so unbelievably wrong, geez and the authoritative tone of your post, I'm so glad some others are/will chime in to the countless other misleading statements. perhaps yer thinking of FFT instead of transient response.
BTW transient response of a unity gain step in control systems of a 2nd order system ie closed box and a BR which is a 4th order which can never be near critically damped, therefore it could be referred to be "slow" in comparison to settling times to say within 5%. I would prefer a closed box with reasonable Qs for a tight sounding and accurate bass and not fast bass, given any BR with equal or esp greater LF bandwidths. In my mind from many simulations, transient response is key in describing differences in sound between AS and BR.
Last edited:
The resonance that occurs in the bass region (say 40Hz) as part of the bass reflex operation is not a pipe resonance, but rather a mass spring resonance where the moving mass is the mass of air contained within the port tube (and extending a bit beyond it each way) and the spring is the volume of compressible air within the cabinet. (excluding the air within the port)"
They are one and the same.
I strongly urge you to take a couple of years of calculus and analytic geometry preparatory to taking a course on Fourier theory as it applies to linear systems, and then go to the back of the chapter where they give you transient response in the form or square wave rise and fall time at various frequencies and expect you to calculate the FR. Then solve the problem where they tell you to compute it the other way around. Then come back and we'll discuss it. BTW, on another web site, a certain famous preamplifier designer who shall go unnamed made exactly the same mistake and when I pointed it out to him, he ascribed his mistake to me. He later admitted he was not trained as an electrical engineer...but he did take a few courses in electronics 😀
YOU need to read at least a introductory course on control theory. haha I'm ignoring any of your advice. I'm calling yer bluff foo
This is off-topic but I thought you might find this interesting.
The series of low-priced "giant killer" Pioneer speakers sold at Best Buy here in the States were designed by a man named Andrew Jones, who has designed speakers for TAD and KEF. The floorstanding version.....
pioneerelectronics.com/PUSA/Home/Speakers/Home+Theater+Speakers/SP-FS51-LR
......includes a design feature I have never heard of, and is explained by Andrew Jones himself in post #58 (avsforum.com/avs-vb/showthread.php?t=1278774):
Btw at the risk of sounding like a shill for Pioneer, this speaker series does not share the tinkly-bright and aggressive sound quality so many inexpensive speakers exhibit at this price point and instead are quite "warm" sounding.....so warm some HT fans think something is wrong with the tweeter. 😉
Bass reflex - Wikipedia, the free encyclopedia
"The air mass in this opening resonates with the "springiness" of the air inside the enclosure in exactly the same fashion as the air in a bottle resonates when a current of air is directed across the opening. The frequency at which the box/port system resonates, known as the Helmholtz resonance, depends upon the effective length and cross sectional area of the duct, the internal volume of the enclosure, and the speed of sound in air.
When this vent air mass/box air springiness resonance is so chosen as to lie lower in frequency than the natural resonance frequency of the bass driver, an interesting phenomenon happens: the backwave of the bass driver sound emission is inverted in polarity for the frequency range between the two resonances. Since the backwave is already in opposite polarity with the front wave, this inversion brings the two emissions in phase (although the vent emission is lagging by one wave period) and therefore they reinforce each other."
An awful idea but it was the best available for box speakers small enough to be practical in most homes before Edgar Villchur came along.
"The air mass in this opening resonates with the "springiness" of the air inside the enclosure in exactly the same fashion as the air in a bottle resonates when a current of air is directed across the opening. The frequency at which the box/port system resonates, known as the Helmholtz resonance, depends upon the effective length and cross sectional area of the duct, the internal volume of the enclosure, and the speed of sound in air.
When this vent air mass/box air springiness resonance is so chosen as to lie lower in frequency than the natural resonance frequency of the bass driver, an interesting phenomenon happens: the backwave of the bass driver sound emission is inverted in polarity for the frequency range between the two resonances. Since the backwave is already in opposite polarity with the front wave, this inversion brings the two emissions in phase (although the vent emission is lagging by one wave period) and therefore they reinforce each other."
An awful idea but it was the best available for box speakers small enough to be practical in most homes before Edgar Villchur came along.
Thanks for the link.
