Depends on the frequency.
If it's near the tuning and the vent is too small, bigger excursion.
Under the tuning there would be less excursion with a port that's too narrow.
At least an octave above tuning, acts like a sealed box in both cases.
Of course there is the awful noise from a port that's too small.
(I didn't read the whole thread)
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alright, we have confusion, plus the formula....
S(V) >= 0.02032 * f(B) * V(D)....give by TA Speaker Topics: Vent FAQ's is maybe should be "adequate port size for NO port noise" because the paragraph only talks about port noise, never makes a reference to Xmax. "adequate" meaning bigger rather than smaller. Maybe both port noise and Xmax? are the same?
Can you give websites which talk about such or can you elaborate in good detail with formulas and such (don't know how many times formulas will be said by me on the thread
).Again, we are looking for Port size calculations to reach Xmax.....anyone chime in please.
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As a side not (maybe it should be in a new thread?), can anyone elaborate on the crazy idea on the crazy idea if the port opening and the box can act like the empty glass bottle and the opening when air flows across right?
sorry if the original thread has been hijacked...
again asking Moonfly how to achieve good "resonance" since "port tuning" and "adequate port length for NO port noise" seem to be set in stone because you can find formulas on such through websites. another thing to consider is "adequate port length to reach Xmax". maybe such is the same as "resonance". and again, maybe another calculation exists for the empty glass bottle
sorry if the original thread has been hijacked...
again asking Moonfly how to achieve good "resonance" since "port tuning" and "adequate port length for NO port noise" seem to be set in stone because you can find formulas on such through websites. another thing to consider is "adequate port length to reach Xmax". maybe such is the same as "resonance". and again, maybe another calculation exists for the empty glass bottle
.....
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A ported box is also known as a Helmholtz resonator, as is a jug.
Given enough power, a speaker will reach or exceed Xmax regardless of port size.
If a port is undersized, it will be ineffective and noisy at large speaker excursions.
Most good box design programs will show port velocity at any speaker drive (power) levels.
To avoid port noise and "compression", the port should be large enough so the port velocity is under around 15 meters per second when powered with enough power to reach Xmax.
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As a side not (maybe it should be in a new thread?), can anyone elaborate on the crazy idea on the crazy idea if the port opening and the box can act like the empty glass bottle and the opening when air flows across right?
A ported box already is a Helmholtz resonator. The port "hoots" at the port tuning, just like the glass jug.
As I recall, the port needs to be sized such that the max velocity of air is less than 10m/sec to avoid "chuffing". This guy did some actual testing of port sizes:
Port Flares - Evaluation of noise
Port Flares - Evaluation of noise
The easiest way would be to use a program like WinISD which calculate port resonances as well. Ideally, resonances would be an octave above the highest operating frequency of the subwoofer, but in reality you can get away with being a little closer.
I'm a little confused about the comment on designing a port to enable a driver to reach xmax. A port actually causes a driver to reduce its amount of excursion within the ports bandpass. Once you drop below port tuning and the system unloads, you have no box control over the driver excursion anyway.
I am sure the glass bottle effect can happen with ported cabinets, but not within normal hearing under normal subwoofer operating conditions. You would need a significant amount of very direct airflow across the port aperture, and the reality is you just dont get that in a home theatre.
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You would need to employ DSP to enable a system to continue to drive excursion up within a ports bandpass, and the results probably wouldnt work too well in reality, not least as you would run out of driver power handling very quickly and create a messy final response. Is the OP talking about trying to make a driver max out its excursion within the ports bandpass? I dont think excursion alone is actually that important, as long as xmax isnt exceeded and the final goal is attained.
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The speaker's excursion is at minima at Fb, increasing drive voltage in the port's bandpass is a good way to let the magic smoke out of a speaker in a hurry.
I really have no idea what wilkes5 means by "looking for port size calculations to reach Xmax".
I have never tested a speaker where I had any difficulty exceeding it's Xmax below or around 1/3 octave above Fb.
don't have any background in car audio besides experience in making "big slot ported style boxes" which to me sound really good. the sound is smooth flowing / echoing /fast attacking bass/ which hits really low also. it seems to me the best way to do such is to make the box bigger than recommended and tune really low. a website talks about such when designing a box for SQ (just for self assurance). have been told by many people such doesn't work...
