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Calculate bass reflex port for a speaker

mt196

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#1
Hi, guys, I want to build a pair of speakers based on the AAM+ by philarmonicaudio, I have all the information about tweeter, the woofer and the crossover, also I know the cabinet dimensions that are the one of the Dayton BR-1 kit, but I cannot find info about the rear bass vent.

It seems to be a 1"x6-1/2" or 25mm x 165mm for us Europeans, but I cannot find a similar one in the EU, the only one I found is 25mm x 102mm, will it be good enough? Maybe if I take one with a bigger diameter I can find a more similar one, but what is the formula to calculate an equivalent port with a bigger diameter?
 

Gringoaudio1

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#2
Hi, guys, I want to build a pair of speakers based on the AAM+ by philarmonicaudio, I have all the information about tweeter, the woofer and the crossover, also I know the cabinet dimensions that are the one of the Dayton BR-1 kit, but I cannot find info about the rear bass vent.

It seems to be a 1"x6-1/2" or 25mm x 165mm for us Europeans, but I cannot find a similar one in the EU, the only one I found is 25mm x 102mm, will it be good enough? Maybe if I take one with a bigger diameter I can find a more similar one, but what is the formula to calculate an equivalent port with a bigger diameter?
If you have the T/S parameters of the woofer that will drive the cabinet dimensions and the port dimensions when you plug the T/S parameters into any of many available online calculators.
Any port that is only an inch in diameter is suspect. You will get chuffing sounds from a port of that dimension.
 
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mt196

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Thread Starter #3
Well I know the dimensions of the cabinet are 8-5/8" (22cm) wide, 14-1/4" (35cm) high with a depth of 11" (28cm), it should result in a total volume of 22L i think. It utilizes a EBS (extended bass shelf) alignment and is tuned to 38 Hz with a rear-mounted port. This tuning results in an F3 of 43 Hz.

Woofer specs are

1590856033024.png


Help me with the port, thanks a lot! (from photos I can say it is long more or less half the cabinet if not more, so 17cm could be real, also its diameter was more or less like the center part of the tweeter (that is 2,85cm or 1-1/8") so it was not so strange for me that the original one was 1" and 6-1/2" long
 

Gringoaudio1

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#4
Plugging those values into a calculator I get this. The port is 2” x11” long approximately. This driver may not be particularly suited for reflex use. The calculator at the site shown in my attached screenshot has an option for Butterworth B4 response as well and the port is shorter and would fit in the proposed box. I have in the past Measured driver T/S and found the commercial cabinets they were in to be unsuited. I redesigned the port properly had a port tube extending from the back of the cabinet by 4” as it was longer than the cabinet depth.
5C9EFE08-2FBA-436F-85B7-B726BDE348AB.jpeg
 

Gringoaudio1

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#5
Also the box dimensions you have chosen is too large. But these things can vary. Learn about T/S parameters and play with online calculators. DIY results are usually disappointing until you really understand the theory. Or buy a kit.
 

Gringoaudio1

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#6
Just using a subwoofer port calculator the port required to tune a 22l box to 43Hz you get a shorter port. That ignores the driver parameters so someone better versed in speaker design can perhaps contribute here. I’ve never understood how box tuning like this is meaningful when you ignore the T/S parameters.
E7080E3B-419A-498C-BCC9-DDFB0E0764AE.jpeg
 

Gringoaudio1

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#7
Use plastic or cardboard tube. No need for ports from a speaker parts supplier. It took me 15 years of playing with drivers crossovers box sizes ports and finally simulation software to come up with a DIY speaker that is nicer than my Sonus Faber speakers.
 
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mt196

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Thread Starter #9
Thanks mate, I will read your post carefully later (it's my birthday right now :) )

I just wanted to point out that I didn't choose the box, I am using the Dayton br-1 kit (I am replicating it since I am in Europe and I cannot find it cheaply here so since I can work with wood I will build it myself) but using the Morel tweeter with a modified crossover by Dennis Murphy from philarmonicaudio, so the box must be the same, maybe what is not completely true is the sentence "It utilizes a EBS (extended bass shelf) alignment and is tuned to 38 Hz with a rear-mounted port. This tuning results in an F3 of 43 Hz" from the Dayton datasheet
 
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