scott_fx
08-20-2015, 08:12 PM
Hey guys. I wrote this up for a Chevelle users group and thought you guys may find this information useful. I also have been compiling some base line components to build systems for different budgets. I can post those as well.
Please ask any questions or challenge any of the concepts that I present I have no issues backing up the claims or learning something myself in the process:
---Car Audio Primer----
Some quick information about car audio. I have 'cliff notes' for the layman and detailed explanation if you're curios as to why i said what i said.
REAR SPEAKERS, DO YOU NEED THEM?? --
cliff notes:
It's far easier to tune a system without rears. being able to control two sets of speakers instead of four will make your life easier. I always recommend driving around with your current system faded all the way forward. Do this for a month. the first 2 weeks or so will be acclimating yourself to the lack of rears. You'll soon forget that they aren't there. When you do.. about week 3. you can start to appreciate the slight improvement of sound quality. If at the end of week 4 you can't stand it... then you have your answer... you're a rear speaker type of person.... and that's ok.
----------------------
detailed explanation:
Rear speakers are very subjective. Through the years we have been conditioned to think we 'need' rear speakers. This is in part due to marketing and a way car manufacturers can charge you more money for a sound system.
In the past, having two larger rear speakers in your car was advantageous. The larger speakers in the rear would play lower (read: bass) and add to the overall volume of the system. When we add a subwoofer, we take care of the the low end.
Premium car audio usually relies on very inexpensive drivers (aka speakers) and some heavy processing to make them sound good. Now if we focus on the 'inexpensive' part of that statement, we can see how advantageous it is for a manufacturer to advertise 'premium 12 speaker audio system' They'll throw in about $40 with of cheap speakers and charge you $3k. So with all those speakers they add them to the front and rear and sometimes the back doors as well. Since they said 'premium' we think that this is better. But take a minute to think of the last time you want to a concert. do they put speakers behind you? or think about all the countless hours that are put into mastering the songs you listen to. they are done with two monitor speakers in front of the engineer.
When you have the same audio signal playing from two speakers (front and rear) you also will get sound that is more 'muddy' (there are ways around this.. but you need a processor design for adding rears. jbl ms8 uses 'logic 7'... but thats a whole different conversation). The reason for this is that our ears are very in tune with minute differences in timing of audio signals. It probably goes all the way back to when we were hunter gatherers... but it still holds true today. When we have a signal playing from two spots in different locations, they both reach our ears at slightly different times. This causes our brain to get confused and not be able to 'localize' the sound as well (remember all those hours spent by the audio engineer to produce the music we listen to? all out the window) There are also the physics of 'comb filtering' and that is the adding and subtracting of soundwaves. This will lead to some frequencies getting slightly hotter or slightly muted based on their frequency and the position where they combine.
#########################
#########################
SPEAKER PLACEMENT --
cliff notes:
If you don't have a processor then your best bet is to mount the tweeter as close to the mid as possible. if you have a dsp then you have more freedom. mount the tweeters in your a-pillars and aim them at the opposite window (driver side tweeter should be aimed at passenger side window). good sounding audio has more to do with your installation and tuning than it does with your speaker selection.
----------------------
detailed explanation:
Back to the studio and production of the track you're listening to. My reference cd for any system i listen to is Dire Straits' "brothers in arms". If you throw in "Money for nothing" and close your eyes; in a properly set up system, you should be able to 'localize each musician in front of you. this is called your 'soundstage'. There is also a term called 'stage height' that refers to where that soudnstage resides. the proper soundstage should be right on top of the dash. Since we can't put our speakers up on our dash we are forced to put the mids low and potentially mount the tweeters up high. There is an issue with this though. Remember how our mind is very sensitive to timing? Well if you measure the distance of the tweeters to your ears v. the mids to your ears... you'll notice that the drivers side tweeter; if mounted high, will be considerably closer to your ear then the mid. The best way to remedy this situation is to mount the tweeter near the mid. that means; usually, mounting them in a kick pod. This is a great solution but it brings down the stage height. a bit. If you have a dsp (digital sound processor) either built into your head unit or as a stand alone device. You can mount your tweeters up higher and use something that is called 'time alignment'. this will slighly delay the speakers that are closer to you so that all of the sound reaches your ears at the same time.
