As I'm sure you can imagine, there's basically no room inside a DeLorean to hide an amp. There is a rear shelf behind the seats that is normally for luggage that some people use to screw down amps. I'd really much rather have mine hidden.

Right now I have a small 2 channel amp screwed into the wall behind the passenger seat. I think the ideal spot would be under the seats, but there's hardly any room. I've been trying to find the absolute smallest 4 channel amp in existence. Any ideas?

-Christian

What dimensions are we talking? What kind of power?

I'd have to take some measurements, but I'm guessing in the 1" thick range. All the amps I've seen are in the 2"-2.5" range. Do they make them any smaller? Are amps generally made large so that they look massive and impressive, or is it really necessary?

Without getting into exceedingly expensive, It's necessary for an AB type amp. They waste a LOT of energy as heat, and as such, it needs to be dissipated by using large bulky heatsinks. Type D amps are what you're looking for.. Unfortunately, there are the most expensive types available.

Here, some light reading:

Amplifier FAQ

Power?
There are different ways in which power is measured by amplifier manufacturers, to make people think that their amps have more power than others. Laws of physics tell us that Power can be obtained by multiplying Current and Voltage. For example, if your amplifier gets 12 volts, and it draws 20 amps, then power would be 240 watts, right? Not exactly. In the real world, amplifiers waste 50% or more of the power in the form of heat. That leaves you with only 120 watts.

Things get more complicated than that. There are different ways to measure power. Power can be measured for top to bottom of the signal (Peak, or Max, etc). Another way to measure power is From the zero-level to the top half (usually called music power). The most accurate way to measure power is RMS (root mean square) watts. The RMS value is obtained by squaring the value of the signal, taking the average, then the square root. This is the equivalent of the actual power delivered.
To get RMS power from peak or max power just divide by three. Music power is just half of peak power. For example, an amplifier is rated at 100w (peak) per channel. The so called Music power would be only 50w per channel. The RMS power would be 33w per channel. Big difference, isn't it? Be careful when checking specifications of amps before buying, to see what you are really getting. Always check the RMS power of an amplifier.

Confused enough? There is more. Some companies rate their amplifiers using unrealistic conditions, for example calculating power at 15 volts, under 2 ohms, at 10% distortion, etc. Make sure you see the actual test voltages and loads.



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How to tell if I am getting a good amp?
Shop for reputable brands. Look at the size, weight of the amp. The more power the amp puts out, the more wasted heat, and the bigger area it will need to dissipate that heat (bigger heatsinks). Some exceptions are "digital amps" (i.e. Infinity). This alone can't be enough to determine if the amp is good or not. Watch out for companies that actually use a much bigger heat sink than needed so that it fools consumer, giving the idea of a much powerful amp.

Look at the fuses that are either plugged into the amp, or specified by the instruction book. If you see a 400w amplifier with a 5-amp fuse, you should be suspicious. Remember what was said above, multiply size of the fuse by around 6 (12v at 50% efficiency), and that will give you a rough idea of what you are dealing with in terms of RMS power.


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How much power do I need?
For mids and highs, anywhere from 30 to 50 watts (RMS) per channel would be decent. For subs you would need at least 80 - 150 watts (or more) per subwoofer. There should always be more total power going to the subwoofers than to the rest of the speakers, since human ears are more sensitive to higher frequencies than lower. For example, if you have 4 x 50 watts going to all your mids and tweeters (total=200 W), then you should have at least 200 W or more going to your subs.

A lot of people wonder if too much amplifier power can burn up the speakers. What damages speakers most of the time is distortion, not power. If the speakers have the proper crossovers and are not distorting, then it is really hard to blow them. A bigger amp just gives you the opportunity to go to higher volumes without distortion.


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What Else to Look For in an Amplifier?
It is a good idea to get an amp with a built-in crossover, so that you don't have to spend extra money later on crossovers. If you are going to be using multiple speakers, make sure the amp is 2-ohm stable (or less). A bridgeable amplifier could come in handy in the future if you are planning to upgrade. Overheat, short-circuit, overload protections are good features that any good amplifier should have. Look for a low THD (total harmonic distortion) rating.


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Amplifier Classes
There are different amplifier designs: Class A, A-B, B and D

Class A amplifiers are the most sonically accurate. On the other hand, they have some drawbacks that make them not be the most common choice. Class A amplifiers use only one output transistor that is turned "on" all the time, giving out tremendous amounts of heat. Class A amplifiers are very inefficient (~25%). More heat means more heatsink area, so even though most class A amps have built-in cooling fans, they are big. Class A amplifiers are usually expensive.

