Recommendations for a magnetically shielded subwoofer?

[TheRealOC]

Morning all

I'm just building out a gaming office (Picture 1) and knocked a hole in the TV wall, to fit an old-school CRT. When it's finished, it will look like a more symmetrical version of the room in Picture 2 - with the CRT living in the back box. The flatscreen will be mounted on a piece of plywood, and the plywood will be attached to to a barn-door sliding kit mounted in front of the CRT. So when I want to use the CRT, I can just grab the flatscreen TV and slide it over to the right.

The problem with setting up a surround setup in this room - is that speakers that sit anywhere near the older CRT have to be magnetically shielded, otherwise they will cause distortion on the screen, and cause long-term damage. And sometimes speakers that are listed as magnetically shielded in their specs sheet can still have this effect (in Picture 4).

I found two front speakers and a centre speaker from Ascend Acoustics that sound pretty decent for the money and are confirmed as bona fide magnetically shielded. Unfortunately I wasn't able to find a magnetically-shielded subwoofer. I could move a regular subwoofer to the opposite side of the room under the rear speakers, but would prefer not to.

Grateful if anyone has any recommendations for magnetically-shielded subwoofers? Thanks!

 

[Swerd]

I don't think I ever saw a magnetically shielded sub-woofer. But I never looked for one.

The old rule of thumb for unshielded loudspeakers was to keep them at least 1½' away from a CRT TV. How difficult would it be to keep a sub-woofer about 2' away?

 

[BoredSysAdmin]

That's unusual. I am guessing you want to use CRT specifically for vintage gaming consoles?

 

[shadyJ]

Speaker magnets have to be pretty close to CRTs to distort the image, so it might not be a problem so long as you aren't placing the sub right next to the TV. I have also never seen a subwoofer driver with a bucking magnet or magnetic shielding. I doubt that you will be able to find one on any powered subwoofer.

 

[-Jim-]

Morning all

I'm just building out a gaming office (Picture 1) and knocked a hole in the TV wall, to fit an old-school CRT. When it's finished, it will look like a more symmetrical version of the room in Picture 2 - with the CRT living in the back box. The flatscreen will be mounted on a piece of plywood, and the plywood will be attached to to a barn-door sliding kit mounted in front of the CRT. So when I want to use the CRT, I can just grab the flatscreen TV and slide it over to the right.

View attachment 60030


View attachment 60029

The problem with setting up a surround setup in this room - is that speakers that sit anywhere near the older CRT have to be magnetically shielded, otherwise they will cause distortion on the screen, and cause long-term damage. And sometimes speakers that are listed as magnetically shielded in their specs sheet can still have this effect (in Picture 4).

View attachment 60031

I found two front speakers and a centre speaker from Ascend Acoustics that sound pretty decent for the money and are confirmed as bona fide magnetically shielded. Unfortunately I wasn't able to find a magnetically-shielded subwoofer. I could move a regular subwoofer to the opposite side of the room under the rear speakers, but would prefer not to.

Grateful if anyone has any recommendations for magnetically-shielded subwoofers? Thanks!

Wow You must be very keen to do all than to use a CRT! I too have never seen a magnetically shielded Sub. I expect putting it towards a corner - even if you use a built in - would suffice. Please keep us posted with photos of your progress. Thanks.

 

[TheRealOC]

I don't think I ever saw a magnetically shielded sub-woofer. But I never looked for one.

The old rule of thumb for unshielded loudspeakers was to keep them at least 1½' away from a CRT TV. How difficult would it be to keep a sub-woofer about 2' away?

That wouldn't be too difficult! The other problem, which I forgot to mention in the OP, is that the unshielded sub could still be damaging the CRT even if the distortion isn't visible to the naked eye straightaway. Bob from RetroRGB (the gentleman in the screengrab) did some additional testing where he moved the subwoofer incrementally closer to the CRT, and took a bunch of photos at each stage with some kind of high speed camera, concluding that the safest thing was to stick the sub on the opposite side of the room (under the rears).

 

[TheRealOC]

That's unusual. I am guessing you want to use CRT specifically for vintage gaming consoles?

Yup! I'm a bit of a light gun addict I built up that back box so that the center of the screen should land close to my shoulder height of my shooting arm. Should feel very similar to using a vintage arcade cabinet.

 

[TheRealOC]

Wow You must be very keen to do all than to use a CRT! I too have never seen a magnetically shielded Sub. I expect putting it towards a corner - even if you use a built in - would suffice. Please keep us posted with photos of your progress. Thanks.

