Keeshwah

Who is she?
2006 USACi Sound Quality World Champion

The following are all direct quotes from Robyn (aka rocketgyrl) from various posts through out the site. This information should probably get stickied since she re-posts this information herself quite often.

Subjects

GENERAL
Car audio is all about compromises. Which drivers play the frequencies you need? Where can you mount these drivers? How large (diameter and depth) are they? What amplifier will you use to drive them?

While 3-way systems have their advantages, I've always been of the mindset where less is more. The two way systems are of course easier to design and install, will require less channels of amplification, etc. Three way systems have more cone surface area, and in some vehicles will yield a better soundstage because you're able to place the smaller, more critical midrange driver where it needs to be - the furthest from the listeners. I can't stress enough how important path lengths are - and keeping them as long as possible, and equidistant.

You'll want the bandwidth of lower than 400hz and higher than 4KHz coming from the furthest distance away from you.

Midbass drivers need to be as wide apart as possible, because humans hear those frequencies in a slightly different manner.

Keep the speakers as close to each other, and on the same axis, as practical.
Wide dispersion tweeters with smooth off axis response, work great in kickpanels, while narrow dispersion tweeters work better near the A-pillars. You don't want the sound ping-ponging between the glass and dash. Get a dash-mat! You can test it for yourself by placing some towels on the dash, and listening for the image to tighten and become focused.

I wouldn't suggest doing rear speakers at all. Think about it - when you're at a concert, the music comes from in front of you. Take that one step further to an acoustic performance, and ALL of the sound from the musicians is coming from a specific location. This is what audiophiles describe as a "sound stage". You can easily determine what's Left, Center, and Right. You can also start to hear sonic cues that relate to Height, Width, and Depth. Ideally in a car, the musicians should sound like they're performing on your hood. ANY sound coming from behind you would only distract from this. Don't worry about rear seat passengers not hearing the music...if you set up the front speakers correctly, they'll hear everything.

Close your eyes, and have someone snap their fingers. Then point to where their hand is. Odds are you're within 3* of their hand. My point is that this is what's called "focus", and you should get that type of accuracy in your car. The vocalist should be centered, and when you close your eyes, you should be able to point (ideally towards your front license plate) and identify exactly where the singer is. This requires a bit of Digital Signal Processing (DSP) - specifically: Time Alignment. When you're at home, you have the ability to sit between the speakers. Obviously in a car, we're sitting offset. This is what kills the afore mentioned sonic cues, and denies us a realistic performance. I strongly suggest you mount the speakers in your kickpanels - see mine on pg. 20 of the car audio sticky thread - to minimize path length differences.

CROSSOVERS
A passive network divides the frequencies going into it, and sends the proper range of sounds to the appropriate speakers. In the case of a two way - like the MBQ system, the higher frequencies to the tweeter (known as "high pass"), everything else to the 6.5" ("lowpass"). Most car audio systems use a subwoofer, creating a 3-way system.
Most systems use some sort of electronic crossover (either on the CD player, amplifier, etc.) to send frequencies below ~80hz to the subwoofer, and above 80hz to the amplifier that's driving the component system. This creates a "bandpass" for the 6.5" speaker. It's now playing above 80hz from the external crossover, and below ~2.5KHz - the start of the tweeter's range.

To remove the passive network, you'll need an additional pair of amplifier channels - a 4 channel amplifier would be perfect in this case. I suggest you find a CD player that has an internal xover - something like the Premier 880 would be perfect. Set the xovers to do the same thing the passive network would do:
Sub: 80hz Low Pass
Midrange: 80Hz High Pass, 2.5KHz LowPass
Highs: 2.5KHz Hihg Pass

DEADENING
Deadening the tC is a night + day difference. Gut the interior. Use your knuckles to knock on all the panels to find out which ones need the most damping. We did the floor, doors, rear 1/4 panels, trunk area, etc.
This is a good read:
http://www.sounddeadenershowdown.com/

BIG 3 UPGRADE
The "Big 3 Upgrade" is replacing the small wires car manufacturers use for larger ones and thus better performance. When Matt and I upgraded the tC's wires, we were shocked (pardon the pun) at how much smoother the engine ran, and it no doubt helped the stereo. The goal of the upgrade is to lower resistance by increasing the wire size between critical components - alternator, battery, chassis, etc.

