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
Like I said, Elliot.  Best to set the L pads where you like the sound.  Then measure the resistance across the L pads.  Then substitute the L pad with a high quality resistor of the value you determined by measurement across the L pad.  The best L pad is no L pad.  If you want further guidance, I recommend 12W Mills non-inductive resistors for this purpose, available by mail from Michael Percy Audio.  For better power handling, you could parallel two or more 12W Mills'.  For example, if the measured R across the Lpad at your preferred setting is 10 ohms, then buy two 20-ohm Mills from Percy and use them in parallel for a net of 10 ohms and 24W of power handling.  Or you could buy four 40-ohm Mills for 48W, etc.
Oops! I see you reject the notion of using a single resistance. That’s your prerogative. Have fun. But please don’t conclude that using an Lpad is superior to replacing an Lpad with a resistor.
I think, 'Functionally/Flexibility' L-Pads, especially a good one, is better,

Because they have alway sounded great, adjusted for 3 different spaces over the years, I would never sacrifice future flexibility for supposed/measured perfection.
If you have a treble control on your preamplifier, which I might guess you do have on the Mac MX110, then you can achieve much the same effect as with an L-pad.  But far be it from me to rain on your parade; I admit to my own set of eccentricities that defy pure logic.  And I would never pretend there is any such thing as "perfection" in this pursuit.  If I recommend Mills resistors, some other guy would say that some other brand or type is superior.
Keep the L-Pads.. Everything I’ve ever built has L-pads for the highs.
They need to be maintained, though.. Mine last 30 plus years.
Ribbons and planars for me.. 300hz to 30khz. L-pads just work..

I’ll go further to say you’ll get better sound, that you like, instead of trying to tame a sound you don’t.. Different approach, and it’s old but it works the best for me.. I think they were removed just like tone control. It cost more and there is a potential for failure.. I suppose that's a good reason from a production point of view..

Regards
If you have a treble control on your preamplifier, which I might guess you do have on the Mac MX110, then you can achieve much the same effect as with an L-pad.
@lewm This isn't correct. The preamp treble control won't control the tweeter output. Its a bit different. The reason the control is there is the same as on your Sound Labs (prior to your modifications); the voltage response of the amplifier is an unknown so the tweeter level (or midrange level) control is there to allow the speaker to accommodate the amplifier.


This idea took a while to go away- from the late 1950s till the early 1970s, by which time the idea of 'voltage driven' loudspeakers had taken over.


OK, but I was more responding to Elliot saying that the sound was too tipped up in the treble, when he tried removing the L-pad entirely. Yes, the mechanism is different, but I thought he might ameliorate the problem with his treble control.  Anyway, the L-pad has apparently become an upgrade in the eyes of some, and I will exit the discussion as gracefully as possible.
Post removed 
I don't feel put upon.  Elliot was actually quite patient with me despite my unwanted advice. Thanks.
Ralph and I go way back.  He is one of the best guys in the audio business.
lewm

I value and learn from your knowledge and advice, (even if I don’t take it). Sometimes I can anticipate your reaction, which is why I specifically said no to resistors in original post which you caught the second time.

Another thing you missed, I AM currently using the treble control, of the Chase RLC-1. It is last in the chain, gives me remote control of everything. It goes directly to the Cayin amp.. As always, I can tweak any track, now using it’s treble. 1st time I ever used it’s tone controls. For fun I will mess with it’s bass control today, Not 1812, but some Ray Brown with Stan Getz I was listening to yesterday after I tamed the shrill beasts.

Chase treble is doing a very good job, surprising to me, I thought it would take too wide a band and the sound would go dull. Happily it has returned the sound to pretty darn good.

Did you read the seller’s description of vintage, currently common, and his pot design? It is interesting, he does seem to know what he is doing.

Before buying I clicked on the right ’see other items’, it’s extensive.



atmasphere

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.

