Okay, so I've been using a borrowed amp for quite a while and I was thinking about buying one of my very own, but I don't know exactly what to look for. I know that I would probably like to get a 5 or 6 channel amp so as to be able to hook up a subwoofer, and it would be nice for it to have a builtin crossover so that the subwoofer would only get the low frequencies, but what I don't know is what sort of wattage I should be looking for. All of the things that would seem to be common sense seem not to apply. My assumption that higher wattage would mean greater volume, all other things being the same, was shot down a while back. I don't really have any other guesses, so someone tell me what I should be looking for.

(As another point, how should subwoofers be mounted? Should its enclosure just be put in the trunk, or should there be some port from the trunk to the cabin?)

My assumption that higher wattage would mean greater volume, all other things being the same

Generally this is true except for the following:

1) The whole point of more wattage isn't necessarily to have higher volume. It's so that you don't have to push your amplifier to the edge of its capacity when you want to listen to the music and a moderately loud volume. Having "power to spare" is a good thing even if you never play the music loud. It means that the music you play will be cleaner and less noise-prone even when playing at low to medium volumes.

2) Make sure you know the difference between RMS wattage and peak wattage. The RMS numbers are more accurate and should be used for all comparisons. Many manufacturers and catalogs will report peak numbers which are essentially meaningless and can't be used reliably for comparison. That's one reason I like Crutchfield, they always quote the RMS numbers.

A five-channel amp that puts out 25-75 watts RMS to the four main speakers, and about 100-200 watts RMS to a subwoofer is often fine for most folks, provided they have good and efficient speakers.

As another point, how should subwoofers be mounted? Should its enclosure just be put in the trunk, or should there be some port from the trunk to the cabin?

Depends on your car. Obviously, the closer a speaker is to your ears, the better. And the less "stuff" between the speakers and your ears, the better.

But in most cars, there just isn't any room for a subwoofer in the cabin, and you have to trunk mount it. I've had to do it that way in my Accord, and provided the subwoofer is tuned correctly and everything is balanced properly, it sounds very good.

Having the subwoofer in the trunk means that certain frequencies are muted, so you have to make sure your car's rear speakers can make up the difference. During normal road travel, I'm probably not hearing much out of the subwoofer above 200hz, so I have to make sure my rear speakers will extend down that low.

Having my sealed-box subwoofer helps, because the bass is tighter and less boomy. This helps reduce a natural boomy-ness that comes from having a trunk-mounted subwoofer.

Crossovers and EQ corrections take care of the rest.

The whole point of more wattage isn't necessarily to have higher volume. It's so that you don't have to push your amplifier to the edge of its capacity when you want to listen to the music and a moderately loud volume. Having "power to spare" is a good thing even if you never play the music loud. It means that the music you play will be cleaner and less noise-prone even when playing at low to medium volumes.

(Sorry to quote so much.) So the idea is that greater wattage does equal greater max volume, not (obviously) that you have to run it that loud all the time. And the farther away from its max at which the amp is actually working usually means that you get a cleaner signal to the speakers (probably due to the fact that it's easier for it to increase and decrease its power output quickly?). (BTW, analog and power electronics are PFM to me.)

Yes.

What I was thinking is that it would make sense to have the subwoofer enclosure in the trunk, but have the ``output'' go directly through a hole in the rear deck by bolting the enclosure to its underside. Does that make any sense at all?

Okay. Good.

But the speakers must have some impact on this as well. I see most of them are listed with both Watts and Ohms. How do those affect the amp's wattage requirement?

A given amp will produce a higher wattage at lower ohm levels. This is why you will see a number of figures listed for each amp. Most car speakers are 4 ohms, so you can base your comparisons on that. Subs, on the other hand, can come in different ohm ratings, and you will want to use the lowest ohm rating that your amp allows. Subs can also be wired in parallel or series to affect the resistance, where stereo speakers can't.

Lower Ohms = More Resistance = Higher Voltage = More Work for the Amp

Matthew
PS: This is rather skimpy overview, i'm sure someone else will explain better.

E=IR, IIRC, where E=voltage, I=current/amperage, and R=resistance. So your statement about more resistance = higher voltage would seem to be true, but I'm pretty sure that more Ohms is more resistance.

