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Quentin Jarrell

SEALED REAR CHAMBER BP ENCLOSURE (4TH ORDER)

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I'll try to put this in Laymen's terms as much as possible.  I will not go into hand calculating as it is tedious and the tables are too much to copy here.  To hand calculate purchase a copy of the Loudspeaker Cookbook.  I use the calculator on Car Stereo's site as it is close to doing it by hand.

 

http://www.carstereo.com/help/Articles.cfm?id=27

 

The reference for the following in formation:  Vance Dickason, "Loudspeaker Design Cookbook 7th Edition," Audio Amateur Press,2006.

 

DEFINITIONS.

A sealed rear chamber bandpass enclosure is basically a closed-box system with the addition of an acoustic filter in series with the front radiation of the driver.

 

TERMS.

fb = tuning frequency of front chamber vent

fl  = f3 of low frequency rolloff

fh = f3 of high frequency rolloff

Lv = vent length

Qbp = q of bandpass rear chamber

R = vent radius

S = passband ripple (variation in magnitude response / boost in output)

Vf = volume of front chamber

Vr = volume of rear chamber

Vt = total volume of both chambers

 

WOOFER SELECTION.

Drivers with higher Qts normally yield lower f3 rolloffs.  If it works well in a sealed box it should work well in 4th order bandpass

 

 

 

 

Using the terms form the cookbook I'll walk through how to use the calculator on carstereo.

 

1.  number of drivers. 

     simple input the number of subs you are using.

 

2. Isobaric or not?

     This set up will not be isobaric.

 

3.enter parameters of the driver.  I'll be using the Ethos 15.

   Qts = .64

   Vas = 95.9 liters / 3.386 cubic feet

   fs = 25.78

 

4. choose an "s" factor

     The "s" or ripple factor is a ripple or a peak or valley shown in the passband between the low and high roll off.  When you model a sub and the line isn't straight and it dips or is raised this is ripple        or "S" factor.  A factor of .7 will have a flatter response than .6 and .5.  "S" factor is also an indicator of transient response and passband.  A "S" factor of .5 will have a degraded transient                    response than .7 however will have a larger passband, but will normally require a smaller box.  As always the triangle applies.  You won't have a small box with a large passband and tight                      response.  For now we will choose a S factor of .7

 

5.  choose fl or lower roll off.

     EVERYONE likes the lows so let's choose 20 hz

 

6.  Hit calculate and see what you get.

     We get:  Vf = 2.718

                   Vr = 7.123 (wow really big this won't fit)

                   Qbp  .78   (normally we would worry about the system Q when modeling by hand.  It's the second thing you look at after S factor.  Qbp is an indicator of sensitivity and normally you want a                                       sensitivity of zero but the calculator calculates sensitivity automatically so Qbp isn't a biggie to worry about.  BUT just like in a sealed box normally a total Q of around .7 is                                               what most people prefer)

                    

                   fb = 31.31 hz

                   passband = 20-49 hz  (high f3 is a bit low, id like to at least play up into the 60's)

                   gain = 3.39 (this is pretty good.  you don't want to go much higher than 3 db.  The higher the sensitivity the less power the sub will need and you might run into mechanical failure if you                                            are not careful)

 

 

7.  This box will definantly not fit.  Since we know "s" factor affects box size let's choose a factor of .6  We recalculate and get the following

                    Vf = 1.997

                   Vr = 4.451

                   Qbp  .85   

                   fb = 34.21 hz

                   passband = 20-58.51 hz  (high f3 is still a bit low)

                   gain = .76 (still in good range )

 

      so, now box is a good bit smaller and will fit in my car BUT I want a higher fH.  