Like pots in receivers, The original Electrovoice AT37’s were attenuators: 0 being no attenuation (just a solder joint), 1-9 progressive cut of signal strength. IOW, no boost, no center position, simply cut the signal. Unless you design the system with 5 as normal. My original Fisher’s AT37’s, the system seems to be based on a center position of the attenuator, say 5, then it’s + or - was toward zero or toward 9 (more attenuation/less signal; less attenuation/more signal.

After the crossover, not altering the response of the driver in any way, just it’s volume, which is why they are not as bad as purists make them out to be.

?.
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
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.






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.






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
Sadly Bob passed away two weeks ago.

dave
That's terrible, I hope not covid, and the family can have a safe goodbye.
oldhvymec

I agree, before I hook up a vintage piece, I take off the bottoms, tops, sides, anything removable, especially the face plates in my shop, You need face plates off for real access to the pots and rotating contacts. Then hose the pots and controls of tape recorders, tuners, receivers, amps, preamps with contact cleaner/lubricant, blow dry with compressed air, repeat. 

Then, frequently, while in the system, I swish em full spin back and forth, keep the contacts clean, re-check balance after doing this just in case.

I also tend to leave my preamp volume set, zero noise, and use more modern equipment's volume control up/dn from there.

Surprisingly, all my tube stuff is and has been dead quiet, My McIntosh SS C28 preamp, noise started at 11 o'clock, that's another reason I like my Remote Line Controller.

Another reason to have efficient speakers, to keep the volume/work of the components in a lower state.
atmasphere

"What you’re looking for is the driver to blend with the other drivers, resulting in flat frequency response".

I qualify flat frequency: IN THE ROOM, at the LISTENING POSITION.

That’s one of the benefits of L-Pads, you buy from company specs, auditions in showrooms, get them home, they start out sounding different.

I say: speakers in generally advisable position and toe in first. Tilt/aim tweeter at seated ear height; then L-Pads for listening spot; then if nodes, problems, sound treatments.

Move them to another space: L-Pads to the rescue!

Too many people, without L-Pads, have to resort to, perhaps need to over-do room treatments!locations.

That’s what I mean by Functionality/Flexibility may be better than perfection offered by a single resistor.

Even better: Advanced L-Pads by Electrovoice, for their 4 way systems like this E V Six

https://products.electrovoice.com/binary/E-V%20Six%20EDS.pdf

had L-pads with 4 or 5 switchable positions, each a specific resistor, that controlled the tweeter and mid range together. Separate Low Bass and Upper Bass drivers with no level controls.

Of course, a specific resistor requires no maintenance, whereas L-pads and their contacts require maintenance.
These risers tilt the speakers back to aim the tweeters at seated ear level

https://critesspeakers.com/heresy-slant-risers.html
I just spoke to Bob Crites’ son, (I think he said Mark, my memory sucks, I should have asked)

They are still doing business.

Two boards, a pair of real 16 ohm L-pads each, $100. + tax/ship.

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

I am going to return the ones I ordered (they already shipped), and buy these.
Elliot...

two things...

- the EV six you referenced does not use an L-pad... advanced or any other type.

-why is this discussion happening in the analog forum where it is decidedly off topic?  Wouldn't the speaker or vintage forum be a more appropriate venue?

dave

intactaudio

 This is a new separate discussion, but it came up in an earlier discussion, I removed them based on advice in that thread.

So, this was an answer to everyone: I tried, it sucked, I need em.

If you scroll down the E V Six link, the wiring diagram at the end shows 5 selectable resistances for the tweeter and midrange together. It has to be a rotary control with 5 specific positions.

I posted a find of an E V Six, local pickup only in CA, great price. If I lived there, I would be over there in a heartbeat. Posted here, some response. Posted on the Speaker Forum, not a single response. I am not known there.

I have friends here that help me with everything I do. You have been helpful here also.

