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Choosing speakers...
I just wanted to share this because I found these articles really helpful. All of which can be found at http://www.polkaudio.com/home/faqad/index.php. I just copied and pasted a few different articles that I found were the most interesting. Some of this may not apply to the speakers you use when you dj... but still informative. =)
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When you're making comparisons between product specifications it helps to understand what they mean, particularly with amplifier power ratings. Everybody knows that the more watts you have, the better. Right? Ah, if it were only so simple. Here's a guide to the wacky world of watts.
The higher the power (watts) of the amplifier, receiver or powered subwoofer, the louder and cleaner the speakers will play. Don't worry about small differences in power: in order to get an audible volume difference (a 3dB increase) you need to double the power. So, if you have a 50-watt-per-channel receiver, the next significant step-up (power-wise) is 100-watts-per-channel.
But beware, because not all watts are created equal. It is common to have two receivers or amps of equal rated power, yet find that one plays louder and sounds better than the other. Why? Some manufacturers measure only one channel operating at a time, rather than all channels driven simultaneously (as you would use it in your living room). Also, standard amplifier tests cannot mimic the same electrical conditions, or load, of an actual loudspeaker. But most of all, specifications cannot measure the quality of sound. So how do you tell which receiver has the better amplifier section? Here are a few clues to look for: Look carefully at the power specifications. Thorough and meaningful power specs would look something like this: "100W/ ch. @ 8 ohms, with no more than 0.1% THD, from 20-20,000 Hz, all channels driven." In this spec you can tell that the power was measured in the way you will use it: at low Total Harmonic Distortion (anything under .5% is low enough), through the whole audible frequency range (20Hz -20kHz) and with all the speakers playing. A lower quality receiver might quote power like this: "100W/ch @ 8 ohms, at 1 kHz, one channel driven." That's like quoting a car's acceleration as "0 - 60 MPH in 7 seconds, downhill with a stiff tail wind."
Look for power ratings lower than 8-ohm loads. (Ohms are a measure of the electrical resistance of the speaker.) Ideally, the amp should be able to pump at least 50% more power into a 4-ohm load than it would into an 8-ohm load. If there is no 4-ohm power rating quoted, chances are that the amp will not drive a 4-ohm speaker. Almost all speakers are less than 8-ohms for some part of the frequency range (impedance varies with frequency) and many fine speakers are 4-ohm speakers. Get a receiver that can safely and robustly drive a 4-ohm speaker.
With powered subwoofers and other self-powered speakers, the power rating, whether FTC government approved or WLS (When Lightening Strikes), doesn't really tell you much. Why? Because loudspeaker efficiency is by far the most important factor in determining how loud a system will play. Efficiency (a.k.a. sensitivity) is usually given as the amount of sound produced by 1 watt at a distance of 1 meter. A medium efficiency loudspeaker rating would be around 87 dB from 1 watt at 1 meter. A highly efficient loudspeaker might be 90 dB. Each 3dB increase in efficiency doubles the sound output for a given power input. So a 100-watt, 90 dB self-powered speaker and a 200-watt 87 dB unit would produce exactly the same sound output.
So how do you evaluate powered speakers? Right now there really isn't a better way than just listening: how loud does it play before it starts to distort? Although listening is the ultimate test of a loudspeaker, there are other clues to quality. Rap your knuckles on the sides of the cabinet: a hollow thud indicates a poorly made enclosure that will probably degrade the sound. The weight of a speaker will give you a clue as to the materials and construction quality. The best speakers offer 5-way binding posts that offer the best possible connection with any type of cable.
Read the manufacturer's specifications to make sure your amplifier and speakers will work properly together. The efficiency (a.k.a. "sensitivity") rating tells you how much sound a speaker will produce when fed one watt of power. Choose a model rated at 86 dB or higher-a low-powered system needs high efficiency speakers. Finally, check the "impedance" specification. If you've chosen an inexpensive receiver, your speakers' impedance should be at least 4-Ohms, and preferably 6-Ohms or higher.
But the best advice of all is to ignore the numbers and simply listen before you buy. Many people get hung up on inches and watts. They assume that the bigger the driver size and the higher the power amp rating, the better the subwoofer. This is simply not so. Bigger doesn't necessarily make better. Your dealer can let you listen to different subwoofers before you buy. If possible, listen with the front speakers you own or intend to get. Does the subwoofer add a deep bass foundation, or does it just "boom"? Listen with music as well as movie sources. Is the subwoofer tight and well defined with music, or does it just add a vague rumble? Trust your ears.
Optimizing the Sound of Your Room
The acoustic characteristics of your room and the placement of the speakers within it have a far greater effect on the quality of the sound you will hear by changing any single piece of electronic equipment. While acoustics can be a confusing subject, and extensive room treatments and alterations can cost thousands of dollars, there are a few simple, inexpensive things you can do to maximize the performance of your room and setup.
There are three important phenomena of room acoustics: room modes, reflections and wall resonance.
