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AR 9 crossover coils melted!


Guest audioslave

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Guest audioslave

Once again I find myself at the mercy of this forum and It's wise members!!

Upon removing the drivers from my one of my 9's I was shocked to find that a 10.0Mh stacked set of coils for the woofer section had melted. The tape wrap on the coils has a burnt brown color and they have melted so badly that I won't be able to separate them. I just got them in December and this damage wasn't present then. This particular set of coils had come loose in transit and I had to reglue them to each other and the board. Any idea for the cause of this one? I've been using a Kenwood KR-9050 receiver with 200 watts per channel to drive them. I'll try to post a picture later and will remove the woofers from the second one to see if it's suffered the same kind of damage.

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Guest Barrydor

>Once again I find myself at the mercy of this forum and It's

>wise members!!

>

>Upon removing the drivers from my one of my 9's I was shocked

>to find that a 10.0Mh stacked set of coils for the woofer

>section had melted. The tape wrap on the coils has a burnt

>brown color and they have melted so badly that I won't be able

>to separate them. I just got them in December and this damage

>wasn't present then. This particular set of coils had come

>loose in transit and I had to reglue them to each other and

>the board. Any idea for the cause of this one? I've been using

>a Kenwood KR-9050 receiver with 200 watts per channel to drive

>them. I'll try to post a picture later and will remove the

>woofers from the second one to see if it's suffered the same

>kind of damage.

Do the woofers still work & measure properly?

Barrydor

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Guest Barrydor

>>

>>Do the woofers still work & measure properly?

>>

>> Barrydor

>

>

>

>Both woofers are working and measure just under 3 ohms each.

What do the coils measure?

Barrydor

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Something is VERY wrong here. In the past, i've run my 9's with 500+ wpc driving the woofers and 400+ wpc driving the mids and tweeter. The woofer amp had prodigious bass capacity and i never experienced any problems. These two amps were "throttled" quite extensively, meaning that the speakers were too.

I replaced both of those amps with an amp that is rated at 1200 wpc ( clips at slightly over 1450+ wpc ) and am running that full range. I have since sent this amp into thermal shutdown two times!!! I did send the amp back to the factory and it was modified / upgraded to provide even more current with less potential for shut-off ( pulled the current limiters and altered the point that thermal protection kicks in).

Outside of causing the spiders to partially separate from the voice coil formers due to excessive excursion*, i've not experienced any other problems out of this or the previous amplifier arrangement. Given that i was achieving appr 114 dB's average at a listening distance of appr 10' from the speakers, you are experiencing some type of equipment failure / malfunction. Then again, it is possible that one of the inductors developed an internal short, possible due to poor / un-even application of enamel on the wire, and finally decided to let loose.

If such is the case, you can probably unwind the coil and find where arcing was taking place. It is possible that you could remove / re-insulate the existing wire and re-wind the coil. This would be a LOT of work. Then again, short of finding some OEM coils, you're only other alternative would be to replace this coil with an aftermarket unit. If you do so, you should make sure that it is a heavy gauge conductor AND i would recommend doing the same for the matching inductor on the other speaker. The use of something along the lines of Goertz foil inductors ( preferred ) or a less expensive Madisound "Sledgehammer" type coil should work fine if not better than the original AR piece. Northcreek also offers some heavy gauge inductors that are rumoured to be quite good, but i've never worked with any of those, so can't say out of experience.

Either way, you should check and see if your receiver is passing DC and / or if it is functioning properly before hooking it up to any other speakers that you value. Sean

>

* If you want to check woofer response, try playing a CD entitled "Faith is in Season" by a band called "Master" at rock concert levels. The quantity and speed of the "kick drums" on this disc are ferocious. For those of you that are "squeamish" about such things, this disc contains both lyrics and artwork that you will find offensive, so be forewarned.

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Guest Barrydor

>

>both coils measure 2.2 ohms. The damage isn't present in my

>other AR 9

>Jeff

>

Do you still plan to upload a photo of the damaged coils?

Barry

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Guest audioslave

>With that in mind I think I'll stick to evaluating woof

>performance with Telarc's 1812 Overture. The lyrics are

>cleaner.

>

>

LOL!! Much cleaner, no "explicit lyrics" warning

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Guest Barrydor

I am certainly baffled by this one

I believe that this choke is in series with the woofers, meaning that any current that passes through it also passes through the woofer coils

I would think that the woofer voice coils would open, possibly melting the former and scorching the cone before the choke would be damaged as the voice coil wire is much thinner. Yet you say the woofers still work

In your photo, the wrapping tape and the wire insulation look OK, but the plastic formers appear melted. Is there any chance the glue you used to reglue the choke in place reacted with the plastic?

Barry

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Looking at the schematic, it appears that there are three coils in the woofer circuit, two are 10mh and the third one is unspecified. I would guess that it is also 10mh which along with the other 10 mh coil connected between it and the input (not the one in series with the 2500uf capacitor) and the 470 uf capacitor shunted to the negative side forms a third order (T) low pass Butterworth filter 3 db down at 200 hz. Perhaps Ken or Tom could correct this explanation if it is wrong. They should be easy enough to replace from Parts Express or any other high quality source. Just be sure that they are air core (not ferrite) and wound with heavy gage wire (I think they offer one which is 17 or 19 gage. I'd buy the heavier of the two.)