Then again, we're talking about power, so P=IE, or P=IIR, so, still, more resistance equals more power.

But as I look at amp specifics, I am seeing things like ``Watts/channel @ 4 Ohms = 50'' while ``Watts/channel @ 2 Ohms = 75''. So there's something I'm missing.

i sorta don't agre with tony on this one.. well i do agree, but i have one differentation to make. You have to make sure you mids meet with your subs, crossover wise... but the whole theory of them being in the rear is not accurate in my eyes. The goal of a well balanced system is that everything sounds like it is coming from the front. , using rear speakers to pick up mid and ront speaker to extend to highs won't get you there, most of the time, imho.

also, you can wire subs in mixed mono additionally, not that it is that popular in non competition cars.

You may also want to state a budget and maybe some of us can guide you towards certain good amps.. yes, everyone has opinions, but for example, ppi and xtant are both considered pretty good general consumer amps, whereas that earthquake 1000 isn't

My 2 cents follows :

Spend good money on your amp(s). I would go with Rockford Fosgate, or JL Audio.
the JL amps are VERY clean, the Rockfords really have the Juice.
If you are going to buy Rockfiord Fosgate, make sure you buy the POWER series and
stay clear of the Punch series. BIG difference, you'd be shocked.
I know, I know you're saying "but, dave, I have Punch amps, and they rock"
not always the case...
Rockford makes 2 lines PUNCH and POWER. The POWER series is great.
Then there are 2 batches of PUNCH amps some that go to authorized dealers,
install shops, etc. those PUNCH amps are OK,
but then there's the PUNCH amps you find online for a good price,
or at the department stres, those are no good the only good way to know is to
check the birth certificate that comes with the amp and see that it was tested
at something like 20 percent more than its power rating,
so if you have an 800.4 that amp does 200watts RMS x 4 channels at 2 ohms
for a total of 800watts, a good 800.4 will test at around 1000 watts,
depending on what the voltage was at the time of test.

A nice beefy amp will make all the difference.
I put in that 800.4 in my Accord and it was my plan to
replace all factory speakers,
then I was real impressed at the difference it made,
I still haven't replaced the factory speakers.
Not that I don't recommend it, or that I'm not going to
I mean aftermarket speakers are THE way to go, for sure,
but get a good beefy amp.

If you are going to really want to crank it up,
then I would suggest that you get a separate amp for the subs.
Reasonbieng is that with a 5 chanel amp when you turn up the volume,
the subs really suck power out of the amp,
which can sometimes take away from the power to your other speakers,
thus leaving you speakers underpowered (more about that later)
I would get a 4 channel amp for in the car,
and a 2 channel amp for the subs.
Mono sub amps are good, but later they (might) offer less flexibility.

Pay attention to OHM ratings.
the Rockford amp does 200watts x 4channels at 2 ohms.
Well, chances are you'll only have a 4 ohm load on each chanell,
so that amp is really only gonna give you 100 x 4 at 4 ohms...
see how that works ?

Conversely, JL makes a 300/4 which is 75 watts x 4 channels at 4 ohms,
so you really have to pay attention, you definately want a 4 ohm load.
Since most speakers are rated at 4 ohms.

50 watts per channel at 4 ohms can make you deaf if it were done right,
75 watts is good to have, so you have a little more juice in reserve, and
100 watts to each of 4 speakers is just about all anyone would ever need.

Also, make sure that you have more amp than speaker.
so if you go with the 75 x 4 amp, look for 50-60 watt speakers,

if you have more amp than speaker,
the speakers have all they need to sound as good as they can,
and you amp can keep its cool running at say 80 percent.

if there is not enough amp for the speakers,
there just isn't enough juice to run the speakers,
so you turn up the volume and the amp is running at 100 percent
trying to deliver the power that the speakers need,
and the speakers don't get the power they need to perform adequately,
result is blown speakers or worse yet, blown amp.
Don't be afraid to over power your speakers,
they'll take what they need, just don't underpower them.

