So back to my original hypothesis that since the port is a "radiator" then the larger the surface of the radiator the more efficiently it will produce lower frequency waves and the lower density air in a larger port would provide a better impedance match for the ambient air, meanwhile the larger port mean less losses from compression, turbulence, heat, etc, as long as the port area is not so large that it can no longer load the driver's diaphragm.
A port contains a slug of air, that air mass moves back and forth in a specific relationship (a phase inversion) with the cone movement, the port's output peaking (Q of the peak determined by TS parameters of the speaker) at Fb.
At Fb, (the box's resonant frequency) the speaker cone movement is at minima, the movement of the slug of air in the port at maximum.
As long as the slug of air remains contained in the port, the output efficiency of a large or small area port is basically the same, other than the frictional losses in high aspect ratio ports previously mentioned in other posts.
You can easily determine that efficiency remains the same with differing port area resulting in the same Fb with various simulation programs.
Once the air mass in a port is large enough to keep velocity under control, there is no reason to go larger.
The better programs include port velocity, so you can determine whether the port will be "blown out" at high excursion.
No. The opposite is true.
A larger area port (and thus longer for the same Helmholtz tuning) will have more viscous loss due to wall friction. But the actual energy lost per unit of wall area will be lower due to the lower air velocity in the port.
However, obsessing over the port efficiency is a waste of time in most cases. The efficiency (Q) of the total system (driver/enclosure/port) is the sum of the Q of the resonant systems. Port Q for all sane combinations of port size and length is many times higher than the Q of the driver, so the driver Q dominates. You can see this when you calculate the Qts value for a driver from the Qms and Qes values. The system Q can never be higher than the lowest Q in the system.
Getting back to to your original efficiency question:
I agree, in theory a smaller port is less efficient at coupling to the air outside the enclosure, it will have a lower radiation impedance just like a smaller driver cone. But this does not equate to lower efficiency in a speaker.
If you halve the area of a driver cone, you have to double the excursion to achieve the same SPL. This requires twice the power, therefore the efficiency is lower. But the same does not apply to a port. Halving the port area will result in twice the air velocity in the port for a given SPL, but does not require twice the power to do so. So, apart from the aforementioned losses in the port, the efficiency does not change.
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Can you point me to some test results or specific programs that will demonstrate this clearly.
And can someone please explain (in english) why the rules that apply to the drivers diaphragm don't apply to the air exiting the port, I was not satisfied with non-answers I got before. All I'm hearing is it just is and I'm getting directed to articles which do not directly address my query.
And I am not a mathematician but am familiar with the basic principals of physics and fluid dynamics.we agree a radiator touches the air to move it like a speaker cone, regardless of whether it is a port or a speaker cone.
we also agree the topic here is ports, not electric circuits.
because your software does it one way does not suggest the entire world must do it the same exact way.
but if you want to call it a radiator, i'm open minded enough to elaborate.
a radiator, a diaphragm, a speaker cone connected to a voice coil.. all three of them push onto the air .. i don't like to slow down conversation to point out a difference when freedom allows multiplicity.
i think we are here to communicate reason, not sit back and hope people can progress further without those reasons elaborated.
what i see clearly is the lack of question as to the word efficient.
are you hoping the port will be as reluctant as the speaker cone's movement of air when the port is bigger?
because that is not always the best seem of sound between speaker and port.
my ports will blow on me faster & harder than the speaker cone, but that doesn't say the sound from the port doesn't match the sound from the speaker cone .. the point i was trying to make.
otherwise you seem stuck as if you need somebody to go through an example of pushing a feather or piece of cotton from the port, as if it has anything at all to do with sound quality when it doesn't.
i don't see the sanity building or talking about building a port that makes an inferior sound from the speaker location regardless of whether the extension goes lower in frequency.
are you hoping the port will be as reluctant as the speaker cone's movement of air when the port is bigger?
because that is not always the best seem of sound between speaker and port.
my ports will blow on me faster & harder than the speaker cone, but that doesn't say the sound from the port doesn't match the sound from the speaker cone .. the point i was trying to make.
otherwise you seem stuck as if you need somebody to go through an example of pushing a feather or piece of cotton from the port, as if it has anything at all to do with sound quality when it doesn't.
i don't see the sanity building or talking about building a port that makes an inferior sound from the speaker location regardless of whether the extension goes lower in frequency.
