Wow, some speaker! Can that little vent handle that 18" behemoth? Or, are there more ports elsewhere?
Less precise woofer specs ? If anything most bass reflex alignments are more sensitive to variations in driver specs than acoustic suspension.
One of the advantages of an acoustic suspension is that tolerance variations of the drivers compliance really doesn't matter - as long as the Vas is very large compared to the box volume...
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I think that the Compact Disc killed the Acoustic Suspension speaker, also named Closed Box.
Just after the introduction of the CD, around 1983, Audio magazines were motivating people for buying CDs. Audio magazine showed that the CD as audio source enabled more bass, deeper bass, more linear in amplitude and distorsion-free in comparison with a vinyle source. To keep people motivated for buying CDs, sound engineers were politely asked to re-equalize the bass range of the songs. This way, as happy customer, you could positively taste that the CD had more bass than a vinyle.
Later on, around 1985, Audio magazines started motivating people for buying new loudspeakers, able to maintain fidelity and endurance in the bass range. The Bass Reflex speaker got presented as the ideal CD companion. The Bass Reflex design demands less cone excursion than a Closed Box design. The Bass Reflex enables more bass output for a given constraint (or amount of money).
Companies like Technics, Sony and Cabasse were slow in adopting the Bass Reflex system. Cabasse had highly sophisticated drivers using honeycomb sandwiches membranes. Technics had flat membrane speakers using honeycomb sandwiches and complicated motor structures. In the same Technics catalog there were Bass Reflex speakers, less expensive, and they sounded more spectacular. It went obvious that even high tech Closed Box speakers had not the bass capabilities of Bass Reflex speakers. If you were trying an american Bass Reflex like a JBL, you had a lot of bass for your money. Then, if you wanted more than just bass, like precise stereo localization and precision, you could listen to Bass Reflex speakers like a Pierre Etienne Leon or a JM Lab.
In 1989, when Bose launched the first Acoustimass system, the idea of keeping the existing closed box and adding one or two subwoofer went hugely popular. The subwoofer was a reality since 1976 with the famous 3a Triphonic (France). Even RadioShack had a subwoofer unit you could hook on any existing gear, in a 2.1 or 2.2 setup. Such RadioShack subwoofer was a two-chamber 4-th order bandpass. The Bose Acoustimass innovation was to use a three-chamber 8-th order bandpass.
Closed-Box woofers and subwoofers are not yet dead. In the seventies, Philips had a system named MFB (Motional FeedBack), a Closed Box loudspeaker where there is an accelerometer on the cone, and a dedicated power amplifier. The accelerometer registers the actual cone movement, and acts as feedback element in a servo loop with the amplifier. You still need the same big cone excursion for delivering a decent deep bass sound intensity, but you annihilate most of the distorsion caused by the big excursion. The Velodyne subwoofers reintroduced the same principle later on.
Just after the introduction of the CD, around 1983, Audio magazines were motivating people for buying CDs. Audio magazine showed that the CD as audio source enabled more bass, deeper bass, more linear in amplitude and distorsion-free in comparison with a vinyle source. To keep people motivated for buying CDs, sound engineers were politely asked to re-equalize the bass range of the songs. This way, as happy customer, you could positively taste that the CD had more bass than a vinyle.
Later on, around 1985, Audio magazines started motivating people for buying new loudspeakers, able to maintain fidelity and endurance in the bass range. The Bass Reflex speaker got presented as the ideal CD companion. The Bass Reflex design demands less cone excursion than a Closed Box design. The Bass Reflex enables more bass output for a given constraint (or amount of money).
Companies like Technics, Sony and Cabasse were slow in adopting the Bass Reflex system. Cabasse had highly sophisticated drivers using honeycomb sandwiches membranes. Technics had flat membrane speakers using honeycomb sandwiches and complicated motor structures. In the same Technics catalog there were Bass Reflex speakers, less expensive, and they sounded more spectacular. It went obvious that even high tech Closed Box speakers had not the bass capabilities of Bass Reflex speakers. If you were trying an american Bass Reflex like a JBL, you had a lot of bass for your money. Then, if you wanted more than just bass, like precise stereo localization and precision, you could listen to Bass Reflex speakers like a Pierre Etienne Leon or a JM Lab.
