New member! Just bought a pair of AR-90's, need advice :)

[Guest radkrisdoc]

Hi everyone!

I have been following this forum for the past 2 to 3 months and immensely enjoyed reading the posts. I have found that the information in each post is highly accurate and there are some great engineers here as well. I am glad that it is back. My interest in AR speakers increased so much that I bought a pair of AR-90's.

The original 8" LMR and subwoofers were parted out and I

bought the enclosure plus UMR, tweeters and crossover. I have not yet

inspected the drivers. I ordered a pair of 8" LMR's from AB Tech this morning.

I would like to hear your thoughts on the following:

Are the AB tech drivers good replacements, if not, why and how do they differ from the original? I am also looking to see if I can use Peerless 10" (1727) subwoofers. The idea is to fit in 2 subs into a 90 liter enclosure for a -3 db response at 32 Hz with a resonance Q of .8. The substitutes should be direct drop-in replacements, that is, no woodworking adventures, so as to preserve the originality of the enclosure. Installing original replacement drivers should be a snap, when needed.

Knowing foam will degrade in a matter of years while the speaker grows on you is not a good feeling. That's why the Peerless idea. Even though the LMR from AB tech has a foam surround, it was very dificult to identify a suitable 8" 4 ohm driver from standard manufacturers like Vifa, Peerless, Audax, etc.

I guess I can work on that part as the AB tech driver's foam degrades over the years. Does it degrade though?

I want to clarify a lot more than the above and I am sure all the good knowledgeable people who participate in the forum will help. Its great to be here as a member! Kris

[ar_pro]

Welcome aboard, Kris, and congratulations on your AR-90s.

While there's nothing *wrong* in using different drivers as an experiment, the consensus of opinion has usually been in favor of keeping the classic AR speakers as stock as possible. And based upon your question regarding the AB Tech replacement drivers, you're already aware that some replacement parts are more "original" than others.

All things being equal, the best way to keep the original sound is with *period* drivers and related parts. Anything else is certain to affect the sound, and compromise its authenticity. eBay provides an outstanding resource for original parts, and makes it relatively easy to keep things authentic.

I've heard the AR-9 with AB Tech's replacement lower mids (circa 1990), and it sounds fine - just like an original-equipment AR-9. It's possible that the sourcing & specs of this driver have changed since then, but I have no way of knowing for certain.

Bill Miller of Millersound feels that current foam formulations will be more stable than the '70s-era stuff, and not be prone to the same type of deterioration. His refoamed AR-9 woofers from 1991 are showing no sign of any problem at all.

[Pete B]

Welcome Kris,

Sounds like a nice project. It would be helpful if you could measure the DC resistance of any drivers that you have, the 8" LMRs for example and the inductors in the crossover. Did you calculate 90 liters for the enclosure?

The 1727s should be a fine replacement however the CSX version is a newer and better driver:

http://www.partsexpress.com/pe/pshowdetl.c...r=297-636&DID=7

The 1727 and CSX have a smooth midrange and they made a lot of sense in the 2ax where it's used far up into the midrange. I believe that a better choice for the AR-90s where the woofers crossover very low to the 8" lower mid is the 10" Eclipse (W1038R) driver at Madisound:

http://madisound.com/eclipse.html

http://madisound.com/imgs/w1038r.jpg

I've used the 8" Eclipse and the best way I can put it is that you'd think it was a 10", an excellent 10". The 10" Eclipse has been an old reliable strong performer, excellent reports. These have 2" voice coils, raised back plates, rubber surrounds, and parameters that should fit well. You might want to run some quick simulations. I don't know for sure if it will bolt right in but Madisound is helpful and should give you the cutout dimension.

Regards,

Pete B.

[rrcrain]

You will find several threads discussing the AR90 crossover here as well. You might consider rebuilding them as well.

[Guest radkrisdoc]

I took a look at the woofers you recommended, but I guess you did not notice, they are 6 ohm drivers....what we want in the AR-90 are two 8 ohm drivers in parallel.

I have also tried simulating the response using WinISD, and it turns out that the Peerless 1727 woofer might fall in place as far as Q is concerned, after including the crossover inductor's DCR. The schematic for the crossover shows that it also has a Zobel network for the woofer combined with the second order crossover. My guess is that the resistor should be disconnected electrically if I use the 1727's, as the resonance frequency will be different from the original drivers and having a Zobel at the wrong frequency will result in an unwanted dip in response.

