There is no BEST principle IMO.
It has to be decided on a case-by-case basis which one of the two principles is better SUITED.
Just a remark: Yes - one can actually tune a reflex enclosure lower in order to achieve gentler rolloff characteristics but in this case the displacement-defined SPL improvement (over the closed box) above the tuning frequency can shrink to approximately 6dB.
I use both - boxes with and without "exhaust". The one with uses a 12" driver and has an f3 slightly below 50 hz. I know some posters here would call this whimpy but keep in mind that it does > 120 dB SPL long-term above 50 Hz.
Regards
Charles
It has to be decided on a case-by-case basis which one of the two principles is better SUITED.
Just a remark: Yes - one can actually tune a reflex enclosure lower in order to achieve gentler rolloff characteristics but in this case the displacement-defined SPL improvement (over the closed box) above the tuning frequency can shrink to approximately 6dB.
I use both - boxes with and without "exhaust". The one with uses a 12" driver and has an f3 slightly below 50 hz. I know some posters here would call this whimpy but keep in mind that it does > 120 dB SPL long-term above 50 Hz.
Regards
Charles
I guess the only thing you cannot do with a bass reflex is
a/ get rid of the time delay of aprox 1/24 second with the bass that comes out of the port,
b/ have a sub bass response that keeps up with the actual driver, lets face it there is only so much noise that will come out of a port or resonator,
Unless you actually play an instrument or go and see orchestra's/ jazz bands regularly, the level of realism is not that important.
P.S I have a ported 12" driver with a 3db down at 72hz. @97db watt/ meter. But such a smooth midrange!
I do have a 12" TL sub that works to 22hz. A very different shaped speaker cone though!
a/ get rid of the time delay of aprox 1/24 second with the bass that comes out of the port,
b/ have a sub bass response that keeps up with the actual driver, lets face it there is only so much noise that will come out of a port or resonator,
Unless you actually play an instrument or go and see orchestra's/ jazz bands regularly, the level of realism is not that important.
P.S I have a ported 12" driver with a 3db down at 72hz. @97db watt/ meter. But such a smooth midrange!
I do have a 12" TL sub that works to 22hz. A very different shaped speaker cone though!
Cameron I think thats an unfair and subjective assessment of the ported box enclosure. Come on now, lets at least be realistic. I too will use each design where appropriate, but to argue that the only benefits of ported boxes is more bass output, and counter it with having slight slight time differences from the port as well as arguing incorrectly that all the sub bass comes from the port. That isn't correct, in the setup I mentioned, the woofer itself is going to be responsible for bass down to 25hz, the port just taking over at that point. I consider that sub bass, don't you?
I dont know if the talk about live music was a stab, but I'm a musician, I have posted my instruments on here before, I attend regular live concerts, be it jazz, classical, or rock. I know what live music sounds like, and frankly, I don't find much of it a very good reference. That isn't to say that some form of natural live music shouldn't be our refrence, but when you listen to a band in a bar, and everything is being reamplified through a crappy PA system, its hard to argue that you are hearing the true sound of a guitar or bass. Even most of the jazz clubs I have been to recently have had the horns, piano's, and basses going through PA systems, and frequently very poorly miced. We have one small jazz club that manages to stay away from that crap, and its a great reference, but man they are getting hard to find. I honostly don't think I would know what a guitar is supposed to sound like if I didn't play guitar myself, its very hard to hear someone playing their guitar either acoustic, or amplified only by the propper guitar amp, which has a very different sound from a PA system.
I dont know if the talk about live music was a stab, but I'm a musician, I have posted my instruments on here before, I attend regular live concerts, be it jazz, classical, or rock. I know what live music sounds like, and frankly, I don't find much of it a very good reference. That isn't to say that some form of natural live music shouldn't be our refrence, but when you listen to a band in a bar, and everything is being reamplified through a crappy PA system, its hard to argue that you are hearing the true sound of a guitar or bass. Even most of the jazz clubs I have been to recently have had the horns, piano's, and basses going through PA systems, and frequently very poorly miced. We have one small jazz club that manages to stay away from that crap, and its a great reference, but man they are getting hard to find. I honostly don't think I would know what a guitar is supposed to sound like if I didn't play guitar myself, its very hard to hear someone playing their guitar either acoustic, or amplified only by the propper guitar amp, which has a very different sound from a PA system.
Hi mastermosfet,
I'm surprised no-one has said you can have both in the same box - yup - that's right.
In my example - i have a dual ported / sealed subwoofer. My 12" driver has a mid Qts (approx 0.4).
I designed for a Qtc sealed of 0.5 (is supposed to be best transient response - although at the cost of power handling). I installed a port - tuned to approx 21Hz. The port has a sealing cap (believe me - it seals well and needs to).
I listed to the sub with normal rock, classical or jazz type music with cap on (sealed) and then cap off for drum and bass / movies (ported).
This gives me the best of both worlds - tighter / leaner bass for music, less driver demands for heavy bass music via a port.
Cheers,
David.
I'm surprised no-one has said you can have both in the same box - yup - that's right.
