Bandpass designs explained |
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Jake_Fielder
Old Croc Joined: 08 October 2007 Status: Offline Points: 4231 |
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Posted: 01 April 2008 at 6:42pm |
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In this message I will illustrate some different bandpass designs.... (Thanks to jsg mashed for explaining this to me)
When working out the order of a bandpass cab;
You get 2nd order for the driver, and 2 more orders for each chamber and port you add on.
When the chamber behind the driver is sealed, it does not add another order.
[So the order of a sealed box "acoustic suspension" cabinet is the same as that of just the driver. This is because the compliance of the air in the chamber "merges" with the compliance of the driver and becomes one element. If you then port that chamber, you separate the two compliances because they no longer act as one. So you get an order for the port and another for the now-separate chamber volume.]
A 4th order bandpass can look like this:
The driver and sealed chamber B are 2 orders, chamber A and the port are a further 2 orders.
Designs like this are also 4th order bandpass:
(like the Infrabass)
The drivers and sealed rear chambers B are 2 orders, and they fire into a chamber A and the port which is two more orders.
Common 6th order bandpass cabs can look like this:
Parallel 6th order is when (like the X1) both chambers A and B are ported to the outside
Series 6th order is when chambers B and A are ported in series IE. B is ported into chamber A which is ported to the outside.
With the two above the driver is two orders, chamber B and its port are two more, and chamber A and its port are two more.
Another form of 6th order:
The driver and sealed chamber B are 2 orders, and chambers A and C and ports make up 4 more orders.
Designs like this are also 6th order bandpass:
Dual parallel 6th order bandpass
A couple of 8th order bandpass designs:
This one above is the same layout as the Mighty dub pass design.
This is like a parallel 6th order but both chambers are ported into a third chamber C.
The 8th order above is like a series 6th order but with chamber A ported into a third chamber C instead of to the outside.
I'll add more to this later, obviously if anyone has anything to add, do so.
Jake Edited by Jake_Fielder - 02 April 2008 at 4:04pm |
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xlogic
Young Croc Joined: 21 August 2006 Location: London Status: Offline Points: 565 |
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Can you explain the benefits and disadvantages of each one with refference to SPL and low and high cutoff frequencys?
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Jake_Fielder
Old Croc Joined: 08 October 2007 Status: Offline Points: 4231 |
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Eventually!!
I'm going to keep updating it and add stuff as I learn it to make a comprehensive bandpass beginners thread. Edited by Jake_Fielder - 01 April 2008 at 9:00pm |
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tb_mike
Old Croc Joined: 01 October 2004 Location: New Zealand Status: Offline Points: 2744 |
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Something important to note is that the more ports,the more critical the tuning.
Also, efficiency bandwidth product(as shown on winisd)shows you which drivers are suitable for sealed/BP4 or ported/BP6 the forum code corrupted the link. http://www.diysubwoofers.org Edited by tb_mike - 02 April 2008 at 7:20am |
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mylesound
Registered User Joined: 08 August 2007 Status: Offline Points: 351 |
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links not working
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Jake_Fielder
Old Croc Joined: 08 October 2007 Status: Offline Points: 4231 |
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www.diysubwooferS.org
I think it exists, but its broken Edited by Jake_Fielder - 02 April 2008 at 9:41am |
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jsg mashed
Registered User Joined: 18 May 2007 Location: United Kingdom Status: Offline Points: 305 |
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Absolutely. And the usual port formulas are very inaccurate because the end corrections don't take into account the internal structure of your cabinet. So there's no substitute for tuning experimentally.
IME you can't get the bandpass band to go much over Fs/Qts or much below FsQts. And you can get a slightly better response shape if you are close to these limits. So, ironically, a high Fs often gives the best results at the bottom end.
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...because Good is Dumb.
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jsg mashed
Registered User Joined: 18 May 2007 Location: United Kingdom Status: Offline Points: 305 |
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I think there's a later revision to that design than the one you've linked to.
It will make discussion easier if the chambers are named. I use "A" for chamber in front of driver, "B" for chamber behind driver and "C" etc for other chambers. And the same letter is used for 2 chambers if they're identical acoustically as with the B chambers in the infrabass.
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...because Good is Dumb.
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snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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Hi
i'm trying to design a parallel 6th order bandpass. I want it to use two 12" drivers and I want it to cover about 70Hz to 300Hz. so was thinking should tune the chambers to 100Hz and 200Hz - is this right. I have an idea what the overall cabinet volume should be and so can take a rough guess at the sizes of the two chambers and the ports needed to tune them. how do I go about determining what a suitable driver is - or whether a suitable driver even exists for the cabinet I have specified? is there any way other than trial and error with simulation software? if I need to use software does anyone know of any that allow you to define the cabinet/tuning and work out driver parameters rather than the other way round?
cheers Phil |
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_djk_
Old Croc Joined: 23 November 2004 Location: United States Status: Offline Points: 6002 |
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"is this right"
NO! Use a modeling program and the actual driver parameters. I doubt you will be able to get that kind of bandwidth. |
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djk
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djeddie
Old Croc Joined: 26 April 2004 Location: Bristol Status: Offline Points: 4125 |
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As djk said the bandwidth will be a problem, normally BP cabs are OK for about one and a half octaves.
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Chas n Dave : it's like Drum and Bass but with beards. E=mc² ±3dB
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snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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okay. any sort of idea what sort of driver I should be trying? I read that Fs/Qts should be high - is that right?
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