Hi,
A thought sprang up in my mind one day and I wanted to check this concept out with you guys.
In a normal BR cabinet one of the challenge is sometimes the port length for the required diameter for low chuffing is just too long for the required frequency. One solution is just to use a 90 degree elbow. Some other solutions is to use a slot port built into the cabinet so you can use the entire height of the cabinet as a port length. The other is just to use a passive radiator.
The reason for the long port length is the air inside the port is used as a mass. So it is the volume. Diameter of the port is the compliance of the spring in the resonance of the box.
What if use a pipe which is narrow at two openings but fat in the middle?
For example. Would these 2 be equivalent.
1) A 1 inch diameter 20 inch pipe length
Vs
2) A 1 inch diameter pipe 8 inch length but the central 4 inch length of the pipe has a diameter of 2 inch.
Any thoughts on this? Would it be the same...
Oon
A thought sprang up in my mind one day and I wanted to check this concept out with you guys.
In a normal BR cabinet one of the challenge is sometimes the port length for the required diameter for low chuffing is just too long for the required frequency. One solution is just to use a 90 degree elbow. Some other solutions is to use a slot port built into the cabinet so you can use the entire height of the cabinet as a port length. The other is just to use a passive radiator.
The reason for the long port length is the air inside the port is used as a mass. So it is the volume. Diameter of the port is the compliance of the spring in the resonance of the box.
What if use a pipe which is narrow at two openings but fat in the middle?
For example. Would these 2 be equivalent.
1) A 1 inch diameter 20 inch pipe length
Vs
2) A 1 inch diameter pipe 8 inch length but the central 4 inch length of the pipe has a diameter of 2 inch.
Any thoughts on this? Would it be the same...
Oon
That would be acoustic low pass filter, aka. muffler 🙂 I don't know how it affects the Helmholtz tuning, or how to calculate. You can try it out and measure what are the positives and negatives of such design comparing to straight pipe.
I tried drill some holes to a vent walls. It raised the resonant frequency a bit (shortened the pipe in regards to Helmholtz tuning) and seemed to attenuate out some of the mid range leakage I had from the vent (which was the goal of the experiment).
I tried drill some holes to a vent walls. It raised the resonant frequency a bit (shortened the pipe in regards to Helmholtz tuning) and seemed to attenuate out some of the mid range leakage I had from the vent (which was the goal of the experiment).
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Hornresp can simulate this just fine. Give it a go.
My bet is that entrance/exit velocities get too high, but I've been wrong before.
Chris
My bet is that entrance/exit velocities get too high, but I've been wrong before.
Chris
Hi Chris,
You are right in the sense that the velocity gets too high. If you shrink the tube diameter. I was thinking more of enlarging the diameter in the middle rather than shrinking the diameter at the side.
I thought about simulating in hornresp but I am I am not any good with it. I tried playing with it before but i am not really sure i keyed in the parameters correctly etc.
If you are fluent in hornresp. Do you mind simulating it for me....?
Oon
Hello,
Agree, flaring the port and making it large enough can avoid chuffing. Nice little program to look at this is at the link below. Flare It program.
Flare-it - Free Speaker Design Software
Regards, Greg
Agree, flaring the port and making it large enough can avoid chuffing. Nice little program to look at this is at the link below. Flare It program.
Flare-it - Free Speaker Design Software
Regards, Greg
Greg,
I managed to check out the website. Very interesting and helpful. Interesting that he specializes in chuffing and how to reduce it.
I was just thinking if someone has so problem making flares another solution is to use PVC pipe reducing piece with the larger side facing out of course...
Oon
I managed to check out the website. Very interesting and helpful. Interesting that he specializes in chuffing and how to reduce it.
I was just thinking if someone has so problem making flares another solution is to use PVC pipe reducing piece with the larger side facing out of course...
Oon
Hi Oon,
Glad you found the flare program interesting. If you are thinking of using PVC pipe, you might want to look at the following link. Think you will be interested.
Heat Moulded Port Flares
Regards,
Greg
Glad you found the flare program interesting. If you are thinking of using PVC pipe, you might want to look at the following link. Think you will be interested.
Heat Moulded Port Flares
Regards,
Greg