I was reading a review of the Wilson Alex V on Stereophile recently. (Published just in time. I’m thinking about picking up a pair. Maybe a couple for the bedroom, too.) And it raised a long-standing question of mine, one that I hope the wiser minds on this site can answer.
Wilson’s big selling point is aligning the different frequencies so they all reach your ear simultaneously. As I understand it, that’s why they have minute adjustments among the various drivers. The woofers put out bass notes that move slowly thanks to their long sound waves while the tweeters are playing faster moving, high frequency notes with short waves. Wilson lets you make adjustments so that they all arrive at the ear at once.
It seems to me, however, that live music isn’t time aligned. Suppose I’m playing the piano and you’re sitting across the room. When I stretch out my left hand to hit the low notes, those notes travel along the same long, slow wavelengths as the notes from Wilson’s woofers. Similarly, the treble notes I play with my right hand move quickly through the short wavelengths. The notes from the piano are naturally out of alignment. If Wilson’s goal is to achieve a lifelike sound, aligning the frequencies doesn’t seem like the way to do it.
Wilson has been selling lots of zillion dollar speakers for lots of years and people continue to gobble ‘em up. Something must be wrong with my line of reasoning. Would someone please point out where I’ve gone wrong? Nicely?
It seems to me, however, that live music isn’t time aligned. Suppose I’m playing the piano and you’re sitting across the room. When I stretch out my left hand to hit the low notes, those notes travel along the same long, slow wavelengths as the notes from Wilson’s woofers. Similarly, the treble notes I play with my right hand move quickly through the short wavelengths. The notes from the piano are naturally out of alignment.
Something must be wrong with my line of reasoning. Would someone please point out where I’ve gone wrong? Nicely?
The time it takes for the low notes to arrive at your ears is slower than the highs no t because they are inherently long but because the voice coil of the woofer is mounted behind the baffle whereas for the tweeter it is mounted almost about the same level as the baffle hence the tweeter is closer to yours ears than the woofer.
With a real piano, various sounds come out of it from various distances. These relative distances must be preserved by the speaker hence the requirements for time cohesion.
I generally find that speaker and sub coherence is best with the front-firing sub pushed a bit in front of the main speakers. Same thing, first with the big Velodyne DD18 and Dynaudio Consequence speakers, in my main system some years ago, and now, in a 'micro' version, in my home office, with single driver Arche FR2 speakers and a small Fostex Submini. Dragging the sub ca 8 cm in front of my speakers and screen looks a bit strange at the desktop but gives the most 'spot on' time alignment, to my ears. I mainly listen for timbre, juice, liveliness, emotional involvement.
Time Cohesion is making sure that the sound from the tweeter gets to your ears at the same time as the sound from the woofer. Lets say theres a piano sitting 10 feet in front of you and a cello sitting 6 feet in front. The sound of the cello hits your ears faster than the sound of the piano. Its the ratio of the speed that needs to be conserved by the speaker. This can only happen if the time cohesion is tuned perfectly.
The master has spoken.
Not exactly… master.
If the piano and the cello are playing the same note, or using a full range driver, then they are already tome coherent from a single driver.
And the cello will still arrive 4 msec before the piano.
If it is a piano playing many notes then we want them all to be time coherent with each other. That is a harder to do with multiple drivers, but pretty common these days.
There is no “ratio of speed”, as the speed of sound is the same for cellos and pianos.
Time Cohesion is making sure that the sound from the tweeter gets to your ears at the same time as the sound from the woofer. Lets say theres a piano sitting 10 feet in front of you and a cello sitting 6 feet in front. The sound of the cello hits your ears faster than the sound of the piano. Its the ratio of the speed that needs to be conserved by the speaker. This can only happen if the time cohesion is tuned perfectly.
