My 2nd Q: 10" subwoofer enclosure

This is my second question; as i was in another forum and want to post all my unanswered questions here. The question is my sister has a 10" Sony Xplod subwoofer that is to go into her car. But is is recommended for sealed enclosures only. Why? Can't it be run in a ported enclosure for more bass? How loud will it be in a .7 cubic ft enclosure, sealed, at 180 watts? And just to satisfy the science part of my brain, why (if it won't) won't it work in a ported enclosure properly? Thanks for all your help.
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
Here are the Thile-Small parameters for this woofer:
Fs 26.6 Hz
Qts 0.43
Vas 1.75 ft.
Xmax 0.17 in.
Recommended enclosure size 0.7 ft. sealed

With the Thiele-Small specifications it has, the Sony Xplod subwoofer should work well in a ported enclosure. There are a couple of reasons why the sealed enclosure would be recommended.

A) If a woofer works well in both a sealed and a ported enclosure, the sealed enclosure will be smaller but have a higher cutoff. In a car, obviously, space is a premium.

B) In a ported enclosure, there is a tendency for the woofer, near the tuning frequency, to travel all the way to the end of it's travel and to exhibit a clipped waveform, highly distorted. Special construction techniques, such as a Faraday ring or extended pole piece, are required to prevent this. Sony makes no mention of these construction features on it's website-it might or might not have them on the Xplod subwoofer.

Assuming it does have these features, the Sony Xplode will work well in a ported box of 1.25 cu ft, tuned to 25 Hz. That would require a port with a 3" diameter and a length of 22 inches. With such a small excursion, (.17"), the woofer would probably work well with a 2" port of 9" length.

Here are 2 plots with the Xplode subwoofer in a .7 cu ft sealed box and 1.25 cu ft ported box. Notice how much more output at 30 Hz there is in the larger, ported box.
 

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Thanks

Thanks for the info, i am building a box that can be converted, it is a strange design, but basically it consists of a large 1.25 cu. ft. ported box with a 2" dia and 9" long port that can be capped off. It also has a rectangular hole on the side with fly bolts that is sealed off for ported use, or a box can be inserted to decrese volume to .75 cu. ft. for those times when I don't wan't it too boomy. It's not the best design for a sealed enclosure, but it is great when udes for ported operation. I saw a friend who had this same design, but he used a motorized box so that he could change to ported by the flick of a switch. Thanks for the help. I just wasn't sure if i could use it in a ported enclosure, so.

Thanks man.
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
Re: Thanks

kingfootga said:
....or a box can be inserted to decrese volume to .75 cu. ft. for those times when I don't wan't it too boomy.

A properly designed ported box should not be too boomy-they got that reputation before Thiele and Small wrote their paper explaining the proper way to build a ported box.

However, your idea of building a convertible box is a good one. Might I suggest that you just cap off the port and leave it like that? A 1.25 cu ft sealed box will have similar response to a .75 cu ft sealed one, just with a little better bass around 30 Hz. It will be almost identical otherwise. If anything, the 1.25 cu ft sealed box will have snappier transient response than the .75 cu ft one.

Here is the graph of your woofer in a 1.25 cu ft sealed box. Compare it to the graph of the .75 cu ft one. I think you might decide that it is not necessary to decrease your volume when switching from ported to sealed mode.

Good luck!
 

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