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Bandpass designs

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Jake_Fielder View Drop Down
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    Posted: 28 March 2008 at 11:09am
Could someone clear this up for me please....?
 
As far as i know....
 
4th order bandpass looks like this:
 
6th order looks like this:
 
8th order looks like this:....?
 
Assuming i got those right....
 
WHATS THIS!?
 
Is it a form of 6th order bandpass?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Disco Stu Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2008 at 11:19am
Presumably 7th order
All you need to know is:
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Jake_Fielder View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jake_Fielder Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2008 at 11:21am
Hmm, do you know of any others? I have heard of 5th order mentioned somewhere before. Is there any reason they're called 4th, 6th ect so i logically work it out?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jake_Fielder Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2008 at 11:23am
I keep thinking its 5th order, but then logically this one would be 7th order not 8th....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2008 at 11:52am
It's all related to the number of poles AFAIK it has cos what you're actually doing is applying acoustic filters.  I really should know the answer to this.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jake_Fielder Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2008 at 11:55am
Its weird cos i keep searching the net for the answer, all i want to see a list of pics like mine saying 4th, 5th, 6th, etc. so that i can understand it. but i cant find the info anywhere.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jsg mashed Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2008 at 3:17pm
Your question has awoken the god of bandpass... which is me!
 
Originally posted by Jake_Fielder Jake_Fielder wrote:

As far as i know....
 
4th order bandpass looks like this:
 
 
Yup.
 
Originally posted by Jake_Fielder Jake_Fielder wrote:

6th order looks like this:
 
Correct. This is one kind of 6th order bandpass, commonly known as Parallel tuned, P6 or type A.
 
 
Originally posted by Jake_Fielder Jake_Fielder wrote:

8th order looks like this:....?
 
 
You are indeed correct. One could conceive of other 8th order topologies, but this is the only one I've seen used. 
 
Originally posted by Jake_Fielder Jake_Fielder wrote:

 
WHATS THIS!?
 
Is it a form of 6th order bandpass?
 
This would be 6th order. It will have the interesting property of rolling off at 24dB/octave at the top end and only 12dB/octave at the bottom end. The usual 6th order designs, like the one you sketched above, are the other way around.
 
Personally I prefer the rear chamber ported for excursion control and extended LF response, but others would disagree including the designer of the Function One speakers.
 
As regards calculating the order, basically you get 2nd order for the driver and 2 more orders for each chamber/port pair you add on. Odd orders can be made acoustically, but most commonly they result from adding series inductors/capacitors to the driver. Here, basically each component adds 1 order.
 
Note that this is a very rough guide. Some cabinet types don't really have an order, since their transfer function is not of the right type to apply an order to. Sometimes you can have two chamber/port pairs that are identical and driven in parallel so they act as one (eg JBL's TCB). Taking into account cabinet wall flexing and airload charateristics change things and that's before you get into non-linearity.
 
...because Good is Dumb.
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Jake_Fielder View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jake_Fielder Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2008 at 3:27pm
Aha just the man, i thought you might respond! The only reason i know what an 8th order looks like is because of your design (i wont mention the name or people may start attacking each other!LOL)
 
Are there any other common bandpass arangments that you have come accross that i havent listed? i'd like to compile a comprehensive list on here for referance.
 
cheers
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jsg mashed Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2008 at 3:43pm
Originally posted by Jake_Fielder Jake_Fielder wrote:

Are there any other common bandpass arangments that you have come accross that i havent listed? i'd like to compile a comprehensive list on here for referance.
 
cheers
 
There's the series 6th order (S6 or type B edit: also cascade 6th). You take the 4th order and add an internal port parallel to the driver. So it looks like a reflex enclosure with both port and driver going into a final resonator.
 
 


Edited by jsg mashed - 28 March 2008 at 3:48pm
...because Good is Dumb.
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Jake_Fielder View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jake_Fielder Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2008 at 3:49pm
Series 6th:
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jake_Fielder Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2008 at 3:57pm
would these monstrositys have a name?
 
 
Would there ever be any use for these last two setups?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jsg mashed Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2008 at 4:06pm
[re: series 6th]
That's the one. It's good for getting low frequency extension far below Fs at the expense of sensitivity.
 
Just another comment on orders - 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 'cause 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 seperate the two compliances because they no longer act as one. So you get an order for the port and another for the now-seperate chamber volume.
 
Also, bear in mind the usual orders are given based on a highly simplified model - there's lots that gets ignored when designating them.
 


Edited by jsg mashed - 28 March 2008 at 4:07pm
...because Good is Dumb.
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