AR-4x rebuild - lost bass response

[philcryer]

I bought a pair of AR-4x speakers that had a newer tweeter in one cabinet, and corroded pots on both, so I decided to rework the pair. I utilized new phenolic ring tweeters - 8 Ohm (http://www.parts-exp...tnumber=270-252), new solen 20uF 400V polypropylene capacitors (http://www.parts-exp...tnumber=027-582) and new L-Pad attenuators - 15W Mono 3/8" Shaft 8 Ohm (http://www.parts-exp...tnumber=260-248) in place of the corroded pots. While the high end is now very well defined, I'm missing the bass that made the speaker sound so full and smooth before I started working on it - overall the sound is very thin. Did the pots contain some sort of resistor that I'm not taking into account with the new L-Pads? Am I missing something, or should I fix the pots and use them instead?

As an aside, thanks to all the contributors to this site who make this learning experience so much fun, this will not be the only time I open up 40 year+ old speakers, next up are some KLH 17's!

Phil

[RoyC]

Phil,

Two possiblitlies come to mind...The first would be woofer polarity. Make sure both woofers are connected the same way, or else they will cancel each other out.

The second is the new tweeter. I personally find that replacement tweeter to be harsh in the midrange, and not in balance with the 4x woofer with the original crossover. Even though you have a tweeter level control, the tendency is to sometimes turn down the overall volume in such instances, which would also attenuate the woofer.

(A third possibility could be that something was applied to the woofer surrounds to "re-seal" them (?). Use the wrong stuff, and say goodbye to the originally intended bass response. I assume it isn't the case since this isn't the Audiokarma forum).

I doubt the bass response is being affected by the use of l-pads, though they would likely exacerbate any midrange harshness. If you want to hear how the pots would sound, simply place a 25 ohm resistor across the tweeter terminals, and keep the l-pads in place. This will approximate the effect of the original pots from maximum down to about the 1/2 way setting

Roy

[JKent]

Hi Phil

The L-pad is a perfect replacement for the pots so that's not it. Some have argued the phenolic ring tweeter is not a perfect replacement but others have used it and in any case that should not kill the bass.

I think the most likely thing is that the speakers are out of phase. Either you just goofed with the speaker wires, either at the amp or at the speakers, or one of the woofers is out of phase. You cannot depend on the red dots on the woofer terminals--you have to test them with a battery.

Maybe some other members have other thoughts.

I just finished a pair of 17s. A worthwhile restoration (as are the 4x's)

Kent

PS: Looks like Roy was typing at the same time I was.

[philcryer]

@RoyC this sounds like it may be a way to go, so a 25 ohm resistor like this? http://www.parts-express.com/pe/showdetl.cfm?partnumber=004-25 and then placed across the L-Pad terminals for the tweeter? The L-Pad came with a schematic, but I'm sure the resistor won't - I can sketch out what I have. Even if this isn't the issue, it seems this may get things more in line with how things would be with the pots, so I may try it.

Your comments about woofer polarity may be my issue...thanks, that's up next.

@JKent how do I test the speakers with a battery? I *think* I had the positive and negative right, but it sounds like what could definitely be it - I'll pull them apart and take a look, but I'm pretty sure + on the woofer goes to the 0 terminal on the back of the 4x's... so doesn't that make the 0 the positive and the 1 the negative?

Thanks for the help.

[RoyC]

@RoyC this sounds like it may be a way to go, so a 25 ohm resistor like this? http://www.parts-exp...rtnumber=004-25 and then placed across the L-Pad terminals for the tweeter?

Your comments about woofer polarity may be my issue...thanks, that's up next.

@JKent how do I test the speakers with a battery? I *think* I had the positive and negative right, but it sounds like what could definitely be it - I'll pull them apart and take a look, but I'm pretty sure + on the woofer goes to the 0 terminal on the back of the 4x's... so doesn't that make the 0 the positive and the 1 the negative?

Thanks for the help.

That is the correct resistor...It can be glued to the back of the tweeter or mounted with the cabinet crossover. It connects between the + and - tweeter terminals, which is the same as going across the #1 and #2 l-pad terminals.

Regarding polarity testing...

First make sure both speakers are connected to your amp the same way . If that is OK, then disconnect the speakers and do the battery test.