I like it here!
I promised myself to stay out of this, but on the bottom of p.2 of the brochure, Figure 3, you have a schematic of the crossover with values.  You could easily rebuild that exact circuit, at least that switchable segment, with modern high quality parts. That would change nothing in relation to adjustability and tonal balance and would probably upgrade the pure SQ, just because modern parts are better.  You might consult any number of speaker builder types on the subject of what to use.  You could have your cake and eat it too.
I qualify flat frequency: IN THE ROOM, at the LISTENING POSITION.

That’s one of the benefits of L-Pads, you buy from company specs, auditions in showrooms, get them home, they start out sounding different.
@elliotbnewcombjr   This is where I side with @lewm ; a tone control would be more appropriate for adjusting the system to the room rather than the driver level controls (although I do understand the temptation).


Proper room treatment works better and as you've stated, proper speaker placement too. Keep in mind that with only two woofers its likely that the bass won't be right, and if the bass isn't right the mids and highs won't be either. So it might be advantageous to add a couple of subs like a pair of Swarm subwoofers, placed asymmetrically in the room so as to break up standing waves that are likely to otherwise be present.
Elliot,

while a 5 position switch and 5 different single resistors may adjust level as shown in the EV crossover,  it is not an L-pad.   When you get into technical discussions, the proper use of terminology is important so people at all levels of knowledge can learn.

dave

Dave,

thanks for the clarification, I yap about an issue but have often been ignorant/wrong when it get’s technical. I wouldn’t recognize an ohm if it crawled out of my boot.

I always referred to these as Rheostats, Then some say Potentiometers, L-Pads, learning about changing/not changing what is shown to the crossover is specifically helpful here, thanks.

..................................

BALANCE CONTROLS TO THE RESCUE

E-V SIX is very illustrative of this discussion and my decision to put mine back.

It is a 4 way system with a 5 ‘STEP-TYPE’ Balance Control (5 selectable/specific resistor settings) 18" Woofer, how about that!

https://products.electrovoice.com/binary/E-V%20Six%20EDS.pdf

Back to E-V SIX

Page 2: ADJUSTMENT OF BALANCE CONTROL “precise adjustment of the system to room acoustics AND personal tastes”.

Bottom of Page 2 is the wiring diagram, showing that the Balance Control alters both the Treble (upper mids) and Tweeter together, Bass and Upper Bass unchanged.

Position #3 ‘Standard’ rooms; #2 and #1 are ‘CUTS’ for ‘hard/live’ rooms; # 4 and 5 are ‘BOOSTS’ for soft/dead rooms.

Page 1, Figure 1, shows 5 frequency lines, each selector position and it’s resulting frequency graph.

……………………….

IMO, PERSONAL TASTE should also be understood as ‘a specific listener’s hearing ability: ‘live or soft’.

FMC: The Fletcher-Munson Curve shows that our hearing ability, effecting personal tastes, changes as we age.

CHANGE: the rooms furnishings may/probably will change, or the speakers may be moved to another room, more dead or alive.

AVERAGE is FAR FROM EVERYBODY; can be SOME, NOT MOST. FMC, like shoe size or desk/chair height, or hearing ability, is an average. I just had a hearing test. My lows are ‘un-characteristically’ still flat, mid to low highs ‘normally’ flat, upper highs decline progressively, ‘normally’. Thus I’m ‘near average’ What about you, or him or her?

………………………..

EARLY E-V systems: 2 way have 1 Balance Control; 3 way like mine, have two Balance Controls: ‘BRILLIANCE’ (only effects the Tweeter) and ‘PRESENCE’ (only effects the midrange). Quite often highly efficient horn systems.

E-V literature of AT37’s and AT38’s describe them as true L-Pads, maintaining 16 or 8 ohms shown to the crossover.

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

..................................

IMO they are an asset, not a detriment. I ordered simple coil type which affects the crossover. Thanks to input from Dave and others I will return them and order true L-Pads with constant 16 ohm shown to the crossover.

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

I spoke to Bob’s son yesterday, they are still in business.