Under the hood - part of the "big 3":


Here's the "Big 3 Upgrade" - that EVERY Scion owner should do:

http://www.the12volt.com/installbay/...TID=73496&PN=1

CHARGING SYSTEM
The car's alternator ampere rating plays the major role in determining how powerful an amplifier(s) you can install. Multiply the alternator's ampere rating by 40%, and you'll get a rough idea of how much reserve current capacity your car's system has.
To calculate the current draw of an amplifier, multiply the number of channels by the RMS watts per channel (a 4 channel amp rated at 100 watts RMS per channel would be 400 watts). Double it to account for amplifier inefficiency (400 watts X 2 = 800 watts), then divide by the average output Voltage of an alternator, 13.8 volts (800 divided by 13.8 = 58 amps). Since the average music signal requires about 1/3rd of the average power in a test tone, divide by 3 (58 amps divided by 3 = 19 amps). The result is the amplifier's approximate average current draw. In short, a 400 watt class A/B amplifier draws about 19 amps when playing music! Most people use a class D amplifier for their subwoofers, which are somewhere around 90% efficient, not the 50% figure I used for the class A/B amplifiers in the example above. So a 1000 watt class D subwoofer amplifier draws about 1100 watts at full power (rarely, if ever happens), and would draw somewhere around 27 amps while playing music. That's about 46 amps (19+27) of current draw while playing music - pretty loud. Again, since music is DYNAMIC, these numbers aren't constant, and will be lower most of the time, giving the alternator a chance to charge the battery!

A fast-and-nasty way to ballpark an amplifier's current draw is to divide the total fuse value of the amp by two. For amplifiers with multiple fuses, the rating of all fuses provided with the amp must be added together. This will likely produce a significantly higher estimate than using the proper formula. Although inaccurate, this will err on
the side of safety.

There's no harm in trying your amplifier with the stock alternator, then upgrading if necessary. You'll notice a voltage drop through the headlights, etc.
I'll let you in on a little secret...I've competed for 2 seasons with a 1600 watt system, put my car though 2 brutal Colorado winters, and won't give up my OEM battery for any after-market unit.
Lead-acid batteries generally fail when one of the 6 internal cells fail (open). I'm unaware if any internal resistance that builds up - but I'll wager that it's a very minor increase over it's usable life, then a catastrophic failure. It's hard to say if your holier than thou Optima's are plagued with this same problem. I can only assume this is a non-issue. The battery either works, or it doesn't...

It's better to have a longer ground cable that works, than a shorter noisy one... I specifically said frame and stainless steel screw for a reason. All the locations you've tried use "rated hardware" ( usually grade 8 ), and while they're stronger than normal screws, they contain a high concentration of zinc, which isn't a very good conductor. Car manufacturers often use Loctite in these locations that would further reduce conductivity.

Again - find the frame. Sand it down. Stainless steel screws FTW. If this doesn't cure your problem, check the amplifier with a known good amp...

ELECTRICAL MYTHS
YES THEY DO! The key is to minimize resistance within the power system (see my previous post), keeping the voltage up. Most systems haven't done this, and thus the myth "caps keep your headlights from dimming" emerged. There are also proper methods to use a capacitor and reap the benefits. For starters, it must be installed as close as possible to the amplifier's power terminals. It should be sufficient capacity to allow longer power drags, but realize this will be a larger load for the alternator and battery to recharge.

As I've said before, I'd be very surprised if the amplifier's internal capacitors aren't sufficient when the (external) power system is capable of delivering the demand.
This is a myth of car audio wiring practices. If the ground is "good", this won't be an issue. The alternator whine is an "A/C" noise that's bleeding into the system from the EMF, created by the power wire (+) and chassis (-). There should be NO A/C in these wires to begin with! Even at high current demands, the EMF is smaller than you think, and wrapping the RCAs around the power wire shouldn't make a difference. IF it does, the terminations/connections aren't good enough.

