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...or "Ending Up With More Questions Then You Came In With!"
So I started reading the AVSForum DIY section on a whim a few weeks ago, and quickly came to the conclusion that I wanted to build a sub (to start.......). I pored through that forum and then this one (which now has a permanent tab in my Firefox session) sucking up information. Most all of my original questions have been answered, but now I have even more to figure out, so I decided to stop lurking and start asking. So here goes....
I'll start off with what I know for sure about my future project. I'm looking at a sealed sub w/ a 12" driver and 500watt PE BASH amp - decisions made because of cost ($600-ish for the project) and environmental (read: what my roommate will let me get away with) factors. Framing of the box will be done with 2x4's (using crackyflipside on AVS's Rythmik Servo box as a model) with additional bracing along the non-equipment bearing walls. The framing will be 16-17 inches^3 (using that volume as the gross box volume). Walls will be either MDF or Baltic Birch plywood, attached to the framing using both wood glue and screws, with the screws sunk below the top plane of the panels to allow fill for finishing. Both the driver and the amp would be mounted directly to the front/back walls. Driver selection is still up in the air, but right now I have images of either a SoundSplinter RL-P12 or Fi Car Audio Q12 (both DVC, 2 ohms per coil, wired in series) dancing in my head. So with all that said....
Qtc
Using the specs posted on each company's site, I've been modeling both the SS and Fi drivers with WinISD. Both drivers model very close to each other, except for the Qtc ratings. Given equal box volumes, the RL-P12's Qtc is coming in at nearly half the Q12. For an example, given a 49 liter net system volume, the RL-P12 comes in at .369, while the Q12 rates a 0.647. Even dropping the volume for the RL-P12 to 32 liters (1.15 cu. ft. - SoundSplinter's recommended system volume for this driver) only pushes it to 0.421. As I understand it, 0.500 is the critically dampened point, and I'm under the impression that that's about the lowest one would want Qtc to be at for a complete system. Am I misunderstanding what value Qtc should be at? Am I modeling the RL-P12 wrong, or will the Q12 be superior for my needs? Is there something I'm missing?
Baffles
In reading through the threads here (both subwoofer and full-range designs), using baffles seems to be very popular - almost mandatory in the full-range speaker designs. I've used them in car audio installations before, but mostly for protection from the elements (front door speakers specifically). What benefits does adding them to home speakers confer? Would my design be improved by adding a baffle (or baffles)?
Box Dampening
I've picked up on using dampening materials to both modify a box's Qtc, as well as decrease vibrations transmitted through the box itself (I'm hoping my frame design helps in that respect as well). If I can adjust my box design for the best Qtc without any fill, would acoustic foam on the inner walls be the best bet for vibration reduction?
Protecting Against Xmax
Depending on the final driver used and final box specifications, there is obviously the possibiltiy of the driver hitting Xmax before reaching the lowest frequencies (whether or not the final system can actually reach below 20Hz at a level I can detect depends on the room of course). I certainly wouldn't want the driver hitting its excursion limits on a regular basis, so a highpass filter placed strategically would seem to be a good idea. Is there an ideal buffer zone (distance-wise) to chop the signal at?
I've got a brain full of other questions, but I don't want to overload a single thread. My questions on finishing alone will be enough for another braindump, I imagine. Overall though, is there anything I missed? Are there critical flaws in my design? And who's this Natalie P. girl?! :B
My thanks in advance for any insights this forum can provide - reading the threads here has given me plenty of new things to think about and try. I fear DIY may be my new addiction, provided I can supply the cash!
So I started reading the AVSForum DIY section on a whim a few weeks ago, and quickly came to the conclusion that I wanted to build a sub (to start.......). I pored through that forum and then this one (which now has a permanent tab in my Firefox session) sucking up information. Most all of my original questions have been answered, but now I have even more to figure out, so I decided to stop lurking and start asking. So here goes....
I'll start off with what I know for sure about my future project. I'm looking at a sealed sub w/ a 12" driver and 500watt PE BASH amp - decisions made because of cost ($600-ish for the project) and environmental (read: what my roommate will let me get away with) factors. Framing of the box will be done with 2x4's (using crackyflipside on AVS's Rythmik Servo box as a model) with additional bracing along the non-equipment bearing walls. The framing will be 16-17 inches^3 (using that volume as the gross box volume). Walls will be either MDF or Baltic Birch plywood, attached to the framing using both wood glue and screws, with the screws sunk below the top plane of the panels to allow fill for finishing. Both the driver and the amp would be mounted directly to the front/back walls. Driver selection is still up in the air, but right now I have images of either a SoundSplinter RL-P12 or Fi Car Audio Q12 (both DVC, 2 ohms per coil, wired in series) dancing in my head. So with all that said....
Qtc
Using the specs posted on each company's site, I've been modeling both the SS and Fi drivers with WinISD. Both drivers model very close to each other, except for the Qtc ratings. Given equal box volumes, the RL-P12's Qtc is coming in at nearly half the Q12. For an example, given a 49 liter net system volume, the RL-P12 comes in at .369, while the Q12 rates a 0.647. Even dropping the volume for the RL-P12 to 32 liters (1.15 cu. ft. - SoundSplinter's recommended system volume for this driver) only pushes it to 0.421. As I understand it, 0.500 is the critically dampened point, and I'm under the impression that that's about the lowest one would want Qtc to be at for a complete system. Am I misunderstanding what value Qtc should be at? Am I modeling the RL-P12 wrong, or will the Q12 be superior for my needs? Is there something I'm missing?
Baffles
In reading through the threads here (both subwoofer and full-range designs), using baffles seems to be very popular - almost mandatory in the full-range speaker designs. I've used them in car audio installations before, but mostly for protection from the elements (front door speakers specifically). What benefits does adding them to home speakers confer? Would my design be improved by adding a baffle (or baffles)?
Box Dampening
I've picked up on using dampening materials to both modify a box's Qtc, as well as decrease vibrations transmitted through the box itself (I'm hoping my frame design helps in that respect as well). If I can adjust my box design for the best Qtc without any fill, would acoustic foam on the inner walls be the best bet for vibration reduction?
Protecting Against Xmax
Depending on the final driver used and final box specifications, there is obviously the possibiltiy of the driver hitting Xmax before reaching the lowest frequencies (whether or not the final system can actually reach below 20Hz at a level I can detect depends on the room of course). I certainly wouldn't want the driver hitting its excursion limits on a regular basis, so a highpass filter placed strategically would seem to be a good idea. Is there an ideal buffer zone (distance-wise) to chop the signal at?
I've got a brain full of other questions, but I don't want to overload a single thread. My questions on finishing alone will be enough for another braindump, I imagine. Overall though, is there anything I missed? Are there critical flaws in my design? And who's this Natalie P. girl?! :B
My thanks in advance for any insights this forum can provide - reading the threads here has given me plenty of new things to think about and try. I fear DIY may be my new addiction, provided I can supply the cash!
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