I still wonder about the impedence of the voice coils of these drivers. If they are four ohms as Tom had stated in a prior posting, wouldn't the parallel combination of 2 ohms be too low? I'd sure guess that they were 8 ohm drivers but if Tom or Ken says 4, I'll take their word for it.

BTW, the combination of the third 10mh coil and the 4700 uf capacitor appears to be the part of the circuit specified in the design description for maintaining overall impedence in the woofer circuit away from the resonance frequency. Anyone care to comment on that guess as well?

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OK, the woofers probably are 4 ohms. looking at 15 gage inductors a 10 mh inductor would have a dc resistance of 1.20 ohms and two in series would bring the two 4 ohm speakers in parallel back to 4 ohms nominally.

It is apparantly very critical that the gage of the wire be correct and for that matter the geometry which will determine the number of feet of wire and therefore the dc resistance as well. I'd measure the dc resistance of a still good coil and check it agaist the replacement before I installed it. This is more complicated than I originlly assumed. (foot in mouth disease? Murphy's law in action?)

Perhaps rewinding it yourself would be best. Check the number of turns and layers if you remove the wire from the old spool so that you can duplicate it as closely as possible.

Here's one, they sell others as well.

http://www.partsexpress.com/pe/pshowdetl.c...r=255-448&DID=7

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Guest Barrydor

>

>It is apparantly very critical that the gage of the wire be

>correct and for that matter the geometry which will determine

>the number of feet of wire and therefore the dc resistance as

>well.

And the inductance, which is the most critical factor

I'd measure the dc resistance of a still good coil and

>check it agaist the replacement before I installed it. This

>is more complicated than I originlly assumed. (foot in mouth

>disease? Murphy's law in action?)

According to his earlier post, the resistance of the good vs. damaged coils were identical

>

>Perhaps rewinding it yourself would be best. Check the number

>of turns and layers if you remove the wire from the old spool

>so that you can duplicate it as closely as possible.

>

Why rewind it or replace it if it may still be electrically OK?

Barry

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I must have missed something. What melted, the wire or just the tape on the outside? If the coil isn't shorted or open then there would be no reason to replace it unless it had become deformed. A change in its geometry would change its inductance. From the photo, perhaps that's all that happened. It wasn't clear to me.

400 watts into 4 ohms is 10 amps. These were new in December. Perhaps their current capacities weren't rated high enough. Were these exact replacements for the originals? If the gage is too thin, they won't be able to handle it. Furthermore, if the speakers are 4 ohms each, then 200 of the 400 watts maximum is dissipated by the coils themselves (100 watts each) and the 400 watt rating is still based on a 100 watt rating for each driver. I'm making a lot of assumptions here so I probably got all of that wrong. I'll bet Ken knows the right answers.

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Guest Barrydor

>I must have missed something. What melted, the wire or just

>the tape on the outside?

From the looks of the photo, it appears to me that the tape and the wire are OK, but the plastic coil formers have melted

> If the coil isn't shorted or open

>then there would be no reason to replace it unless it had

>become deformed.

> A change in its geometry would change its

>inductance. From the photo, perhaps that's all that happened.

You are right about that. A check with an LCR meter would confirm inductance

From the photo, it doesn't appear to me that the coils deformed enough to make a large difference

> It wasn't clear to me.

Maybe audioslave will clarify soon

Barry

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Read pages 2,3, and 4 of Tim Holl's technical description for the AR9. It is clear that the DC resistance of the chokes in the crossover network is critical to control the system Q and obtain the best bass response. If the wire gage is too small, the resistance will be too high, the response will be less than ideal and too much power will be dissipated by the coil in series with the 2500 uf capacitor when the bass signal is away from resonance. It seems to me still that the coils must be an electrical exact duplicate of the originals including not only L but R and maximum power dissipation. Therefore the wire gage will have to be the same and the type of insulation would have to be the same in order to be able to dissipate the heat.

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Guest audioslave

>>I must have missed something. What melted, the wire or

>just

>>the tape on the outside?

>

>From the looks of the photo, it appears to me that the tape

>and the wire are OK, but the plastic coil formers have melted

>

>> If the coil isn't shorted or open

>>then there would be no reason to replace it unless it had

>>become deformed.

>

>> A change in its geometry would change its

>>inductance. From the photo, perhaps that's all that

>happened.

>

>You are right about that. A check with an LCR meter would

>confirm inductance

>From the photo, it doesn't appear to me that the coils

>deformed enough to make a large difference

>

>> It wasn't clear to me.

>

>Maybe audioslave will clarify soon

>

> Barry

>

The coils are original. I just got the 9's in December, so they were new to me, however the parts are all original.

The dcr of both the melted coil and the non melted from the other AR 9 are within 10%. I was incorrect in stating that I had reglued this coil --it was actually another coil.

The dcr of the woofers for this cabinet are 2.5 and 2.6 ohms. The 2 woofers in the other cab are 2.4 and 2.6 ohms.

