My Poor 3000gt Vr4-help Me Change Speakers-long!!!

I'd mount the potentiometers somewhere you can get to them, just run good gauge speaker wire to wherever they are at.
You can (and probably should) get locking potentiometers, so they don't vibrate out of place.

Send Dan an Email (or maybe he'll see this) and ask him... 1200 watts, RDO operation, would this void the warranty. I'd guess no... although usually warranties simply don't cover thermal failures, so you'd have to feel comfortable that you wouldn't have a thermal failure, wired this way.
The actual fact that you'd be running it in RDO won't impact your warranty, any more than say running it sealed, or dual-chamber vented, or free air would void your warranty.

The four Illusions are your easy option, but it also seems the least likely to give you any gains over what you have now, that's all.
After all - at least by virtue of their specs... the ND12 isn't "in another class" or anything, where the Brahma would be (and mostly by motor architecture and Xmax rather than by traditional T/S specs):

Alchemy Xmax: 12mm ND12 Xmax: 15mm Brahma Xmax: 27.5mm
Alchemy Vas: 3.8cu.ft ND12 Vas: 3.6 cu.ft Brahma Vas: 1.31 cu.ft.
Alchemy Qts: .39 ND12 Qts: .26 Brahma Qts: 0.45
Alchemy Fs: 22hz ND12 Fs: 26hz Brahma Fs: 28hz

The ND12 has a slight Xmax advantage, and it looks like the ND12 likes a smaller box as well. The caution flag would be a very low Qts, which would seem to indicate that the ND12 probably would be more ideally suited to ported apps.
The strong motor of the ND12 (low Qes - .28) and higher resonant frequency does indicate that the ND12's should be very much more efficient than the Alchemy's, and that they will also be stronger in the upper end of their spectrum, rather than the bottom octave, which (ironically, right?) should be where the Alchemies are more ideal.

Unless the Alchemy is currently in a box that's simply too small for it...
The ND12 being happier in a smaller box might "fit" better, if that is the case.
And it's higher efficiency might make you happy... might even warrant a conservative reduction on your gain controls, which has potentially some benefit in terms of cleanliness.

That low Qts is the only thing that has me concerned at all. And EBP, actually...
I don't have any experience with the ND12's, but if you can find people who have, I'd bet you can get some opinions of their performance, sealed.
Generally, a Qts below about 0.45 means "ported"...
And an EBP (which is simply Fs/Qes) over 50 generally means "ported" also...
This sub's Qts is .26, and EBP is 93., that's why I say that.

But it really boils down to how it will peform relative to what you have now, that's what we care about.
Is the Alchemy currently squeezed into a box that's too small, by chance?

 

2 SI mags.....they will work very well with 600 watts and vented......K-mart has 2 in the trunk of his 240SX and it is damn loud and sounds real nice with about 700 or so watts apiece......I am only going to send mine 700 watts when i get it....hopefully nest week.

Scott, SC

 

Hatches and trunks have shown incredibly flat (as far as F3's are concerned) responses with single Magnums. With numerous Magnum installations there is usually a slight rise in the response below 25 Hz due to the results of compound woofer alignments. MValley heard a pair of them up at a WV meet a while back. He can vouce for their "lack" of low-end. Kevin (the black 240SX on my web page) is doing 140's at the headrest at 30 Hz. The silver Camaro (hatch) on my web page also has a slight rise at 20 Hz on an RTA with a single driver in 0.8 cubes sealed. Not to mention sounding incredible at the same time. We had soooo many people ask us "you have tweeters in the A-pillars don't you" when we were at the Atlanta import show this august. That's really cool when your front speakers are literally on the floor.

 

You won't be cutting the power in half if you do the RDO thing.
Two Brahma 15's would be happy with 1200 watts in RDO mode... per Adire's own documentation.
And then you'd have the 1 ohm total load you are looking for.B)

Regardless though, don't think of "power = output"
I'd much rather think "efficiency = output", and that's a function of the enclosure, relative to the subwoofer.
So, you haven't heard "2400 watts worth of output"...
You've heard four subwoofers in that enclosure whose resulting efficiency was such that it took 2400 watts to reach the output level you were experiencing.
Put another way...
You'll likely see larger swings in output by varying the enclosure size, given a particular subwoofer and amplifier, than you would by varying amplifier power, given that particular subwoofer in a given single enclosure.

The four Illusion ND's, I'd see if you can gather (from forums) opinions of people who have run them sealed, see what the thoughts are.

My vote (especially since your concerns are SQ and output) is absolutely for the two Brahma 15's in that enclosure (with a new baffle), running RDO, rather than running them on just 600w each.
Although I think you'll WELL eclipse the output of your four Alchemies right now, if you did do the Brahma's traditionally, on 600w each.
That is a lot of power, after all.

 

With that power, and the space you have to play with, you could seal the Brahma 15s and expect alot more output and better SQ than you are seeing with the Alchemies. Simple gainmatching will suffice, so no, you woln't need to overdrive the amp. If you choose to port 2 B15s in a hatch of a car that small, you are a braver man than I am.

The Tumult, I cannot really comment on it yet. I will be using one in the SPL Camino, but right now I am not. I might be a bit concerned of overbearing low end thanks to the ungodly FS. To me that is a plus (a bit of tweeking should flatten it really nicely). Such a low FS and the ability of the added excursion to keep the responce of such low notes flat. I love crushing low bass . Actually I like the ability of the woofer to go low. Nothing says well done system like a totally neutral responce from 20Hz to 20KHz.

As far as the Sexy factor... It is a shame you can't invert, because the Brahma and Tumults have sexy butts B)

 

It's a shame you can't just leave them out there like this:



Now THAT is sexy

 

Well, consider that the box for two Brahma 15's sealed, for a 0.707 Qtc alignment, works out to 5.5 cu.ft... Sound familiar? :lol: You said you've got 5.7, right? A new top on the box, and it's a drop-in affair.
The RDO can be set to leave the subs with their existing Qts (and Qtc), with a 0.707 alignment.

Remember... wired for RDO, Qts (or Qes, or BL..) won't be any different at all than it would be if you had the voice coils wired in parallel.

But it would be fun to have that little potentiometer, to bring the Qtc UP from 0.707, for a little more kick here or there... just like having it in a smaller box, essentially... a little more aggressive curve.
Just an additional control that you'd be afforded, in addition to the double the RMS power that you'd be able to feed the subs.
Two birds with one stone... even though you only requested one of those birds, right? :lol:

Read this document a little more closely.
Let me select a few statements from the document:
"[RDO] allows you to vary the Qts of the driver... [anywhere] from the "nominal" Qts up to nearly double that value."
"[RDO] is typically useful in sealed or infinite baffle installations."

There are very fundamental reasons why RDO operation differs from throwing a resistor in-line.
First of all, consider that any electromagnetic motor (including voice coils) can function either:
1) as a motor (when fed electricity, they will generate motion)
2) as a generator (when motion is induced, they will generate electricity)

But in order to operate as a generator, a load needs to exist. The higher the load, the higher the amount of current that the generator will try to generate.

What you are doing is feeding just one coil of the subwoofer, which makes it move, obviously.
The second coil is just empty.
If you just shorted it, it wouldn't generate any electricity, wouldn't do anything, sub would behave as normal.
In putting a potentiometer (or resistor) across it, you are making that second coil behave as a generator, which has it's own counter-effect on the motion of the voice coil.
You are manipulating back-EMF to your own benefit, if desired (you can always, with a potentiometer, turn it "off" )
And the current being generated through the potentiometer is dependent on the impedance curve of the subwoofer, and the frequency the subwoofer is moving at. Pretty cool. B)

On the other hand, if you just stuck a resistor in-line, you would simply be presenting a higher impedance load (subwoofer impedance + resistor) to the amplifier... it would produce less power, and then some portion of the power it did make would then be bled across the resistor... and for no good. Just waste.
Definitely wouldn't accomplish the same thing.



Your 5.7 cu.ft. is virtually ideal for a pair of Brahma's, sealed.
Ported, they would like a bigger box, and your efficiency would definitely be compromised. I don't think you could do two Brahma 15's ported.
Sealed, yes... ported... I'd do the 12's instead.

If you are going to go with two Brahma 15's sealed, why not go RDO?
If you don't, you'll send 600 watts to each of them.
If you do, you'll send 1200 watts to each of them.
That's my logic behind it. :yes:

Yes, I think 600 watts would be fine for a single Brahma. That's a lot of power, after all, and we've got some big, high-excursion beasts here.
But I also think you'd like to have the 1200 watts per each on-hand, and I don't think in your experienced hands it would be too much power for them..

You could just run one voice coil per Brahma without doing RDO also, if you don't think you'd use it (just short the other voice coil with a jumper wire)...
But since potentiometers can be set down to 0 ohms of resistance anyways, why not do the RDO if you were going to go this route anyway? B)

 

The amp is simply seeing one voice coil per subwoofer.
The other voice coil the amp never sees - it's not getting any signal from the amp at all... it's simply not in the amp's equation.

So your amp would see 1 ohm... two ohms per Brahma (one voice coil), wired in parallel to give your amp that 1 ohm load.
That's all your amp sees.
And it won't vary one bit with the potentiometer setting.

Now, picture the other two voice coils.
Electrically not connected to anything.
Until you hook up a resistor or potentometer across it. B)

Like I said, an electromagnetic motor can act as:
1) a motor (when electricity is fed into it, it turns it into force)
2) a generator (when force is applied to it, it generates electricity)

So, you have VC #1 powered up, the subwoofer is moving in and out as it should.
VC #2 isn't doing anything.
But when you hook up a resistor across it, essentially it's generating electricity that's being dissipated through the resistor. And as such, that presents it's own impedance to the circuit. It's controlled back-EMF if you will.

