I have a hard constraint and I know not the best but it is what it is. When I surface mount a 5.5" woofer, the magnet will just about touch the back panel. The woofer has a pole vent in the center of the magnet. I'm thinking: place a thin high density foam donut the size of the magnet (donut hole in middle) to seal off the cabinet. Drill a hole in the back panel to allow the pole vent to vent to the outside. This should also help the speaker's thermals since it is getting air from the outside and the foam should help with any vibration and actually stiffen the back panel.
Any problems?
Thanks
scott
Any problems?
Thanks
scott
The first big problem is: how do you cope with the fact that is the CONE in the nearby of the surface, and the magnet is only a small concern.
Regarding that, I guess that is a matter of humidity and dust that may reach the back of the dustcap ( then distributing those bad particles around the voice coil and gap ), that's why the speaker should stay in a protected environment.
It's better to have a deep enclosure -FWIW as long as it is balanced with the various coefficients of velocity and frictions as the volumes of the boxes predicted by the Thiele & Small tables for alignements - than a "shallow" one : the air is compressed in between and the reaction ( bounce) makes the cone movement altered.
A deep hollow enclosure would have a different behavior -making the internal reflections negligible but provocking...a hollow sound !
Regarding that, I guess that is a matter of humidity and dust that may reach the back of the dustcap ( then distributing those bad particles around the voice coil and gap ), that's why the speaker should stay in a protected environment.
It's better to have a deep enclosure -FWIW as long as it is balanced with the various coefficients of velocity and frictions as the volumes of the boxes predicted by the Thiele & Small tables for alignements - than a "shallow" one : the air is compressed in between and the reaction ( bounce) makes the cone movement altered.
A deep hollow enclosure would have a different behavior -making the internal reflections negligible but provocking...a hollow sound !
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I see your point about having the pole piece vent to the outside world. It would improve thermal performance.
There are other considerations, though:
- wind noise
- T/S parameters
You'll have to make sure that whatever hole you drill will not whistle when bass comes along. A nice roundover should help, and make sure the hole is smooth and continuous with the pole vent.
The T/S parameters are derived with the magnet and cone sharing the same airspace.
I don't know exactly what will happen if you seperate the two, but it might not be good. The dustcap will effectively have its own bass reflex port, and it's entirely possible that air from the cone side could make it through the spider/voicecoil venting and out the pole vent, too.
If you go ahead, I'd recommend checking the impedance curve to make sure everything's behaving okay. Bonus if you can try it at a few different voltage drives.
Chris
There are other considerations, though:
- wind noise
- T/S parameters
You'll have to make sure that whatever hole you drill will not whistle when bass comes along. A nice roundover should help, and make sure the hole is smooth and continuous with the pole vent.
The T/S parameters are derived with the magnet and cone sharing the same airspace.
I don't know exactly what will happen if you seperate the two, but it might not be good. The dustcap will effectively have its own bass reflex port, and it's entirely possible that air from the cone side could make it through the spider/voicecoil venting and out the pole vent, too.
If you go ahead, I'd recommend checking the impedance curve to make sure everything's behaving okay. Bonus if you can try it at a few different voltage drives.
Chris
Are the cabinets already built? If they aren't built you could just remove material (using a router or chisel if you prefer hand tools and hard work) from the cabinet wall directly behind the magnet. If they are already built you could cutout the panel behind the magnet (using a hole saw, router, sabre or jigsaw, etc.) and then add another panel on top of the existing panel. This will increase the enclosure size but will also stiffen the rear wall and give some room for the pole vent to breathe.
Thanks you'll - very helpful hints. I should have mentioned that it is a 3.5" TB w3-2108 so maybe the size helps my situation.
With regards to:
1. Cone being close to the surface - I think you mean the side or back surface - It will be close to the back surface which might be a problem with back pressure
2. Dust = good point - maybe some kind of filter will help
3. good idea about how to make the hole.
4. The magnet and the cone will be in the same air space - Same as normal - just that the magnet's back will be touching the back panel (with some foam for vibration control) I'll check the impedance curve - good point.
5. This is going into a pre-existing unit. "cut a hole and add a panel behind" = Neat but how much space behind the magnet do I need to leave for the venting of the "pole?" It would only give me about 1/2" inch - Is that enough?
Thanks guys,
scott
With regards to:
1. Cone being close to the surface - I think you mean the side or back surface - It will be close to the back surface which might be a problem with back pressure
2. Dust = good point - maybe some kind of filter will help
3. good idea about how to make the hole.
4. The magnet and the cone will be in the same air space - Same as normal - just that the magnet's back will be touching the back panel (with some foam for vibration control) I'll check the impedance curve - good point.
5. This is going into a pre-existing unit. "cut a hole and add a panel behind" = Neat but how much space behind the magnet do I need to leave for the venting of the "pole?" It would only give me about 1/2" inch - Is that enough?
Thanks guys,
scott
1) most (all?) forget that there already is a hole in that pole`piece so its influence, if any at all in the TS parameters is already included in them, since it was there when they were measured.
2) there is some possibility of dust and debris getting near the VC, but in every vented pole speaker I have ever seen, that is also taken care of, by small foam or felt plug and in many cases a grid covering it.
Or a cloth disk glued to the magnet.
3) if anything, the foam plug is a problem in itself, because after 10 or 20 years it disintegrates and gooey particles *can* fly inside.
4) you can add a rubber/cork/foam disk between magnet and back panel, mainly to guard against possible rattling, for peace of mind cut a few radial slits to let the polepiece vent "breathe" inside the cabinet, no need to vent it outside and much safer.
5) no big deal in getting cone near the backpanel, it´s not that near anyway, plus it´s inevitable , so, why worry 🙂 ?
And in fact magnet thickness is between them, the cone is .... ummmm ..... "conical" so there is even more free space between it and back panel ..... so don´t worry 🙂
2) there is some possibility of dust and debris getting near the VC, but in every vented pole speaker I have ever seen, that is also taken care of, by small foam or felt plug and in many cases a grid covering it.
Or a cloth disk glued to the magnet.
3) if anything, the foam plug is a problem in itself, because after 10 or 20 years it disintegrates and gooey particles *can* fly inside.
4) you can add a rubber/cork/foam disk between magnet and back panel, mainly to guard against possible rattling, for peace of mind cut a few radial slits to let the polepiece vent "breathe" inside the cabinet, no need to vent it outside and much safer.
5) no big deal in getting cone near the backpanel, it´s not that near anyway, plus it´s inevitable , so, why worry 🙂 ?
And in fact magnet thickness is between them, the cone is .... ummmm ..... "conical" so there is even more free space between it and back panel ..... so don´t worry 🙂
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Thanks - I hadn't thought about # 4 since there is about 1/8" between the magnet and the back panel which is the size of the foam. So I think I will glue 4 small pieces of foam on the magnet which will allow air to move between the very small foam pieces Plus I will cover the hole with some type of filter.
thanks
thanks
Not if they were measured with the delta-compliance method.
I suspect it'll be fine, but see my post further up the page for reasons it might not be 100% according to simulation.
Chris
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