Printer Friendly Forum Posts - How Does a Fibreglass Enclosure Work w/Sub Facing Inwards?

Hello all,

I was wondering how a fibreglass enclosure works when the sub is facing inwards. Is there a certain amount of room needed inside the enclosure? Is it less than a sealed rectangular enclosure?

If you do not know what kind of box i am talking about, this is quite similar.

posted_image

Thank you

It works the same as a woofer normally mounted. Sealed enclosures are pretty forgiving of miscalculations of sizes, up to 30% if I'm not mistaken, so just build it to the specs of the sub and it should work just fine. Go for it!

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Pure Noize

Works exactly the same as a normally mounted sub, this is becuase when you have the woofer basket mounted outwards (inverted) you wire the sub backwards ( ie + becomes - and - becomes +). The airspace is simliar to that of a normal box but rember the sub dusnt displace any airspace like it would in a conventional box. Good to see another aussie on here

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Clarion DB36MP
Infinity Kappa Perfect 10"
Respone 800w Mono
ALPINE MRP-F250
*Custom fabrications*

I just got done with this one, this sub is going to be reverse mounted also.
posted_image

that mountng style is often used when enough air space isn't available. doen't make much difference in sound.

The concept of the speaker working in that type of enclosure is all the same. When the cone/magnet end of the speaker is inside the enclosure, it takes away from the internal volume, which is the reason its a good idea to have the specs around when building an enclosure. So, if you poke the speakers rear end (magnet/basket) out of the enclosure, the enclosure can be smaller...a little. So, when the speaker is inverted like this, the cone actually contains air specific volume also. It should be figured as additional volume with the enclosure volume.

So now there is 2 ways of figuring: The enclosure can be smaller because it no longer contains the speaker magnet, basket, and the rear airspace of the cone. Additionally, the enclosure can be even a little smaller because the cone is reversed, which adds to the overall internal air volume....regardless of the type of enclosure.

otto34 wrote:

I just got done with this one, this sub is going to be reverse mounted also.

Oh......I see. From the first picture you posted I assumed you were using a sealed enclosure, but what you are building is a ported one so the 30% rule does not apply. Ported boxes are not as forgiving. I am not sure how far off you can be on a ported box...it depends on the tuning frequency you are shooting for, especially if you are going for spl or just an overall uniform sound. That brings in a lot of factors like roll of frequency, resonant frequncies of the interior and sub, etc.. If anyone can chime in with a more clear answer help me out, otherwise I gotta dig out my notes! posted_image

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Pure Noize

It was mainly to save room with the box, its going in an extended cab sonoma so I needed all the room I could get. And I am sure the dimensions on a ported box have to be damn near dead on for the box and the port rather than a sealed where you can be off a tad and it wont matter.....

hi guys

will anyone let me know is the sub encloser is only the fiber glass or is the mdf also in it is there any cal for the encloser

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domant

jlord16 wrote:

Works exactly the same as a normally mounted sub, this is becuase when you have the woofer basket mounted outwards (inverted) you wire the sub backwards ( ie + becomes - and - becomes +). The airspace is simliar to that of a normal box but rember the sub dusnt displace any airspace like it would in a conventional box. Good to see another aussie on here

You're joking right? Are you telling someone to reverse the polarity of their sub?

Yes, thats what you are suposta do when you invert a sub

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Clarion DB36MP
Infinity Kappa Perfect 10"
Respone 800w Mono
ALPINE MRP-F250
*Custom fabrications*

jlord16 wrote:

Yes, thats what you are suposta do when you invert a sub

Ummm, I think I'm gonna call BS. Subs (or any speaker for that matter) operate on AC current (i.e. waves a.k.a. soundwaves) so that necessary isn't so unless you had phase problems which are almost nil with sub frequencies and also he seems to be using only one sub. If I'm wrong about this someone's gonna have to prove it. Keep positive and negative the way they are and things will be fine, but I will say reversing them won't hurt either.

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Pure Noize

domnic wrote:

hi guys
will anyone let me know is the sub encloser is only the fiber glass or is the mdf also in it is there any cal for the encloser

I' m not exactly sure what you are asking but I'll take a stab at it. If you are asking if a sub enclosure is fiberglass or mdf the answer is it can be either or a combination of both. Calculating enclosure size is done with the finished product no matter what the material used to make it. There is a woofer enclosure calculator in the blue section of the page over here <----------------------------------------- under "car audio".

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Pure Noize

Most people invert subs polarity when they are inverse mounted. in some cases normal polarity is best. It depends on many factors that can only be found out by trial and error. The idea is so that the sub is still in phase with the rest of the speakers. Of course it wont hurt the sub. Do a search if you dont beleive me, might be suprised what you find............

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Clarion DB36MP
Infinity Kappa Perfect 10"
Respone 800w Mono
ALPINE MRP-F250
*Custom fabrications*

Oh ok. You may be right b/c I know some pioneer head units have a way to set the head unit for the sub if it is inverted which just maybe a phase switch.

