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Trends in Speakers and Amplifiers


The new Hitachi DE99 Microcomputer controlled cassette deck with auto tape response system.


1981 was an interesting time for the Hi-Fi world. Despite the ubiquitous recession, business appeared to be ticking over nicely.

Amongst the trends there has been general acceptance at last of active speaker designs, the re-introduction of DBX noise reduction systems and a gradual but noticeable move away from turntable obsession.

Crystal ball gazing is a dangerous business but I venture to predict that the emphasis will again turn back towards speaker systems.

Active speakers are at last becoming more common, although there is some way to go before they become standard. The improvements in sound come from perfect drive unit integration and superior transient response. Their acceptance means that more adventurous designs are possible once the 'sacred cow' of flat amplifier response is overcome. Most speaker systems, even the most expensive, suffer from response anomalies that could be removed by contouring the amplifier's response.

In fact, if one goes back a few years to examine the original aims of Hi-Fi equipment, they make interesting reading. For example: 'The function of a turntable is only to rotate at a constant speed without adding to or subtracting from the signal'. Even in the Linn Sondeck/Oracle era this rings true.

Amplifiers should be 'Wire with gain'. This is probably the most controversial of statements. It is interesting to note that scientifically controlled tests with selected listening groups could not reveal significant differences between good quality amps.

The frequency response required for good reproduction of sound has also been a disputed issue for decades. During the second world war, the BBC's own research department issued a report stating that perfect reproduction of voice and music could be obtained with a bandwidth of 30Hz - 15kHz. Since then we have seen amplifiers with bandwidths extending from DC to several hundred kHz.

The issue is about to become contentious again because of the introduction of digital technology. The upper frequency limit of a digital system is half the sampling frequency. Since the higher the sampling rate, the more expensive the equipment, standardisation is sure to be a problem.

On the periphery of audio other developments are poised to intrude. Sony's 35W/channel digital power amplifier for example. Perhaps, even more ominously, the combined video/digital tape recorder from Japan. When and if this is released on general sale here, the price is likely to be under a thousand pounds.

And what of micros? We have already seen these used to optimise tape bias on cassette decks. With the introduction of digitally encoded signals, the field seems wide open for their large scale involvement in future designs.

Unfortunately, British industry is not exactly poised to take advantage of these developments.

Minimax Speakers.


Small Speakers



In recent years small speaker systems have gained wide acceptance with the public. It's easy to see why, for they have a lot of things going for them. For example, a smaller drive unit has, all things being equal, a lighter cone than it's larger brethren and thus provides a better transient response. Small cabinet size means greater dispersion and hence a better stereo image. Lastly, but by no means least, it is far easier to strut a small speaker cabinet to reduce colouration due to flexing panels.

The only drawback of the small speaker is its limited bass extension. This a natural consequence of the small cabinet which pushes up the fundamental resonance of the bass unit. In principle, this drawback can be overcome by making the enclosure less efficient. Nevertheless, this is a difficult thing to do properly and requires careful design.

The Minimax speakers have been amongst the front runners in the small speaker market and I recently had the opportunity to listen to a pair of these at some length. At £70 a pair I must confess that I wasn't expecting miracles, but I was pleasantly surprised at their response.

The Minimax 2 is a two-way bass reflexed system with a 5" woofer and a 1" dome tweeter. Crossover is performed by a 6-element board mounted on the interior back panel. The crossover frequency chosen is 3.5kHz. The cabinet is soundly built of 19mm chipboard of the high density type and veneered in teak.

Apart from acoustic considerations, the speaker is an object lesson in how to produce a simple high quality enclosure and is well worth the attention of those who roll their own.

As with all equipment that I review, the speakers were humped around and connected to several different systems for evaluation.

First let it be said that the usual lack of bass extension was not as noticeable as might be expected. The bass that came through certainly lacked the solidity of larger systems, but was still well defined. The mid range was slightly recessed, but the upper registers were full of clarity. Stereo image was good, as expected, but the proviso here is that the speakers have to be used well away from the walls for their true abilities to be appreciated. As mentioned earlier, these speakers are reflexed. Unusually, the port is a length of steel tube inset into the enclosure from the front baffle.

Having listened to the system at some length, I was genuinely impressed by their performance. I feel that these speakers would be of interest to those who are not unduly worried by the lack of deep bass or whose situation precludes the use of larger speakers — often the case in the home electro-musician's studio. Efficiency was quite reasonable. The manufacturers quote a maximum recommended amplifier power of 40W/channel. In practice I found that 20W was sufficient in my own 15' x 12' x 8' room to do justice to the speakers. I am often accused of listening to music at deafening levels anyway!



Previous Article in this issue

Warren Cann's Electro-Drum Column

Next article in this issue

Delta Lab DL-5 Harmonicomputer


Electronics & Music Maker - Copyright: Music Maker Publications (UK), Future Publishing.

 

Electronics & Music Maker - Sep 1982

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Feature by Jeff Macaulay

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