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Bostonjlguy
05-02-2012, 01:30 AM
I have a sealed box that was built for 2 12's. The box itself is about 26" wide 14 inches tall and 32 inches deep. The box has cut outs for 2 12's on the front. I planned to put the box in the trunk so those two subs would be rear firing. I would like to put two more 12's in the box; however, I cannot fit them on the same face of the box. I was thinking about putting them either on the sides of the box towards the back to keep the woofers as far apart as possible. I am curious if this will cause sound canceling due to being out of phase. The box is braced down the center currently making two separate chambers. I am wondering if it would be best to put two dividers to make it a four chamber box, or should I just build a box putting all subwoofers rear firing. I am putting these in a trunk so space is kind of an issue. I don't want to hear just go with a 15 or 2 12's. I have been doing car audio a long time and am looking to experiment and have a little fun. Suggestions please.

Ionakron
05-02-2012, 01:44 AM
lol. Experiment? mount the subs cone* to cone*. lol then you can fit them both on the same face!

edit-wire the subs on the outisde of the box out of phase.

dirtyunclerandy
05-02-2012, 01:46 AM
could you do all four on the top of the box? I think that would be your best bet.

Bostonjlguy
05-02-2012, 01:50 AM
Split into 4 chambers each compartment would be would be a over a square foot. Subs require a square foot. It is more an issue of sub placement and sound canceling.

---------- Post added at 11:49 PM ---------- Previous post was at 11:48 PM ----------

Can you do that with any sub? How does it sound?

---------- Post added at 11:50 PM ---------- Previous post was at 11:49 PM ----------


could you do all four on the top of the box? I think that would be your best bet.

I don't think they would all fit, and I would have to rip out the center brace

Bostonjlguy
05-02-2012, 01:51 AM
lol. Experiment? mount the subs cone* to cone*. lol then you can fit them both on the same face!

edit-wire the subs on the outisde of the box out of phase.

So wire the subs isobaric and then wire the voice coils backward on the subs on the outside of the box?

Ionakron
05-02-2012, 01:51 AM
yessirrr. Do it right and it'll be louddd.

dirtyunclerandy
05-02-2012, 01:54 AM
you might need a new box. I don't think subs on the front and sides would sound very good. Sure someone with more knowledge will chime in.

Bostonjlguy
05-02-2012, 01:54 AM
I think I will try that! For fun! I never thought of that. I have been doing car audio for a long time, but I posted this because of reasons like that. Sometimes its best to get ideas from other people.

Ionakron
05-02-2012, 01:56 AM
I think I will try that! For fun! I never thought of that. I have been doing car audio for a long time, but I posted this because of reasons like that. Sometimes its best to get ideas from other people.

The whole push-pull(isobaric) idea likes smaller boxes tbh i believe but should still work to play around with. I'm not a car audio expert though. Someone feel free to chime in on this!

Bostonjlguy
05-02-2012, 01:57 AM
yessirrr. Do it right and it'll be louddd.

How would you wire the dual voice coils. I was gonna wire them all together series parallel to get a 2 ohm load. My mono block does have 2 sets of terminals parallel to one another. So if I can at least wire two of them together to get a 4 ohm load, I can use the amp to get the final impedance to 2 ohms. What would that do to the polarity though. Would that mess with my amp having a positive and negative current?

myjaja
05-02-2012, 02:00 AM
If you dont want to hear "keep the two 12's and put them in a good ported enclosure," then I say you can get a good idea from this guy.


http://www.youtube.com/watch?v=PldKRy7eFeg&feature=related

Ionakron
05-02-2012, 02:03 AM
How would you wire the dual voice coils. I was gonna wire them all together series parallel to get a 2 ohm load. My mono block does have 2 sets of terminals parallel to one another. So if I can at least wire two of them together to get a 4 ohm load, I can use the amp to get the final impedance to 2 ohms. What would that do to the polarity though. Would that mess with my amp having a positive and negative current?

Unfortunately i can't help you here. Unless you're amp has a Phase switch on it : p Somebody help this guy out! come on!

Bostonjlguy
05-02-2012, 02:10 AM
Unfortunately i can't help you here. Unless you're amp has a Phase switch on it : p Somebody help this guy out! come on!