The melted coils have a dcr of 2.2 ohms, the unmelted set has a dcr of 1.8 ohms. earlier I stated "both coils have a dcr of 2.2 ohms"....this was the two coils that melted together. Hope this clears things up a bit.

Jeff

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You have convinced me of one thing and that is while I understand the principles of this design based on Tim Holl's technical description, when it comes to the actual details of the design, even after looking at the schematic, I don't have a clue as to what is going in. I think I will run a few numbers just to see if I can figure it out but frankly, I don't expect to learn much. I can't seem to reconcile the driver impedences with the crossover design. Losses in the crossover network at bass frequencies just seem too high. I'm sure I'm missing someting.

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Guest audioslave

>>

>

>

>The dcr of both the melted coil and the non melted from the

>other AR 9 are within 10%. >

>

This is an incorrect statement. 10% is close, but the two sets of coils are not "within" 10%

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The Telarc recording may be great for checking extension and output, but it will not test transient response ( both attack and decay ) or power handling in the same way as the disc that i mentioned. Momentary blasts are not the same thing as repeated high speed, high amplitude thrashings of large diameter drums. Sean

>

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Guest audioslave

>The Telarc recording may be great for checking extension and

>output, but it will not test transient response ( both attack

>and decay ) or power handling in the same way as the disc that

>i mentioned. Momentary blasts are not the same thing as

>repeated high speed, high amplitude thrashings of large

>diameter drums. Sean

>>

Sean,

Without a doubt you have more expertise in this than I do so maybe you can answer this..

Wouldn't high speed double bass have more attack and less decay? If a drummer is playing double bass sixteenth notes in 4/4 time at a tempo of 120 beats per minute, that works out to be 8 bass notes per second. If recorded acoustically, wouldn't the decay of the initial strike get choked by the second? Also, in a recording, wouldn't there be large amounts of compression on the bass decay to give the impression of more attack? Even when using a digital drumset or triggers, wouldn't the decay be compressed? I always assumed that slower bass would yeild more transiet information.

Jeff

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Sustained organ pedal notes are the gold standard by which the low frequency performance of high fidelity loudspeakers are judged. The fundimental frequency can go as low as 16 hz. This is why Acoustic Research chose to use that for demonstration of the bass capabilities of the AR 12 inch acoustic suspension woofer system. Musically valid and technically challenging, it has no offensive words to get by. Some musical compositions which when well recorded will give a bass reproducer a workout is Richard Strauss's Also Sprach Zarathrustra (the opening low frequency tone should shake the walls) and I like the Bach Toccata and Fugue in D minor. Although I do not often enjoy Laser Light recordings, the one which reissued Virgil Fox's recording made in Garden Grove California as a direct to disc by the famous engineer Bert Whyte is IMO excellent.

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Guest dogmeninreno

>Sustained organ pedal notes are the gold standard by which

>the low frequency performance of high fidelity loudspeakers

>are judged. The fundimental frequency can go as low as 16 hz.

> This is why Acoustic Research chose to use that for

>demonstration of the bass capabilities of the AR 12 inch

>acoustic suspension woofer system. Musically valid and

>technically challenging, it has no offensive words to get by.

>Some musical compositions which when well recorded will give a

>bass reproducer a workout is Richard Strauss's Also Sprach

>Zarathrustra (the opening low frequency tone should shake the

>walls) and I like the Bach Toccata and Fugue in D minor.

>Although I do not often enjoy Laser Light recordings, the one

>which reissued Virgil Fox's recording made in Garden Grove

>California as a direct to disc by the famous engineer Bert

>Whyte is IMO excellent.

You mention several recordings. Do you have details of a selection that I could find? Searching under your names produce various results. I am interested in the organ selection you mention?? Thanks, Dale

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Happy to.

Both of these pieces of music are very widely recorded. Here's the Laser Light recording; number 15 313. It is called; Virgil Fox. The orginal recording was made on Aug 28 to 31 1977 and was re-released on this cd in 1990.

If you get another recording, be certain that it is digital because this is one time when the analog recording medium often can't do this justice. Especially vinyl phonograph records.

The first few measures of Also Sprach Zarathustra was used in the beginning of the movie "A Clockwork Orange." Back in the 1970s or whenever that movie was made, many audiophiles used it to test and inadvertantly destroy their sound systems. The one I'm holding in my hand right now has a nice collection of Sci Fi movie and TV music very well recorded by the Boston Pops under John Williams Called "Out of This World. Philips 411 185-2. If you like this disc, it was part of a 4 disc set from Philips which included Pops in Space Philips 412 884-2, Aisle Seat, Great Film Music Philips 411 038-2, and That's Entertainment Philips 416 499-2 all with John Williams and the Boston Pops and all recorded on Philips Digital Classics. Excellent recordings IMO.

Unfortunately thre is no way to tell in advance if a recording is really good. You just have to hear it. Even my favorite label, DG occasionaly has a less than wonderful recording and their analog re-released organ cds sometimes just don't produce the deep bass you'll often hear in a purely digital recording IMO.

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