As far as subs go seald box in the trunk seems to work the charm,
folow same powerring rules as above, and you're golden...

yes this is called porting, but is usually unnecessary, however, if you are in an e36 mbmw, you may have to do this for a good sound. This is why many people feel hatchbacks are better for ICE

Well, from what I've read, porting is when you have a tube that extends into the rear of the enclosure which allows it to move air from behind the speaker, and that allows it to be a little louder, but most people are claiming that it also reduces definition. Since I'm not looking for pure volume, I thought I'd go with a seealed enclosure, but if I just put that in the trunk, then the output of the speaker will be muted by the materials that separate the trunk from the cabin. What I was suggesting is having a normal sealed enclosure, but then mount it underneath the rear deck so that it points upward through a hole I've cut in the deck itself. That would still keep the sub and the enclosure in the trunk, but it would allow unfettered sound to get into the cabin. (The reason I'm thinking about this is because I would like to get better bass response, but I hardly want to have my whole car vibrate down the road, and I'm afraid that that's what I'll end up doing unintentionally.)

So the deal is that the wattage of a speaker is what it needs to run. And the wattage of the amp is how many watts it can provide.

What does the wattage of the speaker imply? That is, assuming I have an amp that could handle either, what advantages would I have in picking 75 Watt speakers versus 50 Watt speakers?

So the deal is that the wattage of a speaker is what it needs to run. And the wattage of the amp is how many watts it can provide.

Yes.

What does the wattage of the speaker imply? That is, assuming I have an amp that could handle either, what advantages would I have in picking 75 Watt speakers versus 50 Watt speakers?

Speaker wattage is how many watts you can cram into them before all the smoke leaks out of them and they stop working. 75 watt speakers can accept more wattage than 50 watt speakers, and thus make more noise before they stop making noise permanently.

Let me see if I can summarize all of this succinctly...

Amplifier Wattage: The more you have, the better sound you can get. Just think of it as the maximum that the amplifier can produce; you don't use all of it, and the less you use (percentage-wise) the better your sound.

Ohms: Smaller Ohms (lower number) means less resistance. Less resistance means it is "easier" for the electricity to go through the speakers, thus they will draw more wattage and play louder. Think of it like a drinking straw -- less resistance = larger diameter. Downside: lower resistance/higher wattage means less clean sound. Top quality competition cars (those competing for sound quality, not for maximum decibels) frequently use 8-ohm speakers.

Speaker Wattage: See second paragraph, above.

Sub Enclosure:: A ported box is louder, particularly at the resonant frequency determined by the area and length of the port. This is likely to give an uneven frequency response, with a "hot spot" at the resonant frequency. A sealed box gives better sound quality, with a more balanced response across the frequency range. It is not necessary to have a direct air path from the trunk-mounted subwoofer into the passenger compartment... IF there is an acoustically transparent path from the trunk to the passenger compartment, such as through rear seats with fabric upholstery.

Channels:: The more the better. My ShoWagon (currently under construction) has eight channels for the front/rear stage, plus four more channels (bridged stereo) for the subs. I highly endorse... hmmm, was it rockstar? suggestion of a separate amplifier just for the subs. It gives many more options for tuning, and relieves the load on the front stage.

Well, this is already a much longer post than I had planned, so enough already. Hope this puts things into perspective.

tanstaafl.

Speaker wattage is how many watts you can cram into them before all the smoke leaks out of them and they stop working. 75 watt speakers can accept more wattage than 50 watt speakers, and thus make more noise before they stop making noise permanently.

But assuming that I never overdrive my speakers (I know, I know), what's the difference? I've read that doubling the Wattage only increases the actual volume level by about 3dB, and that to double the volume would require a tenfold increase in the Wattage. Based on that, 75 Watt speakers drawing 75 Watts would only be marginally louder than 50 Watt speakers drawing 50 Watts. Or is that information totally incorrect?

I guess what I'm asking is what the advantage is to having higher Wattage in the system. You say that ``lower resistance/higher wattage means less clean sound'', so why would I not go with 25 Watt @ 4 Ohm speakers and a 50 Watt at 4 Ohm amp, assuming that I'm looking for sound quality as opposed to just volume? Would the volume be way too low?