Class B amplifiers are the most common and use two output transistors. One for the positive part of the cycle and one for the negative part of the cycle. Both signals are then "combined". The problem with this design is that at the point when one transistor stops amplifying and the other one kicks in (zero volt line), there is always a small distortion on the signal, called "crossover distortion". Good amplifier designs make this crossover distortion very minimal. Since each transistor is "on" only half of the time, then the amplifier does not get as hot as a class A, yielding to a smaller size and better efficiency (~50%).

Class A-B amplifiers are a combination of the two types described above. At lower volumes, the amplifier works in class A. At higher volumes, the amplifier switches to class B operation.

A not very popular kind is the class D amplifier (known as digital amplifier). These amplifiers are not really digital (there is no such thing), but operate similarly in the same manner as a digital-to-analog converter. The signal that comes in is sampled a high rates, and then reconstructed at higher power. This type of amplifiers produce almost no heat and are very small in size, but really expensive. Efficiency is much higher in class D amplifiers (~80%).


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Amplifier Installation
The remote turn on wire goes to the head unit. When the radio is on, it puts out 12 volts that turn the amplifier on. If you are using a factory radio that does not have a remote turn on (or power antenna wire) you can tap into, hook it up to the ignition, so that the amplifier does not remain on when you turn the car off. If you are using more than two devices (amplifiers, crossovers, equalizers, fans, etc), you might have to add a relay, since typical turn-on wires in a radio can't handle more that 300mA.

Even though amplifiers are easy to install, a lot of things could go wrong. The most important thing to consider is where to get the power from: Straight from the battery. ALWAYS put a fuse as close to the positive battery terminal as possible. If the wire going to the back of the car shorts out, then the fuse will blow. If you don't install a fuse or breaker and the wire shorts out, then the wire will carry so much current that the insulation will melt and could catch your car on fire. The size of the fuse should be the same rating as the fuses used by the amp(s). The ground (-) should be hooked-up to a metal part of the car. It is not necessary to run a ground wire all the way to the battery.

It is not essential to spend a lot of money in getting 99.999999% copper 0-gage wire and gold connectors unless you are installing a competition system.

When running power wires to the amp, keep them as far away from the RCA wires (see alternator noise section for more info), ideally on the other side of the car. It is OK to run the turn-on wire from the radio along with RCA's, since it carries very little current.


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Electrical System Upgrades
If your car's electrical system does not have enough power to keep up with your amp's current demands, then some changes have to be made to your car. If you feel that your amps can't really handle transients (going instantaneously from low to high volumes), the first thing to do would be to add a stiffening capacitor. What a capacitor does is act as a secondary battery that reacts very quickly to sudden current demands. A rule of thumb is to have 1 farad of capacitance for every 1000 watts of power. Capacitors should be installed as close to the amplifiers as possible, with the positive lead going right into the positive lead of the amp, and the ground to a metal part of the car (not to the ground terminal of the amp). When a capacitor is first installed, it has no voltage in it, so if it is hooked up to a battery, it will act as a short circuit and draw a LOT of current (not a good sight). Capacitors need to be "charged up" first. This is simply done by either putting a resistor (1k-ohm or more) or a test light between the positive post of the battery and the positive terminal of the cap (with ground hooked up to metal). After a few minutes, the capacitor will be charged up, and it can be connected. Every time the capacitor is "drained" i.e the lights were left on in the car and battery is dead, the capacitor should be DISCONNECTED, battery charged, and then capacitor has to be recharged and reconnected.

Another upgrade would be to get a high output alternator, and to add a secondary battery to keep up with higher system's demands. This should be done by someone who has a fairly good understanding of a car's electrical system, since computers are designed to control the factory components. Always keep in mind that when a car is running the batteries become loads that take power away from your amps. The advantage of secondary batteries is that when the car is off, you can listen to your stereo for longer periods of time. Adding more batteries will not make your stereo perform any better when the car is running. In fact, a second battery will steal power from the electrical system when the car is running. A battery isolator should be used to avoid batteries draining each other

Type D amps are what you're looking for

That is a very nicely written tutorial.

I take issue with only one part of it -- where you proselytize about the benefits of a Class-D amplifier.

