[John Casler]

VMPS SUBS (thinking INside the BOX)

Interestingly enough, I frequent several Audio Forums to keep up on as much of what is going on as possible.

To that end there are any number of posts regarding SUBWOOFERS.

While few really delve deeply into the criteria some of the posters use to judge a sub good, or great, it seems that it is often based primarily on SPL capability, and lowest frequencies produced.

While these are NO DOUBT very important (especially for HT) I might suggest that unless a sub can be musically accurate, that is is NOT really a Great or even Good sub

To be musically relevant a sub has to be low in distortion and have the capability of producing the same level of harmonic information, and resolving deep levels of detail.

The final determinant is not really from the sub (Cabinet, Drivers, Wiring) but from the Electronics or Room treatments used to shape the sound to your environment.

After all if the various wave length energies are crashing/bouncing into each other forming sonic peaks and valleys at your listening position then NO MATTER how good your sub is it will not sound its best.

So what do we need to have the best SUB?

1) The Best Quality Drivers
2) A Well Made and Solid Cabinet
3) Good Quality Wiring
4) High Performance Amplification
5) Tuning and Equalization
   A) Driver Synchronization and Distortion Reduction
   B) Sufficient Equalization Capabilities

DRIVERS

Brian has a selection of Woofers he either makes, or are made to his specs.  Quite often this include selected cone materials, his own baskets, and other parts.

But he also offers some of the best drivers available commercially such as the new MegaWoofers, and the new TC Sounds Drivers used in the OMG Series.
From the 6" MegaWoofer with 40 oz magnets and Woven Carbon Fiber cones, to the 15" TC Sounds OMG WOOFERS you pretty much have the best selection one can expect from a Woofer Driver at a particular price point.

But when speaking of Drivers we cannot ignore the very unique design Brian employs with both ACTIVE and PASSIVE driver combinations. To that end we now have what B calls the BIG BUMP Passive Radiator to accommodate the much larger "excursion" of the High Output Active drivers like the TC Sounds Woofs.

CABINETS

All VMPS cabinets are well constructed and braced with strong and rigid parts and materials.  Of particular note in this area is the VSS sub cabinet.  VSS is an acronym for VERY SOLID SUB, and it is.  All the walls of this sub are 1.5" MDF with the front baffle being 2"!!!  It is a veritable BRICK Sxxxx House of a sub.

One might also see from Brian's cabinets that he likes SIZE.  Yes, in the best subs, SIZE does matter, and there is no substitute for internal cabinet volume.  Surely one can build a small box sub equalized to death for high distortion for the booms and explosions of HT, but if one is serious about a Musical Sub, the better path is one of less equalization, distortions, and more cabinet volume.  This is of particular importance with the Active Passive design of VMPS

As well, all VMPS subs have the correct amount of internal damping material to create the precise internal cabinet pressure variations that will cause the best results between the active and passive drivers when well tuned.  One can also upgrade to the SR-71 package which is a damping material that tends to cause the drivers to "see" an even larger internal volume due to its damping qualities.

WIRING

What can you say about wiring?  B, uses the highest quality binding posts, solder, and quality level of wiring like Analysis Plus and Bolder Silver.

AMPLIFICATION

For the longest time Brian was rather against placing an amp "IN" the sub like most commonly done today.  Why?  Because most sub amps were open and exposed to the huge amount of vibrations and forces that occur millions of times during a number of healthy listening sessions.

As well cutting a gaping hole in your sub could do nothing but make the cabinet weaker. 

Then placing something inside the sub, no matter how small reduces the internal volume.

But we finally found an OEM that had a sub amp that was enclosed to some degree shielding the electronic parts from a good portion of the vibration.  So he relented and we can now offer subs with 500w and 1000w plate amps of reliable quality and performance.

However, it is our preference to offer the "external" version of the same amp with the same 1000w capabilities "outside the box" so when it comes to subs, Brian thinks OUTSIDE THE BOX. (is still the best)

TUNING and EQUALIZATION

(to be continued)

[John Casler]

   Driver Synchronization and Distortion Reduction   

No matter how good your sub parts and components are, they can't and won't sound good if you screw the pooch by not addressing high distortions and room created distortions (Modes/Nodes)

Driver Synchronization and Distortion Reduction

While it is often thought that it is acceptable to have a certain amount of distortion in bass frequencies, or that it is unavoidable, it is NOT.

Distortions can be cause by many things, but for the most part in a woofer, it is because the driver is not responding exactly to the input signal and produces an inaccurate waveform.

