Hello folks,
When I do searches on the internet on the practical difference btw sealed and ported subs, the usual stuff I read is that sealed is described as "tight", "clean", "good transient response". (I don't even know what these terms mean, technically.) Whereas ported can play louder and to a lower frequency. My understanding is that due to box and port tuning, a port boosts the overall loudness of a sub right as the driver's response is starting to pitter out, meaning that the overall frequency response goes a bit lower. And if you go even lower in frequency, then the dropoff is more steep.
That's all fine and good, but is there some other parameter, aside from frequency response, that gives sealed subs their "tight" and "clean" description? I think many, if not most, commercial subs these days have an amplifier and eq built in, so their frequency response is fairly flat for either type. In that case, is there still an effective difference between these two type of subs, playing at frequencies above the roll-off point? (e.g. 50 hz)
When I do searches on the internet on the practical difference btw sealed and ported subs, the usual stuff I read is that sealed is described as "tight", "clean", "good transient response". (I don't even know what these terms mean, technically.) Whereas ported can play louder and to a lower frequency. My understanding is that due to box and port tuning, a port boosts the overall loudness of a sub right as the driver's response is starting to pitter out, meaning that the overall frequency response goes a bit lower. And if you go even lower in frequency, then the dropoff is more steep.
That's all fine and good, but is there some other parameter, aside from frequency response, that gives sealed subs their "tight" and "clean" description? I think many, if not most, commercial subs these days have an amplifier and eq built in, so their frequency response is fairly flat for either type. In that case, is there still an effective difference between these two type of subs, playing at frequencies above the roll-off point? (e.g. 50 hz)
I think to appreciate the difference you would need to hear two speakers of similar quality and cone area.
But trying to find a similar quality sealed bass speaker may be difficult, since almost all PA equipment is either vented or horn.
Then you would need to find a sealed version that had a similar frequency response to the vented to complete the comparison.
But trying to find a similar quality sealed bass speaker may be difficult, since almost all PA equipment is either vented or horn.
Then you would need to find a sealed version that had a similar frequency response to the vented to complete the comparison.
You raise a good question and make some good points.
Basically, the port adds a slightly delayed reinforcement to the sound, which can be audible, or it's easy to get the tuning/design wrong/inappropriate. Also, the rolloff is sharper which creates a bigger/quicker phase change.
In a sub you will always be playing in a relatively narrow frequency band so the port will always be playing a big part in the overall sound. But yes broadly speaking, above the resonance the sound will be the same for either loading.
Basically, the port adds a slightly delayed reinforcement to the sound, which can be audible, or it's easy to get the tuning/design wrong/inappropriate. Also, the rolloff is sharper which creates a bigger/quicker phase change.
In a sub you will always be playing in a relatively narrow frequency band so the port will always be playing a big part in the overall sound. But yes broadly speaking, above the resonance the sound will be the same for either loading.
Last edited:
Hi beanbag'
All of the statements that were made by Andrew, richie', and yourself (above), are 100% true. But I think the reason that we use terms at times like, tight, clean, punchy or explosive, is because "audio reproduction", much like 'music itself', is part science (math), and part art. To explain... When comparing a sealed box to a ported one, technically speaking, it's like a scientist, comparing Rain to Snow. The ingredients' in both are similar at least, but I think that makes it somewhat difficult to describe each of them without using any of the same terms, so we struggle for words.
Now, I've always been a big fan of "bass reflex", horns, and "horn-reflex" cabinets. Being a bass player in a band most of my life, and like most bass players, I've struggled to be heard on-stage; to say nothing of being heard way in the back row. So "high efficiency" drivers/enclosures are always my objective, as well as plenty of power in the rack. But very recently, I've been introduced to a new candidate to go into my arsenal of gear... "The sealed box"!
I wanted to build a "subwoofer system" for an suv that I'd gotten not too long ago. I naturally thought I needed to get a Bass reflex cab cuz that's what I always use, ~and here's my main point to you 'beanbag'~. I ordered two ten inch, high-end "car audio" drivers from JL Audio, wired them up, and mounted them in a 3 cuft' ported box that I had just gotten. The box was tuned to about 39hz IIRC / 33hz f3. (I'm leaving a lot out to save ^X).
