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#1
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Frequency response, mass vs. inductance
I have a question. Someone on a message board I usually post on talked
about woofer speed. I assume what this translates to is frequency response (ie 1/time=frequency). He also posted a link, which I read: http://www.adireaudio.com/Files/Tech...ooferSpeed.pdf At the end of the page it shows a graph, with the frequency response of the speaker they used. To me, inductance would have little or no effect on a speaker unless, it were a midrange or a tweeter. And from this graph, mass still seems to dampen the signal more throught the frequency range than does the inductor, which is should I would think. (ie xl=2(pi)(f)(l)) When it does eventually does get to the higher end the inductor does not seem to cut the signal all that much. So what I would like to know is, if the inductance is the most important part, why not make it small, and increase your frequency response of the speaker? This probably would not effect a woofer all that much if the woofer was used for bass only or would it? I find it hard to believe that the mass of the cone has nothing to do with this at higher frequencies, which is why you cannot use a tweeter for a woofer. And by cutting down the inductance would also mean a smaller coil and maybe larger wire? Wouldn't that be a problem? |
#3
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"Todd H." wrote ...
Ding! It's a juggling act and there are tradeoffs. Want less inductance, use fewer turns of wire, but... oops, now you need more current to achieve the same force to move a given mass with a given transient response, and ah crap, also need bigger wire to achieve the now-great power handling requirement, so you use a better magnet, but that adds cost and/or heft, perhaps more than your target market will be willing to pay. And so on on. Which is why JBL took ordinary (round) magnet wire and ran it through a home-made kludge that flattened it into a ~rectangular shape. They pointed out this device on a tour of the factory I took a couple decades ago. They claimed this exercise allowed them to... 1) Pack more turns (mean cross-sectional area) in a given space by more efficiently using the space (filling in the corners, etc.) 2) Make self-supporting voice-coils so they didn't have to use the fiber (paper) coil forms seen in other drivers. I believe they claimed this allowed smaller gaps (increasing flux) and made the coils better at shedding heat (no insulating coil form on the inside of the solenoid). They had a lathe-like device where they would edge-wind long solenoids of coil, slathering them with something that held them together. Then heating the coil and allowing it to cure (overnight). After that, they could take the big coils and chop off just the amount needed to make a voice coil with a bit extra to bring out the leads. At least that is the way I remember it. |
#4
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wrote in message
oups.com I have a question. Someone on a message board I usually post on talked about woofer speed. I assume what this translates to is frequency response (ie 1/time=frequency). He also posted a link, which I read: http://www.adireaudio.com/Files/Tech...ooferSpeed.pdf At the end of the page it shows a graph, with the frequency response of the speaker they used. To me, inductance would have little or no effect on a speaker unless, it were a midrange or a tweeter. And from this graph, mass still seems to dampen the signal more throught the frequency range than does the inductor, which is should I would think. (ie xl=2(pi)(f)(l)) When it does eventually does get to the higher end the inductor does not seem to cut the signal all that much. So what I would like to know is, if the inductance is the most important part, why not make it small, and increase your frequency response of the speaker? Because frequency response isn't everything. Dispersion is also important. Dispersion is largely based on the diameter of the radiating surface. The larger the diameter of the speaker, the less dispersion at high frequencies. As a rule, people don't want beamy-sounding speakers, speakers that beam sound like tight laser beams, speakers that have a sweet spot the size of a dime. This probably would not effect a woofer all that much if the woofer was used for bass only or would it? Exactly. A very high proportion of all woofers in 2-way speakers have additional inductance placed in series with them. The inductance is part of the speaker's crossover, and the goal of the woofer crossover is to further limit the high frequency response of the speaker. The idea of fast woofers is a fallacy because almost all woofers are driven through low-pass filters that reduce the high frequency response and slow down the transient response of a woofer even more than the mechanical limits thusfar described. Another reason why electrical circuits are used to slow down woofers and reduce frequency response well below mechanical the mechanical