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AR 9 Tweeters and Upper Mids Again


brianw

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I know its been talked about on this forum before, and I have red a lot of discussions on tweeters and replacement tweeters. But I decided after acquiring another set of AR 9's that have some failed and aged or weak drivers it was time to resurrect this subject as the spare parts do get harder to find and when you do find originals you often have the problems associated with age and what you actually get when buying such an old component.  I recently found my second pair of AR 9's had a very veiled sound, after swapping tweeters from a pair of AR 91 speakers I discovered it was a tweeter problem probably related to ferro fluid that has either hardened or gotten gummy after 40 years, i am told.

I am no Mr. sound engineer although I have been playing with sound since about the age of 12, ( now let's just say above 50 now), Have built a few speakers from scratch back around 22 using kef drivers, EV drivers, isophone etc.,  and just tinkered with crossovers. Have a electronics degree, ( but getting rusty), alng with a few other papers, built and sold several Technology companies except the last two that I currently own.   So my passion I have finally had the time to play with, sound.

The last pair of AR 9's have now had new Mundorf Aluminum oil Capacitors, upgraded wiring and some minor refinishing. NOW the big question and hoping to get some solid suggestions from those with more experience in audio.   I have read some old post, 2005, newer and older as to substitute drivers.  So I have found two of the obvious tweeter replacements.  ABtech, Simply speakers and Midwest Speakers.

ABtech 
http://www.abtechservices.com/index.html

These guys were helpful and at least spoke to me. Also explained it was the same speaker that Simply Speakers sold.

Simply Speakers
https://www.simplyspeakers.com/acoustic-research-replacement-tweeter-12000840.html

The fellow I spoke to at simply was essentially rude and emailed they only have the info that was on the site. I phoned and got the remark "well it is an old speaker and that's what they have, so take it or leave it. They implied I would not notice any sound difference as the old speaker was probably so bad this would improve"

Midwest Speakers
https://www.midwestspeakerrepair.com/shop/home-audio/mw-audio-mt-4121-75-inch-dome-tweeter/

The guys at Mid West and actually sent out a full spec sheet on their tweeter, something else no one else could seem to offer.


And then the question crossed my mind why not upgrade, Dayton Audio, Scanspeak, Seas, they all offer some amazing dome tweets that have extended range to 25k or 40k and UMR units that are cleaner and smoother, and why not tinker with improving if at all possible.  So now the question of trying to figure out how we can improve on a couple or three drivers and get even a cleaner natural sound.   

So I am looking to the pro's, hobbyist and the experienced for ideas, discussions and suggestions.  And why not it's a hobby that I totally enjoy and enjoy the results of..

 

Brian

 

 

 

 

 

MT-4121-4 New.doc

2019-01-25 21_55_09-Window.png

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AB Tech went out of business awhile ago and quickly re-opened as CM Tech by a former employee to sell remaining "new" inventory. All of the original AR parts were acquired by "Vintage_AR" (Larry Lagace) at that time. Apparently it is doing business as AB Tech again...same phone number. AB/CM Tech's AR replacement parts are sold to retailers like Simply Speakers. The drivers usually fit the cabinet holes, but original performance specs seldom match original.

If originality is the goal , there is currently nothing better than the excellent Midwest 3/4" tweeter as a replacement for the later 3/4" dome tweeters used in the AR-11/10pi and AR-9 series.

Plopping various drivers into an existing successful design seldom results in improvement, and is usually counterproductive. Essentially you are suggesting a thread on re-designing the AR-9. Good luck with that. :)

Anyway, this thread should be moved to the "Mods and Tweaks" section of the forum.

Roy

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14 hours ago, brianw said:

crossed my mind why not upgrade, Dayton Audio, Scanspeak, Seas, they all offer some amazing dome tweets that have extended range to 25k or 40k and UMR units that are cleaner and smoother, and why not tinker with improving if at all possible.

So what if they extend out to 25 and 40kHz. I bet at 50 something you can't her above 15kHz if that high. I'm more than 10 years beyond you and I top out at 14kHz. More than that there just isn't much music above 15kHz anyway. And I'm with RoyC on 2 points: Midwest has a great drop in replacement and good luck with re-engineering the 9 for a new and different tweeter.

