Hurst Audio - building powerful speaker systems

When some speakers are called upon to reproduce solid bass, the results can be decidedly underwhelming. However, what the speakers lack individually, they may well achieve collectively. This is because, driving speakers in unison improves the efficiency at bass frequencies, and increases the power handling capacity at all frequencies. For example, a stack of four Wharfedale Diamond 1's has a sensitivity of 86dB SPA, and a power handling capacity of 140 Watts RMS. With a 100 Watt RMS per channel amplifier, the output capacity is 106dB SPA per stack. So if output levels above 100dB are your bag, enjoy!

However, the ability to reproduce rock music at ear splitting levels is not the only, nor even the primary, objective of the system. Rather, if instead of "power handling" you read "headroom", you are closer to the mark. This is because, in addition to the efficiency and power handling improvements, each stack is as easy to drive as one of the speakers alone, and has reduced intermodulation distortion. Which adds up to an ability to effortlessly reproduce music of a wider range of genres.

Four Speaker Series/Parallel Arrays

Connecting four speakers in a series/parallel array has the effect that, together, they have the same impedance and sensitivity as a single speaker but with four times the power handling capacity.

Then, to connect the stack to the amplifier:

This layout is then repeated for the right channel...

Choosing Suitable Speakers

Some factors to bear in mind when choosing the speakers are:

Note: Similar effects can be achieved over the lowest octaves using multiple sub-woofers.

Achieving a Wider Stereo Field

Another aspect of a "big" sound is the size of the stereo field. Stereo recordings can capture sounds from a horizontal arc up to 180 degrees. However, the stereo field that can be produced by two speakers is limited to the distance between them. So, if the speakers are placed 1.2m (4ft) apart, the stereo field produced is 1.2m (4ft) wide (or less). Whereas four speaker stacks placed 1.2m apart can produce a stereo field up to 2.4m (8ft) wide. Doubling the width of the stereo field is dramatic and draws you into the imagery.

Note: Each stack requires a separate amplifier channel. These may be four monoblocks, two matching stereo amplifiers, or the "front" and "surround" channels of an AV amplifier. If the latter, please ensure that all AV manipulation of the signals is disabled.

The four stacks should generally be placed in line with the longer wall of the room. The outer pair may be turned inwards, whilst the inner pair face forwards. The listener should be at least as far from the speaker line as the speaker-to-speaker distance, whilst some listeners may prefer being up to three times that distance.

Note: Further information on building the stacks, and any other enquiries should be addressed to tlhurst@hotmail.co.uk

Last update: 9th May 2022.