If the cabinet is sealed, below tuning frequency, lower frequencies are attenuated logarithmically, which if plotted relative to amplitude, produces a linear acoustic rolloff, but the sound itself is still being reproduced at the same "speed"- movement relative to time (frequency: measured in Hertz) and "position"- rate of frequency relative to time (phase: measured in degrees). As a matter of fact, sealed cabinets have the BEST innate transient response because there are no phase interactions distorting the output. Ported cabinets have port-phase distortion and open-backed cabinets have secondary coupling (boundary reflections) interacting directly with the driver.
You are wrong, my man. First, transient response <> phase response though poor phase response can ruin the benefits of good transient response. Confusion of transient and phase response is additionally not helped by the fact that both can be measured using the same test - square wave response (but different parts of the test speak to transient vs phase response characteristics). Transient response is merely how quickly the transducer will react to program signal input and, accordingly, start moving from it's point of equilibrium. Phase response is how coherant the aggregate response of the entire enclosure is with respect to the given program element that is being reproduced - e.g. in a multiway system in the crossover region, the tweet and woof can be reproducing the same program element, but they don't (without a lot of design work) do so in the exact same time frame. Additionally, they are not a point source (unless coaxial) so the distance to your ear creates a further timing differential and therefore phase discrepancy... and yes this happens with ports and those other things you mentioned too). The fact of the matter is that due to the nature of how acoustic suspension cabinets work, the driver requires more power to move as it is facing greater mechanical resistance due to internal cab air pressure. That is by definition, poor transient response.
Further, sealed cabs do have at least one critical phase-related issue: backwave distortion (ported suffer from this as well).
I never made an assertion as to whether the TR of a sealed is better or worse than ported, leaving the matter to something like 'both are not so great in that regard' compared to other types.
Yes, open back do have a major phase issue, but only (significant) starting at the point where the distance from the cone to the rear opening is 1/4 of the wavelength of the frequency, which is why the bass response disappears there (cancellation due to approximately opposite phase from the front and rear; I say approx because of the time it takes for the sound to travel around the cabinet makes it not exactly opposite even if it is a near-negligible difference - I wouldn't be so particular about that detail if I wasn't talking to you, as you tend to jump on me for such oversimplifications), but since the driver is essentially operating in "free air" it has the lowest mechanical resistance to movement possible and therefore better transient response than a sealed cab. It is actually the characteristic that (at least somewhat technically inclined) open back lovers (guitards as well as hifi) cite as the reason they love them so much.
"Bass reflex" is just a fancy way of saying "ported."
Yep, I used both terms and thought I was clear on that (... though to be really accurate, not all cabinets with a port are bass reflex - see Tapered Quarter Wave Tubes, Transmission Lines and Bandpass for example). I kinda fail to see your point here; maybe I typoed somehow in my original post and you didn't include that in the quote.
Until tuning frequency, ALL cabinets act as open-backed. In an open-backed speaker installation, the low frequency limit is the cone resonance. Below that, the driver literally has nothing to 'grab' and converts all of the power below resonance into heat until either the voicecoil burns up (at the thermal limit- aka "RMS" wattage rating) or the cone suspension tears loose, both resulting in a destroyed driver if enough power below cone resonance is fed to the driver.
With regard to frequency response, yes (if maybe a bit oversimplified, see for example backwave distortion, which affects sealed and ported cabs but not open backs; close enough though). Transient response I am not 100% sure, but doubt that it has no effect until resonance (but it is probably maximal approaching resonance). Phase response will vary among cab types at least slightly due to size/shape (e.g. baffle diffraction is a function of cab shape/size vs wavelength, rather than a function of speaker resonance).
...in which case, you've just made it into some sort of enclosed cabinet.
No - I think you misunderstood me here. I did not mean (capital letters) Infinite Baffle, so much as (small letters) a larger baffle (than, say, a guitar combo) - see open back hifi speakers; the baffles can be multiple meters wide and tall and still open back - yes there is still a point of phase cancellation, but the idea is to make the baffle large enough so that this point is moved further downwards, ostensibly below the effective range of the drive unit or below the range of human hearing, but that is not always possible/feasible due to the dimensions/wavelengths involved. Not very practical but some people swear by them (not me, but never really tried them out due to too damn big).