1- An interesting situation exists in the case of line-source loudspeakers, a good example being the Magnepan MG3.7i. This speaker has a long, vertically-orientated ribbon tweeter (a real good one), with magnetic-planar drivers for midrange and bass frequencies running along side the tweeter. In the instruction manual for the 3.7i, it is advised that the speaker be positioned so that the tweeter is slightly further away from the listener’s ears than is the midrange driver. The reason for that is that the speaker’s crossover creates a slight time lag in the midrange driver. With the tweeter and midrange driver equidistant from the listeners ears, the two drivers are not quite time/phase aligned. 3.7i owners need to experiment with varying degrees of toe-in, until the highs and mids sound coherent. With a dynamic loudspeaker (cone & dome drivers in a box)---with the drivers aligned vertically, as most are these days---tilting the enclosure forward or backward can sometimes be used the same way. Raising or lowering the enclosure instead achieves the same result, of course.
2- In a number of his YouTube videos, Danny Richie explains why tweeter and midrange drivers should be mounted as close together as possible. And why the higher the x/o frequency between them, the closer they should be to each other. That is because at the high frequencies tweeters are producing sound, the wavelengths are very short. Danny explains it all far better than can I, so if interested do a search on YouTube for GR Research. A free primer in loudspeaker design basics!
Hello Paul6001. All the sound waves move at the same speed. The wavelengths vary with frequency, but not the speed of their travel. We are trying to reproduce music that arrived sometime in the past on the diaphragm of a microphone. We do not want to add any more time "smear" when we listen to that recrded music. The microphone(s) "hear" what you would hear sitting in the same place as the microphone(s). We want to produce the same sonic patterns in our room that the microphones picked up. So we don't want parts of that recorded sound to reach our ears earlier or later than other parts. Don't mess up the puzzle! If it gets messed up, we won't be able to reassemble in our brains the sound pattern that hit the sensitive parts of the "mikes." If we distort that pattern, we will not be able to successfully reconstruct the performance captured on the recording. The feeling of "being there" depends on an accurate reconstruction of the sound patterns in the recording. Woofers are generally larger than tweeters. If we mount them on the same panel, the voice coils that vibrate to reproduce sound are at different distances from the panel (this is why flat panel speakers have an advantage in accurate sound reproduction - all the sound leaves from the same place). So the sound from the woofer arrives a bit later than the sound from the tweeter. That's the problem some speaker builders try to solve by either moving the tweeters backwards or moving the woofers forward. That leads to some odd loking boxes, but, if perfect reproduction is the goal, it's worth it. Ideally, all the sound producing parts of the speaker system are at equal distance from your ears. Happy listening.
To those suggesting that phase coherence doesn‘t matter: listen to a recording in- and out of polarity (i.e. reverting phase) and pay attention particularly to the leading edge of instuments. If you can‘t hear the difference either buy a better system or have your ears checked.
Regarding time allignment: the wider the diaphragms are appart, the harder it is to achieve since 1st and subsequent reflections will be affected by the distance between diaphragms. This particularly affects higher frequencies with their more bundled dispersion characteristics.
Time alignments are somewhat necessary for good sound but most loudspeakers are only time aligned at one listening position unless concentric or full range. Still, it's best to get proper alignments or you have a frequency imbalance, not just a time issue. If tweeters are too close output is higher if farther away it's lower other transducers are also similarly affected.
Thanks to bdp24 for a patient, thorough explanation. I would add a couple of related points (For the record, I have a pair of Thiel CS6 speakers that were designed to be time and phase coherent).
At the PNW Audio Fest I attended a talk by Andrew Jones on speaker design. The subject of time alignment and phase coherence came up. With his witty sense of humor he made a very good case that this is not a major reason why one speaker sounds better than another. It sounds good in theory but in practice it is not a major factor in good speaker sound.
I've heard large Wilsons at three audio shows. At one of the rooms I waited until a slow time when I could sit in the sweet spot and I heard the holographic effect that people were raving about. It was impressive but there were other characteristics of the sound that I didn't like. In another room, however, I heard the same holographic effect - perhaps to an even greater degree. These were Acapella horn speakers that make no claims of time alignment. The sound was so enveloping and the location of the instruments so defined that it was spooky. I thought my Thiels imaged well but this was another level. Due to this experience I'm not sure that time alignment is the key if your major criteria is holographic imaging.
