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Downsizing the Sub (Planning the design, some questions)
Hi, everyone. I'm considering a new project, and I'm looking for input.
The Setup:
For nearly three years, my current subwoofer has been satisfying my every desire for plentiful, deep bass, no matter what the program material, yada yada. I'm very happy with it from a performance point of view. It uses an AE Speakers AV12 MKII woofer built by TC Sounds, powered by a 500W Parts Express plate amplifier, and supplemented by two 15" 1400g passive radiators, which were also made by AE Speakers. The enclosure has an internal volume of 3 cubic feet. However, with the use of double layered 3/4" MDF construction, and the addition of upper and lower caps adding one and two more layers of MDF respectively, and with external dimensions of 22"x24"x26", this thing ended up being extremely large, and extremely heavy to the tune of nearly 120 lbs. It requires two people to move, and only just fits through doorways. After lifting and moving this subwoofer up a couple flights of stairs, I already began thinking about ways to decrease this subwoofer's weight, as well as its size. This is even more of an issue because I am a college student, and will soon be an apartment dweller. I've moved my current sub in and out of various living arrangements seven or eight times, and it's a back-breaking affair.
Problematic Issues:
Someone will wonder why I don't want to simply use the passive radiators from my old design and just build a single-layer enclosure without all the extra junk on it. However, the mass of the two passive radiators tunes the 3 cubic foot enclosure to 20 Hz, and a practical vented alignment would either require a larger box (not good) or a vent system that would create an unnecessary amount of port noise due to undersized vents. I would like to build something that is more similar in size to the various store-bought subs available today. Their most attractive feature is their small footprint. But to build a 2 cu. ft. enclosure, it would be very difficult to achieve a balance of port length and diameter that could accomodate the airflow produced by a high-excursion driver. It is my intention to down-size, but not to take a significant hit in performance.
My Initial Thoughts:
On the Driver...
The thing that's going to govern the kind of performance I can achieve from my smaller subwoofer is the driver used. Ideally, I would just use the AV12 woofer from my current sub, but during the construction of that sub (when I was not an experienced craftsman), I dropped an allen wrench into the shiny center of the cone, putting two large and very noticeable dents into the cone. In addition, the cone received several scuffs on the surround during handling, and attempts to rub them out only produced worse scuffing. This driver has been around for a while, and I still think I'd like to give it a new lease on life as a car subwoofer, but for the home subwoofer that I'll be showing off to friends and colleagues in the future, I'd like it to be representative of my best work, not my past stupid mistakes. That's why I'm financially prepared to invest in a new driver. I lamented the passing of AE Speakers, because I was quite a fan of the aesthetics of the AV series woofers (with aluminum cone and aluminum inverted dust cap). That's why I was happy to learn that TC Sounds was selling its drivers directly to customers. Perusing their site, I found that the 12" woofer of the TC 1000 series would be a direct drop-in replacement for the dented AV12. And at just a hair under $200, it is only $25 more expensive than the original AV12 from AE Speakers had been. For my performance desires and aesthetic preferences, the 12" TC-1000 with single 4ohm coil is the front-runner in my driver consideration. Also, the 500W amplifier I already own would be able to use the TC-1000 to its full potential.
