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The Deliberate Design of Offset Tweeters: The Trohet Speaker and Edge Diffraction

The Trohet’s have an offset tweeter, and at first glance, it can easily be thought to be an aesthetic consideration.

Speaker edge diffraction offset tweeters explained

Is the offset tweeter really just about looks? Well as the saying goes, function follows form, and while it provides a unique look, there's more to what meets the eye.

To understand why the offset tweeter was chosen, we need to look at a phenomenon known as acoustic diffraction. Hold tight, this can get complex, so I’ll try and keep it simple for now.

Foremost among the diffraction types found in loudspeakers lies the baffle diffraction, chiefly transpiring at the edges of the speaker's front panel, where the tweeter and woofer are mounted.

As sound waves emanate from these drivers and reach the baffle's edges, they confront a sudden bending of the wavefront; the sound waves travelling parallel to the front baffle are forced to change direction just like water flowing down a river and then meeting the edge of a cliff to form a waterfall.

These newly bent soundwaves reflect in all directions, with a portion traveling towards the listening position. These diffracted soundwaves converge with the direct sound produced by the tweeter and woofer, and as a result, effect of the sound that reaches the listeners ears.

in simple terms, the diffraction causes the tonality to be altered in unfavorable ways.

It should be noted that edge diffraction is particularly an issue for higher frequencies, as low frequencies wavelengths are just too long for diffraction to occur on domestic loudspeaker systems.

So given that high frequencies are of concern, we need only to focus on the tweeter and its relationship to the front baffle edges. See where this is going?

So, by placing the tweeter in a location that is asymmetrical on the front baffle, we can greatly reduce the amplitude of the sound waves that are reflected from the front panel edges.

The graph below shows what the Trohet frequency response would look like if the tweeter was centered (Red line) vs the offset configuration (Green line). We can see that the response between 3 Khz and 10 Khz is far smoother with the tweeter being offset. This translates to a sound with greater fidelity and less change to the tonality of the original recording.

The next question is, well if this works so well then why don’t all speakers have the offset tweeter treatment?

The simple answer is cost. Speaker companies choose to not utilise offset tweeters as manufacturing a left and right speaker adds considerable expenses, not to mention logistic and inventory costs, which all impact profit. But we do see some high-end speaker brands such as Serhan and Swift using the offset tweeter design, which I think is highly commendable.

In the next newsletter I will talk about rounded cabinet edges and the impact it has on the sound. Until then read on for this week's album recommendation below.

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