The bass sounded powerful, I mean it sounded "OKAY", but... I wasn't happy with it for some reason (just couldn't put my finger on it). Then it hit me. No matter how I adjusted the bass w/E.Q., it still sounded mushy, and lacked Impact, kinda like going for a swim... in a pool of mud! The long and short of it is, I sealed up the box (the exact same box), stuffed it w/poly-fill, fired it up and viola! Now not only does it dig deep, but it hits hard and sounds "tight, clean, good transient response" yada, yada, yada! lol!
I personally think that the sealed box sounds a lot cleaner, flatter and quicker; like richie said in his statement, the port in the bass reflex adds some delay (group delay), which is inherent or characteristic of it's design, but that's one of the "trade-offs"; There's no free lunch! On the other side of the same coin, the sealed box alignment forfeits a huge amount of it's efficiency, to gain a flatter response and slower "roll-off" below box frequency (Fb). Hope this helps just a little.
rigtec, cheers!
Hi,
how could CB and BR be explained?
Maybe this anology helps.
Think of table tennis. 😉
A CB is like playing TT, by playingthe ball with a racket.
The racket representing the drivers diaphragm, the ball representing the room.
Now You may know this kid toy where a ball is connected to a TT racket with a rubber chord.
The racket representing the drivers diaphragm again, the ball representing the port opening and the chrrd representing the coupling air volume of the cabinet.
The ball moves much more than the racket, but it only functions well if the moving actions of racket and ball are synchronized.
Playing a BR in a room would mean to add another ball to our anology, trying to hit this ball with the racket-ball.
Obviously it will be more difficult to get things right and going.
In fact its almost impossible as the room-ball represents a almost uncalculable factor.
PA is a different set of applications to home audio.
Here the room is taken more - or completely- out of the calculation.
As the rooms are typically much larger or ´infinite´ (i.e openair), all acoustic room parameters are shifted towards lower frequencies, possibly ino the infrasonic range, hence outside the working frequency range.
In other words, we get more of the Box behaviour (freeair condition) and less Room behaviour.
Here the more linear amplitude reponse below the driver´s base resonance comes to the advantage of BRs.
In smaller home HiFi rooms BRs suffer from the roomgain, while the effect just counters the natural falling amplitude response of a CB.
In other words, the amplitude response of a BRfits large rooms or freeair conditions, but doesn´t fit or match small room acoustics.
Also PA demands high efficiency, but low frequencies and high efficiency contradict.
So they rely on any assistance they can find, either Horn or BR.
BR beeing the simplest, cheapest and most sensitve alternative for PA.
For home HiFi BR just suits to allow for smaller drivers and to make things cheaper.
Just my two fairytale cents 😉
jauu
Calvin
how could CB and BR be explained?
Maybe this anology helps.
Think of table tennis. 😉
A CB is like playing TT, by playingthe ball with a racket.
The racket representing the drivers diaphragm, the ball representing the room.
Now You may know this kid toy where a ball is connected to a TT racket with a rubber chord.
The racket representing the drivers diaphragm again, the ball representing the port opening and the chrrd representing the coupling air volume of the cabinet.
The ball moves much more than the racket, but it only functions well if the moving actions of racket and ball are synchronized.
Playing a BR in a room would mean to add another ball to our anology, trying to hit this ball with the racket-ball.
Obviously it will be more difficult to get things right and going.
In fact its almost impossible as the room-ball represents a almost uncalculable factor.
PA is a different set of applications to home audio.
Here the room is taken more - or completely- out of the calculation.
As the rooms are typically much larger or ´infinite´ (i.e openair), all acoustic room parameters are shifted towards lower frequencies, possibly ino the infrasonic range, hence outside the working frequency range.
In other words, we get more of the Box behaviour (freeair condition) and less Room behaviour.
Here the more linear amplitude reponse below the driver´s base resonance comes to the advantage of BRs.
In smaller home HiFi rooms BRs suffer from the roomgain, while the effect just counters the natural falling amplitude response of a CB.
In other words, the amplitude response of a BRfits large rooms or freeair conditions, but doesn´t fit or match small room acoustics.
Also PA demands high efficiency, but low frequencies and high efficiency contradict.
So they rely on any assistance they can find, either Horn or BR.
BR beeing the simplest, cheapest and most sensitve alternative for PA.