#########################
#########################
COAXIAL, ACTIVE or PASSIVE SPEAKER SYSTEMS. WHAT IS THE DIFFERENCE?? --
cliff notes: If you dont' plan to amp your speakers, go with coaxials. if you want something to just plug and play and you plan on running an amp, go with passive components. If you want the best you can get and the ultimate experience; for not much more $$... then go with raw drivers using an active processor.
----------------------
detailed explanation:
There are 3 main types of speaker configurations. Coaxial, Passive Component and Active Component/ aka raw drivers.
-Coaxial: These are the cheapest and easiest to install. The mids and tweeters are in the same frame on the same axis. these are the speakers that have the tweeters mounted in the center of the mid speaker. They are designed to work with low power and usually just have a simple capacitor to block high frequencies from damaging the tweeter.
-Passive Components: These are often the most expensive option. They have separate midbass speaker, a tweeter and a crossover network. (this is a 2 way. you can also get a 3-way which will add a 3rd speaker; usually 3"-4") The whole system is designed as a symbiotic package. The passive crossover is like a traffic cop. it send the high frequencies to the tweeters and the lower frequencies to the mids. They often also have components built into the crossover that would tame a speaker if there is any 'break up' due to the design of the driver (aka speaker). These often are dependent on all the components being present. you can't easily swap out/upgrade one piece of the system with good results.
-Active components These are just the basic drivers. You purchase the mids that you want and the tweeters that you want. All of the 'traffic cop' signal routing is done by a separate processor (either in your head unit or a separate unit). This is your most versatile set up. you can mix and match the speakers you want and usually you can buy the raw drivers at a cheaper price for the quality that you get. The one catch.. you need an amplifier that can power each driver individually. This means that you would need a four channel amp instead of a two channel amp that you'd get away with if you want with a passive system. This usually isn't a huge increase in price. most amps will be $20-50 more for the 4 channel variants. The raw drivers you are getting could; in theory, make up that cost difference. in practice though... you usually will just end up getting a lot better speakers and not save the $50. The advantage of going with an active system is greater dynamic range, and the ability to tune each speaker individually. the results can be dramatic. Also, $300 worth of raw drivers would easily outperform a passive component system valued at at least 2x that.
#########################
#########################
DEADENING --
You do not need 100% coverage to dampen the sound of a panel. you just need to put the mass toward the center of the piece. large flat runs need dampening. the pieces with corners or other architectural beads/folds will not reverberate like a flat panel. If you want to same time or money then just go panel by panel. tap the panel, add some deadeing to the center. tap the panel again. if it still sounds like a drum then you may need to add more. if you go to the sound deadener showdown website, there is a great write up on how to apply deadener following the 20% rule.
on top of deadener you need a sound 'absorber' this is usually in the form of closed cell foam or mlv (mass loaded vinyl). this is what will cut down on noise. this you will need 100% coverage... luckily it's light and relatively inexpensive. \
#########################
#########################
TWEETERS--
cliff notes:
Fabric dome small tweeters are usually the choice amongst the masses. they are warmer and are easier to listen to for long periods of time.
----------------------
detailed explanation:
tweeters are the most finicky driver you will have to deal with. unfortunately there isn't a ton that can be done if you get the wrong one. This is where it pays to go to a stereo shop and listen to their soundboard. There are three primary types of tweeter. Dome, Horn loaded, and ribbon. Domes are usually made from fabric/textile or metal. Metal domes are very accurate but are often times a lot harsher to listen to. Textile domes have a less accurate sound and are warmer but are usually more pleasant to the general listener. If you can fit a large format tweeter up high, you'll be able to raise your soundstage and give the tweeter more of the signal to play. This is usually hard to do cleanly and almost certainly impossible to do stealthly. in that case a smaller tweeter may be your better option.