On the enclosure loading:
I pretty much assume by this point that whatever I design will require the use of passive radiators. It won't be practical to achieve the tuning that I want to achieve with typical reflex ports. For a while, though, I did contemplate using a pair of chrome smokestacks from a diesel truck in order to achieve the port length required. It would have been unique, and certainly comical, but not very elegant. So it's a passive radiator, then. But searching for appropriate passive radiators led me back to the Dayton passive radiators which are a cosmetic match for their DVC woofers. They certainly had a beefy look to them, but not enough linear travel. It would be nearly impossible to fit the dual 15" AE Speakers passives into a 2 cubic foot enclosure without increasing the size of the footprint, and perhaps going to a difficult trapezoidal cabinet shape. This being the limiting factor, I had placed this project on the back burner indefinitely, nearly resigning myself to lugging my enormous current subwoofer up and down stairs and up and down hallways for years to come. This morning, I checked back at the TC Sounds web site, and found that finally their passive radiators were available - the TC-VMP series. They use a large threaded stud, which allows the simplified addition of mass afforded by threaded mounting (though I'll want to use some loctite on the threads), but more importantly, they offer 40mm one-way displacement limited by the suspension's compliance, which adds up to 80mm peak-to-peak motion, which the site claims is enough to keep up with a driver of equivalent diameter that has 20mm of Xmax. TC Sounds is also using the same style of aluminum cone that is found on their other drivers. I had half-hoped that they would have used a flat diaphragm, but...whatev. The aluminum cone makes possible some interesting design ideas from an aesthetic point of view, anyway. Finally, a passive radiator exists that would let me achieve the kind of design I really want to achieve - a small-footprint subwoofer that can use its active driver to its fullest extent, but without costly multiple PRs to achieve the required displacement. At under $140 for the 12" version, it's more expensive than your typical passive radiator, but it also has the displacement of two or more typical 12" radiators, so a little bit of extra expense for the part is justified in order to reduce the overall cost of the loading scheme. So the TC-VMP 12 is my passive radiator of choice, because it makes my design goals attainable with a single passive radiator to be matched to the active driver. This is the only reason why I'm finally pursuing this project in the first place. To use any other 12" radiator (that I am aware of) would require two of them, at least, to match to the driver that I am considering. As for a tuning point, I wonder if it is just too impractical to shoot for response below 20 Hz. My current subwoofer (based on the Stryke Audio Thunder 12.3) is tuned to 19 Hz, but this time I think I'd like to tune higher, around 25 Hz. This should put my F3 somewhere around 20 Hz. Expecting a 12" driver and passive radiator to do more than this in an open-plan house where it might someday be used is probably too much to ask, even from TC Sounds components.
On the amplifier:
The TC-1000 handles 400W RMS thermally, so I'm confident that I'll be able to use my current 500W plate amplifier (the Dayton HPSA500). The plate amp offers a 20 Hz rumble filter, but it also offers something I've never seen on any other plate amp, which is their "Soft Clipping" circuitry -- a limiter that compresses the output of the amplifier to keep it from hitting the rails. In my mind, this amp has proven its reliability and great sound with my previous subwoofer, so this is what I'll be using with this subwoofer, unless it happens to die sometime between now and this Christmas.
On the enclosure:
As far as the enclosure is concerned, I'd like to mount the passive radiator on the front and the active driver on the rear (like the new DSP-controlled Klipsch subwoofers) since the passive radiator is beefier and will be having the higher excursion of the two diaphragms. This idea is simply for aesthetic coolness-factor of watching an aluminum diaphragm undergoing 80mm peak-to-peak motion. I've also decided I don't want to go with the double-layered MDF construction -- a single layer of MDF with a center window-brace is all I intend to use for this. Glue-and-screw construction.
Now, for a few questions.
1) First of all, keeping in mind my previous configuration with the AE Speakers AV12 and two 15" passives in three cubic feet, can you see that I'd be losing anything major in the transition to a much smaller enclosure and single passive radiator, with a higher enclosure tuning frequency?
2) Do you think that the single-layered enclosure (dimensions 16"L*12"W*18"H) with a window brace in the center will be rigid enough? Or should I really design with more internal bracing when using 3/4" MDF for the construction?
3) For my router, I have a 1"-long spiral upcut bit that I plan to use with a circle cutting jig that I will make from plexiglass. When I've used it in the past, it has screeched terribly, and produced lots of smoke and carmelization of the MDF's glue matrix on the bit. Should I go get a longer spiral upcut bit? Or should I simply use a lower speed and a faster/slower feed rate?
4) I also solicit any other comments, criticisms, angry outbursts, whatever. This site is a great resource for experience in speaker design. If you think I should completely rethink my design plans, let me know what you'd do.
Thanks for all your help.
