"Wave Launch" and Subwoofer Placement?

[musicfirst1]

There seems to be two schools of thought on this.
One: The optimum placement of subs has more to do with the nulls and nodes in the listening room and;
Two: The subs should be first and foremost placed with wave launch considerations. I assume wave launch optimization being achieved by testing the impulse response of a low frequency series of pulses.

Assuming the main speakers are good to 30 Hz. Does the wave launch criteria of the subs matter?
What is the relationship between sub placement, wave launch, and phase? My subs only do 0 and 180 degrees.

There was a good article (from JLAudio?) that covered multiple sub placements in excellent detail, but I can't find it, and don't recall if this topic was covered..

 

[Kal Rubinson]

Can you explain or provide a link to explain what "wave launch" is?

 

[Folsom]

And the difference between a null and node?

 

[Mike Lavigne]

my twin tower Evolution Acoustics MM7 speaker system is (on paper) -3db down at 7hz and -6db down at 3hz.

according to Kevin Malmgren, the speaker designer, since it uses a first order crossover, if the twin towers are equa-distant from the listener, then there will be a coherent wave launch and it will result in optimal perceived impact and articulation. he further said that this is in ideal room conditions. many rooms need the bass towers to be located at places not equa-distant to the listener as the main towers. the performance is still very good but not potentially quite as optimal.

i'm no expert; whereas i think my speaker designer is one. and my ears tell me a fully coherent wave launch is pretty awesome when you have lots of driver surface and amplifier overhead to spare.

 

[musicfirst1]

A correct 'wave launch' as I understand it is the ability for a system to handle a pulsed sine wave of varying frequncies (say 50 hz down to the lowest output of the subs) this can be done by ear listening for optimum impact and articulation, (think kick drums or kodo percussion) I believe it can also be done by test equipment, but I trust my ears.

As for nulls and nodes, by placing a sub in the listening chair and playing music or test tones with 20 to 40hz content and carefully and slowly walking/or crawling around the listening room, the locations where the bass response is reinforced are called nodes, where they are weak are called nulls.

The locations where the bass is reinforced is where one wants to locate their sub(s).

 

[Kal Rubinson]

A correct 'wave launch' as I understand it is the ability for a system to handle a pulsed sine wave of varying frequncies (say 50 hz down to the lowest output of the subs) this can be done by ear listening for optimum impact and articulation, (think kick drums or kodo percussion) I believe it can also be done by test equipment, but I trust my ears.

Isn't there anything in the way of an objective scientific definition? Is this real or something just conjured?

 

[LL21]

I have read about this somewhere and i am not techie. Is this a generalist concept that relates to clean transmission of a clean, coherent sound into the room with minimal interference from things like the cabinetry?

I thought I read somewhere that the reason for how speaker designers (like Rockport, Tidal) design the tweeter wave guides, shape the cabinet and even the edges around each cone (like Rockport Arrakis, Wilson speakers, Tidal La Assoulata,) was to address wave diffraction, etc...and ultimate this ties back to a so called 'clean wave launch' as in clean transmission of the wave from each cone into the room. And then there is also the idea that the wave launch also has to consider tweeter/treble vs midbass delivery in a coherent fashion?

1. see Robet Harley on the Altair 2....https://cakeaudio.com/rockport-altair-review/

"Design Overview
The $97,500 Rockport Altair is a formidable loudspeaker, weighing in at 515 pounds out of the crate. Seen from the listening position, the Altair doesn’t look all that big. But step around to the side and the speaker’s volume becomes apparent. The relatively narrow baffle provides an ideal wave-launch platform for the front-firing drivers, and the depth provides the enclosure volume as well as a baffle for the side-firing 15? woofer. "

2. And from Andy Payor in an interview on Stereophile: https://www.stereophile.com/content/rockport-technologies-avior-ii-loudspeaker

"According to Andy Payor in an e-mail, this waveguide "improves the acoustic impedance match of the tweeter at the low end of its range, and allows for lower distortion and greater dynamic expression from the tweeter itself, as well as improved dispersion characteristics at the midrange/tweeter crossover point.