In my (admittedly limited) experience, Class D amps are good for one thing only: getting maximum amount of noise out of a subwoofer with minimum amount of input power.

A class D amplifier gets its efficiency by aggressively filtering out the higher frequencies at the pre-amp stage. This makes a Class D amplifier ideal for a subwoofer amplifier, because you don't want those high frequencies going to your subs anyway, so why waste power generating them.

This also makes a Class D amplifier somewhat less than ideal for a subwoofer amplifier, because without some of those higher frequencies, all you are left with is the boom; you lose the tight crispness and the warmth that a subwoofer can produce if you get brave enough to raise the crossover point above the normal 80-100 Hz. I cross my subwoofers (dual 10"s in a common enclosure) at about 800-900Hz.

And of course for running a complete stereo system with speakers ranging from 1" (or smaller) up to six inches (plus, of course, your subwoofer(s)) a Class D amplifier is exactly what you do not want if sound quality is even remotely important to you.

Now, I could be mistaken about all this -- this is just a summary of my own personal experiences -- and would be quite interested and not the least displeased to be proven wrong.

tanstaafl.

I went through this when doing the install in my Ferrari. In an effort to find the thinnest amp(s) possible I came up with a brand called Helix. They are a very high quality german made amp. I've got two of them in two different cars and can strongly reccomend them.

http://www.theautophile.com/products/HelixAmps.html

I have the HXA400 MKII in the Ferrari, and a HXA40 in my SO's Miata.

They are about 1.25" thick if I remember correctly.

No afilliation, yada, yada, yada, just a happy consumer.

Jeff

Learned a lot in what must be a top-ten entry for longest post, thanks.

Like Tanstaafl, I'm not sure about some of your comments about class D amplifiers.

As I understand it, Class D amps have to use filtering to filter out the sampling garbage in ultra-sonic range. This is commonly done through coils between the output devices and speaker terminals. Big disadvantage is that, as a result, frequency response becomes dependent on the actual impedance of the speaker connected. So unless you have the exact right and constant impedance, you may experience exessive or dull highs

BTW, there is a true digital amplifier; not class D. The Tact Millenium accepts S/PDIF in and sounds truly awesome, in particular with serious High-end speakers.

There's some interesting "room-correction" stuff there too. Need a bigger wallet

Cas.

I should have been clearer, that was NOT my FAQ, I just found it informative and interesting and reposted it.....

That amp's hella cool.

i have got a Helix by Brax and it is the best i have ever heard. it is very small and it has all protection that you could think of. so check it out http://www.audiotec-fischer.de/index2.html

All I can say is wow. That was a very informative post, from where ever you got it. I wish I had read that a few years ago when I was shopping for amps for my current system. While I am happy with what I have, it would have been nice to know more at the time. That article was written in such a way that even a non-audiophile such as myself can understand the concepts.

I am now off to the manufacturers website to see just how well my current amp stacks up afterall!

Hey, what's the URL for this FAQ? I just got my empeg installed and it has NASTY whine. Though I haven't read the empeg FAQ and stuff yet, I think it's alternator whine, but I don't know. I saw "alternator whine" mentioned in the FAQ quote you posted so I want to read their take on it. Thanks.

Though I haven't read the empeg FAQ and stuff yet, I think it's alternator whine

The empeg FAQ has an extensive discussion of ground loops and alternator whine, including links to several online documents that detail the necessary troubleshooting steps. Before discussing noise problems here on the BBS, make sure to go through all of the diagnostic steps listed in all of those documents. Be thorough, because the smallest detail could be the thing that's causing the problem.

This is from an audio engineer

In reply to:

---

Class D is a like a digital switch, 1 or 0, open or closed, on or off. Everytime a change is made, inertia slows the process down a tad. Class A amps on the other hand (rarely found in mobile audio, but all over pro audio) are always on, which allows a faster response...better slew rate. This is why people do not like Class D amps, however, they do work extremely effiencently, especially in the lower frequencies.

The ultra-sonic mess they referred happens all around us. The accepted human hearing range is 20 Hz - 20kHz...right? Anything above is ultrasonic. And what happens to such frequencies in a speaker...they create heat, and lots of it...not a good thing. Okay, back to the filtering out of ultrasonic frequencies, this is basicallly an anti-aliasing filter. I'm not going to get into the details right now because I've been awake for over 24 hours right now.