 

8.  lets choose a s factor of .5 since we now know "S" factor effects volume and we get:

                    Vf = 1.387

                   Vr = 2.963  (awsome box is even smaller)

                   Qbp  .94  

                   fb = 37.74 hz

                   passband = 20-71.21 hz  (high f3 is now where I want it)

                   gain = negative 2.61 (wow this box will be down almost 3 db in its passband )

     Since we know "s" factor affects box volume and passband and those are good lets change the low rolloff and see if it'll fix the sensitivity. 

 

9.  lets set it to 25hz.  I think that'll be low enough and we get:

                         Vf = 1.387  (see we used the same s factor and it remained the same)

                   Vr = 1.814

                   Qbp  .1.08

                   fb = 43.65 hz

                   passband = 25-76.21 hz  (high f3 is a bit high but I'll use the filter on the amp to bring this down a bit.

                   gain = 3.21         

                   This looks like it'll be the best compromise.  Small enough box to fit in my car, passband is pretty good for the sub stage, and the gain is not too high that i'm gonna have to worry about                        damaging my sub. 

 

 

 

 

 

 

 

 

 

 

 

 

 

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goyou.gif  Great job on making this as simple as possible. So much easier to understand than anything else ive read.  Ill have to use this in future builds. It'll make things so much easier. Sticky this? Maybe post this up in SQL/SPL fabrication section as "4th order bandpass for dummies" or something like that.

Edited by NickHall

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goyou.gif  Great job on making this as simple as possible. So much easier to understand than anything else ive read.  Ill have to use this in future builds. It'll make things so much easier. Sticky this? Maybe post this up in "SQL"/SPL fabrication section as "4th order bandpass for dummies" or something like that.

I wouldn't treat it as gospel.  It's just how I do it.ninja.gif

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Finally, an easy (easier) way to design more SQ-oriented 4th orders ;)

 

The link appears to be dead, though. Or the site is down.

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When is it the right time to use a 4th order BP? When are use supposed to use it and when is a reg ported box better?

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When is it the right time to use a 4th order BP? When are use supposed to use it and when is a reg ported box better?

When you have to build the enclosure in one compartment and transfer the output to another, like a sealed trunk into the cabin of a vehicle. That is really the only reason that I can see for using a bp in a vehicle. We'll see what the experts say though...

Edited by ricksi30

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When is it the right time to use a 4th order BP? When are use supposed to use it and when is a reg ported box better?

When you have to build the enclosure in one compartment and transfer the output to another, like a sealed trunk into the cabin of a vehicle. That is really the only reason that I can see for using a bp in a vehicle. We'll see what the experts say though...

 

 

Then how come people in suv's do it with a wall? It's all one whole compartment there though. Not doubting you or saying I'm right just throwing that out there too since they're both different things. I've also heard that. Like how blow through and using the ski hole.

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When is it the right time to use a 4th order BP? When are use supposed to use it and when is a reg ported box better?

When you have to build the enclosure in one compartment and transfer the output to another, like a sealed trunk into the cabin of a vehicle. That is really the only reason that I can see for using a bp in a vehicle. We'll see what the experts say though...

 

 

Then how come people in suv's do it with a wall? It's all one whole compartment there though. Not doubting you or saying I'm right just throwing that out there too since they're both different things. I've also heard that. Like how blow through and using the ski hole.

 

From my understanding, the vehicle's cabin affects a bandpass less than a standard ported box. I haven't researched this myself, though.

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^^ Not really.

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And good job, Quentin.

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Nice!!!

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more SQ-oriented 4th orders

I only know of 2 cars with "sucessful" competition enclosures built like this ...

... And I am so aggrivated that Ican not fimd my pics from these ...

One is from a Todd Crowder built car I got to demo at USACI 2010 World Finals in Shreveport, La ...

The other I got to demo at 2013 SPring Break Nationals ... One of the best Sound Quality vehicles in the world ...

Scott's G35 (all pics copy and paste from Google)

303893_10150284221168947_189181953946_79

309751_10150284222218947_189181953946_79

Yes, that's 4 Hybrid Imagine 6.5's in this enclosure ...