I definitely will

 

[TheRealOC]

Speaker magnets have to be pretty close to CRTs to distort the image, so it might not be a problem so long as you aren't placing the sub right next to the TV. I have also never seen a subwoofer driver with a bucking magnet or magnetic shielding. I doubt that you will be able to find one on any powered subwoofer.

Just had a thought as I was reading this... surely vintage subwoofers from the 1980s up to the mid 2000s, which were designed to be used in home surround setups using a CRT, would have had some form of magnetic shielding? I have a cheap Panasonic home-theatre-in-a-box setup that was designed for 5 speakers to be hooked up to an active subwoofer, which was meant to be hooked up to a DVD player.

Maybe the vintage subwoofer market would be the way to go?

 

[j_garcia]

"Vintage" subs are usually dead or soon to die subs, definitely not the way to go. As mentioned, just keep it far enough away and it won't be an issue. Back when I had a CRT, I had 15" sub about 3 ft away with no issues.

 

[-Jim-]

Yup! I'm a bit of a light gun addict I built up that back box so that the center of the screen should land close to my shoulder height of my shooting arm. Should feel very similar to using a vintage arcade cabinet.

Time Crisis?

 

[Eppie]

I agree that 3' feet away on the floor should suffice. We don't usually recommend mini subwoofers, but this might be a good case for the SVS 3000 Micro or one of the small KEF subs but the cost will be much higher. There can be a fair bit of deep bass content in games, though, so I would lean towards something larger.

 

[lovinthehd]

I had looked for such a sub after seeing this thread, and did see a couple, including a Genelec 5040A as well as a Sony SA-WMSP85. I do remember placing a large sub near a RP CRT set I had for a while....it did cause an issue....but it was easy enough to reposition the sub, too.

 

[its phillip]

I've got no recommendations for a suitable sub but I'm glad to see a vintage gaming setup being built with a CRT. I also have a CRT for NES/SNES/PSX/PS2 gaming but I haven't hooked it up in years

 

[TLS Guy]

That wouldn't be too difficult! The other problem, which I forgot to mention in the OP, is that the unshielded sub could still be damaging the CRT even if the distortion isn't visible to the naked eye straightaway. Bob from RetroRGB (the gentleman in the screengrab) did some additional testing where he moved the subwoofer incrementally closer to the CRT, and took a bunch of photos at each stage with some kind of high speed camera, concluding that the safest thing was to stick the sub on the opposite side of the room (under the rears).

I think you are overblowing this. Back in the day I ran a Sony Trinitron TV with two speakers with powerful unshielded magnets right under the TV. It did no harm whatever.
I have always had trouble verifying this claim about magnets and CRTs and so have others. After all a CRT uses a yolk of powerful electro magnets to bend the the electron beam. I believe there was also an AC flood to the yolk coils on shutdown, to demagnetize, so it did not shut down with a magnetic field in place. All I can tell you is my experience.

Magnets of speaker anyway are strongly focused on the VC gap. Also the magnetic field dies with the square of the distance from the magnet. So if the speaker is moved from one foot away to two, the magnetic filed at the tube is reduced ten fold, and if you move it four feet, then it is reduced a hundred fold. So my advice is not to worry about this.

 

[TheRealOC]

I think you are overblowing this. Back in the day I ran a Sony Trinitron TV with two speakers with powerful unshielded magnets right under the TV. It did no harm whatever.
I have always had trouble verifying this claim about magnets and CRTs and so have others. After all a CRT uses a yolk of powerful electro magnets to bend the the electron beam. I believe there was also an AC flood to the yolk coils on shutdown, to demagnetize, so it did not shut down with a magnetic field in place. All I can tell you is my experience.

Magnets of speaker anyway are strongly focused on the VC gap. Also the magnetic field dies with the square of the distance from the magnet. So if the speaker is moved from one foot away to two, the magnetic filed at the tube is reduced ten fold, and if you move it four feet, then it is reduced a hundred fold. So my advice is not to worry about this.

It wouldn't be the first time I overanalysed something Seems the final outcome will most likely be getting an unshielded sub and keeping it at the rear of the room... but first I would like to make an effort to find a suitable shielded one, for a couple of reasons:

Obviously there's the convenience of being able to place it wherever in the room it sounds best, regardless of where the CRT is. Also, even if the chance of damaging the CRT with subwoofer magnets is low, it would be a big expense/effort to repair the damage in the event that it did happen (I only know one guy who can repair CRTs). And also, I've already gone to the effort of tracking down a magnetically shielded front pair (Ascend Acoustics CBM-170SE Bookshelf Monitor Pair) and centre speaker (Ascend Acoustics CMT-340SE2 Signature Series), so it would be great to have cohesion between the subwoofer and the existing speakers. (My AVR is a Yamaha Aventage RX-A2040 from 2015)

I think I've confirmed six relatively new subwoofers with magnetic shielding - @lovinthehd mentioned the Genelec 5040A and the Sony SA-WMSP85, and there's a bunch of Velodyne models (about 10-15 years old) that would also be magnetically shielded. What I'm unsure about is how well any of these would pair up with the Ascend Acoustics front left/right and centre in the room.