Being that I am an electronic technician, you would think I could answer this question for my self. I mostly deal with chip boards and chips.

hispls
05-02-2012, 02:20 AM
If you're dead set on the idea, where you mount them in the box shouldn't make a lot of difference. For preference I'd do 2 firing back and 2 firing to either side, though up and back may do about the same.

Bostonjlguy
05-02-2012, 02:25 AM
If you're dead set on the idea, where you mount them in the box shouldn't make a lot of difference. For preference I'd do 2 firing back and 2 firing to either side, though up and back may do about the same.

Yes, but you can actually have sound canceling which would make 4 subs pointless at that point it would be the same with 2

hispls
05-02-2012, 02:27 AM
Yes, but you can actually have sound canceling which would make 4 subs pointless at that point it would be the same with 2

In that application you'll 99% probably gain. As some point out, probably more gains to be had with other methods, but considering the pathlengths and how close you are to any given wall in the trunk phase issues between subs will be negligeable. We used to do a lot of those back in the day and I have used up and back with success.

sacsking916
05-02-2012, 02:28 AM
Didnt read, just build a new box. You'll have a helluva time getting it to fit being the box is built to correct specs

sacsking916
05-02-2012, 02:31 AM
Yes, but you can actually have sound canceling which would make 4 subs pointless at that point it would be the same with 2

Not really. A lot of people use boxes that have 2 subs up and 2 subs forward/back

Bostonjlguy
05-02-2012, 02:42 AM
In that application you'll 99% probably gain. As some point out, probably more gains to be had with other methods, but considering the pathlengths and how close you are to any given wall in the trunk phase issues between subs will be negligeable. We used to do a lot of those back in the day and I have used up and back with success.

Would you separate the subs into 4 individual chambers or 2 subs in each chamber?

hispls
05-02-2012, 02:46 AM
Would you separate the subs into 4 individual chambers or 2 subs in each chamber?


Separate chambers is typically optimal.

Moble Enclosurs
05-02-2012, 08:58 AM
Hey Guys,
Well, as far as using the amount of subs and displacement within a trunk, and as long as the box is sealed, you will not notice much of a difference from a sealed obx of the same or similar volume if they were on the same baffle. If you were using them for a larger "room" then that is where the phase differences will start to matter more, but since they are low frequency waves, and you are using them in a vehicle, 90 degrees on either top, bottom, left, or right will not make a big difference with a sealed design because it already has a smooth phase from minimized cancellation acoustically anyhow. The only issue you would run into is if you were wiring them incorrectly in this case, BUT if the enclosure is large enough (though in this case it is not), it can make a difference as well regardless of the environmental factors.
SO, for 4 12s in a vehicle in an averaged 1 cube per sub, you will not have many changes from that of a single planed baffle design, with the exception of wiring phase. Now, you WILL notice a drop in the lower range a BIT more than normal if you were to compare, but it should be less than an audible difference greater than 3dB.
Simply put, with enough power, and the correct wiring (as 90 degrees is not a major change in phase at all) you will be fine, but do not expect it to outperform more efficient layouts or styles (ported, tapped, quasi, etc).
The idea of isobaric in this situation is not a bad idea if running sealed. Mainly you will notice an increase in output from 2 drivers and not a notice in response curve cutoffs. So, they will "perform" quite similar to a dual 12 setup with double the volume, but with the ability to increase power handling and control from a smaller volume. In turn, that will flatten out the response more.
The more compression you have at the listening area, the more smoothness in the curve will be noticable. For example, those with 6th and 4th order walls that get a great amount of passband range. That is due to the ratio of box volume to cabin volume being closer to a 1:1 than say a 2 cubic ft box in an suv. The more compression you have, the better the output and with power as a factor in relation to output, the more efficiency you will have AS LONG AS you have the power to run your setup efficiently.

Hope that helps!

Moble Enclosurs
05-02-2012, 09:13 AM
Separate chambers is typically optimal.

