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ANNIHILATION Sub coming SOON! - Page 4

post #91 of 140
"Well i was worried about it being so close to the back of the enclosure and having an infinite port tuned to the unknown..."

not quite sure what you were saying there. :-)

here is a peak inside an svs pb13ultra subwoofer. ports are close together. ports are just over one port width from wall.



http://www.hometheaterequipment.com/subwoofers-64/svs-pb13-ultra-subwoofer-indepth-user-review-876/

...

"Just want a functional build."

of course!
post #92 of 140
Thread Starter 
Quote:
Originally Posted by LTD02 View Post

"Well i was worried about it being so close to the back of the enclosure and having an infinite port tuned to the unknown..."

not quite sure what you were saying there. :-)

here is a peak inside an svs pb13ultra subwoofer. ports are close together. ports are just over one port width from wall.



http://www.hometheaterequipment.com/subwoofers-64/svs-pb13-ultra-subwoofer-indepth-user-review-876/

...

"Just want a functional build."

of course!

Awesome! But that makes me feel better about them being close together but as u said there ports are just over one port width away from back. When we tuned the box to 18hz the ports were 27in and gave us around 4in ish. Lol away from the back which wouldn't be ideal because im using 6in ports and i would need a min of 6in from back of port. No?
post #93 of 140
Nice pic LTD. SVS best practices are getting bester. That’s a saver and I might actually use it today in a thread I’m thinking about. tongue.gifbiggrin.gif
post #94 of 140
There's nothing wrong with ports being close to things or each other so long as it's designed to work that way. There's trade offs like increased risk of chuffing, but in return, you can use a shorter port to get the same tuning freq.

An example of a designed "flaw" so to speak. The F16 is aerodynamically unstable and requires a fly-by-wire system to keep it airborne, but in return, its performance is increased.

So as long as a "flaw" is taken into account, it can be used to your advantage.
post #95 of 140
"Lol away from the back which wouldn't be ideal because im using 6in ports and i would need a min of 6in from back of port. No?"

it is a trick to get a lower tuning. it is using something that is generally thought of as a disadvantage (being a little too close) as an advantage (slightly lower tuning all other things equal). :-)
post #96 of 140
Quote:
Originally Posted by LTD02 View Post

"Lol away from the back which wouldn't be ideal because im using 6in ports and i would need a min of 6in from back of port. No?"

it is a trick to get a lower tuning. it is using something that is generally thought of as a disadvantage (being a little too close) as an advantage (slightly lower tuning all other things equal). :-)

Buggers! make note to self.. wink.gif
post #97 of 140
Thread Starter 
Quote:
Originally Posted by LTD02 View Post

"Lol away from the back which wouldn't be ideal because im using 6in ports and i would need a min of 6in from back of port. No?"

it is a trick to get a lower tuning. it is using something that is generally thought of as a disadvantage (being a little too close) as an advantage (slightly lower tuning all other things equal). :-)

Im sorry for being a pain. Just trying to understand. I see it as like this you plug it all into winisd you get a length of 27in which gives you 18hz. I understand you say its a lil trick to get lower tuning. Ok so maybe ill get 16 17hz. But it might increase the chances of chuffing which i wouldn't want. Also how do you know its lowers a lil and not alot. We dont know how low it might really make it or what effect it plays on the tuning. Now you saying eqing will help this all out? Should i leave it at 26 27in length? You know alot more then me and much more experience.
post #98 of 140
And now I regret piping in. I think I am causing apprehension with my statement and LTD is trying to do a little damage control.

If it were me, I would use the longer ports and then check the tuning freq once it's built. If it's too low, cut the pipes. More than likely, you will end up with pipes/ports a little shorter than what WinISD will quote you, but right now, no one knows exactly how much shorter. It could be 1" or it might be 7".
post #99 of 140
no worries bomber! piping in is always good. the points were valid. we may have missed something.
post #100 of 140
frankie, if you go with 6" from the back, it will be fine. :-) the large low tuned subs are much less sensitive to an inch here or there.

two 6" diameter ports in a 16 cubic footer arranged as you have them should bring you in around 16hz +/-. calculators will show about 33" or so length, but that is where the adjustment factor comes in. if you don't believe in the adjustment factor that ltd02 discusses, you will end up at about 17.9hz. if ltd02's adjustment factor is too small, you may end up at 15hz +/-.

bottom line. don't get too concerned about it. nobody really knows exactly. and, it doesn't matter. :-)
Edited by LTD02 - 10/15/13 at 12:36am
post #101 of 140
+1 15-16-18 it's all good..
Warning: Spoiler! (Click to show)
post #102 of 140
Quote:
Originally Posted by LTD02 View Post


bottom line. don't get too concerned about it. nobody really knows exactly. and, it doesn't matter. :-)

+1

Don't get bogged down in the minutia. Just go with a best guess and let the dust fly!
post #103 of 140
Thread Starter 
Okay we spec out the box to 15cuft but after driver displacement and bracing prob looking at 13.5. So with the ports that long at 27in. What would the tunning be? And should i stuff the box?
post #104 of 140
your cab is 32" deep, right? total external dimension.
post #105 of 140
Thread Starter 
Quote:
Originally Posted by LTD02 View Post

your cab is 32" deep, right? total external dimension.

