Sealed Vs Ported (SQ vs SPL)

[squeak9798 5,000+ posts]

If anything, its 'precious capability' is better demonstrated in a sealed enclosure where cone excursion vs BL distortion output are much more relevant. To imply you simply aren't getting the full potential from a Brahma when sealing it is to imply your main concern is simply SPL output, not sound quality. Some SQ purists would consider it a waste to port such a nice sounding sub as a Brahma. *shrug*

//content.invisioncic.com/y282845/emoticons/word.gif.64b12e39f936af3b4fff38a1c0bd0244.gif

I was going to say something worth while......but audioholic pretty much covered it...LOL

 

[60ndown 10+ year member]

BL distortion output ??

what xactly is it?

shed a little light on this will for me will ya!

pleze!

bass line ?, bad licks?, brocken leg? ...??? B.L.???? :stuck:

 

[60ndown 10+ year member]

and its relationship to cone excursion??

science????????????

breifly

 

[audioholic 5,000+ posts]

BL distortion output ??
what xactly is it?

shed a little light on this will for me will ya!

pleze!

bass line ?, bad licks?, brocken leg? ...??? B.L.???? :stuck:

BL is a measurement of motor force (basically). BL distortion is distortion caused by irregularities in the motor force (which can/will hurt cone control). The flatter a sub's "BL curve", the more constant the motor force is on the cone (and it's motion), which means better control and less distortion output.

BL distortion is directly related to cone excursion. The further a sub moves from its enter position, the more of a problem BL distortion becomes, which is where xbl^2 and similar 'BL optimized' motors really shine.

Here's a link to Adire's tech briefs that explains it:

http://www.adireaudio.com/Files/XBL2TechPaper.pdf

 

[audioholic 5,000+ posts]

The reason I said Brahmas (and other BL optimized drivers for that matter) really show their capabilities when sealed is because sealed systems utilized a sub's maximum excursion capabilities much more than a vented system. In other words, a sealed setup will push the sub to its excursion limits much easier than a vented system, and its in high excursion situations that BL optimized subs like the Brahma really show their performance advantage over traditional motor topologies in terms of sound quality (lack of distortion).

This is not to say Brahma's do poorly in vented systems (obviously they do very well), but strictly in terms of maximizing gain from a BL optimized motor, sealed systems need it/use it/display it better.

 

[60ndown 10+ year member]

'In other words, a sealed setup will push the sub to its excursion limits much easier than a vented system"

i believe you, but it makes no sense to me?....in a sealed box driver moves forward-creates 'vacume' behind itself...forward motion is harder.....so surely with no box ...or a vented box the driver is able to reach its 'x max' more easily?? please help a struggleing not so new but vey interested in how and why car audion enthusiast...........

 

[audioholic 5,000+ posts]

'In other words, a sealed setup will push the sub to its excursion limits much easier than a vented system"
i believe you, but it makes no sense to me?....in a sealed box driver moves forward-creates 'vacume' behind itself...forward motion is harder.....so surely with no box ...or a vented box the driver is able to reach its 'x max' more easily?? please help a struggleing not so new but vey interested in how and why car audion enthusiast...........

First off, forward motion of the cone in a sealed system is no harder than the rearward motion, its exactly the same. When the cone moves out, it creates a vacuum as you said, thereby restricting cone motion. But as it moves in, it compresses the air molecules, giving the same cusion effect with equal force. The amount of force it takes the push a specific sub to its excursion limit will be determined exclusively by the enclosure size. The bigger the box, the more air to compress (or create vacuum), there by giving less resistance.

Vented boxes are an entirely different animal. Many (if not most) people think a vented box simply allows the cone to move freely as the air from the back of the cone has an exit. But this is not true, the 'exit' (port) is designed in such a way that the amount of air the subwoofer moves cannot fully move in and out of the box without restriction. Simply put, the sub is capable of pumping more air faster than a properly designed port can accomodate in through-put. Follow me? //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif Now another thing to consider is in vented systems its all frequency dependant. The closer your signal frequency moves toward the enclosure's tuning frequency (lower and lower), the more the cone is trying to move, and thus the more air the speaker is trying to push out the port, creating more and more back-pressure. This creates a situation where even as output is going up (reaching closer and closer to the boxes tuning), actual cone excursion is going down and down. Many people do not understand this phenomenon because they do not consider that a vented enclosure's efficiency is based on frequency. Closer and closer you move towards tuning gives more and more output even as cone motion is decreasing, BUT enclosure efficiency is rising, which explains the rise in over all output.

