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post #91 of 264 Old 09-10-2013, 10:42 AM
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as for voltage, the inuke appears to be fairly easy to drive:

Gain is 42dB with controls at maximum and therefore for full power you need an input of 0.82V rms for full power into 8 Ohms or 0.71V rms for full power into 4 Ohms assuming music conditions.

http://forum.speakerplans.com/behringer-inuke-nu6000-vs-kam-kxd7200-bench-tested_topic69202_page4.html

not sure what your receiver outputs.

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post #92 of 264 Old 09-10-2013, 10:51 AM - Thread Starter
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sweet. the Inuke 6000 is looking to be a great value amp then. If I can't find a solid deal on something like an XTI2002 or a dirt cheap EP4000 this wills probably be my go to amp
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post #93 of 264 Old 09-10-2013, 11:17 AM - Thread Starter
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ok, here is hopefully my final calculations before I go buy wood



long story short... 2.5 inches high x 21 wide slot port... 33 inches long... tuned to 17.5 hz

utilizing 2x2's as bracing (1.5x1.5 in reality) using the "grid" pattern every 7 or 8 inches

double front baffle.




if someone could just make sure my calc's look ok that would be cool (especially the port.. slot ports are a bit new to me.
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post #94 of 264 Old 09-10-2013, 01:12 PM
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in the calculator, there is no accounting for the double front baffle, unless you put it in with the bracing.

might want to reduce length from 49 to 48.25 to reflect the extra panel.

that takes net volume from 12.04 to 11.81 cu ft all other things equal.

21" x 2.5" x 33" slot port in 11.8 cu ft gives tuning of ~17.5 hz in winisd, so looks good to from over here.

if the double baffle is in the bracing number, then 21" x 2.5" x 33" slot port in 12.04 cu ft gives tuning of ~17.3 hz in winisd, which is fine too. :-)

winisd 0.7.0.900 (windows 7 version) doesn't allow for direct port length adjustment, so it is a bit of a guessing game and so my calcs may be off by a nit. :-)

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post #95 of 264 Old 09-10-2013, 01:16 PM - Thread Starter
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yup, I added the double baffle into the bracing already... that's what I was doing when I asked you about if you had included a double bracing in the marty sub so I could calc it out
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post #96 of 264 Old 09-11-2013, 10:10 AM - Thread Starter
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weird. I realized that I was plotting one single slot port of 21x 2.5 inches tall and 33 inches long. but with those 1x3's in the center it actually creates three seperate 7 inch wide ports which would require 35 inches of length to get the same tune... weird, glad I looked at them before I started cutting
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post #97 of 264 Old 09-11-2013, 11:32 AM
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^^ there is not that much precision in the model.

changing the end correction factor will have that much impact easily and in version 0.7.0.900 end correction factor can't even be changed.

that is why i keep saying things like "good enough" because your really only guessing at something like +/- a couple hz tuning anyways.

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post #98 of 264 Old 09-11-2013, 11:36 AM
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this calculator is probably about as accurate as you are going to get.

http://www.calculatoredge.com/new/ventlength.htm#factor

the question is what is the right end correction factor.

http://www.ctc-dr-weber.de/speaker/PortCorrection.jpg

that is why folks are probably coming in a little under winisd estimates.

i suppose that is good to know information!

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post #99 of 264 Old 09-11-2013, 11:36 AM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

^^ there is not that much precision in the model.

changing the end correction factor will have that much impact easily and in version 0.7.0.900 end correction factor can't even be changed.

that is why i keep saying things like "good enough" because your really only guessing at something like +/- 1hz tuning anyways.

ahhh, so it's not as accurate as they make it out to be.

okee, I'll calc it at 36 inches for the slot port and keep it at that. gives me a flat 17 hz tune according to the box... I'm gonna lose my sanity if I keep running and re-running these calcs
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post #100 of 264 Old 09-11-2013, 11:41 AM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

this calculator is probably about as accurate as you are going to get.

http://www.calculatoredge.com/new/ventlength.htm#factor

the question is what is the right end correction factor.

http://www.ctc-dr-weber.de/speaker/PortCorrection.jpg

that is why folks are probably coming in a little under winisd estimates.

i suppose that is good to know information!

whoooooooaaa, that's a whole nother ballgame... the end correction factor in that last one lists a slot port as 2.227 end correction... that gives me a 40 inch slot port vs a 36 incher...

just out of knowledge sake, what IS the end correction for in the modeling? what is it describing
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post #101 of 264 Old 09-11-2013, 11:47 AM
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i believe it is a measure of the fluid dynamics that occur around the entry and exit of the port, which of course will change again with roundovers as well.

the slot port that exits on the floor uses the floor as something of a semi boundary to synthetically extend the length of the port, while a port exiting up in the air has no such synthetic extension.