I have to work on that part yet. I have not found any speaker designing software that includes the crossover inductor DCR and subsequent change in Qes and Qts. If anyone here knows of a software that has the function, please let me know.

Thank you for the input Pete,

regards, Kris

[Guest radkrisdoc]

>You will find several threads discussing the AR90 crossover

>here as well. You might consider rebuilding them as well.

Yes, that is also on my mind. For starters I am going to use the speaker with no 10" woofers; that will give me a system with a crossover at 200 Hz. I have an inexpensive Polk sub that will cover the rest. Before I buy the 10" woofers, I want to gather all the electrolytics (bipolars) in the original crossover and replace them one by one. I am aware that electrolytics can go "dry".

Next in mind is that I want to take the crossovers out, make them external, after I get the 10" woofers. That way, if I want to adjust them in anyway it will be possible. I am also looking at rewiring the whole system with Monster cable. While I'm at it, I will possibly try to scrape the glue out of the LMR compartment and use air tight soldered binding posts instead. The holes that the wires come through should be far too big for the glue to give any real support, taking in account that there is a lot of bracing and strengthening elsewhere. I might be wrong, but the thought of air tight binding posts is more comforting than glue.

This whole endeavour may seem too complicated, but I have decided to work on it over months, not a day or two. I enjoy it anyway.

[rrcrain]

The original posts aren't glued in, but are actual 5 way posts. Consider using Kimber project wire rather than Monster. It's an ultra pure copper made specifically for speaker rewiring, gives extremely good results and is less (a lot less) than speaker to amp wire. It's what I used.

As many changes as I made in my AR90s, I am still a bit of a purist and woudn't recommend doing away with the 10" woofers. Those side firing woofers will give more bass than you expect and are only out done by their larger brother, the AR9 with dual 12" woofers. Being side firing, side wall placement can be a bit of a problem and for best results, they should be placed within 3 inches of the back wall to allow for bass loading. Distance from the back wall has a very noticable impact on bass performance.

To summarize a bit of the other threads, I did a total crossover rebuild using poly caps and solen perfect lay coils; the new capacitors having the major impact on sound quality. I also redid the crossover splitting out the bass section allowing the speakers to be bi-amped.

[Guest radkrisdoc]

>The original posts aren't glued in, but are actual 5 way

>posts. Consider using Kimber project wire rather than Monster.

>It's an ultra pure copper made specifically for speaker

>rewiring, gives extremely good results and is less (a lot

>less) than speaker to amp wire. It's what I used.

No, I didnt mean the binding posts, but the holes through which the wires to the 8" mid travel to reach the driver in its separate enclosure. Those (the holes and the wires) are definitely glues in. Kimber advice taken, thank you!

>As many changes as I made in my AR90s, I am still a bit of a

>purist and woudn't recommend doing away with the 10" woofers.

>Those side firing woofers will give more bass than you expect

>and are only out done by their larger brother, the AR9 with

>dual 12" woofers. Being side firing, side wall placement can

>be a bit of a problem and for best results, they should be

>placed within 3 inches of the back wall to allow for bass

>loading. Distance from the back wall has a very noticable

>impact on bass performance.

The Polk sub is just a stop gap. I intend to put in funds slowly, as I get the time to work on each aspect. I agree, nothing like four 10" woofers.

>

>To summarize a bit of the other threads, I did a total

>crossover rebuild using poly caps and solen perfect lay coils;

>the new capacitors having the major impact on sound quality. I

>also redid the crossover splitting out the bass section

>allowing the speakers to be bi-amped.

Point taken. For the coils, I also have to measure DCR so am also in the process of searching for a good multimeter as I am starting from scratch for this project. Alternatively, these being air wound coils, are already of a very high standard. I might opt for changing only the caps.

[rrcrain]

Try a bit of silicone sealant on the wires going to the lower midrange. Excellent seal with minimal cost AND no mechanical electrical connection to corrode or come loose at a later date.

