from Eargle doesn't mean its forbidden or can't use one on a driver, simply means its not optimal.

One can still use a T-pad if he wants to or prefers that, in fact Eargle shows how to make one for any impedance, using 2 X R1 and 1 X R2 (vs 1 X R1 and 1 X R2 in the L-pad).

However, with T-pad the driver will be looking back into a higher resistance than the L-pad does, for the same attenuation, then why bother?

In other words no need to add unnecessary resistance when its not required in a speaker cab, is the point.

[maxserg]

Well thanks I see.

so more resistance to the driver, efficiency loss...