DIY sound system

This is a subject that's hard to recommend for, because it's largely based on personal taste.

Most surround sound receivers are 6-8 ohm stable, so it's not really that hard to pick out speakers for the amp. I'm sure you're familiar with ohms law? I'll give you the benefit of the doubt and assume you do, let me know if you don't.

Picking out the speakers are where the majority of the "personal taste" factors in. It's not hard if you're not too worried about "the perfect sound" but I'll give some examples.

There are certain materials that some people prefer over others. especially tweeters.

Tweeters:
Some people like Aluminum because they think it sounds "sharp", Silk because they think it sounds "Smooth", Ribbon because they think it sounds "True and Accurate" and has a larger radiating area, perfecting imaging. Some people like Pro Audio style "Bullet" or "Horn" style tweeters, mostly because they're extremely efficient (get louder with less power)
http://en.wikipedia.org/wiki/Tweeter.

Midranges:
some people prefer the sound of 3 way speakers over 2 way. Essentially, it's a driver that's crossed over below the tweeter, and above the woofer. The reason being is that sometimes the lowest frequency and tweeter can accurately produce, and the highest frequency a woofer can produce, don't overlap or even meet. The midrange is there to fill in the gap. You've got PA style midranges, and regular style. Again, the PA style is very efficient, the regular style is usually thought of more of a smooth and accurate sound.
http://en.wikipedia.org/wiki/Midrange_speaker

Woofers:
This subject is less "cut and dry" than the subject of tweeters. There's really only three major subdivisions. PA Style, Midwoofers, and Woofers. The PA style is very efficient, the midwoofers are used to play the frequencies between the tweeter and the subwoofer, or the woofer is used to play from the tweeter (if possible) or the midrange, down through the bass.
http://en.wikipedia.org/wiki/Woofer

Subwoofer:
Used to pick up the lower octaves (usually 80Hz on down), from the lower octaves of a bass guitar, to the kick drum, down into the subsonic "rumble" in movies.
http://en.wikipedia.org/wiki/Subwoofer


Amps:

I'll stick to the 3 most common types.

Class T (Tube Amps): Some people like tube amps, because they feel that they can have a more "Warm" sound to them. They are often expensive, and hard to find with high power outputs. Any amp you find with a high output is ridiculously expensive lol. tube amps are most prominent in electric guitar amplifiers, very high end home theaters, and very high end sound quality competition vehicles.
http://en.wikipedia.org/wiki/Tube_amplifiers

Class A/B: The most common in Home, Car, and budget PA amplifiers. These are usually mosfet amplifiers designed to try and "mimic" class A/T amplifiers. These are usually some of the better "watt per dollar" amplifiers. You really do get what you're paying for in this area, they can range from cheap and of bad quality, to moderately priced and of moderate quality quality, to kinda expensive and high quality.

quote Wikipedia

Class AB
Class AB is intermediate between class A and B, with better power efficiency than class A and less distortion than class B.

The two active elements conduct more than half of the time, producing less cross-over distortion than class-B amplifiers. In the example of the complementary emitter followers, a bias network allows the quiescent current to be adjusted, providing an operating point somewhere between class A and class B. Sometimes a figure is added (e.g., AB1 or AB2) for vacuum-tube stages where the grid voltage is always negative with respect to the cathode (class AB1) or may be slightly positive (hence drawing grid current, adding more distortion, but giving slightly higher output power) on signal peaks (class AB2). Class-AB circuits with large negative feedback provide excellent distortion characteristics with good power efficiency, and are widely used for solid-state amplifiers.

Class D: Most prominent in car audio, mostly subwoofer amplifiers. These are mosfet amplifiers like the class A/B but they have a different power managing system. They are typically more efficient than class A/B. audiophiles typically critique the sound quality of them, but like class A/B you get what you pay for here too. Some of the most recent trophy holders in car audio sound quality competitions used class D amplifiers.
http://en.wikipedia.org/wiki/Switching_amplifier



Honestly, if I were to do a home theater, I'd go with a nice class A/B or class D amplifiers. Crown is a really good brand, they make quality PA rackmount amplifiers that are well revered in the Home Theater and PA communities.


If this is all above you head, and you're looking to piece together a system, I can recommend a few options!

quote hiigaran

the law, yes. the significance, perhaps not. im guessing amps have a certain output voltage that shouldnt be exceeded, or else the current burns out the speaker/amp?

Yeah, pretty much. They design the amps to remain thermally stable at a certain resistance. Anything lower than that will overheat the amp. It could possibly "clip" (distort) while it's doing so, and distortion is 10x worse for a speaker than overpowering it.

That's why some people believe that "underpowering" a speaker is bad for it. Underpowering a speaker isn't bad in itself for a speaker, but when you attempt to "compensate" by turning the gain past clipping point, then you are damaging a speaker.

quote

when you talk of efficiency, i assume you refer to actual power consumption, yes? what kind of differences are we looking at between better quality, and efficiency? and will it be significant while there is a sound output?