If you need to mount them lower, it's best to use a larger tweeter like a Tymphany XT25TG30-04 or Seas 27TDFC and make use of their larger design to play more of the audio signal (this is done with a dsp active system)
There are options besides those. You can get horn loaded drivers (what im running) or ribbon tweeters. The ribbon tweeters are usually a bit harder to install but they have some of the best imagine you can achieve. They are rebuildable and can be a bit fragile if you touch the ribbon directly. Due to their size you would normally see these in the kick pods.
#########################
#########################
MIDBASS/MIDWOOFERS --
To me, this is where the sweet spot is. this is what kicks you in the chest with rock or edm music. it's what makes you say 'wow' in a system. The larger the better in this category. Try to stay away from metal cones. Paper cones sound the best but they don't hold up the best in a car. I prefer a coated paper cone, but there are carbon fiber, poly, even bamboo cones. each have their pros and cons.
#########################
#########################
SUBWOOFERS --
cliff notes:
the larger the better. besides some weight and space savings there is no advantage of an 8" over a 12" speaker. The 12" will play just as 'tight'. For a balance system you should look for a speaker that is designed for 300-500wrms as a general rule of thumb. This should be able to overpower most systems and give you enough bass to where you may want to dial it back.
----------------------
detailed explanation:
IMHO people spend WAY too much time on bass. Bass plays in the two octaves that our ears/mind are least sensitive to. The most important thing to sub-bass is the design and construction of the enclosure. This will make or break the sub. If you want more volume (aka spl) you have 3 options. increase the cone surface area (with either a larger sub or more of them) increase the power you give to them (you will need about twice the wattage to hear/feel a noticable difference. or 3rd. the enclosure design. A ported box will be about 3 db louder than a sealed box. this will be a much more complex box, it will be a lot larger box and it will be not as accurate (but can still sound good)
#########################
#########################
AMPLIFIERS --
cliff notes: Go with more power than what your speakers are designed to handle. Then look up videos on youtube about how to set your gains with a multimeter.
----------------------
detailed explanation:
There are two schools of thought about amps. Some people believe that you need to spend a lot of money to get good sound (usualy an audiophile) then there is the school of thought that 'a watt is a watt' meaning that there is little difference between two similarly designed amps (aka class a/b amps). I'm kind of in the middle but I believe that you'll gain a lot more from a less expensive amp with a lot of headroom v. an expensive amp with less headroom or under powered. The best way i can describe what headroom is would be to relate it to towing a jet ski. You have the option of two tow vehicles. A V8 Silverado 1500 or a Chevy SS (the new little compact car) Both will be able to tow the jet-ski trailer but one will do it a hell of a lot easier and will be more fuel efficient and will run a lot cooler. Its the same with amps. The more you turn up your volume, the more noise that the amplifier will make. If you have an amplifier that has 150 watts available, you can keep the amp running in a cleaner and cooler portion of it's power output while achieving comfortable listening levels. In contrast, if you have an amp with 15 watts (aka a typical headunit). you are going to have to push that amp a lot harder... and make it play in a much noise spectrum of its noise curve.
Another thing to note. the thing that will kill a speaker the fastest is distortion. If you have more power available and your gains are set correctly, you'll be less likely to get a distorted signal and your speakers will last longer. You'll probably come across the saying 'you will destroy a speaker a lot faster by under-powering it than overpowering it". Obviously under-powering wont hurt a speaker. if it did, every time you turned you volume down.. you'd blow your speaker :) Rather... under-powering a speaker usually lends you to turn up the volume more and then that is when you get into distortion.
