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Old 3rd December 2009, 08:10 PM   #1
loddie is offline loddie  United States
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Talking Bandpass design considerations

I drafted several different bandpass enclosure designs. However, I'm not sure if all the variations can be successfully implemented. Hopefully the resident experts can chime in and offer feedback.

Consider design #1. Typical bandpass. Nothing unusual here.

Consider design #2. What happens if the tuning port (red) is placed parallel to the plane of the driver? Does the tuning port have to be perpendicular to the mounting plane of the driver?

Consider design #3. Can the port be extended out of the box? If so, do the volumes of chambers a. or b. change? Does the tuning port change in length or diameter?

Consider design #4-6. Can the tuning port be routed? If so, which design would be optimal of #4-#6? I'm guessing #6 is ideal.

In my application, I am considering a bandpass enclosure for midbass (50-250). Would a bandbass enclosure cover ~2.25 octaves?

Thanks in advance!
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Old 3rd December 2009, 08:59 PM   #2
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They all will work. #4 will have a lower tuning than #6 if the lengths are exactly the same. I would angle the inside of the port on #6 too. Regarding #2, you want more than the port's diameter between the speaker plate and the rear of the port. Regarding #3, technically the vollume of b. should be made smaller. You might be able to design a front loaded horn to go from 50-250hz with Hornresp. The box will probably be big if you want a -3 to 0 db @ 50hz.

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Old 7th December 2009, 05:33 PM   #3
infinia is offline infinia  United States
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another idea> Place the port inside transversing the closed portion of the enclosure. Design the box dimensions to fit both the port length and the dual internal volumes.
Bandpass designs are really best for an octave or less when efficiency is a goal. Play with some t/s design programs to get a better idea, besides midrange sounds emiting from a port would sound a bit weird.
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Old 7th December 2009, 06:17 PM   #4
Ron E is offline Ron E  United States
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Quote:
Originally Posted by loddie View Post
Does the tuning port have to be perpendicular to the mounting plane of the driver?
No

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Originally Posted by loddie View Post
Can the port be extended out of the box? If so, do the volumes of chambers a. or b. change? Does the tuning port change in length or diameter?
You might be able to make it slightly shorter, but the difference won't be much if the port is not a substantial fraction of the enclosure volume. The actual vented volume subtracts the volume of the port. Moving the port outside would slightly increase the volume and lower tuning very slightly.

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which design would be optimal of #4-#6?
5, the larger radius on the bend, the better

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Would a bandbass enclosure cover ~2.25 octaves?
It could, but why? I think a direct radiator here would be best.
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Old 7th December 2009, 07:23 PM   #5
infinia is offline infinia  United States
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Originally Posted by loddie View Post
In my application, I am considering a bandpass enclosure for midbass (50-250). Would a bandbass enclosure cover ~2.25 octaves?
Might save you some gyrations
What is the application as specific as known? & Why the focus on BP boxes to cover that frequency range ?
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Old 7th December 2009, 11:37 PM   #6
loddie is offline loddie  United States
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Thanks for the responses. The application is a vehicle. The goal is not high volume, but sound quality. I am willing to sacrifice efficiency to achieve the desired bandwidth.

I had been experimenting with modeling bandpass enclosures. I noticed if you increase the number of ports, the ports have to be longer. In my vehicle, I cannot place the midbass drivers in the locations most desirable for sound quality (far and wide). However, with a bandpass enclosure with 2 or three ports, I could locate the enclosure where space is available and port the sound to the desired exit point in the vehicle (of course the proper dimensioning would be adhered to).

It is relative easy to find info how to model bandpass enclosures. However, it is difficult to find info describing how it works and its design limitations. For example, the LDC does answer my questions.

I should have been more specific. The attached file (multiplie ports are not shown) would be a better example of what would actually be implemented. However, without understanding the relationship between the port, the port volume within the enclosure, etc., I have no way of knowing if it would work. Is design #7 possible, or this the does most of the volume of the port have to be in enclosure b?

Links to websites, articles, books, etc. are appreciated.
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Old 8th December 2009, 12:02 AM   #7
loddie is offline loddie  United States
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You might be able to make it slightly shorter, but the difference won't be much if the port is not a substantial fraction of the enclosure volume. The actual vented volume subtracts the volume of the port. Moving the port outside would slightly increase the volume and lower tuning very slightly.
Ron E, now you understand my desire to deliver sound via the port to a specific location, can you expand? Does a substantial volume of the port have to be within enclosed chamber (enclosure "b")? If so, at what ratio (port volume within enclosure to port volume outside enclosure) does the bandpass design no longer work?

If the port(s) must be substantially within the enclosure, my idea would not work unless enclosure "b" followed the port (assuming correct volumes for the port and enclosure, of course). See attached design #8. Much harder to fabricate, but possible.

Are there more advanced bandbass modeling programs that I should look at that consider the actual location of the port(s) volume?
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Old 8th December 2009, 01:23 AM   #8
infinia is offline infinia  United States
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What car are we discussing? How is the upper band implemented ie mid and tweeter. Why are u breaking up the freq band at 250Hz ie the mid s/be crossed lower?
Using your idea wont the end locations mostly determine the length of tube/s then not tuning per se?
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Last edited by infinia; 8th December 2009 at 01:35 AM.
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Old 8th December 2009, 03:22 AM   #9
loddie is offline loddie  United States
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What car are we discussing?
VW new beetle

Quote:
How is the upper band implemented ie mid and tweeter. Why are u breaking up the freq band at 250Hz ie the mid s/be crossed lower?
That's a topic for a different thread. For now, I'd like to focus on the design of bandpass enclosures.

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Using your idea wont the end locations mostly determine the length of tube/s then not tuning per se?
I would calculate the optimal port length and then locate the enclosure at the end. So I would let the port length determine where the enclosure could be instead of starting with the enclosure location and letting the resulting length influence the tuning. Kinda the inverse
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Old 8th December 2009, 05:19 AM   #10
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Ron E, now you understand my desire to deliver sound via the port to a specific location, can you expand?
I believe the point of Ron E's quote was that the physical volume taken up by the port isn't considered part of enclosure b's internal volume. If you remove the port from that box, the effective volume "b" has been increased, and thus Fb will decrease if port dimensions are held constant.

Do you have an estimate as to how long the ~250Hz port would need to be? Practical limitations my be a problem, it may need a very large surface area if the port length is to be very long.

None of the port has to actually exist inside enclosure "b".
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Last edited by tsmith1315; 8th December 2009 at 05:28 AM. Reason: habitual editor
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