How does a 4th order bandpass work?

[0kriz]

No pressure wave escapes because it is sealed.
Sealed = no leaks. How can something escape if it has no way out?

given that the sealed chamber prevents the pressure wave, how can it regulate the upper bandwidth of the 4th order?

 

[mat3833 10+ year member]

A thin layer of wood cannot block all pressure waves, even 10" of concrete cannot block low frequencies totally.

You aren't wrong, but we aren't talking about vibrations traveling through anything other than air. A sealed enclosure is just that, sealed. No air escapes the enclosure and no pressure wave can escape. The transmission of energy from vibrations is much different than the pressure waves we are talking about.

Look up compression and rarefaction. Your speaker produces one "compression" wave and one "rarefaction" wave.

Matt

 

[0kriz]

You aren't wrong, but we aren't talking about vibrations traveling through anything other than air. A sealed enclosure is just that, sealed. No air escapes the enclosure and no pressure wave can escape. The transmission of energy from vibrations is much different than the pressure waves we are talking about.

Look up compression and rarefaction. Your speaker produces one "compression" wave and one "rarefaction" wave.

Matt

oh, didnt know that, ill look it up, thanks, maybe it will help me understand this fascinating enclosure design better.

 

[shredder2]

Ugh... I hate to be that guy.
Complicating things with theory and abstract minutiae has already been beaten to death.
Enclosure design is knowing what works, a higher order enclosure even more so.
Goals, suitability and install factor into every design, I can't count the times people wanted BIG lows outta a 3:1 4th utilizing something with an EBP of 130+. They saw it on YT so it must be true... lol
Of course its to be stuffed into a Cobalt trunk or similar.
Get with a designer and study his design, real world... you'll understand results and any recommendations along the way will make sense.
A legit design =

 

[0kriz]

Ugh... I hate to be that guy.
Complicating things with theory and abstract minutiae has already been beaten to death.
Enclosure design is knowing what works, a higher order enclosure even more so.
Goals, suitability and install factor into every design, I can't count the times people wanted BIG lows outta a 3:1 4th utilizing something with an EBP of 130+. They saw it on YT so it must be true... lol
Of course its to be stuffed into a Cobalt trunk or similar.
Get with a designer and study his design, real world... you'll understand results and any recommendations along the way will make sense.
A legit design =

View attachment 39338

Complicating this thread as much as possible with theory and examples was my hope with this thread. As long as equations dont come up, im afraid that will be beyond me.

 

[Jimi77 5,000+ posts]

A thin layer of wood cannot block all pressure waves, even 10" of concrete cannot block low frequencies totally.

Wow, just wow. If you cannot accept basic building premisses that have been accepted and proven over and over again, then you're on your own. Good luck reinventing how speaker enclosures work.

 

[Grimmjoww]

Your either a Scientist, Engineer or are Trolling lol. Little box go boom but tight, Big box around little box go boomer but with release, big square hole in box go Big Boom with all the wind.

 

[mat3833 10+ year member]

Ugh... I hate to be that guy.
Complicating things with theory and abstract minutiae has already been beaten to death.
Enclosure design is knowing what works, a higher order enclosure even more so.
Goals, suitability and install factor into every design, I can't count the times people wanted BIG lows outta a 3:1 4th utilizing something with an EBP of 130+. They saw it on YT so it must be true... lol
Of course its to be stuffed into a Cobalt trunk or similar.
Get with a designer and study his design, real world... you'll understand results and any recommendations along the way will make sense.
A legit design =

View attachment 39338

I'm a little bit confused here. There isn't really any "theory" or "abstract minutiae" in this thread. All of the principles are simple. A basic fundamental understanding doesn't require "theory" nor anything abstract. Literally the most complex thing in this thread so far has been my reference to a rarefaction wave...

Enclosure design beyond a basic sealed or ported enclosure is in its very nature complicated. "knowing what works" is the funniest thing I have heard in reference to a 4th or 6th order enclosure. Yea, the math is there. But for anything more complex than a ported enclosure it is a waste of time and wood to just plug numbers into a calculator and build it. You need to take into account the transfer function of the vehicle, the amount of air being moved by the subs to optimize port area/volume, the customers musical preferences, the list goes on.

You can just throw some wood together and make a leaky sealed or ported box that isn't anywhere near ideal and get decent results. If you have a leaky bandpass enclosure, it's going to be a bad time and most likely end up with damaged woofers.

Your picture looks pretty. Depending on what subs/how much power you are going to run, that port area looks pretty small. Is that a 2:1 SPL oriented box or do you just want to do hair tricks like the cool kids?