[Pete B]

Your welcome Kris. Madisound is just honest, they rate them at 6 ohms because the DC resistance is around 5 or 6 ohms, don't have the data right in front of me. Many would call them eight ohms because the impedance rises at resonance, a bit due to motional impedance, and due to voice coil inductance. The 2ax woofers I measured here were in that same DC resistance range IIRC. I've simulated most of the drivers that I talk about so you might be very surprised if you ever tried those 1038s and I've got other reliable sources. I'd say your jaw would probably drop if you heard an original system side by side with these drivers. I believe they would offer a bit more extension, and lower Qtc, lower distortion and better power handling but one would have to simulate to veryify this. I'll help if your interested.

Unibox is a good free T&S simulator that will handle Lvc but not cone break up modes, there are many other simulation packages out there. I use CALSOD for full system simulation, it is an old DOS based program but it is reliable and I like it so I'm sticking with it for now.

Here's a link to another discussion about speakers and crossovers where we discuss inexpensive microphones, and free analysis/simulation software, these things are discussed on many message boards, see post #9 in that thread:

http://www.diyaudio.com/forums/showthread.php?threadid=51514

You talk about a zobel, does your crossover match the one here with 3.83 mH in series with the woofers then 50uF - 1 ohm in series as a shunt across the woofers? Have you traced out your crossover? I'm willing to help if your interested.

Pete B.

>I took a look at the woofers you recommended, but I guess you

>did not notice, they are 6 ohm drivers....what we want in the

>AR-90 are two 8 ohm drivers in parallel.

>I have also tried simulating the response using WinISD, and it

>turns out that the Peerless 1727 woofer might fall in place as

>far as Q is concerned, after including the crossover

>inductor's DCR. The schematic for the crossover shows that it

>also has a Zobel network for the woofer combined with the

>second order crossover. My guess is that the resistor should

>be disconnected electrically if I use the 1727's, as the

>resonance frequency will be different from the original

>drivers and having a Zobel at the wrong frequency will result

>in an unwanted dip in response.

>I have to work on that part yet. I have not found any speaker

>designing software that includes the crossover inductor DCR

>and subsequent change in Qes and Qts. If anyone here knows of

>a software that has the function, please let me know.

>Thank you for the input Pete,

>regards, Kris

[rrcrain]

There should be schematics for the AR90 crossovers on this web site as well as a layout print. If they haven't been restored yet, I still have a copy of both files.

[rrcrain]

Here's a link to the AR90 crossover discussion thread.

http://www.arsenal.net/dc/dcboard.php?az=s...ing_type=search

[Guest radkrisdoc]

Thank you for the thread link. The ideas there are very good, I am also upgrading the caps, following the northcreek mix and match formula. Kris

[rrcrain]

What is the Northcreek mix and match formula, or where can it be found?

[r_laski]

>>What is the Northcreek mix and match formula, or where can it

be found?<<

http://www.northcreekmusic.com/CapacitorFAQ.html

You can also read about capacitor bypassing here:

http://www.northcreekmusic.com/Bypassing.html

Rich

[Guest Bret]

Welcome to the AR obsession.

>Are the AB tech drivers good replacements, if not, why and how do they differ from the original?<

AB Tech sometimes changes what they sell as replacements. If they sold you what they sold me, the new drivers are a sort-of poly-paper hybrid.

They aren't terrible but if I were you I would try to find originals and have them rebuilt.

Why? I bought mine for a pair of AR-9s that I hadn't heard in a while - so the replacement 8" drivers sounded pretty good to me.

Then I bought some originals and installed them. Oh yeah. . . much, much better "balance." I don't have test equipment but I suspect that the new driver probably has superior specs to the original, but they are too efficient (loud).

I have some inconclusive experience with replacing capacitors. In a pair of 90s, a friend of mine and I replaced many of the capacitors with el-cheapo miniture NPE caps. The difference was amazing. As I said in another thread from some time ago -> I don't know that speakers are "right" but I know they are "righter."

I was/am rebuilding 10pi's. A friend of mine has 10pi's as well. In every pair of AR-10pi's I've seen except mine, all the capacitors are Sprague Compulytic. My 2500uF and 100uF are Callins and I don't know who manufactured the 20uF, 10uF, and 40uF. I went half-hog and bought Solens (whole hog being Audio Cap or Crescendo or any other $300 capacitors).