I suspect someone will be along soon who has repeated, successful experience in rebuilding/restoring the 9-series tweeter #200029.

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1 hour ago, DavidR said:

So what if they extend out to 25 and 40kHz. I bet at 50 something you can't her above 15kHz if that high. I'm more than 10 years beyond you and I top out at 14kHz. More than that there just isn't much music above 15kHz anyway.

Agreed, David...and the use of any other tweeter and/or upper midrange driver will require crossover changes to correct resulting issues in much more critical frequencies.

Roy

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2 hours ago, RoyC said:

AB Tech went out of business awhile ago and quickly re-opened as CM Tech by a former employee to sell remaining "new" inventory. All of the original AR parts were acquired by "Vintage_AR" (Larry Lagace) at that time. Apparently it is doing business as AB Tech again...same phone number. AB/CM Tech's AR replacement parts are sold to retailers like Simply Speakers. The drivers usually fit the cabinet holes, but original performance specs seldom match original.

If originality is the goal , there is currently nothing better than the excellent Midwest 3/4" tweeter as a replacement for the later 3/4" dome tweeters used in the AR-11/10pi and AR-9 series.

Plopping various drivers into an existing successful design seldom results in improvement, and is usually counterproductive. Essentially you are suggesting a thread on re-designing the AR-9. Good luck with that. :)

Anyway, this thread should be moved to the "Mods and Tweaks" section of the forum.

Roy

Hi Roy 

Not suggesting redesigning the AR 9, I love my fully working pair, my first set. The second set is getting final touches, this third set is more of a problem  so thought I would see if other drivers are out there that were very close in performance to the original AR 9   before trying to do a ferro fluid cleanup and replacement or find someone who can do a repair on the tweeters or  UMR  But from what you said, I think I will order a couple of the Mid West tweeter and keep an eye for some UMR in good shape.

Brian

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1 hour ago, DavidR said:

So what if they extend out to 25 and 40kHz. I bet at 50 something you can't her above 15kHz if that high. I'm more than 10 years beyond you and I top out at 14kHz. More than that there just isn't much music above 15kHz anyway. And I'm with RoyC on 2 points: Midwest has a great drop in replacement and good luck with re-engineering the 9 for a new and different tweeter.

I suspect someone will be along soon who has repeated, successful experience in rebuilding/restoring the 9-series tweeter #200029.

Good point, from my younger days I probably cut off 14K or so as well, maybe its actually time for an ear test also. My concern was difficulty getting good components.

Brian 

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4 hours ago, brianw said:

Hi Roy 

Not suggesting redesigning the AR 9, I love my fully working pair, my first set. The second set is getting final touches, this third set is more of a problem  so thought I would see if other drivers are out there that were very close in performance to the original AR 9   before trying to do a ferro fluid cleanup and replacement or find someone who can do a repair on the tweeters or  UMR  But from what you said, I think I will order a couple of the Mid West tweeter and keep an eye for some UMR in good shape.

Brian

Hi Brian,

I was primarily responding to your statement, " And then the question crossed my mind why not upgrade, Dayton Audio, Scanspeak, Seas, they all offer some amazing dome tweets that have extended range to 25k or 40k and UMR units that are cleaner and smoother, and why not tinker with improving if at all possible.  So now the question of trying to figure out how we can improve on a couple or three drivers and get even a cleaner natural sound."   ...which, along with the required crossover changes, would essentially be a re-design. It would easily position the endeavor in "mod and tweak" territory. 

The primary difference between the AR-11/Midwest tweeter and the AR-9 tweeter is the AR-9 tweeter's recessed dome. They are otherwise identical. Use of foam, felt, or other faceplate treatments can be experimented with to reduce dispersion if deemed necessary.

Roy

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That is great having and getting the spec sheet but do you know if these have ferro fluid?

The impedance peak shows double bumps like a vented system, and I once hypothesized

that this was due to the front chamber (box) under the dome, coupling through the V-notches

(port) to the voice coil cavity (room).  The issue is that the "port" output does not combine

to augment the front of the dome which would cause a notch in the frequency response at

the minimum impedance between the peaks which can be seen at 2.4KHz.  The depth of that

measured amplitude notch suggests that it is a very high Q undamped resonance.  Most

tweeters with double bumps have a 1-2 dB dip in the response.

