roy@alanine.phri.nyu.edu (Roy Smith) (10/16/90)
I want to put a pair of speakers on my boat, for a stereo.
Unfortunately, the place where the speakers should go is within a couple of
feet of the compass, so anything magnetic is bad. Are there speakers which
do not generate any magnetic fields? They should be weatherproof too.
--
Roy Smith, Public Health Research Institute
455 First Avenue, New York, NY 10016
roy@alanine.phri.nyu.edu -OR- {att,cmcl2,rutgers,hombre}!phri!roy
"Arcane? Did you say arcane? It wouldn't be Unix if it wasn't arcane!"jws@thumper.mlb.semi.harris.com (James W. Swonger) (10/17/90)
You can get piezo tweeters, which are about as non-magnetic as you can get - aside from the fields generated by the drive current. For the woofers you are in a bit of a jam - most get their punch from a big cone and a big magnet. However, since the bass component of sound is pretty non-directional (the wavelength being long) you might get satisfactory results by mounting the piezo tweeters in your planned location and the woofer(s) in a remote spot. I have a 6" polysomethingorother woofer I got at the Shack a few years ago which looks like it would do OK if the backside were protected (w.r.t. the salt spray problem). Maybe you can find a location that will not interfere with the compass. Another possibility: to try and contain the flux from the speaker magnet somehow. You might be able to cob up a flux return path as part of the enclosure that would suck up the stray flux and feed it back to the poles.
frank@ulticorp.UUCP (Frank Cannavale III/1024000) (10/18/90)
In article <1990Oct16.140417.15202@phri.nyu.edu> roy@alanine.phri.nyu.edu (Roy Smith) writes: > I want to put a pair of speakers on my boat, for a stereo. >Unfortunately, the place where the speakers should go is within a couple of >feet of the compass, so anything magnetic is bad. Are there speakers which >do not generate any magnetic fields? They should be weatherproof too. So sorry, but no. Most speakers are basically electric motors. Linear motors rather than rotational motors you are familiar with. Usually there's a permanent magnet fixed by a frame. A coil of wire is attached to the speaker cone. As alternating current (from the stereo) is feed to the coil, it produces a varying magnetic field that is alternatively attracted or repulsed from the PM. That's about it. There are some rather exotic alternatives. The first that comes to mind is electo-static. Usually a charged membrane with a grid placed near it. The amplifier feeds a transformer that steps the voltage up. The voltage potential causes the charged membrane to be attracted and repulsed from the grid. Very expensive for full range speakers. Also very large. The Accoustats <sp?> I saw were 2x8 feet each! (and a few grand too) The 1x8 model did not generate much bass and required a sub-woofer. This speaker type is not useful on a boat. (Makes a good tweeter only though.) The second alternative (I'm really fuzzy on this one) used a hot wire to drive a cloud of electrons off. The electrons were moved by using a high voltage charge. That explanation does not make much sense to me either, I just don't remember the technique very well. Basically, pick another location. Sony and Babs make ok marine type speakers. I have the Sony's and an Alpine car stereo on my boat. They are ok, but not as good as, say ADS or Boston Acoustics car stereo speakers. -- Frank Cannavale III !uunet!ulticorp!frank The Ultimate Corp, E. Hanover, NJ "Yes, you can afford the Trojan 12 Meter that is fiscally irresponsible for you to buy. And I'm not talking about loans here. Banks suck, forget about banks." ... "Technically, if the bank owns the boat, then it owns the bilge, and who wants to wipe his banker's bilge?" - Berkeley "Bonefish" Breathed
clark@juggle.gg.caltech.edu (Clark Brooks) (10/19/90)
In <410@ulticorp.UUCP> frank@ulticorp.UUCP (Frank Cannavale III/1024000) writes: >In article <1990Oct16.140417.15202@phri.nyu.edu> roy@alanine.phri.nyu.edu (Roy Smith) writes: >> I want to put a pair of speakers on my boat, for a stereo. >>Unfortunately, the place where the speakers should go is within a couple of >>feet of the compass, so anything magnetic is bad. Are there speakers which >>do not generate any magnetic fields? They should be weatherproof too. >There are some rather exotic alternatives. The first that comes to >mind is electo-static. Usually a charged membrane with a grid placed ... >sub-woofer. This speaker type is not useful on a boat. (Makes a >good tweeter only though.) The second alternative (I'm really fuzzy on ... Frank overlooks the fact that woofer placement is not so important to sound quality. Electrostatic tweeters where you want them, and a woofer anywhere might solve your problem. Paranoia recommends shielded speaker cables. You don't say how much weather these speakers will get... -- clark@csvax.cs.caltech.edu Neuro-linguistic programming is simply the zig-zag and swirl of menorgs and disorgs acting under the suction and pressure of the morphogenetic field.
