Obviously there's the listen test,
For some people, the listen test is all you need. But the problems I see with just the simple listen test are:
1) How well do you know the sound of what you're hearing, NOT through the speaker (IE real life). How familiar are you with teh audition material itself?
2) What effect is the audition room having on what you are hearing? Does this truly represent what your final listening environment will be?
3) Are you really listening during the audition, like you would in real life? How loud do you really like it? Is the audition amplifier the same type of power you'd be feeding it with?
4) Is the salesperson biasing your perceptions in any way, without yourself realizing it?
5) How good is our acoustic memory? If we go to five different shop, how well will we be able to compare the performance of the 15 products we listened to?
but from a technical standpoint what do you look at to decide what's right for your Home Theater?
Distortion. What a speaker's job is, is to give you a recording as it was intended. What a speaker's problem is, is that it will most certainly, introduce distortion to the mix.
That's where we run into problems.
Sources of distortion include
1) Frequency Response. If a speaker is emphasizing specific frequencies more prominently than others, it's distorting the sound. Some might prefer elevating/recessessed bass response or treble or midrange but make no mistake, each of those is a distortion. A frequency response graph can really highlight this. Especially we look for +/- 2db tolerance from 200hz to 8khz. Below ~300hz the room dominates the sound, and above 8khz we aren't overly sensitive to what we hear beyond perception as "air between instruments".
2) Off axis frequency response. What we hear isn't the speaker in a vacuum. we hear a speaker in a room, and so we hear both listening window response as well as the reflections that accompany it.
3) Decay/intermodulation/harmonic distortion. Speakers might ring or go through cone break up which affects various aspects of what we hear. A waterfall graph can really highlight these issues. Part of what might make one speaker sound better than the other, is they you are not hearing any additional sounds produced by the speaker - just what is in the recording!
4) Crossover integration. Speakers are usually a collection of drivers, and the integration behaviour between those drivers makes a huge difference. If you can pick out individual drivers making individual sounds, or a missing frequency region, suspect a crossover phase issue.
5) Cabinet quality. Speakers don't just project air out, they pressurize air in. What goes on inside the cabinet, and along its panels, can make a difference in what we hear in the lower midrange, upper bass, and the bottom part of its bass tuning. This is also visible in a waterfall graph.
6) power handling. It might sound nice at a low level, but what about when the volume goes up... does it start to sound "too loud" or not? Can it handle impactful dynamic transients in the content you listen to or watch? Can it handle warming up from compressed content you listen to?
The other measurement to normally take a look at, is your ability to drive it with your amplification. That is, Sensitivity/Complex Impedance/Electrical Phase. You don't want $1500 speakers, that will ask you to buy a $2000 amplifier just to drive them properly in your room... it's absurd. Your room and speakers should be where you're focusing your budget on, not your electronics!!
Also what brands are the best?
First and foremost, it depends on some factors involving room size and the content that will be going through it, as well as your budget. And even superior brands can put out a poor product here and there! But a few brands that are reasonably well respected, include:
JTR Speakers
Revel Speakers
Philharmonic Audio
JBL Professional
JBL Synthesis
KEF
Vapor Audio
Gedlee
Pi Speakers
Magnepan
Audio Kinesis
Gradient Audio
SoundLAB
Focal Professional
Salk Sound
Ascend Acoustics
Pioneer/Pioneer EX/TAD
Seaton Sound
Genelec Professional
PMC Speakers
Bamberg Engineering Sound Lab
SVSound
ATC Loudspeakers
Danley Sound Labs
RBH Sound/EMP Tek
Soundfield Audio
PSB
Aperion Audio
Dynaudio
and for subwoofers
Funk Audio
JTR Speakers
Seaton Sound
Epik
Rythmik
SVSound
HSU
but what stats/specs tell you this?
My advice, is find speakers with flat on-axis/
smoothly tapering off axis frequency response (out to at least around 60 degrees), and a clean waterfall graph, and then go from there with more measurements and auditions and reading reviews and whatever else you like. The list I gave you, is probably a good place to start. For example, if you were to go the Philharmonic website, you can see a higher resolution frequency response graph along with off axis response that is almost ideal!
http://philharmonicaudio.com/philharmonic1.html
If you think about it, speakers that introduce the least distortion to the mix, really should sound MOST similar!! At that point it might be a small difference in presentation or the results of "pick your poison" design choices that make small differences, rather than huge differences. The best speakers, in my opinion, are LEAST dependant on what room you place them on. Inferior speakers, sound
1) incorrect consistently.
2) dependant on the room they are in.