Edited by Cablguy184

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Amazing write up

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more SQ-oriented 4th orders

I only know of 2 cars with "sucessful" competition enclosures built like this ...

... And I am so aggrivated that Ican not fimd my pics from these ...

One is from a Todd Crowder built car I got to demo at USACI 2010 World Finals in Shreveport, La ...

The other I got to demo at 2013 SPring Break Nationals ... One of the best Sound Quality vehicles in the world ...

Scott's G35 (all pics copy and paste from Google)

303893_10150284221168947_189181953946_79

309751_10150284222218947_189181953946_79

Yes, that's 4 Hybrid Imagine 6.5's in this enclosure ...

 

 

I was thinking the gentleman that won Trunk 1 in Meca was a 4th bandpass build. The green Camaro?

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Man... that's customer service. you make it very difficult to even look at other subs... I guess Ethos 15 it is for the trunk of my wife's Jetta through a ski-pass.

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I was thinking the gentleman that won Trunk 1 in Meca was a 4th bandpass build. The green Camaro?

I'm sure there's more ... That's just the only 2 that I know for sure because I seen them up close and got demos from ...

I'm not sure what Trunk 1 is ?? That's a SPL class ??

But I do remember a Green Camaro in SQ, but I never got a chance to look at it or get a demo ...

We may be talking about the same car with Arc Audio products ???

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I was thinking the gentleman that won Trunk 1 in Meca was a 4th bandpass build. The green Camaro?

I'm sure there's more ... That's just the only 2 that I know for sure because I seen them up close and got demos from ...

I'm not sure what Trunk 1 is ?? That's a SPL class ??

But I do remember a Green Camaro in SQ, but I never got a chance to look at it or get a demo ...

We may be talking about the same car with Arc Audio products ???

 

Yah SPL class. His name was Jordan Smith. Surprised quite a lot of people. He was db drag and Meca champ.

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more SQ-oriented 4th orders

I only know of 2 cars with "sucessful" competition enclosures built like this ...

... And I am so aggrivated that Ican not fimd my pics from these ...

One is from a Todd Crowder built car I got to demo at USACI 2010 World Finals in Shreveport, La ...

The other I got to demo at 2013 SPring Break Nationals ... One of the best Sound Quality vehicles in the world ...

Scott's G35 (all pics copy and paste from Google)

 

There are "SQ" advantages to a 4th order bandpass enclosure.  But no one ever focuses on those because the SPL guys latched on to the design for their narrow band efficiency and sort of ruined the original intent of the design and many of their advantages.

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Found this on the MTX site.

Due to the fact that all the sound from this type of enclosure is produced by the vent, sound quality may not be as good as that of a properly designed sealed or ported enclosure. However, there are times when bandpass enclosures are the best choice to use. In a sedan application, bandpass enclosures are often used due to the inability to have multiple drivers mounted in the rear deck. In a limited space situation, efficiency can be sacrificed to gain deeper bass extension. In a situation where ultimate SPL is the goal, you can sacrifice bass extension, and enclosure size to produce a very efficient enclosure. Efficiency gains in the range of 5-10dB are not uncommon! As with any enclosure design, there is no free lunch. As you change one parameter to gain another, many times sound quality is degraded as well.

The frequency response in the pass band of a single reflex enclosure can be described with an “s factor”. S values that are of interest to us fall between .7 and .4. Values beyond this range either have peaky response, or poor sonic quality. An s of .7 refers to the flattest pass band available, where an s of .4 refers to the widest useable pass band.

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So taking another look at this write up, I've confirmed the results as well with other sources. The Vf value is the PORTED section, while the Vr is the SEALED section. So can someone please please provide an explanation, why EVERY BP Enclosure I see, the PORTED section is LARGER than the SEALED section? Generally speaking, the owner will describe their BP as an 1:1 / 2:1 / 3:1 ratio . And when they describe that's their enclosure, it, again, is referring to 1 ported to 1 sealed, 2 ported to 1 sealed, or 3 ported to 1 sealed. But this is TOTAL opposite of not only the cookbook, but other sources, including this write up by Quentin. 