And lastly, the audio industry is becoming very good at selling their products with a story. In marketing is is called a Unique Selling Proposition (USP). Most of the ultra high end products have an elaborate story about a certain characteristic of their product that explains why it is different from its competitors (and worth more money). The audio cable companies are the champions in this category. It ain't easy justifying $10,000 for a pair of wires. Wilson has settled on Time Alignment along with it's cabinet materials. If you read Stereophile or TAS I'll bet that if I named off 5 other high end speaker companies you could tell me their USP off the top of your head.
Bottom line is that how a speaker sounds is the most important factor regardless of it's design parameters and marketing story. You just can't sell a pair of speakers for more than a 2 bedroom house without making the buyer comfortable that he (face it, it's a guy thing) is getting something really cool.
I am glad I am a speaker designer and Not a Physicist like some here. Sound is altered not only by distance. Especially when yo consider that the speed of sound is relatively SLOW. Sound is altered and affected by Temperature, Humidity, Barometric pressure... So once again, when it comes to speaker design, I am so glad I don't know anything about sound propagation. One of the first things I worked with 40+ years ago was where I placed my drivers, front to rear. In an effort to find the best placement and the least sound cancelation. If this placement wasn't a factor then room treatments would also be meaningless.
I mentioned just a couple of days ago how I was tweaking the Cant/Tilt to my speakers experimenting on how it changes the WHOLE soundstage. Just by a few degrees. and what it the main thing that is being modified, the forward position of the individual cones by just a few centimeters at a time. This is a simple inexpensive experiment that ANYONE can do on their own at home. You must also realize though that if you are using something like Diraclive this will change how your system is tuned by Dl.
Also, though Diraclive does wonders on manipulating reflective signals and how they interact with each other, it is minimal AT BEST when looking at Frequency.
Supposing that you use a sub, try it moved forward and then backward during a listening session. Beside having the effect of the wall, you should be able to tell that time alignment does have an effect on the sound. [Adjustments on a Wilson will be less dramatic].
Time alignment has nothing to do with instruments placement in an orchestra, that will (or sould) show up in the recording of said orchestra.
Remember, we are reproducing the recording of the orchestra and that recording includes cues as to where the sound of each instrument originated at the time of the recording.
Also, the speed of sound doesn’t change with frequency --
As mentioned above, time alignment in speakers has to do with the sounds coming out of different drive units. Take a guitar for example and a two-way speaker. Assuming that some of the notes of that guitar are reproduced by the tweeter and some by the woofer, you realise that a delay in the sound emanating from the woofer will sound odd --
As mentioned above, Wilson (and others) tries to minimise delays by aligning the drive units vertically - for example, the back of a tweeter with the back of a woofer, meaning the woofer cone will seem to be well in front of the tweeter.
The rest of the delay compansation has to be done in the xover -- a very difficult task and AFAIK very few speaker manufacturers attempt it.
You also have to take the room size , and room treatment or lack of
for 1st reflections ,bounce reflections and hard surfaces ,as well of bass nulls n the room ,setup and damping ever more so effecting the sum ,Everything counts !!
Related is the issue of keeping your speaker wires the same length. The lengths we use are very small relative to signal speed, but, I still follow the rule. Makes a big difference using expensive cable.
I am pretty sure that the speed of sound is relatively constant at a given temp.
The speed of light is also a constant, and the speed of electricity is usually a bit slower than the speed of light for most cables.
The main reason to keep the cables the same length is more for resistance and the other electrical parameters like inductance and capacitance.
It has nothing to do with the shorter cable getting the sound to the speaker faster, slower or at an equal speed as the longer cable.
I once did an experiment and replaced one of my Skogrand cables (12 meteres long, btw) with a simple 14 gauge wire from Home Depot, but cut to the precise length, and when I played the first song ("Thunder Kiss '65" by White Zombie) the difference in the music's arrival at my ears was so disorienting, I got nauseated and lost my lunch of Beluga caviar. It was dreadful. (sarcasm for the humour impaired).
I'll go with what the actual physicist says about sound waves in post 2.