(Also, will n Watt speakers always draw n Watts from the amp, or is that the max, depending on volume or some other magic variable?)

well that is part of the game, finding speakers that sound good and are efficient. I think both my jl series are very efficient.. i am running 2 sets of components and a 10" sub off a ppi 4400.2 it doesn't overheat and it soudns good (albeit in need of further tuning)

But that is part of the deal.. any you really need to wade thru the crap that people boast xxx watts.. there are certain names that are more known for clean pure amps. I had an xtant amp that was like 25x2 competition power, it pounded the HELL out of 2 10's that i had that were very power hungry, and never even warmed up. your ave amp goes about $1 a watt, step that up to $2 a watt and you get a much better amp IMHO. There again, crap components with fantastic tuning will sound the same or better then great components with crap tuning. Stay away from place s like audio express, payfor decent stuff, or do the install yourself and order online.

caraudioforums.com is a much larger bbs about this sort of thing, you may want to check it out.

If you want my opinions on it, i have yet to find a manufacturer that puts oout the consistently good amps like ppi for anywhere near the price. So i would say get precision power amp(s)

maybe this amp for your components
http://www.precisionpower.com/pcx480.html

or this for a full system
http://www.precisionpower.com/pcx5800.html

this for subs
http://www.precisionpower.com/pcx2125.html

xtant is great but they are more expensive.

could throw this in for the highs for a nice clean sound
http://www.xtant.com/html/products/X604.cfm

i think you lost me on the ref, i couldn't find out what you were referring to tha ti said, but i am really sick right now so i could be blind... for sure the more channels the better, but you can still have great sounding systems running off 1 amp

also, when i said porting, i meant porting the decklid, nto the box.

A higher power speaker can reproduce a signal more accurately.

think of a the sound of the song you are hearing
as you look at the spaker move in and out.
notice how it moves in an out to create the sound you hear.
A higher powered speaker tends to be more accurate
as to where the cone should be at any split second.
Because there is more power available, the accuracy goes up,
but also, the distance (throw) that the cone is able to move
in and out while still creating quality sound is increased,
giving the higherpowered speaker a wider range of
accurate sound production,
Now, the speaker that is moving in and out more, moves more air,
which is where the general idea of more wattage means more volume.

Lower powered speakers can oly move the speaker in and out a little,
and there is less extra power laying around to increase accuracy.
Less volume and less accuracy.

I can't think of a good analogy for this right now, but I will,
and I'll post it when I do. For now, Hope this helps.

If your amp is 75 watts x 4 chan at 4 ohm,
You could buy 1 of 2 things for about the same money...
A high quality set of 50 - 60 watt speakers or a lower quality set of 75 watt speakers.
I'd go with the 50 - 60 watt speakers. or I'd spend the moey for the better 75 watt sspeakers.

Now if you have a JL Audio 300/4 (75 x 4 at 4ohm) then I would go with JL speakers (all rated at 75 watts) get the biggest separates you can fit in your car (6.5" if you can)
Size matters. If you're gonna have subs, bass comes from the rear. a 6.5" speaker up front will compensate for that much more than a 5.25 will.

The other thing is I would get a nice big am 75- 100 watts x 4. put that in and see how it sounds.
then replace the front speakers and see how that sounds, then replace the rear speakers,
you may find no need to replace the rear speakers, leaving more budget for the fronts.

While he's finding out about this, does anyone have a good resource on the web for learning about resistance as it pertains to car audio? I've got my amp all tweaked out, and I _think_ everything's running at 2 ohms, but it's the one part of it all I don't understand. I'd like to learn for when i upgrade some stuff. Thanks!

So it sounds like I've two ways to proceed. Either figure out what speakers I want first and match the amp to them, or buy an amp that has a large RMS rating so that it'll be unlikely that any speakers I decide on later will be underpowered.

Does that sound reasonable?

the first step is to set a budget, i mean that seriously. FIgure out what you are willing to spend, then buy an amp, for 2 sets of components you are looking at roughly the same price as a decent amp.. then you have to allocate for a sub/subs

budget, amp(s), components, sub(s) that would be my pecking order

and that link is actually www.caraudioforum.com i got it wrong before.. that should also answer the ohms ?'s

I dont know where you would find specifics but I can give you a run down on ohm loads, Just tell me what is you are trying to find out.

