Amp/Speaker compatability

[ramos]

Hi, I'm totally new to the world of proper home audio and have just grabbed myself a Sony STR DE 585 amp on e-bay.

I was wondering if anyone could do a kind of FAQ on speaker compatability.

Questions I have are:

What is the importance of ohmage on speakers? Can you have speakers that are higher or lower than the amps ohmage?

If my amp is 5.1 surround do I need to connect a whole set of speakers to it or can I just have two to start with?

I have a Gale active sub, will that work with the amp?

If the amp is 100 watts can I use speakers which say two are 130watts and the two surrounds are 60watts? What are the no-nos?

Basically what is important to check when buying speakers in order to not blow the amp or the speakers?

Cheers guys and girls!

 

[Leprkon]

ok. alot of questions here but most are pretty important.

in general, the lower the ohm rating on a speaker, the harder it makes your receiver work. a 4 ohm speaker is a very tough load for a smaller receiver, and most can only drive 2 such speakers. An 8 ohm (which is what most sub-$2,000 speakers are) is a much easier load.

you only have to connect 1 speaker to hear anything. the system will be perfectly happy with 2, it just has the capability to attach more.

any sub will work with your system, if it has the right connections. your active sub will probably have an RCA-type jack to match to the one on your receiver. check the books on the receiver and the sub, as it may want a special 75-ohm cable to carry the sound. these are generally shielded to limit noise interference, since the signal is still in a milli-volt level. the signal doesn;t get amplified until it reaches the sub, so any noise seems like alot. on your main speakers, the signal is already amplified, so noise is less of a problem.

if the amp is 100 watts all the way around, it will work very well with 130 watt speakers. this means you won;t be overdriving your speakers, BUT, if you play the amp too loud, it may generate alot of noise rather than music. Noise at lower levels can still damage your speakers... they are not vibrating in harmony, it's more like anti-harmony (disharmony??) but the speaker magnets are trying to move two directions at once and will often blow.

the 60 watt rear speakers may be a concern.. check the receiver book to see if it actually has a lower rating for the rears, as may do. It may have 100 watts across the front, but only 70 across the rear (this is a typical set-up for some of the entry-level Sony's).

Even if the receiver is rated for 100 watts all the way around, the speakers will probably still be safe, even at moderately high levels, if you are playing movies. Movies tend to use the rear speakers in spurts, and they will absorb a "peak" signal for a short period of time.

If you are running high-end audio (like SACD or DVD-audio), you are running full watts out to all the speakers all the time, so you will have to keep at lower volumes (like maybe 60 to 70 % of the receiver's max volume).

If you have the option, simply set your rear speakers to a "small" setting, then the receiver will cut some of the signal out for you.

if you can, get the same model line from the same manufacturer for your front three speakers. these speakers are designed to work well together and are called "timbre-matched". a set of speakers with matched timbre will give you a smooth movement of sound in a surround movie from the left to center to right without any interruption. if the timbre doesn;t match, you may have a little interruption as the sound goes across the screen.

the back speakers do not have to match so critically. it's nice, but not completely necessary. you have a lot more distance for the sound to travel, so you don't notice a timbre mismatch quite as much.

Depending on whether you plan to go more for movies or music, the center speaker can be the most important piece (especially since you already have a sub). In most surround-sound movies, the mains (front left and front right) will carry alot of music and special effects, but the center carries most of the talking. so plan to spend a little extra on that piece to make the dialogue as clear as possible.

One more note, it's important to get decent wire to connect your speakers, but don't fall into any traps. A decent gage (16 or better) wire can be had for about fifty cents a foot at RadioShack, axiomaudio.com, impactacoustics.com, or partsexpress.com.

Don't sink a ton of money into the wires, but don;t short yourself. You can get well-made, good-looking, fully assembled cables made to length to match your speakers and receiver at impact acoustics for about half the price of just the cable from Monster. If you have to make a run over 50 feet to get to your rear speakers, get 16 gage or larger for the best signal.

sorry for all the tech stuff in such a small package, but hopefully you have enough information to start out. good luck and welcome to the hobby.