Room Modes (also known as standing waves) are a function of the dimensions of your room and create uneven bass response throughout a room. To hear the effect of standing waves, play a CD with deep, sustained bass. Unless you are one of a lucky minority, you will hear the bass loudness go up and down as you walk around the room. Where there is more bass and where there is less bass is a function of the dimensions of the room and your speakers' placement. The closer your room is to being a cube (equal length, width and height), the more uneven the bass response will be. If you live in a cube-shaped room-move. For the rest of you, keep reading for advice that will help you minimize room mode problems.
Reflections are just that, reflections of the sound off walls and other objects. Reflections are not bad per se. You just want to avoid strong, coherent reflections. Strong, coherent reflections will color the sound, make the system sound "bright," and ruin any chance of getting lifelike imaging. If you have ever heard a sound system in an empty, hard-walled room, you know what we mean. The reflections you have to deal with the most are those that happen within a few feet of the speakers.
Wall construction will also effect the sound of your system. Walls can act as big resonating panels that can add "boomy" coloration to the sound. Bang in between studs on the center of a long wall in your listening room. The odds are good that the wall will vibrate and make a booming noise. Sound waves from your speakers will excite the natural resonance of the wall in much the same way. If your room walls are either 1/2" drywall or wood paneling the effect is even more pronounced.
Placement
Speaker and listening positions will have an enormous effect on the sound of your system. We don't have room in this issue to fully explore this topic, but we can give you some general advice.
If your system uses a subwoofer, the main "stereo" speakers should be placed at least two feet (farther is better) from walls, especially the wall behind the speakers to get the most natural midrange and most open imaging. If your system does not have a subwoofer, vary the speakers' distance from adjacent walls until you get the best balance between bass impact and midrange clarity.
Avoid equal-distance placement. A speaker's distance from the front wall (the wall behind the speakers) should not be within 33% of he distance from the side walls. For example, don't place a speaker 24" from the wall behind and 24" from the side wall. If the speakers are 24" from the side walls, place them at least 32" from the front wall.
Avoid placing your listening chair up against a wall. The sound will be artificially bass heavy and boomy. The best spot is at two-thirds of the length of the room. If that isn't practical, move your chair at least a foot away from the wall. If you must have the chair close to the wall, move your main speakers and subwoofer farther away from walls.
Room Treatment
You can minimize bad reflections by placing your speakers far away from walls and by absorbing or diffusing the reflections.
The first thing to do to improve the sound of your room is fill it with "stuff." Any kind of stuff: books, furniture, drapes, knick-knacks, paintings. The stuff can be soft, hard, big, little; it hardly matters as long as the stuff isn't flat like the walls. The more irregular the wall surfaces, the greater the diffusion of reflections and the better the sound. Do whatever you can to break up large expanses of bare, flat walls and windows, especially the areas near the front speakers.
The most critical areas to treat are the walls behind and alongside the front speakers and at the first reflection points along the side walls.
To find the first reflection spot, sit in the main (center) listening position and have a friend slide a hand mirror along the side wall at tweeter height. When you can see the nearest speaker in the mirror, you have located the first reflection spot. Treat that area, and the wall opposite, with either sound absorbing materials (drapes, tapestry, or professional materials - see resource list below), or sound diffusing materials (irregular surfaced furniture, broad-blade wood blinds, or better yet, RPG diffusers). If you want to eke out a little more performance, treat the second reflection spot. Have your helper slide the mirror farther down the side wall until you can see the opposite speaker in the mirror. That's the second reflection point.
Subwoofer Placement
Before we begin, let us give you a few warnings.
1 The methods here will help get you the most accurate bass. If your goal is strictly maximum "slamitude," just stick your sub in the corner, turn up all the knobs and have fun.
2 Finding the perfect settings and location takes time. If you have low tolerance for moving speakers and twiddling with your audio gear, quit reading now. But realize that you're missing a few simple techniques by which you may be able to greatly improve the sound of your system.
3 Let your ear be the final judge. We'll give you some techniques and advice, but the science of room acoustics is so complex it defies easy answers.
The Goal
"It's relatively easy to put a subwoofer into your system and hear more bass. What's difficult is making the subwoofer's bass integrate with the sound of your main speakers�A well-integrated subwoofer produces a seamless sound, no boomy thump, and natural reproduction of music. A poorly integrated subwoofer will sound thick, heavy boomy, and unnatural, calling attention to the fact that you have smaller speakers reproducing the frequency spectrum from the midrange up, and the big subwoofer putting out low bass."1
Positioning
Room acoustics have an enormous impact on the sound of speakers, including subwoofers. A phenomenon called "standing waves" makes bass response uneven from place to place in your room. To experience this for yourself, put on a CD with a strong, consistent bass line. Notice how the volume of the bass goes up and down as you move around the room. Stand in one place and then squat down-you will probably notice that the bass changes in the vertical plane as well!
Because the subwoofer's location affects how standing waves are created, the first step to getting accurate bass response is finding the right spots for your subwoofer and your listening position. We'll share a few guidelines that may be helpful, but in the long run nothing beats trial, error and your own two ears.
Stick It In The Corner-
This is the advice most often given and it certainly will yield loud bass. But corner mounting may make the woofer sound "one note-ey," and boomy on music. If lack of bass volume is your biggest subwoofer problem, this may be the answer for you.