when it comes to subwoofer... you will more commonly hear about "ohms" this is the impedance of the speaker. An amplifier is design to run at a minimum 'impedance' If you go below that rating, your amp will most likely go into 'protect mode' and shut off. or it could fry itself. An amp can power a speaker above it's rated impedance. It does come at a cost. the amp will produce less power... BUT the amp will be cleaner sounding and run cooler. The reason why you see sub amps rated at 2 ohms and 1 ohms is that the noise isn't as noticable in the 2 octaves that sub plays at. so we are kind of cheating. A draw back of running below 4 ohms is that the amps start to be less and less efficient. So the current draw from the alternator will not be linear between the same amp playing at 4 ohms, 2 ohms an 1 ohm. This means that the lower impedance you're driving... it may end up taxing your electrical system too much and wearing out your alt and possibly getting light dimming when the bass hits. I run my sub amp at 2 ohms without any issue.
#########################
#########################
WIRING --
wire is expensive.. but dont skimp on it. make sure you get a big enough gauge to handle the current (amperage) demands of your system. If you get wire that is too small you'll rob your system of power. The best budget amp wire you can get is welding cable. I'm running some 2 awg Radaflex cable. it's about half of what you'd pay for a 'car audio' amp wire. Be very weary about wallmart, amazon, and ebay wiring kits. A lot of time they'll measure the jacket to get the gauges wire. This means that you may see 4 gauge but the actual amount of wire is equal to an 8 awg wire. aka.. you're getting duped.
With our cars, you should always do the 'big 3' upgrade. This means to upgrade the wire for the following three connections:
battery ground to chassis wire, the chassis to engine block wire, and the alternator possitive to battery possitive wire.
#########################
#########################
BATTERIES --
there are very few instances where you need a second battery (or a capacitor). If you notice dimming of your lights you should first check to make sure your grounds are all solid. you should remove the paint in the area that you are grounding your amp to. next make sure you did the big 3 finally you'll need to look into a bigger alt. Just adding a battery is a band aid fix. Batteries store power, they dont produce it. If you add a second battery to solve your lack of current issues... then instead of producing more power, they are actually taking power (as much as another 15 amps) in order to charge up the battery.
The times you need a second battery are usually if you do a lot of engine off listening or compete in those spl drag races (how loud your subs are)
Please ask any questions or challenge any of the concepts that I present I have no issues backing up the claims or learning something myself in the process:
---Car Audio Primer----
Some quick information about car audio. I have 'cliff notes' for the layman and detailed explanation if you're curios as to why i said what i said.
REAR SPEAKERS, DO YOU NEED THEM?? --
cliff notes:
It's far easier to tune a system without rears. being able to control two sets of speakers instead of four will make your life easier. I always recommend driving around with your current system faded all the way forward. Do this for a month. the first 2 weeks or so will be acclimating yourself to the lack of rears. You'll soon forget that they aren't there. When you do.. about week 3. you can start to appreciate the slight improvement of sound quality. If at the end of week 4 you can't stand it... then you have your answer... you're a rear speaker type of person.... and that's ok.
----------------------
detailed explanation:
Rear speakers are very subjective. Through the years we have been conditioned to think we 'need' rear speakers. This is in part due to marketing and a way car manufacturers can charge you more money for a sound system.
In the past, having two larger rear speakers in your car was advantageous. The larger speakers in the rear would play lower (read: bass) and add to the overall volume of the system. When we add a subwoofer, we take care of the the low end.
Premium car audio usually relies on very inexpensive drivers (aka speakers) and some heavy processing to make them sound good. Now if we focus on the 'inexpensive' part of that statement, we can see how advantageous it is for a manufacturer to advertise 'premium 12 speaker audio system' They'll throw in about $40 with of cheap speakers and charge you $3k. So with all those speakers they add them to the front and rear and sometimes the back doors as well. Since they said 'premium' we think that this is better. But take a minute to think of the last time you want to a concert. do they put speakers behind you? or think about all the countless hours that are put into mastering the songs you listen to. they are done with two monitor speakers in front of the engineer.