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post #102 of 264 Old 09-11-2013, 11:49 AM - Thread Starter
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eeeef,,,, my brain is about to explode lol... I think I'll keep it at my original estimation of 36-38 inches of length with a roundover on the inside end of the port.... It's sounding like it won't make a big deal one way or the other
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post #103 of 264 Old 09-11-2013, 11:49 AM
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"whoooooooaaa, that's a whole nother ballgame... the end correction factor in that last one lists a slot port as 2.227 end correction... that gives me a 40 inch slot port vs a 36 incher..."

a higher correction factor means more synthetic port, so less actual port for a given tuning frequency. so by moving to a higher k value, the port should get shorter all other things equal.

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post #104 of 264 Old 09-11-2013, 11:52 AM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

"whoooooooaaa, that's a whole nother ballgame... the end correction factor in that last one lists a slot port as 2.227 end correction... that gives me a 40 inch slot port vs a 36 incher..."

a higher correction factor means more synthetic port, so less actual port for a given tuning frequency. so by moving to a higher k value, the port should get shorter all other things equal.

weird. I changed it to the 2.27 value of a slot port from the .614 it was giving me standard in winisd and it shot me up 4-6 inches in length
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post #105 of 264 Old 09-11-2013, 11:53 AM
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"eeeef,,,, my brain is about to explode lol..."

your pain-in-the-azz questioning and exploding brain are good things...i didn't know the end correction factor worked that way and it is something that nobody really discusses. thanks!

so with that in mind, i'd probably suggest that the marty sub port vent length be shortened down to about 33 inches (or maybe even a hair less).

i'll look at it again with fresh eyes later and make a suggestion.

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post #106 of 264 Old 09-11-2013, 12:00 PM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

"eeeef,,,, my brain is about to explode lol..."

your pain-in-the-azz questioning and exploding brain are good things...i didn't know the end correction factor worked that way and it is something that nobody really discusses. thanks!

so with that in mind, i'd probably suggest that the marty sub port vent length be shortened down to about 33 inches (or maybe even a hair less).

i'll look at it again with fresh eyes later and make a suggestion.

lol, yeah , sorry, I tend to be a perfectionist. keeping it at "one flanged end. it gives me 35.24 inches, and two free ends as 36

I spoke wrong... changing the end correction to 2.27 does crap... I was looking at it wrong. whenever I changed something in the end correction field it would change it to 0.000 end correction and shoot me up to about 40-42 inches in port length for a 17 hz tune. if I just change the "frequency" section in winisd it auto goes to .614 and changing the box doesn't do anything but default it to 0 end correction which is why I was seeing the higher number

two free ends gives a 36.2 inches and 35.24 inches for having one flanged end.
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post #107 of 264 Old 09-11-2013, 12:02 PM
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use the calculator that i linked up. i don't think winisd is calculating end correction properly, which is probably why it was left out in the windows 7 version.

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post #108 of 264 Old 09-11-2013, 12:04 PM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

use the calculator that i linked up. i don't think winisd is calculating end correction properly, which is probably why it was left out in the windows 7 version.

delete
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post #109 of 264 Old 09-11-2013, 12:23 PM - Thread Starter
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ok, I've been talking with Mike P and a few others on HTS... they've done a lot of slots. from what they said, just model it and then subtract 1/2 the height of the slot port for end correction... (1.25 inches in our case) from the model. and bingo.


sooooooo with the shortened slot port I get it at 17.12 hz tuned.... 33.75 inch port (modeled at 35 inch port bud adjusted for end correction) 12.009 cubic ft volume....


there. think I'm done... brain will pop if I think about it anymore... that's about as close as I'm gonna get
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post #110 of 264 Old 09-11-2013, 12:37 PM
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i suspect that he is talking about something slightly different that has more to do with the roundover/termination of the port vs. the synthetic port extension from the boundary along the port floor or wall. :-)

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post #111 of 264 Old 09-11-2013, 12:41 PM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

i suspect that he is talking about something slightly different that has more to do with the roundover/termination of the port vs. the synthetic port extension from the boundary along the port floor or wall. :-)

actaully that's exactly what he was talking about. not the roundover/termination. they said that winisd doesn't do end correction for slot ports and that for slots you just change to a square port and adjust the 1/2 height of the slot port to compensate for the port thinking it's longer due to the extension of the box to the back/top wall (depnding on if it's a bent slot port) ... basically it's not a perfect formula but rather gets real close.

