Bandpass 101

loddie · 14th January 2008, 03:03 AM

I would like to learn how to model bandpass enclosures. Mostly what I have found online is geared to making a one note box for car audio. I am interested in designing a bandpass box to have as wide a frequency response as possible (hopefully three octaves: 200-1400). The enclosure will feed into a Unity Horn (I have come across Patrick Bateman's threads)

Please suggest books and websites where I can learn more about bandpass enclosures. Also, what does "sqrt" represent in this formula: Fm=sqrt(Fh X FL)? Is it square root?

What are the best programs for modeling bandpass enclosures (multiple ports, etc)?

Thanks!

Ron E · 14th January 2008, 11:54 PM

In order to make a 4th order bandpass box to cover that range, you would need to make a port or PR with a resonance of ~sqrt(200*1400)=~500Hz. Yes, sqrt=square root

Designing short ports for such high resonances is a little tricky, not something a standard program will do well at all, probably will need some cut and try. Good luck.

I'm trying to imagine (without any calcs) a driver that would work in such an enclosure. Maybe a small sealed back midrange?

sreten · 15th January 2008, 08:55 AM

Hi,

The real question is why ? what is the point of a BP at those frequencies ?

/sreten.

loddie · 16th January 2008, 12:53 AM

Thanks Ron. I was thinking most software would struggle with this type of bandpass application. I will probably have to resort to trial and error.

Sreten, this reason is the application, an automobile. The dash, window, and pillars will form the horn. Bandpass allows the driver to be remotely located, although limited to be port constraints

Ron E · 16th January 2008, 05:01 AM

I think the whole concept is flawed. Using the bandpass port as some sort of sound channeling system isn't likely to work well. If the ports are longer than ~1/4-1/2 wavelength at any in band frequency because otherwise there will be port resonances in or near the passband. If your planned ports are shorter than this, then why bother with bandpass at all?

loddie · 18th January 2008, 08:12 PM

To get back on topic, does anyone have suggestions for excellent books and/or websites to further one's education of bandpass enclosures?

Thanks!

GM · 18th January 2008, 09:46 PM

Only Prof. Leach's papers: http://users.ece.gatech.edu/~mleach/.../HornPaper.pdf

Thawach · 19th January 2008, 03:49 PM

hi

I think about bandpass that the airflow pass the port slowly.
The transience is not well. But The SPL is high. The automobile
like it. I don't know why it is.

Ron E · 19th January 2008, 05:25 PM

Quote:

Originally posted by loddie
To get back on topic, does anyone have suggestions for excellent books and/or websites to further one's education of bandpass enclosures?

What is your math tolerance?

If low:
You can look at http://www.diysubwoofers.org
You can get the Loudspeaker Design Cookbook, from which most of the information at diysubwoofers is taken.
If high (Engineer, physicist):
You can learn about acoustic equivalent circuits and modeling, then you can read Earl Geddes' and Laurie Fincham's articles in the JAES. You can learn to model them yourself... Don't forget to model the complex impedance of the port. Prraps once you've mastered that you can model the flare rate of your windshield, etc...

Or you could just build it.

loddie · 20th January 2008, 01:44 AM

Unfortunately my math tolerance is now low. I've read the diysubwoofers site and played with their spreadsheet. I will pick up the LSD Cookbook and just start building! I already picked up Geddes "Audio Transducers" book

14th January 2008, 03:03 AM	#1
loddie diyAudio Member Join Date: Apr 2006 Location: Colorado Springs, CO	Bandpass 101 I would like to learn how to model bandpass enclosures. Mostly what I have found online is geared to making a one note box for car audio. I am interested in designing a bandpass box to have as wide a frequency response as possible (hopefully three octaves: 200-1400). The enclosure will feed into a Unity Horn (I have come across Patrick Bateman's threads) Please suggest books and websites where I can learn more about bandpass enclosures. Also, what does "sqrt" represent in this formula: Fm=sqrt(Fh X FL)? Is it square root? What are the best programs for modeling bandpass enclosures (multiple ports, etc)? Thanks!

14th January 2008, 11:54 PM	#2
Ron E diyAudio Member Join Date: Jun 2002 Location: USA, MN	In order to make a 4th order bandpass box to cover that range, you would need to make a port or PR with a resonance of ~sqrt(2001400)=~500Hz. Yes, sqrt=square root Designing short ports for such high resonances is a little tricky, not something a standard program will do well at all, probably will need some cut and try. Good luck. I'm trying to imagine (without any calcs) a driver that would work in such an enclosure. Maybe a small sealed back midrange? __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan* Science is a way of thinking much more than it is a body of knowledge. --Carl Sagan

16th January 2008, 05:01 AM	#5
Ron E diyAudio Member Join Date: Jun 2002 Location: USA, MN	I think the whole concept is flawed. Using the bandpass port as some sort of sound channeling system isn't likely to work well. If the ports are longer than ~1/4-1/2 wavelength at any in band frequency because otherwise there will be port resonances in or near the passband. If your planned ports are shorter than this, then why bother with bandpass at all? __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan Science is a way of thinking much more than it is a body of knowledge. --Carl Sagan

18th January 2008, 09:46 PM	#7
GM diyAudio Member Join Date: Jun 2003 Location: Chamblee, Ga.	Only Prof. Leach's papers: http://users.ece.gatech.edu/~mleach/.../HornPaper.pdf __________________ Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.

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15th January 2008, 08:55 AM	#3
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, The real question is why ? what is the point of a BP at those frequencies ? /sreten.

16th January 2008, 12:53 AM	#4
loddie diyAudio Member Join Date: Apr 2006 Location: Colorado Springs, CO	Thanks Ron. I was thinking most software would struggle with this type of bandpass application. I will probably have to resort to trial and error. Sreten, this reason is the application, an automobile. The dash, window, and pillars will form the horn. Bandpass allows the driver to be remotely located, although limited to be port constraints

18th January 2008, 08:12 PM	#6
loddie diyAudio Member Join Date: Apr 2006 Location: Colorado Springs, CO	To get back on topic, does anyone have suggestions for excellent books and/or websites to further one's education of bandpass enclosures? Thanks!

19th January 2008, 03:49 PM	#8
Thawach diyAudio Member Join Date: Dec 2007	hi I think about bandpass that the airflow pass the port slowly. The transience is not well. But The SPL is high. The automobile like it. I don't know why it is.

20th January 2008, 01:44 AM	#10
loddie diyAudio Member Join Date: Apr 2006 Location: Colorado Springs, CO	Unfortunately my math tolerance is now low. I've read the diysubwoofers site and played with their spreadsheet. I will pick up the LSD Cookbook and just start building! I already picked up Geddes "Audio Transducers" book

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