Gary's Prelude Audio FAQ

So you want to upgrade your stereo? Before you do anything, you should have a clear idea of what you're getting yourself into! I hope by describing some things I did during my modifications, it will help others save time and/or get a better understanding of what can be done with their unique audio system.

The stock system -- how does it work from the factory? How does AFBS work?
Working with the stock system -- what mods can I make?
General car audio -- tips and pointers.
Gary's mods -- a journal of my audio adventure
Wiring for Surround -- How to do the crazy thing I did with my system
Other Links

DISCLAIMER: I am not an audio professional. I am not responsible for any damage that is caused in any changes you make to your audio system. If you are not familiar with car electronics, have a professional install your gear.

The stock system

In General

The head-unit (deck) is actually pretty nice, for a stock system. (Let's get this out of the way at the start -- most stock systems are adequate at best, and even "premium" systems with famous name brands are not as good as a decent aftermarket system with high-end speakers.) The front speakers have separate woofers and tweeters in the doors, and the rears produce good amounts of bass (along with the AFBS system). The head-unit has good FM tuning (I can pick up distant stations as good or better than other radios I've owned), and a clean-sounding CD player (with skip-ahead feature, and optional CD changer in the trunk). This should be all the system most people need; if you're not particularly demanding of music, and you don't need booming bass hits from techno or rap, this may be Good Enough.

AFBS -- Acoustic FeedBack System

This is the part everyone wants to know about, as it is unconventional for a car audio system. What it does is analyze the sound from the rear speakers for distortion, then feeds that information back into the amplifier to help eliminate it. This is similar in concept to how the servo subwoofer that might be in your home audio system works.

Each rear speaker has a microphone attached. Under the right-rear speaker, there is a small box that is both a small amplifier and the feedback system. Apparently, the head-unit has nothing to do with AFBS (despite the label affixed upon the front)! Normal speaker outputs are sent to the rear, which is amplified by the AFBS box. The AFBS unit sends a monophonic signal to both of the rear speakers. Yes, that's right, the rear is wired in mono. No, you can't change how the AFBS does that. (This is not as bad as it first seems -- most of us on the Prelude lists didn't even notice until someone brought it up! It's extremely difficult to detect the lack of stereo in the rear, because the audio image should be coming from the front part of the car. Personally, I ran my stock setup with it faded quite a bit towards the front.)

There is one other important piece of information about the rear speakers -- they are 2 ohm speakers, not the usual 4 ohm. The consequence of this is that you will overheat the head-unit if you attempt to connect these directly to a typical head-unit (if you are trying to by-pass the AFBS amp); most aftermarket amps can handle 2 ohms, however. There's only so much modification that can be done with the rears. (If you disable AFBS, I recommend replacing the rear speakers as well, or running them with an aftermarket amp; do not hook up the rear speakers to a head-unit.) The advantage of 2 ohm speakers is that they are twice as loud as 4 ohm speakers, so with AFBS, the tiny amp, and 2 ohm speakers, everything combined puts out pretty good bass in a stock system, and saves the limited trunk space. As a system, it does what it is designed to do; since it is a system (a combination of 2-ohm speakers, microphones, and an amp), modifying part of the system is difficult. In general, either like it, or replace the system (rear speakers & unplug the rear amp).

Modifying the Stock system

Intro

Modifying just parts of the system is a good thing to try, when you're tight on funds! Just keep in mind that it's a slippery slope, and if you really get the audio bug, you might end up with more peices of equipment down the road (especially if your first modifications are not sufficient to your liking).

Replacing the Front Speakers -- Discussion

I think replacing the speakers only (without other modifications to the system) works great, provided that the replacement speakers are loud enough (in other words, if they have a good sensativity rating). You don't want it to be more quiet when you get you new speakers in there. I say this, but I really don't know for SURE what rating is needed, but I've seen speakers rated anywhere from 89 to 95db, and that is a huge range in terms of sound level! A 95db speaker will make a 12watt head unit sound as loud as a 89 db speaker with a 45 watt amp!

