Jump to content

Advent/2 voice coil and refoam questions - beginner


Bandolino

Recommended Posts

Hello all. I have been reading this forum with (rabid?) interest for a little while, and now it's time for me to finally post something.

WARNING: I tend to get long-winded. I can already tell that this post is going to be longer than it should be. As I am ignorant of many small details, I am asking some detailed questions that many of you more experienced folks may find extremely boring. So, read at your own risk! And for those of you who do read this, than you in advance for your patience.

I just bought a couple old pairs of speakers, and all the woofers and mid-range drivers need to be refoamed. One pair are Acoustic Research AR93s, and I will surely be posting more about those later. The other pair, as you might guess, are Advent/2 speakers made in 1974.

I am a complete and utter beginner. I have never refoamed a driver before. I have been reading everything I can find on the internet about how to do this. It sounds as if it is possible to do it oneself, but also possible to damage the voice coil and thus destroy the driver, if it is done wrong. I intend to attempt the refoaming of the Advent/2 woofers myself, both because I am too poor to pay someone to do it, and because I am interested in the process, and eager to learn how. I decided to start with the Advent/2 because I bought them very cheaply, and they don't seem to be a terribly high quality speaker to start with, so if I mess up, it's a small sacrifice for my learning process before I start in on the AR93s.

By the way, for any other beginner reading this post, the best description of how to refoam a driver I have found online so far, including a nice, clear diagram of the parts of a driver, is here:

http://www.citlink.net/~msound/refoam/

I want to start out with questions about voice coil damage. When I brought home the Advent/2 and opened one up, I saw that the woofer foam was already completely detached from the frame flange. The guy I bought these from said he had played them within the past few months, so he had almost certainly played them while the foam was rotted this way. I have read that playing a speaker with damaged foam surrounds can damage the voice coil. So the voice coils on these woofers may already be damaged, it seems.

Before I get going, I want to verify my understanding of the construction of the driver, and in particular, the situation of the voice coil. From the web site referrenced above, and from other sources, I have gathered that the voice coil, spider, and cone of a driver come as one assembled unit. It looks as if there is a hollow metal cylinder called the voice coil former. The voice coil is made of copper wire wound around this cylinder near the bottom, the spider is glued onto the cylinder a little higher, and the cone is glued on near the top of the cylinder. The voice coil former fits snugly around a solid metal cylinder called the pole piece. Around the outside of the voice coil former, very close to the voice coil, is the top plate. Is this description correct? Am I misunderstanding something crucial?

Here is my list of questions about voice coil damage:

1. How does damage to the voice coil occur? My best guess is that if the voice coil/cone assembly moves in such a way that the voice coil scrapes against the top plate, the voice coil wire can be broken. Is this the essence of the problem? Can the voice coil wire be a little bit damaged, and still work ok? Does even a little damage distort the sound it produces, or make it incapable of producing sound?

2. Is there any safe way to visually inspect the driver to see if the voice coil is already damaged? If not, is there any other way to determine if the voice coil is damaged?

3. Once the drivers are refoamed and the speakers are played, what are the auditory signs of a damaged voice coil?

4. How should I store and handle drivers with rotted or missing foam surrounds in order to prevent or minimize damage to the voice coil? Is it ok to store them mounted in the loudspeaker boxes as is, or should I remove them and store them differently?

Well, that is enough for now, I guess. I have even more questions, of course, especially about refoaming the Advent/2. I haven't even gotten to that, even though it's in the title. Is this the right forum for me? Am I going to drive everyone bananas with my wordiness? I hope that someone hangs in there with me, because I do need help, as you can tell.

Oh, one little tidbit of information about the strange Advent/2. When I opened the box, I found to my surprise that it was filled with pink fiberglass insulation! It was just like the stuff you might find in the walls of your house. Is that unusual for a speaker from 1974? The fiberglass seems a little more dense than the acoustic fiberfill usually found in a speaker. I wonder if it has any unique acoustic effects. I hope it's not too important, because I can't bring myself to reuse it, given the cancer-causing effects of fiberglass.

Ok, that's really it for now, and many thanks to those who made it through this entire post. ;)

Link to comment
Share on other sites

>Hello all. I have been reading this forum with (rabid?)

>interest for a little while, and now it's time for me to

>finally post something.

>

>WARNING: I tend to get long-winded. I can already tell that

>this post is going to be longer than it should be. As I am

>ignorant of many small details, I am asking some detailed

>questions that many of you more experienced folks may find

>extremely boring. So, read at your own risk! And for those

>of you who do read this, than you in advance for your

>patience.

>

>I just bought a couple old pairs of speakers, and all the

>woofers and mid-range drivers need to be refoamed. One pair

>are Acoustic Research AR93s, and I will surely be posting more

>about those later. The other pair, as you might guess, are

>Advent/2 speakers made in 1974.

