Brentworth Sound Lab speakers

Speakers. Brentworth Sound Labs. Never before has a single product so dramatically upset the normal rules of system architecture. Combining high efficiency (100 dB for 1 watt and over), no cross-over and, depending on the model, only one, two, or four, 6.5" drivers these speakers redefine resolution, clarity, dynamics and tonal and timbral accuracy. Finally a speaker that does not have to be 'fixed' by the electronics. Suddenly the path is open to simply chose amplification that sounds good. And, without the need for high power, this speaker can make use of better sounding lower output amplifiers. The fewer gain stages in the amplification the better. All things being equal the same design will sound better at 25 watts than it will at 50 watts. This is not to say that all low powered amps sound better than higher powered ones, that is simply not true. In fact we would argue that the lowest powered amplifiers available have very little to do with fidelity. 

Below is some information directly from BSL. I include it because they do a pretty good job of explaining their concept.


THE PROBLEM It is recognized (even assumed) that reproduction of music utilizing conventional loudspeaker technology fails to be convincing. The major impediments as seen and addressed by BSL, in a revolutionary new design are:

1) The use of crossovers and multiple drivers which severely alter the original wave forms (phase distortion or group-delay) thereby irretrievably sacrificing the timbre of the instruments which gives them their unique sound.

2) The low efficiency inherent in these designs that results in a suppressed dynamic range, and requires costly high output amplification while excluding a broad range of decidedly musical but low-power audiophile-type amplifiers (for example: single ended tube designs).

3) The employment of high-mass drivers which are incapable of immediate response and are therefore, insensitive to shading and nuance.

DESIGN CRITERIA

From the foregoing it may be assumed that the case for true reproduction of a musical event would be better served through the use of low-mass drivers in a crossover-less design. Brentworth Sound Lab has dedicated itself to this end and achieved remarkable results

ENGINEERING AND DESIGN

Attempts to eliminate crossovers (and thereby phase and group delay distortion) has thus far been relegated to either exotic driver design (i.e.: planar or electrostatic designs) or variations of conventional drivers (i.e.: Walsh, Pinfold and Jordan). From the limited success of these efforts we reasoned that although the driver is indeed an integral part of the whole, the enclosure which embraces it is many orders of magnitude more important. An example would be the relationship that exists between violin string and violin. This analogy indicated that the elusive "point-source" goal might be achieved with an enclosure built on principals more familiar to a violin maker than to a box maker. Shedding preconceived ideas and relying totally on the science of acoustics, an extraordinary development took place; BSL created the Stradivarius of enclosures.

The technology has been termed Dynamic Loading System (DLS) and refers to the enclosure's ability, through an intricate line and "valve" system to load the driver at low frequencies while simultaneously unloading the driver at higher frequencies. The effect is that low frequencies are coupled to the room with massive amounts of air, thereby negating the necessity for large and uncontrollable woofers (producing bass in this manner is directly analogous to a bass violin creating bass from the relatively small vibrations of a string). At the same time, the driver remains almost completely unrestrained to reproduce high frequencies.

Lastly, the design calls for the entire chamber to be mated to, and damped with, a non-resonant substance to control spurious resonance. The material chosen for this purpose is Gibraltar', a high-tech, solid-surface material available in a variety of colors and finishes. Strikingly beautiful when finished, Gibraltar' is also used to fabricate the matching stands supplied with the Type 1 speakers. The specially-made, 6.5 inch drivers are incredibly light and stiff, capable of reproducing 20 Hz - 20 kHz when reinforced (acoustically) in the enclosure. The drivers operate in an essentially pressure-free environment and are coupled directly to the amplifier.

A Bass Contour Module was developed as an integral part of the overall design. This unit is inserted between the control amplifier and power amplifier or in a tape loop if preferred, and can be switched out for comparison or special purposes.

With DLS (Dynamic Loading System) technology, Brentworth Sound Lab takes a bold step forward in music reproduction. BSL believes this technology is the closest approach thus far to "Point Source Sound" and therefore to the elusive goal of "Live" music. The absence of phase and time anomalies together with a completely unrestrained driver results in perfect reproduction of musical timbre with a clarity and definition that is truly remarkable. At the same time, their extreme sensitivity (a result of the driver's direct coupling to the amplifier) allows these instruments to capture the shading, nuance and dynamic range of a live performance with even the most delicate amplifier!

A great many problems in music reproductions can be traced directly to a basic flaw which appears as a necessary characteristic of the conventional loudspeaker - Phase Distortion. Of all the speaker ailments, phase distortion is the most critical, the hardest to cure, and probably the least understood by both stereo enthusiasts, and the average consumer alike.

Using easy-to-understand models, and non-technical terms, this pamphlet will enable you to understand phase distortion and the critical role it plays in the reproduction of music through loudspeakers.

To understand phase distortion, one must first understand the meaning of the words Frequency and Cycles. The concept is easily grasped if we form a mental picture of a person sitting at the edge of a quiet pond, making small waves by striking the water with his hand.