32d
22w
48h
post #106 of 140
so with 0.75" off the back for the rear panel, you've got 31.25" six inches off that, just so you can sleep at night, gives you 25.25".

13.5 cubic feet in winisd or whatever with 2 x 6" diameter round ports 25.25" long gives 19.5hz roughly. now, that needs an adjustment factor. i suggest 20% (which is 1/0.8) or 25% longer effective, so the ports will behave as though they are about 30.6" long in winisd, again my guess. that gives you an effective tune of 17.9hz.

if you choose to stuff a couple of pillows in the sub, that will reduce the tuning frequency by 1-2hz or possibly a 3rd, so you are likely to come in around 16.5hz +/-, which seems like what you were shooting for.
post #107 of 140
Thread Starter 
Quote:
Originally Posted by LTD02 View Post

so with 0.75" off the back for the rear panel, you've got 31.25" six inches off that, just so you can sleep at night, gives you 25.25".

13.5 cubic feet in winisd or whatever with 2 x 6" diameter round ports 25.25" long gives 19.5hz roughly. now, that needs an adjustment factor. i suggest 20% (which is 1/0.8) or 25% longer effective, so the ports will behave as though they are about 30.6" long in winisd, again my guess. that gives you an effective tune of 17.9hz.

if you choose to stuff a couple of pillows in the sub, that will reduce the tuning frequency by 1-2hz or possibly a 3rd, so you are likely to come in around 16.5hz +/-, which seems like what you were shooting for.

Okay thanks ltd02. Thats what i was thinking thats all i was asking appreciate your help. But no need for the digs..
post #108 of 140
Instead of wondering about theoretical correction factors, just build the ports slightly long and measure. Trim the length and re-measure until you get the tuning you want.
Set them in place for measurements with tape or blutak and glue them in when completed.
post #109 of 140
not a dig at all. having that space will give you better peace of mind.
post #110 of 140
Thread Starter 
Quote:
Originally Posted by LTD02 View Post

not a dig at all. having that space will give you better peace of mind.

Lol okay thanks again man greatly appreciate the help and info.
post #111 of 140
Thread Starter 
Quote:
Originally Posted by A9X-308 View Post

Instead of wondering about theoretical correction factors, just build the ports slightly long and measure. Trim the length and re-measure until you get the tuning you want. Set them in place for measurements with tape or blutak and glue them in when completed.
Thanks man but how would i measure the tuning fq?
post #112 of 140
one method is to play test tones and monitor the driver excursion. at the tuning frequency it is minimal. above and below, it increases quite a bit.
post #113 of 140
Quote:
Originally Posted by frankie2075 View Post

Thanks man but how would i measure the tuning fq?
Use a large value series resistor, in series with a DVM (ammeter mode) in series with the sub, and slowly sweep the frequency range and look for the lowest current. Works the same as LTD's method, but easier to see the exact minimum.
post #114 of 140
Quote:
Originally Posted by A9X-308 View Post

Use a large value series resistor, in series with a DVM (ammeter mode) in series with the sub, and slowly sweep the frequency range and look for the lowest current. Works the same as LTD's method, but easier to see the exact minimum.

What is a DVM? Is the resister and DVM connected to the receiver? If so, how?
post #115 of 140
Quote:
Originally Posted by A9X-308 View Post

Use a large value series resistor, in series with a DVM (ammeter mode) in series with the sub, and slowly sweep the frequency range and look for the lowest current. Works the same as LTD's method, but easier to see the exact minimum.

?.. Care to explain :-)
post #116 of 140
Quote:
Originally Posted by Martycool007 View Post

What is a DVM? Is the resister and DVM connected to the receiver? If so, how?
Power amp + terminal to 1kR/10W resistor in series to DVM (digital multimeter) using the current terminals to speaker +. Speaker - to amplifier -. Obviously you need speaker cable to connect it too.
post #117 of 140
i think he was asking about current min vs. current max on the tuning frequency.
post #118 of 140
Quote:
Originally Posted by A9X-308 View Post

Power amp + terminal to 1kR/10W resistor in series to DVM (digital multimeter) using the current terminals to speaker +. Speaker - to amplifier -. Obviously you need speaker cable to connect it too.

I dont get this method. Are we not looking for the -highest- current? What is the resister for? If you put such a large resistor in series you will only have a few mA flowing unless you really crank the volume.. ?
post #119 of 140
I think he suggested it as a protective measure. Cooking a multi-meter is easy if you don't know what you are doing and/or if yours doesn't have a protective fuse.
post #120 of 140
Thread Starter 
virtually complete now need to start working on physically.

632d5e89-39ca-4649-a857-c592c741ddbf.jpg
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