If you want to experiment with different sensitivity ratings to determine how much amp wattage you will need, check out my Speaker Loudness Calculator.

When I bought my speakers, the salesmen insisted that I needed an aftermarket amp. Based on my experience, I'd say no, it's not strictly necessary when it comes to the Boston Pro's (although, there would still be an improvement in sound quality with an external amp, as well as more volume), but their sensitivity rating is higher than most brands (95db). In summary, if you install aftermarket speakers with the stock head-unit, it may not be loud enough, in which case you'll need to add an aftermarket amp as well.

Replacing the Front Speakers -- How To

The woofer comes out easily with 3 screws. You'll notice that the stock speakers are very shallow 6.5 inch speakers. I had trouble putting a 6.5" aftermarket speaker, so I installed a 5.25" one with adaptors to fit the 6.5" holes. If you look in the door where the speaker goes, you'll see plastic baffling -- this needs to be removed (by cutting it out). Few, if any, aftermarket speakers will fit with that baffling left in place. For my install, I also needed to put electrical tape on the metal at the bottom of the opening, to make sure it didn't short with the speaker's terminals.

At the woofer is a connector with 4 wires. Two wires are the speaker outputs from the head unit, and the other pair lead to the tweeter in the upper part of the door. To install an aftermarket component system, using the existing wiring, you'll need to cut a pair of wires, in order to disconnect the woofer from the tweeter, and then connect them to the crossover appropriately. Plan this all out before you start, and it'll make life easier. (I said easier, not easy. ;-) ) You probably want to use the factory wiring, so that you do not have to run wires through the door; don't ask me how to do that, I poked at it for a short bit, and decided the thin factory wires would work just fine! :-) (In a bit more detail, I removed the factory woofers, looked at the stock connectors, decided I could cut the tweeter wires and leave the stock connector attached, and use that for the woofer. I noted what connector I would need to match this. I then went inside and cut wires, and crimped connectors; it's a good idea to be really sure which connectors you need, as it's a pain if you end up having to redo, especially if you do not have a lot of spares. Also, allow a much longer length of wire for the woofer, as you need slack when you install it.)

The tweeter is a bit harder to get to; here's where the Helm service manual comes in handy. There is a screw that needs to be removed which is beneath a round cover. The panel then pulls out, kinda to one side. The rest should be obvious. When it comes to mounting the aftermarket tweeter, you're on your own. I managed to snug-in mine, and then secured them with electrical tape. Low budget, I know, but hey, it works.

About the crossovers, you'll want to fasten them out of the way, so that they do not fall into the track where the window goes down into the door.

Ok, everything seems wired correctly, you've tested it out, and you're ready to screw everything in place. Some people have noticed that the mid-bass from the front speakers is aided greatly by putting some silicon sealant around the woofer, to make an air-tight seal.

Adding an Amp (for a sub)

To add an amp to the stock system, you'll need to tap into the speaker outputs (which come from the head-unit). Many cheap amps already come with speaker-level inputs. If you buy a converter, you can get one as cheap as $20 or so. All 4 speaker lines that are needed seem to be available at the trunk; just be sure you splice into them BEFORE the rear factory amp! Don't use the lines after the "acoustic feedback" processing has been done. In other words, it should be wired such that you could unplug the rear amp connector, and it'll still play. At least that's what I did; I don't trust the factory system to handle modifications, so wire outside of the circuit.

Since the original writing of this section, someone has confirmed that they get odd and horrible feedback from tapping at the speakers and not before the AFBS, so definitely keep that in mind. Here are the wires to splice into:

RR+ = Red with yellow stripe RR- = Brown with white stripe LR+ = Blue with yellow stripe LR- = Grey with white stripe

They're all at one "end" of the connector. At the other end, one of the wires is a constant 12v (even when the car is turned off!), so be careful about what you splice into. A multimeter helps with this sort of thing too.

