my math is correct, why more excursion at tuning? - Home Theater Forum and Systems - HomeTheaterShack.com

Old 10-23-09, 01:53 AM Thread Starter
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Ryan

Join Date: Jul 2009
Location: sfsd
Posts: 1,074
my math is correct, why more excursion at tuning?

My enclosure is 21 cubic feet after sub/port displacement, tuned to 15.42Hz. The port is a 7.75" sonotube 19.5" long, leaving 8.25" port clearance at the back.

external 42" wide = 40.5" wide internally
front 38 tall, rear 32 tall = 36.5" + 30.5"= 33.5" average height
bottom depth 30.5" top 28" = 29 + 26.5 = 27.75" average depth

40.5 x 33.5 x 27.75 = 21.788 cubs before sub/port displacement

7.75" x 19.5" = .532 cubes port displacement + .22 sub displacement = .752 total disp

WinISD with 21 cubes with 7.75 x 19.5 says 15.42Hz tune, and I round under, so close to 15Hz.

So here is my problem. Bass I Love You has a 16Hz tone. I had more excursion at the 16Hz tone than I did on the 30Hz and 25Hz tones. Please excuse the very poor quality of this video, turn your speakers down!

also note, very little port velocity. that 2 liter bottle barrely moves, and not much air blew through without the bottle in it either.

Now here is sub_junkie's vid. He is 7.6 cubic feet tuned to 15Hz as well. IDK where his SSF is set to, but mine was at 15Hz. You can turn it back up for his vid.

http://s536.photobucket.com/albums/f...rSale005-1.flv

his excursion is just the opposite: more excursion on the 25Hz and 30Hz, very little on the 16Hz, as it should be, correct?

Here is another video of mine with a much better camera just to get a better view and listen of things. Please bear with me, it's a rap song, but the bottom note on this track is 26Hz I believe. Willie The Kid : Love For Money

same song, different vid

Last edited by Ryan Anderson; 10-23-09 at 01:58 AM.
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Old 10-23-09, 02:23 AM
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Mike

Join Date: Apr 2007
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Re: my math is correct, why more excursion at tuning?

Quote:
also note, very little port velocity
First things first. Verify you port tuning with test tones.
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Old 10-23-09, 04:19 AM Thread Starter
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Ryan

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Re: my math is correct, why more excursion at tuning?

Quote:
Mike P. wrote: View Post
First things first. Verify you port tuning with test tones.
I'll have to grab a new solder iron, no longer have my butane, so I can finish the recone. Then I'll run some sweeps. How far from tuning will no longer control excursion? Say tuning is off by 5Hz... will excursion really be that high again 5Hz away?
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Old 10-23-09, 05:10 AM
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Mike

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Re: my math is correct, why more excursion at tuning?

Add 5 hz to the tuning in your modeling and see where the excursion is.
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Old 10-23-09, 05:12 AM Thread Starter
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Ryan

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Re: my math is correct, why more excursion at tuning?

I just ran out and measured diameter... I'm only 7.5 inches! Plus I round down, so say 7.5" diameter and 21.25 cubic feet, I still get 14.94Hz

With 1700 watts I'm seeing the outter limits as 13.4Hz and 19.2Hz for 30mm Xmax, but only 15mm at 16Hz

Last edited by Ryan Anderson; 10-23-09 at 05:23 AM.
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Old 10-23-09, 05:18 AM
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Mike

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Re: my math is correct, why more excursion at tuning?

Then your tuning is 15 hz. You don't have any boost applied on the amp do you?
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Old 10-23-09, 05:30 AM Thread Starter
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Ryan

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Re: my math is correct, why more excursion at tuning?

nope, I never use bass boost. weird huh? I need to get that recone done so I can test this. However, my batteries, amp, and car are gone... and I retuned it to 17Hz with 13.5" length....painted it all purdy... so I'll test it as it is now, then rip it out again and go 19.5" deep again for 15Hz.

here's some current pics

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Old 10-23-09, 05:34 AM
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Mike

Join Date: Apr 2007
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Re: my math is correct, why more excursion at tuning?

Another thought is maybe it's not a 16 hz tone on the song. After the recone is done you won't be able to model this sub due to the second coil changing the parameters.
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Old 10-23-09, 05:38 AM Thread Starter
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Ryan

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Location: sfsd
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Re: my math is correct, why more excursion at tuning?

I heard it was 18Hz, which is why when I redid it I went to 17Hz instead of 15Hz. I really need to get handy with a spec analyzer so I don't have to take people's word for it. I've got one somewhere but never took the time to really figure it out. I'm bassing 16Hz off Ricci from the GTG thread. Still, 16Hz, 18Hz.... sub_junkie's is reacting much different than mine, we have the same tuning, maybe his SSF is cutting more than mine?
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Old 11-01-09, 04:15 PM
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Re: my math is correct, why more excursion at tuning?

Quote:
Ryan Anderson wrote: View Post
nope, I never use bass boost. weird huh? I need to get that recone done so I can test this. However, my batteries, amp, and car are gone... and I retuned it to 17Hz with 13.5" length....painted it all purdy... so I'll test it as it is now, then rip it out again and go 19.5" deep again for 15Hz.

here's some current pics

Dude, sweet ghetto box!!
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