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When did the dual-woofer trend catch on?
(Simon Byrnand) wrote:
(Nousaine) wrote in message ... Kalman Rubinson wrote: ...snip to content ...... Do two 6" drivers have the same bass output as a single 12", but with greater control, and thus more accuracy? Its a question of the total cone area assuming adequate driving motors. Two 8-inch drivers generally approximate the piston area of a 12-inch drivers. A pair of 6 or 6.5-inch drivers approximat the piston area of a single 10-inch. Well, not exactly. A couple of 8" woofers and 12" woofers I have which are fairly representitive of how much actual cone area you get from a nominal frame size give the following figures: 8" driver - actual cone diameter 16.5cm, so Sd = 213 cm^2. 12" driver - actual cone diameter 25cm, so Sd = 490 cm^2. So in this case it takes 2.3 8" woofers to equal 1 12" woofer, and thats not taking into acount differences in Xmax etc... I also conducted an experiment where I used 8,10,12 and 15-inch drivers of a given line of woofers. In this case the SPL capabilities were improved by 50% with each increment in nominal basket size. While Vd increased by 50% with a step up in basket a good share of the improvement came from increased Xmax that can be garnered with larger baskets. But there's more to it than cone area because Vd also depends on the Xmax (excursion) of the drivers as well which is a function of both motor and suspension stroke. Generally speaking, the geometry of a larger basket typically comes with a bigger motor and more suspension excursion. Yep, a point frequently overlooked. Also the fact that a 12" woofer in general is just plain built tougher and more rugged, including the suspension, and the voice coil etc... Other factors forgotten in the surface area comparision is the size of the magnets, and the Fs of the driver. Getting a low Fs is much harder with a smaller driver because the cones are so much lighter. Now you have your moving mass seperated into multiple drivers, EACH of which needs to try and obtain a low Fs rather than the total moving mass being concentrated in one driver and providing ONE low Fs. Equivilent surface area isn't much use if the resulting Fs is 20Hz higher  That depends on other system factors as well. So depending on the particular application a pair of 6-inch drivers may approximate the displacement of a single 10-inch but there's a fair amount of units that fall somewhat short of that capability. As mentioned better directivity control and thinner cabinets are the main advantages. Assuming that you believe that a narrower cabinet gives "better" directivity control, a moot point which is open for debate. What is "better" in this context ? In my opinion, "better" is not as wide a dispersion as possible at high frequencies, but rather trying as much as possible to obtain a constant directivity from 200Hz or so up, something which is worse on a narrow baffle, not better. I was referring to directivity matching near the upper crossover frequency. A 6.5-inch speaker has directivity more closely matched to a midrange or tweeter near the crossover frequency that an 8,10 or 12-inch driver. In the former case the possibility of staggering the operating ranges of multiple drivers and having one positioned close to the floor help control the 200-300 Hz "floor bounce" common to tower style speakers. Or, you could just do it properly and have a 3 way system with a 12" woofer close to the floor operating up to 300Hz, and not have floor bounce issues at all  Two small, highly positioned woofers are still going to give floor bounce problems, but now you have a couple of moderate dips at two frequencies, instead of one humngous notch at one frequency....neither very satisfactory outcomes... That, again is dependent on the given design. I wasn't advocating anything only suggesting why certain topologies gain favor. The only way to (almost completely) eliminate floor bounce cancellation is to have the woofer relatively close to the floor, and relatively large, to maximize the height differential between the floor and the top and bottom extremes of the woofer... Regards, Simon This is a good discussion. If there's anything we haven't covered I'd hope someone would question that. |
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#123
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When did the dual-woofer trend catch on?
(Simon Byrnand) wrote:
(Nousaine) wrote in message ... Kalman Rubinson wrote: ...snip to content ...... Do two 6" drivers have the same bass output as a single 12", but with greater control, and thus more accuracy? Its a question of the total cone area assuming adequate driving motors. Two 8-inch drivers generally approximate the piston area of a 12-inch drivers. A pair of 6 or 6.5-inch drivers approximat the piston area of a single 10-inch. Well, not exactly. A couple of 8" woofers and 12" woofers I have which are fairly representitive of how much actual cone area you get from a nominal frame size give the following figures: 8" driver - actual cone diameter 16.5cm, so Sd = 213 cm^2. 12" driver - actual cone diameter 25cm, so Sd = 490 cm^2. So in this case it takes 2.3 8" woofers to equal 1 12" woofer, and thats not taking into acount differences in Xmax etc... I also conducted an experiment where I used 8,10,12 and 15-inch drivers of a given line of woofers. In this case the SPL capabilities were improved by 50% with each increment in nominal basket size. While Vd increased by 50% with a step up in basket a good share of the improvement came from increased Xmax that can be garnered with larger baskets. But there's more to it than cone area because Vd also depends on the Xmax (excursion) of the drivers as well which is a function of both motor and suspension stroke. Generally speaking, the geometry of a larger basket typically comes with a bigger motor and more suspension excursion. Yep, a point frequently overlooked. Also the fact that a 12" woofer in general is just plain built tougher and more rugged, including the suspension, and the voice coil etc... Other factors forgotten in the surface area comparision is the size of the magnets, and the Fs of the driver. Getting a low Fs is much harder with a smaller driver because the cones are so much lighter. Now you have your moving mass seperated into multiple drivers, EACH of which needs to try and obtain a low Fs rather than the total moving mass being concentrated in one driver and providing ONE