For home HiFi BR just suits to allow for smaller drivers and to make things cheaper.
Just my two fairytale cents 😉
jauu
Calvin
Last edited:
When modeled as an electrical filter, per Benson/Thiele/Small, a sealed box is represented as a 12 dB/octave high pass. A vented box corresponds to a 24 dB/octave high pass. The more complicated "filter" (i.e. the vented box) has a more complicated response to transient signals, with more "ringing"
That is, the sealed box cone starts and stops more quickly and more cleanly compared to a ported box.
Now, that is all theory, based on small signals. At higher power, things are more complicated. You can also make a boomier sealed box and "tighter" vented boxes depending on the exact specs of the design.
That is, the sealed box cone starts and stops more quickly and more cleanly compared to a ported box.
Now, that is all theory, based on small signals. At higher power, things are more complicated. You can also make a boomier sealed box and "tighter" vented boxes depending on the exact specs of the design.
IMHO, it comes down to this choice, and its almost entirely subjective:
Sealed boxes will always have higher distortion than ported boxes for a given output (assuming ported box is within designed frequency range).
Ported boxes will always have time-delay-related issues.
Your choice depends on what you're sensitive to.
Some people really don't like time-based distortion of the sound. As in, delayed signals, stuff like that. Those people don't "get" open baffle systems, as the impulse response of the system (in room) will be all over the show.
Other people won't mind time delays so much, but can pick up on distortion much better than others.
Everyone will be somewhere along that scale, and ought to pick and choose accordingly.
For the former, a sealed box is fairly mandatory. For the latter, heading toward resonant alignments may well be the answer. You can't please everyone, but you should definitely please yourself.
Chris
Sealed boxes will always have higher distortion than ported boxes for a given output (assuming ported box is within designed frequency range).
Ported boxes will always have time-delay-related issues.
Your choice depends on what you're sensitive to.
Some people really don't like time-based distortion of the sound. As in, delayed signals, stuff like that. Those people don't "get" open baffle systems, as the impulse response of the system (in room) will be all over the show.
Other people won't mind time delays so much, but can pick up on distortion much better than others.
Everyone will be somewhere along that scale, and ought to pick and choose accordingly.
For the former, a sealed box is fairly mandatory. For the latter, heading toward resonant alignments may well be the answer. You can't please everyone, but you should definitely please yourself.
Chris
Best of both 'worlds' is to 'critically damp' a vented alignment to basically get a sealed alignment's SQ with more usable LF gain BW.
GM
GM
Isn't it 18 dB/octave on the ported?
As FIR is getting progressively cheaper and cheaper it would be interesting to do comparisons of ported vs sealed where you have corrected phase so both are linear phase. Who knows, they might sound and measure almost identically except that one has more output =)
You can make a 3rd-order ported alignment (smaller box) at the expense of higher F3. Typically they are 4th-order though.
The SBB4 alignments have the best transient response of all the vented alignments. The Qtc of the SBB4 is overdamped and so minimises mechanical 'ringing'.
An SBB4 designed around a driver with a Qts=3.12 gives the smallest size, highest efficiency, and deepest bass extension. Add a low-cut filter with a Q=2 at the box tuning frequency (a feature available on most plate amplifiers) turns the SBB4 into a B6 (maximally flat).
A 2 cu ft 2nd order sealed box with an F3 of 30hz can only be 0.18% efficient (84.55dB).
A 2 cu ft 4th order vented box with an F3 of 30hz can only be 0.36% efficient (87.56dB).
A 2 cu ft 6th order vented box with an F3 of 30hz can only be 0.90% efficient (91.54dB).
Using dual drivers allows for push-pull operation. Warning, this cabinet sounds very different, like a servo controlled system.
An SBB4 designed around a driver with a Qts=3.12 gives the smallest size, highest efficiency, and deepest bass extension. Add a low-cut filter with a Q=2 at the box tuning frequency (a feature available on most plate amplifiers) turns the SBB4 into a B6 (maximally flat).
A 2 cu ft 2nd order sealed box with an F3 of 30hz can only be 0.18% efficient (84.55dB).
A 2 cu ft 4th order vented box with an F3 of 30hz can only be 0.36% efficient (87.56dB).