………………………………………

Using Balance Controls was easy in the MONO era, but for a STEREO PAIR, matching L to R is far from easy. I have often said, I value/need my McIntosh MODE Control to achieve matching frequency performance L to R; Volume Balance; Room Balance. Then remotely adjust volume and occasionally refine a specific track’s balance via my Remote Line Control. Now using RLC-1’s Treble control while waiting for my new L-Pads to arrive.

And, MONO or STEREO, they need maintenance perhaps replacement over time.

Aside from costs, I think it became hard for manufacturers to trust their use and maintenance to the general public. Hard to trust that in an given user’s space, unknown acoustics, unknown adjustments, that they would sound ’proper’ to any/everyone who might decide to buy/not buy them.

.............................................

Oh yeah, the listening position diagram, 30-40 degree angle, is quite interesting. Mine is similar, but with toe-in, which I adjust for wider center for pretty decent imaging 2 listeners.

Elliott


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

While I am a big fan of appropriate use of tone controls and EQ in general speaker L-pads are not one of my favorite things. The main issue with them is reliability. Wipers and high power don’t work very well and can degrade rather quickly IMHO. A line level tone control, with voltages ~ 1 V or less, and milliamps of current is much more reliable.

Suit yourself, but these devices are just not that reliable and often degrade over time.

Best,

Erik


lewm,

Yes, it occurred to me I could make a 5 ’step-type’ resistor type as you would surely prefer. Would have to, but could find the ’exact’ resistors for my specific driver’s (not the SIX). Figure out the mechanics for changing individual selection. It would not be inexpensive.

Or, stick with a simple progressive level of adjustment via proper high quality L-Pads.

After 46 years designing Corporate Offices, each plan, decision, budget, schedule, light fixture (I designed my own frequently), hvac system decision (I hired my own engineers), each item selection the ’best’ choice I can find/make for clients:

when I retired I decided to leave the constant search for perfection behind.

These things worked well then and now, you know I like vintage, not to mention I have two 1-3/4" diameter holes in each speaker’s rosewood back panel. High in the rear corners where I can reach them without moving the speaker out of position.

I will transfer what I buy from Crites into my original face plates. Fisher’s Recessed Cup and push on knob, both Bronze. They fit these 4 holes and recess into the 3/4" back panel. I will position them, not like EV AT37’s were, 0 to 9, but as Fisher did: up is center attenuation, then up or down from there. These drivers/this 3 way system was originally designed to perform ’normally’ in the center of the attenuation range. That’s why they are so screechy without attenuation.
Of course if I really wanted to be a scoundrel I'd troll with something like :

Using a transformer with multiple taps is the only proper way to implement variable driver levels.


But I'm not a scoundrel.  :-)

Erik
In the course of this discussion, I came to appreciate that you are most interested in preserving the original or vintage sound of your speakers. Which is surely a worthy goal. That is why I suggested you can keep the frequency divider network as it is, and yet improve it by upgrading the parts inside. When you put an aftermarket L pad in there, there is a risk you will come up with a sound that is quite different. I look forward to your reporting the results of installing a new L Pad. By the way, I don’t see why you say my idea is expensive. You need to buy five high-quality resistors per speaker  and if you want to get really crazy, you could also replace the associated capacitors but there is no need to spend huge dollars on those parts and the rest is DIY. There is a bUsiness, Madisound, that specializes in speaker parts. Anyway, carry on.
Erik,

Scoundrel Thou Art.

The other thread was about my 16 ohm speakers, my amp having 16 ohm taps, and sadly it’s bias adjustments only with the bottom off.

Maintenance, I found the wires of the original L-Pads fried when I blew the tweeters blasting In-A-Gadda-Da-Vida. Replaced them, 16 ohm L-Pads were easy to find those days.

lewm made me remove them. As long as they are out, sounded terrible, thought I would find better ones to re-insert. 16 ohm no longer easy to find. Hooray for Crites, they seem to be high quality,

Lewm,

Did I forget the punch line: I’m lazy.