Addendum - I just looked back over my post and found that I repeated myself in a couple places. I tried to go back and eliminate that.
The Setup:
For nearly three years, my current subwoofer has been satisfying my every desire for plentiful, deep bass, no matter what the program material, yada yada. I'm very happy with it from a performance point of view. It uses an AE Speakers AV12 MKII woofer built by TC Sounds, powered by a 500W Parts Express plate amplifier, and supplemented by two 15" 1400g passive radiators, which were also made by AE Speakers. The enclosure has an internal volume of 3 cubic feet. However, with the use of double layered 3/4" MDF construction, and the addition of upper and lower caps adding one and two more layers of MDF respectively, and with external dimensions of 22"x24"x26", this thing ended up being extremely large, and extremely heavy to the tune of nearly 120 lbs. It requires two people to move, and only just fits through doorways. After lifting and moving this subwoofer up a couple flights of stairs, I already began thinking about ways to decrease this subwoofer's weight, as well as its size. This is even more of an issue because I am a college student, and will soon be an apartment dweller. I've moved my current sub in and out of various living arrangements seven or eight times, and it's a back-breaking affair.
Problematic Issues:
Someone will wonder why I don't want to simply use the passive radiators from my old design and just build a single-layer enclosure without all the extra junk on it. However, the mass of the two passive radiators tunes the 3 cubic foot enclosure to 20 Hz, and a practical vented alignment would either require a larger box (not good) or a vent system that would create an unnecessary amount of port noise due to undersized vents. I would like to build something that is more similar in size to the various store-bought subs available today. Their most attractive feature is their small footprint. But to build a 2 cu. ft. enclosure, it would be very difficult to achieve a balance of port length and diameter that could accomodate the airflow produced by a high-excursion driver. It is my intention to down-size, but not to take a significant hit in performance.
My Initial Thoughts:
On the Driver...
The thing that's going to govern the kind of performance I can achieve from my smaller subwoofer is the driver used. Ideally, I would just use the AV12 woofer from my current sub, but during the construction of that sub (when I was not an experienced craftsman), I dropped an allen wrench into the shiny center of the cone, putting two large and very noticeable dents into the cone. In addition, the cone received several scuffs on the surround during handling, and attempts to rub them out only produced worse scuffing. This driver has been around for a while, and I still think I'd like to give it a new lease on life as a car subwoofer, but for the home subwoofer that I'll be showing off to friends and colleagues in the future, I'd like it to be representative of my best work, not my past stupid mistakes. That's why I'm financially prepared to invest in a new driver. I lamented the passing of AE Speakers, because I was quite a fan of the aesthetics of the AV series woofers (with aluminum cone and aluminum inverted dust cap). That's why I was happy to learn that TC Sounds was selling its drivers directly to customers. Perusing their site, I found that the 12" woofer of the TC 1000 series would be a direct drop-in replacement for the dented AV12. And at just a hair under $200, it is only $25 more expensive than the original AV12 from AE Speakers had been. For my performance desires and aesthetic preferences, the 12" TC-1000 with single 4ohm coil is the front-runner in my driver consideration. Also, the 500W amplifier I already own would be able to use the TC-1000 to its full potential.
