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 Post subject: Large speaker magnet resting on a steel chassis?
PostPosted: Sep Thu 12, 2019 5:04 am 
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Location: Phoenix AZ
I am replacing an old radio speaker with a new speaker with a large exposed magnet that will be resting on the chassis. As a result, the entire chassis becomes magnetized, obviously the closer to the speaker magnet the magnetic field is stronger. The only mechanical support of the new speaker rim to the chassis will be 2 screws, so I like the additional support in the back of the speaker.

The question, is it bad for the speaker or the radio? Off-hand I don't see any problem having the speaker magnet resting on and touching the chassis but what do I know, I am only an Electrical Engineer.


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 Post subject: Re: Large speaker magnet resting on a steel chassis?
PostPosted: Sep Thu 12, 2019 5:48 am 
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Joined: Sep Thu 23, 2010 6:37 am
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Location: Powell River BC Canada
Magnet or magnet and pole structure ?

A photo would help. Imagination is a ferrite magnet ring touching the chassis.

The chassis could care less. A tuning eye pattern can be distorted.

How magnetic is the chassis, in terms of, will 4-40 steel nuts cling loosely ?

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 Post subject: Re: Large speaker magnet resting on a steel chassis?
PostPosted: Sep Thu 12, 2019 8:09 am 
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Having the speaker magnet resting on the chassis will have no negative effect whatsoever on anything. I've done the same with speaker replacements in several radios. Magic eye tubes are normally located above the chassis, so even that wouldn't be affected.

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 Post subject: Re: Large speaker magnet resting on a steel chassis?
PostPosted: Sep Thu 12, 2019 10:28 am 
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Location: Near Brandon, Iowa
A bare magnet would impose a considerable magnetic field over its immediate surroundings. But loudspeaker magnets are not "bare magnets": they are enclosed in a steel structure that (mostly) confines the magnetic field to itself. This is required for the operating physics of the dynamic speaker; but it had the side benefit (back in the the days when low-coercivity alnico magnets were used) as functioning as a "magnet keeper" to minimize the possibility of demagnetization.

What magnetic flux leakage exists (and of course there will be some) is not enough to pose a problem even a short distance away. Consider the millions of TV sets that were manufactured with cathode-ray picture tubes (which are extremely sensitive to magnetic fields) in close proximity to the set's speaker.


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 Post subject: Re: Large speaker magnet resting on a steel chassis?
PostPosted: Sep Thu 12, 2019 6:50 pm 
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If that is not a large bare magnet then I don't know what is.


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 Post subject: Re: Large speaker magnet resting on a steel chassis?
PostPosted: Sep Thu 12, 2019 7:09 pm 
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It doesn't matter what the physical size of the magnet is, it won't bother the electronics whatsoever.

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 Post subject: Re: Large speaker magnet resting on a steel chassis?
PostPosted: Sep Thu 12, 2019 8:45 pm 
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Location: Powell River BC Canada
Just don't sell the restored radio to some old salt with an antique mariners
compass .

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Amateur Radio Literacy Club. May we help you read better.
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 Post subject: Re: Large speaker magnet resting on a steel chassis?
PostPosted: Sep Thu 12, 2019 11:47 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Seattle WA US
If the speaker magnet structure is resting against a panel, not attached to it, I would be concerned about parasitic vibrations between the speaker and panel when driven by loud sound. I would place a pad of rubber between the two, or a big glob of non-hardening weatherstrip adhesive.

-Chuck


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 Post subject: Re: Large speaker magnet resting on a steel chassis?
PostPosted: Sep Fri 13, 2019 1:48 am 
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Shush y'all. Never suggest anything to an engineer who has something that already works. :roll:

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 Post subject: Re: Large speaker magnet resting on a steel chassis?
PostPosted: Sep Fri 13, 2019 5:09 am 
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Na... not my philosophy, it is usually the bean counter philosophy.


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 Post subject: Re: Large speaker magnet resting on a steel chassis?
PostPosted: Sep Fri 13, 2019 5:41 am 
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K7MCG wrote:
If the speaker magnet structure is resting against a panel, not attached to it, I would be concerned about parasitic vibrations between the speaker and panel when driven by loud sound. I would place a pad of rubber between the two, or a big glob of non-hardening weatherstrip adhesive.

-Chuck

I don't think that he's referring to a high wattage amplifier here; just an AA5/6, and as such, doubtful that the speaker frame would ever get the kind of sonic vibrations you are referring to. The ones that I have done like this have had NP in that, or any other regard.

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