The impedance peaks being so high suggest that there is either no ferro fluid, or a very low

viscosity type.  The AR-11 (200011-1) tweeter that I measured also had the peaks but they

were much lower in height:

From my post back in 2005:  http://www.classicspeakerpages.net/IP.Board/index.php?/topic/1381-ar-11-tweeter-200011-1-measurements/

 

Some measurements on an AR-11 tweeter (200011-1) are given below. Measured with LAUD.

The input impedance curve showed a double bump which is common with chambered tweeters, has anyone had the dome off to see if the center pole is vented into the rear? The impedance peaks were heavily damped due to the ferro fluid. The lower frequency peak at 1360 Hz was 5.26 ohms, the minimum in between at 1865 Hz was 4.65 ohms, and the upper peak at 2427 Hz was 5.30 ohms. The tweeter was 4.0 ohms in the passband at 5 kHz.

Here are the basic measurements based on only the input impedance, and assuming that the upper peak is the fundamental resonance:

Fs = 2427 Hz

Re = 3.55

Qe = 2.76

Qm = 1.57

Qt = 1.00

It would be better if I could measure several more samples of the AR-11 tweeter especially a

few that have not been driven too hard.

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On 1/26/2019 at 5:12 PM, RoyC said:

Hi Brian,

I was primarily responding to your statement, " And then the question crossed my mind why not upgrade, Dayton Audio, Scanspeak, Seas, they all offer some amazing dome tweets that have extended range to 25k or 40k and UMR units that are cleaner and smoother, and why not tinker with improving if at all possible.  So now the question of trying to figure out how we can improve on a couple or three drivers and get even a cleaner natural sound."   ...which, along with the required crossover changes, would essentially be a re-design. It would easily position the endeavor in "mod and tweak" territory. 

The primary difference between the AR-11/Midwest tweeter and the AR-9 tweeter is the AR-9 tweeter's recessed dome. They are otherwise identical. Use of foam, felt, or other faceplate treatments can be experimented with to reduce dispersion if deemed necessary.

Roy

Roy

Are you saying a ar9 tweeter sounds like a ar11 tweeter?

 

 

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2 hours ago, harry398 said:

Roy

Are you saying a ar9 tweeter sounds like a ar11 tweeter?

Not exactly...I'm saying the AR-11 tweeter can be made to sound like the AR-9 tweeter by modifying the faceplate. The AR-9 tweeter is the AR-11 tweeter with a recessed dome. The recessed dome, however, does not make it ideal for the AR-11. On the other hand, some people may actually prefer the AR-11 tweeter's greater dispersion when used for the AR-9.

Roy

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2 hours ago, RoyC said:

Not exactly...I'm saying the AR-11 tweeter can be made to sound like the AR-9 tweeter by modifying the faceplate. The AR-9 tweeter is the AR-11 tweeter with a recessed dome. The recessed dome, however, does not make it ideal for the AR-11. On the other hand, some people may actually prefer the AR-11 tweeter's greater dispersion when used for the AR-9.

Roy

HI RoyC

Would better dispersion not be a desirable thing, and would it not provide better clarity and range at different listening angles.  Was there a particular reason for the recessed tweeter in the AR 9 ? 

 

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1 hour ago, brianw said:

HI RoyC

Would better dispersion not be a desirable thing, and would it not provide better clarity and range at different listening angles.  Was there a particular reason for the recessed tweeter in the AR 9 ? 

 

Hi Brian,

I'm not sure the more exposed dome of the AR-11 type tweeter would make much of a difference to most people, but it is worthy of experimentation. Listening room acoustics, speaker placement, recording types, and personal preference usually have a much greater influence on acceptability and overall satisfaction.

With the AR-9, AR moved away from the wide dispersion characteristics of the early models. "Acoustic blankets", foam trim rings, recessed tweeter domes, and the added plastic ring around the upper mid (the 9's upper mid is essentially the AR-3a/11 mid with the screen replaced by the raised ring around the dome) were apparently all part of an effort to provide more controlled on-axis response. The 9's side-firing woofers were crossed over much lower than the 3a/11 models, relegating them strictly to bass-only duty.