limits of the driver relates to the smoothness of frequency response. Just because a speaker responds to some higher frequency doesn't mean that the response is smooth in that area. The extreme case relates to bandpass woofers that often have peaks in their response at relatively low frequencies like 250 Hz or less. These speakers are going to sound pretty honky in the lower midrange unless an electrical network is used to roll-off the woofer's response below this peak. I find it hard to believe that the mass of the cone has nothing to do with this at higher frequencies, which is why you cannot use a tweeter for a woofer. You've got that reversed. The mass of the cone has a lot to do with low frequency response, which is why you can't use a tweeter for a woofer. When you add mass to a speakers cone and retune the enclosure for the new massier woofer, you get greater bass extension at the cost of lower efficiency. And by cutting down the inductance would also mean a smaller coil and maybe larger wire? Wouldn't that be a problem? Voice nductance is usually relatively unimportant in woofers because it is common to put even larger external inductors in series with their voice coils. |
#5
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No one has made the observation that all things the same, a woofer cone
driven by a sine wave of a given frequency will have a greater velocity at a higher excursion. I think that is what "fast woofer cone" really is all about. Also consider the fact that at low frequencies, a woofer tends to move much like a piston, while at higher frequencies, the force from the coil tends to propagate from the center of the cone to the edge as a transverse wave in the cone material, otherwise known as ripple. "Arny Krueger" wrote in message ... wrote in message oups.com I have a question. Someone on a message board I usually post on talked about woofer speed. I assume what this translates to is frequency response (ie 1/time=frequency). He also posted a link, which I read: http://www.adireaudio.com/Files/Tech...ooferSpeed.pdf At the end of the page it shows a graph, with the frequency response of the speaker they used. To me, inductance would have little or no effect on a speaker unless, it were a midrange or a tweeter. And from this graph, mass still seems to dampen the signal more throught the frequency range than does the inductor, which is should I would think. (ie xl=2(pi)(f)(l)) When it does eventually does get to the higher end the inductor does not seem to cut the signal all that much. So what I would like to know is, if the inductance is the most important part, why not make it small, and increase your frequency response of the speaker? Because frequency response isn't everything. Dispersion is also important. Dispersion is largely based on the diameter of the radiating surface. The larger the diameter of the speaker, the less dispersion at high frequencies. As a rule, people don't want beamy-sounding speakers, speakers that beam sound like tight laser beams, speakers that have a sweet spot the size of a dime. This probably would not effect a woofer all that much if the woofer was used for bass only or would it? Exactly. A very high proportion of all woofers in 2-way speakers have additional inductance placed in series with them. The inductance is part of the speaker's crossover, and the goal of the woofer crossover is to further limit the high frequency response of the speaker. The idea of fast woofers is a fallacy because almost all woofers are driven through low-pass filters that reduce the high frequency response and slow down the transient response of a woofer even more than the mechanical limits thusfar described. Another reason why electrical circuits are used to slow down woofers and reduce frequency response well below mechanical the mechanical limits of the driver relates to the smoothness of frequency response. Just because a speaker responds to some higher frequency doesn't mean that the response is smooth in that area. The extreme case relates to bandpass woofers that often have peaks in their response at relatively low frequencies like 250 Hz or less. These speakers are going to sound pretty honky in the lower midrange unless an electrical network is used to roll-off the woofer's response below this peak. I find it hard to believe that the mass of the cone has nothing to do with this at higher frequencies, which is why you cannot use a tweeter for a woofer. You've got that reversed. The mass of the cone has a lot to do with low frequency response, which is why you can't use a tweeter for a woofer. When you add mass to a speakers cone and retune the enclosure for the new massier woofer, you get greater bass extension at the cost of lower efficiency. And by cutting down the inductance would also mean a smaller coil and maybe larger wire? Wouldn't that be a problem? Voice nductance is usually relatively unimportant in woofers because it is common to put even larger external inductors in series with their voice coils. |
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