there's some discussion of it on parts-xpress forums as well

but from what I gather it's not a wild thing to worry about since it only affects it by a 1/2 of a hz or something miniscule like that

I'll be building mine with about a 34-35 inch slot port (12.008 cu ft volume) tuned to about 17 hz (give or take a litte for error) now to order the drivers as soon as SI updates their sept sale prices (grumble whine whine wink.gif )
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post #112 of 264 Old 09-11-2013, 01:29 PM
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Here's what I'm aware of regarding the background of the end correction calculation. Beranek's Acoustics, published in 1954, has the math behind this. The derivation is complex, so I won't get into that. But the end result is this:

leff = lact + lf + luf

leff = effective length of tube (in meters)
lact = actual length of tube (in meters)
lf = end correction for flanged end of tube (in meters)
luf = end correction for unflanged end of tube (in meters)

The actual length is self-explanatory. Formulas for the two end corrections are as follows:

lf = 0.8488 * a
luf = 0.6132 * a
where "a" is the radius of the tube in meters

Beranek further says:
Quote:
Originally Posted by Beranek 
"If the tube is not round, we may replace a by sqrt(S / pi), where S is the cross-sectional area of the tube.

Of course, this is the same as replacing the diameter d by 2 * sqrt(S / pi).

This comes from section 5.6 of Beranek, pages 131-133. For lf and luf, Beranek actually uses 0.85 and 0.613 respectively, but I've replaced these by a slightly more accurate calculation from the electroacoustics book by Leach.
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post #113 of 264 Old 09-11-2013, 01:35 PM - Thread Starter
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lol, I've been too long out of math ... this whole thing is making me want to build sealed just to forgo screwing up the slot port lol.

building a slot port is a lot harder than it seemed modeling in winisd


BUUUUT, I think I'm gonna go for it. 34 inch long port, 12 cu ft (+/- maybe a 10nth of a cu foot) tuned to 17.14 with the "one flanged end" for the end correction. unless of course anyone thinks differently
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post #114 of 264 Old 09-11-2013, 02:10 PM
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If you'd like, I could calculate the port length from the Beranek formulas and post the results along with a spreadsheet. I don't know your port area though.
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post #115 of 264 Old 09-11-2013, 02:12 PM - Thread Starter
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Quote:
Originally Posted by andyc56 View Post

If you'd like, I could calculate the port length from the Beranek formulas and post the results along with a spreadsheet. I don't know your port area though.

that would be appreciated, that way I can compare with what WinISD is telling me...see if I'm just obsessing over baby details, or whether I really do need a major alteration


my port is gonna be 2.5 inches high x 21 inches wide x whatever length it needs to be... tuned to around 17 hz....12 cu ft box
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post #116 of 264 Old 09-11-2013, 02:23 PM
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I came up with 33.88 inches, assuming

Box volume = 12 cubic feet
Port cross-sectional area = 52.5 square inches
Box tuning frequency = 17.14 Hz

Attached is a spreadsheet that can be reused for other designs. You enter the three quantities above and it calculates the port length per Beranek section 5.6, assuming the port is unflanged at one end and flanged at the other. port_length.zip 2k .zip file
Attached Files
File Type: zip port_length.zip (2.2 KB, 2 views)
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post #117 of 264 Old 09-11-2013, 03:35 PM
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"Formulas for the two end corrections are as follows:

lf = 0.8488 * a
luf = 0.6132 * a"

that is probably why winisd uses 0.732, as it is right in between the two values that you mention.

however, for a slot port along the floor, the other link that i provided suggests that the correction factor might be as high as 2.2 or something near that.

edit: it looks like winisd results are identical to this:

http://www.ctc-dr-weber.de/speaker/PortCorrection.jpg

so maybe that 2.2 value isn't so far off....

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post #118 of 264 Old 09-11-2013, 03:43 PM
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converting to an equivalent round port, 2.5" x 21" is 8.18" diameter round. at k=2.2, 33" gives about 15hz tuning suggesting that port is still too *long*.


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post #119 of 264 Old 09-11-2013, 04:24 PM - Thread Starter
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ahh, 33.88 inches comes in right about my estimates.. and then LTD02 HAAAAS to come in and ruin it wink.gif

you know I could have this place condemned. I could put stricknine in the guacamole
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post #120 of 264 Old 09-11-2013, 04:31 PM
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I wish people putting formulas like the one on that German site would reference the paper or book from which they got their data. In looking at the AES site, I did find this article, but I don't know if that is the one, and one has to pay to get it.
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