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Annoying resonance in more than 1 type of AR


Andre_Db66

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I have discovered a very annoying fact about AR speakers i have. 2 sets of AR3a and LST perform the same way.

On certain piano notes or specifically that same frequency it becomes a honky sound as though there is a strong resonance added. It is very annoying and can become quite loud especially in case of piano music as that particular note can be emphasized by playin it louder on the piano. I dont know how to tackle this and if this is familiar to anyone here.

My best guess would be the glass wool has been in and out of the cabinet and needs to actually be placed in a specific way. The weight is known but is it for example that it should be mostly be stuffed behind the mid and tweeter leaving a cavity behind the woofer? It is now all fluffy spread in the cabinets and perhaps wrong approach.

Please any help is welcome as i almost find them annoying to listen to. The focus of attention is drawn too much here so it becomes unenjoyable. The drivers perfom well btw...

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Coincidentally I came across this on another forum yesterday. I cannot vouch for its validity or effectiveness, but it may be relevant to your issue/perceptions.

"From Altec - 1974
The normal method to check speaker damping is simple, but is easiest if you start out with too little fiberglass. We recommend the battery test method to check for damping. Attach a short length of speaker wire to the loudspeaker terminals in the normal manner, and bring the loose end around front – where you can easily listen to the loudspeaker sound while testing. Hold one of the speaker leads to either end of a standard 1.5 volt flashlight battery. Then touch the second lead to the other end of the battery and release. A properly damped loudspeaker will reproduce a clean “click” as contact is made and released.

The underdamped speaker will reproduce the battery contact as a “whomp” sound. Fiberglass may be added in a loose manner to the enclosure until the proper “click” is obtained, and then stapled into place according to above practices relating to the specific type of enclosure.

The overdamped speaker is more difficult to observe. It is a matter of degrees that becomes familiar with one or two experiments. Thus, the recommendation to start tests with too little, build up, and then go back down as required."

 

If you do try it perhaps let everyone know the outcome ? Thanks.

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Four speakers with an identical distortion flaw,in the same room, connected to the same source path, is an improbable speaker problem. The most likely source is dirt or a slightly loose connection upstream, especially if you are using vintage electronics before fader controls or digital circuitry.   

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57 minutes ago, Aadams said:

Four speakers with an identical distortion flaw,in the same room, connected to the same source path, is an improbable speaker problem. The most likely source is dirt or a slightly loose connection upstream, especially if you are using vintage electronics before fader controls or digital circuitry.   

I am not referring to the same hardware upstream. The speakers are producing this flaw with different electronics in that position, different room aswell. However, they have all been opened up and emptied of damping material at one point. There are undoubtedly cavities behind behind mentioned drivers and my suspicion is that the free resonance of those drivers against the backside of the baffle is causing this. At least, this is what i suspect because it sounds that way. I know that damping of mid and high drivers is crucial to avoid this kind of behaviour maybe i should just try what i mentioned myself. I have noticed seeing in either Goodmans or Advent speakers where the resonance chamber of the woofer is empty but the foam is only around the cabinet lining and behind the mid and high stuffed tightly.

I have opened up virgin AR speaker cabinets and there were slabs of fiber glass instead of torn up fluffy as i have replaced it. It is also only with the very specific frequency mentioned, otherwise playing terrific.

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43 minutes ago, Aadams said:

Solo piano?  Which piano key? Or what frequency?

 

I yet have to test this with a tone generator as i have no clue which piano key it is exactly. However there is always the same note region that seems to be overamplified and stings the ear as it becomes very abundant and aggresive compared to the rest of the music piece. Judging by watching youtube piano music it is somewhere in the mid section of the piano, if that helps any...

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On the speakers in question ,from low to high, the first 51 keys are substantially in the woofer, the next 4 or 5 are in the crossover transition but there are powerful  harmonics that extend way into the midrange from most keys along that section of the keyboard. Do you have a link to the youtube being used?   

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9 minutes ago, genek said:

For the AR-3a, the stuffing should be fluffed up and fill the cabinet right up to the front opening. The only space behind the woofer should be whatever is created by the magnet depressing the crepe or fabric barrier.

Fair enough...

