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Old 11-05-2014, 05:18 AM
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Default 2:1 vs. 1:2 6th order BP?

Hi Gent's,

Hope y'all doing great and everything is going great for y'all,

I know there a LOT of variables but please focus on the ratio I mean if everything remains the same but ratio, I have heard the 6th order bp's aren't the same as the 4th order bp's, the 4th order bp usually we need bigger ported for more output and narrower bandwidth while the 6th order bp's don't need big front chamber I mean with just half the rear chamber volume or less it can pressurize greatly and going with bigger front chamber just make the response very narrow and not musical at all with very minimal gain while in 4th order bp we gain and stay musical??

So how is the 2:1 6th order bp vs. 1:2 6th order bp if we have everything remains the same but ratio?

Thank you, any reply would be greatly appreciated,

Kindest Regards.
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Old 11-05-2014, 08:20 AM
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Seems like nobody but Hackmunch and he is already left since a long time ago!!!

Anyway thank you,

Kindest Regards.
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Old 11-05-2014, 08:29 AM
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Alot of very knowledgable guys have left the forum
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Old 11-05-2014, 08:31 AM
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Yep you can add 80inches to the list but he isn't here much.
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Old 11-05-2014, 11:00 AM
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It's hard that all of our Audio Gods already left!

Kindest Regards.
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Old 11-05-2014, 11:50 AM
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There's two things that define how a 6th order will act: (1) there is no direct radiator, all of the output is coming from the ports, and because of this (2) the roll off on either side of a port tuning frequency is 24dB/oct vs 12dB/oct for a direct radiator (sealed or IB).

First a bit about how ports act. For a regular ported box, you can think of the enclosure as having two speakers: the direct radiator, which acts like it's in a sealed enclosure above the tuning frequency, and the vent, which acts like a narrow-tuned radiator around it's tuning frequency. Think of it like two separate responses that merge together, with the top of the response determined by how the speaker would act in a sealed enclosure and the bottom of the response determined by how the port acts. In a small vented enclosure, the "sealed" or "direct radiator" portion of the response becomes peakier and fb (sealed resonance) goes up in frequency. Because of this, the speaker itself isn't doing much to excite the port, and you don't get much output from the port around it's tuning frequency. Conversely, a large ported enclosure will allow the speaker to excite the port quite a bit, and you get more gain around the port tuning frequency. If you keep making the enclosure larger, you notice that the top end of the bandwidth (the "sealed" part) continues to stay the same (because it's effectively acting like an IB), and the bandwidth around the port will get peakier and eventually you can't get any more gain out of it. There's also a third "section" of the frequency response, and that's below tuning. I'm sure everyone knows what happens here - the speaker just acts like it's on an open baffle and goes free-air, which is what causes the roll-off to be 24dB/oct on the low end.

Now we can translate that to a parallel 6th order (I'm focusing on parallel because it's easier to visualize). Take the picture below, where there's two chambers, the one on the left tuned to 25hz and the one on the right tuned to 50hz. Below both tunings, at for example 10hz, both ports are out of their resonant bandwidth and act like free-air openings. The arrow shown in the port represent that. There's just air being pushed in and out of the ports with no gain. As you go up in frequency to say 30hz, this falls below the tuning of the 50hz chamber, which means that the right side of the speaker is acting like it's in free air. This is, however, in the bandwidth of port excitement on the left chamber, so you get output from that port. I tried to visualize this by using a squiggly line to show that the port is resonating. Now go up further in frequency to 50hz. This is well above the tuning frequency of the left chamber, so it starts to act like a sealed chamber. I represented this by adding a line on the end of the port in that chamber. At that frequency, the other chamber's port is excited and you get output from that side. As you go higher in frequency, to 100hz, you're well above the tuning frequency of both ports, so both chambers begin to act as sealed enclosures. That's why you have a sharp drop-off of 24dB/oct on the top end of the enclosure as well.
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Last edited by SPLEclipse; 11-05-2014 at 01:59 PM.
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  #7  
Old 11-05-2014, 11:52 AM
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If you look at the picture below under the first diagram, you can see three vented enclosures, all using the same sub and tuned to 30hz. The green line represents 2 CF (cubic feet), and you see a nice smooth transition from the upper "sealed" response to the lower vent response. Lowing the volume to 0.5 CF (teal line) makes the upper "sealed" response peakier and restricts port excitation, making the vent virtually useless around tuning until the speaker unloads at lower frequencies and the response drops off at the very low end. Going the opposite way and increasing the enclosure to 10 CF (purple line) shows virtually the same "sealed" upper response but nets more gain around the tuning frequency as the port response becomes peakier.

Ok, so now that we know how ports react to enclosure size, and how direct radiators react to enclosure size, you can see how completely taking the "sealed" or "direct radiator" portion of the response out will look. This is what happens in a parallel tuned 6th order. You have two vents each acting as an independently tuned radiator. Make the enclosure size larger and the port gain goes up and gets peakier. I won't go over all of the responses in the second diagram, but I will point one out: the orange line represents what happens if you have a 1:1 ratio both tuned to the same frequency (in this case 30hz). Because both ports in both chambers are acting the same way but on opposite strokes of the sub, they are exactly out of phase.
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Old 11-05-2014, 11:59 AM
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You'll notice that the gain profiles of each port acts a little bit differently, with the upper frequency gain looking peakier while the lower frequency gain looking smoother, depending on how you balance out the ratio. That's because if you look a couple posts up at the first picture I posted of how the ports behave on either side of the enclosure, you'll notice something: at upper frequencies, the enclosure is acting more as a 4th order. This is why you typically see a lot of 6ths that are more close in size ratio wise. If you decrease the size of the lower ported chamber too much to get a big ratio, you also increase the resonance of that side and get a huge peak on the upper end of the response. That's great for burping, but not-so-great for daily.
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Old 11-05-2014, 12:01 PM
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I'll kick in and say, we haven't lost anyone worth keeping {except the mods that left during the ownership change}

what makes me sad are the stupid rule of thumb bullshit theories

like port per cu ft{fail}

and ratios for bandpass{which fail compared to an actually designed bandpass}

and quasi bandpass.. {give it a real name}{and don't guess what it'll do.. know!}

there have been no new design developments in the last 25 years {nor advancements}

just more power and heavier subs
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Old 11-05-2014, 01:18 PM
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Quote:
Originally Posted by iamsonic View Post
I'll kick in and say, we haven't lost anyone worth keeping {except the mods that left during the ownership change}

what makes me sad are the stupid rule of thumb bullshit theories

like port per cu ft{fail}

and ratios for bandpass{which fail compared to an actually designed bandpass}

and quasi bandpass.. {give it a real name}{and don't guess what it'll do.. know!}

there have been no new design developments in the last 25 years {nor advancements}

just more power and heavier subs

Dear sir,
I didn't say there is a magic ratio that gets the most of all the sub's but I need something to rely a lil' bit on I mean like a starting point, putting a well suited to ported/6th order sub in 2:1 ratio or 1:2 ratio and test or visualize as Mr.SPLEclipse does is great to start with, yes port to cu ft. Ratio is dumb but you can start with it and shrink from there, I'll do a lot of Trial and Error to squeeze my equipment but we should have something to start with it's simple as that sir!

Thank you,

Dear Mr.SPLEclipse I thank you very very very.. Much, that helps a lot I mean that's a HUGE help, and please I'm not saying people still around here aren't smart enough but I brought what I see which is missing such great response so sorry, SPLEclipse you're the MAN!!!

2:1 (bigger rear chamber) is the way to go in my opinion specially for daily and lows,

Thank you again, I greatly appreciate it sir,
Kindest Regards.
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