I think this thread has reached a point of redundancy. One of the major issues with this "thread" is that all of T/S methodology is based on electric circuits. This not I, nor you, nor the OP can escape from. To truly understand where T/S methodology comes from and it's implications, ones needs to first be FULLY acquainted with damped double-mass double -spring harmonic oscillator/resonator theory a, electro-mechanical analogues, and in particular, solutions for the equations of motion of said oscillators/electrical analogues via linear/non-linear 2nd order differential equations. When I say "fully acquainted", I mean actually be able to solve the equations and obtain suitable solutions. All one needs to do is to read the link for Small's paper on Direct Radiator Loudspeaker Analysis to see that the truth lies in all the symbols and equations. If one cannot extract the needed information, then they simply lack the formal training to do so, mathematically.
Nice! Someone finally got it right in this long, rambling thread.
I will say that looking for an "efficient" port design is perhaps the root of the confusion in this thread, as efficiency can mean many things. Perhaps it would be better stated to seek the "least lossy" port design. It is worth reading the paper that OscarS posted in the other thread. I know that Polk had a "power port" concept that they were able to measure as having lower losses than a rather larger straight port - google for it. These ports were basically a port with a large radius flared entry and exit that had a diffuser of sorts to help turn the air around the flare.
I kinda sorta agree, but at the level of this kind of questioning, if one doesn't know that the least compression is precisely equivalent to "least lossy" then the discussion is out of their league, for the mere existence of dB compression is because of losses.
The polk power port with the 90° diffuser is indeed "talked about" in the PDF I posted, which is here again: 11094.pdf
I'm reviving this because I remain somewhere between confused and unconvinced. I have a cabinet in which I have a choice of ports: 60 x 140, 50 x 180, or 2 x 40 x 125. Assuming I have plenty of headroom when it comes to cabinet volume, and all tuning frequencies being equal - what would be best?
I have enough resonators in my house to give me information that conflicts with the math and theory.
My 'best' sub blows like Moby Dick. The port can dry washing at 10 feet. In between exhausting and refilling the resonator, theory suggest the port is always going to be a day late and a dollar short in getting involved in any action. My floor-standers have the opposite issue, the ports have little or no interest in proceedings and at full volume couldn't extinguish a match.
So, here's my pseudo-logical theory: There is a relationship between port volume, cabinet volume and Vas. Ideally, it would efficient to maintain the same volume of air inside the resonator at all times. A port that blows out 1 litre during a 'kick' and sucks it back in before the next kick will perform better (faster) than the port that expels 10 litres and has to suck it back in before resuming its duties. In that time your resonator is operating in negative pressure. You cannot omit the speed of sound (air pressure) from your calculations.
Bigger port, better bass.
I have enough resonators in my house to give me information that conflicts with the math and theory.
My 'best' sub blows like Moby Dick. The port can dry washing at 10 feet. In between exhausting and refilling the resonator, theory suggest the port is always going to be a day late and a dollar short in getting involved in any action. My floor-standers have the opposite issue, the ports have little or no interest in proceedings and at full volume couldn't extinguish a match.
So, here's my pseudo-logical theory: There is a relationship between port volume, cabinet volume and Vas. Ideally, it would efficient to maintain the same volume of air inside the resonator at all times. A port that blows out 1 litre during a 'kick' and sucks it back in before the next kick will perform better (faster) than the port that expels 10 litres and has to suck it back in before resuming its duties. In that time your resonator is operating in negative pressure. You cannot omit the speed of sound (air pressure) from your calculations.
Bigger port, better bass.
I was so confused right on the first page. Like, isn't it obvious with the port size? As everything, there is optimal curve to it, not a line.