low Fs. Equivilent surface area isn't much use if the resulting Fs is 20Hz higher That depends on other system factors as well. So depending on the particular application a pair of 6-inch drivers may approximate the displacement of a single 10-inch but there's a fair amount of units that fall somewhat short of that capability. As mentioned better directivity control and thinner cabinets are the main advantages. Assuming that you believe that a narrower cabinet gives "better" directivity control, a moot point which is open for debate. What is "better" in this context ? In my opinion, "better" is not as wide a dispersion as possible at high frequencies, but rather trying as much as possible to obtain a constant directivity from 200Hz or so up, something which is worse on a narrow baffle, not better. I was referring to directivity matching near the upper crossover frequency. A 6.5-inch speaker has directivity more closely matched to a midrange or tweeter near the crossover frequency that an 8,10 or 12-inch driver. In the former case the possibility of staggering the operating ranges of multiple drivers and having one positioned close to the floor help control the 200-300 Hz "floor bounce" common to tower style speakers. Or, you could just do it properly and have a 3 way system with a 12" woofer close to the floor operating up to 300Hz, and not have floor bounce issues at all Two small, highly positioned woofers are still going to give floor bounce problems, but now you have a couple of moderate dips at two frequencies, instead of one humngous notch at one frequency....neither very satisfactory outcomes... That, again is dependent on the given design. I wasn't advocating anything only suggesting why certain topologies gain favor. The only way to (almost completely) eliminate floor bounce cancellation is to have the woofer relatively close to the floor, and relatively large, to maximize the height differential between the floor and the top and bottom extremes of the woofer... Regards, Simon This is a good discussion. If there's anything we haven't covered I'd hope someone would question that. |
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#124
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When did the dual-woofer trend catch on?
(Simon Byrnand) wrote:
(Nousaine) wrote in message ... Kalman Rubinson wrote: ...snip to content ...... Do two 6" drivers have the same bass output as a single 12", but with greater control, and thus more accuracy? Its a question of the total cone area assuming adequate driving motors. Two 8-inch drivers generally approximate the piston area of a 12-inch drivers. A pair of 6 or 6.5-inch drivers approximat the piston area of a single 10-inch. Well, not exactly. A couple of 8" woofers and 12" woofers I have which are fairly representitive of how much actual cone area you get from a nominal frame size give the following figures: 8" driver - actual cone diameter 16.5cm, so Sd = 213 cm^2. 12" driver - actual cone diameter 25cm, so Sd = 490 cm^2. So in this case it takes 2.3 8" woofers to equal 1 12" woofer, and thats not taking into acount differences in Xmax etc... I also conducted an experiment where I used 8,10,12 and 15-inch drivers of a given line of woofers. In this case the SPL capabilities were improved by 50% with each increment in nominal basket size. While Vd increased by 50% with a step up in basket a good share of the improvement came from increased Xmax that can be garnered with larger baskets. But there's more to it than cone area because Vd also depends on the Xmax (excursion) of the drivers as well which is a function of both motor and suspension stroke. Generally speaking, the geometry of a larger basket typically comes with a bigger motor and more suspension excursion. Yep, a point frequently overlooked. Also the fact that a 12" woofer in general is just plain built tougher and more rugged, including the suspension, and the voice coil etc... Other factors forgotten in the surface area comparision is the size of the magnets, and the Fs of the driver. Getting a low Fs is much harder with a smaller driver because the cones are so much lighter. Now you have your moving mass seperated into multiple drivers, EACH of which needs to try and obtain a low Fs rather than the total moving mass being concentrated in one driver and providing ONE low Fs. Equivilent surface area isn't much use if the resulting Fs is 20Hz higher That depends on other system factors as well. So depending on the particular application a pair of 6-inch drivers may approximate the displacement of a single 10-inch but there's a fair amount of units that fall somewhat short of that capability. As mentioned better directivity control and thinner cabinets are the main advantages. Assuming that you believe that a narrower cabinet gives "better" directivity control, a moot point which is open for debate. What is "better" in this context ? In my opinion, "better" is not as wide a dispersion as possible at high frequencies, but rather trying as much as possible to obtain a constant directivity from 200Hz or so up, something which is worse on a narrow baffle, not better. I was referring to directivity matching near the upper crossover frequency. A 6.5-inch speaker has directivity more closely matched to a midrange or tweeter near the crossover frequency that an 8,10 or 12-inch driver. In the former case the possibility of staggering the operating ranges of multiple drivers and having one positioned close to the floor help control the 200-300 Hz "floor bounce" common to tower style speakers. Or, you could just do it properly and have a 3 way system with a 12" woofer close to the floor operating up to 300Hz, and not have floor bounce issues at all Two small, highly positioned woofers are still going to give floor bounce problems, but now you have a couple of moderate dips at two frequencies, instead of one humngous notch at one frequency....neither very satisfactory outcomes... That, again is dependent on the given design. I wasn't advocating anything only suggesting why certain topologies gain favor. The only way to (almost completely) eliminate floor bounce cancellation is to have the woofer relatively close to the floor, and relatively large, to maximize the height differential between the floor and the top and bottom extremes of the woofer... Regards, Simon This is a good discussion. If there's anything we haven't covered I'd hope someone would question that. |
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