Tannoy Dual Concentric Brochure

Dual Concentrics for Contractors

INTRODUCTION

For over 40 years Tannoy has been manufacturing Dual Concentric drive units and loudspeaker systems. Over that time the loudspeaker industry has developed increasingly sophisticated drive units and horn systems to control the way sound is dispersed into the world. They have tried, in part, to duplicate the inherent advantages of the true point sour ce – the Tannoy Dual Concentric.

Tannoy has continued to develop the Dual Concentric concept, even when other more overtly ‘modern’ products such as the constant directivity hor n wer e capturing the headlines.

It is popular to say that loudspeakers haven’t changed at all in the last half century. But there have been a huge number of incremental improvements pr oduced by better understanding of the nature of sound propagation, the use of vastly improved development tools and computers, and the use of ever more sophisticated materials and manufacturing techniques. As well as sounding so much better, today’s drive units have the power, reliability and SPL capabilities of a dozen of their earlier predecessors.

Whilst standing the test of time, the Tannoy Dual Concentric has not stood still. Tannoy has been constantly improving the capabilities of the drive units, and recently our engineers returned to ﬁrst principles and designed an entirely new drive unit. This new unit applies Tannoy’s long experience and advanced understanding of loudspeaker and acoustic theory taking the Dual Concentric into the next century.

In this White Paper some of the inherent advantages of using a point source, and why the Dual Concentric is seeing a renaissance in the contractor industry, are explained.

Page 1

ONE SOURCE IS BETTER THAN TWO

In the ideal world manufacturers would like to produce a single drive unit that copes with all of the frequency range. But the laws of physics being what they are, a driver that works well for low frequencies will not work well for high frequencies and visa versa. So separate drive units are used for different areas of the frequency band. Most manufacturers have developed completely different drive units and placed them in a single box or in several boxes to create a full range system.

Unfor tunately as soon as you br eak the audio signal into separate sections and transmit it from different points in space all sorts of problems occur.

LARGE PISTON AREA LARGE POWER INPUT MORE OMNIDIRECTIONAL  CABINET NEEDED

Sound pressure (dB)

10 100 10000 200001000

DISPLACEMENT OF SOURCES

TIME ALIGNMENT

PHASE DIFFERENCES

Frequency (Hz)

SMALLER PISTON AREA LESS POWER INPUT CONTROLLED DISPERSION DIFFRACTION CONSIDERATIONS

• Covering the whole audio spectrum requires differ ent approaches at differ ent frequencies for optimum solutions.

• A seamless joining together at crossover is essential.

Page 2

Inter ference over the critical cr ossover ar ea

Over the crossover area, both HF and LF drive units are producing acoustic energy. Since the drive units are a little (or sometime large) distance away fr om each other, the signal path to the listener from the HF and LF drive units will be slightly dif fer ent. The sound from the mor e distant driver will take slightly more time to reach the listener than from the nearer one.

In one seat, the sound from the two drive units will be in phase with excellent perceived level, but in a nearby seat they could be out of phase and the level will be down or even reduced to zero over a narrow band of fr equencies. Consequently when separated HF and LF drive units are used, the sound coverage in the crossover area will always be somewhat inconsistent.

One way to get over this is to use very steep crossover slopes, so the crossover area, where both drive units are working, is minimised. However, steep ﬁlters can create phase errors and other electronic artefacts generating more problems than they solve.

Phase Error Changes with Position

HF 

SOURCE



Bass Cab

Plan View

LF 

SOURCE



OUT OF PHASE AT CROSSOVER

IN PHASE AT CROSSOVER

OUT OF PHASE AT CROSSOVER

HF horn

Ver y Steep Filter Slopes Less Steep Filter Slopes

Very Steep Filter Slopes

Less Steep Filter Slopes

AMPLITUDEPHASE



AMPLITUDEPHASE



• A true Point Source gives the same sound from seat to seat.

• Dual Concentrics can use simpler, better sounding and more ef ficient crossovers.

Page 3

Harmonics

Every sound created in the natural world has harmonics that give us clues to the type and quality of the signal source. The harmonics of a single note may extend beyond the limits of hearing.

A fundamental note, with fundamental frequency lying within the range of the LF driver, will have many harmonics repr oduced through the HF driver. If these are separated, either in time or space, then in most listening positions the fundamental of the note will be heard at a slightly dif fer ent time to its harmonics, which does not lead to the most accurate reproduction of the sound.

The Tannoy Dual Concentric Preser ves the Harmonic Str uctur e of Complex Sounds

RESULTANT

POINT  SOURCE

FUNDAMENTAL

THIRD HARMONIC

SECOND HARMONIC

Time

Harmonic relationships preserved using a single point source

DIFFERENT RESULTANT

DISPLACED SOURCES

Time

Harmonic relationships using multiple sources

DISTORTED MULTIPLE-SOURCE RESULTANT ORIGINAL SINGLE-SOURCE RESULTANT

Time

Signal

Original versus distorted resultant

• Dual Concentrics have better harmonic alignment.