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Pure Noize

It all depends on the equipment and other variables :)

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Clarion DB36MP
Infinity Kappa Perfect 10"
Respone 800w Mono
ALPINE MRP-F250
*Custom fabrications*

jlord16 wrote:

It all depends on the equipment and other variables :)

Yeah, I kinda knew that but I wanted YOU to clear it up for the new guy. He might have took your first post as "gospel" without realizing there are other factors to that decision. I'm not doubting your knowledge but would just like to clear up any misconceptions about acoustic theory before they got out of hand. From my experience you wire them up normally unless something just doesnt sound right. Thanks for the info!!

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Pure Noize

Alright point made. Its just that "most" times the question is asked on any car audio forum, they say wire in reverse first, then evaluate, and it has worked in my expericence (is the glass half empty or half full sorta approach) Thanks for that :)

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Clarion DB36MP
Infinity Kappa Perfect 10"
Respone 800w Mono
ALPINE MRP-F250
*Custom fabrications*

Ok, I'll step in here and say NEVER reverse polarity of a sub, unless you want to be buying a new one anytime soon posted_image

I would suggest you go back and revise your electrical theory before posting further comments that embarrass you posted_image

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Clarion DB36MP
Infinity Kappa Perfect 10"
Respone 800w Mono
ALPINE MRP-F250
*Custom fabrications*

IM WITH JLORD16 ON THIS ONE.

crazyjim wrote:

Ok, I'll step in here and say NEVER reverse polarity of a sub, unless you want to be buying a new one anytime soon

Here's a heads up....the electrical signal that makes the driver (woofer, tweeter, etc.) move is actually AC current which means it switches polarity. They are marked as positive and negative as a reference so all of the drivers would be in unison a.k.a. "electrical phase". If it (the driver) were driven with DC current which is only one way then it would stay pushed out (wired correctly) or pushed in (wired in reverse). Hope this helps.

(HOW DID A FIBERGLASS POST TURN TO ELECTRICAL THEORY?!?!?! LOL!!!)

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Pure Noize

A subwoffer is simply a pump which is fuled by the switching of current and the effects of a electro megnetic field. A sub runs on AC current. Negative is simply a reference, that allows a positive to be established. A subwoffer or ANY speaker for that manor will no suffer any mechanicla or electrical problems or be put under undue stress by inverting the wiring. Inverting a current simply chages the reference point and a new one is establised. The voice coils on a speaker are capable of taking current in any direction, the only thing that will be effected is which way the cone will move with a differnt signal (in phase or out of pahse). And on that matter, the pahse of a speaker is only an arbitary reference point that says + is + and - is -. When you are more familiar with electrial theory come back and correct yourself posted_image

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Clarion DB36MP
Infinity Kappa Perfect 10"
Respone 800w Mono
ALPINE MRP-F250
*Custom fabrications*

jlord16 wrote:

A subwoffer is simply a pump which is fuled by the switching of current and the effects of a electro megnetic field. A sub runs on AC current. Negative is simply a reference, that allows a positive to be established. A subwoffer or ANY speaker for that manor will no suffer any mechanicla or electrical problems or be put under undue stress by inverting the wiring. Inverting a current simply chages the reference point and a new one is establised. The voice coils on a speaker are capable of taking current in any direction, the only thing that will be effected is which way the cone will move with a differnt signal (in phase or out of pahse). And on that matter, the pahse of a speaker is only an arbitary reference point that says + is + and - is -. When you are more familiar with electrial theory come back and correct yourself

Are you concuring with me or u saying I need to become more familiar with electrical theory because we are saying the same thing.

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Pure Noize

Bhaha im the only person i know that uses the word "concuring" lol. But yeah i agree with you, that was my response to what our little n00b friend said

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Clarion DB36MP
Infinity Kappa Perfect 10"
Respone 800w Mono
ALPINE MRP-F250
*Custom fabrications*

aiya... I disappear for a couple of months (lots of hell) and the first thread I peek into has another monster...

Can't be helped I guess... rhysem123 listen to the veterans... they may seem like they are fighting, but they are just repeating the same thing with different vocabulary...

as for crazyjim, his information is misleading. rversing the polarity does not hurt the sub. It affects sound quality, but that is based on how you are setting your system up and the various factors on how your system is put together.

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Never send your ducks to eagle school.
The difference between ordinary and extraordinary is that little extra.
The 3Ls of life: Learn from the Past, Live for the Present, Look to the Future.

rhysem123, sorry for highjacking your thread but i had to prove a point and djdowdell and i are now prity much in agreeance, hope this has helped your knowlege abit mate

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Clarion DB36MP
Infinity Kappa Perfect 10"
Respone 800w Mono
ALPINE MRP-F250
*Custom fabrications*

jlord16 wrote:

rhysem123, sorry for highjacking your thread but i had to prove a point and djdowdell and i are now prity much in agreeance, hope this has helped your knowlege abit mate

I "concur" with your apology to rhysem123!!!

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Pure Noize

I will go back to the original post regarding reversing the sub. The amount of room the sub will take (or give) by being reversed will be very small. WAAAAY less than the 30% variance. You are probably looking at .1 ft3 maximum that the sub takes up when mounted normally. Inverting the sub may change the internal volume by about .11 max. It shouldn't be a deal breaker, even with a ported box. Usually, when you are tight for room, inverting the sub is worse cause you now take up more physical space on the outside than if you built the box to fit the sub volume in the first place. That's just my opinion.

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The Flakman
I feel strange. I have deja vu and amnesia at the same time.

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