In my example - i have a dual ported / sealed subwoofer. My 12" driver has a mid Qts (approx 0.4).
I designed for a Qtc sealed of 0.5 (is supposed to be best transient response - although at the cost of power handling). I installed a port - tuned to approx 21Hz. The port has a sealing cap (believe me - it seals well and needs to).
I listed to the sub with normal rock, classical or jazz type music with cap on (sealed) and then cap off for drum and bass / movies (ported).
This gives me the best of both worlds - tighter / leaner bass for music, less driver demands for heavy bass music via a port.
Cheers,
David.
Yep, I remember that project, Dave.
Glad to see it worked out so well for you..
As a general rule, as Novak pointed out in the 1950's, if you take a sealed box with a box QTC of 0.5 or thereabouts, and port it, you will have a pretty well tuned ported enclosure.
Most ported boxes are well planned out, by now. So it you just seal up the ports, you have a very workable sealed system.
Glad to see it worked out so well for you..
As a general rule, as Novak pointed out in the 1950's, if you take a sealed box with a box QTC of 0.5 or thereabouts, and port it, you will have a pretty well tuned ported enclosure.
Most ported boxes are well planned out, by now. So it you just seal up the ports, you have a very workable sealed system.
Quoting pjpoes "We have one small jazz club that manages to stay away from that ****, and its a great reference, but man they are getting hard to find. I honostly don't think I would know what a guitar is supposed to sound like if I didn't play guitar myself, its very hard to hear someone playing their guitar either acoustic, or amplified only by the propper guitar amp, which has a very different sound from a PA system."
Buskers in the street help. Even if they are out of step, off key, and nervous.
It used to be that drivers were designed with a particular cabinet in mind. With the availability of T&S specs, I think a lot of people assume they should go towards BR. T&S figures apply to sealed cabs as well. If size is not an issue I'd go for large sealed anyday, for it's transient and phase response. To me that's more relevant than a few dB at 30 Hz.
Buskers in the street help. Even if they are out of step, off key, and nervous.
It used to be that drivers were designed with a particular cabinet in mind. With the availability of T&S specs, I think a lot of people assume they should go towards BR. T&S figures apply to sealed cabs as well. If size is not an issue I'd go for large sealed anyday, for it's transient and phase response. To me that's more relevant than a few dB at 30 Hz.
kelticwizard said:
This can, in some cases, allow you to take a full range ported speaker and use them with a sub without a hi-pass filter. You only need to adjust the lo-pass filter point of the sub. I would do this with a set of bookshelf speakers when the main speakers were in renovation.
umm no it was not.
What I love about DIY is that there are so many things one can try, and I have tried many different aspects and theories over the last 20 years and have enjoyed the ride.
Firstly boxes are not the ideal shape, 11 sided boxes are made by several hi end companies, wood is not the best material to make speakers out of (concrete would be better). Sealed boxes are not so efficent but generally have a nicer mid bass. ported has a more extended response, TL has both better midbass and bass extention but what a bitch to get right! and I personally love the sound of Altec horn loaded loudspeakers.
I am simply trying to point out the minor problems of bass refex designs. To many the small issues are non issues. Who cares if a double bass sounds a slight bit muddy unless one actually plays it? Classical music is mixed and mastered on different speakers than pop, Films are mastered differently yet again, different speakers and many more tracks.
With the buying public wanting the smallest box with the biggest bass, combined with lifestyle marketing, well thats whats in the shops. Here we can make anything, but lets not pretend that any is ideal, Simply the best and most practical for each application. Its more fun as a designer that way.
mmm post 16
Easiest way would be to design a large bass reflex box, listen to the results, temporarily seal the port, boost the sub bass electronically, and then decide for yourself
There are several ways to explain/express/sell something. Let's have a look at politicians, car salesmen, spokes persons etc and you know what I mean.
So I define the only (and IMO minor) disadvantage of a closed box as being more expensive than the other topologies for achieving the same results.
Regards
Charles
So I define the only (and IMO minor) disadvantage of a closed box as being more expensive than the other topologies for achieving the same results.
Regards
Charles
Uhmm...me...Cameron Glendin said:
In the jazz and other recordings (I'm not much into classical) I've got, if it doesn't sound like the bass, then it sounds like one of those 'doof doof' cars you get in the streets now-a-days. Not that I'm picking a fight or anything
But that doesn't really count for anything when you're listening to it, does it? It's what it sounds like to you in your room. And considering the number of mixes done with Yamaha NS10's, it';s surprising that anything sounds any better than radio (by that argument). The speakers are used to hear different artifacts from the music/soundtrack to either accentuate or downplay them - but what is heard in the studio is not necessarily exactly what is intended to play in peoples' home environment. Please don't take these as fighting words...Cameron Glendin said:
Cameron Glendin said:
I have here the sim of two Swan 305's in isobaric configuration in the recommended bass reflex enclosure of 1.29 cu ft and 31 Hz tuning. Also the Swan 305 in two larger boxes as well, but let us concentrate on the recommended enclosure. Red is the recommended enclosure size.