This also explains why it is easier to push a sub to its excursion limits in a sealed system rather than a vented one. A vented box actually has more restriction on cone motion over a given frequency spectrum than does its sealed counterpart (assuming a properly designed box). And considering that the lower the frequency the note is, the more air that's needed to be displaced to reproduce that note at a given decibel level. In a sealed box, the lower you go, the more excursion rises. Vented systems do just the opposite. If you try to reach maximum excursion at low freqs, at or near tuning, you will end up pumping so much wattage thru the sub that it will fail thermally before it reaches mechanical limits (overheat). And if you try to do it far from tuning where cone restriction is the least, by the time you get far enough away from tuning in the vented box so as excursion restriction from the port is gone, you've already gone well above the frequency range the sub is meant to play (or that your crossover will allow).

 

[60ndown 10+ year member]

wow,thanks.i understand,well explained,i will cut paste that and 'refer' re-fer, to it when i need too,i get it tho, very interesting, thanks for takeing the time to educate me, its not what i imagined was going on in the boxes but after reading that i see!

 

[60ndown 10+ year member]

hey audioholic ,can i buy an enclosure desighn from you? pm me! $$

 

[60ndown 10+ year member]

bump

 

[audioholic 5,000+ posts]

Sorry, I do not do that service. There are several excellent people on this board who do however design enclosures with documentation, if you want to make a new thread asking about it.

 

[60ndown 10+ year member]

Sorry, I do not do that service. There are several excellent people on this board who do however design enclosures with documentation, if you want to make a new thread asking about it.

trouble with that idea is i doubt if ANY of them (except squeak obviously,wanna desighn a box squeak?) have half the knowlege and ability you do judjgeing by your posts

yea i tried that,gave $10 to a guy (paypal) and he sent me some specks and a cut list for the wood,trouble is 3/4 of the way thru building the box i noticed some discrepancy between the calculated box and the actual box? i emailed him,he said 'oh its ok just cut a bit off here and it'll go together good' ?????

so i then noticed a disrepancy between the way he was measureing his port lengths and the way they tell you too in the jl tutorial pages? i asked him and he said ' oh its only off by a little,your box will just be tuned a bit lower??

my confidence in him dissapeared and i now have a 3/4 finished box in the garage im not sure what it'll do if i put the sub in it?

and he supposedly is good at it?

i havent put his name out cos im nice like that! i should really as he might be makeing the same mistakes with others?

 

[squeak9798 5,000+ posts]

except squeak obviously,wanna desighn a box squeak?

Sealed; sure. Ported, no thanks //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

No offense; but I absolutely hate the "design" phase of box building //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

However, you unforunately experienced one of the downfalls of this forum. Everybody thinks they are a box builder and is out to make a quick buck, when many of them just learned how to calculate port length last week. Only 2 or so of the "advertised" box builders would I actually trust. And one of them I'm not even sure is still in the "business" of box design.

 

[audioholic 5,000+ posts]

Good point squeak. I should not endorse builders/designers without knowing for sure their abilities. The only one that pops into my head by name at the moment that I know can design excellent boxes is mr marv. Im not sure if he's on this board, but he's a regular on elitecaraudio.com if you want to look for him there. Im sure finding positive referals would be no problem, he's made ALOT of boxes for people. I even see subs advertised with a "mr marv box" on ebay once in a while. I wouldn't hesitate to use one of his designs.

And yeah, I of course would endorse a design from squeak, the guy's like freakishly smart.

 

[squeak9798 5,000+ posts]

Good point squeak. I should not endorse builders/designers without knowing for sure their abilities. The only one that pops into my head by name at the moment that I know can design excellent boxes is mr marv. Im not sure if he's on this board, but he's a regular on elitecaraudio.com if you want to look for him there. Im sure finding positive referals would be no problem, he's made ALOT of boxes for people. I even see subs advertised with a "mr marv box" on ebay once in a while. I wouldn't hesitate to use one of his designs.

x2 on Mr. Marv.

And yeah, I of course would endorse a design from squeak, the guy's like freakishly smart.

I think you mean freakishly sexy //content.invisioncic.com/y282845/emoticons/naughty.gif.94359f346c0f1259df8038d60b41863e.gif