I have the Dayton UM18-22 in my car and I want to build a new box as the old one is sealed and the wrong dimensions to fit in the back (its in the back seat right now not the cargo area).
I want to make sure that the port or ports are big enough as to not have port noise. The xmax is 22mm and dayton claims 2 inches of movement.
Another concern is space. It's in a scion tC (hatchback) and I'm willing to devote the entire back cargo area to the subwoofer but it cant go much farther than the seat backs because that's the only decent place for the amps to go.
I figure I can make a 4-5 ft³ box and still have enough room that the sub wont be insanely close to the back window. But the port lengths I'm getting out of winisd are pretty damn long and not super workable. Even with 30hz tuning and a 5ft³ box I would need almost 2 feet of port length for an 8 inch diameter port.
Hopefully there is a sweet spot where I can have enough port area but not an insanely huge amount to make the box and tuning a pain. The recommended build on dayton's website has 2 4 inch diameter ports but that seems a little risky for a 18 inch woofer that's supposed to move 2 inches.
Bonus question what is the air velocity I should avoid for the port?
I want to make sure that the port or ports are big enough as to not have port noise. The xmax is 22mm and dayton claims 2 inches of movement.
Another concern is space. It's in a scion tC (hatchback) and I'm willing to devote the entire back cargo area to the subwoofer but it cant go much farther than the seat backs because that's the only decent place for the amps to go.
I figure I can make a 4-5 ft³ box and still have enough room that the sub wont be insanely close to the back window. But the port lengths I'm getting out of winisd are pretty damn long and not super workable. Even with 30hz tuning and a 5ft³ box I would need almost 2 feet of port length for an 8 inch diameter port.
Hopefully there is a sweet spot where I can have enough port area but not an insanely huge amount to make the box and tuning a pain. The recommended build on dayton's website has 2 4 inch diameter ports but that seems a little risky for a 18 inch woofer that's supposed to move 2 inches.
Bonus question what is the air velocity I should avoid for the port?
.I want as much vibrations as possible. Also I'm trying to keep the port speed below 20m/s in my models. It's OK, I have had a vented 15 in a scion tC before I know that some things will rattle. It actually wasn't that bad with the bass on full the rattling would be covered up mostly.
SO SERIOUSLY WHAT PORT SPEED IS TOO HIGH FOR THIS APPLICATION?
SO SERIOUSLY WHAT PORT SPEED IS TOO HIGH FOR THIS APPLICATION?
The "Shoehorn" PPSL2x15" has a Hornresp calculated particle velocity peaking around 34m/s at the 40 Hz Fb, falling to around 8m/s at 90 Hz (the slot output reaches a maximum of 16m/s at 78 Hz).
The actual measurements show only one dB compression in the port range over a 10 dB increase in power.
The upper response exhibits more compression, while using only a fraction of the LF power, it appears that calculated particle velocity is not adequate to predict compression effects.
Neither the 34m/s Fb or slot particle velocity 16m/s at 78 Hz "chuffing" were remotely audible at the SPL produced when reaching those levels with typical music, even when crossed at 125 Hz with nothing above. If you are talking about a home theater sub reproducing VLF 20Hz "rumble" sound FX in the absence of upper sound, different story- shoot for 15 m/s.
Think of the port velocity as "wind noise", your air conditioner (or heater) fan will be making more noise than the port, you wouldn't choose to sweat over that noise, would you?
SERIOUSLY, NO, YOU WOULD NOT.
Cheers,
Art
Ah now it makes sense why the recommended car box for this sub has 2 4" diameter ports. Im aiming for 1.5-2 times that area to be on the safe side. Sweet it should all fit.
FINAL QUESTION. I'm looking to add some stuffing / acoustic polyfil to the port and box to help dampen and reduce box size. Should i shoot for a 5% smaller box and 5% shorter port if I am going to add some stuffing to both? I want to hit my target tuning as best I can and may use the polyfill to adjust.
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Yes, I have tinnitus, and yes- no effing free lunch, don't stuff ports or box for subs if max SPL are your design goals!
Art
What about putting the ports on top or sides.
Ports too close will affect the tuning making it act like a longer port. But there may be an up side, I have read on a couple of occasions that making the port slightly longer will counteract the fb's natural tendancy to rise a few hertz under heavy use( making it boomy). Can't remember what the mechanism is though.
Ports too close will affect the tuning making it act like a longer port. But there may be an up side, I have read on a couple of occasions that making the port slightly longer will counteract the fb's natural tendancy to rise a few hertz under heavy use( making it boomy). Can't remember what the mechanism is though.
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