Ported enclosure issues

[Luke 0]

Hey everyone,

I'm having issues designing an all purpose (SQ while being loud) ported enclosure for my RE '06 XXX15 sub. I had a ported enclosure built. Its approx. 3.5ft^3. It has a rectangular L port with a port area of 60in^2. At the time when I designed the enclosure, I hadn't discovered WinISD or any other similar programs and just used the RE L Port calculator. This enclosure was supposed to be tuned to 35Hz. In short, its a mess. There is alot of port noise and it barely reporoduces anything under 35Hz.

So I went back to the drawing board and learnt how to use WinISD. From what the program is telling me, it can't be tuned to 33Hz (which I want to achieve) unless the enclosure is about 11ft^3 I'm planning on using 2 6" aeroports (or PVC pipe ). Basically the absolute maximum sized enclosure I can have is 6.5ft^3. On WinISD, if I put in a 6.5ft^3 enclosure tuned the 33Hz with 2 6" round ports, the gain on the graph shows that it will peak at around 38-40Hz.

My question is, is there a way I can achieve a tuning frequency of 33Hz in a 6.5ft^3 enclosure or smaller with as little port noise as possible? Keeping in mind, this sub moves a truck load of air. I'm probably going to have to compromise somewhere but I was hoping this might be possible

Cheers!

[kickerlivinloud 0]

There is no reason why you can't achieve a tuning of 33 or less in that space. I never use WinISD so idk why it says you can't. I've found the best way to do ported enclosures is to do it all by hand. This formula is all you need. You just need to know how much gross air space you have, how much port are you want and what tuning you want to have. With those 3 variables this formula will give you correct port length needed. Then if you really want to be accurate you'll need to account for "end correct factor" which is very easy. All you need to do is take half your port area and add it to your port length.

LV= Port Length

Av= Port Area

Vb= Gross air space

Fb= Desired freq

Hope this helps you out a little bit...

Jon

[Luke 0]

Thanks for the reply

I'm pretty sure I worked it out but the numbers are:

LV Port length = 5.61737957^14 inches

Av Port area = 56.54866776in^2

Vb Gross air space = 10368in^3

Fb = 33

I'm pretty sure that port length equates to 14.268144cm. That sounds about right but does that mean because I have two ports, they should be half that length each?

Edited May 9, 2007 by Luke

[Acidburn 10]

read this page: http://mobile.jlaudio.com/support_pages.php?page_id=165

[Luke 0]

Thanks for the link, its a good read!

I did it properly this time. I came up with a port length of just under 7.5inches for each port. Does that seem a bit short?

[helotaxi 46]

Then if you really want to be accurate you'll need to account for "end correct factor" which is very easy. All you need to do is take half your port area and add it to your port length.

The "add half the port width" is to determine the effective port length given the physical port length. If you are calculating what the port should be, the equation gives you the effective length and you subtract half the width to get the physical length that you need to build. This only applies to slot ports where one of the port sides continues past the opening of the port. If you're using round ports, this is totally irrelevant. For figuring flared ports http://www.subwoofertools.com/forum/flare.htm that calculator should give you what you need. To figure the flare radius measure the overall diameter of the flare, sbtract the diameter of the tube and divide by two.

Vb= Gross air space

Should be 'net' not 'gross.'

[kickerlivinloud 0]

Vb= Gross air space

Should be 'net' not 'gross.'

Isn't Net air space, what your sub has to use after port/sub/brace disp??? Least thats the way I've always thought about it. Gross was total air space and net was total air space that the sub uses...

Just trying to clarify...

Jon

[Tirefryr 1,742]

Vb= Gross air space

Should be 'net' not 'gross.'

Isn't Net air space, what your sub has to use after port/sub/brace disp??? Least thats the way I've always thought about it. Gross was total air space and net was total air space that the sub uses...

Just trying to clarify...

Jon

Yes, just like when you get a check, the number before taxes is your gross. Take away the taxes (damn government pigs) and that is the net.

[Luke 0]

Then if you really want to be accurate you'll need to account for "end correct factor" which is very easy. All you need to do is take half your port area and add it to your port length.

The "add half the port width" is to determine the effective port length given the physical port length. If you are calculating what the port should be, the equation gives you the effective length and you subtract half the width to get the physical length that you need to build. This only applies to slot ports where one of the port sides continues past the opening of the port. If you're using round ports, this is totally irrelevant. For figuring flared ports http://www.subwoofertools.com/forum/flare.htm that calculator should give you what you need. To figure the flare radius measure the overall diameter of the flare, sbtract the diameter of the tube and divide by two.

Vb= Gross air space

Should be 'net' not 'gross.'

That caluculator makes it so easy. I put the following figures into the calculator:

Box volume: 5.5ft^3

Tuning frequency: 33Hz

Tube diameter: 6"

Number of ports: 2

Flare radius: 1.5" (?) - With the 6" ports flared to 9", is that right?

Coming up with a length of 26.125" (without flares) and an overall length of 29.125" (with flares).

When it says "Box Volume," does this mean "net volume" or "gross volume?" I calculated the driver displacement and port (internal) displacement to be 0.437331ft^3 in total. Does this mean I should build a 5.9ft^3 enclosure?

Edited May 10, 2007 by Luke

[mrray13 30]

luke...yeah, the calculator is using net volume.. you'll want to build a 5.9ft^3 INTERNAL gross enclosure.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[Luke 0]

Awesome! I think I've finally figured it all out. Now I just need to build another enclosure for SPL I can't be bothered messing around with replacable ports. That'll probably come later on....

Thanks everyone for your help. I'll post some pics when its eventually done