A 2 cu ft 6th order vented box with an F3 of 30hz can only be 0.90% efficient (91.54dB).
Using dual drivers allows for push-pull operation. Warning, this cabinet sounds very different, like a servo controlled system.
Last edited:
Thanks for the replies so far.
From some subwoofer tests, I see that there are plots of group delay vs freq. I assume that this means that for a steady state sine wave, it represents how much a woofer cone lags the actual signal. So is this just some electro-mechanical artifact of some kind of driven damped harmonic oscillator, or some kind of fundamental / mathematical limitation due to the fact that the phase of a signal gets messed up when you have a steep filter / mechanism that rolls off the amplitude? In other words, if you have a theoretically perfect servo system, will it still have these problems? I see in some of these tests that the Rythmik servo subs have less group delay, but they still have it.
One other thing I don't understand is why a subwoofer is said to have a transient response, or to be able to start and stop quickly. Doesn't a sub ALWAYS receive a low passed signal, so there shouldn't be any sudden changes in the signal anyway? A sharp "transient" has high frequency components, and the midrange and tweeter would take care of those.
Finally, if one had DSP and servo powers, would it be theoretically possible to make a sub that has zero group delay and perfectly outputs the electrical signal, all the way down to a low frequency, and then somehow taper off the amplitude without messing up the phase? (Assume the system has time to pre-process the music signal before sending separate outputs to mains and sub.)
From some subwoofer tests, I see that there are plots of group delay vs freq. I assume that this means that for a steady state sine wave, it represents how much a woofer cone lags the actual signal. So is this just some electro-mechanical artifact of some kind of driven damped harmonic oscillator, or some kind of fundamental / mathematical limitation due to the fact that the phase of a signal gets messed up when you have a steep filter / mechanism that rolls off the amplitude? In other words, if you have a theoretically perfect servo system, will it still have these problems? I see in some of these tests that the Rythmik servo subs have less group delay, but they still have it.
One other thing I don't understand is why a subwoofer is said to have a transient response, or to be able to start and stop quickly. Doesn't a sub ALWAYS receive a low passed signal, so there shouldn't be any sudden changes in the signal anyway? A sharp "transient" has high frequency components, and the midrange and tweeter would take care of those.
Finally, if one had DSP and servo powers, would it be theoretically possible to make a sub that has zero group delay and perfectly outputs the electrical signal, all the way down to a low frequency, and then somehow taper off the amplitude without messing up the phase? (Assume the system has time to pre-process the music signal before sending separate outputs to mains and sub.)
1) All real transducers lag in LF response compared to the original signal, the electro-magnetic properties do not require additional filters to lag, though filters do introduce additional delay. Servo control can reduce LF ringing, but AFIK do not eliminate LF phase shift.
2) Perfect LF transient response would require instant starting and stopping of the moving mass, the starting of a low passed driver is not as much of a problem as the stopping, additional movement after the signal has stopped "ring", persisting as a time smear.
Of course, rooms ring too, far more than any decently damped LF system...
3)FIR filters can completely flatten a systems phase response, but do require fairly long delay times (on the order of one second) to accomplish that task down to very low frequencies.
Well, the alignment called "QB3" stands for "Quasi Butterworth 3rd order" emphasis on the Quasi. It still rolls off 4th order eventually. Basically it is still a 4th order box, with a softened rolloff shoulder. An one example of what I mean by saying you can tune ported boxes to be somewhat more "sealed" sounding 😀
Ah, yes, what people call "fast bass" and so on. In a job interview for a loudspeaker design position, I mentioned the "transient response" of a sub. The interviewer started to debate me saying the same sort of thing you ask about-it's only low frequencies, so you don't have a sharply changing signal, so it's wrong to say "transient response."
I replied that "transient response" in terms of a sub was not about high frequencies at all, it was about the cone not perfectly following the input signal (like what the previous poster mentions). It's the response when a signal starts and stops, and due to the physics of accelerating a moving mass there are still imperfections in that response (lag at the start, and ringing oscillations once the signal stops). An example would be a car going over a bump-the car still bounces up and down for a little while even when the bump is finished. Or a mass hanging on a spring-poke it and it keeps bouncing long after the poke.
I was offered the job the same day, by the way 😛
Last edited:
- Status
- Not open for further replies.