In 1989, when Bose launched the first Acoustimass system, the idea of keeping the existing closed box and adding one or two subwoofer went hugely popular. The subwoofer was a reality since 1976 with the famous 3a Triphonic (France). Even RadioShack had a subwoofer unit you could hook on any existing gear, in a 2.1 or 2.2 setup. Such RadioShack subwoofer was a two-chamber 4-th order bandpass. The Bose Acoustimass innovation was to use a three-chamber 8-th order bandpass.
Closed-Box woofers and subwoofers are not yet dead. In the seventies, Philips had a system named MFB (Motional FeedBack), a Closed Box loudspeaker where there is an accelerometer on the cone, and a dedicated power amplifier. The accelerometer registers the actual cone movement, and acts as feedback element in a servo loop with the amplifier. You still need the same big cone excursion for delivering a decent deep bass sound intensity, but you annihilate most of the distorsion caused by the big excursion. The Velodyne subwoofers reintroduced the same principle later on.
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Midrange leakage from the port in a bass reflex is indeed a significant problem that many designers overlook, especially when the ports natural tube resonance tends to put a sharp peak in the midrange, (often the output at this peak is greater than that from the driver!) however there is a solution for that.
Put the port(s) on the back instead of the front. Yes it is really that simple.
Not being able to put as much stuffing inside to control midrange standing waves is an issue though, although more so with a 2 way than a 3 way...
Standard sealed box (sorry about that, I should have included more detail in my original post).
Though to further clarify that, I mean a box intended to house a woofer described by others here as having a relatively heavy cone, extended excursion capabilities and a "loose" suspension. Such a woofer seems to be almost non-existent these days, though drivers intended for subwoofers come pretty close, though their suspensions - despite large rubber surrounds and amazing excursion ability - can be quite stiff.
Oops, forgot about NHT!
I shouldn't be surprised since IIRC some of NHT's founders came from Advent...or was that AR?Interesting theory. CDs can contain bass that can, in my opinion anyway, technically speaking surpass what vinyl can deal with i.e. more extended and higher in volume, along with less distortion. So now fans of electronica and pipe organs could finally experience true 20Hz notes, but now an acoustic-suspension speaker that could reproduce those notes would really place a strain on the amplifier! (this was before relatively inexpensive "digital" amps debuted). Not to mention the increased cost of the construction of the driver itself.
I suggest that maybe it's the directionality in the top range of the 12" that may give you difficulties with off-axis imaging?
Maybe this is why I usually prefer the sound of an acoustic-suspension design over a bass-reflex, because - and I hate to use this subjective term but it fits! - bass output from an a.s. speaker almost always sounds "cleaner" to me.Midrange leakage from the port in a bass reflex is indeed a significant problem that many designers overlook, especially when the ports natural tube resonance tends to put a sharp peak in the midrange, (often the output at this peak is greater than that from the driver!) however there is a solution for that.
Put the port(s) on the back instead of the front. Yes it is really that simple.
Not being able to put as much stuffing inside to control midrange standing waves is an issue though, although more so with a 2 way than a 3 way...
Plus there's the issue of the increased "speed" of an a.s. design that others have also mentioned in this thread. I have read elsewhere that the perception of increased speed can be explained by the fact that an a.s. speaker's bass frequencies usually do not reach down as far as an equivalent bass reflex design, so the a.s. seems to sound "faster" since what is does reproduce is higher in frequency (hope I explained that correctly).
But I'm not sure about this, because the Advents, ARs, Infinitys and the few modern sealed subs I've heard seem to reach as deeply as a bass reflex and still sound cleaner, etc.
Must add a remark. What if you want to build a Closed Box having a decent deep bass extension like -3dB at 45 Hz, and a decent power capability in the bass ?
You need a long-throw 12 inch woofer with rubber periphery. It is quite expensive. If you want to keep the overall cost reasonable, you need to stay two-way, which means a woofer and a tweeter. And that's terrible. Because with a 12 inch woofer, the distance between the woofer and the tweeter emission centres is too big. You'll get a bad stereo imaging and you'll endure fatigue while listening. And more terrible, a 12 inch woofer stops working correctly above 2 kHz. You thus need a steep crossover (say 4th-order), somewhat expensive, operating at something like 1400 Hz. Which causes the next issue : the tweeter needs to be quite large (say a one inch diameter tweeter, these are not the cheapest) for coping with low crossover frequency.