"Back in the 1950s, Harry Olsen showed the effects that different enclosure shapes have on the baffle step, as well as edge diffraction. Both of these phenomena can be mitigated with a large chamfer or radius on the enclosure's edge. However, the small ¾" radius or chamfer that you typically see on an enclosure doesn't begin to solve the problem. In order to be effective, these chamfers need to be much broader surfaces, more like large facets, to significantly affect diffraction issues. The Avior II's large, broad baffle facets do an excellent job of making the transition from 2pi to 4pi space much smoother. The baffle step still exists, but the transition is less problematic.

"The other issue that the broad chamfer helps solve is edge diffraction, where the soundwaves move across the baffle and encounter a sharp discontinuity at the cabinet's edge and the wave essentially 'snaps' off the baffle and creates a new, secondary source of sound. This new source of sound is slightly disparate from the driver's original direct radiation and of course combines with the original radiation to create a whole host of comb-filtering artifacts and phase anomalies. Enclosures that don't address edge diffraction or the baffle step never really get entirely out of the way sonically, and draw attention to themselves during playback."

 

[Folsom]

A node is not where a frequency is emphasized. That is a mode. Nodes and nulls are the same thing based on your description of a null. FYI.

I'd be interested in seeing some information to substantiate the idea of wave launch. It doesn't make a lot of sense from a frequency perspective since the cues for bass are usually higher frequency than the bass itself. If you turn off everything but the subwoofers you'll hear what I mean.

 

[Kal Rubinson]

A node is not where a frequency is emphasized. That is a mode. Nodes and nulls are the same thing based on your description of a null. FYI.

Yup.

I'd be interested in seeing some information to substantiate the idea of wave launch.

Agreed. So far, it seems a marketing concept. With a little Googling, I found a few patents that refer to the term but without any scientific definition and a large number of speaker-related web items that use the term, again without definition. It is, of course, a good term which conjures images of a coherent projection of sounds from a source but that is all. Finally, I found reference to a Legacy Sound Launch Processor which apparently has be succeeded by a Wavelet Processor. Wavelets can be defined.

 

[Folsom]

Sometimes terms like this are used to make the general audience be able to comprehend a more difficult subject.

But this one doesn't make sense yet. Mike is believing so because his stereo sounds good to him by following the approach. I think that undermines his designed room and adjustment to it, giving credit where it isn't really due. The bass sounds good even when you're not sitting in the chair.

 

[musicfirst1]

As an engineer and an audiophile, I'm all ears. I know there is a school of thought and design that alignment of the acoustic centres of the individual drivers in a loudspeaker is an important if not critical parameter in the design of speakers throughout the years.

 

[Kal Rubinson]

As an engineer and an audiophile, I'm all ears. I know there is a school of thought and design that alignment of the acoustic centres of the individual drivers in a loudspeaker is an important if not critical parameter in the design of speakers throughout the years.

That is so and there are others who discount its importance. OTOH, is that the definition of "wave launch?"

 

[Duke LeJeune]

There seems to be two schools of thought on this.

One: The optimum placement of subs has more to do with the nulls and nodes in the listening room...

I presume you are referring to something like a distributed multisub system, the intention of which is to smooth out the in-room bass... and for the record, ime the specific placement of the subs is generally non-critical as long as some basic rules are followed.

.... and Two: The subs should be first and foremost placed with wave launch considerations. I assume wave launch optimization being achieved by testing the impulse response of a low frequency series of pulses.

I assume you are talking about having the initial bass energy arrive coherently... which includes, arriving at the same time.

So, if I understand correctly, School of Thought One prioritizes smooth bass, while School of Thought Two prioritizes impact.

In my experience, "smooth bass" is what makes the biggest difference, and is a PREREQUISITE for satisfying impact... if the bass is lumpy, then the PERCEPTION of impact is lost in the mud.

