And so it begins............. (New build started) - AVS Forum
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post #1 of 105 Old 02-06-2014, 07:04 AM - Thread Starter
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Well, after many months reading the forum I finally got started. I saw the SI clearance sale and it was too good to pass up.
I just ordered 2 SI 18 D2
My plans for my huge 5,000 cu ft room is as follows:

2 x Slot vented 11 cu ft net enclosures. Outer dimensions 37.5 x 21.5 x 30.75

I planned the port to be 2 x 19 x 24 which should be tuned around 17hz.

I have narrowed the amps down to two choices:

1. Samson sx2800. It will put out 900W per side at 4ohms.
I like this amp because of the class H circuitry and binding posts so I wont need to mess with speakon connectors.
2. QSC GX5: 700w rms per channel @ 4ohms. This amp is slightly cheaper but also has a bit less power. I don't really think I would notice a difference in the power just a bit more headroom on the Samson. I like this amp for the binding posts AND RCA inputs. No need to mess with xlr adapters or speakon connectors.

If anyone has a comment on either of the above amps for this application it would be appreciated. I don't think I need any more power than these provide.

I am dead set against Behringer for the simple fact that they overstate their rated power. I know a lot of members here use and love these Inuke amps but if there is one thing I have learned from purchasing car audio amps over the last 20 plus years its that companies that overstate their output power don't generally have a quality product. I will take 1000w of clean true power over 3000w of BS any day. If you can't clearly state your continuous unclipped clean power rating something is wrong.

Comments, tips and suggestions are appreciated.

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post #2 of 105 Old 02-06-2014, 07:37 AM
 
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Good luck with the build. How do you know that the amps you are looking at have 100% of their stated power?
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post #3 of 105 Old 02-06-2014, 08:37 AM
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Do you plan on employing a filter down low?

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post #4 of 105 Old 02-06-2014, 09:19 AM - Thread Starter
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I have read information on the QSC forum that all their amps are advertised at continuous power here: http://forum.qscaudio.com/forum/viewtopic.php?f=8&t=3726

Samson are advertised as RMS power on several sites.
Plus if they were to overstate their power the ratings would be much higher than advertised. By Behringer standards these amps are over 4000w

As far as the low pass filter goes I think it would be wise to do so. I haven't decided on a solution. Are there any suggestions?
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post #5 of 105 Old 02-06-2014, 09:35 AM
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If you’re set on that size vent, ( single 2X19) you need to employ one at 15-17hz to keep your air velocity down not to mention over excursion below tune.

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post #6 of 105 Old 02-06-2014, 09:40 AM
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Quote:
Originally Posted by jfreeman420 View Post

Well, after many months reading the forum I finally got started. I saw the SI clearance sale and it was too good to pass up.
I just ordered 2 SI 18 D2
My plans for my huge 5,000 cu ft room is as follows:

2 x Slot vented 11 cu ft net enclosures. Outer dimensions 37.5 x 21.5 x 30.75

I planned the port to be 2 x 19 x 24 which should be tuned around 17hz.

I have narrowed the amps down to two choices:

1. Samson sx2800. It will put out 900W per side at 4ohms.
I like this amp because of the class H circuitry and binding posts so I wont need to mess with speakon connectors.
2. QSC GX5: 700w rms per channel @ 4ohms. This amp is slightly cheaper but also has a bit less power. I don't really think I would notice a difference in the power just a bit more headroom on the Samson. I like this amp for the binding posts AND RCA inputs. No need to mess with xlr adapters or speakon connectors.

If anyone has a comment on either of the above amps for this application it would be appreciated. I don't think I need any more power than these provide.

I am dead set against Behringer for the simple fact that they overstate their rated power. I know a lot of members here use and love these Inuke amps but if there is one thing I have learned from purchasing car audio amps over the last 20 plus years its that companies that overstate their output power don't generally have a quality product. I will take 1000w of clean true power over 3000w of BS any day. If you can't clearly state your continuous unclipped clean power rating something is wrong.

Comments, tips and suggestions are appreciated.


I am very interested in your build, I am just about to order 2 of these subs as well and was going with a sealed enclosure but from what I see on your dimensions is not that big. I do have a question thought, when I do the math 37.5 x 21.5 x 30.75=24,792.18 / 1728 I get 14.34 cf, I know you have to account for the port, but I don't think the port material will take up over 3ct. Did I figure something out wrong? I admit I don't know much at all, these forums are my classroom. I am interested because I would love ported instead of sealed, if I can get the box small enough.