mhughes@loft386.uucp (Mike Hughes) (10/19/90)
In article <1990Oct16.140417.15202@phri.nyu.edu>, roy@alanine.phri.nyu.edu (Roy Smith) writes: > > Unfortunately, the place where the speakers should go is within a couple of > feet of the compass, so anything magnetic is bad. Are there speakers which > -- Electrostatic speakers do not have magnets, but they have to be quite large to have any base response. They are also very expensive and require high-voltage power supplys. The MagnaPlaner brand of speaker is not electrostatic and does have magnets. Piezo tweeters don't have magnets, but most of those I have seen reproduce only very high frequencies. I think you must get the things away from the compass! You might consider free standing speakers which could be hung on brackets. This would also let you get them out of the weather. I'm not sure any worthwhile speakers can really stand to live in the cockpit. I just leave the hatch open and keep the stereo below. -- Mike Hughes Lofty Pursuits (Public Access for Rapid City SD USA) bigtex!loft386!mhughes
lstowell@pyrnova.pyramid.com (Lon Stowell) (10/19/90)
>In article <1990Oct16.140417.15202@phri.nyu.edu> roy@alanine.phri.nyu.edu (Roy Smith) writes: > >There are some rather exotic alternatives. The first that comes to >mind is electo-static. Usually a charged membrane with a grid placed These do create magnetic fields...as does any transformer or other moving electrical field. You may wish to try some of the SHIELDED speakers advertised for placement next to color TV's which don't much care for magnetic fields either..... These plus just a few feet of distance should keep from affecting your compass... An irreverent suggestion is to kill the music when you want to use the compass....besides haven't seen ANY boat compass that is so accurate that a simple speaker would seriously affect navigation.....if you need that kind of precision use a gyro..
jfh@netcom.UUCP (Jack Hamilton) (10/19/90)
Speakers also cause problems with the pictures on TV sets if they are too close (the magnets pull on the electrons and cause the picture to smear). Boston (and probably other manufacturers too) makes special speakers which have magnetic shielding. I think they use something called "mu metal". I don't know whether those speakers are sufficiently shielded to use on boats. -- Jack Hamilton jfh@netcom.uucp or netcom!jfh@apple.com
witters@tc.fluke.COM (John Witters) (10/25/90)
In article <1990Oct16.140417.15202@phri.nyu.edu> roy@alanine.phri.nyu.edu (Roy Smith) writes: > > I want to put a pair of speakers on my boat, for a stereo. >Unfortunately, the place where the speakers should go is within a couple of >feet of the compass, so anything magnetic is bad. Are there speakers which >do not generate any magnetic fields? They should be weatherproof too. How about using speakers that are designed to be placed next to television sets for TV stereo sound? These have some magnetic shielding to keep the TV picture from getting messed up. Of course, the shielding may not be good enough to keep your compass from being affected. I doubt that many of these are weatherproof too. Anyway, Radio Shack used to sell speakers that were designed to be used near TV sets. You could also try posting your request to rec.video or rec.arts.tv. -John -- * * * John Witters voice: (206) 356-5274 * \ * John Fluke Mfg. Co. Inc. * \ * P.O.B. 9090 M/S 241F fax: (206) 356-5116 * DRIVING * Everett, Washington 98206-9090 or (206) 356-5174 * \ * * \ * domain: witters@tc.fluke.COM * * * uucp: {sun,microsoft,uw-beaver}!fluke!witters
whit@milton.u.washington.edu (John Whitmore) (10/25/90)
In article <1990Oct16.140417.15202@phri.nyu.edu> roy@alanine.phri.nyu.edu (Roy Smith) writes: > > I want to put a pair of speakers on my boat, for a stereo. >Unfortunately, the place where the speakers should go is within a couple of >feet of the compass, so anything magnetic is bad. Are there speakers which >do not generate any magnetic fields? There are piezoelectric tweeters (which have no magnet), but basically all woofers are magnet-based. So what? You only care about the field far from the speaker, right? Most magnet designs for speakers are self-shielding. The leaking magnetic field at 2ft distance is typically a third to a tenth of the Earth's field (I'm not guessing; I got a gaussmeter and checked a couple of speakers). If you find a well-designed woofer, it could have even less field at a distance. Try visiting a store with a compass in hand. Find a patient salesman and orient a speaker various directions (twist it on a wooden stool or chair) while you watch the compass (preferably 2 ft. due East or West of the speaker) for fluctuations. If you find a speaker which doesn't move the needle, buy it. If you find a speaker which only moves the needle a small amount (a degree?), buy it and BOLT IT DOWN before you install and trim the boat compass. Most good compasses have enough trim capability for such minor variations. The magnet is a PERMANENT magnet, so the field shouldn't change while the speaker is kept in place. John Whitmore whit@milton.u.washington.edu
phys169@canterbury.ac.nz (10/31/90)
In article <9878@milton.u.washington.edu>, whit@milton.u.washington.edu (John Whitmore) writes: > There are piezoelectric tweeters (which have no magnet), but > basically all woofers are magnet-based. I think Quad electrostatic speakers cover the full range without magnets, and I seem to recall Inophone (or something like that) producing not just tweeters. Somebody may be able to confirm this. Anyway, there are sure to be work-arounds, e.g. wearing headphones :-). Mark Aitchison, University of Canterbury, New Zealand.