A correct 'wave launch' as I understand it is the ability for a system to handle a pulsed sine wave of varying frequncies (say 50 hz down to the lowest output of the subs) this can be done by ear listening for optimum impact and articulation, (think kick drums or kodo percussion) I believe it can also be done by test equipment, but I trust my ears.

Imo you are absolutely correct to trust your ears! BUT...

The ear cannot hear the bass energy of a kickdrum or kodo drum separately from the room's contribution, so what you are perceiving as "optimum impact and articulation" INCLUDES the room's effects. The reason for this is, the ear has very poor time-domain resolution at low frequencies. The ear cannot even begin to detect the presence of a bass tone from less than one wavelength, and must hear multiple wavelengths before it can begin to hear pitch. Think for a moment about how long bass wavelengths are relative to the distances to room boundaries and you will see that by the time you hear the bass, you are also hearing the room.

Mike Lavigne posted something very interesting above:

According to Kevin Malmgren, the speaker designer, since it uses a first order crossover, if the twin towers are equa-distant from the listener, then there will be a coherent wave launch and it will result in optimal perceived impact and articulation. He further said that this is in ideal room conditions. Many rooms need the bass towers to be located at places not equa-distant to the listener as the main towers. the performance is still very good but not potentially quite as optimal.

It sounds to me like Mike's acoustician got his room right to such an extent that the bass energy is exceptionally smooth throughout the room, so his twin sub towers can be placed for optimal simultaneous arrival at the listening position with no compromise to the in-room smoothness. This may well be as good as home audio bass can get, but it may not be what works best in lesser rooms.

A "best of both worlds" approach in most rooms might be possible by adjusting the delay times of each distributed sub for simultaneous first arrival at the primary listening position. Intuitively it seems to me that this would tend to maximize the tactile sensation of impact, but I would expect some equalization to be called for to fine-tune the bass smoothness.

In my experience smooth bass = "fast" bass, and whenever I have made an adjustment which improved the in-room bass smoothness the net result was better perceived impact, INCLUDING when that adjustment also de-correlated the initial bass "wavefront". So I would suggest giving priority to in-room bass smoothness over preservation of initial wavefront coherence, but I wouldn't try to talk anyone out of achieving both simultaneously.

(The reason I specified "initial" wavefront coherence is that we actually want the in-room bass energy to be de-correlated in general. Well-correlated in-room bass energy results in large peaks and dips, with those peaks decaying into inaudibility more slowly than the rest of the spectrum. Strongly de-correlated in-room bass energy is smoother in frequency response and decays into inaudibility more uniformly... and the decays matter because the longer a tone persists, the louder we perceive it to be.)

 

[musicfirst1]

I think I need to refocus the question: Other than picking the optimum modes in the room, is it important for the acoustic centres of subs to be in line with the ACs of the main drivers if the mains are designed with aligning ACs? or do you loose something in this setup otherwise?

 

[Duke LeJeune]

...is it important for the acoustic centres of subs to be in line with the A/C of the main drivers if the mains are designed with aligning ACs?

Imo the same principles and priorities apply in the subwoofer region regardless of the architecture of the mains.

Assuming the main speakers are good to 30 Hz.

If your mains are perfectly phase-and-time coherent down to 30 Hz, what matters most in the bass region is still the smoothness of the frequency response. In my opinion.

If you get the bass quality you want with the acoustic centres of the subs "in line with" the acoustic centres of the mains, that's great! If not, then personally I'd give priority to in-room bass smoothness over alignment of the acoustic centres, because I think that's what matters more to the ears.

 

[musicfirst1]

Thx Duke!

 

[Duke LeJeune]

Thx Duke!

You're welcome, hopefully somewhere in all of my ramblings there is something useful.

