3 Way Shelf Speaker Cauchy

One of our customers asked for a 3 way, shelf, bass reflex speaker with compact size. We had to pass there. The only speaker that came to our mind was the Intertechnik Comet - due to lack of drivers no longer available.

The beginning of the design stage. What do we expect from a 3 way speaker?
Low bass that is powerful and clean is certainly a prerequisite.

What efficiency should the speaker have? The laws of physics cannot be fooled. At a given cabinet volume the designer has to go for efficiency or low bass.

The efficiency should not be much lower than 90 dB, but should reach (-8 dB) approx. 30 Hz. Here are the contenders:
- Alcone AC 10 HE (90 dB, from 30 Hz, in 48 litre cabinet)
- BassExciter BX 10 (87.5 dB, from 30 Hz - in 29 litre cabinet)
- Eton 11-581 (88 dB, from 28 Hz, in 37 litre cabinet)
- Eton 8-800/37 HEX (89.5 dB, from 26 Hz, in 75 litre cabinet - a bit too big)
- Monacor SPH-300 KE (89.5 dB, from 27 Hz, in 56 litre cabinet)
- Peerless CSX-257 (88 dB, from 24 Hz - but with 85 litre low bass section too big)
- Ravemaster AXX 1212 (89 dB, from 33 Hz, in 33 litre cabinet)
- Ravemaster TW 3000 (89.5 dB, from 28 Hz, in 65 litre cabinet)
- Seas WD 215 (88.5 dB, from 28 Hz, in 45 litre cabinet)
- Visaton W200 S8 S8 (88 dB, from 32 Hz, in 22 litre cabinet)

We went for a upmarket bass driver that is suited for 90 dB and has been praised by many of our customers: Alcone AC 10 HE. Which midrange driver should we use? The AC 5.25 HE-S is not sufficient from an efficiency point of view; therefore, we chose the AC 6.5 HE. Regarding the tweeter we had to consider not only the quality, but also the price, since the speaker should not cost much more than EUR 300.

Later, we realised that high quality crossover components for a 3 way design would increase the final price much more than using a 2 way design, since large capacitors and coils for low frequencies are not necessary here.

The crossover frequency determined so that the midrange driver doesn't have to battle with low frequencies; 200 - 300 Hz seemed adequate to us. The crossover frequency to the tweeter was fixed at 2.2 kHz; this was the limit where the tweeter's resonance was just not audible anymore. Cauchy,

Driver arrangement. The most compact solution would be:
- bass driver at the bottom
- tweeter and midrange next to one another above the bass driver

Placed side by side, however, the tweeter and the midrange radiate at a narrow horizontal angle requiring exact directional positioning of the speaker towards the listener.

Therefore, we chose the classic arrangement where the tweeter is above the midrange. The resulting free space was used to incorporate 3 bass reflex tubes.

We carried out some diffraction tests. The frequency response becomes less flat when the tweeter is placed off centre. One reason for this is also the fact that the distance from tweeter to side edge is similar to the distance from tweeter to top edge. This is still emphasised by diffraction.

As a result, we placed the tweeter - aesthetically pleasing - dead centre. Those who prefer an even flatter frequency response should round-off the edges of the cabinet by 1 cm.

Everything is determined now. Here are the:
- Cauchy description
- Cauchy lab results
- Cauchy building instruction
... and, like with almost all new speakers, a tempting introductory offer

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