The woofer is located relatively high above the floor in that tall enclosure - maybe that reduces certain undesirable sonic problems? That is O.K. with me, though such a design has lower WAF - Wife Approval Factor - than a cubical enclosure (here in the States at least, since MP3 players debuted owning a home audio system has almost become an embarrassment 🙁 so that is why I believe so many companies try to design components that are as inconspicuous as possible 🙄).
Soundminded and infinia please take it down a notch or two..
Good response. I enjoyed that.
I've always felt the linearity of air vs. linearity of the typical woofer suspension was overstated. In my experience the greatest distortion factor is always motor/coil related. Although long travel spiders are available (and a decent half roll surround offers more excursion than needed), keeping the driver in control under extremes of drive often requires a carefully chosen nonliner spider. Progressively stiffenng spiders will prevent bottoming and DC offset problems, and at some frequencies will lower distortion (when excursion and drive force are out of phase).
I've stated before that there was a strong element of marketing in the AR acoustic suspension story. Taking a typical driver from the 50s and giving it infinite compliance would not have allowed much reduction in enclosure size. The real innovation, to Vilchur's credit, was in designing the woofer and enclosure as a system and piling on the mass to make the response flat, unlike the light cone, grossly overdamped drivers typical of the era.
David S.
Thanks for the link.
The woofer is located relatively high above the floor in that tall enclosure - maybe that reduces certain undesirable sonic problems? That is O.K. with me, though such a design has lower WAF - Wife Approval Factor - than a cubical enclosure (here in the States at least, since MP3 players debuted owning a home audio system has almost become an embarrassment 🙁 so that is why I believe so many companies try to design components that are as inconspicuous as possible 🙄).
An idea of designer is that woofer not near the floor rises less room resonanses and integrates better to satellites if they are small.
In third section "rakenne" you'll see that enclosure has mid wall that has relatively small leakage area so I think that enclosure is called closed resistance. It should control the driver better than ordinary closed box with less air suspension.
I once owned a pair of speakers, which I had actually got for free.
These had some Goodmans 10" drivers which i wish had never been stolen from my flat the following winter......
I believe these were AS types. basically a thick paper cone, at least 1" wide super soft roll surround, and from that a low Fs
they were originally housed in a vented cab which produced some extrordinary level bass down to subsonics, but they didnt like the volume being too high..........
once put into sealed boxes, they sounded far more controlled and surprisingly, ALMOST as deep reaching. maybe 40hz F3...low enough for my rock tastes, and good enough to DJ for a wedding......
If i knew what the drivers were, Id be hunting them down as we speak!
These had some Goodmans 10" drivers which i wish had never been stolen from my flat the following winter......
I believe these were AS types. basically a thick paper cone, at least 1" wide super soft roll surround, and from that a low Fs
they were originally housed in a vented cab which produced some extrordinary level bass down to subsonics, but they didnt like the volume being too high..........
once put into sealed boxes, they sounded far more controlled and surprisingly, ALMOST as deep reaching. maybe 40hz F3...low enough for my rock tastes, and good enough to DJ for a wedding......
If i knew what the drivers were, Id be hunting them down as we speak!
Sealed enclosures are good because of the gentle roll-off of the frequency resposnse in the sub 100Hz range. A ported speaker will generally have a flatter near-field response with better extension but it sometimes causes a boomy interraction with the room acoustics. I found this is a problem when ported drivers are used with F3 point below 40Hz, but it also depends on the room size and shape.
Reasons why Acoustic-Suspension died:
1) Large bulky speakers with huge internal volumes went out of fashion because they are ugly. Smaller woofers allow a narrower more attractive style of cabinet.
2) Ported design allows smaller drivers -> Less cost, better dispersion, better midrange sound. That is Win-Win-Win!
3) Foam cone surrounds go rotten far too quickly.
Reasons why Acoustic-Suspension died:
1) Large bulky speakers with huge internal volumes went out of fashion because they are ugly. Smaller woofers allow a narrower more attractive style of cabinet.
2) Ported design allows smaller drivers -> Less cost, better dispersion, better midrange sound. That is Win-Win-Win!
3) Foam cone surrounds go rotten far too quickly.
Last edited:
No they're not.
The pipe mode resonance of a pipe that is open at both ends occurs at a frequency where the pipe is a half wavelength long, and it's length is the only factor in determining the resonant frequency.
