Does Time alignment and Phase coherency make for a better loudspeaker?

Can any of you change the group delay on any part of your loudspeaker system from the listening position? Can any of you change absolute phase from your listening position?

I can and these are my observations. I can not hear any difference at all changing absolute phase. Both directions sound absolutely the same. I should also add that my entire system is balanced. I have Three drivers on each channel. The main speakers are one way ESLs. Then there are the subwoofers, two on each channel. The critical timing is between the subwoofers and the ESLs. I can delay either. Once you get into 5 ms delay or more deterioration in bass impact and definition becomes obvious. What you hear depends on the crossover point and slopes. You can see the group delays with a measurement microphone. The only way you can adjust them is with digital signal processing or moving loudspeakers. This is a problem for subwoofers because they work besy only in certain locations, in corners and up against walls. Being able to put the speakers where they work best and deal with the delays digitally is a large advantage. There are many processors on the market that will do this and some are very reasonably priced. 

@tomic601 , You are looking at it the wrong way tomic. It has nothing to do with musicians on stage. Each instrument is a singularity. Lets take a bass drum. When the pedal hits the drum there is an attack followed by the primary resonant frequency of the drum. Some drummers dampen this which I think is a shame. The attack is at higher frequency and can get caught in the crossover frequency of subwoofers. If the sound of that attack reaches you at different times from the subwoofer and main speakers you first smear the attack and if the delay is long enough you get an echo. Improperly timed subwoofers numb bass transients. Also remember that time shifts phase. Everyone knows what happens if you shift phase 180 degrees. If you don't, wire one of your speakers backwards and listen to what happens. The effect is much less obvious at higher frequencies but it is there. listen to what happens to the image. In order to shift phase 180 degrees at 100 hz you would have to move a main speaker 5 feet forward or backward. This can easily happen with some set ups. Using a swarm system is a way around his problem. 

@audition__audio , that is your own bias at play. It is just about numbers, ones and zeros. The very first step in the modern recording process is turning the music into those numbers. Once you are in numbers you can do just about anything without any added distortion. It is all about the programming which has improved over the past 30 years but the basics were well known 30 years ago. 20 years ago some very sophisticated processors were available but the mentality of us audiophiles shunned any added complexity. Our culture was used to the problems of analog devices and I think we generalized those problems to digital devices.

The improvements that can be made with digital processing far outweigh any downside. I digitize my phono stage to run it through a digital preamp/processor. You can go back and forth between the analog turntable and the 192/24 digitized one all day long and you can not hear the difference. The two major advatages of digital processing are being able to adjust frequency response, matching channels precisely and digital bass management with time and phase correction. IMHO you can not get to state of the art sound without them. Another way of looking at it would be, you can make any system sound better with digital processing. Also you can not get to state of the art sound by listening. You have to measure.

@tomic601 , An engineer does not need ears to develop a phase coherent loudspeaker, just a measurement microphone.

In order to be accurate (I did not say sound good) a speaker has to start with a flat frequency response and be time coherent which as unsounds relates assures phase coherence. Unfortunatly, for speaker designers this has to include the room the speakers are set up in. For state of the art accuracy one has to be able to adjust frequency response so that the speakers are flat from 20 Hz to 20 kHz. This also assures that both channels have exactly the same frequency response which is very important for imaging. If a subwoofer is added one has to make sure they are time coherent with the main speakers. The only way all of this can be done is with digital signal processing. Afterwards the frequency response can be adjusted so the system sounds good to the owner. I like mine up 5 or 6 dB at 20 Hz and down 6 dB at 20 kHz. Done this way the difference between speakers is based on the way they radiate into the room and what kind of source they are point vs line.

Generally, speakers with controlled radiation patterns sound better because they cause less room interaction. Horns, dipoles and line arrays come to mind. Omnidirectional speakers require much more room treatment and produce a smaller soundstage like sitting at the back of the hall. This can sound quite natural depending on the recording. 

@jjss49 , flat is always the best place to start. It is a reference point from which adjustments can be made to suit. You can tell me you like your bass boosted 3 dB. 3dB from where? Frequency response and group delays can be easily measured with a $300 microphone and computer program. What can not be measured is the speaker's radiation pattern but this can be determined exactly from the design of the speaker. It is important to remember that the room, the speaker and where the speaker is in the room have to be considered as a unit. Frequency response curves can change dramatically just by moving the speaker a few feet. Identical speakers will have different frequency response curve depending on where they are in the room. Even in what appears to be a symmetrical room they will measure differently. It seems that only people who have no experience measuring loudspeakers in rooms think good sound is hard to measure. Once you know what type of      soundstage you like and choose the appropriate type of speaker, assuming the speaker is well designed you optimize the system in your room by measurement. You can not get to the most accurate sound without it. You start with accuracy then tune it to sound good to you.  If you have a shrill recording and have to ability to punch in a Grundy Curve (BBC curve), wonderful. I have one on a preset if I need it.

@jeffvegas , I will do it for you. One way, 8 foot ESLs are King.

@holmz , you can be snarky all you want as long as you are right. If I posed as a Buddhist everyone would die laughing.

Although timing errors can affect imaging frequency response variance between channels causes much more damage and that is easy to demonstrate.

