How to shield cabinet using unshielded drivers?

[feke67]

I am looking to use some unshielded drivers (mid-basses & tweeters) in a cabinet that will end up as a center channel near monitor. Are there any lessons learned or recommendations to shield the cabinet for this application? Will lining the inside of cabinet with mu-metal or copper work? I welcome any experience on this subject.

Thanks,

feke67

[mrfeedback]

Hello feke67,
The commercial magnetically shielded drivers that I have seen have a simple 2mm thick iron cup shaped pressing glued over the the magnet assembly.
Take a look in a typical modern television or modern 3in1 speakers.
Some have an additional magnet glued to the back of the magnet assembly.

Eric.

[pinkmouse]

Will lining the inside of cabinet with mu-metal or copper work?

Sorry feke67, copper has very little effect on magnetic fields, and mu-metal is very expensive, it would be cheaper just to buy proper shielded drivers!

The commercial magnetically shielded drivers that I have seen have a simple 2mm thick iron cup shaped pressing glued over the the magnet assembly.

Correct Eric, that is the case, but as the shielding and magnet can interfere with a driver's T/S parameters, unless very well designed, (unlikely in a tv), modified drivers may not work as advertised, and the shielding may be less effective than on a commercial shielded driver.

But feke, why not try it anyway if you have access to the right materials, and please post a follow up to the forum if it works.

[mrfeedback]

In my experience, good quality shielded drivers can sound even better.

Eric.

[Praudio]

Galvanised sheet metal 20-24gauge do a nice job ,try it between
you speaker box and tv screen before final fixing inside.

[annex666]

ok, sheilding drivers hmm...

...there are two methods to sheilding drivers, the first of which is to use a bucking magnet and the second of which is sheilding.

A bucking magnet is a magnet with the same shaped field as the driver only having its opposing pole facing the driver - this does not stop the magnet field it merely creates an area where the net field is zero by the two fields cancelling each other out.

So-called mu-metals are metals that have a certain structure as to allow magnetic fields to permiate them easily - using mu-metal shields creates a path of short magnetic resistance so the magnetic field lines pass along the planes of the metal rather than through the air.

I hope this helped?


A-level physics does come in handy sometimes I guess!



Also shielded magnets rarely sound better than a comparable unsheilded magnet as they consist of two interacting fields - this inherantly loses the exponential flux density of a single magnet.

[planet10]

The little cans on the magnets of shielded speakers are there to act as a magnetic shunt over the magnet+the bucking magnet glued to it.

One can add a bucking magnet (or build a bi-pole with the two drivers magnet-to-magnet). This tends to lower the Qts because more of the field is concentrated in the gap.

I don't know really how well mu-metal works in this situation (be easy enuff for me to do some experiments -- i have a whack of it for sale http://www.diyaudio.com/forums/showt...=&postid=50348. It has been suggested that shielding the TV would be more effective than shielding the speaker.

I'll do some experiments and get back.

dave

[thylantyr]

I'm going to use the mu sheilding metal and line the chambers
for my design. Once I picked the drivers that I like there is
no going back.. catch 22....

[feke67]

Planet10 & others! Thanks for the replies.

Please post findings after experiments.

Thanks,

feke67

[Lligior]

How did the shielding project go? I think I'm in the same boat here, need to shield some speakers the didn't come that way.