The pro guys I know would all say air doesn't like to turn a corner. Which is why what I see in the 12" is not a corner, but radiused bends, which is a different story. What I was railing against was like in the ad, or when folks use those sharp PVC corners.
From experience, I would not hold up B.I.C. as a shining example of hifi
. Actually there are many manufacturers I would not hold up as shining examples of how to make a port...including some pro folks (heavy mesh covering high flow ports???? ugh)
Also true that I doubt speaker simulation programs really can simulate turbulent airflow. Maybe the most sophisticated ones.
From experience, I would not hold up B.I.C. as a shining example of hifi
. Actually there are many manufacturers I would not hold up as shining examples of how to make a port...including some pro folks (heavy mesh covering high flow ports???? ugh)Also true that I doubt speaker simulation programs really can simulate turbulent airflow. Maybe the most sophisticated ones.
"I would not hold up B.I.C. as a shining example of hifi"
Just goes to show what you don't know. It's not about the quality of the sound of their product, but the efficacy of their bent shelf-type ports.
BIC had a demo unit with a plex side and powered it with a 60hz transformer to show air-flow. It works and has low noise. The method I proposed results in even better air flow and is quite easy to build.
Just goes to show what you don't know. It's not about the quality of the sound of their product, but the efficacy of their bent shelf-type ports.
BIC had a demo unit with a plex side and powered it with a 60hz transformer to show air-flow. It works and has low noise. The method I proposed results in even better air flow and is quite easy to build.
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If that was true a horn or transmission line wouldn't work.
The pro guys I know would all say air doesn't like to turn a corner. Which is why what I see in the 12" is not a corner, but radiused bends, which is a different story. What I was railing against was like in the ad, or when folks use those sharp PVC corners.
From experience, I would not hold up B.I.C. as a shining example of hifi
Also true that I doubt speaker simulation programs really can simulate turbulent airflow. Maybe the most sophisticated ones.
The horns and transmission lines you're referring to generally will have much larger cross-sections, so the airflow is relatively "slow." Often they'll have corner angles as well, rather like what djk showed.
But those are not really right angle bends; I was complaining about right angle bends.
As for BIC, I'm curious what product had the plex demo. I heard a number of their models (not every single one, of course) and my buddy was enamored of his Venturi ported 3-way omnidirectionals. OK sounding stuff but not amazing. I wonder if the speakers in the ad really had ports that looked like such a right angle.
But those are not really right angle bends; I was complaining about right angle bends.
As for BIC, I'm curious what product had the plex demo. I heard a number of their models (not every single one, of course) and my buddy was enamored of his Venturi ported 3-way omnidirectionals. OK sounding stuff but not amazing. I wonder if the speakers in the ad really had ports that looked like such a right angle.
Can we say, that we need to increase x% cross-section with each degree bend?
And this would neutralize any ill effect if bends.
If we could derive some kind of equation it would make use of bends easy.
"As for BIC, I'm curious what product had the plex demo."
IIRC, it was a BIC Formula 6 demo model that had a plex side on it. It also had a small transformer and a push-button to power the woofer. It had streamers in the port that would wave back-and-forth when you pushed the button. It sure moved a bunch of air!
"Can we say, that we need to increase x% cross-section with each degree bend? "
I don't think that is needed. Most horn designs try and keep it as constant as possible, some actually constrict it a bit, the position of the corner reflectors can increase the amount of HF going around the bends (not wanted for a port).
IIRC, it was a BIC Formula 6 demo model that had a plex side on it. It also had a small transformer and a push-button to power the woofer. It had streamers in the port that would wave back-and-forth when you pushed the button. It sure moved a bunch of air!
"Can we say, that we need to increase x% cross-section with each degree bend? "
I don't think that is needed. Most horn designs try and keep it as constant as possible, some actually constrict it a bit, the position of the corner reflectors can increase the amount of HF going around the bends (not wanted for a port).
Bending the port - depending on the kind/angle/sharpness of the bend - may
cause an increase of friction.
There is no problem in tuning the box correctly to the desired Fb with
a bend, but Qb may decrease a bit and with a bend too sharp nonlinear
effects (and port noise) may show up at even lower velocity than with a
straight and well rounded port.
If Qb lowers significantly, it may be desirable to tune the cabinet higher.
I already have used kinds of flexible drainpipes bended in all shapes you can
think of, it works reasonably well and noise is much less than expected.
However one may have to estimate the "effective cross sectional area" experimentally.
It will usually turn out smaller then the inner geometrical cross section.
Some textbooks state, that port length should be less than 1/12 of the wavelength
of the highest frequency, where you expect the port to act as a pure mass
reactance. That wavelength would correspond to the upper resonance of
a vented enclosure, showing up as the upper impedance peak. So port length
is quite limited.
http://img.alibaba.com/photo/243856875/flexible_drain_pipe.jpg
cause an increase of friction.
There is no problem in tuning the box correctly to the desired Fb with
a bend, but Qb may decrease a bit and with a bend too sharp nonlinear
effects (and port noise) may show up at even lower velocity than with a
straight and well rounded port.
If Qb lowers significantly, it may be desirable to tune the cabinet higher.
I already have used kinds of flexible drainpipes bended in all shapes you can
think of, it works reasonably well and noise is much less than expected.
However one may have to estimate the "effective cross sectional area" experimentally.
It will usually turn out smaller then the inner geometrical cross section.
Some textbooks state, that port length should be less than 1/12 of the wavelength
of the highest frequency, where you expect the port to act as a pure mass
reactance. That wavelength would correspond to the upper resonance of
a vented enclosure, showing up as the upper impedance peak. So port length
is quite limited.
http://img.alibaba.com/photo/243856875/flexible_drain_pipe.jpg
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