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post #7 of 105 Old 02-06-2014, 09:41 AM - Thread Starter
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Is there a better option for the vent? I went with that size so it wouldn't have to be too long since the cabinet is only 30" deep.

Will the minidsp be good for the low pass? Any other option for low filter?
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post #8 of 105 Old 02-06-2014, 09:51 AM - Thread Starter
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Quote:
Originally Posted by cessna1466u View Post

I am very interested in your build, I am just about to order 2 of these subs as well and was going with a sealed enclosure but from what I see on your dimensions is not that big. I do have a question thought, when I do the math 37.5 x 21.5 x 30.75=24,792.18 / 1728 I get 14.34 cf, I know you have to account for the port, but I don't think the port material will take up over 3ct. Did I figure something out wrong? I admit I don't know much at all, these forums are my classroom. I am interested because I would love ported instead of sealed, if I can get the box small enough.
The dimensions are the exterior of the box. Interior dimensions are smaller
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post #9 of 105 Old 02-06-2014, 09:54 AM
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Gotcha! but I'm comeing in at 27" long.. Are you useing correction or something? mini is good..

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post #10 of 105 Old 02-06-2014, 09:58 AM
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Quote:
Originally Posted by jfreeman420 View Post

The dimensions are the exterior of the box. Interior dimensions are smaller

Duh, see what I mean. Learn something new everyday.
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post #11 of 105 Old 02-06-2014, 10:12 AM - Thread Starter
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Quote:
Originally Posted by steve nn View Post

Gotcha! but I'm comeing in at 27" long.. Are you useing correction or something? mini is good..
Yes it does come out to 27" long at 17htz and 23" long at 18hz.
I figured 24" would be a happy medium and account for any miscalculation on internal displacement accounting for the volume of the port itself and bracing.
Does that make sense or am I over thinking it?
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post #12 of 105 Old 02-06-2014, 10:22 AM
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Quote:
Originally Posted by jfreeman420 View Post

Yes it does come out to 27" long at 17htz and 23" long at 18hz.
I figured 24" would be a happy medium and account for any miscalculation on internal displacement accounting for the volume of the port itself and bracing.
Does that make sense or am I over thinking it?

I see, ok yes 18 looks a lot better. You don’t want the back of your port running to close to the back of your enclosure as I’m sure you know. What I would like to see though (considering bracing) is two ports so you could tie the top to the bottom in a nice way and strengthen your vents at the same time. Wouldn’t take much for it to be affective.

EDIT> I’ll let you come up what space you have to work with. I’m at 11cf internal after displacement now though.

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post #13 of 105 Old 02-06-2014, 10:29 AM - Thread Starter
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would it be better to use round ports instead of the slot? I would be just as easy to cut two holes instead of making the slot port.

I only figured this type of vent due to the simplicity of the build. two corner ports would require miter cuts and I don't have the equipment or the confidence for that
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post #14 of 105 Old 02-06-2014, 10:32 AM
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Let me look for yuh! You want me to look at 11cf internal after displacement at 18hz tune correct? I can play with it some also if you like?

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post #15 of 105 Old 02-06-2014, 10:35 AM - Thread Starter
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yes any help would be appreciated.
Thank you!
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post #16 of 105 Old 02-06-2014, 10:57 AM
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Two 6” ports at 38” L looks really good. It puts you under air velocity wise and good 1st p r. A single 7” puts you to close to the back of your enclosure and changing tune brings up other issues.

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post #17 of 105 Old 02-06-2014, 11:01 AM
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Quote:
Originally Posted by steve nn View Post

Two 6” ports at 38” L looks really good. It puts you under air velocity wise and good 1st p r. A single 7” puts you to close to the back of your enclosure and changing tune brings up other issues.

So would his box have to be at least 40" long to allow for the lenght of the port plus a few inches more? Or can it be an angled 38"? Like say 25" a 90degree and then another 13"?

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post #18 of 105 Old 02-06-2014, 11:11 AM
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The slow transition is best albeit your at 17 m/s now at max. If you go the elbow route, it would be best to use a elbow that has the soft 90. I can't find a pic I thought I saved.