A pipe of 245mm will resonate at 700Hz. (I was slightly out in my memory of the figures in my previous post)
For a pipe resonance to occur at 43Hz it would need to be a half wavelength long at 43Hz - which is 4 metres. Where is the 4 metre long pipe in my example speaker, whose longest cabinet dimension is 0.63 metres ? Obviously there isn't one...because a Helmholtz resonance is not a pipe mode resonance.
There are two different resonances going on at the same time - a wanted Helmholtz resonance at 43Hz, involving the air mass in the pipe moving as a lumped unit, and the compliance of air in the cabinet acting as a lumped spring, and a completely independent and unwanted pipe mode resonance occurring at 700Hz within the pipe only.
In the 43Hz resonance the air in the pipe is acting as a lumped mass moving back and forth together, in the 700Hz resonance there is a modal resonance occurring along the length of the pipe, much like a room mode between two opposing walls, but at a much higher frequency due to the much shorter distance.
Something else which I think is frequently overlooked in the whole linearity of air vs suspension discussion is that the linearity of the combined air/suspension system only matters below resonance where the driver is operating in its compliance controlled region.
As soon as you go above the system resonance into the mass controlled region it doesn't matter - the inertia of the cones mass is in control, and inertia is completely linear. Above resonance but below first cone breakup linearity is therefore almost entirely a function of the motor linearity, and acoustic suspension or not makes no difference...
The implication of this is that for a given driver the smaller box is not necessarily more linear, at least at some frequencies. If the resonance frequency is very low in a large box (lets say 35Hz) then frequencies much above 35Hz will have low distortion (if the motor is good) because it's mass controlled, even if the suspension isn't particularly linear.
Now place that same driver (one with a large Vas) in a much smaller closed box that pushes the resonance up to say 70Hz, and apply a linkwitz transform to achieve the same system roll off as before.
Must be more linear, right ? Well, not necessarily...yes the compliance is probably a bit more linear, but only if Vd of the driver isn't more than about 10% of Vb, and in the process you've doubled the mechanical resonance to 70Hz, so now everything below 70Hz is in the compliance controlled region, so for the frequency range from 35Hz to 70Hz chances are distortion is actually higher than it was when 35Hz-70Hz was mass controlled in the larger box.
On top of that you have higher motor distortion due to greater power levels and motive force - greater voice coil heating, greater flux modulation, greater Le modulation, and these sources of distortion will intermodulate with frequencies present above resonance too.
For acoustic suspension to have any real benefit in reducing distortion the resulting mechanical resonant frequency would need to be very low without any assistance from things like Linkwitz transforms, to keep the mass controlled region extending as low as possible.
That means a specially designed driver with extremely soft suspension and heavy cone rather than a more conventional driver with active equalization.
Many sub-woofer designs (except those with VERY heavy cones) have a high mechanical resonance frequency with active equalization to transform the response to a lower cutoff frequency, but that does nothing for the higher distortion below the actual mechanical resonance frequency....(unless they have motional feedback as well)
Last edited:
I'm sure no one misses adiabatic vs. isothermic gas laws. It is often forgotten that air is not linear, although it is generally more linear than most suspensions. Air is easier to rarefy than to compress until a limit is reached and rarefaction approaches vacuum: then air may be compressed further, but not rarefied any more for obvious reasons. The former phenomenon occurs in small boxes; the latter in horn throats. Admittedly these nonlinearities can be considered negligible under most circumstances.
That, and to a lesser degree probably to minimize diffraction from the port.
Exactly. What's lost in this thread is that any system capable of response in the modal region (say, for the sake of argument, 40-120Hz) is going to have a sonic signature that's primarily that of the room modes down low.
Generally, vented systems are more efficient in this region. So people notice the problem more. But that's not a "fault" of the vented box.
The answer is not necessarily to close all the boxes, but to spread the drivers producing these frequencies around the room. That can be done with either closed or vented boxes. (Or bandpass, "horn," etc.) But, one will often used closed-box bass units in such a system, simply because they are
(a) smaller, and
(b) if they have enough throw and one throws enough power behind them, one can EQ the response below box tuning, whereas with a vented (or PR) sub one cannot really do that. The vent/PR's resonance sets the LF cutoff. (One can, of course, use a longer vent if it'll fit, or mass the heck out of a PR.)
The bottom line is one should choose the alignment for the drivers playing lowest by size requirements, output requirements, and bandwidth requirements. And spread them around the room to smooth out the effect of room modes.