• Better harmonic alignment results in a clearer, more intelligible, more natural sound.

Page 4

Constant Time Delay

A single pulse of sound, such as a drum beat can be considered a combination of many acoustic elements up and down the frequency spectrum. A loudspeaker system should behave as a constant time delay with every element of the audio spectrum being delayed by the same amount as it passes through the driver and crossover.

If, as is often the case with complex crossovers and separate drive units, the delays are different for dif ferent ar eas of the audio spectr um then these elements will be hear d slightly staggered. The ‘crack’ of the stick hitting the drum skin from the ‘thump’ of the lower fr equencies produced by the drum skin vibrating will be heard as separate events.

This can only be par tially r esolved by introducing delay pr ocessing to re-align the elements. Additional processing, with its associated signal degradation, is made unnecessary by using a Dual Concentric.

Phase Response of a Typical Discrete Non-Aligned System

 (180°)

= K

 (-180°)

Phase not independent of frequency

Phase Response of a Typical Tannoy Dual Concentric System

 (180°)

100 Hz

Phase substantially independent of frequency

 (-180°)

20 kHz100 Hz

. = K

20 kHz

• An integrated Dual Concentric approach provides a constant time delay.

• Constant time delays over the frequency spectrum give better overall sound quality and transient perfor mance.

• Constant time delay behaviour removes the need for separate HF delay lines that need careful and time consuming on-site adjustments.

Page 5

Attempts to emulate the Dual Concentric

There have been two trends in system design to try and emulate the single source approach. The ﬁrst is to bolt the HF horn in front of the LF or MF sections. This places the two sources in the same axis but only in two planes – one driver is still in front of the other. To integrate the signals, some form of delay has to be applied to one unit to make it coherent with the signals coming fr om the other unit. This is costly to do well, making the crossover very complex – and complex crossovers can af fect sound quality or use up power that could be better used powering the driver.

As well as creating problems within the electronics, placing the HF driver and hor n directly in fr ont of a low frequency driver produces a whole set of non-linearities caused by the LF waves being masked and reﬂected back onto the driver cone.

Engineers are increasingly concerned with the acoustic effects of relatively acoustically transparent obstacles such as the grilles. Placing a large solid HF driver or a less solid (and more r esonant) horn with all the associated mounting hardware directly in the way of the LF driver is not a satisfactory engineering solution.

A Tannoy Dual Concentric does not suf fer from r eﬂected energy storage or mid-range shadowing

LF LF

Obstruction and interference

Single  horn profile

Discontinuity of HF

Typical Coaxial unit Tannoy Dual Concentric

• A Point Source driver simpliﬁes nearly every aspect of a system installation.

• The Dual Concentric is the only practical way of creating a full frequency range Point Source driver.

• Other ways of approaching the Point Source goal suf fer from identiﬁable drawbacks.

Page 6

More attempts to emulate the Dual Concentric

Another trend in system design is to create systems from full-range cabinets, rather than separate bass, mid and HF cabinets, which were the fashion in the 70s and early 80s. For both hire and installation work the convenience of the compact full range cabinet, inherent in the Dual Concentric approach, is becoming increasingly appreciated. But bringing the drive units closer together in smaller boxes of fers only partial solutions to the problems of time domain, phase, dir ectivity, crossover complexities.

A well designed Dual Concentric drive unit resolves these problems by being a tr ue point source.

HF SOURCE

MF SOURCE

LF SOURCE

HF, MF AND  LF SOURCE

• Compact, full range boxes are the system design route for the 90s.

• Even in a small box, separated drive units cannot emulate a true point source unit, they will still suffer from all the pr oblems of being of non Dual Concentric design.

Page 7

ONE DRIVER – ONE DIRECTIVITY

A lot of energy has gone into the design of constant directivity hor ns that control the acoustic dispersion from the HF driver. This is important to maintain an even coverage at all fr equencies over the target area.

Controlling the directivity also allows the sound from the speaker to be more accurately targeted to where it is needed. Targeting keeps the sound wher e you want it, and away from the walls and ceiling. This cuts down the amount of high level reﬂections that cause at best, reduced intelligibility, and at worse, resonances and feedback.

In this age of tighter controls on working conditions it is also important to keep sound levels down in work areas. Levels that are acceptable on a discotheque ﬂoor, will not be acceptable in the nearby bar area where staff are working all the time.

Dispersion pattern for Constant Directivity

0°

30°

60°

270°

90°

1kHz

270°

5kHz

Dispersion pattern for Non-Constant Directivity

0°

30°

60°

270°

90°

270°

0°

30°

60°

90°

270°

0°

30°

60°

90°

10kHz

0°

30°

60°

90°

270°

0°

30°

60°

90°

1kHz

5kHz

10kHz

• The ideal system is one where the sound dispersion is well controlled, and does not dramatically alter with frequency.

• Dispersion control must be achieved without introducing problems in other areas

Page 8

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