I understand that this phase relationship between the woofer and the port is frequency dependent. It isn't a fixed number.. Here is a great visualization. It isn't super scientific, but it demonstrates how the port resonance changes by frequency.
Simulation software shows us the SPL of the port resonance vs the cone, and the combined output. So it is important to note that when the two are competely out of phase, the contribution of the port is negligible.
Simulation software shows us the SPL of the port resonance vs the cone, and the combined output. So it is important to note that when the two are competely out of phase, the contribution of the port is negligible.
Also, if the port and woofer are separated, as in one in front and one in back, there could be some "lobing" at frequencies that are a little out of phase like what they demonstrate in this video. But to observe it you would have to measure in half space with no reflections? I believe this would be a small effect since the out of phase portion is lower energy. And this effect would be nullified by reflections and room modes....(pun intended)
1 Transient vs. steady state behaviour is very different for resonating systems vs. direct radiator
2 There is phase shift in the output signal of the resonator (port or passive driver). Delay as term is not relative to frequency like phase shift!
3 Summed spl of nearfield measurements is a simplification that gives false result
As an example look at Amir's measurements again! https://www.audiosciencereview.com/forum/index.php?threads/jbl-4309-review-speaker.27255/
-these are steady state measurements!
- impedance measurements tell that tuning frequency is 45Hz, but woofer's spl minimum is at 37Hz
- notice also what ports do at 700Hz!
2 There is phase shift in the output signal of the resonator (port or passive driver). Delay as term is not relative to frequency like phase shift!
3 Summed spl of nearfield measurements is a simplification that gives false result
As an example look at Amir's measurements again! https://www.audiosciencereview.com/forum/index.php?threads/jbl-4309-review-speaker.27255/
-these are steady state measurements!
- impedance measurements tell that tuning frequency is 45Hz, but woofer's spl minimum is at 37Hz
- notice also what ports do at 700Hz!
But how many small drivers, like 6" or smaller, can extend down to 100hz in a sealed enclosure? I have a project where I am trying to do this, and I have not found very many! Like I said, the problem is subwoofers. If we could cross our midrange drivers higher than 100hz, it wouldn't be a problem.
This is a 6.5" I found out, and we can see it barely makes it down to 100hz on it's own. The output below this is all port.
So, you still believe that no driver made is 1) airtight and that 2) no enclosure can be airtight, ever. Gotcha.
I am not sure what you are getting at, but if I put a few fractions of a PSI into an otherwise sealed enclosure with an air fitting threaded into it, then close a valve with the cone displaced, you are alluding that the air will somehow escape magically?
Putting DC into a low Re driver for minutes at a time, no, I am not going to do that.
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Or a nice reminder to take some care of your bass reflex port and not just slam in some simple tubes!
It's still work in progress, but here is my contribution:
https://www.diyaudio.com/community/...sonance-absorbers-and-port-geometries.388264/
Again, the confusion stems from faulty methodology. You simply can’t look at time/delay and draw conclusions with a steady state signal. Plse redo with a transient, f.i. a step, and get back.
Ok guys I admit being a bit arrogant! I'm aware of problems with small sealed and open baffle speakers too. Some issues can't be avoided at all but in general the designer always has some constraints as limiting freedom of choices. Annoying, even frustrating... Finding ways to eg. effectively reduce port noise can be difficult, please try to find a pic of Genelec small 2-way monitor's reflex tube! I have seen those at the factory...
My blessing is that I'm just a hobbyist and all my own desins have closed box woofer, dsp and classD amps.
Data-Bass gives more info and comparisons https://data-bass.com/#/articles/5cb774640ca6e70004e10828?_k=rlpi9a
My blessing is that I'm just a hobbyist and all my own desins have closed box woofer, dsp and classD amps.
Data-Bass gives more info and comparisons https://data-bass.com/#/articles/5cb774640ca6e70004e10828?_k=rlpi9a
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Oh yes, TL is even worse... https://audio.com.pl/testy/stereo/kolumny-glosnikowe/3901-pmc-prodigy5#laboratory
Graphic presentation is summed nearfield spl
Graphic presentation is summed nearfield spl
But many more cycles to decay once the resonant energy has been built up in what is simply a poorly damped Helmholtz resonator. This time smearing after the signal has ceased is minimised in a sealed enclosure.
Depending on music and room it could be audible?
Would be interesting now who can give feedback on audibility with equally EQed systems...... not so common such elaborate listening tests.
I once had a listening test and had the subjective impression that closed box had better transients but more distortion than bass reflex system.
As a speaker builder however I prefer low tuned reflex systems over closed box because loudspeakers in general are so ridiculously inefficient
Would be interesting now who can give feedback on audibility with equally EQed systems...... not so common such elaborate listening tests.
I once had a listening test and had the subjective impression that closed box had better transients but more distortion than bass reflex system.
As a speaker builder however I prefer low tuned reflex systems over closed box because loudspeakers in general are so ridiculously inefficient
Damping is provided by the driver and is defined according to the response, calling it good or bad would be a reflection on the alignment.
I have calculated twice now recently how much of a myth this is.
Unless you live under incredible harsh conditions.
But in that case I think loudspeakers will be the last thing on your mind.
Correct, I think we might need an explanation of minimum-phase systems here so I'll do my best:
Minimum-phase refers to a set of predictable behaviors in harmonic systems that vibrate or oscillate. The essence of these 'rules of behaviour' is that frequency response and phase are inextricably linked and mathematically predictable. This means that any adjustment to the frequency response of a loudspeaker will result in a corresponding and predictable change in phase, both transient and steady-state.
The key here is that minimum-phase systems are not only found in the mechanical world like loudspeakers and resonators, but also in electrical circuits. They are functionally equivalent and can be interchanged. For instance, a resonance causing a peak in a loudspeaker's frequency response can be neutralized by a counter resonance in an electrical circuit, which will adjust both the frequency response and the phase behavior of the system.
Thus, if the combined behavior of a port and driver in a loudspeaker constitutes a minimum-phase system, the phase behavior—including transient response, ringing, and decay—is determined by the frequency response. If EQ, which is also minimum-phase, is applied to make a ported system's frequency response mirror that of a sealed system, the phase response will mirror as well. Conversely, if a sealed system is EQ'd to enhance its bass as in a ported system, it will exhibit the same phase behavior as the ported system.
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The measurements @stv and myself have shared show that while the combined port and driver system is indeed minimum-phase with no 'excess delay' in time of arrival, the individual components of the woofer and port do take a different share of the load on the first few cycles of a waveform. The distortion and max SPL will therefore suffer in a dynamic and non-linear way, even regardless of EQ, but those two metrics will never be worse than without the port.