There's nothing wrong with mixing gauges. Ideally, you'll want to use the largest wire you can. Ground loops are created by different grounding points (re: distances) from the battery. My guess is that with one amp grounded on one side, and another amp grounded to the other side, and the RCAs connecting the two amps together is causing your noise problem. You should also upgrade your "big 3". Sand down to the bare metal where your amplifiers are grounded, and use a "regular" screw - NOT a zinc material, as found on "rated hardware" (ie: shock towers, seat belt bolts, etc.). If possible, ground the amplifiers to the frame of the car.

OPTIMA BATTERIES
Do yourself a favor and avoid Optima batteries at all costs! There are several other batteries that are MUCH better, including Kinetic, Scosche, Batcap, etc.

What makes you feel you NEED an Optima (or any other) battery?

Have you upgraded your "big 3"? I suggest doing this first.

I'm assuming you're looking at getting or already have a stereo system - with some "big amps". Usually the only thing a larger/upgraded battery will provide is longer engine off system play time.

Most amplifiers have enough internal capacitance to withstand even the most demanding bass tracks, and external caps are only a bandaid fix. Again, upgrading the "big 3" is key, and 99% of the time will cure any head light dimming, etc. Also make sure you've got the proper size positive cable(s) to the amps.

The differences between the Optima Red, Yellow and Blue are the rates at which they can charge/discharge. The Blue Top is the slowest (deep cycle), designed for marine use, and generally not a good idea for cars and/or car audio purposes.

The Yellow top is suggested by Optima as the battery for cars with upgraded stereo systems...BUT, they're wrong! Car stereo systems need to have the ability to draw energy quickly, and these batteries over time will fail due to the constant starting of the engine, and slower ability to accept a charge from the alternator. Add in the demand of the stereo, and you can see how this is making a bad situation worse....

Their Red Top is their most "normal" battery, with the quickest charge/discharge rate they offer. If you're 100% sold on Optima, this would be the only battery I'd consider. Again, look into Kenetic, Scosche, Batcap, etc. I've known too many people in the car audio community that have horror stories of the Optima batteries failing with no warning.

Let's take your beloved Optima Red Top (starter) battery for example. I looked at their website, and found a nice round number of 1000CA on their largest model. Cranking amps (CA) is the amount of current a battery can provide at 32 °F or greater. The rating is defined as the number of amperes a battery (at that temperature) can deliver for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12 volt battery). Peukert's Law expresses the fact that the capacity available from a battery varies according to how rapidly it is discharged. A battery discharged at high rate will give fewer ampere-hours than one discharged more slowly.

That being said, I submit that NO street stereo system will draw anywhere near 1000amps - especially for 30 seconds because music is dynamic. Add the fact that the alternator is constantly charging the battery. I realize there are additional loads on the charging system, but still - plenty of power is available for street systems. The Scion alternator in the tC is 100amps.

You stated: A farad is the amount of capacitance that requires one second for a one ampere flow of charge to change the voltage by one volt - which is correct. As I've mentioned before, the ESR of any capacitor is MUCH lower than a battery, and will therefore charge and discharge faster - maintaining a smooth voltage. Once again, I've yet to find an amplifier that can not sustain regular music play (re: not 'burps') when proper wire gauge is used, making the addition of an external capacitor unnecessary.

The car's alternator ampere rating plays the major role in determining how powerful an amplifier(s) you can install. Multiply the alternator's ampere rating by 40%, and you'll get a rough idea of how much reserve current capacity your car's system has.

To calculate the current draw of an amplifier, multiply the number of channels by the RMS watts per channel (a 4 channel amp rated at 100 watts RMS per channel would be 400 watts). Double it to account for amplifier inefficiency (400 watts X 2 = 800 watts), then divide by the average output Voltage of an alternator, 13.8 volts (800 divided by 13.8 = 58 amps). Since the average music signal requires about 1/3rd of the average power in a test tone, divide by 3 (58 amps divided by 3 = 19 amps). The result is the amplifier's approximate average current draw. In short, a 400 watt class A/B amplifier draws about 19 amps when playing music! Most people use a class D amplifier for their subwoofers, which are somewhere around 90% efficient, not the 50% figure I used for the class A/B amplifiers in the example above. So a 1000 watt class D subwoofer amplifier draws about 1100 watts at full power (rarely, if ever happens), and would draw somewhere around 27 amps while playing music. That's about 46 amps (19+27) of current draw while playing music - pretty loud. Again, since music is DYNAMIC, these numbers aren't constant, and will be lower most of the time, giving the alternator a chance to charge the battery!

