Transcendent Sound

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Planar Tweeter Turbocharges Tang Band

As good as the Tang Band is, the desire for improvement is unstoppable.  A new planar tweeter is now available that is a perfect match.  An add on tweeter assembly has been developed boosts performance to the next level.

This planar transducer uses the air motion transformer principle.  These types of speakers are known for incredibly fast transients, clarity and low distortion.  They all have one common problem.  They have excellent horizontal dispersion but poor vertical dispersion. This causes high frequency beaming in the vertical plane.  By arranging two tweeters perpendicular to each other and wired in series, this problem has been completely overcome.  This arrangement provides very wide and symmetrical dispersion both horizontally and vertically.  The result is the elimination of the “sweet spot”.  The entire room becomes the sweet spot.  Excellent coverage is obtained everywhere.  The sound opens up into a wall of sound.

Some significant technical hurdles had to be overcome to mate the two drives for seamless reproduction.  Refer to the graphs below.


           Dayton Audio AMT3-4 Tweeter                                           Tang Band W8-1772

The Tang Band is a 95 dB efficient speaker.  Notice that the tweeter has an equivalent efficiency from about 4 kHz on up.  The series pair has a combined flat impedance of 6.8 ohms.  The Tang Band has an impedance of 12 ohms at 3 kHz and slowly rises to 28 ohms at 20 kHz.  This means the tweeter will have to padded down to balance the sound.  An L-pad has been included adjust the tweeters level.  Also notice that the tweeter starts naturally rolling off at around 2.7 kHz.  The tweeter has been crossed over at that same frequency.  Since the output is usable but down about 5 dB at the crossover point, the Tang Band needs to be crossed over a bit higher, but not so high as to dominate the upper registers.  It was decided to utilize the Tang Band’s internal compensation circuit so it could still function as a stand alone speaker.  A high-pass crossover was developed that works in conjunction with it and provides adjustability.

The attenuation circuit for the Tang Band has the following characteristics with its control set at minimum rotation which is maximum attenuation.  (See webpage for details.)

1 kHz: 0 dB

2 kHz: -1 dB

3 kHz: -2 dB

4 kHz: -3.2 dB

6 kHz: -5.5 dB

8 kHz: -6.5 dB

10 kHz: -8.5 dB

20 kHz: -12 dB

The crossover at these same frequencies reduces the drive to the speaker as follows:

1 kHz: 0 dB

2 kHz: -0.5 dB

3 kHz: + 0.5 dB

4 kHz: +1.5 dB

6 kHz: -2.0 dB

8 kHz: -9.0 dB

10 kHz: -14 dB

20 kHz: -20 dB

The two networks sum to give the final attenuation of:

1 kHz: 0 dB

2 kHz: -1.5 dB

3 kHz: -1.5 dB

4 kHz: -1.7 dB

6 kHz: -7.5 dB

8 kHz: -15.5 dB

10 kHz: -22.5 dB

20 kHz: -32 dB

This is an ideal response characteristic.  It stays nearly flat until 4 kHz and then drops like a stone.  The sight reduction from 1 kHz to 4 kHz is not  problem because the tweeter is making a contribution in that range.  Listening tests confirm that this works best.  The tweeter’s level control sounds best at about the 10 o’clock position but this is a matter of personal taste and room acoustics.

The enclosure is not involved acoustically as the tweeters have sealed backs.  It only serves as a means to mount them and house the crossover components.  It measures 7 1/2 inches wide by 11 1/2 inches tall by 6 inches deep.  It is important to keep the front panel small to minimize diffraction effects.  It is also essential to place the tweeter enclosure so the front panel lines up with the back edge of the Tang Band front panel.  Moving it rearward will seriously degrade the sound. 

The tweeters need at least 10 hours to break in.  The first three hours make a huge difference.  They offer quite an improvement over the stock Tang Band.  In addition to the wide open soundstage, there is more detail and delicacy to the treble.  They are very smooth without any harsh sounding peaks and resonances.  They must be mated with a very fast speaker.  There are not many drivers on the market that can provide a sufficiently detailed midrange and efficiency to match these tweeters.  It is suggested not to deviate from this arrangement.