Now you know why the whole industry adopted the Bass reflex.
For the same amount of money you can design a Bass Reflex using two 6 inch woofers in a d'Appolito configuration with an inexpensive 3/4 inch tweeter crossing at 4 kHz, possibly 2nd-order. It will deliver 45 Hz at -3 dB. It will handle the same power in the bass like the above Closed Box design. It will behave much better above 2 kHz. And being narrower (6 inch woofers instead of a 12 inch woofer), it will integrate easier in your interior.
You need a long-throw 12 inch woofer with rubber periphery. It is quite expensive. If you want to keep the overall cost reasonable, you need to stay two-way, which means a woofer and a tweeter. And that's terrible. Because with a 12 inch woofer, the distance between the woofer and the tweeter emission centres is too big. You'll get a bad stereo imaging and you'll endure fatigue while listening. And more terrible, a 12 inch woofer stops working correctly above 2 kHz. You thus need a steep crossover (say 4th-order), somewhat expensive, operating at something like 1400 Hz. Which causes the next issue : the tweeter needs to be quite large (say a one inch diameter tweeter, these are not the cheapest) for coping with low crossover frequency.
Now you know why the whole industry adopted the Bass reflex.
For the same amount of money you can design a Bass Reflex using two 6 inch woofers in a d'Appolito configuration with an inexpensive 3/4 inch tweeter crossing at 4 kHz, possibly 2nd-order. It will deliver 45 Hz at -3 dB. It will handle the same power in the bass like the above Closed Box design. It will behave much better above 2 kHz. And being narrower (6 inch woofers instead of a 12 inch woofer), it will integrate easier in your interior.
FYI, 2 cents:
Only for those who don't know:
An AS closed box speaker is only defined for a compliance ratio of α= Vas/Vb=greater or equal to 3.
An α=3 have the consequence of increasing the driver Qts to Qtc=2 x Qts in a closed box and as well by pushing the fs to a cutoff frequency of fc= 2x fs.
If the driver has an Qts of 0.707/2 then fc would be equal to f(-3dB) too.
See a calculation for a driver in a closed box that is qualified to be an AS design.
As-Sub:
http://www.diyaudio.com/forums/atta...1968-60ndowns-merged-subwoofer-thread-sub.jpg
More AS discussion in this thread (page) Read at least 10-11 postings:
Start here:
http://www.diyaudio.com/forums/subw...s-merged-subwoofer-thread-10.html#post2603558
b
Only for those who don't know:
An AS closed box speaker is only defined for a compliance ratio of α= Vas/Vb=greater or equal to 3.
An α=3 have the consequence of increasing the driver Qts to Qtc=2 x Qts in a closed box and as well by pushing the fs to a cutoff frequency of fc= 2x fs.
If the driver has an Qts of 0.707/2 then fc would be equal to f(-3dB) too.
See a calculation for a driver in a closed box that is qualified to be an AS design.
As-Sub:
http://www.diyaudio.com/forums/atta...1968-60ndowns-merged-subwoofer-thread-sub.jpg
More AS discussion in this thread (page) Read at least 10-11 postings:
Start here:
http://www.diyaudio.com/forums/subw...s-merged-subwoofer-thread-10.html#post2603558
b
FYI: now that I think about it, those modern subs I mentioned above actually only included two models, one from Cambridge SoundWorks that was sold in the early 90s and one from Martin-Logan I listened to about five years ago. The CSW used a 12" woofer paired with a 120 watt amp in an @2cu/ft enclosure; the M-L "Depth" included 3 eight inch drivers.
Interesting design feature of the CSW: to increase in-room bass performance, you could buy (I worked at a certain big-box retailer at the time) what they called a "slave subwoofer" which was identical to the powered version but omitted the ampliifer. You connected the slave to the powered version via a lengthy supplied cable.