To power the amp, you'll need to run wire from the battery. Don't forget the fuse. (If you buy an "amp wiring kit", it should have everything you need.) You also need to wire the "remote turn on". Since the Prelude does not have a powered antenna, there is no "radio on" signal, as far as I could tell. [NOTE: someone has told me that a remote line exists! I'll leave it as an "exercise for the student" to find it. Translation: I have no idea which wire it is, and I'm not going to look into it any time soon. Seriously, if I hear more details, I'll post it.] I tapped into one of the "option connectors" near the fuse box which only comes on when the ignition is turned on to "II"; that's Good Enough.

Can I convert the Rear Mono speakers into Stereo?

There are 2 things you can do, but any way you do it, you must disconnect
the rear factory amp, and replace the rear speakers. (Well, you
could add an aftermarket amp to the rears, disconnecting the factory amp,
but without the feedback system, the quality might be pretty poor.)

Note: the below suggestions all include disconnecting/disabling the AFBS unit.

1) replace the 2 rear speakers, and connect them to an aftermarket amp.

Disconnect the harness to the rear factory amp, and splice into the wires to get the left & right speaker wires, and use those to input into your aftermarket amp (speaker-level inputs). This'll probably set ya back about a couple of hundred bucks, even with relatively low-end stuff. Spend a bit more, and buy the right 6x9's, and you could probably get enough bass to not need a small sub. This is probably what I'd try, if I didn't already have the subwoofer. Think of all the trunk space you'd save! Kicker makes a set of 6x9's that's made specifically to work like a subwoofer. (With this option, you could have either the stock head-unit, or an aftermarket deck.)

2) replace the rear speakers, and drive the rear speakers off of either the stock or a new head unit.

Warning, it'll be stereo, but it won't be "louder", IMHO. I doubt it will be as loud as the AFBS system, so do not choose this option if you're after a "subwoofer" effect, but only if you're wanting a "stereo" effect in the rear of the car.

Can I use a new head-unit with the AFBS engaged?

Ooh, this is a tricky one! It would make sense to assume that the AFBS amp is only designed to handle the power from the stock head-unit; given that, it is probably not a good idea to put more power than that into it. At least one person posted that this worked for him. Leave the rear amp and the rear speakers in, and install the aftermarket stereo.

Car Audio Tips

For beginners

If you're not comfortable doing electrical wiring, but are determined to do it anyways, try to study up on it. It's not hard, but some things are not obvious at first.... Myself, I had a friend show me. It's still somewhat of a pain. For instance, when you power an amp, you need to run power from the battery. That means the power wire needs to be run through the firewall. Luckily, there's tons of room in the stock Prelude wiring grommet (just don't cut any existing wiring, of course!). It helps to have the $60 Helm service manual so that you know how to remove the interior pieces, plus it labels the wires in the stock audio system, etc. The # for Helm is in the back of your Prelude manual.

Regarding wiring, when you run power to anything, put a fuse on it! If you buy an amp wiring kit, it should come with one for the power line you'll run to the amp; make sure the fuse is in-line near the battery. This is in case the line gets cut or shorts to ground, it'll trip the fuse rather than burn your car to the ground. Nice, eh? No, really, battery power is very dangerous. Wiring doesn't have to be pretty, but it should be crimped inside connectors when making connections.. it's too hard to describe how to make a good connection with wires; please find someone who can teach you. Also, I find it easier to buy a $10 box of assorted wire connectors, just to make sure that I have enough. Or, some hardware stores may have them pretty cheap. Even Wal-mart has a decent selection. If you're replacing the head-unit, I recommend spending the extra $15 bucks and getting a wiring harness. This makes it easy to put the original unit back in, if you go to sell the car or the new one has a problem.

Anyways, I can't really describe to you how to properly do many things. It's SOOO much easier when you can just see someone do it. I'm just hitting the highlights just to emphasize what you're getting into! Yeah, anyone can do it, but you need to know what you're doing! It'll be so difficult at first (and maybe later), but it's also a fun project.