Be sure to not confuse time alignment with linear phase. Wilson speakers are time aligned, not linear phase, fundamentals and harmonics do not arrive at the same time. What time alignment is concerned with is when seperate drivers play the same frequency at the same time. You want those frequencies to arrive at the ear at the same time. That's time alignment and it occurs at and around the crossover frequencies between two drivers and or when two drivers are acoustical mirrors of each other such as dual mid ranges, both of which circumstances occur in Wilson speakers. And this is what is solved, albeit best for one seat, in Wilson speakers. There are compromises such as aligning voice coils but they are not as accurate as Wilson's adjustable enclosures. I suspect time alignment is important especially in speakers where the many other problems are well handled. Just keep in mind what time alignment is and what it isn't and what it does and what it doesn't do.
As you go down this particular rabit hole, you‘ll end up concluding that time allignment isn‘t sufficient. For anything but deep bass having a point source is ideal because you avoid both phase and differential reflection issues: hence Tannoy dual concentric and various other point source designs.
Wilson makes some of the most remarkable speakers I have ever heard. I am always impressed… and I am sure they fiddle with them on the basis of time. But it is marketing hype… maybe it is true… but it doesn’t mater, not a reason to buy or not buy their speakers. I never pay any attention to that stuff.
By far, the most amazing audition I have ever had (a couple hours) was with Wilson’s top of the line at its time… carefully set up, simply amazing… 3D images in space. Like holograms in audio. I left with my head spinning and saying that is the best system I have ever heard, I don’t want that, but the most incredible I have heard.
I would decide if they move you and connect emotionally. How they do it is not important. I love Sonus Faber speakers, someone was upset that the cones were made out of paper (a gross oversimplification)… I don’t care… they sound simply splendid to me.
Each driver has a different distance to it’s acoustic center. Tweeters are shallow, woofers are deep, and we must take this into account in designing the crossover.
Here’s the problem. From the front the tweeter is say 2" closer to your ear than the woofer but at 90 degrees to the side they are the same distance. This means that the phase relationships you take into account in the crossover only hold perfectly true in front of the speaker.
If on the other hand we step the drivers back so that the acoustic centers (usually near the magnets) are exactly aligned, the phase relationship directly in front and at the sides is the same.
Great! this simplifies crossover design. However, if you look at an impulse response in either case, they will still not be perfect. That is more involved. :-)
Another approach here is also to use higher order filters, which D'Appolito recommends for MTM designs. Steeper filters (also like Joseph Audio's older infinite slope speakers) minimize the phase matching problem off axis in all directions.
Suppose you (the woofer) hit the bass keys of the piano and someone else (the tweeter) hits the treble keys, but not at the same time. The music is no longer time aligned. But if you both hit the keys at the same time, is is aligned even though one frequency gets to the ear first. It's part of the experience of listening to the piano.
Physical time alignment of drivers is accomplished by building them into the cabinets so that the magnets/voice coils are vertically aligned so they are radiating the same info in temporal alignment, reaching the listeners ear at the same time.
What is audio time alignment?
In other words, the high frequencies and low frequencies much reach the listener's ear at the same time. A system which meets this criterion is said to be “time aligned.” One way to accomplish this is to place the tweeter further away from the listener than the woofer, and this is done in many speaker systems.
My Sonner Legato Unum are time aligned and sound fantastic in my system.
As are the entire Sonner line. Simply a wonderful speaker no matter what amplifier I use. Much of this is due the the driver time alignment.
The Legato Series was engineered in a way that they can be driven by a small or large vacuum tube or solid state amplifier and easy placement or set up in a room. Sophisticated cabinet design utilizing one piece molded curve cabinet, state of the speaker drivers, and high quality crossover components work in harmony with our Symmetrical Panoramic design crossover network to deliver a natural sound, effortless micro and macro dynamics, huge soundstage with a sense of air around the musician and instrument while maintaining music emotion.
This series was created to deliver musical expression, huge soundstage and vivid imaging on a small foot print with a more attainable price point.
TECHNOLOGY
At Sonner Audio, our focus is on providing you sound quality that is authentic and emotionally rich. Our Creative Development Team finely tunes each speaker beyond computer modeling and simulation, with extensive human listening tests to bring a completely unique, realistic and dynamic experience to fellow music enthusiasts like you.
A reason why you want time aligned drivers in a multi-driver loudspeaker is that you want the fundamental frequency to arrive at your ear at the same time the overtones arrive. There are multiple ways to achieve time-alignment in a loudspeaker including the placement of the drivers. As mentioned above by others, some people think it's important and others don't.
