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L-Pads. Speakers Awful Without Them, New Ones Ordered

I removed the L-Pads, the tweeters are way too bright, screechy above mids. Disturbing. Played my best source: R2R, Sgt. Peppers. Normally magnificent. Unlistenable!

Using my Chase Remote Control to cut Treble temporarily, until new L-Pads arrive.

I ordered these 16 ohm pads:

https://www.ebay.com/itm/153892668925

mine don’t have the issues he discusses, my insulation is modern, crossovers are tar filled metal cans, not much heat in 6.3 cu ft; these and originals were large ceramic body.

Will put the tweeter ’Brilliance’ ones in first, listen. Then add ’Presence’, listen, decide: leave in, or out. IN more than likely. They (orig and 1 set of replacements) have been IN for 62 years.

My original bronze ones came from original Fisher console, they were a custom version, still labeled ’Brilliance’ and ’Presence’.
.................................................

Many of these old Electro-Voice designs had L-Pads (16 ohm used AT37 Attenuators; 8 ohm used AT38). 2 way have one. 3 way designs have two: ’Brilliance’ and ’Presence’.

You can balance the drivers to each other, and to each space, and as you age, ability to hear highs diminishes, you can creep the tweeters up speck by speck. Imbalance due to irregular spacing: adjust each individually

I’m not going to measure and install a fixed resistor, I want future adjustability.

’L-Pads: Terrible Idea’. Bullshite, everyone who ever heard them loves them!

And, let’s not forget, the originals, with L-Pads, first one mono speaker, later two for stereo, are the designs that made these companies successful.






elliottbnewcombjr
intactaudio
300 posts
 
Well the first thing you need to do is define what you mean by L-pad. It appears as if what you purchased on ebay is a simple rheostat or a linear attenuator which is not the same thing as an L-pad.

In my opinion on the most basic level the goal of an L-pad is two fold.  It attenuates AND keeps the impedance presented to the source (crossover) constant.  This means that the crossover frequency will not change as you adjust the level.  In order to do this you need discrete step / resistor combos and while a simple tapped resistor (rheostat) will reasonably approximate the behavior of a true L-pad, it still adjusts two parameters (level and crossover frequency) as you turn it.  Granted, the difference between say 8 and 9dB of attenuation may be inconsequential in the whole scheme of things, but as you get to coarser changes the waters get a bit murkier.

I sure EV was well aware of this and chose to install variable resistors in place of true L-pads and coined the terms brilliance and presence to get around the fact that the adjustments change both the level and frequency range fed to the driver.

dave
atmasphere's avatar
atmasphere
11,793 posts
 
You mentioned this before, L-Pads are for the amp, not the drivers.

I don’t understand.

Right or Wrong?

L-Pads, like any pot in a receiver, volume, balance, bass, treble determine how much juice, more or less, i.e. each one a signal strength control, modifying the amount of the signal it will pass to the amps (L/R).

To boost or cut bass or treble, they must be designed with a center amount of juice as normal, then pass more or less.

L-Pads like these are after the amp, in fact after the crossover. Aren’t they also just controlling how much juice, more or less, (after amplification, after basic crossover band filtering) i.e. modifying the output of individual drivers, thus how their volume blends with other drivers volumes.

What you're looking for is the driver to blend with the other drivers, resulting in flat frequency response. Generally there is no control for the woofer; usually the midrange and tweeter are more efficient (and are often different from each other in that regard).


The midrange might be 8 ohms while the tweeter might be 16 ohms. Or vice versa. If the amplifier has a high output impedance (which was common in the 1950s and before) then it will put out different power levels into 8 ohms and 16 ohms. So the level controls are there to allow you to equalize the levels to get flat response.





elliottbnewcombjr OP
5,330 posts
 

intactaudio

I looked up L-Pad, I see what you mean about 2 stages to maintain impedance shown to the crossover (or amp).

https://en.wikipedia.org/wiki/L_pad

The original electro-voice AT37 Attenuator was indeed an L-Pad, maintaining a 16 ohm load to the crossover. (AT38 was the 8 ohm version)

I remember it having the dual 'stacked' design.

https://products.electrovoice.com/binary/AT37%20and%20AT38%20EDS.pdf

I replaced them years ago with 16 ohm L-Pads, (also dual stacked design) the ones I just removed, I still have them. The speakers sound awful without them.

When I wanted to put level controls back in, why not new? I searched and found the ones I ordered, not understanding about constant impedance shown to the crossover.

They do seem to be a single resistance design, thus they would vary the impedance shown to the crossover, thus affecting the crossover frequency. Their screw terminations mean I can avoid solder, try em, keep or return them.






elliottbnewcombjr OP
5,330 posts
 
I just found Bob Crites web site

https://critesspeakers.com/electro-voice-crossovers.html

email:   bobcrites@gmail.com

I wrote and asked for prices for new diaphragms for 62 year old horns; new x336 three way crossovers; new AT37 L-Pads
intactaudio
300 posts
 
Sadly Bob passed away two weeks ago.

dave
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