EDIT> 1st in third row or third in second row. https://www.google.com/search?q=soft+90+degree+elbow&biw=1680&bih=881&tbm=isch&tbo=u&source=univ&sa=X&ei=i9_zUrnQLZPpoATIn4HYCQ&ved=0CIEBELAE

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post #19 of 105 Old 02-06-2014, 11:19 AM - Thread Starter
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So I could do 2 ports 19.5" long each to avoid bending?
Will this sound better than a slot port?
What about chuffing?
i haven't seen any port flare that are 6". Would it be ok to just use standard pvc without any flares?
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post #20 of 105 Old 02-06-2014, 11:26 AM
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I’m out the door, but if you go with PVC you’re fine since you’re under. (chuffing) Run down towards the back and then up what ever distance you need to. Measure from the middle of the ports and keep the end away from the wall. The rule is the d of the port if you want your tune to come in as projected.. well close.

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post #21 of 105 Old 02-06-2014, 11:31 AM
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I really need some coffee, I didn't think that you could do 2 ports at half the lenght and that would eliminate having to do a bend. Maybe I should stick to sealed enclosures.

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post #22 of 105 Old 02-06-2014, 02:57 PM
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I know it seems weird but when a guy increases from one port to two the length doubles. You need to go to two on account of keeping the air velocity down so your sub won’t chuff like you brought up. 18”s in general need a lot of breathing room. You can do a shorter straight length, but you would have to build the sub about 10” deeper for it to work out with a single 8” port 32” long. A slot might be the way for you to go? The 2X19 slot puts your air speed a little over though at 25. Since your vent is only 2” that’s a little high. You could run your 8" round vent from the top though.
http://www.subwoofer-builder.com/vents.htm

EDIT> You have the option of running the slot vent from the top back down also.

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post #23 of 105 Old 02-08-2014, 07:58 PM - Thread Starter
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I think I would prefer the slot port. If I increase the port to 2.5" the length would come in just over 30" which wouldn't leave any room for a bend and would not work with the 30" deep design.

I really want the port on the bottom front of the box for aesthetic reasons. These will not have grills and I feel the ports will add a bit to the look.

My other option is to make the port 3" x 19".

This would make the port around 40" long which would be enough length to put a bend in it and still keep it 3" from the rear wall.

My concern is that this will take up additional interior volume which will result in an incorrect tune. I would like it to be tuned between 17hz and 18hz so if the port will take up additional volume I am assuming it should be shorter to compensate and not be tuned too low.

Any thoughts on this? Any advice on how to compensate for the additional volume of a longer and larger port?
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post #24 of 105 Old 02-08-2014, 08:03 PM
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if you run the port along the bottom toward the back wall and stop with one port length from the back wall, it will actually function like it is a little longer than it appears.

the 3" high port just has extra port velocity anti-chuffing margin built in. 2.5" should work ok.

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post #25 of 105 Old 02-08-2014, 08:04 PM
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kind of like atabea did with his:

http://www.avsforum.com/t/1496365/another-ltd02-designed-sub-build/0_50

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post #26 of 105 Old 02-08-2014, 08:19 PM - Thread Starter
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problem is I am trying to make the box taller than deep so there is less room to run the port front to back.

Is there anyway to give me the length of the interior wood panel that will make up the port considering the dimensions 21.5w x 36"H x 31.5" deep? The interior will only be 30" deep from front to back. Figure 17hz to 18hx tune. I don't expect it to be exact but I would prefer to be on the higher side of the tune rather than lower to have more usable frequency at tuning.

If I do opt for the 2.5" port and run it from the top I would have room for a 30" port. My concern is it will only be about 6" from the bottom. Would that be enough space considering the plan is 36" tall?

Would it be easier to just go taller and not as dee? Maybe a vertical martysub....
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post #27 of 105 Old 02-08-2014, 08:31 PM
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since the port runs to the front of the cab, measurement begins flush front.

outer dimension of 31.5" front to back of cab, subtract 0.75" for back panel, subtract 2.5" for one port height of clearance to rear wall, gives 31.5" - 3.25" = 28.25" port board.

that would give an effective port length of 30-31" or so, maybe a hair more.

you've got about 11-11.5 cubic feet there, so a 2.5" tall port about 19" wide (net after side and slot braces) will give a tune or around 17-18hz.

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post #28 of 105 Old 02-08-2014, 10:13 PM
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Hey John.. I was thinking if he went the two slot route he then could tie into the brace that supported the slot on up to the top. As it sits with just the one slot, the bottom isn’t braced. Might you have a good suggestion on how to get around this with going the single slot? Thnx

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post #29 of 105 Old 02-08-2014, 11:50 PM
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I would go with two braces running along the slot. I think it looks cool. :-)

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post #30 of 105 Old 02-09-2014, 05:02 AM
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^^ After reloading I see what you’re saying. I was hung up on distance from the back of the enclosure with going two slots instead of three at 2.5

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