Multi-Principle Technology

Multi-Principle Technology, for which the MPT-48 is named, enabled the realization of a singular building block concert array module.  Multi-Principle Technology is a design scheme that requires an engineering project to be conceptualized from many angles at one time.  A total system possessing natural balance is the general goal; which, incidentally, is a good place to start in order to reproduce sound in a high fidelity manner.  Fidelity, clarity, intelligibility, directivity control, efficiency, and array-ability are among the many requirements met by the MPT-48.

The Human Ear

The MPT-48 has been designed to respect the fact that the human ear is most sensitive in the vocal range.  This area of response (~200Hz to ~4000Hz) should be reproduced by one component.  The midrange drivers produce this entire range and are integrated with high fidelity high frequency drivers, which extend response all the way up.  Not only are these two components configured in a point source manner, they actually emit from one horn.  This unique arrangement is accomplished by locating the two drivers very close together in terms of the Z-axis.

The Top Seven Octaves

With a small amount of time alignment the two subsystems combine and emit from the same horn producing a singular wave front that represents the top seven octaves (200-20,000Hz). This configuration is optimal for reducing phasing problems between the midrange and high frequency transducers as well as between cabinets.  The MPT-48 mid/high section provides you with clarity and seamless-ness that is expected from high-end reference monitors: 111 decibels of esoteric smoothness (1W1m), to be exact.

The Bottom Four Octaves

The two bass horns, which complete the system, are responsible for the bottom four octaves and are arranged above and below the mid/high section, maintaining the point source architecture.  The bass section yields 104.5 decibels (1W/1m), on  average, and produces 100.5 dB @ 50Hz.  Directivity control is still displayed @ 80Hz by minus 6dB 30 degrees off axis.  Systems of six or more produce flat response down to the bottom octave, without effort.  The MPT-48 incorporates carefully developed subsystems into a module that produces more sound from less space which inherently gives you the sonic advantage.

Many types of arrays can be built by incorporating the MPT-48 as a singular building block.  Point source arrays are the best for overall flexibility.  The MPT-48 can cover odd asymmetrical intended coverage areas with ease.  Asymmetrical hybrid arrays of MPT-48 loudspeakers will allow you the flexibility to cover anything. 

When built properly, an array of MPT-48 modules will diminish the need for delay clusters.  Excluding delay clusters greatly reduces temporal linearity problems while enhancing clarity and imaging.  What this will mean to you is simply a much happier audience! 

Two MPT-48 modules easily produce more than 114dB of full bandwidth output @50ft (50Hz-17Khz +/-4dB), measured.  Calculated maximum and continuous output @1m is 144dB and 138dB, respectively.  Sound pressure output and headroom are easily delivered even for the most demanding situations.  With our high Q multi cell horn design you’ll enjoy precision directivity control and smooth integrate-ability; singular building block integrate-ability. 

Our Multi-Principle Technology required a multi-cell approach, a full bandwidth completely point source product, and precisely optimized sub systems.  Our goal has been obtained: the MPT-48. 

All of the technical aspects that we required the MPT-48 module to adhere to are beyond the scope of this brochure.  In general, though, our secret lies in the combination of old school size horns and our new school format along with unique component choice and configuration. 

We made a lot of decisions on what this speaker must do well before the drawing board.  At the drawing board we threw away nothing; instead, we added to the list.  What we came up with is a tightly packed system possessing natural balance. 
 

The MPT-48 low frequency subsystem is comprised of two 15” transducers matched to free space via 36” long and 46.5” wide exponential birch horns.  The horns control directivity well below 80Hz and increase sensitivity into the bottom octave thanks to a carefully designed pre-throat area volume and precisely calculated exponential waveguides. The bass section yields 104.5dB 1W/1m sensitivity, on average, which quickly adds up to ground shaking bass response.   A minimum array of 3 to 6 modules will eliminate the need for sub-woofers, allowing for a truly full bandwidth point source sound image.

The 15” transducers have 3” voice coils and 95 oz. magnets for best sound quality and efficiency; (4” models are available upon request).  They also use a bumped back plate allowing for high inputs @ 16Hz.  Each bass driver is loaded by a 3 ft2 sealed chamber, which, in conjunction with our proprietary horn technology produces esoterically deep, smooth, and natural sounding bass.

Ask any hi-fi nut and they’ll explain that a sealed bass cabinet provides for the deepest and smoothest response.  That’s precisely where we started.  Then we increased efficiency and added directivity control that only control freaks will fully appreciate.  They present more directivity control at lower frequencies than any single competitive product will even dream of delivering and that’s some control!

Powerful deep realistic bass response is definitely a requirement for high fidelity.  The low frequency section of the MPT-48 was carefully perfected to address the needs of this total system loudspeaker in terms of the bottom four octaves, and it does so with great fidelity.  Fidelity, efficiency, integrate-ability, and functionality are what the MPT-48 low frequency section has to offer.  You’ll find that it possesses more positive attributes than other low frequency systems and will give you much better bass response! 
 

While not to discount good bass response we would like to explain why the MPT-48 mid/high section is our secret to creating majestic imaging and a united wave front.  This section is responsible for the reproduction of the top seven octaves (200Hz-20,000Hz).   Included in this range are two octaves, 1KHz-4KHz, where the human ear is particularly sensitive and important speech intelligibility is found to reside, but most systems split this range causing phasing issues and detectable incoherencies. 

