by Jonathan » Mon Apr 18, 2005 4:49 pm
Just because you have a low inductance 15" sub doesn't mean it will sound good at higher frequencies, though. Size makes a difference, from both a mass and a physical size standpoint, it has more to do with resonance and the drivers damping, affecting the frequency response. Added mass is much harder to control than a smaller moving mass, requiring more suspension and generally resulting in more overthrow. With a physically larger driver, you have a higher chance of standing waves since at those frequencies the cone isn't moving as much as a homogenous unit. At these frequencies, you'd do best to think of the sound wave as starting at the base of the cone (at the voice-coil former/cone joint) and propagating outward towards the edge of the cone. When the wave hits the edge of the cone, it is reflected back toward the base of the cone (towards the voice-coil former). When the wave hits the voice-coil former, it is again reflected back towards the edge of the cone, and the whole process starts again. In both situations, significant standing waves result, and these standing waves can produce really, really huge peaks and dips in the response of a driver unless steps are taken to counteract it, but it occurs with all drivers, even $75000 home drivers. The larger the driver, the lower in frequency this occurs at, which is why 15" drivers aren't renowned for higher frequencies, even those with lower inductance. Even on Adire Audio's PDF about woofer speed when they added mass and decreased inductance of a driver and compared it to a lower mass higher inductance driver, while the lower inductance driver was capable of playing a higher frequency, the driver had nastier peaks and dips in the frequency response compared to the low mass driver. Add a lower frequency where standing waves occur, and you have a pretty rough sounding driver at that frequency. Adire was proving that higher inductance affects frequency response, not that mass or size didn't make a difference. If mass wasn't an issue at all, I would think that Adire would be using heavier cones (like metal) and rubber surrounds.
Of course, though, on top of that, 15" subs are generally built more for SPL than their 12" and 10" counterparts, so you'll also get higher inductance coils due to the longer throw the drivers are built for.
Just because you have a low inductance 15" sub doesn't mean it will sound good at higher frequencies, though. Size makes a difference, from both a mass and a physical size standpoint, it has more to do with resonance and the drivers damping, affecting the frequency response. Added mass is much harder to control than a smaller moving mass, requiring more suspension and generally resulting in more overthrow. With a physically larger driver, you have a higher chance of standing waves since at those frequencies the cone isn't moving as much as a homogenous unit. At these frequencies, you'd do best to think of the sound wave as starting at the base of the cone (at the voice-coil former/cone joint) and propagating outward towards the edge of the cone. When the wave hits the edge of the cone, it is reflected back toward the base of the cone (towards the voice-coil former). When the wave hits the voice-coil former, it is again reflected back towards the edge of the cone, and the whole process starts again. In both situations, significant standing waves result, and these standing waves can produce really, really huge peaks and dips in the response of a driver unless steps are taken to counteract it, but it occurs with all drivers, even $75000 home drivers. The larger the driver, the lower in frequency this occurs at, which is why 15" drivers aren't renowned for higher frequencies, even those with lower inductance. Even on Adire Audio's PDF about woofer speed when they added mass and decreased inductance of a driver and compared it to a lower mass higher inductance driver, while the lower inductance driver was capable of playing a higher frequency, the driver had nastier peaks and dips in the frequency response compared to the low mass driver. Add a lower frequency where standing waves occur, and you have a pretty rough sounding driver at that frequency. Adire was proving that higher inductance affects frequency response, not that mass or size didn't make a difference. If mass wasn't an issue at all, I would think that Adire would be using heavier cones (like metal) and rubber surrounds.
Of course, though, on top of that, 15" subs are generally built more for SPL than their 12" and 10" counterparts, so you'll also get higher inductance coils due to the longer throw the drivers are built for.