As long as DSP has control over individual drivers it can perfectly adjust timing in one listening location. Most multiway speakers do not allow for this. They have to be bi or tri amped. However, time alignment is most important for subwoofers as diminished transient response affects impact. Fortunately, subs are amplified separately. DSP was extremely effective 25 years ago with the advent of Radomir Bozevic's TacT Audio. He wrote the book on "room Control." With the faster processors we have today it is even better due to increased bit depth. My solution to the problem since 1979 was to use one way loudspeakers with subwoofers. There was no easy way to time align subs until the mid 90s with TacT's processors. Today the best are probably Trinnov's units. But inexpensive and effective ones are available from MiniDSP and DEQX. Used correctly they can improve almost any systems performance even the ones owned by digitally phobic people. It is all just lay instinct. 

Rooms certainly are "Time" sensitive. Reflections occur in time and their timing determines how we will hear them. Unless you like listening to bands in a closet early reflections are always bad. People say that late reflections are in part a benefit and one should not get rid of all of them or the room will sound "dead." I am not so sure about that. Timed reflections are in the recording giving you a sense of the size of the venue the recording was made in. Studio recordings frequently have fake late reflections added (reverb). The problem for home reproduction is that these sounds do not come from the right direction. I am beginning to think that in most home situations there are no late reflections only strong vs weak early reflections. If the room is big enough you get echo which is peculiar to that room and only pollutes the music with sounds that are not supposed to be there. 

@holmz , phase and time are attached at the elbows. It is certain easy hear what happens to imaging if you compare the two channels 180 degrees out of phase. The smaller the phase angle the harder it is to hear. Time, when you are talking about a few milliseconds or less with subwoofers is audible if you cross where I do up at 100 Hz. Lower down it is something you feel. As time variation increases the transient response of the bass has the edge taken off and you do not feel the impact as abruptly. Go to a small jazz club.  Listen and feel the bass drum. That is what you are shooting for. Time aligning subwoofers empirically is a real PITA. With a measurement mic you can do easily and know that you have it right on. The advantage of DSP here is that you can keep the subs where they perform best and align but delaying the signal of which ever speakers are early. 

As for room acoustics I have come the realization that too much absorption is better than too little. The acoustics of the venue are either in the recording or are being created with echo. There are not many instances where we listen to music in small rooms. You really want to minimize all early reflections but in a small room they are all early until they bounce around several times. Speakers that have sharp dispersion limits such as horns, planar speakers and linear arrays have large advantages acoustically in residential rooms. A properly deadened  small room say 16 X 30 sounds better than a really big room with high ceilings because these rooms usually have acoustic signatures that are harder to get rid of, they echo.

Reflections certainly change frequency response which can be easily seen with a measurement mic. But, they also smear detail and ruin the image.

@holmz , no argument from me. I would just like to state for the record that slow phase shifts are likely to be less noticeable than abrupt ones. It is really what happens at the cut off frequency that counts. I avoid your scenario almost entirely by using one way main speakers. All I have to worry about is the subwoofer crossover and one phase shift. IMHO the best crossover is no crossover. This is not an endorsement of dynamic "full range" drivers. The crossover is the lesser of two evils and those drivers are really not full range. Most of them have a 6 dB/oct mechanical crossover to a whizzer cone. The only real full range driver I am aware of is an ESL and even they have to have some wizardry performed with their transformers to make it work.   

@fleschler , sounds very nice. I like cherry very much. Echos are very disruptive.

@cindyment , Hi! Thanx for joining this post. I do not believe we have met before.

I am only advocating a flat frequency response as a reference to start because it is the only reference that makes sense.  What else would you use? My own system is boosted below 100 Hz at 2 dB per octave going down and rolled off above 10 kHz at 6 dB per octave. This is the actual measured in room frequency response at the listening position from either channel.  

What most people think of as "flat" is "uncorrected."  Having a flat, in room frequency response with an uncorrected system would be like winning the lottery. In room frequency response can vary wildly. If you tell me a system is rolled of at 6 db/oct above 10 kHz I still have no idea what the system sounds like because I have no idea what the response was to start with. It gets even worse. The individual channels have different frequency response curves and can easily be 10 dB off of each other at certain frequencies even though they are exactly the same speakers. Imagine what this does to imaging! 

Very few audiophiles have a measurement system which in this day and age is a travesty. For $300 you can get an excellent USB measurement microphone and computer program with which you can measure group delays and frequency response. You can mess around with speaker positioning and room treatment or if you really want to dial it in get a digital signal processor.  All I can do when people tell me they can do this by ear is smile.

I saw this ad for a speaker company. It looked like it came out of Better Homes and Gardens. Two black tower speakers on either side of a black fireplace with white walls, a 12 foot ceiling and black granite floors. One side wall was solid window. Imagine what that sounded like. 

@cindyment , my program runs sine sweeps from 10 Hz to 20 kHz and reads same. My speakers, Sound Labs 645-8's are "on axis" over a 45 degree arc. Any frequency response variation would be a manifestation of the room. I prefer to be interested in the listening position only. The rest of the room is background music as far as I am concerned. All my comments about frequency response are in regards to the listening position only. I could actually program presets for corrections aimed at various locations in the room but it is a lot of work for locations where the music is purely background. The system was tuned to be flat at the listening position then adjusted to the target curve I like which I mentioned above paying special attention from 100 Hz to 10 kHz keeping both channels within a dB of each other across that band. This was done by making small adjustments and repeated measuring. I would like to get it closer but right now the resolution of the system I am currently using is not good enough. But, I do have my eye on a new one. Like you I am totally into digital signal processing as I do not believe there is any other way to get the job done. There is no other way to do it to be honest but, if you say that here you will get cable elevators launched at your head. I suggest you get yourself a nice set of audiophile fuses to throw back.