Seriously, I try to think long: For me, I prefer the ability to tame the tweeters now, and easily achieve progressive boost, speck by speck, as my ability to hear highs diminishes. I die, Donna, who loves them, might move in with her twin sister, then give them to my son Chris. Who knows who and where they will be in the future. That’s the beauty of Balance Controls of any kind.
...................................................

Making new speaker cables has led to a full ’long’ look at these speakers, what should I overhaul? Spares?. To keep going for the next generation, people who know nothing except they sound great.

Woofers: just replaced one 15W with dried out paper cone (near the hot-air wall vent) with my re-coned spare; bought a recently re-coned 15W; bought a cone kit for my dried out one, will have a spare pair.

Horn Mid: Original, 62 years old still sounding great, 1 spare downstairs

Horn Tweeters: T350’s, 16 ohms at least 50 years old, pair of spares downstairs. (not sure if 16 or 8 ohm versions).

And, a spare pair of the original tweeters from 1956: smaller T35b’s, 16 ohm (early smaller magnet than later T35’s) They were re-coned by E-V many years ago after Iron Butterfly blew them. That’s when I put the T350’s in (and cut their +3db higher efficiency/output with you know what).

How can the diaphragms of these 62 year old horns still sound great? E-V said: "virtually indestructible phenolic-impregnated linen".

I asked Bob Crite’s son, he said, yes, if working leave them alone, they can last forever.

Crossover: Original x336, tar filled can. Crites says leave them alone. I can easily revisit that later.

Given that I am leaving the crossover, horns, re-coned woofers, I don’t think lewm or many of you would qualify any part of these ’best’, and in context, I think real 16 ohm L-Pads fit right in with the other decisions.

yap yap yap, even I’m getting tired of this
Hey Erik,

Paul Klipsch must be one of those scoundrels because he routinely used autoformers for level matching and in keeping up with the scoundrels...I for one think all L-pads and resistive networks for attenuation should be binned in favor of a magnetic approach for attenuation. :-)

boy this has gotten way off topic... apologies to anyone who feels this thread has been an off topic use of analog bandwidth.

dave
I've done "nothing" to my speakers and they sound great...albeit, using a pea size dollop of blu-tac between stand and base at each corner. 
OH YEAH!

New 16 Ohm L-Pads installed, back to wonderful (more wonderful?).
..................................

the whole story

1. Ruin a good thing:

L-Pads removed as advised. Actually, they were 8 ohm pots, I didn’t know better way back when I replaced the original 16 ohm L-Pads. The Pots worked as needed, but altered the resistance shown to crossover, whereas the original L-Pads maintained 16 ohms shown to the crossover.

Speakers without controls were very screechy, horrible. Used RLC-1 to cut treble, at least sounded listenable while looking for a solution.

2. Research:

The Fisher President II I inherited used all Electro-Voice drivers, L-Pads, Crossover. They are in my new enclosures.

The Vintage Fisher consoles, and Electro-voice speakers were designed with L-Pads: AT37 (16 ohm) or AT38 (8 ohm). Two way had 1; Three way had 2 (Brilliance and Presence, like mine).

Adjust from Normal for room and personal taste.

NORMAL Room: Center position: Half attenuated.
LIVE, BRIGHT Room: add attenuation progressively
DULL, DEAD Room, reduce attenuation progressively
EARS AGE: reduce tweeter attenuation as ability to hear highs progressively reduces.

Model EV-SIX had a unique 5 position step-type attenuation control using resistors. As they were not progressive, 5 frequency graphs were shown in the engineering bulletin.

3. Re-install new L-Pads:

Ordered High Quality Pots, thinking they were L-Pads, returned them.

Ordered 16 ohm L-Pads.

Installed L-PADS yesterday. RLC-1 tone control back to neutral.

OH YEAH!