 

I'm looking for a real answer to this question, not just, "their doing it wrong", or "because they seen it on youtube". Like, there has to be some truth to why the masses are doing it this way. This way being the ported section is larger than the sealed section. 

 

That's the first thing I have in question. Second thing.

 

Continuing with this write up/example that Quentin has provided:

 

lets set it to 25hz.  I think that'll be low enough and we get:
                         Vf = 1.387  (see we used the same s factor and it remained the same)
                   Vr = 1.814
                   Qbp  .1.08
                   fb = 43.65 hz
                   passband = 25-76.21 hz  (high f3 is a bit high but I'll use the filter on the amp to bring this down a bit.
                   gain = 3.21

 

If the Vf value is 1.387, and the Vr value is 1.814. Does the Vf value INCLUDE port area, or is that another factor not listed? Do we even need to include port area in this calculation? If so, then how do we calculate the port area that is needed, and add it in?

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So taking another look at this write up, I've confirmed the results as well with other sources. The Vf value is the PORTED section, while the Vr is the SEALED section. So can someone please please provide an explanation, why EVERY BP Enclosure I see, the PORTED section is LARGER than the SEALED section? Generally speaking, the owner will describe their BP as an 1:1 / 2:1 / 3:1 ratio . And when they describe that's their enclosure, it, again, is referring to 1 ported to 1 sealed, 2 ported to 1 sealed, or 3 ported to 1 sealed. But this is TOTAL opposite of not only the cookbook, but other sources, including this write up by Quentin.

I'm looking for a real answer to this question, not just, "their doing it wrong", or "because they seen it on youtube". Like, there has to be some truth to why the masses are doing it this way. This way being the ported section is larger than the sealed section.

That's the first thing I have in question. Second thing.

Continuing with this write up/example that Quentin has provided:

lets set it to 25hz. I think that'll be low enough and we get:

Vf = 1.387 (see we used the same s factor and it remained the same)

Vr = 1.814

Qbp .1.08

fb = 43.65 hz

passband = 25-76.21 hz (high f3 is a bit high but I'll use the filter on the amp to bring this down a bit.

gain = 3.21

If the Vf value is 1.387, and the Vr value is 1.814. Does the Vf value INCLUDE port area, or is that another factor not listed? Do we even need to include port area in this calculation? If so, then how do we calculate the port area that is needed, and add it in?

Well, the reasons for them using the ported side varies from my experiences. A larger ported side will be more efficient, thus more spl at the cost of frequency response, and some people want that type of response. Others i have talked with are just guessing and dont know what changing any of it does, so they are just doing with what they have seen.

Btw, this thread should be stickied, because it is very informative and it would make it easier to find later down the road, especially since i sometimes post it for others to read.

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So taking another look at this write up, I've confirmed the results as well with other sources. The Vf value is the PORTED section, while the Vr is the SEALED section. So can someone please please provide an explanation, why EVERY BP Enclosure I see, the PORTED section is LARGER than the SEALED section? Generally speaking, the owner will describe their BP as an 1:1 / 2:1 / 3:1 ratio . And when they describe that's their enclosure, it, again, is referring to 1 ported to 1 sealed, 2 ported to 1 sealed, or 3 ported to 1 sealed. But this is TOTAL opposite of not only the cookbook, but other sources, including this write up by Quentin.

I'm looking for a real answer to this question, not just, "their doing it wrong", or "because they seen it on youtube". Like, there has to be some truth to why the masses are doing it this way. This way being the ported section is larger than the sealed section.

That's the first thing I have in question. Second thing.