I definitely don't pretend to understand the specsheets of subwoofers when it comes to stuff like frequency response, SPL or nominal impedance etc etc, but this Audioholics article seems to suggest that there's no need to match your subwoofer to the rest of your speakers based on these specs anyway? With that in mind, maybe my best approach would be to get any affordable 12-inch* vented shielded subwoofer I can find, and try it out?

(*12-inch because the room is 8ft x 12 ft x 12 ft=1152 cubic feet, vented because it would be mainly used for movies and games)

 

[TLS Guy]

It wouldn't be the first time I overanalysed something Seems the final outcome will most likely be getting an unshielded sub and keeping it at the rear of the room... but first I would like to make an effort to find a suitable shielded one, for a couple of reasons:

Obviously there's the convenience of being able to place it wherever in the room it sounds best, regardless of where the CRT is. Also, even if the chance of damaging the CRT with subwoofer magnets is low, it would be a big expense/effort to repair the damage in the event that it did happen (I only know one guy who can repair CRTs). And also, I've already gone to the effort of tracking down a magnetically shielded front pair (Ascend Acoustics CBM-170SE Bookshelf Monitor Pair) and centre speaker (Ascend Acoustics CMT-340SE2 Signature Series), so it would be great to have cohesion between the subwoofer and the existing speakers. (My AVR is a Yamaha Aventage RX-A2040 from 2015)

I think I've confirmed six relatively new subwoofers with magnetic shielding - @lovinthehd mentioned the Genelec 5040A and the Sony SA-WMSP85, and there's a bunch of Velodyne models (about 10-15 years old) that would also be magnetically shielded. What I'm unsure about is how well any of these would pair up with the Ascend Acoustics front left/right and centre in the room.

I definitely don't pretend to understand the specsheets of subwoofers when it comes to stuff like frequency response, SPL or nominal impedance etc etc, but this Audioholics article seems to suggest that there's no need to match your subwoofer to the rest of your speakers based on these specs anyway? With that in mind, maybe my best approach would be to get any affordable 12-inch* vented shielded subwoofer I can find, and try it out?

(*12-inch because the room is 8ft x 12 ft x 12 ft=1152 cubic feet, vented because it would be mainly used for movies and games)

If you are that worried about it, then I would make your own shield. I would order a sub of your choice, not based on shielding and shroud the magnet is MuMetal.

That is what I would do.

Lastly, even if your tube should suffer from magnetism, they can be easily degaussed.

 

[Swerd]

It wouldn't be the first time I overanalysed something

I think you're not overanalyzing things, you've mis-analyzed it .

If you loose sleep over having an un-shielded sub-woofer, and MuMetal looks too costly, why not wrap a sub-woofer in aluminum foil? If you're clever enough, line the interior of the cabinet with foil. I recommend the heavy duty aluminum foil that comes in 18" wide rolls over the lighter foil in 12" wide rolls.

I briefly searched for foil wrapped sub-woofers, but only came up with this.

 

[TheRealOC]

Just a postscript to this topic - I did end up finding an awesome Yamaha magnetically shielded subwoofer, that would match the rest of the set, and going on a bit of an online odyssey to track one down (as alas they’re not being made anymore ).

Found a bunch of them for sale on the hifishark aggregator website but all of those auctions that it forward-linked to were on German and Polish online auction sites that really go out of their way to make international orders impossible (to the point where they blacklist German/Polish IP addresses used by NordVPN and Surfshark).

Then I finally found the subwoofer for sale new on Amazon India and Amazon UAE, but no luck there either. I did find reputable parcel forwarding services that provided virtual postal addresses in India and Dubai respectively (for forwarding onto Ireland). But alas high value electronics and specifically speakers are on their prohibited items list (ironically because they have magnets in them ).

So for now, I’m going to see if the magnetic shielding on this speaker makes any difference as far as its eligibility for international delivery goes, and if not, I’m gonna sit tight and see if it ever comes up for sale on proper eBay.

I remain cautiously optimistic…

 

[William Lemmerhirt]

If you are that worried about it, then I would make your own shield. I would order a sub of your choice, not based on shielding and shroud the magnet is MuMetal.

That is what I would do.

Lastly, even if your tube should suffer from magnetism, they can be easily degaussed.

Yes. This. Makes soooo much more sense.