I found this interesting

[dave_Edwards 1]

http://www.buwaldahybrids.com/phpBB3/viewt...?f=7&t=3362

any thoughts?

[johnecon2001 82]

Sounds like it's just phasing the stereo mix out and letting the abnormalities of a song through.

Theoretically, you wouldn't have any cancellation with the fronts because the speakers are already canceling out most of the sound. At least that's how I understand it working.

Dunno if judges would like that or not. Depends on how much he/she likes the "cool" factor that day.

[///M5 2,833]

And you need this in your car to improve what exactly??? Personally I think it is a joke.

[Aaron Clinton 2,372]

I am slightly confused, maybe I need more coffee before detailed topics such as this.

[jonbearsmt 919]

4 ohms two speakers positive to each channel then the negitaves wired togather would be 8 ohms mono. right

[johnecon2001 82]

4 ohms two speakers positive to each channel then the negitaves wired togather would be 8 ohms mono. right

It's more complicated than that.

It's almost like strapping two amps together.. but then again not.

You're forcing the amp to send power to itself, except with a huge resistor in the way. Essentially putting most of the sound out of phase.

[Dave Brooks 0]

I thought it was interesting too. I've seen threads out there on the same topic in the past, but I've never gotten up the gumption to interrupt whatever the project of the day is to try it.

One of these days though... 'cause I'm curious like that.

[ramos 2]

http://www.buwaldahybrids.com/phpBB3/viewt...?f=7&t=3362

any thoughts?

I gotta thought, get the idea out of your head we need to clean up your trunk and the center stack first

[johnecon2001 82]

Did some more digging. Looks like impedance changes when you fade left to right. Presenting an ever fluctuating ohm load. One speaker acts as a ground and the other as a positive L and R.

http://www.audioasylum.com/scripts/t.pl?f=...ge&m=122267

http://www.geocities.com/quadaudio/page13VariousVariety.html

http://en.wikipedia.org/wiki/Quadraphonic#Hafler_circuit

Crazy stuff, I need to read MOAR!

[ramos 2]

It is an interesting concept that has been talked about several times . Just never had time to play around with it

[DevilDriver 28]

I don't think quadrophonic sound is of quite as much use in a vehicle, although I do feel that employing the Haas effect can do wonders for your midbass output and "ambience". From what I posted on CA.com...

Bored.....

So on topic:

Re: Localization of subwoofer

- Given the appropriate lowpass filter, a subwoofer's direct sound is not easy to locate. It's the reflected sound that is a concern: it typically excites resonance in various parts of the vehicle that have considerable storage problems. From this, it can be quite easy to localize a subwoofer. Thus, it is good to cross your mids as low as possible (or bring a subwoofer up front).

Re: Left/Right vs Front/Back

- If there were front/back information available in a stereo recording, I would agree that it was as important. However, there simply isn't. There are circumstances in which it can be important, but never as important as L/R.

Re: Why midbass?

- Typical 6.5" midrange drivers are virtually devoid of quality midbass output. A lot of drivers out there should not even be used below 100 Hz (particularly in those pre-made component sets that so many people use). So in the rare event that someone has designed a quality driver with good midbass, it is worth noting. Let's not forget that there is a lot of fundamental and second or third order harmonic information below 200 Hz.

Re: The use of rear fill

- This is a long one. First, space up front is limited. Is it the easiest location to put an 8" or larger midbass? Definitely not. So how do we achieve that visceral output from the midbass that is so enjoyable? The only option left is to find a spot in the rear (typically rear deck in sedans).

Concerns about localization are valid. But it is a complex issue. In terms of stage width (ie. localization along the horizontal axis), there are two key concerns. They are ITD (differences in arrival times) and IID (differences in SPL). It should be noted that ITD is a dominant effect below 1-2 kHz and IID is a dominant effect above that. There is some overlap, of course.

But there is something very important in this particular argument: it's called the Haas Effect, named after the German Helmut Haas. Basically, it says that if the difference in arrival times between two sources with the same material is less than 25-35 ms, then the perception of the latter of the two sources is suppressed. Here is where Time Alignment comes in really handy: if you can't account for this physically, you can electronically delay the front speakers to make sure the difference between front and rear is less than the Haas Effect....and thus, the rear speakers should be hard to locate.

Of course, the concept isn't just cut and dry. Since we localize using ITD at low frequencies, everything is fine (for the most part) in the midrange and midbass frequencies. However, at high frequencies, we use IID to localize. The addition of a second source creates a comb filtering effect, ie. dips and nulls are created in SPL. This isn't a big deal for low frequencies, but it directly affects our localization along the horizontal axis at upper frequencies.

So in short, we should draw the conclusion that the addition of a second source in the rear is not a big deal at low frequencies if we manage the Haas Effect appropriately. However, it can be detrimental in localization in the treble. And although it doesn't affect the localization at low frequencies, the creation of peaks and nulls in SPL at low frequencies is still a problem if an even, accurate response is the goal. Of course, the use of an EQ goes a long way here...but at least localization isn't a problem.

Re: Is midbass in the rear practically realizable?

- It is important that conclusions we draw in theory are realizable in practice, otherwise the theory is inaccurate. And if you look around, there are a number of installs that either use multiple midbass or midbass in the rear (or both) with great success. Off the top of my head, there are some guys you might have heard of known as SpeakerWorks who have had great success using midbass in the rear.

It isn't a tactic that is used often because it is still widely misunderstood, but offers great potential. Imagine, for a moment, that you have a small 6.5" driver up front. You play it down to the crossover point but obviously lack the output you're looking for. Good news! You may keep it in the current bandwidth, add large midbass drivers in the rear, keep the difference in front/rear arrival times below 30 ms, lowpass below the frequencies at which IID becomes prominent, EQ out any unevenness, and gain output with no effects on localization. Much like the use of a subwoofer in the rear, it is important to minimize resonance of surrounding panels. It's complicated but the result is worthwhile.

[johnecon2001 82]

Damnit Neil, I didn't need MOAR to read.

[DevilDriver 28]

[///M5 2,833]

While indeed Helmut was more than right, the act of knocking out panel modes and other issues in the rear of a car make this a bit nonsensical to me. Of course all of my cars are drivers.