---

Most whines and ground loops can be taken care of by simply grounding your empeg directly to your amps with nice, 10 guage cable. All 3 of my amps, my cd/radio, and my empeg share a common ground lead and everything is crystal clear. I know it's not always convenient, but hey, what's more important? Better sound, or a 1 time pain-in-the-ass install? The other key is to make sure the gain on your amps is set as low as you can. Make your player do the work volume-wise. Make sure you won't hurt your speakers when you turn everything all the way up. I have my empeg all the way up all the time. Yeah, I could turn the gains on my amps up to go louder, but who REALLY needs to?

Just as an side comment/opposing opinion of digital amps: Sharp came out with the SM-SX100 1-bit all digital amp that picked up top notch reviews in all the audiophile rags and webzines.

This digital amp costs $16,000 (!!) and has no analog circuits in the signal path from input to speakers. The digital data stream is used to directly drive the amp output (!). Since it runs at such a high frequency, noise is shifted high enough that it is not heard or reproduced.

Calvin

16 grand and it's still butt-ass ugly. What a shame.

tanstaafl,
You cross your subs between 800-900 ??
Does'nt that kind of defeat the purpose of having subwoofers? maybe a mid bass might be more effective

I am of the understanding that subs are ment for operation between about 10-200Hz max.

Your subs must sound very , muddy,
but - to each his own, whatever sounds right for you is the go !!

cya

Nope, he's got a competition-quality system. I have never heard his system, but I know him well enough to know that his subs would NOT under any circumstances sound muddy.

If he crosses them at 800, it's because the enclosures, the cones, the amplification, and the interaction with his other speakers all add up to a system where 800 happens to be the perfect crossover point.

How can you trust a guy that sups up a taurus station wagon?

In reply to:

---

As for the crossover comment, I cross my sub over at 150Hz usually, but I don't really go higher than 250Hz depending on the music I'm listening to. I find that above 250Hz, a lot of sound is produced that isn't meant to be heard through a boomy subwoofer - it usually hits my ears as deep wobbling noise that doesn't sound pleasant. While I do agree that going above the standard 80-100Hz is definitely better, 900Hz? That's reaching well into vocal range (a man's, at least)...I couldn't imagine such noise.

---

This is from another message board

How can you trust a guy that sups up a taurus station wagon?

I take personal insult on my friend's behalf. I beg to differ with that comment. He did no such thing.

No, what he did was drove all the way across the North American continent to pick up an already souped-up taurus station wagon.

is that suppose to be in his defense

How can you trust a guy that sups up a taurus station wagon?

Hey, watch it, Rice Boy!

tanstaafl.

You cross your subs between 800-900 ??
Does'nt that kind of defeat the purpose of having subwoofers? maybe a mid bass might be more effective

No.

Remember, I am running a pair of 10" subs in a common enclosure. A 10" speaker (of sufficient quality) will produce pretty decent sound up to about 800 Hz. Because of the acoustic coupling provided by the common enclosure, I get the better part of two worlds: the brightness, tightness, responsiveness, and tonality of a 10" speaker, but also with the capability of reaching the same low frequencies that could be attained with a 14.2" subwoofer (if there were such a thing), as the lowest frequency a speaker system will produce is a function of total cone area within the enclosure.

I am of the opinion that a subwoofer can and should do a lot more than go "blumph blumph blumph" every time it plays a drumbeat. The improvement in sound quality in my car is quite significant when I raise the crossover point from the common 100-200Hz up to the 800-900 Hz range. This may be a freak occurrence unique to my particular car and stereo system but I get a warmth and presence that suffuses the entire car once I start getting actual tonality from those speakers, and the higher frequencies, far from sounding muddy, impart a crispness that is lacking when I cross them at 200 Hz.

I had this argument at stereo competitions several times with my old car (another Taurus wagon) and the only way to end it was to put the disbeliever in the car, and then play the stereo, switching the crossover on, and then switching it off so the speaker (single 10" in that car) played full range. Nobody ever argued the point after hearing the results.

tanstaafl.

Alpine used to have some quite thin amps. A two channel (MRH-T305), a four channel (MRH-F254) and a five channel (MRH-F255), all 35 mm thick, that's about 1.4".
I used to have the F255 under the passenger seat of my Plymouth Duster. Not great but definitely OK if you are not into high end car audio but dig your empeg for other reasons.

