Yep, that's rot. Foam surrounds deteriorate over time. About the most you can reasonably expect out of a foam surround is ten to fifteen years. Yes, they sometimes last longer, but I wouldn't bet the farm on it.
Oh, and yes, that torn-up part around the rim of the cone is called the surround.
Note that the deterioration proceeds regardless of whether you are using the speaker or not. You can put foam surround drivers on the shelf and never play them and they will still do that. It's not a consequence of playing them.
Rubber (neoprene, whatever...), cloth, and crimped paper surrounds do not deteriorate in this manner. Only foam. I will refrain from getting on my soapbox about this at this time.
The ball's in your court, man. It's your time, your money, and they're your speakers.
Shims? We don't need no stinking shims! Take a piece of notebook paper and roll it into a tube. Slide it between the pole piece (the center post of the magnet structure) and the inside of the voice coil. It won't fit the first time because it's too thick. That's just what you want. Unroll the tube and cut an inch or two off. Roll it back up and try it for fit. If it fits, great, otherwise cut a little more off and try again. Cheap, effective, and readily available.
If you choose to try to recone the drivers...good luck. If you sit back and rethink your position...good luck.
Either way, have a nice holiday.
Grey
Oh, and yes, that torn-up part around the rim of the cone is called the surround.
Note that the deterioration proceeds regardless of whether you are using the speaker or not. You can put foam surround drivers on the shelf and never play them and they will still do that. It's not a consequence of playing them.
Rubber (neoprene, whatever...), cloth, and crimped paper surrounds do not deteriorate in this manner. Only foam. I will refrain from getting on my soapbox about this at this time.
The ball's in your court, man. It's your time, your money, and they're your speakers.
Shims? We don't need no stinking shims! Take a piece of notebook paper and roll it into a tube. Slide it between the pole piece (the center post of the magnet structure) and the inside of the voice coil. It won't fit the first time because it's too thick. That's just what you want. Unroll the tube and cut an inch or two off. Roll it back up and try it for fit. If it fits, great, otherwise cut a little more off and try again. Cheap, effective, and readily available.
If you choose to try to recone the drivers...good luck. If you sit back and rethink your position...good luck.
Either way, have a nice holiday.
Grey
Told you guys. I listened to the same sound for months, it's my Dad's pair of rotted 901s that brought me here in the first place.
You can go on ebay and order a cloth kit from simply speakers if you'd like. Or maybe that is too much? well, go with the normal foam surrounds. They are based in California and have a pretty good relationship with customers on ebay. Plus, you get a good deal too!
You can go on ebay and order a cloth kit from simply speakers if you'd like. Or maybe that is too much? well, go with the normal foam surrounds. They are based in California and have a pretty good relationship with customers on ebay. Plus, you get a good deal too!
For the 901s that I'm familiar with, I don't know what Series they are. It could be that there are significant changes over various models. I have been told that they are meant to be used both grill side forward for dispersed sound or port side forward for more directional sound.
That comment about needing lots of power would be consistent with my friend preferring the dual Brystons vs. an older Hafler that he said sounded anemic in comparison.
One comment about distortion... there is a definite increase in distortion when any of the outboard EQ settings are moved away from flat. As with most users, maybe there is probably too much smiley face going on.
It would be interesting to find out if anybody has ever used a different set of drivers in a 901 cabinet.
ensen.
That comment about needing lots of power would be consistent with my friend preferring the dual Brystons vs. an older Hafler that he said sounded anemic in comparison.
One comment about distortion... there is a definite increase in distortion when any of the outboard EQ settings are moved away from flat. As with most users, maybe there is probably too much smiley face going on.
It would be interesting to find out if anybody has ever used a different set of drivers in a 901 cabinet.
ensen.No High's no Lows must be bose!
I guess if your hard pressed for something to listen to you might be able to stomach listening to them. They are not accurate or efficient by any means. I would suggest installing new surrounds on them and promptly selling them on ebay to someone that owns a bose 1801 amplifier.
I guess if your hard pressed for something to listen to you might be able to stomach listening to them. They are not accurate or efficient by any means. I would suggest installing new surrounds on them and promptly selling them on ebay to someone that owns a bose 1801 amplifier.
GRollins said:
Rubber can harden and crack, cloth can rot and accordian surrounds can get brittle and tear. Speakers are temporary. Cloth is probably the best for longevity, IMO. Foam is cheap and it has very nice acoustical properties. Rubber is quite variable with temperature and it is heavy and not suitable for fullrange drivers - when's the last one you sever saw?. I have seen rubber surrounds self destruct after 3 years in a car, so..... Accordian surrounds have limited linear excursion.... It is very understandable why most MFG's go with foam. ...
Resurrounding drivers is tedious, but relatively easy. IIRC, Bose will factory fix your 901's with rotted foam surrounds for about $700 - around half the cost of new..