For Intermediate/Experts

Ok, you want to have a 1000 Watt system with 12" woofers? I'm probably not going to be much help then! I think once you've gone past the Prelude-specific notes above, it's just standard car audio, so you don't need me for that. Visit your local audio shops, your buddies, etc. I only know a few things that may or may not be news to you. Some people will just gut everything, which will give you the best system, but at a high cost. If money and trunk space is no object, then that's the way to go. But where's the challenge in that? :-) And judging from my sound level meter, using the Boston Pros with the stock radio is sufficient to give me permanent hearing damage, so don't assume that you necessarily, need to gut everything and install a completely custom system. How loud do you want it, and what are you trying to accomplish?

Gary's System

So, specifically, what did I do to my system? Well, I've tried a few things. I started by adding Boston Acoustic 5.4 speakers. These things are great! A bit harsh on the high-end frequencies, but excellent in detail. There are other good brands if you are looking for great sound, but the Bostons are very efficient, allowing me to run them off the head unit, and still get a great deal of volume out of them. Still, I have to take care to not turn them up TOO loud. I already had an old Kicker Substation, which is an 8" subwoofer in a tube-like (rectangular) enclosure, but I needed an amp. I bought a 35w/ch Profile amp., which, when bridged, would provide 70w. It was pretty loud, but not quite loud enough -- the 8" still had a bit more to give. The bass from the sub just did not sound right with the AFBS plugged in, so it was better with it unplugged, but it was still underpowered. Still, I had bought the amp, so I was going to live with it.

Now that the AFBS was unplugged, what should be done with the rear speakers? I wanted to have a surround-sound effect, which can be done with an expensive processor, or a no-cost wiring of the speakers to produce an out-of-phase signal. Rather than do what I recommend and replace the stock rear speakers (since they are 2-ohm), I wanted to try to make use of them, hoping that the strain on the head unit would not be too bad if I didn't put bass through them. Most of the bass gets stripped out automatically when you use the out-of-phase signal. Some "bass blocker" capacitors can take out even more. Even so, I can only turn them up but so much before there's a problem. At lower volumes with the rear speakers turned up enough to be barely audible, it can be rather cool with electronic music; you definately can get a surround effect.

So, how do you wire out-of-phase? DISCLAIMER: IF THIS SCREWS UP YOUR AMP OR HEAD-UNIT, IT'S NOT MY FAULT! NOT ALL EQUIPMENT IS GUARANTEED TO HANDLE THIS! THIS OPERATION IS NOT NORMAL! Ok, if you still dare...disconnect from the wires from the "-" terminals of the rear speakers and connect a wire between the "-" terminals. Yes, it's that simple. Use a test disk and make sure it's really producing ONLY the surround signal. (By the way, when I say to disconnect the wires above, if you unplug AFBS, you'll have to run your own (new) wires anyways, but I'm assuming that you can figure out that I mean that you wouldn't connect the "-" wires at all, but I think it's easier to understand how to do the out-of-phase trick with the first explanation. Er, if this is too confusing, then never mind. It was confusing to write. :-) It really is easier than it sounds.) Ok, what's the problem with doing this? The speakers are wired in series which increases the effective ohms from 2 to 4, which is good (easier on the amp), but then we're bridging now, which cuts the ohms from 4 back to 2 (effectively), so we're back to where we started -- a hard load for the head-unit, and sure enough, I cannot turn them up loud at all. A better solution would be to drive 'em with an external amp and/or get new rear speakers. (For a later solution to this problem, which may be an "abuse" of the AFBS system ;-) , see my notes a couple of pages below.)

To complete the "surround" system, I needed a center-channel speaker. The easiest way to do this is bridging. Since I already bridged to the subwoofer, I simply wired a midrange speaker in parallel with that (and of course used more "bass blockers" to the midrange). The quality of the speaker is much lower than the quality of the main Boston Acoustics (I wish they made a small midrange), so I'm not sure if this is a good move or not. However, the center channel does help center the voices, helping imaging. My other problem is that the cheap amp produced alternator whine through the midrange, which is an annoying sound, but only occurs while driving. Where did I put it? I yanked out the air vent, and wedged it in there. It just barely fits, with a little bending of the plastic vent (behind the grill).