I have plucked it apart completely putting small fluffy pieces in to make it more voluminous. It is not how i encountered it in virgin cabinets. Where indeed it was like you describe. I am using very thick constructiin fibre glass that i tear apart. I was wondering to place simply thinner layers in the manner as i encountered. That would be the way you describe it behind the woofer, but i cannot recall how it was behind the mid and high driver. Anyway, i think somehow it is playing a big role in my concerns...

It seems that it is either the mid or woofer not the tweeter. IMHO...

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At 17:38 to 18:24 there are some obnoxious sounds emanating from that piano.  I think it must be the way it is miked.  I listened on AR3a and AR9.  It was more apparent on the 3a.  If your 3a mid pots are turned up past the mid point it would be awful.  The LST mids are running at max all the time IIRC.

The note she playing is close to middle C (262hz), maybe a bit above.  The harmonics of that one note on an acoustic piano will extend strongly to at least 2000hz. 

 

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25 minutes ago, Aadams said:

At 17:38 to 18:24 there are some obnoxious sounds emanating from that piano.  I think it must be the way it is miked.  I listened on AR3as and AR9.  It was more apparent on the 3a.  If your 3a mid pots are turned up past the mid point it would be awful.  The LST mids are running at max all the time IIRC.

 

Gee.. thanks! I will dig into this a bit deeper when i have opportunity to find out if there are other examples i can muster. As i said there have been more occasions when i was surprised by this nasty sound. So it just became obvious that it was AR after i last heard it on my LST. They are hooked up to a class D that i only have a week. The last time i heard this was from a yamaha class a/b amp. I think I also noticed it with a modern tube amp. Problem is i have not noted down any specifics. I just disliked it. Since i have a lot of gear (GAS head), i shall have to focus on the problem. This will take more time than just emphasizing the last music piece i heard on AR, performing in this manner

(BTW... i tend to have tweeter pots opened up and mids tempered.)

First i might simply try a tone generator. It will pinpoint more precise i guess... I will try to find other examples.

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Pianos are difficult instruments to record....

Thank you for that video link.

I will let that play asap. When i conclude the flaw, i shall try diferrent speakers consecutively to eliminate upstream issues or possibly even room gain. It will take some time so probably sunday earliest i can commence. In the meantime when listening i shall refurbish my Sansui AU919.

I do know class D is something else... i am finding this a whole new way of listening to music. It makes AR speakers sing in a very different and distinct way. It is also very unforgiving. Most recordings apparantly are not mixed with this in mind as a lot doesnt sound right, but is the flattest uncoloured sound i have ever heard. There is amazing control of the woofer, which given the acoustic suspension is a major plus. It sounds extremely tight and much less boomy/woolly. My LST are now on class D, driven by a neutral Bryston. I have not yet tried a tube pre though...(paradox)

Andre

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The tweeters and midrange drivers are sealed, and have their own resonance chambers. So we’re talking ONLY about the woofer and the cabinet here.
 

On my resto of the 2ax and small 4x, I left all of the rock wool in place, except what I needed to remove for access to the crossover boards. Later, I replaced the rock wool as it was when new. Rock wool doesn’t wear out or degrade over time.
 

Piano is challenging. I use concert grand piano recordings to test styli I have rebuilt on vintage cartridges. The stylus’ ability to track piano is a key test. Resonance in the stylus assembly is laid bare by piano. 
 

I don’t know why SO MANY people replace the AR rock wool when they refurb the AR speakers! 
 

I haven’t had any resonance issues from the woofers in my AR speakers. The original factory placement of the rock wool works well. It was designed to work well. I still have no idea why folks remove all of the rock wool; it isn’t necessary.

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2 hours ago, genek said:

Rock wool produced prior to 1980 is likely to contain asbestos. It shouldn't be an issue in a sealed cabinet, but if you're a tinkerer and may open it up again and again...

That is very disturbing to find out... i have been very dismissive of health and safety precaution. In another thread i am talking about why fibre glass is used in the first place as Goodmans and Kloss used foam sucessfully...

OTOH as a child i used to play in building construction sites jumping down floors into this stuff.... pre 1980.

Still here

I will be more careful and search for foam slabs to experiment because of both issues, fibre glass and resonances. I will copy the Advent/Goodmans method.

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