For my GAYA2 upgrade with Purifi drivers, i have an opportunity (technically) to support the midrange PPTT4.0M80-NAC04 by its magnet against a pretty massive part of the cabinet. The top 30cm is filled with a stack of MDF layers with a small cavity of some 4.7 liters . This will be filled with pertinax sheet and epoxy, to be reduced to 1.2liters.
The wall of the cabinet (110cm high) is made of thin layers of pertinax (hartpapier) glued with epoxy. Again heavy, stiff and curved, the horizontal crossection is an ellips. The baffle is made of ticker layers of pertinax, with cld layer in between(also in the enclosure wall).
Massive enough to consider it vibrationally dead. So perfect to mount the magnet against.
The basketframe of the driver will then be mounted with some resilience and vibration absorption putty to both relieve the basket from stress and damp resonances in the basket.
But the driver mounting itself will be difficult. Interesting challenge, the question is: is it worthwhile to do. And if so what benefits to expect?
Has anyone gone into this rabbithole?
And what are the results?
The wall of the cabinet (110cm high) is made of thin layers of pertinax (hartpapier) glued with epoxy. Again heavy, stiff and curved, the horizontal crossection is an ellips. The baffle is made of ticker layers of pertinax, with cld layer in between(also in the enclosure wall).
Massive enough to consider it vibrationally dead. So perfect to mount the magnet against.
The basketframe of the driver will then be mounted with some resilience and vibration absorption putty to both relieve the basket from stress and damp resonances in the basket.
But the driver mounting itself will be difficult. Interesting challenge, the question is: is it worthwhile to do. And if so what benefits to expect?
Has anyone gone into this rabbithole?
And what are the results?
Linkwitz did so…
https://www.linkwitzlab.com/orion-WA-kit-assembly.pdf
This was discussed some time ago (found the thread while looking for linkwitz‘s research report,which I havent found…)
This is it: https://www.linkwitzlab.com/frontiers_2.htm#N
https://www.diyaudio.com/community/threads/mounting-a-woofer-by-the-magnet.56284/
https://www.linkwitzlab.com/orion-WA-kit-assembly.pdf
This was discussed some time ago (found the thread while looking for linkwitz‘s research report,
This is it: https://www.linkwitzlab.com/frontiers_2.htm#N
https://www.diyaudio.com/community/threads/mounting-a-woofer-by-the-magnet.56284/
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Hi, best way to have a grip on the magnet might be similar to lathe chuck, at least thats how the parts were held when machining 
There is always the problem how to attach everything inside the cabinet. Either have the chuck tightening screw access outside, or a latch door you can open to reach inside. Or, perhaps have a bolt sticking out back of the cabinet and tapped hole on the chuck and you'd screw in the driver basically, except now all your wiring is spun around the driver
It's interesting. problem, and makes sense techically as allenb says.
There is always the problem how to attach everything inside the cabinet. Either have the chuck tightening screw access outside, or a latch door you can open to reach inside. Or, perhaps have a bolt sticking out back of the cabinet and tapped hole on the chuck and you'd screw in the driver basically, except now all your wiring is spun around the driver It's interesting. problem, and makes sense techically as allenb says.
easiest way to brace the magnet is to place a plywood partition web at the centerline with a cutout for the basket and size it so the edge snugs up against the back of the magnet when you fasten the driver to the baffle. I put a thin (like 1mm) pad of EPDM on the wood to cushion. if the pole is vented make a relief cut to let it breathe.
The stack of MDF is massive, but if we assume a connection with the magnet, the magnet movement will not sense the entire mass. MDF is a bit soft.
On the contrary if i use pertinax, almost twice the mass of MDF and much stiffer , also troughout the thickness.
That is my idea to fill the cavity (in order to reduce the volume) with pertinax glued with an epoxy of ~ same young's modulus, i create a stiff mass.
The weight of the MDF stack and the pertinax filling weighs about 25-30kg, the magnet an assumed 1 kg, so should provide a ground to the magnet.
How the energy (sound waves) will travel through the mass and how much will return to the magnet, is an unknown, nor the amount of damping during the travel. I can add a special cld in the pertinax layers (it is ment for stiff constuctions). this should also absorb some of the energy.
all this not easy to make a choice, as a ground rule still applies: there are always resonances.
The magnet -2- basket mounting of PURIFI drivers has a isolation/damping layer in between. So if i mount the magnet perhaps with some stiff damping in between, and the basket to the baffle with say per bolt soft washers below and on top of the rim, and a damping putty under the rest of the rim, the basket should be well damped.
Anyhow, not an easy challenge ;-)
On my cheep Omni speakers I used car coaxial drivers, removed the tweeter and used the mounting holes for the tweeter (that goes through the main driver magnet) to mount a 4.5 kg lump of cast iron. On my current WAW I've used a lump of cast iron spring loaded against the magnet of the BG 17 main drivers, there is a small ball bearing that locates in a simple on the driver and a matching dimple on the cast iron. I've also used bits of foam between the magnet and internal structure to dampen vibration. I think Eclipse use the idea of mounting by the magnet on their TD range of speakers.
The fitting was more stable and rigid, as opposed to the regular method, which allowed slight rocking of the driver when perturbed by hand. Ultimately, I decided to keep the magnet support as the horn was not very strong. The compression driver was a bit heavy, as usual.
BTW, I got the idea here: https://www.audioheritage.org/vbulletin/showthread.php?18822-Compression-Drivers-Why-so-heavy
hi Jan,
yes it makes a lot of sense. the Newton forces of the motor originate here and should be terminated into something heavy and stiff that does not radiate acoustically. Our spk16 uses screws in the basket to the front panel but with a soft layer (rubber) between screws and frame. the yoke of the motor is pressed again the internal bracing with a thin layer of visco elastic material. This has worked really well.
cheers, Lars@Purifi
yes it makes a lot of sense. the Newton forces of the motor originate here and should be terminated into something heavy and stiff that does not radiate acoustically. Our spk16 uses screws in the basket to the front panel but with a soft layer (rubber) between screws and frame. the yoke of the motor is pressed again the internal bracing with a thin layer of visco elastic material. This has worked really well.
cheers, Lars@Purifi
Yes, one of the cases i found as well, however if i read thecimage and text correctly it prevents thecheavy magnet from sacking under itsxweight. It does nod provide axridgid support in the axial direction.
Interesting idea, I can see some potential. I can see a problem with using the springs or gravity, since the driver could theoretically jump against them in one direction and slam down again.
Yes, you have to pull the rod properly when you do the mounting.
Or use something like this company makes.....Non ferrous springs.
https://www.airedalesprings.co.uk/blog/non-ferrous-materials-in-spring-manufacturing/#0
But for me this is the only "real good" way to get rid of the screws, and still have a solid mounting for woofers.
Regards John
I think the speaker frame will act as a brace in the cabinet, making it even more rigid, so that's probably going to be a good thing to secure the magnet too.
If you feel it worthwhile I'd also look at some absorbant pads on the inside of the basket, to damp out backwaves reflecting back out the front. Probably that will damp down some frequency peaks - but that's a different subject. It's a shame manufacturers don't include some relief in the frame pressings, to allow sound to escape through the back more easily, some type of curved or twisted pressing on the main frame bits would make a positive difference IMO.
If you feel it worthwhile I'd also look at some absorbant pads on the inside of the basket, to damp out backwaves reflecting back out the front. Probably that will damp down some frequency peaks - but that's a different subject. It's a shame manufacturers don't include some relief in the frame pressings, to allow sound to escape through the back more easily, some type of curved or twisted pressing on the main frame bits would make a positive difference IMO.