The difference was startling AND disturbing. Holy moley! Grain. The sound was so grainy, so harsh, so stinging that I thought "what have I done!?" I was beyond disappointed, I was stunned, amazed. . .and appalled.

Interestingly - Every old capacitor I removed was very close to spec (by a capacitance meter). There is NO WAY that the caps I replaced were good; proving only that I wasted a bunch of money on a capacitance meter.

Almost all of the caps that came out of the AR-90s were out of tolerance, but some of them were like 150% of their original values. As I say, that was not true of the 10pi's old capacitors. But there is no doubt that the 10pi's capacitors needed to be changed. As we've put hundreds of hours on the Solen capacitors they do seem to be mellowing.

So my friend, having heard the improvement in my speakers, replaced the capacitors in his. This time we used NPE caps from parts Express and still didn't change the 2500uF caps. The change in his speakers was immediate, and immediately it was an improvement. Most of his Sprague Compulytics were either in-spec or just out; Reinforcing my impression that capacitance may not be the only important spec.

People talk about "lifting a blanket." Replacing the caps in the friend's speakers was like lifting a thick blanket. Mine? My speakers sounded like you moved a cow out from in front of them.

BUT ! ! !

My speakers are much brighter than his and always have been and swapping the drivers doesn't change that. Something's rotten and I'm guessing there's something wrong with *my* crossover wiring through the switches (and transformer).

So the tinkering continues. I'm going to do something about the 2500uF caps and the resistors in mine and see if something else will change.

From what I'm hearing so far, my AR-9s are going to get NPEs. I'm not convinced that more expensive is better in this case. We'll know soon enough.

Bret

[Pete B]

Thanks, I have the schematic, I was just wondering if Kris's system matched the schematic. The 1 ohm - 50 uF is not a Zobel.

>There should be schematics for the AR90 crossovers on this

>web site as well as a layout print. If they haven't been

>restored yet, I still have a copy of both files.

[Pete B]

Hi Bret,

Measuring the transfer function from the input terminals to each of the drivers loaded in the system would be the way to figure out the difference between the two crossovers, since you've already swapped drivers and ruled them out. Poly caps typically have an ESR value in the 10s to 100 milli ohm range, large NPEs in the .1 to .5 ohm range. In most cases this difference is insignificant but the ESR sometimes becomes significant with low impedance drivers or low impedance resonant branches in the XO. ESR can make a large difference when it is the only loss element in a resonant branch but this is rare. NPEs usually have higher ESL also but this is usually not a problem in crossovers.

A capacitance meter only measures at one frequency and the capacitance of real caps is usually a function of frequency. I measure the impedance vs. frequency of caps which gives ESR, ESL and capacitance versus frequency.

There are many PC based audio measurement systems that will do most of these measurements, some are free. Some work with inexpensive sound cards and the only worry is applying too much voltage say from a power amp and blowing out an input OP amp. There's a simple test jig for use with "Speaker Workshop" that makes it easier to connect to the soundcard and avoid damaging it. Electrical measurements are much easier than acoustical and it's a good way to get started if your interested.

Pete B.

>I have some inconclusive experience with replacing capacitors.

> In a pair of 90s, a friend of mine and I replaced many of the

>capacitors with el-cheapo miniture NPE caps. The difference

>was amazing. As I said in another thread from some time ago

>-> I don't know that speakers are "right" but I know they are

>"righter."

>

>I was/am rebuilding 10pi's. A friend of mine has 10pi's as

>well. In every pair of AR-10pi's I've seen except mine, all

>the capacitors are Sprague Compulytic. My 2500uF and 100uF

>are Callins and I don't know who manufactured the 20uF, 10uF,

>and 40uF. I went half-hog and bought Solens (whole hog being

>Audio Cap or Crescendo or any other $300 capacitors).

>

>The difference was startling AND disturbing. Holy moley!

>Grain. The sound was so grainy, so harsh, so stinging that I

>thought "what have I done!?" I was beyond disappointed, I was

>stunned, amazed. . .and appalled.

>

>Interestingly - Every old capacitor I removed was very close

>to spec (by a capacitance meter). There is NO WAY that the

>caps I replaced were good; proving only that I wasted a bunch

>of money on a capacitance meter.

