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Discussion Starter #1
Would you be able to hear the port noise while sitting in the car?


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Would you be able to hear the port noise while sitting in the car?


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Not as much, but there is still compression to consider, you can get away with much higher port velocity in a trunk until compression becomes a problem.
 

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I have been modeling Dayton subs and to keep port lengths reasonable I am in the 30-40 m/s range for most of my models with a best case scenario at 27 m/s


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I have been modeling Dayton subs and to keep port lengths reasonable I am in the 30-40 m/s range for most of my models with a best case scenario at 27 m/s


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30 m/s shouldn't be too bad in a trunk.
 

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For what it's worth, I ran a single 15 with a 4 inch square port 1 foot long (tuned at 26 hz, 35 m/s port velocity, no flares) in a hatchback and I never noticed the noise until it got down into the low 30's. That was a 150 db setup with 1200 watts on up to 2200 watts, port compression kept it from going louder with the extra power.
 

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For what it's worth, I ran a single 15 with a 4 inch square port 1 foot long (tuned at 26 hz, 35 m/s port velocity, no flares) in a hatchback and I never noticed the noise until it got down into the low 30's. That was a 150 db setup with 1200 watts on up to 2200 watts, port compression kept it from going louder with the extra power.
That makes sense. I am not running enough wattage to lose any db so I better keep it under 30 m/s


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Good to know. I keep reading online that people aim for 17m/s or less, nice to hear some real world examples.
These are considered generalizations:
17 is audiophile
30 is general use
42-45 is fine for SPL
60 is in the range of starting to cause some compression but it depends on port style

Most of the noise is created by the reversing as the air crashes into itself and the flared ports spread this area out but it's difficult to quantify as the effectiveness changes depending on size. The bigger the port the more and more effective simply due to increased surface area. Also the lower the port is tuned the more velocity you can get away with as the velocity approach to reversing is spread out more. Big slot ports can get away with even more velocity as that peak only occurs in the center of the port.

A pair of SI SQL15s in a 9 cu ft HT enclosure with a flared slot port tuned to 18 Hz modeled to 45 m/s and the owner uses it as a coffee table with no concern about port noise. But that brings in another caveat, how often are you planning to run at max spl?

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Discussion Starter #11
But that brings in another caveat, how often are you planning to run at max spl?

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Very good point and the answer, in my case, could very well be almost never after tuning and equalization.


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Very good point and the answer, in my case, could very well be almost never after tuning and equalization.


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So between being in the trunk (less noticeable from noise perspective) and not running at peak excursion and assuming your using a circular port then you should be good up to a calculated max of 45-50 m/s.

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Good to know. I keep reading online that people aim for 17m/s or less, nice to hear some real world examples.
17 m/s is the target for zero to minimal port noise without flares, but some of us would need an 8 inch round port 6 feet long to hit that goal. Compromise is key to making car audio work.
 
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17 m/s is the target for zero to minimal port noise without flares, but some of us would need an 8 inch round port 6 feet long to hit that goal. Compromise is key to making car audio work.
If you ever want to put an SQL15 in your trunk I figured out a way to put a 10' long port (it's actually 9' 11") on a 3 cube box... 18.5Hz Baby
296314
 
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How is port velocity and/or noise affected by adjacent surfaces? I only have approximately a 1-2” gap between my port exits and the seat back.
4th order BP e30 convertible
SQ system fully active
It’s been a few years since I crunched the numbers but I recall trying to stay under 20 or so. It sounds great, I’ve just always wondered. In fact, I have a stack of washers to maximize the gap.




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It's all about surface area. If the gap is equal to or greater than the surface area of the port then there's no problem. For circular ports its a 4:1 ratio (for every inch of port diameter you need 0.25" of clearance) so a 1-2" gap would support between a 4-8" port. It gets a little more complicated when the ports are within the diameter of the port beside each other but that can be calculated as well.

Depending on how dead or reactive the seatback is you may get some boundary effect but that's a whole different rabbit hole.

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The most problematic is Laminar air flow that accours in the port and it causes port compression. When using Aeroports this laminar flow is less problematic and cause less port compression leading to increased SPL and minimized port noise. The shape of aeroport do have big impact on final result.
 

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If you ever want to put an SQL15 in your trunk I figured out a way to put a 10' long port (it's actually 9' 11") on a 3 cube box... 18.5Hz Baby
View attachment 296314
Sweet! But 88 Camaros can't fit large box-shaped boxes, my last ported 15 took up the entire hatch tail lights to back seat below the window level. No more of that crap for me, I'll just run sealed.
 
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