Avoid Sitting Up Against the Wall-
Bass waves build up and "hang out" at room boundaries (walls). Your system will sound thick and heavy when your listening chair is up against a wall. If you must sit against the wall because of furniture layout, place your subwoofer away from walls and corners.
Avoid Symmetrical Placement-
"Avoid putting the subwoofer the same distance from two walls. For example, if you have a 20' wide room, don't put the subwoofer 10' from each wall. Similarly, don't put the subwoofer near a corner and equidistant from the side and rear walls. Instead, stagger the distances to each wall."1
Put The Subwoofer As Close To The Main Speakers As Possible-
Even though bass sounds are non-localizable, cabinet resonance and other factors conspire to make this less true in practice than in theory. It'll be much easier to get seamless blending between sub and main speakers if they are on the same side of the room. If possible, put the subwoofer behind the plane of the main speakers. At very least, keep the subwoofer in the front half of the room.
Here's An Old Trick-
Put your woofer in the same spot as your listening position. It's best to raise the subwoofer off the ground to seated ear height (use a sturdy, non-resonant platform). "Play a piece of music with an ascending and descending bass line such as a 'walking' bass in straight-ahead jazz [see recording suggestions]. Crawl around the floor on your hands and knees�until you find the spot where the bass sounds smoothest, and where each bass note has about the same volume and clarity. Avoid positions where some notes 'hang' longer and/or sound slower or thicker than others. When you've determined where the bass sounds best, put the subwoofer there."1
Use Two Subwoofers-
Using two asymmetrically placed subs will minimize the effects of standing waves in your room, yielding smoother bass response (as well as better dynamic range). But don't run out and buy another sub just yet. Get the sub you have now to sound its best before spending more money. You may be perfectly happy with just one sub once you've tried our suggestions.
Are small speakers as good as large ones?
It depends! If you don't mind large speakers in your room and you have the space to place them properly, then choose large speakers. They'll sound great. If you have a small to moderate size room and you don't have the space to place large speakers properly, then small speakers will sound better. It's easier in this instance to place small speakers in locations to provide superior imaging and it's also easier to place a subwoofer for better bass response. You might be pleasantly surprised how good small speakers can sound.
But there are some tradeoffs with tiny speakers. They won't play as loud as large speakers (although plenty loud enough for most people and rooms). Those little satellites cannot reproduce bass of their own, making it tough to achieve a seamless blend between satellite and sub. There is often a "hole" or weak response in the lower midrange area (bottom range of a male voice) where the satellite's response leaves off and the subwoofer takes over. When evaluating sub/sat systems listen closely to male voices, if they sound "thin" the system suffers from this midrange suck-out problem.
The other issue is bass response. Some of the so-called "subwoofers" in these systems are passive (not amplified) and should really be called "woofers" because they don't reproduce the truly deep bass with authority. If the system is to be used for only music, that may not be a problem. But if the primary use is home theater, you may later find the need for an additional powered subwoofer. Many sub/sat systems now come with powered woofers that are worthy of the name sub-woofer. As always, listen before you buy and trust your ears.
What is Dipole and Bipole and how are they different?
Dipole and Bipole refer to speakers that have drivers on opposite baffles. To put it crudely, they squirt sound out of both ends. Our feeling is that this type of sound radiation isn't desirable for front channel speakers. You get a spacious soundstage but at the sacrifice of image specificity. Soloists sound as big as the room. Pavorotti may be a large guy but he's not 10' wide. Orchestras may be large but you should be able to precisely locate individual instruments within the group. If not done properly, dipolar or bipolar speakers may also exhibit frequency response problems due to phase cancellations (particularly true with narrow baffle designs). Polk front channel speakers use wide dispersion drivers to provide open, spacious sound-staging while maintaining pinpoint localization.
But the lack of image specificity of dipolar or bipolar speakers is just the ticket for rear channel use, especially in Dolby Pro Logic systems in which the surround channel is mono.
In a Dipolar speaker, the two sets of speakers are out-of-phase with each other, while the drivers are one side are pushing, the opposite side is pulling. The result is that there is a "null" or a dead zone of sound in the area along the 90 degree axis of the speaker (see illustration below). Why is that good? When properly set up, a pair of dipole speakers used as surround speakers will provide a very open, enveloping rear effects soundstage without allowing you to pinpoint the location of the speakers themselves. That's a good thing. But for all this to work properly, the speakers need to be positioned "in-line" with the listening position as shown on the illustration below. If you are sitting out of the null area, the effect is ruined. What if you can't or don't want to place your surround speakers and listening position as required? That's where bipoles come in handy.
In a Bipolar speaker, the two sets of drivers are in-phase with one another - both sides push air at the same time. The result is greater sound output where the dipolar speaker's null would be. Theoretically, a bipolar speaker approaches a 360� soundfield - it squirts sound all around the room. That's a good thing if you need to position your surround speakers behind your listening position or anywhere outside of the null area. Some people prefer the greater localization of bipolar speakers when used in digital discrete (Dolby Digital 5.1, DTS) systems.
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