At 30 Hz, the group delay is 15 milliseconds. That is much, much less than 1/24 of a second, which would be 42 milliseconds.
Please explain.
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It was explained to me that the port was aprox, 1 frame out of sync with the image in a standard cinema system, with 24 frames per sec , perhaps because each frame is repeated twice, this would actually make it 1/48th.
Cinemas all seem to have bass reflex designs, So to experience the difference the next cinema I installed was all infinate baffle boxes. installed in a baffle wall. the results were the most realistic I had ever heard in a cinema at that stage. It was only bettered by a 4 way active horn loaded system designed by the amplifier pioneer John Bernett of Lenard Audio.
The main point is that there is delay which no matter how you look at it, or want to quibble about. causes a distortion.
So do you think a 15 millisecond delay is going to create a more accurite sound than a speaker that does not have any delay?
Perhaps you should gentally blow some air over a coke bottles opening, what spl does your test equipment show? what happens when you blow harder?
Cinemas all seem to have bass reflex designs, So to experience the difference the next cinema I installed was all infinate baffle boxes. installed in a baffle wall. the results were the most realistic I had ever heard in a cinema at that stage. It was only bettered by a 4 way active horn loaded system designed by the amplifier pioneer John Bernett of Lenard Audio.
The main point is that there is delay which no matter how you look at it, or want to quibble about. causes a distortion.
So do you think a 15 millisecond delay is going to create a more accurite sound than a speaker that does not have any delay?
Perhaps you should gentally blow some air over a coke bottles opening, what spl does your test equipment show? what happens when you blow harder?
Cameron Glendin said:
I guess the group delay depends on how deeply the box is tuned.
Below is a chart with the frequency response and group delay for that Swan driver. In all cases, the box is 2.5 cu ft.
In the red, the actual Swan 12 inch is put into a box tuned to 31 Hz. The Fs is 24 Hz.
Fs and Bl were modified in the Swan to give lower F3 in the same volume box at the same sensitivity. I will list the Fs changes-the Bl changes I will not.
Green line: Fs is 12 Hz. Fb is 16 Hz. Group delay is 30 milliseconds.
Olive line, (peak not shown): Fs is 9 Hz. Fb is 12 Hz. The olive line peaks at 40 milliseconds.
The olive line will correspond to a 1/24th frame. So if the cinema subwoofer is tuned to 12 Hz-a possibility-then indeed the port will be "one frame behind".
The deeper the tuning, the greater the group delay, even in the same size box. If the box were tuned to 22 Hz, it would be a half a frame behind.
So whoever told you about that "one frame behind" business is accurate if the box is tuned deep enough-are cinema subs tuned to 12 Hz, (full frame behind), or 22 Hz, (half frame behind)?
Remember that it has been shown that perception of such things as group delay goes down as frequency goes down-a group delay value such as 10 msecs would be very good at 25 Hz, not good at 100 Hz. That has to be considered as well.
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Cameron Glendin said:
Actually, if the driver in question is going to go up into the midrange, the midrange will be considerably less distorted with the ported, since the excursions the cone must make in the bass will be considerably reduced. Cone excursions in the bass region absolutely muddy the sound in the midrange region, if the speaker is driven that high.
If the driver is used as a subwoofer, however, this will not be an issue.
In that case, nobody is arguing that if you have unlimited volume, and enough drivers to move the air to supply the necessary SPL at the bass frequencies you wish, that closed box or infinite baffle is not the way to go.
We ported fans only argue that:
A) In cases where volume of the enclosure is NOT unlimited, the ported box will supply more SPL, down to a certain frequency, than the Infinite Baffle will in the same size box. If that frequency reaches down to where you need, then that is quite an advantage. If it does not reach down to where you need, that is a different story.
B) In cases where you do not have an unlimited amount of drivers, or not enough excursion in them, the ported box can produce the same SPL as a closed box can with 1/4 the excursion. So if Fb reaches down far enough, you will need FOUR Infinite Baffle speakers to produce the SPL of ONE ported speaker-at Fb. That is quite a saving.
C) In the same size box, same F3, the ported speaker can contain a driver of higher SPL at one watt. More efficiency. Of course, if you are going to line up a whole bunch of infinite baffle boxes in a cinema, you'll have plenty of sensitivity anyway. But in the cae of an enclosure of limited size, the ported box has a sensitivity advantage.
In other words, if you've got all the room in the world, and all the drivers necessary, and cost is not a real big problem, by all means go Infinite Baffle for a clean, clean bass.
I believe it is, Rich. I just kept the parameters the same as possible, changing only Bl and Fs on the Swans, to give a comparison.
Of course,parameters also determine where F3 is in relation to Fs. The better, (lower Qts) setups also give higher F3.
At some point, I'll see if I can do a comparison of bass tightness of ported speakers with the same F3, but different Qts and different Vas/Vb values.
However, for all practical alignments, group delay will be larger in the ported systems, although there will be differences among the ported systems.
As I recall, the best practical ported system had a step response similar to a closed box of a Qtc of 1.3. But I will see what I come up with later.
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