As a good first go at it, it worked pretty well, but there were still some problems. The main problem was not being able to crank it before it was upset, and I could never seem to get enough bass out of the cheap amp.

My progress:

3/5/99:

I eventually decided to solve the underpowered sub problem by buying an MTX amp which not only provides more power, but it is more suited for tough loads, such as bridging a sub. It is substantially louder now! Lots of bass for an 8". No, it's still not going to be louder than some 10's or 12's and a larger amp, but you'd be surprised. Now I can use the original amp for the midrange & surrounds.

What's next? Maybe remove the center-channel, at least for the moment, until I can figure out the noise problem, and drive the rear speakers with the Profile amp., so the head-unit should be happy. Drive the fronts with the Profile amp? A good idea if the noise problem could be eliminated. Maybe a new head-unit?

3/12/99:

I've resorted to only using the cheap amp on the rear speakers, only (which I've wired out-of-phase, for a surround-sound effect). With all of the noise, this was just not going to work. Not only that, but because of the way I wired the rears in surround, I was having trouble bridging a proper center-channel (I was getting the surround-sound mixed in as well). So I had two problems -- noise, and I couldn't do surround AND center-channel on the same amp! Crap.

Tonight, I was determined to make a breakthrough. I tried all sorts of combinations, and had a brilliant thought -- run the center channel off of the head-unit's rear channel, and since I'm not getting alternator noise from the fronts, I probably won't off the rears either! The only thing the cheap amp is driving is the rears, and the volume is low on those, so noone's going to hear any noise from them. I'll test out the alternator noise problem tomorrow while driving. Best of all, I get a true center-channel! Yes! IMPORTANT NOTE: by bridging the center-channel speaker, I'm running a 2-ohm load on the rear channel, which is not good for the head-unit. From a few minutes of testing, it seemed to do well, however; it probably helps that I use caps to strip out the bass. Previously, when I had run the rear speakers off of the rear channel, I could shut down the head-unit pretty easily (due to overheating) just by cranking it up. I'm kind of pleasantly surprised that this works as well as it does. I need to spend more time with it and put it through its paces.

BTW, my new sub amp works great, but I had to not connect the "common" terminals in the speaker-level input. The head-unit can't seem to handle the common lines being tied together, and was giving me "crackling" noises (distortion) at moderate-to-high levels. Removing the common lines, I had to turn up the gain on the sub amp, but that's OK -- no more crackling!

Now, I can crank it pretty darned loud with reasonably low distortion & noise, and get an incredible 3D sound.... Electronic music sounds fantastic when you get 8 speakers goin' in matrix sound processing! :-) The only thing a true surround sound processor would do for me is give some delay to the rear speakers and perhaps provide "steering", but I don't think either of those is needed. I am *SO* psyched-up! After all the trouble, it looks like it's all coming together.

You wouldn't believe the mess of wires I have...

5/1/99:

Plagued by noise problems, the center channel had to go. I'm not sure if it was the wiring or the amp, but it seemed to get alternator noise through both! No combination of circuitry seemed to work (I even tried a R.S. power line noise suppressor, with no effect) and the noise in the rears was more audible than before, so I removed the older cheaper amp., and the center speaker. Just to add insult to injury, I don't think I was getting the "true center channel" I had hoped for (or else I can no longer figure out how I did it); I experimented quite a bit, and I'm not sure how to get the signal without a processor. [Much later, someone suggested a wiring scheme where it should be possible, however, an amp needs to be dedicated to the task of center channel, and nothing else.] Still, the "summed mono" center channel was better than nothing.