I'm glad it works for you, but it's unusual. I doubt it sounds muddy though, raising the X-over point shouldn't do that, a crappily designed box might but that's not what you have.

I can get the same "warm effect" by simply turning up the bass, and it sounds to me like you're basically doing the same thing... By nature a little extra bass sounds warm, and most people prefer it. Some old-timers (Clark and Navone) did some tests with musicians setting an EQ where they thought their own music sounded best, and it was always ramped up at the lower end through an RTA.

I would be very certain that your front main speakers are not also crossed at the same point - that would sound horrible. Instead you just have a whole lot of overlap, right? I've heard other people run that way, because they didn't know how to set the crossovers in their amp (NOT accusing you of that). Yeah there was extra bass, and to me it sounded bad, but I don't like rap And it was also pulled to the back of the car, playing something like Korn where the singer has a deep voice was funky - not only did the voice image travel all over the place, but certain ranges of it were way too pronounced where the subs duplicated what the front speakers were playing.

I'm not going to say your system sounds bad - I haven't heard it. In my experience though, I like the front speakers to play as much music as possible, and the subs to play only the very bottom end that they can't handle. I use equalization to make it sound "warm" and accurate and everything else, where needed, and as little as possible.

If you like it, that's all that matters. Everything is worth trying out I guess.

tanstaafl:

[homer]Your ideas intrigue me, and I wish to subscribe to your newsletter.[/homer]

Seriously though, what kind of subs are you running? Are they in a sealed or ported enclosure?

It's really a pretty neat idea, for someone with a wagon or hatchback. I would think that you'd have one huge problem, though - as you get into the higher frequencies, don't you start to get some serious directionality going on? I would think it would mess up your imaging something fierce.

so if i decide to go for 4 regular 6 1/2" speakers in a common enclosure... will i be able to do the same thing you're doing and eliminate the need for subs and midbass?

well, aside the fact that your soundstage would be screwed , i guess it'll work.

so if i decide to go for 4 regular 6 1/2" speakers in a common enclosure...

In theory, this would give you the equivalent of a 13" subwoofer on the low end, but with the undistorted highs that a 6.5" speaker is capable of producing. In practice, this acoustic coupling business does not perform as well as in theory -- but the effect is nonetheless noticeable. I find my dual 10's seem to go down about half an octave lower than my single free-air 10 in a previous installation would reach.

Note that you have to feed a single monaural signal to all four speakers so they act in unison in order for this to work.

tanstaafl.

Seriously though, what kind of subs are you running? Are they in a sealed or ported enclosure?

I am running a pair of Diamond Audio dual voice coil 2-ohm speakers, connected in series for a 4-ohm load. They are in a common, sealed enclosure that is built into the sidewall of the rear of the station wagon (see attached picture). The volume of the box was as close as we could get to optimum, given the constraints of working with the shape of the car. It is probably about 20% larger than absolute optimum.

as you get into the higher frequencies, don't you start to get some serious directionality going on?

Some -- but not a lot. Remember, those subwoofers are about eight feet behind me, and low frequency sound isn't all that directional. I use the term low frequency somewhat loosely here -- 900 Hz isn't all that low. But when you consider that the front stage is sometimes producing sound at twenty times that frequency, that may put it into perspective a bit better. Perhaps another contributing factor is that the subwoofers are not pointed towards the front of the car -- they are pointed sideways across the back of the car, and reflect off the windows a few times before arriving at the listening position. This would tend to further degrade directionality. I lose more imaging, I think, from the two 6.5" speakers back in the roof than I do from the subwoofers.

Perhaps the most persuasive argument I can make is purely anecdotal: I had to stop telling the IASCA judges how I was crossing over my subs, otherwise they scored me on what they thought they should be hearing, instead of what was actually there. When I kept them ignorant, my scores were quite respectable. Another anecdotal example: This will sound like I am bragging, but remember, I am a medium sized fish in a very small pond here in Alaska. Just about everybody who has listened to my system says it is the best they have ever heard, and not a single person has ever thought it sounded better with the subwoofers crossed over at a low frequency. About 80% of the people who hear it will use the words "clear" or "clean", completely unprompted, sometime in the first 20 seconds. Now, keep in mind that a system that is really outstanding in Alaska would probably be considered good but not all that special somewhere like Los Angeles. I wouldn't win any prizes competing there -- but I wouldn't be embarassed, either.

tanstaafl.