The waves, both large and small, depending on the force exerted, travel across the pond at the same speed, so that the distance from crest to crest remains unchanged once they are set in motion. This crest-to-crest (or trough-to-trough) distance is called wavelength and can be changed by striking the water at a faster or slower rate.

Let us assume that another person is sitting on the other side of the pond counting the number of complete waves (one crest to the next) as they pass a given point in a certain length of time. For example, if the wavelength is long, then not many waves will pass the point in, let's say, a minute. If the wavelength is short, then a large number of waves will be counted. In science a complete wave is called a Cycle, and the standard length of time is the second, which would give us "Cycles for every one second," or, simply stated, "Cycles per second." The number of cycles per second is referred to as Frequency.

Frequencies with a long wavelength we hear as low tones, those with a short wavelength, as high tones. We do not however, hear all tones. The average human may hear frequencies that range from about 30 cycles/second to 16,000 cycles/second. Perhaps you have had experience with a "silent" dog whistle. Silent that is, for humans, but not for dogs, whose hearing is attuned to much higher frequencies.

When a musical instrument generates a tone, the tone is composed of the fundamental note and whole family of harmonics. As an example, if a bass note is struck on a piano, a fundamental frequency of 73.42 cycles is produced, along with harmonics or "overtones" that may range up to 7,000 cycles, all of which are radiating from the same impact point on the string, at the same instant of time. The interweaving or wave pattern of this family of vibrations creates the tone quality or Timbre of the instrument. It is, in fact, the reason why each guitar, even though made by the same company, has its own unique sound. However, only a single point source can reproduce this slight difference.

To visualize why a single point source is important, picture a large stone and small stone dropped into a pond at the same time and in the same place. The subsequent pattern of large and small waves emanating from this common origin, can be directly related to instrument timbre. We say that the waves are "in-phase."

On the other hand, if the two stones are dropped at the same time but at different points in the pond, the intermixing of these waves (occurring somewhere in the middle) merely resembles our original example; they do not copy it. They are "out-of-phase."

It should seem apparent that in order to reproduce accurately the music on a record and have it "in-phase," we need a single source, capable of reacting to all frequencies. In other words, we have to drop our stones at the same time, in the same spot.

Now, a vibrating diaphragm of any size can produce low frequency tones. For example, the diaphragm in a microphone is 1 inch or less while the usual headphone diaphragm is 1/2 to 2 inches. Cones (or drivers) of this size, while large enough to create bass in your ear canal, are too small to move enough air to create bass in a room.

In a conventional speaker the bass is produced by using large massive drivers called "woofers." However, their very mass makes them sluggish and slow and the problem then becomes one of producing the high frequencies. This is solved by using a small driver (or a series of smaller drivers) called a "tweeter." Typically, midrange driver are also used for those frequencies which fall between.

This multiple driver system requires an electronic circuit called a crossover to be inserted in the system to direct the appropriate signals to the various drive units. The end result is that although the conventional loudspeaker produces all frequencies, it is using many sources of propagation which causes the music to be out of phase and time alignment with the subsequent loss of instrument timbre.

Unfortunately, the loss of instrument timbre is only one of the unpleasant side-effects of phase distortion. Another is loss of clarity. Music from the conventional loudspeaker most often seems to be heavy, muffled, and coming from the inside of the speaker box. The listener may feel as if he was listening to a performance through a thick blanket. This inevitably leads to a problem in imaging and presence, as they are known in the audio business.

Imaging is the mental picture one should get of the performers and their stage position. Presence refers to how much a speaker sounds "out-of- the-box-and-into-the-room." The more presence a speaker has, the easier imaging becomes.

To understand the final and most damaging side-effect of phase distortion, we must return to our pond. This time, let us assume that there is one person on either side of the pond, and that both are making identical size waves. As the waves meet in the middle, the water at any given time will be both choppy and calm in the same area.

When the crests of two identical waves meet, their effects become additive and the resulting wave crest is twice as high as either of the originals. For example, the crests of two 2 inch waves would join to form a four inch wave. The same result occurs at the meeting of two troughs. These cases are referred to as constructive interference.

Logically then, if a 2 inch crest meets a 2 inch trough, their effects are canceled and the water is smooth. This is termed destructive interference. By the same token, we would expect to find intermediate size waves in areas where the interference was neither completely destructive nor completely constructive.

With this in mind, it is easy to understand how in a conventional speaker with many sources of propagation, some frequencies may be totally or partially canceled causing a mute, or, in the extreme case, complete absence of musical instruments.

In theory then it would seem reasonable to build a speaker that uses a single source for all the frequencies thereby eliminating the need for woofers, tweeters, crossovers and the attendant problems of phase distortion, time alignment, clarity, sluggishness, etc.

At BSL, this was accomplished with our proprietary Dynamic Loading System (DLS) whereby a single driver is used, and the cabinet becomes the generator of bass frequencies in the same way that the body of the bass violin creates a large amount of bass from so small an object as a vibrating string.

A further advantage of this system lies in the "quickness" of the bass response since the "woofer" in this case is small (6.5 in.) and easily controlled by the amplifier.

© NorthCountry Audio and CadNor LTD 2014. 315-287-2852 northcountryaudio@cadencebuilding.com