Tom Tyson can probably provide more insight into AR's later design philosophy.

Roy

 

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5 hours ago, RoyC said:

Not exactly...I'm saying the AR-11 tweeter can be made to sound like the AR-9 tweeter by modifying the faceplate. The AR-9 tweeter is the AR-11 tweeter with a recessed dome. The recessed dome, however, does not make it ideal for the AR-11. On the other hand, some people may actually prefer the AR-11 tweeter's greater dispersion when used for the AR-9.

Roy

Roy

So you are saying the Ar-9 tweeter is the ar11 tweeter with a recessed dome.

That means the dome structure is identical? material?

All I know is my impression of a AR11 tweeter is not pleasing, while the ar9 tweeter is very good and does not exhibit the negative aspects that I hear with the ar11 tweeter.    2 COMPLETELY different sounds.   The ar9 tweeter is extremely good and brilliant.....while I wouldn't run a ar11 tweeter in anything I own.   Its night and day to me.

What I am getting from your comment is the sound is affected by the recessed dome?

The ar9lsi dome is even further recessed!   that is a pleasing tweeter and also exhibits none of the harshness the ar11 dome has.  The ar11 tweeter is sharp and outputs the "S" too much ....

The Hivi is slightly recessed....and that tweeter is also pleasing and exhibits nice tones and none of the harshness the ar11 tweeter exhibits.  The hivi is a bit colored , but its a nice tweeter.

 

As for dispersion.....I do find the ar9 tweeter to be more narrow projecting......certainly more narrow than the ar9LSI series tweeter.  Dispersion is an interesting topic, but for me not so important ....in that all sorts of sound changes occur as you move in the room and or the speakers actual placement.   I cannot expect a tweeter to perform the same in such a wide area......But I do want it brilliant and crisp, but not irritating.........and I find the ar11 tweeter irritating.     

 

so back to the point.....if you are stating the ar11 tweeter is essentially the same as a ar9 tweeter except the recessed (and releaved- like a countersunk screw) dome....you are saying that the total sound difference is attributed to that?    

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9 hours ago, brianw said:

HI RoyC

Would better dispersion not be a desirable thing, and would it not provide better clarity and range at different listening angles.  Was there a particular reason for the recessed tweeter in the AR 9 ? 

 

@brianw  I would not use this MT-4121 tweeter, the input impedance is wrong which will cause

the crossover transfer function to be far off from spec and the frequency response 

has a deep notch in the passband.  It also has a 10 dB change in frequency response

across the passband.   No tweeter of any value would have a response like that.

It was clearly made to look like an AR-11 tweeter but does not perform like one.

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8 hours ago, harry398 said:

Roy

That means the dome structure is identical? material?

 

Yes, though the use of ferro fluid is a variable, which also makes the later AR-11 tweeter a bit different than the earlier one. You can easily tame the AR-11 tweeter with something like a felt damping ring, which will recess it and calm it down.

To be clear, I'm not advocating replacing the original AR-9 tweeter when it is available. I'm just suggesting alternatives to consider when the original tweeters are not available.

Regarding the use of the Midwest tweeter...The AR-9's and AR-11's tweeter crossover point is quite high, and some of the theoretical disadvantages may not be as apparent as suggested by the spec sheet. Practical experience is more informative than conjecture, and DavidR has had a subjectively favorable result with it in the AR-9.

Roy

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2 hours ago, RoyC said:

Yes, though the use of ferro fluid is a variable, which also makes the later AR-11 tweeter a bit different than the earlier one. You can easily tame the AR-11 tweeter with something like a felt damping ring, which will recess it and calm it down.

To be clear, I'm not advocating replacing the original AR-9 tweeter when it is available. I'm just suggesting alternatives to consider when the original tweeters are not available.

Regarding the use of the Midwest tweeter...The AR-9's and AR-11's tweeter crossover point is quite high, and some of the theoretical disadvantages may not be as apparent as suggested by the spec sheet. Practical experience is more informative than conjecture, and DavidR has had a subjectively favorable result with it in the AR-9.

Roy

10 dB variation and a notch is fact, subjective tests must be done with a reference and

preferably blind.  A goal and bragging point for AR speakers is flat response and this

tweeter does not qualify in any way.

