Bandpass design considerations

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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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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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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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Does the tuning port have to be perpendicular to the mounting plane of the driver?
No

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.

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

Would a bandbass enclosure cover ~2.25 octaves?
It could, but why? I think a direct radiator here would be best.
 
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).:D

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.:bulb:
 

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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.:eek:

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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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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What car are we discussing?

VW new beetle

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.

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:confused:
 
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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Are there more advanced bandbass modeling programs that I should look at that consider the actual location of the port(s) volume?

You do not need to have the port inside the enclosure. Making volumes into long tubes is not a good idea, in any case. Long tubes can have organ pipe resonances at frequencies in band. http://www.physics1.howard.edu/undergraduate/Labs/GenLab1/10-resonance.pdf

Another type of organ pipe resonance, due to the port, is a major source of out of band noise in bandpass boxes. This organ pipe resonance for a port will be at F=13572/(2*L) and multiples, where L is the length of the pipe in inches. THe longer you make this pipe, the lower the frequency. To keep out of band resonances an octave away from your bandpass, you would want a port length no longer than ~13.5".
 
Tim/Ron, I understand now.

Ron, thanks for the explanation regarding pipe resonances. It should be possible to keep the length under 13.5", although its does place more constraints on possible enclosure locations.

I have been modeling different drivers to see if one worked in the desired pass band (~55-250Hz) using this calculator:

Shavano Online - Sub Woofer; 4th Order Bandpass Calculator

I found several drivers that modeled well such as the Eminence Pro-8A:

Parts-Express.com:*Eminence Delta Pro-8A 8" Midrange 8 Ohm | Eminence Delta Pro-8A 8" Midrange mid driver pro mid pa high pack newEminence010809

The Shavano calculator is free and allows one to select the desired 3db rolloff. The subwoofer I plan to use only extends to 55 HZ, so it was selected as the cutoff and .6 was selected as the "S" response curve as it is relatively flat (although in a vehicle it will be anything but flat:eek:). The resulting calculation indicated a lower F3 of 44Hz and the higher cutoff or 354Hz. The suggested port length is 12.01", just under the 13.5" maximum length to avoid pipe resonances.

Once disadvantage of the Shavano calculator is the lack of a frequency response graph. So I tried modeling the same driver with AJ Bandpass Designer 2.0 as it is free and provides both freq. and power response graphs. In the AJ bandpass calculator, the lower F3 was ~166Hz and the higher F3 ~496.

AJ Audio Subwoofer Box Enclosure Design Software - Sub Speaker Cabinet Building Program Downloads

The difference between the two calculators leads me to several questions.
First, in a bandpass enclosure, is it possible to run the driver below its Fs? Will doing so physically destroy the driver? :eek: The Shavano calculator modeled a frequency response below the driver Fs.

Second, why the different frequency response between the two programs? I would expect some variation, but the results aren't close.:(

Third, the Shavano calculator does not allow a Vas input of less than 0.5. Why? Will selecting a driver with a Vas of less the 0.5 self destruct due to inadequate air suspension?

Most of the drivers I modeled (6-8" and <$100 ea.) had Vas greater than 0.5. However, I was hoping to use a push-pull configuration, requiring an input of Vas/2 in the calculator. This means the drivers selected must have a Vas>1.0. to be modeled.

Thanks for the responses so far. I have spent many:eek: hours lurking here.
 
The designer of The Shavano Calculator references "To simplify matters somewhat, I used equations found at: http://www.diysubwoofers.org/"
I use http://www.diysubwoofers.org/bnd/bandpass.zip , WinISD, & AJ Bandpass to design BP1 boxes. I like the bandpass.zip because I can draw the box on a added Excel worksheet within the program. Also, there are no VAS limitations with that program.
An externally hosted image should be here but it was not working when we last tested it.
 
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Just a quick hint:
When using Hornresp or any other program that you want to capture a picture of, you don't need any printer driver, especially one that wants you to pay money for what comes free with Windows.

1. Make sure the Hornresp window is the active window (click on it).
2. Press "Alt-PrtSc" (Press and hold Alt key, then press PrtScr key).

A picture of the window is now on the clipboard.

3. Open "Paint" (Start --> Accessories --> Paint)
4. Past the picture (Ctrl-V, or Edit --> Paste)
5. Save with a descriptive name, file type PNG (best for Hornresp type graphics).

Repeat as required.

There are also free utilities around that will let you select a window and save it directly to file without going though Paint.
 
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