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Vented bandpass horn? |
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tomr_29 
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Joined: 23 February 2009 Location: West Midlands Status: Offline Points: 540 |
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 Topic: Vented bandpass horn?Posted: 22 July 2009 at 11:38am |
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Looking into a re-design for my current bass cabs to offer a bit more versatility with the music they can play. Need something that can still keep up well with dance music but will still drop low enough to be adequate for some dubstep and DnB. The design can’t be too large but I don’t mind having to sacrifice some efficiency to achieve this. Desired Spec: Low cut-off of around 38Hz Upper cut-off of 120Hz or more Enclosure approximately 750 x 900 x 560mm Due to cost I will be using my existing PD186 drivers (one per cab) and building just one cab per side and then having the possibility of adding more if successful. (I do also have 2 PD184s if they would be more suitable). Was thinking possibly something along the lines of a bandpass horn (since I like the kick they offer) but with a ported / vented rear chamber to lower the cut-off. Example a USB but with a rear chamber similar to that of the X1:
Would this be something along the lines of a 6th order bandpass with horn? I think I understand the concept of bandpass but not the effects each parameter has on the output, especially when it comes to combining them with horns. Hence trying to ‘glue’ two successful designs into one… Could this be modelled in Hornresp? |
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tomschute
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Joined: 15 May 2006 Location: Mid Wales Status: Offline Points: 1817 |
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Posted: 22 July 2009 at 11:49am |
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You will indead need to master HR for this project. Small variations will have relatively, quite drastic changes to the output.
There are a couple of similar projects about so do a search - I think Jake developed a 15" very similar to this. And Startec (search dj-panoramix ) has several plans on here that fit the bill. Good luck, Tom |
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Out to lunch... stableaudio@hotmail.co.uk
www.stableaudio.co.uk Speaker Building Services |
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Jake_Fielder
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Joined: 08 October 2007 Status: Offline Points: 4231 |
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Posted: 22 July 2009 at 11:51am |
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Ported horn and hybrid are words people use to describe this, i have made 4 very similar to your design, ceharden has made 4x 15" ported horns,
Its a good design and can be modeled in hornresp very easily. I think the technique is to tune the rear chamber to about one octave below the horn cut off (mines tuned just above this), mine have a similar sized front chamber, others have said they found it works better with no front chamber.
you could also call this a 6th order bandpass with a big flared port if u like.
I did a thread about my design in the new project forum, quite a while ago,
i'll get a link
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Jake_Fielder
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Posted: 22 July 2009 at 11:53am |
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http://www.speakerplans.com/Forum/jf-vented-horn-paudio-e18600a_topic15928_post154226.html?KW=#154226
Oh yeah, for got to say "JaKe" made some 15" ported horns with a twist, the rear chamber is ported into the throat so the horn is used for the front and rear of the drivers output.
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tomr_29
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Joined: 23 February 2009 Location: West Midlands Status: Offline Points: 540 |
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Posted: 22 July 2009 at 1:26pm |
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I can model the rear chamber along with driver parameters (although I'm missing the Rms and Le values of the PD186 for Hornresp) but if I'm honest I have no idea how to model the bandpass horn part. Feel cheeky for asking but is there any chance of some help regarding what to input for the throat and horn section?
Thanks, Tom
Unrelated but there also seems to be a descrepancy on the PD website stating that the xmax of the 186 is 9mm on the page, then 10.5mm in the brochure
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Jake_Fielder
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Posted: 22 July 2009 at 1:40pm |
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Bollox, i just wrote a big post and lost it, i'll write it again later....
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Jake_Fielder
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Posted: 22 July 2009 at 1:47pm |
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A few rough measurments to start you off,
Throat: gap between the piece of wood sticking out infront of the driver and back wall in cm2, probably about 700-900cm2 would be good.
Mouth: As big as you can afford to make it, about 4000cm2 would be good
Horn length: as long as poss, but about 70-100cm would be ok i think.
I'd tune the rear chamber to about 35hz,
Check out my thread i posted a link to for my input data to see where i got the figures from ect.
Also the hornresp help thread goes into detail about all aspects of horn response.
Other than that have a play about and see what works, i check the excursion graph to see the tuning frequency of the rear chamber (the point where it drops to nil)
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Jake_Fielder
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Posted: 22 July 2009 at 1:50pm |
If you double click on the values you dont know then hornresp will ask you a couple of questions and calculate the unknown value
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tomr_29
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Posted: 22 July 2009 at 1:52pm |
Haha, hate it when that happens. I've gotten into the habbit of selecting all and copying before I click post.
Thanks tho. I should probably actually get some work done anyway... Amazing how time just disappears on here  . Should have some time to get my head around it later (work permitting of course  ).Edited by tomr_29 - 22 July 2009 at 11:03pm |
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Proper capitalisation is the difference between helping your Uncle Jack off a horse and helping your uncle jack off a horse.
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tomr_29
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Posted: 22 July 2009 at 11:02pm |
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Well I've gone through what I can with Hornresp and what I'm getting doesn't look too pretty.
 Input Parameters (not for same graph exactly but very similar result):  Am I doing something wrong or is my design really THAT bad? Lol. |
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Proper capitalisation is the difference between helping your Uncle Jack off a horse and helping your uncle jack off a horse.
www.facebook.com/tremoracoustics |
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Jake_Fielder
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Posted: 22 July 2009 at 11:10pm |
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input data looks roughly right, what you need to do is click >tools >combined response > distance "0cm"
This includes the out put of the port in your graph, at the moment its only showing the horn output, so it drops to zero at the tuning frequancy
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tomr_29
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Posted: 22 July 2009 at 11:30pm |
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Yeah that looks loads better That's a dumb mistake I won't make again...
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Proper capitalisation is the difference between helping your Uncle Jack off a horse and helping your uncle jack off a horse.
www.facebook.com/tremoracoustics |
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tomr_29 wrote: