If your headunit has a highpass crossover that you can use, then you could use the highpass built into the headunit to highpass the signal. Then you would just need the amplifier to lowpass the signal.

And why do you want/need so many speakers?

Just tossing speakers in the rear doesn't give you "surround sound". The sound might surround you, but it's not "surround sound" in the sense used today with the rear speakers playing the proper (i.e. non-staging) sound information. Surround sound and other similar formats would need to be properly mixed in that manor into the recording (or a suitable processor capable of "upconverting" standard stereo to such a format). The vast majority of music is recorded and replayed in a standard 2-channel stereo format.....in which case, the rear speakers are typically a hindrance as helotaxi pointed out. Confusing the soundstage and producing undesirable frequency response affects.

That said; there is some merit the a properly utilized rear stage. This isn't as simple as just tossing some speakers in the rear of the vehicle. To begin to approach a useful result with rear speakers, you would need a L-R (left minus right) summed signal, bandpassed and time delayed. The speakers here wouldn't play a prominent role in the system. They would be used for ambiance only since basically any of the real "center staged" info is removed from the signal via the left minus right signal summation, leaving you essentially with only the left and right ambiance/reverb stuff. Never tried it, but always sounded kinda fun. Though with all of the true surround sound processors available, those are probably a better/easier option since that's specifically what they were designed to accomplish.

Some people swear by surround sound (actual, properly implemented surround sound) for the added ambiance and spaciousness. I did listen to GrampaDon's (another user on here) system in Logic7 and to be honest....it didn't sound all that different. Though it could have been something in the setup or vehicle.....he has a long vehicle with the rear speakers all the way in the back, and IIRC he was just using the 20w amp built into the MS-8 for rear amplification.

700 bucks for a driver with no T/S specs? No thanks...

2nd page of the manual lists T/S parameters: http://www.bostonaco...s/SPG555Man.pdf

I mean the signal being input into the amplifier would need to already be bandpassed. Yes, most commonly accomplished either with the crossover capabilities of a headunit or an external processor. I don't know off hand if the 360.2 has the capability to bandpass or not.

aint no way to make an L7 sound good..I have tried..square subs sound like they are chewing down a good meal

when the hz drop to the floor...

Then you didn't do something right.

Being square has nothing to do with it.

Personally I would try to step up to 0ga.

But the length of 4' isn't a problem.

its going to be around 4ft. at 4awg wire.

How much power are you going to be running?

Is there a short in the power wire somewhere, or possible that the connection is making contact with something?

Can you make the event happen, or is it completely random?

Are you using the internal amplifier in the headunit?

The chassis of my vehicle, so 15' or so.

Just saw this up on a site

http://www.wardsweb....o/sub_foam.html

It seems the installer added foam inside his box???? I understand that this is a home install, and HT and Car audio is two different animals, but surely there is a point to doing this? I see people puting things like, resisn and fiberglass insides boxes to help strenghting the box,. And I've seen people putting clay and other material in as well to change the inside parameters or what not. But what could be the reason in putting foam inside???

When I google the question I'm asking, I get this

http://answers.yahoo...24075957AAgbJXA

So @ this link, is this the answer, well correct answer? If so, then why haven't I seen any builds on here using the stuff?

They are different beasts, but physics remain the same. Some people do things more because it gives them a warm, fuzzy feeling inside than any logical acoustic purpose. But, let's look at this a little more.

First, we would need to determine the potential for standing waves within the enclosure. From what I could find the formula for determining the fundamental frequency for standing waves is;

f = V/2d

Where:

f = Frequency

V = velocity of sound

d = dimension of the parallel walls

His enclosure looks to be around 54" tall (based on the approximately 18" cutout on the baffle, it looks like the overall height is around 3x the size of the cutout, so we'll guesstimate 3 * 18 = 54). The velocity of sound is around 1130ft/sec, or 13560in/sec. Using the above equation, this would give us:

f = 13560/(2*54) = 125hz

So, the fundamental of the standing wave in that enclosure would be 125hz (there will be standing waves at the harmonics as well, but we'll ignore those for the moment since they'll be far enough outside of the bandwidth to not really matter).

Where is the typical subwoofer crossed over? 60-80hz? With a fairly steep slope? With a 60hz lowpass and 24db/oct crossover, the output from the subwoofer itself would be attenuated by 24db before you would reach the standing wave. You would be well outside the operating bandwidth of the subwoofer, at 125hz the output from the main speakers should be dominating the response of the system. So that standing wave won't really be much of a problem to begin with because it will be well enough attenuated and outside of the bandwidth of the subwoofer .