A fast-and-nasty way to ballpark an amplifier's current draw is to divide the total fuse value of the amp by two. For amplifiers with multiple fuses, the rating of all fuses provided with the amp must be added together. This will likely produce a significantly higher estimate than using the proper formula. Although inaccurate, this will err on
the side of safety.

School's out.

Box Building
Birch ply is a stronger and stiffer material than MDF. A birch ply box will flex less than a MDF constructed box. I'll let someone else explain why box flex is undesirable. Box flex can and should be minimized through the use of braces. Please see JL's page for bracing tips/tricks: http://mobile.jlaudio.com/support_pages.php?page_id=166

There are many grades of birch ply and even more grades of plywood available. Far too many to be listed here. Care must be taken when purchasing your plywood.

In general:

Birch faced ply: This is plywood faced with a birch wood veneer. The internal laminates are minimum grade spruce and birch in alternate layers.

Birch ply: All laminates are birch. Face layers are also birch. Standard number of plies for 3/4" thickness = 13

MDF: Chips about 3/4" in length from either softwoods or hardwoods are thermally softened before being past through a machine which mechanically refines the chips into bundles of fibers or individual fibers. These fibers are mixed with a synthetic resin then pressed into a sheet. The fibers are randomly arranged within the material. This mat is then pressed again whilst subjected to elevated temperatures and pressures to cure the resin and produce a sheet of the desired thickness.

Mechanical properties: In layman's terms, strength is an indication of how much load a material will withstand before failure and stiffness is how much the material will flex, or deform, when subjected to a given load.

We are not really interested in the ultimate strength of our sub boxes as they seldom fail, so the material strength is of little use. However, we are interested in how much a box will flex. Therefore, we will concentrate on the stiffness of sub box materials.

Eb = Modulus of elasticity in bending.
Eb describes how stiff a material is under bending. The higher the number, the stiffer the material is and the less it will flex. It allows us to easily compare the stiffness of different materials.

The following properties are all based on 18mm (3/4") sheet materials (Engineers know to use the friendly metric system):

Birch faced ply:-
Eb = 2700 N/mm^2 perpendicular to grain
4600 N/mm^2 parallel to grain
Density = 11.6 kg/m^2

Birch ply:-
Eb = 3400 N/mm^2 perpendicular to grain
4600 N/mm^2 parallel to grain
Density = 12.4 kg/m^2

MDF:-
Eb = 2200 N/mm^2
Density = 10.8 kg/m^2

It can be seen from the above, that the plywood properties are directional depending on the orientation of the grain. For the purposes of this analysis, we can assume the stiffest properties as sub box panels are generally supported on all four edges. MDF is a homogeneous material and the mechanical properties are identical in any direction.

Comparing the Eb values given above it can be seen that the birch based plywood is over twice as stiff as the MDF. Therefore, if two identically sized sub boxes were fabricated, one from 3/4" MDF and the other from 3/4" birch ply, the MDF box would flex twice as much as the birch ply box.

That's quite an improvement from simply using a different material for your enclosure.

Thickness vs. Material stiffness:

Birch ply is expensive and MDF is relatively cheap.

It's often asked, "Do I use 3/4" Birch ply or 1" MDF for my new sub box?"

As discussed above, birch ply is a stiffer material than MDF. It's just over twice as stiff. However, the thickness of the material has a far greater effect on the overall stiffness than the actual material stiffness.

Example: It is common to 'double up' on the baffle thickness of a sub box from 3/4" to 1.5".

You'd imagine that by doubling the thickness, you'd double the stiffness and effectively half the flex of the baffle. However, this couldn't be further from the truth…

By doubling you in fact increase the stiffness by a factor of 8. The 1.5" baffle will be 8 times stiffer than the single 3/4" baffle.

This is derived from the second moment of area of the section given by Ixx = (bd^3)/12

Where d is the depth, or thickness in this example. The thickness value is cubed to arrive at the section stiffness.