>

>Almost all of the caps that came out of the AR-90s were out of

>tolerance, but some of them were like 150% of their original

>values. As I say, that was not true of the 10pi's old

>capacitors. But there is no doubt that the 10pi's capacitors

>needed to be changed. As we've put hundreds of hours on the

>Solen capacitors they do seem to be mellowing.

>

>So my friend, having heard the improvement in my speakers,

>replaced the capacitors in his. This time we used NPE caps

>from parts Express and still didn't change the 2500uF caps.

>The change in his speakers was immediate, and immediately it

>was an improvement. Most of his Sprague Compulytics were

>either in-spec or just out; Reinforcing my impression that

>capacitance may not be the only important spec.

>

>People talk about "lifting a blanket." Replacing the caps in

>the friend's speakers was like lifting a thick blanket.

>Mine? My speakers sounded like you moved a cow out from in

>front of them.

>

>BUT ! ! !

>

>My speakers are much brighter than his and always have been

>and swapping the drivers doesn't change that. Something's

>rotten and I'm guessing there's something wrong with *my*

>crossover wiring through the switches (and transformer).

>

>So the tinkering continues. I'm going to do something about

>the 2500uF caps and the resistors in mine and see if something

>else will change.

>

>From what I'm hearing so far, my AR-9s are going to get NPEs.

>I'm not convinced that more expensive is better in this case.

>We'll know soon enough.

>

>Bret

[Guest radkrisdoc]

>Thanks, I have the schematic, I was just wondering if Kris's

>system matched the schematic. The 1 ohm - 50 uF is not a

>Zobel.

>

Please tell me what that 1 ohm-50 uF is. I thought it was a Zobel, obviously my guess is wrong.

[Guest radkrisdoc]

Hi Bret!

Nice to hear from a very active member on this site

Solen caps are metallized PP's and they are infamous for making it sound grainy. That is why film and foil caps are more expensive. Try bypassing with a film cap, even a .01 uF might work and smoothen the sound.

Pete pointed out that it might be the "ESR" or equivalent series resistance at work, I think that too. I was looking for a good replacement bipolar electrolyitc myself. Here's what I found:

1. Black Gates are almost gone from the market, the few that are available are expensive due to the scarcity. These are manufactured by Rubycon, here's some info:

http://www.audionote.co.uk/kits/black_gate...ms_feb_2003.htm

Anyway, in case you are interested, you have to look for the AC series from Black Gate for crossover networks. Thing is with what I found the exact values are not available, adding them (in parallel) would not be practical.

2. Digikey.com has a huge selection of Panasonic caps; of these, the SU series bipolar caps seem to be very good, at almost no cost difference to the caps from Partsexpress.

I am still gathering info and have not decided which ones to try.

[rrcrain]

Do you have a link to a schematic of for the test jig or software you prefer?

Also, I'll second the statement that Solen caps can be edgy or ragged, especially when new. Thankfully, they calm down a lot within a few hours of high volumn play and take several hundred hours to really settle down.

[Pete B]

I use LAUD which works well but has been replaced by Praxis which is much more expensive. I've seen reports that Speaker Workshop works well, is free, and I'm just letting people know, I have no experience with it:

http://www.gti.net/wallin/audio/audua/audua.html

http://www.speakerworkshop.com/

http://www.diyaudio.com/forums/showthread....7012&highlight=

>Do you have a link to a schematic of for the test jig or

>software you prefer?

[Pete B]

The inductor and cap form a second order network, the resistor lowers the Q of the network, and provides a zero in the transfer function.

>

>Please tell me what that 1 ohm-50 uF is. I thought it was a

>Zobel, obviously my guess is wrong.

[Pete B]

Just in case anyone wants to build an inexpensive measurement mic:

http://www.linkwitzlab.com/sys_test.htm#Mic

>>Do you have a link to a schematic of for the test jig or

>>software you prefer?

>

[Guest Bret]

>Thing is with what I found the exact values are not available, adding them (in parallel) would not be practical.<

Counting the number of capacitors I'd need for the 9s and the number of parallel caps I'd have to have for the values I could cook-up . . . well, as much as I'd like to, for the same money I think I would rather have a small country to call my own.>Try bypassing with a film cap, even a .01 uF might work and smoothen the sound.<

I may have to try that. Why not? It’s only money.

Bret