I would think a shelf port is what you commonly see on music instrument speakers - the port is across the full width at the bottom of the cabinet with the timber defining the top of port extending to the front of the cabinet, creating something looking like kitchen cupboard "shelf" - port area below shelf, speaker / grille above shelf.
Same rule applies - area of port same as area of tube, length of port the same (only port length this time starts from extreme front of cabinet and therefore does not extend quite as far into the cabinet).
Cheers
Same rule applies - area of port same as area of tube, length of port the same (only port length this time starts from extreme front of cabinet and therefore does not extend quite as far into the cabinet).
Cheers
I was going to try a double chamber reflex with slot/shelf porting. I was wondering if there would be a problem with tuning. They were going to be 1/4" high slots the entire width of the cabinet. Let me know if anyone tries it, and how it works out. As soon as I stop being lazy, I might be able to tell you the same, haha.
This is for a P17:
This is for a P17:
Attachments
Do you have any idea how LONG they would have to be at 1"!?!?
Seriously, it's not possible in this cabinet.
I was worried about that though. It's definitely a problem with a small opening. That is one reason I put it on the rear of the enclosure. I wonder if the velocity would really be that high, considering there is a lot of area at the port exit (they are fairly long).
what do you think?
Seriously, it's not possible in this cabinet.
I was worried about that though. It's definitely a problem with a small opening. That is one reason I put it on the rear of the enclosure. I wonder if the velocity would really be that high, considering there is a lot of area at the port exit (they are fairly long).
what do you think?
That's can't be correct, since for a given tuning frequency as you increase port diameter the required port length increases as well. Thus, there is a very large range internal port volumes which all give the same tuning frequency (with correspondingly large variations in port velocity as well).usekgb said:
Other than that, yes... convert a round port to a rectangular one by keeping both length and cross-sectional area the same, and try to maintain a reasonable aspect ratio.
nobody special said:
I understand the problem you are facing. You have plenty of surface area, but with a narrow opening like that, if starts to behave less like a port, and more like a whistle. Even though there is plenty of area across the entire port, a narrow port like this can start to behave similar to several smaller ports. There is so much turbulance building up that one side of the port can't "see" the other side of the port, and they won't resonate at the same frequency. If you can't get a wider port, and can't get the Mach speed of the air moving through the port under 0.1, you may just have to go to more traditional ports.....i.e. round.
Cheers,
Zach
At a practical level, it will add a little more mass loading to the driver, but with normal carpentry there is enough error in our box construction that the volume error of the enclosure will be much greater than the error introduced by the grille. I'm thinking that it will act more like a diffuser. The volume of air moving back and forth through the port will be the same, but less smooth. It will act a lot like stuffing, only instead of filling the volume and creating an obstacle, it acts like a sieve.
ensen.
ensen.
The grille cloth thing might work pretty well. It might raise the tuning frequency of the port though. Try to use a pretty open cloth material though. You still want to let the air get in and out of the port as freely as possible. Another option is to divide the slot port in to three different ports by using dividers. This will allow you to use a wider port, thus slowing down the airflow through the ports. This is a little trick I use quite often to reduce the airflow through my ports. Insted of using one 4" port, I'll use two 3" ports. I can usually cut the air speed in half doing this. It takes a little more wood working, but it works very well.
Cheers,
Zach
Cheers,
Zach
Amperiodic?
But at some point this becomes an amperiodic box if you continue to increase the # and reduce the size of your ports.
"Just thought that I would add that flared ports give the port noise of a straight port of twice it's cross-sectional area. The larger the cross-sectional area, the less the noise.
So a 2" flared port has the noise of a 3" straight port, but the shorter length of a 2" straight port.
Other members have said that, when using a flared port, add one inch extra to the straight port length to make up for the flare. So a 10" flared port will tune a box the same as a 9" straight port of equal diameter.
Programs will calculate the length of multiple straight ports of any crossection. WinISD is one of the easiest."
Hmm, that's the only remotely relevant post I can dig up, but I distinctly remember seeing a thread a while back on this subject nd someone posited that while you can get away with multiple smaller ports for a while, if you tried to use too many it would "go amperiodic" and forgoing significant LF from the port.
-fortyquid
But at some point this becomes an amperiodic box if you continue to increase the # and reduce the size of your ports.
"Just thought that I would add that flared ports give the port noise of a straight port of twice it's cross-sectional area. The larger the cross-sectional area, the less the noise.
So a 2" flared port has the noise of a 3" straight port, but the shorter length of a 2" straight port.
Other members have said that, when using a flared port, add one inch extra to the straight port length to make up for the flare. So a 10" flared port will tune a box the same as a 9" straight port of equal diameter.
Programs will calculate the length of multiple straight ports of any crossection. WinISD is one of the easiest."
Hmm, that's the only remotely relevant post I can dig up, but I distinctly remember seeing a thread a while back on this subject nd someone posited that while you can get away with multiple smaller ports for a while, if you tried to use too many it would "go amperiodic" and forgoing significant LF from the port.
-fortyquid
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