When you have the same audio signal playing from two speakers (front and rear) you also will get sound that is more 'muddy' (there are ways around this.. but you need a processor design for adding rears. jbl ms8 uses 'logic 7'... but thats a whole different conversation). The reason for this is that our ears are very in tune with minute differences in timing of audio signals. It probably goes all the way back to when we were hunter gatherers... but it still holds true today. When we have a signal playing from two spots in different locations, they both reach our ears at slightly different times. This causes our brain to get confused and not be able to 'localize' the sound as well (remember all those hours spent by the audio engineer to produce the music we listen to? all out the window) There are also the physics of 'comb filtering' and that is the adding and subtracting of soundwaves. This will lead to some frequencies getting slightly hotter or slightly muted based on their frequency and the position where they combine.
#########################
#########################
SPEAKER PLACEMENT --
cliff notes:
If you don't have a processor then your best bet is to mount the tweeter as close to the mid as possible. if you have a dsp then you have more freedom. mount the tweeters in your a-pillars and aim them at the opposite window (driver side tweeter should be aimed at passenger side window). good sounding audio has more to do with your installation and tuning than it does with your speaker selection.
----------------------
detailed explanation:
Back to the studio and production of the track you're listening to. My reference cd for any system i listen to is Dire Straits' "brothers in arms". If you throw in "Money for nothing" and close your eyes; in a properly set up system, you should be able to 'localize each musician in front of you. this is called your 'soundstage'. There is also a term called 'stage height' that refers to where that soudnstage resides. the proper soundstage should be right on top of the dash. Since we can't put our speakers up on our dash we are forced to put the mids low and potentially mount the tweeters up high. There is an issue with this though. Remember how our mind is very sensitive to timing? Well if you measure the distance of the tweeters to your ears v. the mids to your ears... you'll notice that the drivers side tweeter; if mounted high, will be considerably closer to your ear then the mid. The best way to remedy this situation is to mount the tweeter near the mid. that means; usually, mounting them in a kick pod. This is a great solution but it brings down the stage height. a bit. If you have a dsp (digital sound processor) either built into your head unit or as a stand alone device. You can mount your tweeters up higher and use something that is called 'time alignment'. this will slighly delay the speakers that are closer to you so that all of the sound reaches your ears at the same time.
#########################
#########################
COAXIAL, ACTIVE or PASSIVE SPEAKER SYSTEMS. WHAT IS THE DIFFERENCE?? --
cliff notes: If you dont' plan to amp your speakers, go with coaxials. if you want something to just plug and play and you plan on running an amp, go with passive components. If you want the best you can get and the ultimate experience; for not much more $$... then go with raw drivers using an active processor.
----------------------
detailed explanation:
There are 3 main types of speaker configurations. Coaxial, Passive Component and Active Component/ aka raw drivers.
-Coaxial: These are the cheapest and easiest to install. The mids and tweeters are in the same frame on the same axis. these are the speakers that have the tweeters mounted in the center of the mid speaker. They are designed to work with low power and usually just have a simple capacitor to block high frequencies from damaging the tweeter.
-Passive Components: These are often the most expensive option. They have separate midbass speaker, a tweeter and a crossover network. (this is a 2 way. you can also get a 3-way which will add a 3rd speaker; usually 3"-4") The whole system is designed as a symbiotic package. The passive crossover is like a traffic cop. it send the high frequencies to the tweeters and the lower frequencies to the mids. They often also have components built into the crossover that would tame a speaker if there is any 'break up' due to the design of the driver (aka speaker). These often are dependent on all the components being present. you can't easily swap out/upgrade one piece of the system with good results.