For the full increase in stiffness to be exploited, the baffles should be glued together so the two layers act together in unison under load.

A double 3/4" baffle is 8 times stiffer than a single 3/4" baffle.

A triple 3/4" baffle is 27 times stiffer than a single 3/4" baffle.

A quadruple 3/4" baffle is 64 times stiffer than a single 3/4" baffle.

And so on….

In general, the thickness of the material is key to minimize flex. The thickness will increase the stiffness far more than a stiffer material would. However, by doubling the thickness you also double the weight of the box.

For ultimate performance, the stiffer birch material should be used in multiple layers. You will then get the best of both worlds. But it is worth keeping in mind that double the layers of material and the weight of the box will also double.

As always in car audio we are faced with a compromise. Box stiffness vs. weight vs. cost.

The choice is yours.

But for someone constructing a simple 3/4" thick enclosure, Birch ply will be twice as stiff and only a fraction heavier than MDF. I know which one I'd go for and I'd double the baffle too while I was at it.

Review
* Do the "Big 3 upgrade"
* Create and use GOOD grounds
* Proper gauge wires (the bigger the better)
* OEM battery and alternator is sufficient for most systems
* CAPs are a "fast" battery - able to charge and discharge quickly - restoring the amplifier(s) power supply. They DO work, provided the above are true, and the cap isn't being used as a "band-aid" fix.

ADRdesignCo

good read

hats off to Rocket gyrl! :D

Tcguy85

she is so smart! :-)

mark1905

Very good information..

But I would have to say that the inference that you absolutely have to have a defined front soundstage, and that you don't need to "do the rears" is a personal opinion of listening taste.

I personally listen to nothing but electronic music.. techno if you want to call it that.. and at very high volumes and ranges.

With electronic music, the sensation of being enveloped and equidistant on all sides is more desirable than having a front and defined soundstage.. at least it is to me. I like feeling like I am completely suspended in the music, wrapped up in it and not being able to tell really where it's coming from.

So, take the listening style comments with a grain of salt I would say and design your system according to what sounds best to you, not what someone tells you sounds best.


Great basic info though.

Keeshwah

Updated a little to the end of the Charging System section and added the Box Building section

chubbykai

iTrader: (1)

what is the big 3? which wires do we exchange out?

....i feel so dumb

RodC

That's a big F-in' trophy!

Keeshwah

Keeshwah

nebster

yes masta mod

PlayinWithFire

get a mod, get it stickied, then have em lock it...

SL is a breading ground for tangents....

mandos

Ok, I'm going to be watching this one...please keep it on topic and take the arguments to PM.

And yes, it was me removing the rather childish banter from here.

I prefer MDF since a non-grained wood is much easier to cut with a CNC machine That and for the sizes of the enclosures/pressure levels inside the box used in most car audio applications, you really shouldn't have to worry about the flexing of the enclosure.

Now, straight up SPL competition, yeah, make damn sure that box is as rigid as can be, but for listening to music at reasonable levels(which an SQ champion would) I don't think it's really that necessary.

And while caps do have their uses, the problem really is that 99% of people don't use them for the right thing. If you want to stop headlight dimming with a cap, install it inline with the headlights

GQQSE13

great info, finally someone else likes kinetic!

MTcX

I'm gonna be watching this thread and will make it a sticky once i"ve had time to go through it entirely. Thanks for the info

TCMan07

iTrader: (1)

I found this to be very informative. But, I would also would like more info on the "Big 3" , such as what wires are the big 3, what gauge wire you replaced them with, and maybe more pics if possible.

I also feel dumb to ask this.

Keeshwah

Thats what this thread is for, I actually omitted a link for the big 3. You should use a 0/1 gauge, you want the least resistance possible.

TCMan07

iTrader: (1)

Thanks for the link. Also, do you remember how much wire you needed to do this, and did you replace the stock or just add to it?

ADRdesignCo

i added my 4awg "big three" onto the stock one (kept the stock). i had about 20or so feet extra, so i went ahead and did the big three in 4awg.

mark1905

Here is a great link for a complete grounding job:

https://www.scionlife.com/forums/viewtopic.php?t=29261

socalsciontc

So is there anywhere to purchase a Big 3 replacement kit or do you just have to make them?