It's a bizarre idea.
I'm wondering how much weight a speaker cone facing up could lift and hold steady in a position along its xmax? Is there a way to figure this out - ballpark - without actually purchasing a driver and doing an empirical test?
Some car audio sub drivers have incredible claimed power handling ratings. (While I'm sure this is for reciprocating motion and would be significantly downgraded in a static condition - that's a noted detail) Let's say I have a $50, 6" unit with dual 2 ohm VCs; I put 12V DC across each for a total VC dissipation of 144 Watts. Specs says certified @ 250 continuous RMS, VC temperature up to 180C, 4 layer copper VC, etc.
For how long would it hold a static force before exuding "that burning smell"? If I pulled cooling air into the VC gap through the pole piece vent (like the big mechanical shaker tables do)?
I'm mostly interested in figuring the force in lbs that a VC motor can push/pull, from ordinary audio params, such as db SPL / Watt. If its even possible to do so.
If not, guess I'll just have to buy it and see for myself, but I thought I'd ask first. Maybe worth considering just for the thought exercise 😀
Thanks,
I'm wondering how much weight a speaker cone facing up could lift and hold steady in a position along its xmax? Is there a way to figure this out - ballpark - without actually purchasing a driver and doing an empirical test?
Some car audio sub drivers have incredible claimed power handling ratings. (While I'm sure this is for reciprocating motion and would be significantly downgraded in a static condition - that's a noted detail) Let's say I have a $50, 6" unit with dual 2 ohm VCs; I put 12V DC across each for a total VC dissipation of 144 Watts. Specs says certified @ 250 continuous RMS, VC temperature up to 180C, 4 layer copper VC, etc.
For how long would it hold a static force before exuding "that burning smell"? If I pulled cooling air into the VC gap through the pole piece vent (like the big mechanical shaker tables do)?
I'm mostly interested in figuring the force in lbs that a VC motor can push/pull, from ordinary audio params, such as db SPL / Watt. If its even possible to do so.
If not, guess I'll just have to buy it and see for myself, but I thought I'd ask first. Maybe worth considering just for the thought exercise 😀
Thanks,
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Joe,
For fun, I have used woofers to lift their own (25+ pound) weight and launch golf balls.
Some guys would just get a cheaper solenoid rated for the weight to push or pull loads ;^).
1) Depends on the weight distribution on the cone/voice coil, if not evenly distributed, very little weight could easily punch through a light cone, but if distributed evenly around the coil, hundreds of pounds of weight could be supported.
2) Well, if by ballpark, you mean +/- 12 dB or so, yes.
3) Ballpark, 15 seconds for an open-air "250 watt" speaker stalled at 144 watts DC before "that burning smell".
4) How many watts does the blower draw in addition to the voice coil?
5) 144 watts can produce 106.21 foot-pounds-force per second before heat losses are considered.
Art
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Art,
Thanks, I appreciate your reply. Fortunately the driver has a "BL" parameter specified @ ~18T. From the Eminence site;
"Expressed in Tesla meters, this is a measurement of the motor strength of a speaker. Think of this as how good a weightlifter the transducer is. A measured mass is applied to the cone forcing it back while the current required for the motor to force the mass back is measured. The formula is mass in grams divided by the current in amperes. A high BL figure indicates a very strong transducer...
So I assume it'll "lift" 18 grams 1 Meter with an amp of current. Let's say Xmax (not given...) is 5mm. So instead of 18 grams for a meter, you can have 3600 grams for 5mm? Or if you load 8 lbs onto the cone, it'll push it up 5mm with 1A current? 5A gets you 40 lbs of force through this small distance?
Is my thinking anywhere near what's really happening with this BL parameter? Just trying to understand.
Thanks,
Thanks, I appreciate your reply. Fortunately the driver has a "BL" parameter specified @ ~18T. From the Eminence site;
"Expressed in Tesla meters, this is a measurement of the motor strength of a speaker. Think of this as how good a weightlifter the transducer is. A measured mass is applied to the cone forcing it back while the current required for the motor to force the mass back is measured. The formula is mass in grams divided by the current in amperes. A high BL figure indicates a very strong transducer...
So I assume it'll "lift" 18 grams 1 Meter with an amp of current. Let's say Xmax (not given...) is 5mm. So instead of 18 grams for a meter, you can have 3600 grams for 5mm? Or if you load 8 lbs onto the cone, it'll push it up 5mm with 1A current? 5A gets you 40 lbs of force through this small distance?
Is my thinking anywhere near what's really happening with this BL parameter? Just trying to understand.
Thanks,
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Yes almost, multiply Bl * I = Newtons
1. The DC current is U/Re, higher than normal.
2. Cms (compliance) * N gives you the excursion in mm without additional weights
with 12V and Re= 3 ohm 4*18 = 72N; 72*0.3 = 21.6mm
The coil will crash against the pole plate with more than 1A or 3V, which is only 3 Watts.
Didn't look up the datasheet just ballpark figures to demonstrate
1. The DC current is U/Re, higher than normal.
2. Cms (compliance) * N gives you the excursion in mm without additional weights
with 12V and Re= 3 ohm 4*18 = 72N; 72*0.3 = 21.6mm
The coil will crash against the pole plate with more than 1A or 3V, which is only 3 Watts.
Didn't look up the datasheet just ballpark figures to demonstrate
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I guess not; I gathered from elsewhere on DIYA;
BL=B x L (Tesla x meter)
where
B = strength of magnetic field
L = length of voice coil wire
@bansuri, so using my BL ~ 18 and, say, 5A current I'd get 90 Newtons, which is 20lbs. The particular driver I'm looking at weighs 10 lbs, so it could easily "lift itself" (not that this is a goal...only jives with what Art said he did with woofers) with a couple-few amps of VC current.
The driver has a Cms of ~138 mm / N, so with 1 amp (138*1*18) it should move about 2500mm against its own "spring" force. 2.5 meters seems ridiculous, so I'm lost.
Perhaps an easier way to measure force would be to use pressure, or psi. Assume the cone is sealed and have it push pressure into a small sealed box, with a pressure gauge to monitor the interior pressure.
If the cone is ~ 5" diameter, that's about 20 sq in and if I'm pushing 20 lbs of force from 5 A of VC current - and dont run out of X displacement compressing the air in the box - I should read ~1 psi. I think... I mention this only because it seems less messy than trying to load 20 lbs uniformly onto a 5" speaker cone, without warping or breaking it.
BL=B x L (Tesla x meter)
where
B = strength of magnetic field
L = length of voice coil wire
@bansuri, so using my BL ~ 18 and, say, 5A current I'd get 90 Newtons, which is 20lbs. The particular driver I'm looking at weighs 10 lbs, so it could easily "lift itself" (not that this is a goal...only jives with what Art said he did with woofers) with a couple-few amps of VC current.
The driver has a Cms of ~138 mm / N, so with 1 amp (138*1*18) it should move about 2500mm against its own "spring" force. 2.5 meters seems ridiculous, so I'm lost.
Perhaps an easier way to measure force would be to use pressure, or psi. Assume the cone is sealed and have it push pressure into a small sealed box, with a pressure gauge to monitor the interior pressure.
If the cone is ~ 5" diameter, that's about 20 sq in and if I'm pushing 20 lbs of force from 5 A of VC current - and dont run out of X displacement compressing the air in the box - I should read ~1 psi. I think... I mention this only because it seems less messy than trying to load 20 lbs uniformly onto a 5" speaker cone, without warping or breaking it.