-Active components These are just the basic drivers. You purchase the mids that you want and the tweeters that you want. All of the 'traffic cop' signal routing is done by a separate processor (either in your head unit or a separate unit). This is your most versatile set up. you can mix and match the speakers you want and usually you can buy the raw drivers at a cheaper price for the quality that you get. The one catch.. you need an amplifier that can power each driver individually. This means that you would need a four channel amp instead of a two channel amp that you'd get away with if you want with a passive system. This usually isn't a huge increase in price. most amps will be $20-50 more for the 4 channel variants. The raw drivers you are getting could; in theory, make up that cost difference. in practice though... you usually will just end up getting a lot better speakers and not save the $50. The advantage of going with an active system is greater dynamic range, and the ability to tune each speaker individually. the results can be dramatic. Also, $300 worth of raw drivers would easily outperform a passive component system valued at at least 2x that.
#########################
#########################
DEADENING --
You do not need 100% coverage to dampen the sound of a panel. you just need to put the mass toward the center of the piece. large flat runs need dampening. the pieces with corners or other architectural beads/folds will not reverberate like a flat panel. If you want to same time or money then just go panel by panel. tap the panel, add some deadeing to the center. tap the panel again. if it still sounds like a drum then you may need to add more. if you go to the sound deadener showdown website, there is a great write up on how to apply deadener following the 20% rule.
on top of deadener you need a sound 'absorber' this is usually in the form of closed cell foam or mlv (mass loaded vinyl). this is what will cut down on noise. this you will need 100% coverage... luckily it's light and relatively inexpensive. \
#########################
#########################
TWEETERS--
cliff notes:
Fabric dome small tweeters are usually the choice amongst the masses. they are warmer and are easier to listen to for long periods of time.
----------------------
detailed explanation:
tweeters are the most finicky driver you will have to deal with. unfortunately there isn't a ton that can be done if you get the wrong one. This is where it pays to go to a stereo shop and listen to their soundboard. There are three primary types of tweeter. Dome, Horn loaded, and ribbon. Domes are usually made from fabric/textile or metal. Metal domes are very accurate but are often times a lot harsher to listen to. Textile domes have a less accurate sound and are warmer but are usually more pleasant to the general listener. If you can fit a large format tweeter up high, you'll be able to raise your soundstage and give the tweeter more of the signal to play. This is usually hard to do cleanly and almost certainly impossible to do stealthly. in that case a smaller tweeter may be your better option.
If you need to mount them lower, it's best to use a larger tweeter like a Tymphany XT25TG30-04 or Seas 27TDFC and make use of their larger design to play more of the audio signal (this is done with a dsp active system)
There are options besides those. You can get horn loaded drivers (what im running) or ribbon tweeters. The ribbon tweeters are usually a bit harder to install but they have some of the best imagine you can achieve. They are rebuildable and can be a bit fragile if you touch the ribbon directly. Due to their size you would normally see these in the kick pods.
#########################
#########################
MIDBASS/MIDWOOFERS --
To me, this is where the sweet spot is. this is what kicks you in the chest with rock or edm music. it's what makes you say 'wow' in a system. The larger the better in this category. Try to stay away from metal cones. Paper cones sound the best but they don't hold up the best in a car. I prefer a coated paper cone, but there are carbon fiber, poly, even bamboo cones. each have their pros and cons.
#########################
#########################
SUBWOOFERS --
cliff notes:
the larger the better. besides some weight and space savings there is no advantage of an 8" over a 12" speaker. The 12" will play just as 'tight'. For a balance system you should look for a speaker that is designed for 300-500wrms as a general rule of thumb. This should be able to overpower most systems and give you enough bass to where you may want to dial it back.
----------------------
detailed explanation:
IMHO people spend WAY too much time on bass. Bass plays in the two octaves that our ears/mind are least sensitive to. The most important thing to sub-bass is the design and construction of the enclosure. This will make or break the sub. If you want more volume (aka spl) you have 3 options. increase the cone surface area (with either a larger sub or more of them) increase the power you give to them (you will need about twice the wattage to hear/feel a noticable difference. or 3rd. the enclosure design. A ported box will be about 3 db louder than a sealed box. this will be a much more complex box, it will be a lot larger box and it will be not as accurate (but can still sound good)
#########################
#########################
AMPLIFIERS --
cliff notes: Go with more power than what your speakers are designed to handle. Then look up videos on youtube about how to set your gains with a multimeter.