Transmission lines are tuned subwoofer cabinets (or any portion of the audio spectrum for that matter) that are baffled both above and below a portion of the audio bandwidth.
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No, it doesn't. It is in a box that is acoustically tuned like a crossover to air-load the driver in a way that it is only operating in in small section of the audio bandwidth. It's cheaper and easier to just do it electronically, which is why crossovers are so common and transmission line cabinets are not.
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You have it backwards. The description of the physical process is mostly correct, but the use of terminology and conclusions are incorrect. A transmission line cabinet only acoustically loads the speaker in the portion of the audio spectrum where it is the most efficient, but it most certainly DOES air-load the driver.
I'm not sure we are talking about the same thing here (some things you said make me think you're talking about Bandpass cabinets, but not sure). Transmission line speaker cabinets are nothing like a crossover and not just for subwoofer (edit: oh I see you don't disagree with that, my bad). They solve the essential problem of what to do with the speaker's backwave by either harnessing it (as useful additional bass response), or nullifying it (depending on whether the line is terminated to a port or a wall, respectively) using what is essentially a delay line (usually with mechanical Low Pass Filter, aka stuffing) which puts the driver's backwave in phase with the front.
This enclosure type is most often used for woofers in a multiway system (or, yes, standalone subwoofers) or full range drivers, but also (at the peak of their popularity in home hifi - the 70s) for midrange drivers in 3-way designs (and since 3 ways as well as TLs are mostly out of style we don't see that anymore).
In the case of a TL that is terminated to a port (99% of commercial and DIY specimens I have ever seen - closed TLs I have mostly seen in use when it is a midrange that is in the TL) the driver does operate in what is very close (if not exactly) free air conditions, as there is no internal cabinet pressure (from cone movement changing internal volume) since there is no bottleneck at the port terminus which is generally at least an order of magnitude, or thereabout , larger than a bass reflex port and presents no mechanical resistance. A design parameter of TLs is for the port (line terminus) to be in the area of 0.8 to 1.5 of the driver's Sd or effective piston area (most often 1 or just a hair more) - this means that there is (little or ) no bottleneck for air moving in and out of the line to maintain equilibrium air pressure and though there may be some effect from having to travel down the line itself (especially if folded to minimise cabinet size) this is negligible (especially compared to sealed/ported).
Anyway, I was talking about these (think of a backloaded horn, with the horn tapered in the opposite direction, or straight in simplified versions.... and linear taper vs log .. and operating on a totally different principle as summarised above):
more info here:
http://www.t-linespeakers.org/and not these (bandpass):
...not so. Ported cabinets have tuning "bumps" at and above tuning frequency (in octave intervals) caused by the phase interaction of the primary baffle, cabinet airspace and the secondary baffle, the port, which produces a VERY uneven frequency response and phase distortion, but with the benefit of better efficiency below natural resonance of a space/driver combination until port frequency, below which point, the driver behaves like it is in open air.
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No, there are "more;" they are the tuning "bumps" I was talking about. Additionally, because of the port's secondary baffling effect, some frequencies are cancelled while others are boosted by the tuning resonances, the phase distortion discussed earlier.
Yes, I don't disagree with you here. I was oversimplifying (for your tastes). By 'flater, longer" I meant that the final bass-end rolloff has a delayed start in ported cabs (relative to sealed), which I am sure you agree with from what you have already said.
That is the characteristic inherent in ALL ported cabinets, phase distortion, and it's not a psychoacoutic phenomena. It is measureable in a number of ways. By adding a secondary baffle, a port, connected to the outside air column, a ported cabinet will ALWAYS have phase distortion because of the time/frequency interaction between the two baffles caused by the physical difference in locations of the baffles.
What do you mean by the first use of the word 'that' here?
Yes, there are measurable response phenomena here but what I was talking about is the tendency for the auditory system to hear the extended flat bass response (with caveats as explained in the point above - yes a simplification, but you must know what I mean - compared to the early rolloff start of a sealed cabinet there is an additional period of relatively flat response... and we all know no speaker is litterally flat anywhere in it's response, or not for very long anyway) of a ported cab and feel like there is more and lower bass there which does not actually measurably exist - somewhat as if the rollof slope of the ported cab was more like that of a sealed - like the ear just does not compute a generally broadband signal just stopping right there /expects more.