This can be improved by using the best drivers available and I think few would argue that Brian surely does this.  In some instances he either has or does build and magnetize the drivers "in house", has then built to spec by a builder, or seeks out the best commercially available examples.

In the VMPS speakers and subs (the exceptions being the 626 and HT speakers) Brian employs a system of active and passive drivers.  This means that the Active Driver creates physical forces both inside and outside the cabinet creating bass frequencies.  The Passive Driver then is "reactive" to the internal pressure changes in the cabinet and produces external wave production too.

These drivers need to be in perfect synchronization to keep from producing distortions or inappropriate reactively produced Wave launch.  When perfectly synchronized  these two drivers act as a single system but at different frequencies because they cannot act at the exact same time, as one is reactive.

So the Passive will always be slower and thus LOWER in frequency than the Active driver.  But for these drivers to act as one system their timing (and phase) must be as perfect as possible.  That is, they must work together for the lowest distortions to occur.  Since the action of the Passive Radiator is motivated by the internal cabinet pressures the first area is to have a "sealed" environment to maintain a "constant" internal pressure chamber.  This insures that there are no drops or changes in pressure that are not associated with anything except the action of the Active Woofer.

However we still need a method of bringing the two into EXACT PRECISE interaction.  Brian does this by adding a MASS, in this case our PUTTY, to the center of the Passive's Cone.  This Putty Mass is of an amount that will cause the PR to react at the speed required to cause the LOWER and slower frequency to be created.

However, movement this slow while creating large powerful wave forms also will have a HUGE room for error or distortions.  Distortions both in the frequency being created, and the precision in timing needed to work as a single system.  To bring these two separate and very different components into harmony, we can either add or subtract this PUTTY (mass) to either SLOW or allow a FASTER interaction of the PR.

Initially this can be done with mass as large as a pea, but to reach more and more precise levels (Brian often claims single digit distortions) it may require amounts measured as "a fingernail full".  This amount might, when rolled up in a ball be a little smaller than a bb or even the head of a straight pin.

While few of you will be so obsessive as to spend significant time adding or removing  this mass in such small amounts, it is reasonable to once every year or two add a bit of the putty back (maybe the size of a marble) and re-tune if you are of such a mind.

The greater point here, is that as a VMPS speaker owner, you have a system that can be adjusted to a greater precision than most any other system out there, and when you have actually heard the results it is like those other AH HA moments when you have made large jumps in performance and let more musical information shine through to your ears.  You just don't know what it sounds like until you have uncovered it by synchronizing the system.

The lack of distortions and the synchronized interaction of thes drivers allows you to clearly hear the rich harmonics of bass like you never knew existed.  Gone is the Wooly, Rumbling or Boomy bass and available is the incredible harmonic overtones and textures that many never hear.

(to be continued)

[John Casler]

Placement, Room Treatment, Sufficient Equalization and Room Capabilities

The third leg of employing a sub is proper "placement", room treatment, equalization and room correction.

I have already explained how VMPS subs are tunable, and have exceptionally low distortions, but with all that, we still need to deal with the PsychoAcoustic limitations of interaction in the room.

Rooms are almost like snowflakes in their differences with the greatest commonality being in room heights which are generally 8-9 feet. 

Low Frequency Wave Lengths radiate hemispherically.  That is, they don't beam like a flashlight, but radiate in all directions until they hit something.  They are large, and powerful, and as such can move through many materials much easier than higher shorter (and less powerful) wavelengths.

As well their energies are so much greater that when they hit some surfaces like floors/ceilings/walls they also reflect substantial return energies.  These reflected energies then travel (based on the angle of incidence) back into the room.  As they do so they are affected by the distances they have traveled to those surfaces.

For example the wave that travels to the ceiling would generally have a shorter and faster trip than the one that travels to a side or back wall.  This sets up a very complicated group of reflected energies that are sent back into the room to encounter the fresh just released waves from you woofers.  Imagine this as waves in a swimming pool that hit the wall and immediately reverse direction and travel back in the opposite direction.

As they travel back into the room they encounter other DIRECT and REFLECTED waves and those encounters cause an EFFECT on all the energies involved. (Again it can be visualized as waves in a pool or pond that encounter each other)

As they collide the energy of each is either increased or reduced.  This is what causes modes/nodes.

As mentioned earlier each room has a "fixed set" of dimensions where these waves will travel, reflect and interact with each other.  These interaction can produce peaks and valleys at specific frequencies as the energies either reinforce each other, or reduce each other as they meet.

Room treatments such as bass traps are useful because they absorb, reduce or trap some of this energy and reduce the amount returned to affect the fresh wavelengths.