----------------------
detailed explanation:
There are two schools of thought about amps. Some people believe that you need to spend a lot of money to get good sound (usualy an audiophile) then there is the school of thought that 'a watt is a watt' meaning that there is little difference between two similarly designed amps (aka class a/b amps). I'm kind of in the middle but I believe that you'll gain a lot more from a less expensive amp with a lot of headroom v. an expensive amp with less headroom or under powered. The best way i can describe what headroom is would be to relate it to towing a jet ski. You have the option of two tow vehicles. A V8 Silverado 1500 or a Chevy SS (the new little compact car) Both will be able to tow the jet-ski trailer but one will do it a hell of a lot easier and will be more fuel efficient and will run a lot cooler. Its the same with amps. The more you turn up your volume, the more noise that the amplifier will make. If you have an amplifier that has 150 watts available, you can keep the amp running in a cleaner and cooler portion of it's power output while achieving comfortable listening levels. In contrast, if you have an amp with 15 watts (aka a typical headunit). you are going to have to push that amp a lot harder... and make it play in a much noise spectrum of its noise curve.
Another thing to note. the thing that will kill a speaker the fastest is distortion. If you have more power available and your gains are set correctly, you'll be less likely to get a distorted signal and your speakers will last longer. You'll probably come across the saying 'you will destroy a speaker a lot faster by under-powering it than overpowering it". Obviously under-powering wont hurt a speaker. if it did, every time you turned you volume down.. you'd blow your speaker :) Rather... under-powering a speaker usually lends you to turn up the volume more and then that is when you get into distortion.
when it comes to subwoofer... you will more commonly hear about "ohms" this is the impedance of the speaker. An amplifier is design to run at a minimum 'impedance' If you go below that rating, your amp will most likely go into 'protect mode' and shut off. or it could fry itself. An amp can power a speaker above it's rated impedance. It does come at a cost. the amp will produce less power... BUT the amp will be cleaner sounding and run cooler. The reason why you see sub amps rated at 2 ohms and 1 ohms is that the noise isn't as noticable in the 2 octaves that sub plays at. so we are kind of cheating. A draw back of running below 4 ohms is that the amps start to be less and less efficient. So the current draw from the alternator will not be linear between the same amp playing at 4 ohms, 2 ohms an 1 ohm. This means that the lower impedance you're driving... it may end up taxing your electrical system too much and wearing out your alt and possibly getting light dimming when the bass hits. I run my sub amp at 2 ohms without any issue.
#########################
#########################
WIRING --
wire is expensive.. but dont skimp on it. make sure you get a big enough gauge to handle the current (amperage) demands of your system. If you get wire that is too small you'll rob your system of power. The best budget amp wire you can get is welding cable. I'm running some 2 awg Radaflex cable. it's about half of what you'd pay for a 'car audio' amp wire. Be very weary about wallmart, amazon, and ebay wiring kits. A lot of time they'll measure the jacket to get the gauges wire. This means that you may see 4 gauge but the actual amount of wire is equal to an 8 awg wire. aka.. you're getting duped.
With our cars, you should always do the 'big 3' upgrade. This means to upgrade the wire for the following three connections:
battery ground to chassis wire, the chassis to engine block wire, and the alternator possitive to battery possitive wire.
#########################
#########################
BATTERIES --
there are very few instances where you need a second battery (or a capacitor). If you notice dimming of your lights you should first check to make sure your grounds are all solid. you should remove the paint in the area that you are grounding your amp to. next make sure you did the big 3 finally you'll need to look into a bigger alt. Just adding a battery is a band aid fix. Batteries store power, they dont produce it. If you add a second battery to solve your lack of current issues... then instead of producing more power, they are actually taking power (as much as another 15 amps) in order to charge up the battery.
The times you need a second battery are usually if you do a lot of engine off listening or compete in those spl drag races (how loud your subs are)