I understand that intuitively it seems like the coherence the designer of the mains fought so hard for should be preserved all the way down, but imo the bass region really is a DIFFERENT ballgame because of how inseparable the speakers and room are. The ears can APPRECIATE time coherence in the mids and highs because they can process the direct sound and reflected sound separately (even though we do not consciously perceive them as separate events), but in the bass region (in most rooms) the ears cannot even process the direct and reflected sounds separately. The reflections start arriving before the ear/brain system knows that it's hearing bass.

 

[christoph]

I presume you are referring to something like a distributed multisub system, the intention of which is to smooth out the in-room bass... and for the record, ime the specific placement of the subs is generally non-critical as long as some basic rules are followed.

Could you elaborate on those basic rules?
And how many subs does it need as a minimum?
And how many subs optimally?
How many subs are the sweet spot regarding a good cost-performance-ratio?

 

[Duke LeJeune]

Could you elaborate on those basic rules [for distributed multisub placement]?

The basic idea is that you want each sub to generate a different room-interaction peak-and-dip pattern, and the sum of these multiple dissimilar peak-and-dip patterns will be much smoother than any one alone... and "smooth" bass is "fast" bass because it is the peaks (which decay into inaudibility slower than the rest of the spectrum) which make bass sound slow or boomy or unnatural.

So as a starting point, I'd suggest something like this: Place one sub in a corner (preferably a front corner), one sub somewhere along each of the two far walls (the walls "opposite" that corner), and any additional subs somewhere else but not too close to any of the others, and not in corners. Also not mirror-imaged or otherwise symmetrical with respect to any of the others. Bonus points if you can elevate one of the subs above the centerline of the room, to get significant distribution in the vertical plane as well.

If you can't follow some of those suggestions, then don't. You'll still be getting worthwhile improvement just by having multiple bass sources spread around the room.

And how many subs does it need as a minimum?

With three subs you can get pretty good distribution of your bass sources, so I'd say three is the minimum for a distributed multisub system.

And how many subs optimally?

As a general principle, the in-room smoothness theoretically increases as the number of distributed bass sources increases. (I use the word "theoretical" because in practice the improvement is never quite as much as the theory predicts.) So two subs are about twice as smooth as one; four subs are about twice as smooth as two; and eight subs are grounds for a divorce in most jurisdictions.

Seriously, I don't think there is a point where adding more bass sources is acoustically detrimental, but obviously there comes a point where more subs is impractical.

How many subs are the sweet spot regarding a good cost-performance-ratio?

That will depend on the specific situation, but I use four subs, which seems to be a "sweet spot" for me for three reasons:

First, my original target market was Maggie and Quad owners, and two monopole subs intelligently distributed have approximately the same in-room smoothness as one dipole source, thus my four small monopole subs are a good match for two dipole mains.

Second, my four 4-ohm passive subs can be wired in series-parallel to present a 4-ohm load which can be driven by a single amplifier (my Swarm system is aimed at a price point which is fairly modest by WBF standards).

And third, four small subs intelligently distributed seem to make enough of an improvement that my customers are happy. I'm sure my customers would be still happy if the Swarm had eight subs instead of four, but then I'd have a lot fewer customers in the first place!

Now IF you already have a good sub or two, then the sweet spot would probably be for you to add more. If you're "rolling your own" distributed multi-sub system, you don't need for all of the subs to go all the way down. So you can have one or two big subs, and the rest can be smaller subs which don't go as low.

 

[kach22i]

I'm currently reading a book published in 1972 by United States Gypsum (USG) called Sound Control Construction....principles and performance ($1.50).

Chapter 1: The essence of sound is literally a chain reaction of vibrations. The sound source which creates the first vibration is a physical disturbance..........

It goes on to say; When a sound source vibrates in a conductor (such as air), it creates a high-pressure layer in the conductor. In an effort to equalize the pressure, the molecules in this layer compress the adjacent layer, just as people standing on a crowed bus pass along a chain reaction to each person that squeezes on.

There are excellent graphics that follow showing a point source of sound and the rings of high pressure and low pressure waves that repeat a cycle around it.

I take that point and the initial disturbance to be our fabled "wave launch".