 

[Leprkon]

almost forgot

most important thing about speakers-- DON'T buy systems with cube-type speakers as mains and centers (I can't name them but a typical underachieving brand starts out B o s __ !!!

when you are shopping for speakers (it sounds like you have some, but I'm not sure), there are a couple of things to look for, even before you listen to a set.

the first is the frequency range. you will see in a catalog or on a website that speaker brand X is rated for (example here) 60 Hz to 18 KHz. 60 hertz is a decently low signal, but many subs will go down to 25 or 30, and alot of mains will go down to 40. These are the kinds of frequencies that give you solid movement due to bass along with the sound itself. The higher number 18 kilohertz is less important. Most people have no hearing above 15 kilohertz, so unless your dog spends his days watching Lord of the Rings, buying a set of speakers because they go all the way to 23KHz instead of "just" 19 won;t impress anyone but techies.

the second specification is the signal to noise ratio. this will generally be a number between 85 and 95, and will be expressed in dB (decibels). the higher the number the better, as you are getting more sound with less noise.

neither of the specifications will tell you how good a speaker will sound to you, but it will tell you how well (technically) the speaker is designed and made.

why not buy the main manufacturer of cube systems ? because they specifically forbid anyone who sells their stuff to publish either number. cube companies don't want to compare technically to anyone else because they most likely don't measure up (there are some very lengthy discussions on this website about the whole issue), but the easiest thing to say is don't.

a couple other minor notes: you'll hear terms like woofer, midrange, and tweeter, and crossover. a woofer is a speaker specifically designed to make good low-range sound up to maybe 100 Hertz. most woofers are 6 1/5 inches or larger. a midrange is a speaker between 3 inches and 6 1/2 inches that carries the main audible range, from 100 to about 1000 Hertz. the tweeter is for the high-pitched range above 1000.

it's important, but not critical, that your main speakers have all three components (woofer, mid and tweeter). in a lot of cases (especially bookshelf speakers) a 5 1/2 or 6 1/2 inch speaker will carry duty for the woofer and mid. alot of companies design bookshelf speakers very well, but they are almost always a little short on base for home theatre work. most companies will recommend you use a subwoofer to fill in the hole at the bottom of the sound when using bookshelf speakers.

if you don't carry the entire sound spectrum (the frequencies from 40ish to 18 KHz), the sound will not be realistic. it will seem to be flat or have a "hole" wherever the sound is missing. this is very characteristic of a lot of cube speaker systems (can you say BOS_ ?? I knew you could). The the 3 inch "woofer" in a cube speaker simply does not carry enough of the lower sounds to make a home theatre sound lifelike. even with a sub, you are missing as much as the range from 100 to 750 Hertz (or almost half the audible spectrum)

your rear and center speakers will often have just the mid and tweeter. why you might ask ?? basically low frequency sound is, for the most omnidirectional. it reflects very well off sources likes walls to quickly fill a room with sound. a single well-placed subwoofer can do a great job of shaking you up.

the center and rears are specifically directional. that's their purpose in life. the mid and tweeter-level sounds are highly directional. they come from whatever the source is. by tossing those sounds around from speaker to speaker, the sound seems to come from those specific points, giving you the surround that makes you feel inside the movie. including a woofer on those speakers would be overkill.

oh yeah.. crossover.. a crossover is a neat little electrical circuit inside your speaker. it's job is to sort out which speaker gets which part of the signal. it wiil route the low frequency stuff to the woofer, for example. Why do you need one in the speaker ? a couple of reasons. first of all, it allows each speaker to do what it does best. woofers make bass, tweeters make high pitch. second, it makes the speaker much more efficient. i

cheap speakers don;t have a crossover, and send all the signal to all the speaker components. Each speaker (woofer, mid, and tweeter) is trying to produce the entire spectrum. if you split up the components of the signal, the woofer, mid and tweeter only try to produce their assigned part. this is much more efficient and keeps the pieces from trying to overlap each other.

alot of speakers (most notably subs) and more and more these days recievers as well will have a variable crossover. it allows you to decide which speaker gets how much of the signal. this lets you match a specific sub to alot of different brands of main speakers and to customize the sound to match your room and personal tastes.

study hard. quiz on Monday.

 

[ramos]

Thanks so much for that Leprkon, an excellent and very comprehensive answer, I feel a lot more clued up now! Thanks again for all the time you must have spent on it,

Cheers,

Rich