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Old 22nd June 2013, 06:07 PM   #311
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OK,
I just found a simple enough Bass Reflex calculation program for my needs:
mh-audio.nl - Vented System

Calculations match exactly Weltersys suggestions (Thanks).

Entering datasheet's woofer parameters:
Click the image to open in full size.

The program calculated an internal volume of 209 liters:
Click the image to open in full size.

Here the software calculations:
Click the image to open in full size.
and the simulated low end frequency response:
Click the image to open in full size.
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Old 22nd June 2013, 06:13 PM   #312
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Some ideas and questions:

1) Looks like the software had found automatically a frequency tunning equals to Fb=32.5hz. I don't have an argument at the moment to think this is right or wrong.

2)The software advices using a port diameter of a third of the woofer diameter. What is the effect of increasing or decreasing port diameter? considering that the software automatically adjusts port length. What is the benefit of using a bigger or smaller port?
I am thinkin about going out to buy PVC pipes of a similar size and the fine tune the lenght given what I could find.

3) Why to use double ports? against my intuition, resulting port lenghts are bigger. Any benefit about using two ports?

Best,
Carlos
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Old 22nd June 2013, 06:16 PM   #313
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4) I am asuming I can change box dimensions with no issues, as long as I preserve the internal volume. I was thinking about building a trapezoidal box that follows the shape of the 2360a horn. but that will be for a version #2. First I will build a squared box to test the sound.
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Old 22nd June 2013, 06:27 PM   #314
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I have found PVC tubes of 110mm.
That gives a port length of 570mm in a single port configuration (isn't it too short?).
Or 386mm in a dual port configuration (seems too long to be practical).

But the software advices about using ports of a diameter at least a third of the woofers diameter. That would be 133mm.

Is it ok to go with 110mm diameter and 57mm long for the port?

Best
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Old 22nd June 2013, 06:53 PM   #315
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Charly,
The problem with to small a port diameter is that they start to make noises that can be audible. Whistles and chuffing can result. Above about 75mm internal diameter is usually large enough at normal listening levels but there is nothing wrong with going with 100mm internal diameter. Larger than that is generally reserved for very large boxes with large diameter drivers used in high power applications. As you are finding as you increase diameter the length of the port can get very unwieldy. What you can also do with a long port length is to bend the port with a 90 degree fitting that can help a long port fit in a shallow box.

On the shape question that is something I have done many times before, I have done some very nice looking trapezoidal boxes in the past. The important point is just the internal volume of the enclosure. Don't forget to add any needed volume to make up for any internal bracing you may add as some people can add extreme amounts of bracing and then the internal volume will change significantly.
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Old 22nd June 2013, 10:22 PM   #316
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Quote:
Originally Posted by charly chile View Post
4) I am asuming I can change box dimensions with no issues, as long as I preserve the internal volume. I was thinking about building a trapezoidal box that follows the shape of the 2360a horn. but that will be for a version #2. First I will build a squared box to test the sound.
have found PVC tubes of 110mm.
That gives a port length of 570mm in a single port configuration (isn't it too short?).
Or 386mm in a dual port configuration (seems too long to be practical).

But the software advices about using ports of a diameter at least a third of the woofers diameter. That would be 133mm.

Is it ok to go with 110mm diameter and 57mm long for the port?

Best
Carlos,

Since you only have ten watts powering the woofer, port "chuffing" and turbulence won't be a problem, but I'd still advise large ports in case you decide to later take advantage of the driver's potential.

Build the cabinet as a trap from the get go, don't waste time with a square/rectangular prototype which won't end up sounding exactly like what you ultimately will build.

Art
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Old 24th June 2013, 03:10 PM   #317
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Hi,
just to clarify,
110mm is not ideal?
what would be an ideal diameter for a 400mm woofer?

Any advantage using dual ports? I've seen good speakers that use this.

Best
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Old 24th June 2013, 04:56 PM   #318
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Ideally the port or ports are sized large enough so vent velocity is still low (less than around 15 meters per second) at Xmax.
A vent appropriate for a 3mm Xmax 15" would be "blown out" with a speaker capable of 15mm Xmax.

110mm sounds like it would be too small to fit the vent velocity metric, but I have not modeled your particular speaker. Of course, at only 10 watts, vent velocity will be well under 15 meters per second.

Multiple ports are often used to fit the available space, and also tend to reduce the amount of reflected (out of phase) mid-range sound coming out of the ports without needing as much fill material.

Last edited by weltersys; 24th June 2013 at 04:59 PM.
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Old 1st July 2013, 10:13 PM   #319
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Hi Guys,

Been away for a while "working". Now I am testing the horn with the Bass Reflex enclosure and the TAD TL-1603.
I still need to glue the front board. No bracing and no stuffing so far.
I want to put some T-nuts for mounting the woofer, so I can glue the front board.

I quickly could realize it sounds way more integrated than before. Before it was like a hole in mid bass frequency. Now it is way more coherent and consistent.

Need to work more on this...
Click the image to open in full size.
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Old 2nd July 2013, 10:31 AM   #320
Helmuth is offline Helmuth  Netherlands
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Your bas-reflex port seems to me much to small for this bas driver Charly.

It can sound boomy when the port is to small.

make it 30% > sD ,and then stuff the port when needed to get the right damping at tuning frequency.
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Last edited by Helmuth; 2nd July 2013 at 10:34 AM.
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