>

>I am a complete and utter beginner. I have never refoamed a

>driver before. I have been reading everything I can find on

>the internet about how to do this. It sounds as if it is

>possible to do it oneself, but also possible to damage the

>voice coil and thus destroy the driver, if it is done wrong.

>I intend to attempt the refoaming of the Advent/2 woofers

>myself, both because I am too poor to pay someone to do it,

>and because I am interested in the process, and eager to learn

>how. I decided to start with the Advent/2 because I bought

>them very cheaply, and they don't seem to be a terribly high

>quality speaker to start with, so if I mess up, it's a small

>sacrifice for my learning process before I start in on the

>AR93s.

>

>By the way, for any other beginner reading this post, the best

>description of how to refoam a driver I have found online so

>far, including a nice, clear diagram of the parts of a driver,

>is here:

>

>http://www.citlink.net/~msound/refoam/

>

>I want to start out with questions about voice coil damage.

>When I brought home the Advent/2 and opened one up, I saw that

>the woofer foam was already completely detached from the frame

>flange. The guy I bought these from said he had played them

>within the past few months, so he had almost certainly played

>them while the foam was rotted this way. I have read that

>playing a speaker with damaged foam surrounds can damage the

>voice coil. So the voice coils on these woofers may already

>be damaged, it seems.

>

>Before I get going, I want to verify my understanding of the

>construction of the driver, and in particular, the situation

>of the voice coil. From the web site referrenced above, and

>from other sources, I have gathered that the voice coil,

>spider, and cone of a driver come as one assembled unit. It

>looks as if there is a hollow metal cylinder called the voice

>coil former. The voice coil is made of copper wire wound

>around this cylinder near the bottom, the spider is glued onto

>the cylinder a little higher, and the cone is glued on near

>the top of the cylinder. The voice coil former fits snugly

>around a solid metal cylinder called the pole piece. Around

>the outside of the voice coil former, very close to the voice

>coil, is the top plate. Is this description correct? Am I

>misunderstanding something crucial?

>

>Here is my list of questions about voice coil damage:

>

>1. How does damage to the voice coil occur? My best guess is

>that if the voice coil/cone assembly moves in such a way that

>the voice coil scrapes against the top plate, the voice coil

>wire can be broken. Is this the essence of the problem? Can

>the voice coil wire be a little bit damaged, and still work

>ok? Does even a little damage distort the sound it produces,

>or make it incapable of producing sound?

Most damage occurs from overheating (too much power applied) or over-stroking; although it's pretty hard with these long wound coils. With the VC supported only by the spider (e.g. fully rotted surround) there is the likelyhood of cocking of the VC if played for an extended period at high volume and scraping the windings against the magnet.

>

>2. Is there any safe way to visually inspect the driver to see

>if the voice coil is already damaged? If not, is there any

>other way to determine if the voice coil is damaged?

You can carefully hold the cone centered and move it up and down a bit. If you hear rubbing sound or it's difficult to move, then most likely the coil is a gonner. A better way is to check the impedance with a VOM. You can borrow or buy a cheap analog unit for $10-$20. If you get no reading, then it's a gonner as well. If it's damaged, junk the entire unit. It's too difficult to repair. Just find another vintage one that works fine.

>3. Once the drivers are refoamed and the speakers are played,

>what are the auditory signs of a damaged voice coil?

The sound will be distorted and un-natural in character.

>4. How should I store and handle drivers with rotted or

>missing foam surrounds in order to prevent or minimize damage

>to the voice coil?

If you must store, they refoam first. The new foam adds to the 'wheel base' effect of supporting the VC in its proper X-axis position. I've attached a photo of a collapsed spider I suspect deformed over time with the woofer's surround gone and the speaker laying on it's back. Perhaps heat and age of the spider's resin impregnaated fabric simply yielded under the weight of the cone. Refoaming seemed to restore it to it's correct position, however.

Is it ok to store them mounted in the

>loudspeaker boxes as is, or should I remove them and store

>them differently?

AGAIN, REFOAM FIRST AND THEY STORE ANY WAY YOU WANT.

>Well, that is enough for now, I guess. I have even more

>questions, of course, especially about refoaming the Advent/2.

> I haven't even gotten to that, even though it's in the title.

> Is this the right forum for me? Am I going to drive everyone

>bananas with my wordiness? I hope that someone hangs in there

>with me, because I do need help, as you can tell.

I strongly suggest you use the site's search function and research your questions first. There is a huge amount of information stored there - most likely questions like yours that have been asked by newbies like yourself (and ansered) many times before.

>

>Oh, one little tidbit of information about the strange

>Advent/2. When I opened the box, I found to my surprise that

>it was filled with pink fiberglass insulation! It was just

>like the stuff you might find in the walls of your house. Is

>that unusual for a speaker from 1974? The fiberglass seems a

>little more dense than the acoustic fiberfill usually found in

>a speaker. I wonder if it has any unique acoustic effects. I

>hope it's not too important, because I can't bring myself to

>reuse it, given the cancer-causing effects of fiberglass.