"Oversizing ported boxes and dragging the duct tuning below Fs will lead to a reduced frequency where total cone unloading occurs but bottom end efficiency falls and a further output dip shows up just above the tuning frequency, while group delay at the bottom increases. Oversizing basically not worth it, but you can look at all this by playing with the parameters in Winisd."
but to a point it works for me...anybody else?
and the answer..
maybe Silent Screamer can provide more details? weltersys, your comment made me upset. just trying to get the info in clear cut manner. the formula posted by me is for "port noise" (adequate port size for NO port noise) and it seems from Moonfly...
port "RESONANCE" (which is the thread topic currently), is maybe just the port tuning given by a normal box program? sorry, can you give a little more detail Moonfly. is port resonance just the tuning of the port? can port resonance be calculated using a formula like S(V) >= 0.02032 * f(B) * V(D)? Also Moonfly, all my experience is with car audio and slot ported subwoofer box design, so, maybe big time differences? however, you seem to believe something like the "glass bottle" exists (as myself), and fpitas doesn't?
please if your going out on a limb without too much knowledge, words like maybe, seems, ect. would give readers more confidence in pursing what is truthful.
"Oversizing ported boxes and dragging the duct tuning below Fs will lead to a reduced frequency where total cone unloading occurs but bottom end efficiency falls and a further output dip shows up just above the tuning frequency, while group delay at the bottom increases. Oversizing basically not worth it, but you can look at all this by playing with the parameters in Winisd."
but to a point it works for me...anybody else?
and the answer..
maybe Silent Screamer can provide more details? weltersys, your comment made me upset. just trying to get the info in clear cut manner. the formula posted by me is for "port noise" (adequate port size for NO port noise) and it seems from Moonfly...
port "RESONANCE" (which is the thread topic currently), is maybe just the port tuning given by a normal box program? sorry, can you give a little more detail Moonfly. is port resonance just the tuning of the port? can port resonance be calculated using a formula like S(V) >= 0.02032 * f(B) * V(D)? Also Moonfly, all my experience is with car audio and slot ported subwoofer box design, so, maybe big time differences? however, you seem to believe something like the "glass bottle" exists (as myself), and fpitas doesn't?
please if your going out on a limb without too much knowledge, words like maybe, seems, ect. would give readers more confidence in pursing what is truthful.
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SO, the the thread topic question "Does a slot port have pipe resonance" is silly because all ported boxes are Helmholtz resonators? is the port tuning the "pipe resonance"? and is the pipe resonance the same as the "empty bottle" theory? it seems like what weltersys is logically saying to me. and weltersys and fpitas could be right? both seem to agree just the port alone is like the glass bottle, it might be. thanks. now can we find what the topic of the thread is about "RESONANCE". and if you guys are right, then the answer is simple, all slot ported boxes have pipe resonance because all ported boxes have ports, and ports are the resonance.
it seems like something else goes into a really good ported box than the "golden ratio", "port noise", etc. formulas can be found for such and wondering if any more exist?
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Silent Screamer's posts 13, 15, and 21 are all pretty clueless. Sorry Silent Screamer, but I calls 'em like I sees 'em.
Your questions "looking for port size calculations to reach Xmax" based on his comment in post 13 are simply not answerable.
Port resonance is not the same as box tuning, Fb.
An example of a port resonance can be seen in the chart below, the box Fb is 36 Hz, the triangular corner slot ports used to make that tuning have a resonance that cause the dip centered around 320 Hz and the peaks at 280 and 360 Hz.
Using round or rectangular ports might change the "look" of the port resonance slightly, but as the resonance occurs over an octave above the sub's pass band, the resonance is of little concern.
When designing for a speaker where the port resonance is within the pass band, the port resonance may be of concern.
As Moonfly mentioned in post 30, a program like WinISD will calculate port resonances, as will Hornresp.
These programs also simulate the port velocity, so rather than "pressing a button" and being spoon-fed a port size, you can make your own choices based on power demands, available size, and desired frequency response.
Art
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??? Xmax or whatever excursion you want to calculate for is already factored into V[D], ergo the formula calculates a low vent noise [acoustically efficient] at the chosen Xmax at Fb.
GM
The explanation is in the rest of that same post.
If it's near the tuning and the vent is too small, bigger excursion.
Under the tuning there would be less excursion with a port that's too narrow.
At least an octave above tuning, acts like a sealed box in both cases.
Of course there is the awful noise from a port that's too small.
Port resonance and port tuning are different things. Although the port tuning is a function of a resonance, in as much as the port and cabinet form a Helmholtz resonator, this isnt the resonance talked about when talking about port resonance. Port resonance is higher frequency resonance present in the port during use which will be excited by the subwoofer under normal use. If you use a program like WinISD, you can see this as a figure it calculates called first port resonance. This would manifest itself as a kind of audible echoing within the port, and you dont want this. All ports will resonate in this way but the trick with subwoofers is to ensure this resonance is up at frequencies that are not within the subwoofers working range, so they become a non issue.
By wanting to design a ported system to make a driver reach xmax, I an only assume you mean you want it to hit xmax above the port tune, right at the point at which it begins to reduce again as the ports effects come in. Again, you can model this in WinISD. Generally larger cabinets will tune lower and aid a driver in reaching xmax, but these goals alone wont guarantee a system that works really well.
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