posted
I know this is similar to a question asked somewhat recently, but what is a good value to shoot for in terms of max air velocity at the port. I'm using slot ports and plan on using a router to smooth the edges. Any opinions?
-------------------- 1995 Grand Am GT Nakamichi CD-45z Pair of Audiocontrol EQT's Audiocontrol 4XS Crossfire TEK100.2 Illusion Audio ND-6 Crossfire VR142 Image Dynamics CD1E V.2
Looking for the following: Image Dynamics IDMAX 12" Crossfire BMF1000d or VR1000d Posts: 48 | From: Buffalo | Registered: Oct 2002
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posted
Well, i finished my design and don't feel like redoing it to accomodate larger ports. I was worried about port noise, but it's for the trunk of a buick riviera, so any port noise should be blocked by the seat.
The design JL audio provided involved a peak port velocity of about 20 m/s, and the box i made will be about 25. But like i said, i'm no longer worried.
-------------------- 1995 Grand Am GT Nakamichi CD-45z Pair of Audiocontrol EQT's Audiocontrol 4XS Crossfire TEK100.2 Illusion Audio ND-6 Crossfire VR142 Image Dynamics CD1E V.2
Looking for the following: Image Dynamics IDMAX 12" Crossfire BMF1000d or VR1000d Posts: 48 | From: Buffalo | Registered: Oct 2002
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posted
All i know is taht it should be less than 17ms with full power (i looked it at winisd pro box program)
Posts: 107 | From: Finland | Registered: Jan 2003
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posted
If the port velocity is too high, the theories pertaining to port enclosures will go right out the window.
-------------------- "The cause and solution to all of Car Audio's problems" That Beerhat Guy 1 C-V Stroker 12d2 ID 6.5 components Kicker XS100 and ZR360 Posts: 251 | From: Houston,Tx | Registered: Sep 2000
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posted
I was discussing this with Wayne Harris when RF started offering the Aeroports and he opined that 5% of mach is the accepted limit for a living room, 9% or so for a car, and 14% for an aeroport.
I have always followed this and my boxes are quiet.
-------------------- Blow your mind - PORT your box!
D R A G U L A Let us Prey.... 1966 Cadillac Superior Crown Royale Hearse SS5+ Posts: 3690 | From: Abbotsford, BC, Canada | Registered: Mar 2000
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posted
I'm at about 50-54 ft/sec in my current box. Newer box will be about 65 ft/sec or so, but my port will be going from 87.5 square inches to 150.
I hope I'll be safe!!!
-------------------- A couple subs... A couple amps... And a couple batteries... Posts: 1319 | From: Grand Forks, North Dakota | Registered: Apr 2001
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posted
Ahh I see. I never thought about it in terms of port noise. I have just always gone by at MIN the smallest port for a 12 would be a 4" port (pushing it) and etc...Never learned the FPS part. Learn something all the time on here.
-------------------- 1994 Ford F-250 7.3L Powerstroke Diesel Super Cab Long Bed 33" Mud Terrains Yeah, it's big, and yeah, it's got balls. Posts: 876 | From: Decatur, IN | Registered: Apr 2002
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Why hasnt anybody used passive radiators instead? All this talk about port noise.... Passive radiators are perfect for cars, as they tune deep in small enclosures, and have NO portnoise.
Posts: 7 | From: denmark | Registered: Sep 2002
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quote:Originally posted by Dukk: I was discussing this with Wayne Harris when RF started offering the Aeroports and he opined that 5% of mach is the accepted limit for a living room, 9% or so for a car, and 14% for an aeroport.
I have always followed this and my boxes are quiet.
5% limit is also recommended by Small in his classic JAES paper. So I recommended it too in WinISD pro help file
Regards, Janne
-------------------- For box/port calculations, try these:
posted
Gander[37] investigated both vent and thermal compression effects in some depth. As regards temperature,a 380mm bass mid driver fitted with a 63mm motor coil was tested,a unit intended for musical instrument applications.The response was compared for a 1w and 100w input (100db and 120db SPL)No compression was evident at the sealed box system resonance of 50hz; elsewhere a significant 2.5db of compression was seen at higher power,almost halving the effective rated power input.
and the best bit!- Vent compression was illustrated in a 125L enclosure tuned to 42hz by one of two choices of vent the first was a 110mm aperture in 19MM thick front panel the second a pair of ducted 110mm ports with 125m tubes,173cm^2 twice the area.At 96db(1w) the vent efficiencies are the same.
However at 116db(100w) the smaller vent lost a surprising 4db in its working range while the loss from the larger held to just 1db.
thats my typing ,reading from the book-the port configuration part doesnt make much sense but i get the idea that the low port area is bad-
i modeled it in winisd - with a different woofer ofcourse- speaker Q unfortuantely changes it alot ive noticed.
the small port is Double the airspeed peak.
meanwhile im wondering how much my mates 147db 2x12ddaudios will go with a 24m/s port instead of his current 50m/s port! must sound disgusting.
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