Hello diyaudio folks! This is my first post here, so if this is the wrong place for this, please forgive me.
I currently have a Sundown SA12 wired to 1 ohm hooked up to a Sundown SAE1000DV2 @ 1000 watts in a box built to Sundown's website provided box plans. It's pretty much a big ol' square box. I'm planning on building a box with an aeroport for simplicity and a bit different shape to open up some trunk room. The plan so far per Torres...
Height: 14.5"
Width: 24"
Depth: 14.25"
Sub displacement: 0.14 cubes
Gross V: 2.16 cubes
Net V: 1.99 cubes
Port diameter: 3"
Port back/Sub back
Port length per Torres: 5.61"
Port length per WinISD: 6" (so let's say 5.75?)
Tuning: 35Hz
The question: Do those port dimensions look good or would one of you lovely people have a different suggestion on length/diameter/etc?
I currently have a Sundown SA12 wired to 1 ohm hooked up to a Sundown SAE1000DV2 @ 1000 watts in a box built to Sundown's website provided box plans. It's pretty much a big ol' square box. I'm planning on building a box with an aeroport for simplicity and a bit different shape to open up some trunk room. The plan so far per Torres...
Height: 14.5"
Width: 24"
Depth: 14.25"
Sub displacement: 0.14 cubes
Gross V: 2.16 cubes
Net V: 1.99 cubes
Port diameter: 3"
Port back/Sub back
Port length per Torres: 5.61"
Port length per WinISD: 6" (so let's say 5.75?)
Tuning: 35Hz
The question: Do those port dimensions look good or would one of you lovely people have a different suggestion on length/diameter/etc?
From all of the research I've done, it seems like going with an aeroport gives a bit more "fudge room" with the length vs going slot port. So, please correct me if I'm wrong, 1/4" - 1/2" difference in length won't be that noticeable due to the end correction. So I think I'm going to shoot for a tuning of 32Hz to smooth out the response curve a bit so there is less of a big ol' peak in the response to make things mesh better with the other speakers. Thanks for the help!
Greets!
With a high Xmax 12" driver in an acoustically tiny box it's obvious that a 3" vent is designed to 'choke' the driver [protect it], so size, length not real critical if based on a factory recommendation.
FWIW, the published T/S specs [and lacking the essential Sd spec] Vs its measured specs [Cms, Mms, Bl] are so contradictory that I can't calculate/'guesstimate' what it is, but IME it's in the 9-10" dia. range for an acceptable vent mach.
With a high Xmax 12" driver in an acoustically tiny box it's obvious that a 3" vent is designed to 'choke' the driver [protect it], so size, length not real critical if based on a factory recommendation.
FWIW, the published T/S specs [and lacking the essential Sd spec] Vs its measured specs [Cms, Mms, Bl] are so contradictory that I can't calculate/'guesstimate' what it is, but IME it's in the 9-10" dia. range for an acceptable vent mach.
Thanks GM!
I'm pretty much going of Sundown's recommendation (2 cubes tuned to 35Hz). Whenever I load the drivers specs into WinISD it states that the parameters fail integrity check, so I'm guessing you see the same issue with the missing specs you mentioned. Could you clarify what you meant by 9-10" diameter range for the vent match?
I'm pretty much going of Sundown's recommendation (2 cubes tuned to 35Hz). Whenever I load the drivers specs into WinISD it states that the parameters fail integrity check, so I'm guessing you see the same issue with the missing specs you mentioned. Could you clarify what you meant by 9-10" diameter range for the vent match?
I wanted to go aeroport this time just for simplicity sake, do you think a tube port with flares on both ends would not give as good of a sound as a slot port?
A flared vent should work fine.
One 3" vent for a 12" car audio subwoofer though? I'd probably go for two...
One 3" vent for a 12" car audio subwoofer though? I'd probably go for two...
You're welcome!
Correct, WinISD is powerful in that up to a point it can reverse engineer missing driver specs to give you 'something', just not likely all that accurate, though obviously better than nothing.
BTW, what [Sd] does it calculate when inputting basic T/S specs?
Vent area [Av] is based on a low % vent mach [speed] with 5% the most common = ~344 ms*0.05 = ~17.2 m/s [~1128.6 ft/s].
