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post #91 of 1010 Old 09-11-2013, 08:02 PM
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Originally Posted by LTD02 View Post

i think most people never measure so don't actually know how much the tuning drops.

there are a few folks around here who have measured carefully and noted drops of 2hz or more.

fortunately, 2hz isn't going to ruin anybody's fun.

but, it is very encouraging to know as this information can be used to create smaller subs while still keeping ports straight as well as making the cross sectional area of the ports larger to reduce chuffing and/or keep ports on the short side to push resonances as high as possible.

who knew marty's build thread would turn into one of the most technical discussions of ports on the avsforum!?!? :-)

lol, so true. I was just nervous that if we were wrong we'd tune too high, but yeah, I can see how the science seems to support it. and having a shorter port is much easier

i think I'll go halfway in between just for safety's sake. go 28 inchs instead of 34 or 23... at worst I drop to a 16 hz tune if we're right, and if wrong then at worst it's an 18.5 hz tune.... still within the 16-18 hz I was shooting for.
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post #92 of 1010 Old 09-11-2013, 08:23 PM
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"lol, so true. I was just nervous that if we were wrong we'd tune too high"

the troels link shows that can be fixed a bit by adding more damping to the enclosure.

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post #93 of 1010 Old 09-11-2013, 08:24 PM
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"oh, and with the decreased port length is that going to affect port velocity very much? or at least in a negative manner?"

port velocity is almost all a function of the cross sectional area, not so much the length, except to the extent that length alters the tuning frequency of the cabinet.

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post #94 of 1010 Old 09-11-2013, 08:25 PM
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Quote:
Originally Posted by LTD02 View Post

"lol, so true. I was just nervous that if we were wrong we'd tune too high"

the troels link shows that can be fixed a bit by adding more damping to the enclosure.

ahhh, yes, extra dampening

oh, and with the decreased port length is that going to affect port velocity very much? or at least in a negative manner?
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post #95 of 1010 Old 09-11-2013, 08:26 PM
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I read through the discussion above Re: port length and correction factors...after I glued my slot panel in place. eek.gif

Well, if there is an easy way for me to measure tuning frequency after this sub is built, I will be happy to post my results. Until then, I will continue to soldier on and post pictures:


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post #96 of 1010 Old 09-11-2013, 08:30 PM
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if you did a full 39 inch slot port as it was originally designed at (and you're recessing the baffle a few inches back like the plan said) then you'll have about a 14.8 hz tune... lower is usually better than higher

if you aren't recessing your front baffle a few inches than you'll have a 14.3 hz tune.... nothing big


last thing. HOW do you measure a sub for it's tuning frequency? I've never done that before
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post #97 of 1010 Old 09-11-2013, 08:31 PM
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that's a lot more done today than yesterday... :-)~

"I read through the discussion above Re: port length and correction factors...after I glued my slot panel in place."

i feel for ya brother...it always happens like that. BUT, keep in mind that having a little lower tuning by a couple hz than model isn't going to lessen the fun. that is probably why the issue has never really surfaced...it doesn't really matter. :-)

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post #98 of 1010 Old 09-11-2013, 08:33 PM
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that is a nice post btw showing how you used masking tape to block off the areas where you will be applying glue.

nice tip. marty, keep that one in mind!

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post #99 of 1010 Old 09-11-2013, 09:45 PM
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Thanks for noticing the progress and the tape job, LTD. I'm just glad you mentioned to paint the port before assembly! smile.gif

Hey Worm. My tuning is slightly different than LTD's final design. My ports are 2" tall (and 36" long) to give me a slightly higher resonance point than the 2.5" ports (188Hz vs. 149Hz, respectively.) Even so, first port resonance is only -26dB with a typical 24dB/Octave crossover at 80Hz.