However, it is virtually impossible to treat away all of the problems, and that is where equalization comes in.  The most important place to equalize is the listening position.  This is where you sit and your goal is to equalize your speakers output so that it will adjust the frequencies that are magnified and reduced at your listening position to give you a more "equal" response to all bass frequencies.  This is accomplished through an equalizer.

The VMPS Bass amp has a small single band parametric equalizer for the largest offender.

Another way to combat more difficult rooms is the new AntiMODE 8033 which provides a DSP (digital signal processing) way to read the room and how the "ALL" the bass frequencies are interacting at the listening position, and then has a small computer chip that adjusts the sub's output to accommodate those modes/nodes.

So to get the best out of your VMPS subs you would want to do the following:

1) Order the SUB or SUBS appropriate for your room and goals

2) Place them in a way that will give you the best response and blend to your main speakers woofers, and achieve a phase coherence and integration with your MAINS

3) Adjust your putty (+ -) to achieve the best Driver Interaction and lowest distortion

4) Treat your room as well as you can for bass frequencies

5) Employ the equalization means you might have available to make your bass response as equal as possible in all bass frequencies.

In the future we can discuss some of the above points in greater detail.

[John Casler]

(more to come)

[John Casler]

The differences between HT BASS and 2 channel Musical BASS

Strangely enough one would think BASS is BASS. . .right?

Well when we are dealing with two separate applications such as the production of good BASS for HT and the same for MUSIC there are different concerns, and many don't seem to make the distinction when considering what to do.

I find this also present in acoustical managementand treatments for the two separate and clearly distinct applications.

To create BASS in a room you have goals.  These goals are what decide how you approach this production.

Common goals:

1) Desired SPLs
2) Desired Frequency Response
3) Reduced Room Interaction


Application Specific Goals HT

1) Extremely High SPL capability
2) Extreme Dynamics
3) Recreation of Sound Effects like Impacts, Explosions and Crashes

Application Specific Goals Audio

1) Realistic SPLs based on what the Musical Event actually sounded like
2) Proper Phasing and Timing of the the BASS to blend with the Main Speakers
3) Reduced Room Interaction
4) Lowest Distortion Possible
5) Ability to produce the rich Harmonic Structures of Bass Instruments

While they often get "lumped" together the goals and acceptable performance characteristics of MUSIC and HT can be different.

HT BASS HEADS often are more concerned with Maximizing:

1) The lowest frequencies
2) The production of visceral sensations
3) The greatest Dynamics for explosions and impacts

The MUSICAL BASS HEAD wants:

1) Accurate frequency reproduction of a Musical performance
2) Accurate Phased and Timed Aligned blending with the Main Speakers
3) Realistic Musical Dynamics
4) Accurate Harmonic Structure and Interaction

Since PHYSICS is PHYSICS the path to many of these goals are similar, but NOT always the same.

For example, it is quite common for both goals to encounter ROOM INTERACTION problems.  Three of the most common resolution paths are:

1) Equalizations
2) Room Treatments
3) Multiple Subs

All of these work, BUT they need to be applied differently.  WHAT?  Applied differently?

Yes, and here is why.  In the Home Theater most of the DEEP and High Impact Bass will be due to sound effects like explosions and high dynamic "foley".  Foley is manufactured and embellished sound.  In most cases it is short, dynamic and of high transient response.  While phasing and timing is of some importance, it IS NOT of the same importance as blending a deep sustained BASS notes and subtle harmonic blendings from an Organ or String Bass.

Multiple SUBS

It is quite popular now to suggest "multiple subs" with the primary goal being to release bass energies from several locations so that no single subs interactions (Modes/Nodes) with the room dominated and all are "smoothed" by the SUMMED interactions.  This is a much easier task with HT BASS, since it is negatively impacted less by timing and phase issues.

In music, the actual release of the bass energy in space DOES NOT occur at multiple locations in a space, and doing so in your room seriously impacts the accuracy of what reaches your ears.  Phase, timing, and sonic coherence are compromised if much care is not taken.  In music, we are not ONLY concerned with simply being able to produce all the frequencies at the same SPL in a particular spot in the room, but those sounds "MUST" be in coordinated, properly phased, and have timed arrival to not be distorted.

So we can approach these two goals with similar paths and in similar fashion, but we MUST understand and consider that Frequency, SPL, and Dynamics are NOT the HOLY GRAIL for all applications.  We need to dig a little deeper and consider a couple other factors if we are interested in producing the BEST musical bass overall.

As soon as I get time, I will write about the methods and concerns that are more specific to MUSICAL BASS, and various means on how to attain them.