(given there is a lot of information in this department that most no one cares to know, plus a lot of usefull things)

Basics:

lower ohm load, more power, but more heat, most amps can handle a 2 ohm load mono these days but anything lower than that will burn them up under constant usage. Also the amount of power you get from droping an ohm load varies from amp to amp.

example:
Decent Rockford amp will more and likely double wattage when dropping from 4 to 2 ohms
where as a competition orion amp rated @ 1 watt @ 4 ohm can be dropped to 1000 watts @ 1 ohm

we have a few relevant papers at:

http://www.teamrocs.com/technical
--
sancho

does anyone have a good resource on the web for learning about resistance as it pertains to car audio?

The best website I have ever come across dealing with car audio, from the absolute basics ("...what is an electron...") to subjects so deep that I don't even begin to have the math to comprehend them, (for example, look here) is:

http://www.eatel.net/~amptech/elecdisc/caraudio.htm

[prosyletize]
This is really a fantastically good website, done as a hobby and labor of love by a man who I believe is retired from the electronics industry. I would actually go so far as to say it is the best website (on any topic) I have ever visited. While the more you know about car stereo the more you will get out of it, even if you know nothing at all it is well enough presented that you can give yourself an education* to equal or surpass that of any installer you are likely to come across in any stereo shop. It is that good. I highly recommend that you bookmark this site.
[/prosyletize]

tanstaafl.

*by education, I mean theory, not practice. A good installer knows "tricks of the trade" that would amaze you!

Ohm's you ask, -eh.
Ijust got my head around them myself
during my mission to install empeg a few months ago, so here 'goes.

Ohms measure the ammount of resistance on a given circuit.
For example purposes, let's say you have a 2 channel amp,
that does 100 watts on each channel at 4 ohms.

This means that if you connect one 4ohm speaker to each channel,
they will each get 100 watts of power. Simple so far.

Now let's say you put one 2ohm speaker on each channel, now the resistance is only 2 ohms,
so "theoretically" the speaker will draw 200 watts out of the amp.
This is contingent on wether or not there is enough voltage powering the amp and
wether or not there is a regulated power supply inside the amp.
Some amps are designed not to allow this theoretical "doubling of power"
some are built on the idea that you can, like Rockford Fosgate's Amps.

A real good way to understand this better is to consider your Sub woofers.
Let's say you have 1 Sub rated 500watts RMS at 4ohm.
And you have a 2 channel amp (250 watts x 2 chan @ 4 ohm) to run it.
First bridge the amp, giving the above mentioned amp (500 x 1 chan @ 4 ohm)

You do this by connectint the LEFT chanel positive to the positive lead on the sub
and connect the negative on the sub to the RIGHT channel's negative.
now your 250 x 2 chan @ 4 ohm amp puts out 500 x 1 @ 4 ohm, pretty simple
and perfect, since this is the exact specification of your sub.

Now let's say you want to add another sub.
Well first instinct is to say, well geez, I need another amp to run it, right ?
Wrong.

You can connect two 4 ohm subs together and they will present a 2 ohm load to the amp.
Do this by connecting Left Positive to positive on sub#1,
negative on sub#1 to positive of sub #2 and negative on sub#2 to RIGHT negative on your amp.
Now you are showing your amp a 2 ohm load which will
turn your 500 x 1 channel @ 4ohm into 1000 x 1 channel @ 2ohm.
Voilla ! free 500 watt amp.
Now bear in mind that you are taxing your amp a bit here,
and I wouldn't do this unless you have a really serious amp.
Do not buy a cheap amp and think you are gonna pull this off.
Rockford Fosgate Amps are great for this. I would recommend them for this.
And of course, as always, RTFM before you do anything.
If the manual is of no help, check manufacturer's website,
and also, your local installer can help you with specific wiring issues.

Also make sure you have some pretty serious power wire from the battery to the amps,
anything over 1000 watts total I would go right to 2 guage wire.
Run it from the battery down the battery side of the car,
(you want the shortest piece of wire possibe)
once it gets in the trunk,
you can put a distrobution block and take off whaterve guage wire your amp(s) require.
then be sure that you RCA wires run down the opposite side of the car.

