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Old 27th February 2007, 06:55 PM   #1
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Default Acoustic suspension vs bass reflex

Hello,

What's better between the two:

Acoustic suspension (sealed enclosure) or bass reflex (vented enclosure) in terms of sound?

I see currently only bass reflex enclosures in the shops, but this not necessarily means that they are better than sealed box.
There are other features such as dimensions, for example, that weigh on the purchase.

Assuming you have no dimensions limits,which type of enclosure would you buy/build in order to achieve good sound results?

Thanks for any feedback

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Old 27th February 2007, 07:23 PM   #2
pjpoes is offline pjpoes  United States
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There are too many factors involved to really say which is better. Actually I recently saw an article in The Absolute Sound talking about Subwoofer design inwhich they claimed the superiority of Acoustic Suspension, suggesting that the only reason to use bass reflex is to get lower boomy bass. I disagree, but unfortunatly this is the sort of myths perpetuated in the media, and its also a result of many poorly designed speakers.

A sealed speaker has the benefit of an air suspension, or cushion that aids in controlling the movement of the cone. You make see, as a result, lower distortion and greater control of the cone in a sealed box. You see a shallower rolloff in the bass, which means that, though the -3db point will be higher up, it will still, potentially be producing bass deeper down. For instance you may see a lower -10 db point than with an equivelant ported box. Sealed boxes are generally able to be made smaller as well. However they are generally less efficient, some of this having to do with what it takes to make a driver have deep bass in a sealed enclosure, so TS perameters, and some of it is simply what happens in an acoustic suspension.

Ported boxes on the other hand can be made to extend down deeper at the -3db point, can can often be tuned, in the case of subwoofers, so low that the -10db point is still lower in frequency than the sealed box, especially when using a bass shelf. However, to achieve this, given that a speaker has T/S specs that allow it to work equally well in either box, the ported box will likely be much larger, as much as twice as large is not uncommon, and at least 50% bigger in my own experience. One problem I see is that, because consumers don't like large boxes, a lot of speakers have portes boxes that are too small, with the port tuning too high, causing a rise in the low end, which makes for boomy bass. It gives the perception of greater bass, but the reality is that this is a coloration in the sound. All too many ported speakers are not tuned properly. Oh yes, and generally ported boxes are more efficient than sealed boxes.

As for the claim that a sealed box has lower distortion and a better transient response, in general that can be seen as true, but its not always true. Also, you have the arguement of, is it audible, and is the effect of greater importance than other factors. Overdampened sealed systems can give things like drums an unrealisticly tight sound, lacking the natural decay that a drum has. The use of servo's in ported boxes allows for better transient response and the better extension that a ported box gives, but these systems are rare. However, the better more linear motors being used in a lot of todays subs also allows for a much better transient response. For example, the new RS line of subs from Parts Express Dayton have excellent transient response in ported boxes, though not quite as good as that of the sealed version, the benefit of greater bass extension more than makes up for the almost imperceptable change in transient response. Getting a sealed sub to play flat down to 20hz or so, even 25hz requires equilization. In TAS, they acted like the Linkwitz Transform cuircit is a miracle cuircit that negates the the benefit of deeper bass from a ported box. However, they forgot that it requires more power and excursion than pretty much any woofer made. Using the JL Audio W7, which has near 30mm of xmax, one of the highest in the industry, along with a very high power handeling level. This is a speaker that you would think could do as well as any with the linkwitz cuircit, and in my experience it does very well. However, it still requires over 3000 watts and will exceed xmax in order to be flat down to 20hz. This really isn't a major issue in the real world, as its rare that you need a 20 or even 25hz tone to be as loud as a 35hz or 55hz tone, very little material is down there, none the less, it shows the massive difference in efficiency between a ported and sealed box in the lowest end of their extension, the sealed box needing much more power and excursion to achieve the same extension. In this scenerio, more than any amp could reasonably supply, or any speaker could reasonably handle.

All of that is true of subs, and much of it carries over to regular full range speakers, but when dealing with things like midbass drivers and such, it becomes more what the speaker will work in best. It's still important to tune everything correctly, a midbass driver in an overdampened enclosure will give an unrealistic sound to deeper male voices, drums, piano, the bass, etc. A ported box with a tipped up bottom end can sound boomy and loose. I've always prefered the midrange from cone drivers that are in open systems, such as ported, open baffle, resistive vent-aperiodic, etc.
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Old 2nd March 2007, 08:46 PM   #3
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Wow!What a knowledge...

