how can sealed subwoofers produce lots of low fast bass? - diyAudio
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Old 6th December 2001, 05:57 AM   #1
pkgum is offline pkgum  Australia
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it has often been said that sealed subwoofers have limited bass in the low frequency region compared to ported subwoofers. Many high end sealed subwoofers such as velodyne and krell have managed to achieve producing lots of low bass (more bass than ported subs and with superior transient response) despite the small sealed cabinet.

how can they achieve this?
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Old 6th December 2001, 06:18 AM   #2
jduncan is offline jduncan  United States
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I'm not sure about the Velodyne but the Krell definitely does NOT use a small box....its huge.

That's how they still get low frequency response...the box is large enough for the drivers they want to use.
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Old 6th December 2001, 07:36 AM   #3
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Default Not exactly,

A sealed enclosure is analogous to a second order high pass, and will go really deep, provided you use a really large enclosure. The bass cutoff is gentler but without as much spl in the pass band.
A ported enclosure is analogous to a fourth order high pass. The bass cutoff is much steeper, but the spl is higher in the pass band. Actually this is much easier to draw than to explain.
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Old 6th December 2001, 08:08 AM   #4
pkgum is offline pkgum  Australia
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then how can the sunfire signature ( http://www.sunfire.com ) , velodyne, and the british made KEL subwoofers( they were the top subwoofers in 'whathifi magazine' their website is: http://www.rel.net ), manage to achieve good bass from smal enclosures?

note: the velodynes are small especially when it is compared to monsters like wilson audio

[Edited by pkgum on 12-06-2001 at 03:11 AM]
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Old 6th December 2001, 08:09 AM   #5
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Many of the Velodyne subwoofer models use motional feedback and a few in conjunction with a mass-loaded passive radiator. If the driver has a very high linear excursion range and high power handling capacity, the frequency response in a given enclosure can be lowered by the use of an appropriately designed filter that lifts the low frequencies upto predetermined levels. Many such alignments are possible: a few examples are, The Bassist from Marchand Electronics, Linkwitz alignment, Multiple Feedback Filter as described by Jeff McCaulay in Electronics World of October 95 (Geoff could correct me about the exact issue, just in case my memory has failed).

Another approach is to design an enclosure too small for the given driver so that the system resonant frequency rises considerably, and then through electronic means operate the driver only below that resonant frequency. Rod Elliot calls it EAS (Electronically Assisted Subwoofer). A company called BagEnd call it LFE (Low Frequency Extension). Rod's project on the said subject can be referred to in his site. Another good reference would be a recent article in Electronics World by Graham Maynard, I think (again Geoff or someone else should come to my rescue). Power handling and Xmax of the driver are of paramount importance in this application.

Many other approaches are possible, but they all invariably require comparatively larger enclosures.
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Old 6th December 2001, 10:03 AM   #6
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pkgum,

If you want a very small-size enclosure with a sealed subwoofer, and still want a lot of low frequency response, relative to the high frequency response, then you need, most likely, a low crossover point and maybe equalization. Moreover, you most definitely need to increase the amount of power by a great deal, especialy with very small boxes, as a decrease in size always results in a decrease in efficiency. And last, high excursion is a must, unless you are using many drivers.

The Sunfire (the original one designed by Bob Carver) needed THOUSANDS of watts and a large amount of excursion (and equalization?) in order to over come the small enclosure and driver sizes, respectively.

Dave
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Old 6th December 2001, 12:10 PM   #7
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If I remember correctly from reading the white pages on the Sunfire(they took them down when the redsigned the site )The driver is a 13inch driver with a 2inch p-p movement. There is also a passive radiator with 1-1.5lbs of weight on it(please correct me if I'm wrong). These coupled with Bod Carvers tracking down converter and a 2700watt amp the size of a candy bar(yes I said 2700watts), give the Sunfire its power.

On the other side I have heard one of the BagEnd 18inch sealed subs and they sound amazing. Get some info on them if you can because they really know what they are doing.

Cheers

huey
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Old 6th December 2001, 12:41 PM   #8
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baby_huey0,

You are right about the Sunfire. I think there were two versions of the Sunfire-True Subwoofer and one used a 10" driver. You are right about the amplifier's power rating.

The BagEnds use Low Frequency Extension and go down to about 10Hz. Less Phase Shift and quick transients is what makes them brilliant. In comparison almost all other types of Subwoofers would sound 'smeared'.

May be its time to try out a design using this principle.
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Old 6th December 2001, 05:17 PM   #9
Won is offline Won
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I have always been partial to those accelerometer-based
motion feedback designs, although the examples I found on the web haven't been particularly spectacular. Certainly less so than one might imagine, but I'm confident that it could be quite a successful project.

-Won
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Old 6th December 2001, 08:51 PM   #10
Ignite is offline Ignite  Canada
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The most general explanation is this:
You cannot have small size, high efficiency and wide bandwidth at once. You can have two, but not three.
These designs usually sacrafice efficiency or bandwitdh for size. In a subwoofer neither matter that much if you have a spare kilowatt amplifier or want to xover at 60Hz.
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