I'm still running the rears in "surround" mode, though, and off the head-unit! (Yeah, I know I said not to do that, but I think the capacitors help, and so far it is OK as long as I don't crank it too loud. If I ruin my head-unit, I figure it's a good excuse to get a new one. ;-) ) The system sounds pretty good, but I'm a little disappointed to fall short of my goal. I'm not sure if I should leave well enough alone, or if I should try another approach. Without a direct comparison, it's hard to get a feel for how much better it could be, but I'm not sure I want to spend hundreds of dollars to find out.

10/16/99:

A lot has happened since my last note! In my never-ending quest for better sound, I decided that the factory head-unit had to go. If I couldn't add an amp, I could at least add a head unit. (I also added head-units to two other cars!) I still wasn't happy with the imaging (the placement of voices, etc.), so I played around with a center channel (again, just using summed-mono, and using a passive "volume control" (L-pad) to dampen the volume), but I can't decide if it helps or just muddies up the imaging. I decided to do a lot of searching on the 'net, and found out that some people flip the phase of various speakers. Normally, you wouldn't want to do this, because if you're between two speakers and you flip the phase on one, it has a "spacey" weird sound that is really annoying (a.k.a.out-of-phase), and you'll lose most of the bass. The trick here is that you are not sitting in the center of the car, and the wavelengths are all different when you sit in your car seat! So I flipped the phase of my left woofer (not the tweet, but I don't think it matters), and I started to get more of a center channel that I was looking for! Voices actually came from in front and not all around! It worked! People also have been moving speakers to the kickpanels, to decrease the difference between the left & right speakers; I am not going to move my woofers, but it was not too hard to move the tweeters down to where the woofers are. This sounds great for the driver position, and not so great for the passenger. But, none of my passengers care about car audio more than I do, so too bad. :-) I think I can pull out the center channel now.

What is going to be of more interest to most of y'all is that I discovered that if you mess with the wiring going into the AFBS amp, you can get AFBS to play the "poor-man's surround sound" trick! (Not everyone likes this sound-effect, but it works well with some types of music.)

Now if I could just figure out my alternator whine problem, I'd be all set. Rather than dedicate it to a center channel, I'd probably use it for the mains, and be done with it.

11/27/99:

[Revised entry -- Whoops, sorry, I got carried away and am repeating myself! Oh well, some of it is new, so I'll just edit out some of the more unnecessary bits...]

I am still psyched about the reverse-polarity trick. It's not 100% perfect, but it is a definate improvement. I now have better center-imaging, and no longer feel the need for a center-channel speaker! It doesn't seem to be better with one, now.

Why did that work? Well, you do not sit directly between the speakers, so when you sit off-center, the phase will be messed up at certain frequencies. By adjusting the phase, it may sound more "normal" even though you're sitting off-center. Anyone sitting on the center-hump is going to think the sound is not right, after this mod. ;-) Anyways, I made this change after reading some messages online where people discussed "time alignment".

As mentioned earlier, I also experimented with moving the tweets down to where the woofers are. That sounds great, but I'm not sure that it sounds significantly better (than in stock upper-door locations). It does not sound better for the passenger, as the steering wheel is in the way.

Oh, I also played with the subwoofer in the trunk again, and there is a HUGE difference between pointing it sideways, where it fits better (because its' a tube-style enclosure), and pointing it rearward -- rear-firing is the way to go.

1/25/00:

Please, someone stop me! ;-) More major changes! I bit the bullet, dug deep in to the wallet, and got an amp for the front speakers. It's an Alpine V12, and best of all, no alternator whine! It sounds great. By adding the external amp., these things have happened: 1) louder volume, of course, 2) less distortion (cleaner sound) even at moderate levels, and 3) spec-wise, lower distortion ratings by using RCA inputs into the amp. I don't think that #2 and #3 are the same thing -- even at moderate levels, and even though the head unit was advertised as having "adequate" power, it just doesn't have as much "umph" as the amp. Therefore, I think that #2 is more of a simple power issue, especially when the music is filled with bass; I had also run into the occasional song that I wanted just a TAD louder. #3 is harder to hear, especially considering there is usually road noise cluttering up the sound, but I like to think that the overall sound is improved. By the specs, it should have a cleaner sound this way, with low distortion levels. (Can you hear 0.8% distortion? Perhaps, but it's awfully subtle. I can definitely hear 3% and maybe 1% under good conditions, so 0.8% is not that far behind. I can now rest easy, not worrying about whether or not I can hear 0.8% distortion. ;-) )

