My software suggests a 5" x 5.8" port, which seems reasonable, but I only have a 3" tube handy. For a 3" port, it suggests a 1" length, which would basically be just a hole in the baffle. Would that be a problem?
(When I started making cabinets, that's all we ever did - put a hole in the baffle, but since the advent of Novak and T-S, it seems tubes are fashionable.)
(When I started making cabinets, that's all we ever did - put a hole in the baffle, but since the advent of Novak and T-S, it seems tubes are fashionable.)
I find that port length predictions are not usually very accurate because there are a lot of assumptions made. End corrections are approximate at best and with a very short port the end corrections can be the entire effect. Its best to start with the suggestion (and short if fine) and adjust from there.
I would take the extra time to get the right sized longer port. If the port is too small in diameter you can get a chuffing sound from the air flow turbulance in and out of the port. That is why ports sometimes have beveled edges to reduce that effect. If you start beveling a short 3" port it changes the effective diameter and length. I wouldn't bother messing with that.
But you could also try it and see what happens. You can always easily go bigger later. Less easy to go smaller!
But you could also try it and see what happens. You can always easily go bigger later. Less easy to go smaller!
Hi,
A 5" port with flaring is not the same as a plain 5" port and sims can't
model flared ports. Three 3" ports are the same as a 5" moreorless
and will have the same length moreorless and be as good as a 5".
(In fact a little longer and a little better regarding port air velocity.)
rgds, sreten.
A 5" port with flaring is not the same as a plain 5" port and sims can't
model flared ports. Three 3" ports are the same as a 5" moreorless
and will have the same length moreorless and be as good as a 5".
(In fact a little longer and a little better regarding port air velocity.)
rgds, sreten.
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It is not fine if port velocity is too low. Chuff, chuff, chuff.
You did not say what this was for.
Ports do not have to be round. You can make one of any cross section. Roll up some cardboard, cut hardboard, slot. Let's see some creativity!
Too high you mean
That's the basic problem with a port that's only a hole in the panel - to get the tuning frequency low enough you have a ridiculously small port area that is going to chuff like crazy because of the high air velocity.
Not just chuffing either, also adding significant harmonic distortion, and unloading of the woofer at higher SPL's, which means dynamic range compression around the tuning frequency and excessive cone excursion that could even lead to damage.
On the other hand make the hole bigger to get an acceptable area and you now have a boombox because you've tuned it WAY too high in frequency.
Just look at many of the speakers from the 60's and 70's and you'll see plenty with ports that are just holes in the panel, suffering from either one or both of the above problems.
I remember one pair I once had given to me that had 10" richard allen wide range woofers as the woofer, the "port" was a 40mm hole in a 16mm thick panel, with dense grill cloth across the front of the hole to boot. Well needless to say that port chuffed like crazy and didn't actually do anything useful
Adding length to a port allows you to lower the tuning frequency while still maintaining an acceptable cross sectional area. If anything its generally better to err a little bit on the side of too much cross sectional area than too little, which means an even longer port.
I can't really think of any circumstances or alignments where a "hole in the panel" port will ever give an acceptable quality result, you're either going to be too small in port area (chuffing etc) or too high in tuning (boombox) or in many cases both at once.
Of course now you have to deal with standing waves in the port at higher frequencies, but there are various ways to do that including not putting the port on the front panel facing the listener, using a rectangular port, etc.
Sorry but I'm not the original poster so I fail to see why you asked me all that.
I was addressing a simple round hole(port) with sufficient low air velocity and rounded edges to avoid wind turbulence. I understand VERY well the physics involved.
I find it amusing how people jump in on here giving all sorts of opinions when the OP didn't even say what driver he was using.All he said was he designed from a 5 inch diameter port down to a 3 inch.
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