Mainly in terms of mechanical limitations. Psycho acoustical effects will be nearly identical from separate chambers to a common chamber of equal volume if all other factors such as placement are the same. For instance, if you consider looking at the layout of a design for say, 2 12s (example), and it uses the common "dual box" idea of utilizing separate chambers (which is like taking 2 boxes of equal physics and gluing them together), and then compare that layout to one with a common chamber where say the port is located on the side rather than in the middle (another example), then the main differences at that point come from port area..not length, not volume.....just area. And area has a direct relation to cutoff frequencies.

SO, if area is the same (constant) and physically all others are constant, the main differences will not be in audible terms, but mechanical terms, where xmax and linearity can be controlled much easier (though linear response is an audible effect, in this case it relates to mechanical distortion more importantly).

This is why having a smaller port area will lower the tuning, BUT also lower the efficiency below tuning, thus requiring more output to maintain audible authority. BUT, take a port area much larger, and you increase efficiency. SO, the differences and relationship between a separate chamber and a common chamber design are minimal and alike if all other factors of the design are constant. They are not identical, just alike enough to consider them similar in terms of output.

The same effect can be said for cutting a port into 2 separate ports of equal length. Those ports, ONLY when compared to a single one with the same AREA, are so similar in output, the differences are usually not very audible.
So, it can be said that optimism in relation to compression characteristics are dependant more on the exact design layout and full specs, rather than a general use of the concept.

hispls
05-02-2012, 11:53 AM
Mainly in terms of mechanical limitations. Psycho acoustical effects will be nearly identical from separate chambers to a common chamber of equal volume if all other factors such as placement are the same. For instance, if you consider looking at the layout of a design for say, 2 12s (example), and it uses the common "dual box" idea of utilizing separate chambers (which is like taking 2 boxes of equal physics and gluing them together), and then compare that layout to one with a common chamber where say the port is located on the side rather than in the middle (another example), then the main differences at that point come from port area..not length, not volume.....just area. And area has a direct relation to cutoff frequencies.

SO, if area is the same (constant) and physically all others are constant, the main differences will not be in audible terms, but mechanical terms, where xmax and linearity can be controlled much easier (though linear response is an audible effect, in this case it relates to mechanical distortion more importantly).

This is why having a smaller port area will lower the tuning, BUT also lower the efficiency below tuning, thus requiring more output to maintain audible authority. BUT, take a port area much larger, and you increase efficiency. SO, the differences and relationship between a separate chamber and a common chamber design are minimal and alike if all other factors of the design are constant. They are not identical, just alike enough to consider them similar in terms of output.

The same effect can be said for cutting a port into 2 separate ports of equal length. Those ports, ONLY when compared to a single one with the same AREA, are so similar in output, the differences are usually not very audible.
So, it can be said that optimism in relation to compression characteristics are dependant more on the exact design layout and full specs, rather than a general use of the concept.

OP is using a SEALED box

Moble Enclosurs
05-02-2012, 12:03 PM
OP is using a SEALED box

Yes, this is true, but the same mechanics apply for cone control and response. Sealed enclosures can be "tuned" and designed incorrectly as well, because a tuning does not control the entire response curve or sound. Only in ported designs does it increase efficiency as a given narrowbanded range. In a sealed enclosure, it is still important to understand the effects of volume.

Bostonjlguy
05-02-2012, 04:26 PM
Yes, this is true, but the same mechanics apply for cone control and response. Sealed enclosures can be "tuned" and designed incorrectly as well, because a tuning does not control the entire response curve or sound. Only in ported designs does it increase efficiency as a given narrowbanded range. In a sealed enclosure, it is still important to understand the effects of volume.

In your opinion, would I be better suited going with the isobaric push pull method or putting all four subs in one box. The box is sealed and is large enough for all 4 woofers. If I go Isobaric, will I still see the same amount of volume as if the subs were in one box. Which set-up would be louder. I have considered building two boxes to house 2 woofers each all rear facing. I think if I built one I would not be able to get it in the trunk; however two I could put them in sideways one at a time so they would fit. You are really informative, and I think your the right person to help me out here.

Brian

Moble Enclosurs
05-02-2012, 04:39 PM
Let me message you from here then. Talk to you soon :D

And for hispls, I wasn't trying to be rude, so I hope I didn't come off the right way man. you made a great point. Just wanted to add some info to it is all :D