Yes. Class D's are generally one of the most efficient amplifiers.

An 100watt amplifier that is 90% efficient will need 110 watts to make the full 100 watts, and a 100 watt amplifier that is 70% efficient will need 130watts to make the full 100 watts.

And amp that is less efficient will waste more power as heat than one that is more efficient, and just like with computers heat is an amps enemy.

Generally, better quality amps are more efficient than lesser quality amps. Efficiency is a better spec to judge an amp by than power ratings. Especially since companies who make lower quality amps generally "overrate" their amps, just like lower quality computer power supply companies generally overrate their PSUs.

Here's a high quality 1500 watt car amplifier:
http://store.soundsolutionsaudio.com/products/sundown-audio-saz-1500d-v-3.html

Notice the efficiency (86%) and fuse rating (150 amps). To determine whether the amplifier is overrated or not, multiply the fuse rating by the input voltage (12.8 with car off, 14.4 with car on) than multiply it by .86 to get a general idea of the highest power output the amplifier can output. In this case, it's 1651watts and 1857watts. This amp is in fact underrated, and very efficient compared to most amplifiers.

Here is a low quality "1500 watt" car amplifier:
http://www.woofersetc.com/p-9109-ph1500m-boss-1500w-phantom-series-mosfet-monoblock-power-amplifier.aspx

I couldn't find their efficiency rating anywhere, and had to go to their product manual pdf to find the fuse rating.

Right off the bat I could tell it's greatly overrated, just looking at their 25 amp fuse rating. I'll assume an 86% efficiency rating, even though I do have experience with "Boss" amps and know that they're freakin' space heaters (I also have experience with Sundown amps too, and mine never get more than lukewarm).

25amps is 275watts (car off) and 309watts (car on).

You can see that this amp will never get close to even their 4 ohm RMS rating, and is greatly overrated. And with my experience with both amp companies, the sound quality difference is greater than night and day.

The reason why higher quality amps are usually more efficient, is because they use higher quality materials that are less resistive. This results in a sound quality, efficiency, and reliability increase.

Yeah, you can use higher resistances, but the higher the resistance, naturally, the lower the power the amp will output.

And I suppose you could do this. I really wouldn't know too much about what you'd have to do to get it to work, though.

I do know that partsexpress has amplifier boards that you might be able to play with, you should be able to get a computer power supply rigged up to it.

http://www.parts-express.com/cat/amplifiers/106?kg=25627|25627

Edit:

Well actually, it doesn't seem like they're mean for 12v applications, but here's a link to some higher voltage power supplies you could use:

http://www.parts-express.com/cat/power-supplies/1474

http://www.youtube.com/watch?feature=player_embedded&v=l8xJivIWZlU#!

quote hiigaran

im assuming this then means that the most efficient system will be one where the speaker impedance is as low as possible, with an amplifier designed accordingly, yes?

Yeah, pretty much.

quote

what kind of quality are we looking at with those amp boards? this one looks like it would handle the kind of speakers id want (and since designed for lower impedance, it should handle a wider range of speakers), but would the sound quality be good?

Yeah, the sound quality should be decent. Maybe not audiophile, but it should be adequate for most people. Also, that's a 1 channel amp. You'd need two of them for stereo.

quote

that brings me to the next question of whether it would be cheaper to order the components and solder them together instead. im guessing it would be, but in that case, what would be the list of components to look for?

is it possible to step up a DC voltage? should be. ive got a handheld bug zapper that delivers a few hundred from a pair of 1.5v batteries. that should solve the problem of insufficient voltage.

I'm sure all of that is possible, but I wouldn't know how to do it. I've focused most of my time studying speaker design rather than amp design.

You'll need a crossover for the speaker components. Parts express also has a selection of crossovers. I also hear that building your own crossovers aren't that difficult, you should be able to find a tutorial on that somewhere.They also have speaker components too (tweets, mids, woofs, subs, everything). They're like the Newegg.com of all things audio related, and my personal choice for all things home audio.

You'll need either an 3 channel amp, or an 1 channel and a 2 channel. The 2x300 watt and the 1x600watt amp would be a good pairing. But that might be difficult to fit in your case. Keep in mind that if you were to get a 600watt amp and use your computer PSU to power it, that'll only leave 340 watts for your computer. (1000 - 660 [90% efficiency])

Umm, not personally.

You could use 3 of this amps four channels:

http://www.parts-express.com/pe/showdetl.cfm?partnumber=320-305

Or get this amp, in case you decide to do surround sound in the future:
http://www.parts-express.com/pe/showdetl.cfm?partnumber=320-307

Or do a two channel in the case, and a plate amp built into the subs enclosure:

http://www.parts-express.com/cat/subwoofer-plate-amplifiers/332

(My roommate has two Dayton Audio plate amps, they're great amps)

No, that amp isn't bridgeable unfortunately.

And it's cheaper because it's 400watts instead of 600watts for the two other amps.

EDIT:

I overlooked the fact that you could use the other two channels for the subwoofer, but the subwoofer would have to have dual voice coils.