There has been alot of good things said in this quote but I have to take issue here.

In reply to:

---

A higher power speaker can reproduce a signal more accurately.
think of a the sound of the song you are hearing
as you look at the spaker move in and out.
notice how it moves in an out to create the sound you hear.
A higher powered speaker tends to be more accurate.....

---

There really is no direct correlation between speaker power and sound quality. For instance sennheiser headphones have a small speaker that puts out 12Hz to 38kHz +-3dB crystal clear. The headphones when worn on the head are generally considered to sound similar to $10,000 speakers. The downside being the can only put out a few tenths of a Watt. Accordingly they need to be a few inches from your ear to sound good.

In actuallity it is harder to make higher powered speaker that can deliver clean sound. This is because the cone of the speaker has to travel farther and the driving mechanism (voice coil) has to be linear over a longer distance. This also adds mass to the driver which further complicates design.

Also somone earlier said P=IIR so if R goes up so should P. The problem with this is that a car amplifier forces an output volage and I=V/R. So Power out as a function of V and R using the above P=IIR is P=V/R * V/R *R or P=VV/R. Power goes down with increasing R.

Rgds,
Eric Fesler
BSEE (power electronics)


This is

True, but power rating has nothing to do with woofer throw.
two speakers could have similar deign and exact same woofer throw,
while the other might require more juice to move the cone.

Your tenth of a watt headphones are simply much more efficient than standard headphones,
much like those really thin home stereos from Bang & Olfsen.
Efficient speakers + clean amp signal is just one way to arrive at accurate sound.

Now I'm sure that there is a wristwatch out there
that is considered to sound similar to the price of tea in china, but
in a comparison like the one the origional poster will soon be making:
"should I buy the 20watt 5.25" coax or the 50 watt 5.25" coax for the front doors of my car,
The solid advice is that the 50 watt speakers will probably produce a a more accurate sound (at higher volume)
We can do algera and find hypotenuse's 'till the cows come home, the bottom line is that in your car, a set of 50 watt speakers will sound better (more accureate at higher volume) than the 20 watt ones that came with the cear, provided they are adequately powered.

The solid advice is that the 50 watt speakers will probably produce a a more accurate sound (at higher volume)

And yet they may well end up producing a less accurate sound at lower volume. As Flatline pointed out, more power capability will (usually) involve more cone movement and more mass to move, requiring more power from your amplifier for the same output.

Sure, the speaker may be able to accept more power than the lower-rated one before the smoke leaks out, but it will also require more power to make any noise at all at the other end of the volume scale. It was precisely for this reason that we decided on 250 watt rated subwoofers instead of the higher-end 500 watt subwoofers for my ShoWagon. I only have 300 watts total for the subwoofers, so having a pair of subs that could eat a total of 1000 watts was a bit of an overkill.

tanstaafl.

In reply to:

---

A real good way to understand this better is to consider your Sub woofers.
Let's say you have 1 Sub rated 500watts RMS at 4ohm.
And you have a 2 channel amp (250 watts x 2 chan @ 4 ohm) to run it.
First bridge the amp, giving the above mentioned amp (500 x 1 chan @ 4 ohm)

---

Not exactly. You see, when you're bridging an amp, you're adding the voltages of both outputs, hence doubling the output voltage, not the power. Since P=U² / R, the power output of the amp will quadruple when you double the voltage. So the 2 * 250W amp becomes a 1 * 1000W amp. You'll need a very good amp to reach those figures though. Cheap amps will only double their output because of inferior end transistors, a good (read expensive ) amp will often near the figures.
Take a look here for example:http://www.audison.com/thesis/ethesi2.htm , you'll notice in bridged mode, it goes from 160 to 600W.

So if you want to end up with 500W, use an 8 ohm sub instead (or 2 * 4ohm subs). Because your impedance is twice as high, the dampening factor (is that the correct word? - I'm Dutch speaking) will double (which is a very good thing for a sub since it quantifies the way it can 'control' the conus of the sub)

Frank