Interesting design feature of the CSW: to increase in-room bass performance, you could buy (I worked at a certain big-box retailer at the time) what they called a "slave subwoofer" which was identical to the powered version but omitted the ampliifer. You connected the slave to the powered version via a lengthy supplied cable.
Market acceptance and cost.
Bass reflex allows a cabinet half the size for the same efficiency and bass extension or another 1/3 octave at the same size and efficiency.
It takes less driver displacement for the same excursion limited output level within the pass-band which for a given beaming tolerance in the midrange lets you move from a 3-way to a 2-way with a potential 50% cost savings.
So there's only positive aspects?
What I have heard is precice and "dry" bass from closed boxes. It is easily heard that bass output is lower than usually in BR, but seldom it is too low. If cone and box is large enough, you can hear what is meant to be. Not with thumb of bass but precicely.
Not necessarily boosting one frequency (37 Hz vs. 40 Hz?), because you'd be using about as extreme of an example of bandpass as I can imagine. However, your remark about room modes is completely wrong. The room modes ("Eigenmodes") are determined by the room itself and aren't dependant on the type of speaker used.
Best Regards,
TerryO
Do you think that BR has better room "behaviour"? In any case? How is 24 dB sloping better than 12 dB?
FWIW, I use "acoustic suspension" in all my speakers.
What gets bantered about in this discussion tends to not actually have anything to do with the perception of bass at LFs in small rooms. The design of the "boxes" has almost ne effect on the end result because its all dominated by the room. In essence, I use all "closed box" sources in my rooms, they are simply easier to work with. But, as I have said many times before, I don't really care what design LF source you use, just make sure that you have several of them, that they are spaced arround the room, and that they are properly setup for that room. The "box" design is irrelavent.
What gets bantered about in this discussion tends to not actually have anything to do with the perception of bass at LFs in small rooms. The design of the "boxes" has almost ne effect on the end result because its all dominated by the room. In essence, I use all "closed box" sources in my rooms, they are simply easier to work with. But, as I have said many times before, I don't really care what design LF source you use, just make sure that you have several of them, that they are spaced arround the room, and that they are properly setup for that room. The "box" design is irrelavent.
Alspe,
24 dB is 100% better than 12 dB.
I believe that with correct design that a BR isn't, or doesn't have to be, inferior to Acoustic Suspension. There's more than one way to skin a cat.
Best Regards,
Terry
Okay, so I did some searching to (of course) support my hypothesis.
I wonder if this Audioholics measurement of the Emotiva EMO-UL12 sub is comparable to other sealed box designs:
Granted the compression doesn't look bad when you think about the level and measurement conditions, but you would think smaller, less robust speakers would be more prone to it. Perhaps leaving a small speaker's bass output to the port and not pushing it's motor/suspension might prove beneficial?
You know, looking at the response of that speaker under those conditions, I kinda want one.
I may have to do my own tests just to see. I've got a certain speaker that seems to do well sealed (more like aperiodic) or ported, but sounds more dynamic to my ears when it's ported. That may have something to do with the diffraction and reflections from the ports, perhaps the sealed is just compressing more, or it is the loss of 1dB of output.
Here's what the frequency change from the port stuffing:
No one get upset, I know my assertions are currently utter bogus, but I'd be surprised if there wasn't some real world data out there to support or refute it.
Dan
I wonder if this Audioholics measurement of the Emotiva EMO-UL12 sub is comparable to other sealed box designs:
Granted the compression doesn't look bad when you think about the level and measurement conditions, but you would think smaller, less robust speakers would be more prone to it. Perhaps leaving a small speaker's bass output to the port and not pushing it's motor/suspension might prove beneficial?
You know, looking at the response of that speaker under those conditions, I kinda want one.
I may have to do my own tests just to see. I've got a certain speaker that seems to do well sealed (more like aperiodic) or ported, but sounds more dynamic to my ears when it's ported. That may have something to do with the diffraction and reflections from the ports, perhaps the sealed is just compressing more, or it is the loss of 1dB of output.
Here's what the frequency change from the port stuffing:
No one get upset, I know my assertions are currently utter bogus, but I'd be surprised if there wasn't some real world data out there to support or refute it.
Dan
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