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Oliver Acoustic Research AR-94 specifications
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Introduction

I started my speaker building hobby with Hifi magazine kit 6/2. By that time I had read some hifi-books and instructions. Diffraction and box bracing were among those things I thought were important. When thought afterwards it was a good choice to build a kit instead of designing whole speaker myself. Even if theories might be simple there is quite a few little details that have to be considered.

Box is made of 18 mm chipboard and veneered with birch wood. Shape is heavily rounded triangle to minimize diffraction. It seemed important at that time. Afterwards I have noticed that even if diffraction usually has significant influence on frequency response it is difficult to hear. Variations are smoothed out from power response.

Box has two compartments. Upper partition is 6 litres for the midrange element; lower partition is for the crossover. This makes it possible to debug cross-over without removing element. Good idea if you need to fine-tune crossover. Other possibility is to double wire elements so that during development all elements are directly connected to connectors.

Dynamic loudspeaker

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Listening experiences

When these got ready I had only very little experience in listening. They were although lot better than any pair of speakers I had listened before. Unfortunately situation changed rapidly. Their sound is very soft, everything sounds little dull. Stereo image concentrates to speakers and narrow space between speakers. There is a lot missing if you really listen to those speakers. But on the other hand, soft sound is ideal for background music or home theatre rear speakers. Those speakers are suitable for many kind of music and there is nothing special that would make listening experience irritating.

Subwoofer

Dynamic loudspeaker

Main speaker project had been successful and I was eager to build something else. I thought that subwoofer might be a interesting project. I started again from nothing. I had never even heard commercial subwoofers and all knowledge were based on few examples and some audio books from library.

First criteria was to have straight response down to 20 Hz or even lower. I had read about box resonances and wind noise problems in reflexed enclosures. Keeping those three issues in mind I designed 100 l box that was tuned to 20 Hz without knowing element parameters. Enclosure is made from 25 mm chipboard and heavily cross-braced. Reflex port is made of 80 mm sewer pipe and rounded from outer end. Box is veneered with birch wood. Lynx was painted to top of the box after there was good lacquer surface. Then enclosure was varnished once more to protect the picture.

Box was first tested with 12" Kenny's element. Sound was horrible with and without the filter. Enclosure tuning was way too low for that element and elements excursion limits were easily reached. Both box size and tuning were wrong for that element but also element itself had extremely poor quality. But what you could expect when price was one tenth of "normal" subwoofer element?

It was clear that Kenny had to be replaced. This time I used a simulator in design process. Focal 13 V 7601DB was rather suitable for the box without massive modifications. Element is robust and reliable looking car element. It has stiff cone, powerful motor and high excursion among others. That element is no longer in production.

Change of element turned a horrible midbass to a subwoofer like it was supposed to be. Kenny was totally impossible to be integrated with main speakers. Apparently distortion coloured upper bass so much. With Focal element it is rather easy to find correct parameters. Even if initial tests were discouraging result was not so bad. Three of my friends have also used the same element in their subs and have been satisfied.