Bose(o):
I wonder if you can do us all a favor, and might prove interesting to you.
Could you do a nearfield measurement of a single 901 driver?
You can either run them in the cabinet, (porting only affects low frequencies), or remove one and measure it. Remember they are only one ohm, so you probably want to hook up a 10 ohm resistor in series.
I am just wondering about the midrange and high range response. I am told that Bose drivers have cone breakup below 20 Khz, full of large peaks and valleys. If so, the equalization won't mean much. Equalization would only work with a driver with a smooth rolloff.
I think this would useful both for msl422, who might be nervous about this frequency response business. If the response turns out to have cone breakup in it, he won't have to worry.
Even more useful is to see what kind of response this famous speaker uses. For all the talk of white papers, etc, it would be fun to see if bose bothers to make a driver that at least goes up to 20 kHz, or near it, before breaking up.
If you are unfamiliar with frequency response tests, I could give you some suggestions, though I suspect you are very familiar with them.
If you decide to go one step further and measure the Thiele-Small specs, I can give you a page which shows how you can add a resistor, measure the Qts with the resistor, then figure the driver's Qts without the resistor.
Are you up for it?
I wonder if you can do us all a favor, and might prove interesting to you.
Could you do a nearfield measurement of a single 901 driver?
You can either run them in the cabinet, (porting only affects low frequencies), or remove one and measure it. Remember they are only one ohm, so you probably want to hook up a 10 ohm resistor in series.
I am just wondering about the midrange and high range response. I am told that Bose drivers have cone breakup below 20 Khz, full of large peaks and valleys. If so, the equalization won't mean much. Equalization would only work with a driver with a smooth rolloff.
I think this would useful both for msl422, who might be nervous about this frequency response business. If the response turns out to have cone breakup in it, he won't have to worry.
Even more useful is to see what kind of response this famous speaker uses. For all the talk of white papers, etc, it would be fun to see if bose bothers to make a driver that at least goes up to 20 kHz, or near it, before breaking up.
If you are unfamiliar with frequency response tests, I could give you some suggestions, though I suspect you are very familiar with them.
If you decide to go one step further and measure the Thiele-Small specs, I can give you a page which shows how you can add a resistor, measure the Qts with the resistor, then figure the driver's Qts without the resistor.
Are you up for it?
An update:
My dad and I pried off the front grill today, which turned out to be much harder than getting the back grill off (that was a simple pry with a knife job). Think prying off 10 thin but deep and practically invisible staples.
The quote from the local speaker shop for a re*foaming* job was $282.
The *cloth* edge kit can be found on eBay for $50.
This seems like a no-brainer to me, unless someone can convince me that I have a significant chance of sending the whole thing to hell with my lack of expertise.
-Mark
My dad and I pried off the front grill today, which turned out to be much harder than getting the back grill off (that was a simple pry with a knife job). Think prying off 10 thin but deep and practically invisible staples.
The quote from the local speaker shop for a re*foaming* job was $282.
The *cloth* edge kit can be found on eBay for $50.
This seems like a no-brainer to me, unless someone can convince me that I have a significant chance of sending the whole thing to hell with my lack of expertise.
-Mark
kelticwizard said:
I know of no fullrange driver that doesn't break up well before 20kHz. I would be surprised if _any_ make it even to 5kHz, actually, and if they did, their first breakup would be really bad - like metal cone drivers. The bose drivers probably don't make it to 500....maybe 1000 since they're small.
901's sound a lot like ESL's in many ways They make huge sound images that aren't very specific. They can sound OK, but are obviously very room sensitive. They are just fine for background music.
BTW, in car audio, there is a big rush back to cloth surrounds....for longevity, as I said in my initial post. Cloth surrounds can be coated so they don't leak.
ERICSPEEd said:
I'm pretty sure they were just like that. When I removed the back grill, there was a fair amount of sticky tack stuff holding the grill on that looked like it had never been disturbed before.
Is this a problem? Could unsecure cones be causing some of the rattling sounds?
Also, will this refoaming job require me to a)take the cones out and/or b)disconnect/resolder any wires?
-Mark
Hmmm... armed with T/S parameters for the originals, it might be possible to improve on the stock 901s with the right choice of replacement drivers. Could be an interesting mod project for people with access to cheap, broken or attic'ed 01 series speakers.
I can see it now... amaze your friends... surprise your spouse.... get the Re-Bose Kit. Only $49.99.... and if you order before Herbie Hancock kicks the bucket, we'll throw in a free Ginsu knife!
ensen.
I can see it now... amaze your friends... surprise your spouse.... get the Re-Bose Kit. Only $49.99.... and if you order before Herbie Hancock kicks the bucket, we'll throw in a free Ginsu knife!
ensen.
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