my dayton rs180 came with a magnet rubber boot that can be taken off. and when i do, the sound becomes more 'ambient' with better defined lower mids. when it's put back on the sound is 'cleaner' with a tad better imaging but overall feel muffled comparison. you may already have guessed that i like it better with the boots off.. 🙂 but i'd still like to know if this ambiance i'm hearing is the magnet ringing from eliminating the boot to serve it's purpose. so what are the rubber boots for? 
Sure, they must provide some damping, and also some protection. They may also add percieved value to the driver and a sense that the magnet is larger than it is.
One question, are they covering up a pole piece vent?
One question, are they covering up a pole piece vent?
no, it's just a ring surrounding the side of the magnet. but i'd like to know the sound of magnet ringing can attribute to more 'air' and resonance around the notes, or if that's entirely a positive side effect from the boots coming off.
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Hi PreSapian
It’s probably like the rubber gasket that JBL used in the 80’s when they replaced the smaller but more powerful alnico magnets (that had a metal magnetic shield cover) with the heavier ceramic magnets where a larger metal shield cap would have added much unnecessary weight.
The original purpose of this metal cap was to refocus the stray external magnetic field back into the voice coil gap which allowed them to use a smaller magnet assembly. It was also a major selling point for them at the time where they were showing off how their drivers had little stray magnetic fields because of the metal end-cap. However when JBL came out with the ceramic magnets on their drivers they wanted to maintain this closed magnetic shielding for both the publicity and the extra power it delivered into the VC gap but a bigger metal cover was just too costly so they used a ferromagnetic rubber that was intended to replace the steel cover.
Later on with the advent of home cinema the importance of magnetic shielding to protect CRT displays became the main reason for using this shield.
Yes removing it or keeping it can and will affect the performance of your drivers and this could also be a major concern if you have a vacuum tube CRT display close-by as it will eventually magnetize the color shadow-mask of your TV.
Cheers
Philip
It’s probably like the rubber gasket that JBL used in the 80’s when they replaced the smaller but more powerful alnico magnets (that had a metal magnetic shield cover) with the heavier ceramic magnets where a larger metal shield cap would have added much unnecessary weight.
The original purpose of this metal cap was to refocus the stray external magnetic field back into the voice coil gap which allowed them to use a smaller magnet assembly. It was also a major selling point for them at the time where they were showing off how their drivers had little stray magnetic fields because of the metal end-cap. However when JBL came out with the ceramic magnets on their drivers they wanted to maintain this closed magnetic shielding for both the publicity and the extra power it delivered into the VC gap but a bigger metal cover was just too costly so they used a ferromagnetic rubber that was intended to replace the steel cover.
Later on with the advent of home cinema the importance of magnetic shielding to protect CRT displays became the main reason for using this shield.
Yes removing it or keeping it can and will affect the performance of your drivers and this could also be a major concern if you have a vacuum tube CRT display close-by as it will eventually magnetize the color shadow-mask of your TV.
Cheers
Philip
I had no idea it was ferric, always thought it was just there to protect the magnet. Must be a lot of iron in it if it's to be effective... seems odd....
They weren't "ferric". They were just rubber boots to dress up the appearance. Ceramic ring magnets aren't pretty and are also very sharp edged. the Alnico pots with the gray crackle paint had a classy appearance and the rubber tires were added to diminish the difference.
(I was there.)
David S.
(I was there.)
David S.
Not only that but on drivers installed into systems most drivers didn't have a foil label or the boot installed. They just had a white stencilled part number. They saved the rubber boots for drivers that were sold individually for apperance sake as David says.
Rob🙂
Rubber rings are placed on the ferrite magnets of drivers that can be sold as individual units to dress them up and keep the magnet from getting struck and chipping. As they are powerful magnets they will tend to smack into each other or anything magnetic nearby.
Indeed, that's what I thought, some of my own JBLs are "PL" versions, standing for "protector-less", and came out of the SR4725.
Yes Speaker Dave
I was there as well during the time of this change-over. I was the Canadian service manager for JBL Canada (Gould Marketing), and I can say with little reservation that I witnessed many letters between Canada and the US discussing marketing strategy on how they would maintain their previous sales pitches with the effective loss of the metal pot when they were to switch to the new ceramic magnets.
JBL’s marketing solution was to use a ferromagnetic rubber sleeve over the edge of the ceramic magnet. In fact several sales brochures were distributed to dealers and to audio magazines explaining the issue at the time.
I personally could not see how this boot would redirect the magnetic flux back into the VC because it seemed to only short out the two magnetic poles and not redirect any flux back towards the VC pole plate.
This solution did not seem to last very long because within a year or two they seemed to have discontinued its use. One reason for this is that many customers (but not all) were discovering that the drivers produced more bass without it (although not necessarily a better bass).
However in PreSapian’s case I don’t know if the rubber is or is not meant for the same use as originated by JBL, although I could see it as being used as a magnetic shield to prevent CRT degradation, He would have to contact his dealer to get the info on it.
Philip
And I thought PL meant Private Label which is why the sticker on the back is the cheap version also.
What is more interesting is the perceived sound quality differences with or without the ring.
What is more interesting is the perceived sound quality differences with or without the ring.
We're talking about the rubber boot (we called it a "tire" at JBL) over the ceramic magnet as on the 15" woofers ceramic magnets, right? These would be on any of the 3" and 4" coil SFG structures, right?
I'm absolutely sure these were just decoration and a small portion of physical protection. You're not thinking about some of the video shielded metal cans are you? Those have been used by many companies for home theater product. They would have a second reverse charged ferrite ring underneath and would both reduce stray field and slightly increase gap flux.
The rubber boots were just rubber boots. If they had any flux conductive qualities this would be detrimental as it would create a shorting path around the magnet that reduced flux in the gap.
Rob3606 has it right that they were left off of the drivers of some of the systems as a cost savings. I remember there was a lot of internal debate about that at the time (I was a "Transducer Engineer" at Northridge from '80 to '83).
SMITH RECALLS
Regards,
David S.
If it's a JBL driver that's all it is. There is no difference between one with or without the boot. They are identical performance wise.
As well as the compression drivers and ferrite versions of the tweeters like a 2405 as an example.
Rob🙂
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