couple more box questions

capitolj80 · Post by **capitolj80** » Mon Mar 10, 2008 10:41 pm

so..i was wondering if there's typically any acoustic difference in the direction the subs are facing in the trunk. it's a relatively large trunk, so i've got versatility on my side. i've been debating on having my rsd's in a slant back (subs facing rear of car) or in separate boxes on the left and right side facing eachother (in front slanted boxes). will i be getting virtualy the same effect either way? also, is 3/4 mdf totally necessary or would 5/8 mdf suffice? (i'm pretty sure that's a dumb question and i'll surely be scolded) i'll be running around 1,000rms.

Post by **fuzzysnuggleduck** » Mon Mar 10, 2008 10:50 pm

If the subs are facing each other, you have a much higher chance of cancellations. However, I *think* you could probably deal with that by futzing with the phase on one sub though.

capitolj80 · Post by **capitolj80** » Mon Mar 10, 2008 10:55 pm

i see...if i had them configured that way, i was gonna have them slanted up somewhat... would that negate the possibility of cancellation?

Post by **fuzzysnuggleduck** » Tue Mar 11, 2008 12:05 am

I think you'll get cancellations no matter what it's just how you manage the severity and effect. Some other people will know better but I think that angling them up will be useful.

Post by **Bfowler** » Tue Mar 11, 2008 8:22 am

the boxes facing each other will result in cancellation, facing them bot backwards is really the way to go.

did you measure it at 5/8's or does the label read 5/8?

lumber is always overmeasure now (like 2x4's being 1/5 x 3/5)

so 3/4 mdf often measures out to 5/8's and works fine.

however if the label reads 5/8's, then it is most likely a bit smaller and not recommended.

Post by **VW337** » Tue Mar 11, 2008 9:22 am

Bfowler wrote:the boxes facing each other will result in cancellation, facing them bot backwards is really the way to go.

did you measure it at 5/8's or does the label read 5/8?

lumber is always overmeasure now (like 2x4's being 1/5 x 3/5)

so 3/4 mdf often measures out to 5/8's and works fine.

however if the label reads 5/8's, then it is most likely a bit smaller and not recommended.

WTF?

2 x 4's are measure the way they do so that once a sheet of standard drywall/sheetrock is applied to one side or the other that measurement comes out to 2 inches or 4 inches, they are not truly 2" x 4" but accounting for the end result.

MDF on the other hand is made for milling purpose and really should be spot on for measurement except for the very edges.

Post by **Bfowler** » Tue Mar 11, 2008 9:34 am

hmm, well any mdf (or even plywood) i have ever bought has always been short on its listed measurement.

i guess we can only wait for him to report back his measurements.

WTF?

2 x 4's are measure the way they do so that once a sheet of standard drywall/sheetrock is applied to one side or the other that measurement comes out to 2 inches or 4 inches, they are not truly 2" x 4" but accounting for the end result.

ok...come look at the studs in my parents house and explain that theory
to me again...

gkitching · Post by **gkitching** » Tue Mar 11, 2008 10:35 am

MDF is exactly 3/4"(or what ever the dimension is). Like Erin stated, because it is manufactured.

Hardwoods are descibed by their sizes PRIOR to milling. A 2x4 stud starts as 2" x 4" raw piece of lumber, then gets planed for straightness and the result is actual 1 1/2" x 3 1/2". The planing process typically will shave off about 1/4" for each pass. Same is true for planking for shelves and basically anything made from hardwoods.

MDF and the like are manufactured to a thickness so they will always be as described.

Post by **Bfowler** » Tue Mar 11, 2008 10:44 am

i am getting scammed then! son of a.

well then i guess to answer the OP's question....5/8 should be ok as i have been using it for a while now!

if you havnt already bought it, 3/4 is better though. box flexing eats up DB's

gkitching · Post by **gkitching** » Tue Mar 11, 2008 10:47 am

capitolj80 wrote:so..i was wondering if there's typically any acoustic difference in the direction the subs are facing in the trunk. it's a relatively large trunk, so i've got versatility on my side. i've been debating on having my rsd's in a slant back (subs facing rear of car) or in separate boxes on the left and right side facing eachother (in front slanted boxes). will i be getting virtualy the same effect either way? also, is 3/4 mdf totally necessary or would 5/8 mdf suffice? (i'm pretty sure that's a dumb question and i'll surely be scolded) i'll be running around 1,000rms.