You don't have to pull the speakers apart to check the woofer polarity with the battery. Attach some speaker wire to the rear terminals. AR-4x terminals are labeled "1" and "2"...1 is negative and 2 is positive. Position yourself in front of the speakers, and touch the speaker wires to a 1.5 volt battery (I use a "D" size) + to + and - to -. If the woofer cones in each cabinet move outward when doing this, your woofers are properly connected. Just touch it quickly, only long enough to see which way the woofer cones are moving.

Roy

[michiganpat]

another possibility would be if there are air leaks in the cabinet around the woofer, tweeter, or terminal plate. that can cause a lack of bass response as well. make sure it's sealed well with some rope caulk or 1/8" thick foam tape.

[RoyC]

another possibility would be if there are air leaks in the cabinet around the woofer, tweeter, or terminal plate. that can cause a lack of bass response as well. make sure it's sealed well with some rope caulk or 1/8" thick foam tape.

Leaks of this sort may limit power handling somewhat, but will not cause significant loss of bass response. Many 4x's were actually designed to allow more air leakage than other AR models.

Roy

[JKent]

I *think* I had the positive and negative right, but it sounds like what could definitely be it - I'll pull them apart and take a look, but I'm pretty sure + on the woofer goes to the 0 terminal on the back of the 4x's... so doesn't that make the 0 the positive and the 1 the negative?

See Post #17 here: http://www.classicsp...7479#entry94813

Always best to check AR woofers with a battery as Roy described.

There's no "0". The terminals are 1 & 2. 1 is - and 2 is +.

Good luck

Kent

[ironlake]

My 4x which is restored original, the tweeters with pot at full have the woofer at the same volume as the tweeter. Turning down the pot results in the woofer being louder than the tweeter. If your tweeter can be made louder than the new tweeter then that could be you loss of bass.

[pb8000]

Very interesting. I too installed PE phenolic ring tweeters in my AR4x to replace some non-AR non-working tweeters someone had put in. (I also did the lower cap - 20uf with 12 in series= 7) and added coil for the tweeter) I also replaced the pots with L-pads. With Roy’s expert guidance I corrected my faulty wiring so that the L-pads operate correctly. Then, last weekend, the test. Poor woofer response. Mushy, loose, low volume. Since the tweeters were not working when I received the speakers I can’t say what the woofers’ response was before my changes. Both speakers sound the same. This weekend I’m going to go back in. First, I’ll test the polarity of the woofers. As I received them the positive wire is NOT to the red dot terminal of the woofer - but that looked original. Maybe the phenolic tweeter is not the way to go. But, Carl said he was about to post a cross-over for the phenolic ring tweeter in the AR 4X.

[philcryer]

One thing, are the L-Pad attenuators - 15W Mono 3/8" Shaft 8 Ohm (http://www.parts-express.com/pe/showdetl.cfm?Partnumber=260-248) that I got correct? The person who sold me the 4x's was asking tonight if they shouldn't have been 4 Ohms instead of 8.

[pb8000]

AR4x is 8 ohms. Yes - thats the L-pad I installed.

[ironlake]

why are you messing with l pads, just get a replacement pot from vintage ar and be done with it and keep the crossover original. pots are what ar used so why shouldn;t you and no resistor etc to mess with.

I have a perfect 4x tweeter and pot I can sell you and you will be at original.

[RoyC]

why are you messing with l pads, just get a replacement pot from vintage ar and be done with it and keep the crossover original. pots are what ar used so why shouldn;t you and no resistor etc to mess with.

I have a perfect 4x tweeter and pot I can sell you and you will be at original.

ironlake,

Unless you are referring to refurbished, used original pots, Vintage AR does not sell new replacements. His pre-wired kits contain new 8 ohm l-pads. He is careful not to call them "pots" in his Ebay listings.

The l-pads are the least of OP's concerns relative to bass response...and as long as he is using the new replacement tweeters original pots are not likely to bring his speakers significantly closer to the original 4x sound.

Roy

[philcryer]

Thank you for all the tips, I've tested the woofers and they seem to be correctly marked, next up I rewired the woofers, using solder in place of the wire nuts, finally I put the 25 ohm resistor across the tweeter - and it sounds sweet! This is what I heard before, although with only one tweeter, the new ones are much smoother and the bass is just there, sounding much bigger than the cabinets would allow you to believe! I'm still going to redope the cloth surrounds on the woofers (and then may refinish the cabs) but for now I'm just going to enjoy the sound, I'm really amazed at how much can be gained with some new caps and tweeters - really nice. Thanks again for the detailed help, I'm having fun now!