Matt

 

[0kriz]

Wow, just wow. If you cannot accept basic building premisses that have been accepted and proven over and over again, then you're on your own. Good luck reinventing how speaker enclosures work.

Its not about accepting the basics, its about understanding them in detail, to mentally visualize all the variables and how they influence each other. If you dont have interest in understanding the underlying workings or you have nothing to add, then this tread is probably not for you.

 

[0kriz]

Your either a Scientist, Engineer or are Trolling lol. Little box go boom but tight, Big box around little box go boomer but with release, big square hole in box go Big Boom with all the wind.

Im non of them, just curious.

 

[0kriz]

I'm a little bit confused here. There isn't really any "theory" or "abstract minutiae" in this thread. All of the principles are simple. A basic fundamental understanding doesn't require "theory" nor anything abstract. Literally the most complex thing in this thread so far has been my reference to a rarefaction wave...

Enclosure design beyond a basic sealed or ported enclosure is in its very nature complicated. "knowing what works" is the funniest thing I have heard in reference to a 4th or 6th order enclosure. Yea, the math is there. But for anything more complex than a ported enclosure it is a waste of time and wood to just plug numbers into a calculator and build it. You need to take into account the transfer function of the vehicle, the amount of air being moved by the subs to optimize port area/volume, the customers musical preferences, the list goes on.

You can just throw some wood together and make a leaky sealed or ported box that isn't anywhere near ideal and get decent results. If you have a leaky bandpass enclosure, it's going to be a bad time and most likely end up with damaged woofers.

Your picture looks pretty. Depending on what subs/how much power you are going to run, that port area looks pretty small. Is that a 2:1 SPL oriented box or do you just want to do hair tricks like the cool kids?

Matt

Good points, I agree.

I might have been a bit unclear in my post tho, my bad… Im not a car audio enthusiast, I actually build pro audio subwoofers for PA use. They can be placed in all kinds of environments, so how a 4th order works excluding the environment is what I want to understand indepth. I did however choose to come to this car audio forum to ask the question since this subwoofer type is more usual in car audio, and I know there are some car audio enthusiasts who knows alot about bandpass subwoofer theory.

 

[SlugButter]

Good points, I agree.

I might have been a bit unclear in my post tho, my bad… Im not a car audio enthusiast, I actually build pro audio subwoofers for PA use. They can be placed in all kinds of environments, so how a 4th order works excluding the environment is what I want to understand indepth. I did however choose to come to this car audio forum to ask the question since this subwoofer type is more usual in car audio, and I know there are some car audio enthusiasts who knows alot about bandpass subwoofer theory.

What type of frequency response do you shoot for when designing an enclosure for PA/pro-audio? A 4th order bandpass has a very limited frequency range, and normally needs a cabin gain function to extend into the lower frequency range while still allowing for a usable bandwidth up to 60-70 HZ. An open air environment is not ideal for a 4th order design IMO, at least for playing music content.

 

[0kriz]

What type of frequency response do you shoot for when designing an enclosure for PA/pro-audio? A 4th order bandpass has a very limited frequency range, and normally needs a cabin gain function to extend into the lower frequency range while still allowing for a usable bandwidth up to 60-70 HZ. An open air environment is not ideal for a 4th order design IMO, at least for playing music content.

With dual 15” cabinets as top speakers, content down to 50hz can be covered. A frequency response down to 35hz is ussaly enough, but flat down to 30 hz tend to be standard for live events with bass/sub oriented music genres.

 

[shredder2]

Literally the most complex thing in this thread so far has been my reference to a rarefaction wave...

Your picture looks pretty. Depending on what subs/how much power you are going to run, that port area looks pretty small. Is that a 2:1 SPL oriented box or do you just want to do hair tricks like the cool kids?

I just saw where this thread was going and decided to chime in, reading all the comments with ensuing questions must have left me a little bit weary.

"Cool kids?"... sure Wilbur. That was a pic of one of the many 4ths I've designed. Without defending its pros and cons it was a lower powered 4 10" musical 4th. NOT a boomy spl enclosure...
Here's another couple pics of another lower powered musical 4th for you to critique since you felt the need...

 

[SlugButter]

With dual 15” cabinets as top speakers, content down to 50hz can be covered. A frequency response down to 35hz is ussaly enough, but flat down to 30 hz tend to be standard for live events with bass/sub oriented music genres.

What about on the high end? is It feasible to limit the woofers bandpass frequency that much outside a vehicle? If you wanted to play down to 30 HZ in free air, you’d basically be limited to a passband of approx. 30-70 HZ. Wouldn’t you need a second set of woofers to cover the frequency range up to where mids take over? A 6th order seems like it would be better to cover a bit wider range in free air. Or a folded horn. Space is obviously not a concern as much in PA applications.