Continuing with this write up/example that Quentin has provided:

lets set it to 25hz. I think that'll be low enough and we get:

Vf = 1.387 (see we used the same s factor and it remained the same)

Vr = 1.814

Qbp .1.08

fb = 43.65 hz

passband = 25-76.21 hz (high f3 is a bit high but I'll use the filter on the amp to bring this down a bit.

gain = 3.21

If the Vf value is 1.387, and the Vr value is 1.814. Does the Vf value INCLUDE port area, or is that another factor not listed? Do we even need to include port area in this calculation? If so, then how do we calculate the port area that is needed, and add it in?

Well, the reasons for them using the ported side varies from my experiences. A larger ported side will be more efficient, thus more spl at the cost of frequency response, and some people want that type of response. Others i have talked with are just guessing and dont know what changing any of it does, so they are just doing with what they have seen.

Btw, this thread should be stickied, because it is very informative and it would make it easier to find later down the road, especially since i sometimes post it for others to read.

Hmmm, interesting. Because even at 2x and 3x events. World champions are using like, big 3 or even 6 to one ratio. But again, that's ported to sealed. Not as suggested by the cook book.

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So taking another look at this write up, I've confirmed the results as well with other sources. The Vf value is the PORTED section, while the Vr is the SEALED section. So can someone please please provide an explanation, why EVERY BP Enclosure I see, the PORTED section is LARGER than the SEALED section? Generally speaking, the owner will describe their BP as an 1:1 / 2:1 / 3:1 ratio . And when they describe that's their enclosure, it, again, is referring to 1 ported to 1 sealed, 2 ported to 1 sealed, or 3 ported to 1 sealed. But this is TOTAL opposite of not only the cookbook, but other sources, including this write up by Quentin.

I'm looking for a real answer to this question, not just, "their doing it wrong", or "because they seen it on youtube". Like, there has to be some truth to why the masses are doing it this way. This way being the ported section is larger than the sealed section.

That's the first thing I have in question. Second thing.

Continuing with this write up/example that Quentin has provided:

lets set it to 25hz. I think that'll be low enough and we get:

Vf = 1.387 (see we used the same s factor and it remained the same)

Vr = 1.814

Qbp .1.08

fb = 43.65 hz

passband = 25-76.21 hz (high f3 is a bit high but I'll use the filter on the amp to bring this down a bit.

gain = 3.21

If the Vf value is 1.387, and the Vr value is 1.814. Does the Vf value INCLUDE port area, or is that another factor not listed? Do we even need to include port area in this calculation? If so, then how do we calculate the port area that is needed, and add it in?

Well, the reasons for them using the ported side varies from my experiences. A larger ported side will be more efficient, thus more spl at the cost of frequency response, and some people want that type of response. Others i have talked with are just guessing and dont know what changing any of it does, so they are just doing with what they have seen.

Btw, this thread should be stickied, because it is very informative and it would make it easier to find later down the road, especially since i sometimes post it for others to read.

Hmmm, interesting. Because even at 2x and 3x events. World champions are using like, big 3 or even 6 to one ratio. But again, that's ported to sealed. Not as suggested by the cook book.

I dont remember what all the cookbook says, but i know if i was making one for myself for music it would be a small ratio or even larger sealed to ported, depending on the subs, but if i was going for spl i would use a large ported to sealed ratio. Also, playibg around with winisd i am rarely able to get a response that has similar output to a bass reflex enclosure without going with a larger ratio of ported to sealed, but then it becomes too peaky for me.

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Because 99.999999% of those boxes you see are NOT bandpass enclosures. Calculate a box with 8 15's in it with a front chamber of say 10 cubic feet with a port say 24 x 24 inches. It's gonna be crazy long. But look at how blows box and his is only one foot long. why? Because it's NOT a bandpass box. All he did was put his drivers in a sealed box and put a loading wall in front of the subs and create a wind tunnel with the small opening the subs have to play through. Joe Blow would have been better off with a regular ported box.

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Or what quentin said. Why are there so many people with "loading" walls? Doesnt make any sense to me

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