But let's say we do feel that the 125hz standing wave is a problem, maybe we plan to use the subwoofer up that high. We can't only worry about the standing wave itself....we also have to look at what is done to "fix" the standing wave problem if one exists. This guy felt that lining his enclosure with OCF (open cell foam) was a good solution to the problem. Now, the absorption coefficient of an open cell foam is directly related to it's thickness (among some other things). He doesn't state what the thickness of the OCF is....but the wood is 3/4", and the foam appears to be somewhere around twice as thick, so let's assume it's 1.5" OCF. What is the absorption coefficient of 1.5" OCF at 125hz? (absorption coefficient is how much energy is absorbed by the material). It's probably going to be ~ .1 or so, which means it's only absorbing 10% of the energy. 90% of the energy is still present. Pretty ineffective treatment, wouldn't you say?

So let's say you have a really large subwoofer enclosure that has a standing wave right in your problem area, say 50hz (you would need to have two parallel enclosure walls approximately 11 feet apart to have a standing wave close to 50hz). You are not going to be able to throw some 1.5" or 2.5" OCF on the enclosure walls and call it a day. The absorption coefficient of that thickness OCF is going to be virtually zero at 50hz. The foam would need to be incredibly thick, and ideally spaced away several inches away from the enclosure walls, to begin to have a noticeable effect. Not something easily accomplished.

So, moral of the story. Most people aren't going to experience problems with standing waves within the enclosure for subwoofers. If they do, then the solution shown in that link (relatively thin OCF) is not going to do much to solve the problem anyways.

Polyfill has a different goal. The goal of the polyfill is to "trick" the enclosure into thinking the enclosure is slightly larger than the physical dimensions. It can work for this purpose. But the lining on the enclosure walls are not polyfill. For polyfill to work, you need to restrict the movement of the air within the enclosure. Polyfill is essentially pillow stuffing.

Folded or not, still not enough length/area to do anything in the true subbass frequencies.

No, you don't need to completely seal the trunk itself (and really, you wouldn't want to for other reasons related to the vehicle itself).

Some people get crazy with silicon and expanding foam and everything else to seal off the baffle. I run my subwoofer "IB" firing through the ski-hole and didn't go nearly that far in sealing. I doubt anyone could tell a difference in my car. I wouldn't leave gaping holes of course. But I didn't use any silicon or expanding foam or anything for sealant.

Just so everyone knows what's going on in the "Days of DC Power" this has become... Look, I know this has been blowed WAY the F*ck out of proportion, but honestly people, why do you all insist on throwing gas on a bonfire instead of just letting it play out and let us finish this before hanging us on the cross??

How you can blow waiting 22 months for an order "way fucking out of proportion" ?

Just as an FYI, you aren't going to fit a horn that actually functions as a horn into the lower subbass region to fit into a car. Most of them won't fit reasonably into a house, unless the house is built around the horn.

Any "horn" that fits in a car, much less in a trunk, isn't functioning as an actual horn for very much of it's operating bandwidth.

Thanks for your opinion ! But so i've been reading more and more on IB and i read that the vas of the trunk should be at least 3x greater than that of the subwoofers? I've read a few different things about that, but does anyone still think i could try the 2 18's ? I mean.... i really want to try this but i don't want to put my new subs in a lot of danger of being damaged rather than using a sealed box. I need some FAITH !

Did you even read my post? I specifically answered your question. Are you trying for a true infinite baffle setup? I don't think you are, and 3x VAS wouldn't cut it if true infinite baffle was your goal. For a true infinite baffle setup, Qts = Qtc and Fs = Fc. You need more than 3x VAS to accomplish this. The 3x VAS rule of thumb is more of a "close enough" approximation to a true infinite baffle alignment.

I think you are trying simply to run "enclosureless", which for the most part is the best we can do in car audio and what we in car audio refer to as "infinite baffle". It's a technicality in definition. Just because you won't be truly "infinite baffle" doesn't mean the enclosureless arrangement won't work. What's the difference between enclosureless in your auto and true infinite baffle? It's easy to model in any enclosure program, and I briefly outlined in my previous post how the drivers will respond to being ran enclosureless in your vehicle.

Any sub can be ran IB. The only fear of "damage" is in the fear of the person operating the controls (you) not knowing when enough is enough....and this can happen in any enclosure, it's just that with IB the mechanical power handlling is lower than a sealed or ported enclosure.

I beg to differ. It's kinda about noise rejection... mostly just for induced noise from the RCAs.

Your argument is stated incorrectly from the start

Higher voltage has nothing to do with rejecting more noise. The same amount of noise would be induced into the signal. The difference is the level that of that noise in relation to the level of the signal.

This is signal-to-noise ratio, not noise rejection.

But to save you some time......if you are picking up enough noise during the signal transfer that a 2V preamp output headunit isn't sufficient....then you have other problems in the system that need worked on first.

If the amplifier is generating enough noise with a higher gain setting that the noise is audible during playback, then you have other issues in the chain that need worked on first.