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56 minutes ago, DavidR said:

In my AR10Pi not my 9's.

Just started doing cabinet work on the 9's.

Oops, sorry David.

Well, despite your satisfaction with the Midwest tweeter, based on a  spec sheet, Pete has concluded your Midwest tweeter doesn't sound good, so don't bother trying it in the AR-9...and Harry says not to bother with the AR-11 tweeter...so hopefully you have perfect original AR-9 tweeters. :)

Roy

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Nothing to be sorry about. One tweeter is original (large ring) the other is an AR replacement (small ring). My 9s are very early with the wood frame for the grille material.

The previous owner lived in a 19th century farm house in mid CT. I'm positive he had them outdoors on damp ground as I am dealing with the issue now. They should be good when I'm done but not perfect. I'm not a miracle worker like GD70.

I think the tweeters in my 10Pi sound fabulous. Especially very high frequencies/notes.

 

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@brianw  I find it odd that you point out that there are modern tweeters with very flat 

response such as this .75" tweeter from SB Acoustics - note the very flat response:

https://www.madisoundspeakerstore.com/soft-dome-tweeters-sb-acoustics/sb-acoustics-sb19st-c000-4-3/4-dome-tweeter-4-ohms/

And you're told that will change the sound of an AR speaker, rather you are told to use

a tweeter that _looks_ exactly like an AR .75" tweeter but does not perform electro-acoustically

anything like the AR original .75" tweeters. 

Drink the coolaid!

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5 minutes ago, Pete B said:

@brianw  I find it odd that you point out that there are modern tweeters with very flat 

response such as this .75" tweeter from SB Acoustics - note the very flat response:

https://www.madisoundspeakerstore.com/soft-dome-tweeters-sb-acoustics/sb-acoustics-sb19st-c000-4-3/4-dome-tweeter-4-ohms/

And you're told that will change the sound of an AR speaker, rather you are told to use

a tweeter that _looks_ exactly like an AR .75" tweeter but does not perform electro-acoustically

anything like the AR original .75" tweeters. 

Drink the coolaid!

that looks interesting Pete

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4 hours ago, RoyC said:

Oops, sorry David.

Well, despite your satisfaction with the Midwest tweeter, based on a  spec sheet, Pete has concluded your Midwest tweeter doesn't sound good, so don't bother trying it in the AR-9...and Harry says not to bother with the AR-11 tweeter...so hopefully you have perfect original AR-9 tweeters. :)

Roy

lol.........its ok to disagree Roy......

How does Larry feel about his AR9lsi?

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14 hours ago, harry398 said:

Roy

So you are saying the Ar-9 tweeter is the ar11 tweeter with a recessed dome.

That means the dome structure is identical? material?

All I know is my impression of a AR11 tweeter is not pleasing, while the ar9 tweeter is very good and does not exhibit the negative aspects that I hear with the ar11 tweeter.    2 COMPLETELY different sounds.   The ar9 tweeter is extremely good and brilliant.....while I wouldn't run a ar11 tweeter in anything I own.   Its night and day to me.

 

so back to the point.....if you are stating the ar11 tweeter is essentially the same as a ar9 tweeter except the recessed (and releaved- like a countersunk screw) dome....you are saying that the total sound difference is attributed to that?    

@harry398  Are your comments about the AR-9 tweeter vs. AR-11 tweeter with each one in 

the correct enclosure, that is AR-9 tweeter in an AR-9 and AR-11 in an AR-11?  Or are you 

trying each tweeter in say an AR-11 or an AR-9?  I ask because the AR-9 has a much higher

crossover point with a 5uF cap and .105 mH inductor vs. the AR-11 with a 10uF cap and a

.05 mH inductor.  The AR-11 crossover drives the tweeter too hard at the bottom end of the

tweeter range in my opinion and that might be the source of the harshness that you hear.

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8 minutes ago, harry398 said:

that looks interesting Pete

It would require an adapter plate of course.

The fundamental resonance is a bit low and it would need ferro fluid added to behave 

more like the AR-11/9 version tweeter.  Or one could try an electrical mod to make it behave

more like the AR-11/9 tweeter.

I have a pair of those SB tweeters by the way but so far I'm too lazy to make an adapter

plate.  Wish I had a 3D printer to make one!

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