Actually, port displacing 10l of air volume would indicate greater SPL. Because the ar mass movement IS SPL. You just don't want to displace it in a 20l box for other reasons.
At this point I'm quite lost on what it is all about. If you use conventional ported box, just make the damn port large, as long as you can do it, and don't need to fold it much.
Actually, port displacing 10l of air volume would indicate greater SPL. Because the ar mass movement IS SPL. You just don't want to displace it in a 20l box for other reasons.
At this point I'm quite lost on what it is all about. If you use conventional ported box, just make the damn port large, as long as you can do it, and don't need to fold it much.
A few pointers I have found invaluable over the past four decades:
- Begin the design with a port area equal to Sd and work backwards until it fits in the box. Size matters.
- Port length should not exceed twice its length.
- Flow should be equalised in both directions to maintain linearity and reduce port rectification.
- Port radius is most important and depends upon application - it's a bit of a 'Hoffman' situation where optimising one aspect detracts from another.
- NO BENDS!
- A single circular port remains optimum.
- Proper port design is a win-win; increased efficiency and lower distortion.
Indeed! Unless you use port for other stuff than just getting SPL out of it.
I could not self correct. You mean width or circumference to length? This will directly collide with other vital goals.
I have heard this many times. Could you elaborate please on the problematics of that? I can only imagine, but I am not sure about severity.
I can assure you there is even more to it. With modern, high excursion drivers, some real magic can be done. Working on it...
If one tunes the port low, and does not use it in most useful band, it doesn´t look to be that bad, once we compare SPL to SPL. Even GD shows that above 50Hz, there is no problem to speak of. Once issues are possible to attenuate and send off-band, things get much more usable and "brighter" for ported box. What I see is that there is no sacrifices made in the name of maximum SPL output of most enclosures, and that indeed will cause very bad reputation.
No free lunch, you are right.
To elaborate on my side - I now started to use ports for cooling purposes, for impedance shaping, for efficiency shaping (power compression control) for little cone excursion control, but not really that much for SPL. The driver must be mostly capable to do the work alone, with just some help. It results in arguably small port with low flow, with smaller effect on output quality. It will take heaps of work to present the data and implications of it though.
At higher volume velocities, a port with a bend is likely to be causing a lot of flow separation in the vicinity of the bend. This will introduce losses and can lead to port noise caused by turbulent flow inside the port. A port with a bend consisting of a sharp right-angle corner, although easy to construct, would likely be particularly bad in this regard.
I have tried that. Yes, it is bad, but it is not end-all be all. For casual builds, sharp turn is borderline acceptable, for better builds, I do two consequent 45degrees turns and it really helps a lot. But I do not run my ports anywhere near full loading. Usually 12-14m/s tops. That might help. It also helps with efficiency overall.
Well, have you seen the Chebychev vented-box alignments, which are usually tuned low? They have a transient response that takes a long time to die away when compared to a quasi-Butterworth QB3 vented box alignment. Of course, here I am referring to alignments that are chosen to produce a relatively flat response in the vented enclosure's passband. Of course, tuning the port such that it doesn't adjust the vented enclosure's response to maximize its flatness will "improve" the transient response by some measures, but at the deleterious expense of usable low-frequency output.
I'm not sure of the benefits of impedance shaping. It seems that this placing of a resonance into the system impedance response, yet not utilizing it to produce more acoustic output, is unlikely to be all that beneficial. Sure, drawing less power around the impedance peak seems to offer benefits, but mitigating the concurrent lack of acoustic output simply ends up requiring lots of extra amplifier power. If one wants good low-frequency, then suitable power is needed, or the system's mass–stiffness–damping characteristics need to be optimized to produce useful results. That's what Thiele discovered back in the 1960s, and he proposed a useful way forward, which has been fine-tuned over subsequent years.
That sounds very much like a filter-assisted low-frequency alignment, again studied by Thiele and others.
A ported enclosure is, when all is said and done, a poorly damped resonant system possessing energy storage significantly in excess of the highly damped cone movement, so cannot help but have a poor transient response. Ported ~ '70s Cadillac. Sealed ~ 2022 F1.