I did a little more experimenting with the "time alignment" -- I flipped the phase of the sub, and got some curious effects. It actually subtly affects the imaging of voices, as well as the volume of bass. I think it's working better out-of-phase. [1/6/01: This is probably due to the fact that I point the sub rear-ward.]

I put the tweets back up in the stock locations. Without being able to A/B them between the two locations, it's hard to say if it was better or worse.

I'm still using AFBS to generate a "surround-sound" rear fill. That seems to be working reasonably well; I don't need a huge amount of volume, just enough for some "air" or "atmosphere".

7/04/00:

While wiring my trunk popper (see Omar's messages from 10/99, on the Prelude web BBS on vtec.net), I also spent some time fiddling with the wiring on the surround-sound. I had read that Dolby surround not only puts the out-of-phase signal in the rear speakers, but it also flips the phase of one of them (presumably to not have so many signals cancel-out). Not sure of which should be flipped, I chose to flip the ones on the driver's side. I think that made a significant improvement.

2002:

I've been running the whole system off of just the V12, using the tri-way mode, where the front speakers and the sub are bridged on one amp., and you use filters on all the speakers. This was to reduce the clutter in the trunk, as I had too many wires and amps all over. Long term, I want to mount the amps and put the sub back on its own amp (where I can adjust the frequencies), but it's hard to say when I'll have time for that.

2003:

I ran an experiment, wiring a WoW (SRS surround) effects device to the front speakers. It makes an interesting sound, but I can't convince myself that it's "better". The sound is brighter, maybe even more interesting, but it didn't really present a more realistic soundstage. I unwired the box and put everything back.

Wiring Notes for AFBS-surround-sound (or, How to Abuse AFBS)

Warning: the AFBS unit was probably not designed for this modification. You do so at your own risk. Having said that, I've been using this modification for a while, and nothing has blown up so far. Still, the safest approach would be to buy a full customized system, and not use AFBS or the rear speakers. Ok, with the disclaimer out of the way, here goes...

The concept: get the rear speakers to output a "surround-sound" type signal, to add to the ambiance often found in recordings, and to make the stereo effect larger.

The problem: You will no longer get any bass out of the rear speakers, so this only makes sense if you also have a small subwoofer to supply the bass. However, you probably want to do this anyways, especially if you like bass-heavy music.

First, we must "fool" the AFBS box into using the out-of-phase material. On the white AFBS connector, I cut the red/yellow and brown/white wires, and swapped them. That's easy enough, and works! But, there's more to the story.

We also want the left rear and right rear speakers to be out of phase, to prevent sound wave canceling, so we need to swap the lines going to one of the speakers. First, find the connector at the bottom of the left speaker. I don't know if it matters whether you use the left or the right, but I randomly chose left. Notice that there are 4 wires; two are for the speaker, and two are for the microphone. We should swap both pairs, so as not to confused the AFBS amp. Since the time that I did the original wiring (where I cut and re-spliced wires), I figured out that you can get a small screwdriver, and work out the individual pins, and swap them. This is cleaner, and what I did for this step. (Or you can cut and splice -- your choice.) Under the Left rear speaker, I unplugged the speaker's connector, and opened the car-side (amp-side) harness. To remove a pin, you must slip the screwdriver in the plug side, and between a (hidden) clip and the center, and the pin slides out. Swap the Pink and Yellow/White pins. Swap the Light Green and (dark) Green/White pins.

The result is a much more spacious sound, with all of the lead singer's voice coming from the front, not at all from the rear.

For more information on wiring for a surround-sound effect, try researching (such as a web search) the "Hafler circuit".