Also, IMO, drivers above the lowest driver in a system should be in closed boxes. That's because I've always found it easier to integrate drivers with 2d order rolloffs and no unloading below cutoff, than drivers with 4th order rolloffs and unloading below cutoff.
Last edited:
I recently built a 2-way with a 2 inch diameter X 9 inch long plastic port. A response measurement taken with my mic poked a bit into the port's mouth shows a hump around 800 hz. I've wondered what could cause that hump. Could it be a 'pipe resonance'?
The box is 15 L tuned to about 42 hz.
it seems (easy to verify with calculations). May-be can chose an other number of ports/diameter/length combinaison to get the "pipe resonance" out of the range of the speaker. Or to tune-it at a frequency your direct response present a little miss ?
Here a nice site (sorry, in French), where you can find all the tools, for near all kind of enclosures:
04 : Baffles et enceintes
The Acoustic Research AR-9 was pretty narrow. 😉
And the Infinity RS IIA was a bit wider than the AR-9 because of its diffraction wings but it was very attractive IMO.
Seriously, I agree with you and while an audio hobbyist + music fan like myself is is not bothered by a couple of large boxy objects in their living room, I realize many music fans who don't share my interest in audio are bothered. And the people who are only casual music fans with no interest at all in audio gear must really get irritated, particularly if they care more about home decorating than music.
I never could figure out why AR started using foam surrounds. 🙁 Because cloth surrounds impregated with rubber(?) or that shiny black substance which resembled creosote was already around back then, along with a sprinkling of rubber surrounds. But maybe that decision was based on economics i.e. AR's managers wanted their customers to come back after @10 years for a new set of speakers. 🙄
*********************************************
Sorry to bring up this company again, but for the younger DIYers* I wanted to mention a classic example of an affordable acoustic-suspension speaker - AR's were quite expensive - that was rather well-known to many music fans (here in the U.S. at least) even if they weren't audio hobbyists. And that was Radio Shack's Mach One. Sold starting in the late 70s, it used a 15" driver with a thick-n-heavy cone and enormous rolled surround, stuffed into a relatively small enclosure, operating along with - of all things - a horn midrange and horn tweeter. Not exactly intended for audiophiles, it was really sold to people who wanted deep bass but which also could produce high sound levels.
Btw the original version of the Mach series used that special glossy foam that didn't rot. RS seemed to be the only company that used that material. FYI: some companies are now selling a replacement woofer that not only looks the same but also supposedly shares the same specs as the original.
* history in general is another one of my hobbies
You would have to crunch a lot of numbers to prove that typical acoustic suspension speakers were bigger than typical vented boxes. Although the efficiency constant view suggests they should be larger, less efficient, or have less extension, that is only if you do total redesigns to make all the other variables constant. This was seldom the case.
Some companies simply preferred AS designs while other companies prefered vented. Box size is always tied to marketing concerns first, i.e. predetermined by what the customer wants. Woofers for the two types tend to be interchangeable and the potential sensitivity bonus for the vented box isn't always realized.
The reality was that many vented systems are in smaller cabinets than they ought to be and tend towards a bumped up bass. This poor design, as much as anything, lead to the assumption the vented systems are inherently boomy.
Look at the older JBL systems such as the L100, L26, L36. Those woofers might have performed well in their respective cabinet volumes if the systems were sealed. As sold they had way underdamped outputs and poor bass extension. On the other hand the L150 took the same 12" woofer as the L100 (IIRC) and doubled the cabinet volume for remarkably extended bass.
David S.
Some companies simply preferred AS designs while other companies prefered vented. Box size is always tied to marketing concerns first, i.e. predetermined by what the customer wants. Woofers for the two types tend to be interchangeable and the potential sensitivity bonus for the vented box isn't always realized.
The reality was that many vented systems are in smaller cabinets than they ought to be and tend towards a bumped up bass. This poor design, as much as anything, lead to the assumption the vented systems are inherently boomy.
Look at the older JBL systems such as the L100, L26, L36. Those woofers might have performed well in their respective cabinet volumes if the systems were sealed. As sold they had way underdamped outputs and poor bass extension. On the other hand the L150 took the same 12" woofer as the L100 (IIRC) and doubled the cabinet volume for remarkably extended bass.
David S.
- Status
- Not open for further replies.