The MPT-48 produces these two octaves by 12” cone drivers.  The drivers are matched to free space via 30” long and 23.25” wide exponential birch horns.  The mid-range drivers used have tightly wound voice coils and 109oz. magnets in order to achieve incredible mid-range power and accuracy.  The 30” horns have smooth sharp overlapping patterns and couple together with a high degree of precision.  This tight Multi-Cell approach greatly reduced phasing issues between horns. 

For the 4KHz to 20KHz range one inch drivers are used for extra clarity.  The two component subsystems are matched coaxially at the horn throat providing for a singular wave front at the mouth that exceeds 200Hz and 20KHz.   This arrangement provides for ultra good phase response and seamless frequency response.

This unique singular wave front will enable your MPT-48 sound system to please the crowd with easily intelligible and extremely high fidelity concert sound.  Our 12” and 1” choices stem from careful listening tests and custom designed drivers.  The unique combination of warmth and clarity of this section is esoteric and really must be heard to be understood!
 

The MPT-48 is the only truly full bandwidth point source array module that we know of; making it reside at the fourth tier of sound reinforcement quality. 

Many applications are in need of a sound system made up of MPT-48 concert array modules.  Be it an acoustically challenging room, very large outdoor concert, extremely distant throws, or even near field reference quality listening you’ll find that the total system design, precision directivity control, singular point source architecture, and extreme efficiency will benefit any of your most demanding applications. 

By choosing Rexroat Sound  to supply you with the loudspeaker you will be able to provide your audience with a quality of sound that obliterates most concert sound systems. Please note that appropriate care should be administered when operating MPT-48 array modules because SPL measurements consistently read higher than expected.  The human ear is able to tolerate higher SPL’s when the sound is smooth, clean, and high fidelity; thus, we do caution engineers when first mixing on a MPT-488 sound system. 

We all know how large-format 2” exit compression drivers can really catch the ear @ 2.5KHz, don’t we?  The MPT-48 sustains this type of output anywhere you want it, and does so with elegance and sound quality that you will want in your own living room!  The word “smooth” is almost always used by newbies.

*note: our SPL specs are relatively conservative!

The MPT-48 array module from Rexroat Sound is a fully point source loudspeaker.  This speaker is full bandwidth, making it capable of being the singular building block to a sound system.  No sub-woofers are needed, allowing the realization of a truly point source array.  This array also reproduces the entire bandwidth for each listening location by only one to four  MPT-48s actually imaging to the location (depending on the location).  At frequencies below 80Hz, the lower loading limit of the bass horns, the array will utilize all of the bass sections in reproducing the bottom two octaves.  This coupling effect has few phasing problems due to the long wavelengths in this sub region, allowing the perception of one sound source emitting sounds exceeding the range of 20Hz to 20KHz.

This full bandwidth point source sound is produced from four specially configured and designed horns in each module.  This arrangement is configured as follows: two 46.5” (118 cm) wide and 36” (91 cm) long bass horns which are placed above and below two side-by-side mid horns which are each 23.25” (59 cm) wide and 30’ (76 cm) long.  Each bass section is designed to cover it’s 30 degree slice, when arrayed properly.  Each mid horn is displayed 15 degrees from each other so that the two, side-by-side, are covering the 30 degree slice the MPT-48 is to be covering in the horizontal.  The bass horns utilized in the module have a calculated cutoff frequency of 80Hz, although the horn device itself will increase sensitivity of the bass driver to below 40Hz.

Phasing problems are greatly reduced due to the quick and sharp overlapping patterns of the two narrow side-by-side mid/high horn configuration. This design allows for an emulation of the ‘old school’ multi-cell horns; a multi horn emission scheme with one sound source.  Phasing issues in the bass region are also inherently reduced because the bass is emitted from the same module as the mids and highs, in a point source scheme.

Both the 15” bass transducers and the 12” mid transducers are enclosed in sealed chambers, such that they do not interact with each other.  The 1” exit high frequency transducers exit coaxially along with the 12” drivers at the throat of the mid/high horns.  The loudspeakers are to be operated by a sufficiently sophisticated crossover system along with digital time alignment.  A digital loudspeaker management system, or an integrated signal processor is recommended.  A 12db per octave, phase aligned, crossover at 4KHz to separate the mid and high frequency transducers shall be incorporated – a Linkwitz-Riley crossover is recommended. 

This crossover scheme applied to this array module allows the vocal range to be realized more naturally than expected from a concert loudspeaker.  The crossover between the bass and mid sections may be realized at any point deemed appropriate; 24db/oct between 150-200 or 12db/oct between 200-300 are recommended.  Depending on the needed throw of specific applications different crossovers may be used.  Although the MPT-48 is intended for large scale, long throw applications utilizing large arrays, it actually exhibits extreme clarity and smoothness up close as well. 

 The module is constructed to be one of supreme quality and structural integrity.  The cabinet is constructed of 13 ply 18mm Baltic birch plywood, and the horn curves of 5 ply 6mm Baltic birch.  The module is coated in a durable epoxy shell.
 

• 15 degree trapezoidal
• 13ply 18mm baltic birch
• 5ply 6mm for horn surfaces
• unibody self bracing constuction for null resonance factor