I would use 3/4" as a minimum. And 1" if available. If you have a 1000watt sub and amp set up you will be testing the structural limits of 3/4"depending on the size of the enclosure walls. The bigger the surface area, the more likely you will have more flexing. Otherwise plan on internal bracing. Which I would probably do in either case.

gkitching · Post by **gkitching** » Tue Mar 11, 2008 10:54 am

Bfowler wrote:i am getting scammed then! son of a.

well then i guess to answer the OP's question....5/8 should be ok as i have been using it for a while now!

if you havnt already bought it, 3/4 is better though. box flexing eats up DB's

Actually, if you've ever been to a real lumber yard (read not Home Depot or Lowes) they still sell real 2x4's but typically twisted, notty and rough. The 'milled' 2x4's aren't that much more expensive so there's little call for the raw wood now adays unless you're doing something rustic or antique or plan on doing your on planing.

Forgive me for being a wood geek. I love a well stocked lumber yard as much as a well stocked electronics store.

Post by **stipud** » Tue Mar 11, 2008 11:11 am

I knew it!

Here's gkitching at home...

gkitching · Post by **gkitching** » Tue Mar 11, 2008 11:14 am

LMFAO! now wait. That can't be me. I can only type with 2 fingers.

Post by **stipud** » Tue Mar 11, 2008 11:16 am

It's too late... we know your secret! You can't hide from us!

Enjoy your new title

gkitching · Post by **gkitching** » Tue Mar 11, 2008 11:37 am

Well you know what they say ... You are what you eat!

HoseHead · Post by **HoseHead** » Tue Mar 11, 2008 1:34 pm

I have a sub box with qty 3 XMax12 - each in it's own sealed chamber, all 90 degrees to the floor and the outside units tilted about 20 degrees to the centre. 3/4" MDF with dadoed, siliconed sealed joints and stuffed with fibreglas insulation.

It was rear facing when I bought the car and it sounded awesome. When I rebuilt the system, I placed the box forward facing in the same location - right behind the fold down seats. OK, but it didn't grab your chest. I returned it to rear face and voila - through the heart bass again. They are wired in parallel (1.33 ohm) and I'm driving them with a bridged MS2125 (The "fat side" of a Frank) set to mono with gain set to 50%. An AC Epicentre control at the driver's seat manages the bump.

My theory is that the subs "use" the trunk cavity to develop the lower frequencies. When I fill my trunk with things like beer and hockey gear, the sound does "change" as I am adjusting the trunk's volume. Trial and error was my engineering process. A pic for your reference.

Post by **stipud** » Tue Mar 11, 2008 1:53 pm

It's partially allowing the bass wave to develop, but predominantly a lack of cancellation. With subs pointed forward, unless you completely seal them into the cabin, then waves will go back into the trunk, bounce, and come forward... thus canceling out the other forward waves resonating off the speaker cones.

Post by **Bfowler** » Tue Mar 11, 2008 2:23 pm

we need to save that image somewhere useful^ i can never find it when i need it...ie now

capitolj80 · Post by **capitolj80** » Tue Mar 11, 2008 2:28 pm

wow...this topic got hot while i was out.... the wood is labeled at 5/8. i found a couple of prefabs that have EXACTLY the internal volume i was gonna build to, but they're 5/8mdf and if didn't think that was kosher...sorry it took so long to chime in and thnx for all the input...i think I'll just go ahead and buy some 3/4 and do it myself...I'll have the subs rear facing too.

HoseHead · Post by **HoseHead** » Tue Mar 11, 2008 3:03 pm

capitolj80 wrote:wow...this topic got hot while i was out....

Then don't be going out.....

You'll find this phorum has huge knowledge, but without arrogance. We generally understand the adage where as the only dumb question is the one you don't ask. I hope we helped answer yours or at least provided some education.

Sometimes we take some time to respond. Today was your lucky day. I'm just doing some bench testing for a system build in a few weeks, stopped to pop a brown and checked the Phorum. Later.

HH

Post by **VW337** » Tue Mar 11, 2008 5:18 pm

stipud wrote:I knew it!

Here's gkitching at home...

Nice beaver shot......

couple more box questions

couple more box questions

Re: couple more box questions