PS - Looking at the step response (Figure 5) this is not a time-aligned speaker. If it were there would be a single rising impulse followed by a long decay. The two peaks are indicators that these speakers are phase aligned.
@carlsbad (edit: and @erik_squires) has/have it exactly correct: all frequencies travel at the same speed---the well-known "speed of sound".
As to time alignment of the drivers, a major objective in a multi-driver loudspeaker is to get the different drivers to be in phase with one another, especially at the crossover "point" (read on). At that crossover point (not a single frequency, but the frequency range withing which driver outputs overlap), if two involved drivers are in phase, their combined outputs will "fill in" the declining slopes of both drivers, thus producing a flat freqency response (for instance, the falling output of the low end of the tweeters output and the falling output of the high end of the midrange drivers output. Those declining outputs are the consequence of the two drivers raw responses combined with the crossover filter slopes). If the two drivers are not 100% in phase at the crossover frequency, that won’t occur "completely", and there will be a "dip" in response. It’s complicated, but drivers are referred to as having certain "degrees of phase rotation", a subject far too technical to explain in this post. The information is available in the literature.
But there is another consideration. "Time aligned" drivers are aligned at a given listening position, that position in relation to the drivers. In his excellent YouTube videos, Danny Richie of GR Research demonstrates how moving a measuring microphone (which is a substitute for ears) effects the phase relationship between drivers. Two drivers in phase at a listening position equidistant between two drivers can become somewhat or even significantly out-of-phase when the mic is moved above or below that equidistant position.
"Time aligned" has become a marketing buzz word, but it is an over-simplification of the complex relationship between drivers in all multi-driver loudspeakers with crossovers. Just buy a Sound Labs or Sanders full-range ESL, a planar-magnetic dipole (Eminent Technology or Magnepan), or a loudspeaker designed by Danny Richie ;-) . The latter are available only as DIY kits, but you can do it!
High and low frequency signals travel exactly the same speed. Proponents of fully time aligned systems like Vandersteen and Thiel, are concerned with say, 1 note of a horn looking like 1 note from a horn when it reaches your ears. Many benefits are supposed to come from this, like increased imaging, clarity, etc.
Time alignment however is the minority approach when it comes to speaker design. Hard to implement in passive crossovers and may over-stress tweeters.
From a personal perspective, I have never heard a time aligned speaker which sounded so good I'd forego all others forever for it.
We should also be careful about not confusing time-aligned with phase-aligned. Phase alignment is similar, but only concerned with the correct and smooth sums from multiple drivers through the individual crossover regions.
I was taught the same about time alignment, slanted front speakers ..., the amount of time alignment difference is relative to seated listening distance of course, and the differences are very very very small, yet it could be bunk.
Related is the issue of keeping your speaker wires the same length. The lengths we use are very small relative to signal speed, but, I still follow the rule. Makes a big difference using expensive cable.
Your point about no time alignment for live music is valid, the drums are way in the back, violins up front, the opposite of what slanted front speakers do.
below they mention a band in a stadium, much greater distances.
I have a time alignment system in my car that allows me to make minute adjustments between woofer, midrange and tweeter.
this function does make a difference in sound quality but it is more of an advantage aligning left to right speakers in a car interior setting.
time aligning the individual drivers of one speaker does have some benefit but you may not find big gains in sound quality.
the best thing it can do for you is to align the speakers at their crossover frequency
which avoids out of phase cancellations of frequencies and adds coherence and more of a point source focus of the sound image. this will lead to a flatter frequency response and better imaging. .
you will need test tones and pink noise with measurement tools to get the most out of it. no way you can adjust by ear with music.
I think it’s the difference between playing vs reproducing a recoding.
Though I am purely hypothesizing.
I imagine a drummer using symbols and kick drum where frequencies travel at different speeds and are captured by a microphone. Then the recording is played back and the timing is impacted by the crossovers.
if you like how Wilssound does it matter why? I view I am paying for the results not the knowledge.
I haven't studied wilson speakers of their claims. However, as a physicist, I'm pretty sure the speed of sound is independent of frequency. Maybe lower frequencies leave the transducer slightly delayed. My initial reaction is skepticism.
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