On the enclosure loading:
I pretty much assume by this point that whatever I design will require the use of passive radiators. It won't be practical to achieve the tuning that I want to achieve with typical reflex ports. For a while, though, I did contemplate using a pair of chrome smokestacks from a diesel truck in order to achieve the port length required. It would have been unique, and certainly comical, but not very elegant. So it's a passive radiator, then. But searching for appropriate passive radiators led me back to the Dayton passive radiators which are a cosmetic match for their DVC woofers. They certainly had a beefy look to them, but not enough linear travel. It would be nearly impossible to fit the dual 15" AE Speakers passives into a 2 cubic foot enclosure without increasing the size of the footprint, and perhaps going to a difficult trapezoidal cabinet shape. This being the limiting factor, I had placed this project on the back burner indefinitely, nearly resigning myself to lugging my enormous current subwoofer up and down stairs and up and down hallways for years to come. This morning, I checked back at the TC Sounds web site, and found that finally their passive radiators were available - the TC-VMP series. They use a large threaded stud, which allows the simplified addition of mass afforded by threaded mounting (though I'll want to use some loctite on the threads), but more importantly, they offer 40mm one-way displacement limited by the suspension's compliance, which adds up to 80mm peak-to-peak motion, which the site claims is enough to keep up with a driver of equivalent diameter that has 20mm of Xmax. TC Sounds is also using the same style of aluminum cone that is found on their other drivers. I had half-hoped that they would have used a flat diaphragm, but...whatev. The aluminum cone makes possible some interesting design ideas from an aesthetic point of view, anyway. Finally, a passive radiator exists that would let me achieve the kind of design I really want to achieve - a small-footprint subwoofer that can use its active driver to its fullest extent, but without costly multiple PRs to achieve the required displacement. At under $140 for the 12" version, it's more expensive than your typical passive radiator, but it also has the displacement of two or more typical 12" radiators, so a little bit of extra expense for the part is justified in order to reduce the overall cost of the loading scheme. So the TC-VMP 12 is my passive radiator of choice, because it makes my design goals attainable with a single passive radiator to be matched to the active driver. This is the only reason why I'm finally pursuing this project in the first place. To use any other 12" radiator (that I am aware of) would require two of them, at least, to match to the driver that I am considering. As for a tuning point, I wonder if it is just too impractical to shoot for response below 20 Hz. My current subwoofer (based on the Stryke Audio Thunder 12.3) is tuned to 19 Hz, but this time I think I'd like to tune higher, around 25 Hz. This should put my F3 somewhere around 20 Hz. Expecting a 12" driver and passive radiator to do more than this in an open-plan house where it might someday be used is probably too much to ask, even from TC Sounds components.
On the amplifier:
The TC-1000 handles 400W RMS thermally, so I'm confident that I'll be able to use my current 500W plate amplifier (the Dayton HPSA500). The plate amp offers a 20 Hz rumble filter, but it also offers something I've never seen on any other plate amp, which is their "Soft Clipping" circuitry -- a limiter that compresses the output of the amplifier to keep it from hitting the rails. In my mind, this amp has proven its reliability and great sound with my previous subwoofer, so this is what I'll be using with this subwoofer, unless it happens to die sometime between now and this Christmas.
On the enclosure:
As far as the enclosure is concerned, I'd like to mount the passive radiator on the front and the active driver on the rear (like the new DSP-controlled Klipsch subwoofers) since the passive radiator is beefier and will be having the higher excursion of the two diaphragms. This idea is simply for aesthetic coolness-factor of watching an aluminum diaphragm undergoing 80mm peak-to-peak motion. I've also decided I don't want to go with the double-layered MDF construction -- a single layer of MDF with a center window-brace is all I intend to use for this. Glue-and-screw construction.
Now, for a few questions.
1) First of all, keeping in mind my previous configuration with the AE Speakers AV12 and two 15" passives in three cubic feet, can you see that I'd be losing anything major in the transition to a much smaller enclosure and single passive radiator, with a higher enclosure tuning frequency?
2) Do you think that the single-layered enclosure (dimensions 16"L*12"W*18"H) with a window brace in the center will be rigid enough? Or should I really design with more internal bracing when using 3/4" MDF for the construction?
3) For my router, I have a 1"-long spiral upcut bit that I plan to use with a circle cutting jig that I will make from plexiglass. When I've used it in the past, it has screeched terribly, and produced lots of smoke and carmelization of the MDF's glue matrix on the bit. Should I go get a longer spiral upcut bit? Or should I simply use a lower speed and a faster/slower feed rate?
4) I also solicit any other comments, criticisms, angry outbursts, whatever. This site is a great resource for experience in speaker design. If you think I should completely rethink my design plans, let me know what you'd do.
Thanks for all your help.
Addendum - I just looked back over my post and found that I repeated myself in a couple places. I tried to go back and eliminate that.
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