I've read different things about IB such as having drivers with a QTS of at least .5 but also read that it should be fine with a daily sub with lower QTS and more subs, bigger sizes.

You have to consider the environment as well. If we were talking about home audio, then yes a Qts of >.5 (ideally closer to .7) and a super-low Fs (<20hz) are pretty much mandatory.

In a car, however, things are different. We get significant boost in the lower frequencies from the transfer function of the vehicle, and most times the trunk doesn't act as a "true" IB alignment. So we don't need the drivers themselves to generate flat response down to 20hz....the car helps us do that

Generally there are two routes that work well for IB in a car.....low Q (< .4) and low Fs (~20hz), or mid Q (~ .5) and mid Fs ( high 20's - low 30's). If you go with a low Q/high Fs driver, then the low frequency response is rolled off too much. High Q/Low Fs (like home audio IB subwoofers) can work with appropriate EQ to tame the bottom end....with out it, they'll be too bloated on the low end.

However, you have to consider how the airspace is going to affect the driver. Chances are you're going to get some increase in Q as a result of the trunk. According to Unibox, in a 15cuft enclosure with two 18" Xcons the Qtc would be .63 with an F3 of 43hz......models pretty well for mating with the transfer function of an automobile.

Maximum output is the same as that of a sealed enclosure because peak output is limited by the same factor; peak linear displacement. So the output potential isn't any lower with drivers mounted IB compared to sealed. The difference is in the response curve. Sealed enclosures will usually have a little more output in the upper-subbass (above 40hz) due to the peak generated by the affect of the enclosure.....however, IB drivers will typically have more output in the lower frequencies (40hz and below) due to the lack of enclosure (a sealed enclosure is essentially a highpass filter, so if you remove that you improve low frequency response). So to say drivers mounted IB have "less output" is typically incorrect as you have to consider what frequency region is being discussed And maximum output potential is equivalent between both alignments.

As for power.....don't apply more than is required Mechanical power handling is reduced for a driver mounted IB since it doesn't have the "spring" of the enclosure to aid it mechanically. Unibox says you wouldn't hit Xmax in a 15cuft enclosure with 3500w until 12hz......but I would focus on what personal experience tells you there.

Long story short....go for it Just be careful, IB drivers are easier to overdrive.

Since u want sq ur doing sealed box right?

Why can't a ported enclosure be used in an "SQ" setup?

Certainly you can. You would however need to externally bandpass the signal, as you can not bandpass all 6 channels at those frequencies with the on-board crossovers. Only channels 3&4 have the appropriate crossovers for your needs.

They don't even post some measurements, some T/S parameters, nothing. Very very limited information on Audioque's website.

Imagine that....they are from AQ, I wouldn't expect any different.

Which is sort of funny because their webpage says "TS measurements taken after one hour break-in from BNIB random samples"....and then they don't actually list any T/S parameters.....?

I'd be a little wary of a 4khz lowpass crossover on a 6.5" mid in a system designed to be used in an automobile. I can only imagine the hole in the FR that develops when these things are mounted off-axis, even if the driver itself happens to be well behaved up to 4khz (which is usually pushing it for a 6.5" driver)........

Not sure I'd base any part of my decision on the opinion of someone who, first, demonstratively doesn't really understand much about acoustics based on the installation and second, bases their decision of "good sound" on how far they can walk away from the vehicle and still hear the sound.

If it is that big of a concern you should design an enclosure without any parallel walls and internally made of constrained layer materials (dampening sort of). This will greatly improve sound (not output!) over a standard 6 wall rectangular/square enclosure made of MDF.

A lack of parallel walls will have zero affect in the subbass. The purpose of non-parallel enclosure walls is to reduce standing waves within the enclosure. For subbass, this isn't going to be an issue to begin with as the dimensions of the enclosure are much shorter than the wavelengths of the sound waves, so standing waves are not going to develop.

For subbass, I doubt there would be an audible difference between a well designed and braced MDF enclosure and some other exotic enclosure material. The resonant frequency of the panels is gong to be too high, and any losses from panel resonance/flexing is going to be too small compared to the driver output to audibly affect the sound. On a meter, I doubt you would see much of a difference either as long as the MDF enclosure was properly braced to begin with.

Notice I explicitly stated I discussing affects in the subbass frequency range here. As we move up the frequency spectrum where the wavelengths are shorter and you are closer to the Fs of the enclosure panels, those issues can start to become problems (although there are far less exotic means of dealing with them). External panel shape can also affect frequency response in other ways in the higher frequency region....but that's neither here nor there.

I believe he was spamming to get to 25 posts, so he could post a WTB in the classifieds.

That is still a waste because you are using the wrong materials for it.

Was getting ready to say the exact same thing.

You want bracing to reduce panel flexing, not CLD.

The question first needs to be: How often do you sit at idle playing the stereo at full out balls to the wall, and what are your goals for the system?