With regards to the lower tune, the main disadvantage that I see is that we lose a bit of efficiency in the lowest octaves and the woofer isn't as well controlled by the port so the power handling is somewhat more restricted. Uh oh. I think I just went off the deep end...tongue.gif
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post #100 of 1010 Old 09-11-2013, 09:56 PM
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another good link on box stuffing: http://sound.westhost.com/articles/boxstuff.htm

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post #101 of 1010 Old 09-12-2013, 05:10 AM
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Quote:
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Thanks for noticing the progress and the tape job, LTD. I'm just glad you mentioned to paint the port before assembly! smile.gif

Hey Worm. My tuning is slightly different than LTD's final design. My ports are 2" tall (and 36" long) to give me a slightly higher resonance point than the 2.5" ports (188Hz vs. 149Hz, respectively.) Even so, first port resonance is only -26dB with a typical 24dB/Octave crossover at 80Hz.

With regards to the lower tune, the main disadvantage that I see is that we lose a bit of efficiency in the lowest octaves and the woofer isn't as well controlled by the port so the power handling is somewhat more restricted. Uh oh. I think I just went off the deep end...tongue.gif


Gotcha. Well your testing will definitely help out our theory on this. see how accurate those calculations are and if we're under or over tuning. Probably be helpful in general for us doing slot ports
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post #102 of 1010 Old 09-12-2013, 06:27 AM - Thread Starter
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Update as of September 12th

I have the first enclosure about 50% of the way done! The 2' by 4' handy panels are indeed handy, but the 2' by 2' panels were off a bit on each side, so I had to go buy some more wood. I will post some pics in a bit!

I am highly considering go with a more traditional round port instead of the slot port. If I do end up going with a round port, I will assume that regular ole PVC would work? If so, what diameter and length should I use?

I will complete everthing on enclosure #1 today with the exception of the front baffle. I will be going to Sears later on to pick up the straight bit for my router, but then I need to find a circle jig. Any suggestions on where I can find a circle jig? Preferabley somewhere that can offer 2nd day air shipping wise??
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post #103 of 1010 Old 09-12-2013, 06:29 AM
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an 8 inch port tuned to 16hz is 40 inches long... an 8 inch port tuned to 17 hz is 34.75 inches long
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post #104 of 1010 Old 09-12-2013, 06:39 AM
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You could always make a quick jig out of a piece of 1/8 if you find yourself in a pinch. It only takes about 10 minutes or so depending how far you take it.

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post #105 of 1010 Old 09-12-2013, 06:40 AM
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Originally Posted by steve nn View Post

You could always make a quick jig out of a piece of 1/8 if you find yourself in a pinch. It only takes about 10 minutes or so depending how far you take it.

yup, it's pretty easy... create a "perch" for the router on one end and drill a hole for the size you want to cut on the other
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post #106 of 1010 Old 09-12-2013, 06:53 AM
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yup, it's pretty easy... create a "perch" for the router on one end and drill a hole for the size you want to cut on the other

I guess we should be nice and warn him to inset the screws that hold the 8th on to the base so he doesn’t scratch his project. Of course I have never done that though. biggrin.gif

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post #107 of 1010 Old 09-12-2013, 06:54 AM
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I guess we should be nice and warn him to inset the screws that hold the 8th on to the base so he doesn’t scratch his project. Of course I have never done that though. biggrin.gif

lol, yes, a countersink bit is a necessity for that... unless he LIKES lines around his sub hole. you never know biggrin.gif
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post #108 of 1010 Old 09-12-2013, 07:04 AM
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lol, yes, a countersink bit is a necessity for that... unless he LIKES lines around his sub hole. you never know biggrin.gif

Thank you for the word I’m looking for. I never can remember countersink no matter how many times I might use it in a day every once in a while. Anyway yeah those scratches don’t sand out that easily by hand. Hey "sub hole".. is that a new word cool.gif That's what they call us DIY bassheads when they get mad at us. biggrin.gif

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post #109 of 1010 Old 09-12-2013, 07:25 AM - Thread Starter
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So let me see if I got this correctly.... I would need a countersink bit instead of a straight cut bit for doing the woofer cutout & port cut out? Or is the straight cut bit just used to make the actual hole for the driver, then using a countersink bit to make the recess??
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post #110 of 1010 Old 09-12-2013, 07:31 AM
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No a straight is what you want to go with. We were talking about a quick jig. I’ll go dig up a pic for you.

