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vnzbd

port size?

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I created a fake driver and ran it through WinSpeaker. Row1 is a single driver, Row2 is 2 drivers 2x volume.

Looks like the port length is 1/2 for 1 vs 2 drivers keeping same diameter. Note Fb and Q stay same.

1or2drivers.jpg

Edited by cfelliot

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Port area? What about port volume? I'm trying to understand, thanks. The only time I've messed with ports is with winisd and it figures it for you.

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I created a fake driver and ran it through WinSpeaker. Row1 is a single driver, Row2 is 2 drivers 2x volume.

Looks like the port length is 1/2 for 1 vs 2 drivers keeping same diameter. Note Fb and Q stay same.

1or2drivers.jpg

Isn't that what i said? half the port volume?

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I created a fake driver and ran it through WinSpeaker. Row1 is a single driver, Row2 is 2 drivers 2x volume.

Looks like the port length is 1/2 for 1 vs 2 drivers keeping same diameter. Note Fb and Q stay same.

1or2drivers.jpg

The port length is double for 1 vs 2 drivers in the above, isn't it?

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Remember that part in the thread where I talked about getting some good software. :)

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You don't need any software for this, although winisd and hornesp are both free...

For half the box volume, it's half the port area....and you don't need to be so exact either. A 2" pvc pipe will be close enough. If you go with a slot, then keep in mind that more square is better. Don't go to 1/2" x 6" because it will be higher distortion and change the tuning due to nonlinear air velocity. Technically you don't want the port up against the wall in the cabinet (unless the original design is that way) because it can change the tuning and every standing wave in the box has a peak near the walls. This gives you unwanted leakage out of the box. A cheap pillow from Target / Walmart can fix that though (just make sure it's not packed in tightly).

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I just wanted to add that a better way to think of this is in the other direction....

Say you have a single driver in a single cabinet tuned to a certain frequency. If you build a second cabinet, it will have the same frequency response. When you put the two cabinets together, they are 6dB louder but have effectively the same frequency response.

When you double the number of cabinets, here's what changes:
1) Volume doubles (two boxes versus one)
2) Port Area doubles (two port mouths versus one)
3) Port length stays the same (both ports are the same length)

Attached is an example using the Klipsch K48: the cabinet with two ports has two drivers and is the orange trace.

post-8246-0-07560000-1385220725_thumb.pn

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Gentlemen, thank you for all of the input! I feel empowered to complete the project. Pics and details will follow next week.

I do have one more line of questioning that I hope to have help with. The stock KLF-10 has a feq responce listed down to 32 hz. I would expect that to be the -3db point. I have no idea how to figure out what the 0 db point is or what the cabinet is really tuned to, just that is how Klipsch designed it. I am looking for the most bang for the buck between 50-150 hz. The stock port may support that as it is now.

If I choose to go with the 2 inch round port, I would think that changing the length would change the tuning of the box and thus maybe output at my target freq range. Am I right on this?

I had read in a chorus 1 thread that if tubes were installed in the front ports that a deeper bass responce was possible. So I guess my second question would be again a rule of thumb. Is a shorter port or less port volume going to raise the box tuned freq?

As always, thank you!

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And then you use software "you don't need ". :)

I needed it, so as a novice I would second the motion to get some software. I paid around $140 for DATS and Winspeakerz and I wish I would have done it a few years ago.

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I created a fake driver and ran it through WinSpeaker. Row1 is a single driver, Row2 is 2 drivers 2x volume.

Looks like the port length is 1/2 for 1 vs 2 drivers keeping same diameter. Note Fb and Q stay same.

1or2drivers.jpg

The port length is double for 1 vs 2 drivers in the above, isn't it?

I am scratching my head.

In the above the port volume of the single driver/box is more than double the port volume of the two driver/bigger box. Isn't it completely the opposite from what many of you are saying. It seems that the calculations are more concerned with the area of the port than the volume. Somebody has to be seeing what I am seeing. Look at the 1 driver box, the port is longer!

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My only reason for posting the picture of what WinSpeakerZ showed was because someone asked and I happen to have the software.

A ported speaker is a LC tank circuit of sorts. The box volume is the "C", While the port is the "L".

The OP is cutting the volume in half. So, either the cross sectional area of the port needs to be / 2 or the length needs to be / 2. Either method produces the same "L".

I'd rather reduce the length, if possible, than the diameter in any case!

No arguments here, I just wanted to explain why I put the picture up!

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My only reason for posting the picture of what WinSpeakerZ showed was because someone asked and I happen to have the software.

A ported speaker is a LC tank circuit of sorts. The box volume is the "C", While the port is the "L".

The OP is cutting the volume in half. So, either the cross sectional area of the port needs to be / 2 or the length needs to be / 2. Either method produces the same "L".

I'd rather reduce the length, if possible, than the diameter in any case!

No arguments here, I just wanted to explain why I put the picture up!

You don't understand. The length is not / 2. It is X 2!

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My only reason for posting the picture of what WinSpeakerZ showed was because someone asked and I happen to have the software.

A ported speaker is a LC tank circuit of sorts. The box volume is the "C", While the port is the "L".

The OP is cutting the volume in half. So, either the cross sectional area of the port needs to be / 2 or the length needs to be / 2. Either method produces the same "L".

I'd rather reduce the length, if possible, than the diameter in any case!

No arguments here, I just wanted to explain why I put the picture up!

You don't understand. The length is not / 2. It is X 2!

Correct. The same would be true if one wanted to replace the single 3" port in the KLF-10 with two 3" ports -- the port lengths on those two new ports would need to double (to maintain the same tuning frequency).

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If I choose to go with the 2 inch round port, I would think that changing the length would change the tuning of the box and thus maybe output at my target freq range. Am I right on this?

You could raise the box tuning, but the midband performance of the driver (50-150Hz) is basically going to stay the same. As you change the box tuning, the only effect you'll have is on the low frequency corner knee. Raising the tuning will cause the knee to have a peak - it'd basically be like adding an EQ.

For the sake of your project, I wouldn't bother with changing the tuning because you could achieve the same effect by adjusting your subwoofer level....and I think that'd sound better because it'd behave more like a shelf that would boost the entire bottom octave rather than a PEQ that will only affect the behavior between 40 and 50Hz.

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Well just an update on the project. It did not get off of the ground due to a design change. I had an oppurtunity from a local forum member to get 2 Cornwall II cabinets for free. He also had 2 of the BC cast woofers that he sold to me. While originally thinking rebuild or cornscala, I got the idea to install the woofers, block the mid-tweeter openings and give it a listen. I powered them up using 2 spare channels on an Emotiva amp and running it through a Rolls crossover @150 hz and down. The cabinets are laying on their sides with the woofers firing right into the couch.

Well they certainly provide the midbass punch I was looling for! I have a HSU sub next to them and the effects are quite different. The cornwalls give the punch and the sub is more of rumble.

The next part of the project will to add some bracing to the Cornwalls and then design/build a console style table around them.

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