The math I have calculates the minimum vent diameter [dv min] based on a ?? % [don't remember other than it's < 5%] vent mach and driver swept piston volume [Vd] [cm^3] = [Sd*Xmax/10]
Box tuning [Fb]: [dv min][cm] = [[20*Vd^0.5]/Fb^0.25]/10
Av = [dv^2*pi/4]
Note too that as a general rule, [Av] shouldn't be > [Sd] unless the vent still has too high a vent mach [resistive], in which case better off loading it with some type of TL.
So, with WinISD specs, what diameter [dv] does it calculate?
Correct, WinISD is powerful in that up to a point it can reverse engineer missing driver specs to give you 'something', just not likely all that accurate, though obviously better than nothing.
BTW, what [Sd] does it calculate when inputting basic T/S specs?
Vent area [Av] is based on a low % vent mach [speed] with 5% the most common = ~344 ms*0.05 = ~17.2 m/s [~1128.6 ft/s].
The math I have calculates the minimum vent diameter [dv min] based on a ?? % [don't remember other than it's < 5%] vent mach and driver swept piston volume [Vd] [cm^3] = [Sd*Xmax/10]
Box tuning [Fb]: [dv min][cm] = [[20*Vd^0.5]/Fb^0.25]/10
Av = [dv^2*pi/4]
Note too that as a general rule, [Av] shouldn't be > [Sd] unless the vent still has too high a vent mach [resistive], in which case better off loading it with some type of TL.
So, with WinISD specs, what diameter [dv] does it calculate?
Again, the vent is so undersized that I seriously doubt it makes a difference and a low vent mach will likely have as large or larger a net volume [Vv] than the box, so personally would load it with a TQWT [inverse tapered TL] if there's enough room or sealed if not.
Anyway, Brian and others are more up to date on what vented alignments work well in your style of mobile audio.
The SD calculated by WinISD is 433.4cm^2. Going off what Brian Steele recommended, I ordered a second 3" double flared port. I modeled the port velocity of the single 3" and it was stupid high (in the 50's). With 2 it get's me down to mid 40's (seems off, but that's what it reads). I figure with the dual flares that will probably relieve some of that port velocity and keep the chuffing at bay. I've seen on other posts on this site and others that if I run the ports along the back and out the side, I could negate a lot of trunk rattles and possibly get a better sound. The current setup is sub back/slot port back (trunk of an '05 Corolla). Torres confirms that with adjusted dimensions of height:15", width:25", depth:14", running 2x 3" ports along the back at 12-13" each puts me at a tuning of just under 35HZ. The old box was my first ever box build and there were small mistakes made (air leaks and such, fixed with silicone on the outside but who knows about the internal walls of the slot port and other small things).
Make sure to measure Fb after you build your subwoofer. Sometimes proximity to side walls and the like can noticeably change (lower) Fb, requiring the vents to be shortened a bit to compensate.
Note also that the port velocity calcs assume a straight vent. That velocity should reduce a bit when it hits the vent flares.
BTW, if you're working with a width of 25", consider using three of those vents 🙂
Note also that the port velocity calcs assume a straight vent. That velocity should reduce a bit when it hits the vent flares.
BTW, if you're working with a width of 25", consider using three of those vents 🙂
What difference would 3 vs 2 make? I think with the depth I'd have the room, but what would the advantage be?
Well, I ended up returning both 3" precision port ports, and opted for a 5' length of 4" PVC pipe from a newly opened local hardware store for the ports. I'll run two 22" long lengths across the back for a tuning just under 35Hz and a port velocity of 31.4. I got the MDF cut for me by the fine folks at Lowes, so this should be a 1 day project. Thanks for your input guys! Pics to come!
I was taught by a highly renowned British speaker designer with whom I used to work that one should start with a port the same area as the speaker's Sd then more or less work backwards until it fits in the box. None of the enclosures I have built in the intervening 45 years have taught me any differently. Triangular ports are the worst, slot-shaped a close second, and correctly flared and dimensioned circular ports the best. Multiple round ports are used for just two reasons - enclosure 'packaging' and impressing the uneducated. One can gain 10dB output around port resonant frequency comparing best with worst designs, and considerably more dB than that in distortion reduction. Remember also that port tuning shifts with increasing spl. A port is so much more than a pipe glued into the baffle, and a well-designed one is almost money-for-nothing so to speak...
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