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post #111 of 1010 Old 09-12-2013, 07:40 AM
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Originally Posted by Martycool007 View Post

So let me see if I got this correctly.... I would need a countersink bit instead of a straight cut bit for doing the woofer cutout & port cut out? Or is the straight cut bit just used to make the actual hole for the driver, then using a countersink bit to make the recess??

This is a very quick and dirty jig. A guy can make much better ajustible but this will give you a idea. We were talking about the screws that hold the wood on to the router. It's good that they are countersunk so they don't scratch your baffle. I added that extra piece of wood on top because it always seems like a guy needs to move the nail a 1/16th and cant get the hole to go in-between two holes that are already there. rolleyes.gif


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post #112 of 1010 Old 09-12-2013, 09:25 AM
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Despite all the masking tape, I neglected to mask off a 3/4" perimeter at the back of the enclosure for bonding the rear panel....3 steps forward...1 step back.
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post #113 of 1010 Old 09-13-2013, 01:59 PM - Thread Starter
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What kind of straight bit should I purchase for the driver cutout? 1/4"? 3/4"? 5/8"? 3/8"????
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post #114 of 1010 Old 09-13-2013, 02:05 PM
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What kind of straight bit should I purchase for the driver cutout? 1/4"? 3/4"? 5/8"? 3/8"????

3/4 would be best.
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post #115 of 1010 Old 09-13-2013, 02:21 PM
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"an 8 inch port tuned to 16hz is 40 inches long... an 8 inch port tuned to 17 hz is 34.75 inches long"

that's with 0.732 end correction right? :-)~

.............

btw, there is something about the word subhole that is just kill'n me. :-)

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post #116 of 1010 Old 09-13-2013, 02:22 PM
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Quote:
Originally Posted by LTD02 View Post

"an 8 inch port tuned to 16hz is 40 inches long... an 8 inch port tuned to 17 hz is 34.75 inches long"

that's with 0.732 end correction right? :-)~

.............

btw, there is something about the word subhole that is just kill'n me. :-)

correct, that's with the standard one end flanged setting in Winisd for a cylindrical port


lol, and yeah,,, it makes me chuckle too
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post #117 of 1010 Old 09-13-2013, 02:30 PM - Thread Starter
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Ok you guys, no need to act like a bunch of subhole's! LoL! J/k

I have decided to go with a circle port, likely with a 16hz tune at 8" by 40". Can anyone tell me if I can find an 8" piece of PVC at Lowes or Home Depot? Or is there another place that anyone can recommend?

Is it ok to just use a PVC pipe? Does it need a flair on the ends? If so, how do I go about doing that?

Almost done with enclosure #1!
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post #118 of 1010 Old 09-13-2013, 02:35 PM
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8" pvc would be quite large. not sure if that is something you might find at a home store.

an 8" diameter cardboard concrete form might be an option.

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post #119 of 1010 Old 09-13-2013, 02:38 PM
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Quote:
Originally Posted by LTD02 View Post

8" pvc would be quite large. not sure if that is something you might find at a home store.

an 8" diameter cardboard concrete form might be an option.

yup, thta's what I was thinking. you can get 8 inch sonotubes at HD all day long
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post #120 of 1010 Old 09-13-2013, 09:57 PM
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Marty, where are your pictures??? I hope you took a bunch of pics along the way!

I worked on adding more bracing tonight (and last night). My question for you guys is: Do I have enough/too much bracing at the rear of the sub near the port entrance?

I plan to add a vertical brace, from the bottom center to the top, to form a basic cross brace for the back of the speaker. This vertical brace will be continued forward to bisect each of the upper cross braces. With this bracing pattern, all of the open spans are less than 12", EXCEPT, for the area around the port entrance, as seen in the photos below.

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