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Jeff Medwin
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I've not measured but assume up to a point a single resistance placed "before" a crossover will work without seriously affecting response. It may be limited in useful range compared to the L-pad,
tapped autoformes are less linear than resistors - the little Klipsch size aren't too shabby if the crossover point is high enough
Karlson Evangelist
The problem with the tandem pots is that you can never get perfectly matched sections and you will get a "chorus effect".
No wait, that only applies to tubes:-)
...more like tandem/coordinated rheostats and not pots. What to do?
So, you have two wipers and two resistive elements, cross wired? AS in a ladder attenuator using pots??That would be pretty good, since its NOT a single wiper, as in some ALTEC speakers, that causes the problem I have addressed.
A sonic improvement for you might be to measure the ohmic values, and employ soldered in wirewound power resistors, eliminating the mechanical interface of the wipers to resistive elements handling speaker-level ( powerful ) signals.
Edits: 01/09/17
Actually, with an Lpad one wiper is in series and one in parallel with driver. Presents what appears to be a constant upstream impedance. Fixed resistors might be the easiest soln but stepped using decent switch is attractive too.
Edits: 01/10/17
I switched to fixed resistors for two reasons:1: I did not like what they did to the sound.
2: To achieve the attenuation I needed, the L-pad needed to be set between 1 and 2 (on a scale of 0-10), making it difficult to match L and R settings.I determined the amount of attenuation needed by using a sound level meter, measuring the difference between wide open and what I liked. I also took AC voltage measurements at the driver, and converted that to dB's.(the results were amazingly close).
Edits: 01/10/17
The two identical pots would be wired in parallel, not an L-pad.
So you have two wipers carrying the signal but now you have to consider the
paralleled resistance and pick the pots accordingly.
I was describing an Lpad. A pot (or parallel pots) cannot present a reasonably constant impedance to upstream components whereas an Lpad pretty much does. As a result, my inclination is to either construct a fixed Lpad out of two appropriate value resistors OR find a quality multi pole/multi position switch and construct a stepped Lpad (vs common continuously variable type made of two way different value rheostats .
A fixed resistive L Pad will avoid switch contacts, which is a good thing . Employ well chosen 10 Watt Rs.
Jeff
maybe the common tandem 100 watt per section L-pad in 16 ohms and paralleled would offer some theoretical improvement ? (I've not looked at the inductance of one)
it nothing else, this would take some power without smoking
Karlson Evangelist
Hi,
Where did you source your 16 ohm L pads? I need some for a Higara Vott xover.
Regards,
David
hi David - seems like I used to see tandem 16 ohm L-pads - but can't locate any now - Parts Express and MCM carry decent mono units.see if these search links work
MCM L PADS
Parts Express L PADS
Karlson Evangelist
Edits: 01/10/17
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