Ok. And what about small domestic set?
I would mean, having a 2 x 100 W RMS power amplifier and thinking to three way speakers, which one would you advice: bass reflex or acoustic suspension?
Talking about diy speakers...
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Old 2nd March 2007, 08:51 PM   #4
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Default which one?

Quote:
Originally posted by mastermosfet
Wow!What a knowledge...

Ok. And what about small domestic set?
I would mean, having a 2 x 100 W RMS power amplifier and thinking to three way speakers, which one would you advice: bass reflex or acoustic suspension?
Talking about diy speakers...
If it were me, I'd go with a high quality driver suitable for ported enclosure.. I've had really good luck with sonotube designs, as well as a mid-bass enclosure good to ~45 Hz using 7" peerless drivers that sounds remarkably tight (but I also have good sealed enclosures ~ 1 ft^3) with bass to below 30 Hz. the Sonotubes go down below 20 Hz with authority, though, and can be built on the cheap...

John L.
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Old 2nd March 2007, 10:30 PM   #5
forr is offline forr  France
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Mastermosfet
Generaly speaking, bass reflex boxes are prefered on the basis of technical arguments (mainly : less cone excursion which means less harmonic distorsion and higher possible level in the bass region ) and closed boxes are prefered on the basis of subjective arguments.
I suggest you make your mind by listening to both types of boxes of similar size. Maybe not easy to find.
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Old 3rd March 2007, 12:30 AM   #6
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Either done well can sound good just as either done poorly can sound bad. If you start with a quality driver with parameters optimized for a ported enclosure, than take that same driver and alter it's parameters to be optimized for a sealed box, it becomes a different driver. Point being there's really no way to make a direct comparison. It's apples and oranges. So as said above, you just have to listen and make your own choice.
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Old 3rd March 2007, 12:52 AM   #7
bjorno is offline bjorno  Sweden
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Quote:
Oh yes, and generally ported boxes are more efficient than sealed boxes.
No! And 'Yes' only if the driver in the ported box also is more efficient.

b
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Old 3rd March 2007, 12:58 AM   #8
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To me the highest quality, or most realistic sounding is actually a Infinite baffle with a low frequency boost.

an Infinite baffle is a really big sealed box, geneally much bigger than usual, it can be 4x the drivers Vas.

Bass Reflex always has port noise issues. Ports do not maintain SPL with the driver, ie as you turn it up it hits its maximum bass fairly low on the dial, and then stays fairly constant.

Personally I like Bass Reflex, I have made many, I do think it has its positives, and there are many reasons why I use it, but ultimatly if realism and natural sound is the aim, Infinate baffle is the key, just need to boost the lowest end.

The infinate baffle will provide a smoother response in the midrange.
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Old 3rd March 2007, 01:39 AM   #9
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Quote:
Originally posted by forr
Mastermosfet
Generaly speaking, bass reflex boxes are prefered on the basis of technical arguments (mainly : less cone excursion which means less harmonic distorsion and higher possible level in the bass region ) and closed boxes are prefered on the basis of subjective arguments.

I've heard that argument about less excursion in ported designs, but it only applies if the signal is above the port's resonant frequency. If you apply a signal below F0, the driver goes into extreme excursion.
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Old 3rd March 2007, 02:57 AM   #10
KBK is offline KBK  Canada
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One of the more interesting aspects of ported design is the problem with unequal loading a ported system, is of the inner air pressure loading of the port vs the front pressure loading.

One trick I tried nearly 15 years ago, to help deal with this issue is of a nature, but in some ways, beyond all the recent attempts, patents, etc..is to put something like a 'flower' on the inner lip of the port. It will, or may require more solid backing that a simple cone cut alone, so consider removing all flex in that inner 'flowered cone'. A simple cut cone, will flex under loading and the flex must be eliminated. I could likely patent such an arrangement , but I dismissed such long ago and only work with sealed boxes since that time - but it may be of use to those of you who prefer ported designs.

What I mean, is to take a old exponentially flared speaker cone, and cut it so it fits over the inner end of the port. Cut it like a multi- 'winged' flower shape. This allows gradual loading of all the standing wave frequencies (pressure nodes, etc) which evolve in the inside of the box. This brings about a very interesting character to the loading which is far more even and benifical to the bass response. Give it an experimental shot, guys. see what you get. Each individal box design will require a different one, obviously.
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