There are a few reasons you might have heard that myth, btw.. that hooking up only one VC is bad. Here's some "off the top of my head" possibilities:
1) is that a newbie might not get the impedance they expected... easy to damage something...
2) is that the sub won't "handle" as much power as rated... easy to damage the sub if you don't know better...
3) is simply that it's not intuitive... what? leave one not connected?
4) could be the Ohm's Law rationale (if you consider leaving one totally unconnected, not shorted)... The more resistance you put across a VC, the more resistance against motion it would have (and vice versa)... well, "unconnected" means "infinite impedance".

This is definitely a case where we know what's going on:
BL won't be any worse than if you wired the VC's in parallel.
Qts can be stock, rated Qts with the potentiometer set down to 0 ohms.
The downside to RDO operation is that your powerhandling is cut by about 1/4...
Well, we're talking about a 1600w RMS sub here... so that would be 1200w RMS, conveniently enough that's what you are feeding it. And probably not even that, because it sounds like you run pretty conservatively anyway. B)

Does that help?
The potentiometer isn't in the circuit at all, between the sub and the amp.
Just picture VC #1 hooked up to the amp, and VC#2 is the one with the potentiometer wired across it.
It doesn't change the resistance or do anything like that for the sub.
It's there to present a "load" for our little "generator", if you will.
Honestly - you could hook up a light bulb, and the motion of the subwoofer (being pushed by VC #1) would cause VC #2 to generate enough electricity to light the bulb. Light bulbs are resistive too! B)
Nifty stuff!

 

I've got a JBL GTi 12" myself here also.

Interesting that you mention it, as your "reference standard".

I'm not sure if you know how well you understand the "how it works" of the XBL^2 technology, or the "how it works" of the JBL GTi...
But I think you should definitely look into it, it's very cool...
http://www.jbl.com/car/products/gti/gti_tech.asp
...and I think you'll be pretty surprised to realize that the two technologies (XBL^2 vs. DDD) accomplish essentially the same thing...

Both work to the end of flattening the BL curve, by creating a motor that allows coil count in one gap to increase as the coils leave the other magnetic gap. Basically, this allows the motor to maintain a constant number of coils in "a gap" at any point in it's linear excursion range, which means BL will be constant at any of those points.
Both technologies accomplish the exact same thing, fundamentally.

It's almost a shame that the GTi approach requires SO many custom parts... custom basket, former, opposite-polarity coils, opposite-polarity gaps, ferrite, neodymium, etc... it's a wickedly expensive implementation that almost seems silly when you consider the simplicity of XBL^2, and that it accomplishes the same thing, essentially with a simple groove being the extent of the non-standard custom manufacturing. B)

You might be even more impressed to find out that not only is the XBL^2 implementation simpler and less expensive, but more successful in it's results (DUMAX confirmable).
In other words, I think you'll have a new standard.

Definitely check out the articles on JBL's tech info page for the GTi that I linked, it's a very cool technology, but I think you'll see what I mean.
I picked up my JBL GTi after my Brahmas and my own XBL^2 prototypes, because their motor technology did accomplish the same thing.
The JBL GTi is the closest competitor, IMO. B)

Especially since you mention the GTi as your "reference standard", I'm going to be particularly excited to hear your reaction to them, and impression of them if you do decide to go the Brahma route.

 

Oh, the OLD ones. Well, I'd still prepare for a new standard. :lol:
The old GTi's were something... but traditional stuff basically.

I've been pondering the idea of hooking up a single potentiometer to both subs...
I'm thinking it might cause troubles in that essentially you'd have those two coils wired together to each other, and one's generated voltage would be able to go right over to the other sub, it's voice coil inherently being lower impedance than the resistance of the potentiometer.

Still, obviously it would be nice to have both subs set to the same resistance (not that you couldn't measure it with a DMM).
I'd suggest a dual-potentiometer like this:
http://www.mouser.com/catalog/specsheets/143109.pdf
I'm not sure how capable your potentiometer will have to be, in terms of wattage, heat dissipation.

That way, you at least have just one knob, coordinated settings. B)

 

Well, SPL is always hard to guess.
More than your Alumapros, I'm sure is safe to say.
Certainly way over my "make me happy" threshhold for SPL.... two 15's and 2400 watts of power behind them... that's SPL-competition material there, not SQ-machine, after all... :lol:

And FR is what makes this so cool... the RDO, I mean...
Your enclosure will essentially result in a nice 0.707 Qtc for your subs. Many regard that as the perfect SQ alignment.

With a twist of the knob, you can actually change that frequency response, raising the Qtc... making it hit a little harder higher up, rolling off a little faster...
You can tweak the sound to your liking with the knob.
Much like being able to vary the volume of your enclosure down and back up with a knob.
How cool! B)