If you only need to remove the woofer for repairs, then you won't need to disturb the FG. Studies discussed here and in the AR area show that FG is probably the best stuffing material. Keep it if at all possible.

>

>Ok, that's really it for now, and many thanks to those who

>made it through this entire post. ;)

It's all about the music

Carl

Carl's Custom Loudspeakers

Link to comment
Share on other sites

Carl, thank you for your helpful answers to my questions. It is very nice to be able to turn to people with a lot of experience with vintage speakers. I will try to keep my posts a bit more reasonable now; I guess I was feeling overwhelmed with all the information that I needed to find out.

I just ordered a pair of foam surrounds from MSound, mentioned above. They were very helpful. I will need to cut a wedge out of the surrounds and reglue the edges together to get the surrounds to the proper size, but I am happy to try it. MSound is sending a sheet of instructions about how to cut and reglue them correctly. Wish me luck. I will post here later to let people know how it went.

I do still have a question about preventing damage to the voice coils before I refoam drivers with rotted foam. Carl, I understand what you said about refoaming them first before storing them, but I was thinking more of short term storage, not long term. What I mean is that it may be a few weeks before I am able to refoam the drivers on my AR93s. For a few weeks only, is it ok to leave the drivers in the cabinets, or should I take them out now and store them in a safer position, maybe face down on a table?

Thanks again to everyone.

Link to comment
Share on other sites

Great shot of the spider Carl!

I too have seen them like that and, like you said, they seem to get corrected when the surround is replaced.

I'm in the middle of rebuilding one of a pair that had the wrong, thick, surrounds on them (it's too bad they used the wrong ones as they did a great job of replacing the originals)and the one made noise with a low (30Hz) frequency fed into it.

I was sure I was going to find loose coils on the V.C. but the only thing I could see was that the yellow tape used between the wires and former was loose in one place. Probably enough to vibrate with that low frequency.

Oh well, I'll find out if that was it once it's back together (I'm waiting for the surrounds).

By the way, I found that the original Zip-Strip finish remover is great for disolving the various adhesives used to assemble speakers.

Bandolino, if you can find a place where there is no voice coil rubbing (move the cone around until it looks centered) as you push on the cone and the spider returns it, the driver is probably OK to refoam.

I have found that real damage to Advent voice coils is pretty rare even if the driver has been played with the surround damaged or missing. They seem to be pretty robust.

Doug

Link to comment
Share on other sites

  • 2 weeks later...

I finally finished refoaming the woofers on my Advent/2 speakers. I ordered the kit from MSound for $30. That was a little more than I was expecting to pay, but I had confidence that he was getting me all the right parts and tools for the job. I did have to cut out a wedge from the surrounds, and glue the ends back together with a small overlap. I put the original pink fiberglass insulation back into the cabinets for damping, and sealed the drivers and the back panel of the cabinets with Moretite weatherstripping putty. I didn't do anything to the crossovers or interior wiring, but I hope to do that later.

The speakers seem to work fine so far. I have played them some over the past 2 days, but not a whole lot, because I want to break them in gently. I am not really sure what kind of break-in they need, so I am keeping the volume on the low to medium side, and not playing them all the time. They do sound nice. Compared to most modern speakers I have heard, they seem sort of laid-back and relaxed, with pretty good detail. They do not gain volume as quickly as the cheapo speakers I was using before, probably because of their 87 db/w efficiency. I am using a Harman/Kardon HK3250 receiver to drive them. It is rated 40 wpc rms at 8 ohms, and 65 wpc rms at 4 ohms. The speakers are 6 ohms. I know that is not the best amp ever, but it is ok, and it is what I have at this time.

I am wondering about the metal grills. It seems to me that they are not acoustically neutral. I can feel the grills vibrating along with the bass notes in the music. I am thinking of replacing them with some cloth grills instead. I also have fantasies of making entirely new cabinets of MDF, wondering if that would make a significant difference in their sound. That is far beyond my current abilities, however. Does anyone have any comments about these ideas?

Link to comment
Share on other sites

Good that you got the 2s refoamed and working Cooper. I wouldn't worry too much about breaking them in slowly. I think they'll take it :^)

As for your ideas regarding making MDF cabinets with cloth grilles, these were available with just that combination in addition to the plastic ones with metal grilles so it is entirely legitimate.

I have never heard the 2s so I don't know if there would be a significant difference in sound. Advent, however, tried to keep the sound the same for any given model regardless of the cabinet chosen. The original Advents in the walnut cabinets (actually walnut veneered MDF)sound the same as the utility model in MDF and vinyl, for instance.

Doug

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...