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Designing The Trohet R - A High End DIY Speaker with the R2904 tweeter

The Trohet was designed four years ago and, for this entire time, remained our highest-performing offering. For most people, this speaker is far as they need to go—it's accurate, smooth, and an engaging listen.

But, over the years, I received numerous requests to use a more advanced tweeter. I was reluctant to do so as I thought that there would not be much improvement. I couldn't have been more wrong.

An existing customer who built the Trohet speaker asked if I could redesign the Trohet to use the Scan Speak R2904 ring radiator. This is an expensive tweeter and is found in some very well-received speakers from the likes of the Mu.2 and other high-end speaker designs.

On that note, some have said the Trohet R is too similar to the Mu.2 from Serhan and Swift. Sure, they use the same drivers, but both speakers are quite different in their sound and design typology. I know Brad Serhan well, and what he has designed is fantastic - he's one of Australia's best loudspeaker designers ever. What I will say is both Brad and I have different styles in design- and just like cooking, we prefer certain flavors. And for everyone who hasn't heard the Mu.2 I highly recommend it! There are good reasons why they're selling like hot cakes.

Now back to the Trohet R, what was also nice was that the tweeter is from the same Scan Speak Revelator line, which the 15W/8530K00 woofer is from. Whether Scan Speak has purposely designed the Revelators to share a similar acoustic characteristic is up for debate, but the end result sure sounds like these two drivers are made for each other.

On that note, given both drivers are Revelators, it seemed fitting to name the new speaker the Trohet R.

We've kept the Trohet cabinet unchanged, allowing all existing Trohet owners a seamless upgrade path. This decision ensures a straightforward transition for those seeking to upgrade their Trohet's to the new R.

The pinnacle of our redesign effort lies in the bespoke crossover, a key element in achieving optimal performance with the Revelator 15W/8530 and R2904 driver combination.

Designing the crossover sure took some time to get right. I initially tried a crossover point of 3000 hertz but found the speaker to sound a bit thin in the mids. Pushing the crossover point down to 2400 hertz was the sweet spot; full mids without glare, which can happen when you push a tweeter too low.

I've heard people say simple always sound best - that's just pure nonsense. Speaker drivers have their own irregularities in their sound which need to be addressed, and if it requires x number of crossover parts then that's what it needs to be.

The final Trohet R crossover includes 8 capacitors, 7 inductors, and 8 resistors for each speaker. Certainly, a very large crossover for a compact two-way design.

At the core of the crossover lies a Linkwitz-Riley 2nd order topology for both the tweeter and woofer, ensuring precise phase tracking and maximally flat summation at the crossover frequency. However, achieving this precision presented a challenge due to the physical offset between the tweeter and woofer as depicted in the sketch below.

We should also note that this offset issue is not new; every speaker designer has to work with it with multi-speaker driver designs. The standard way of dealing with it is to use asymmetrical crossover filters, with the most common being a second order on the woofer and third order on the tweeter. This is a good solution as it's easy to build and does not require a whole lot of crossover components. The only issue is that the power response is not optimized. For this new Trohet R, I wanted to ensure that we achieved a power response that is optimized for every room, even rooms that are highly reflective.

Time alignment loudspeaker

To overcome this, a time correction filter, also known as a ladder delay network or all-pass invert filter, was introduced. This electrical circuit aligns the tweeter and woofer diaphragms without compromising off-axis listening characteristics, crucial for maintaining audio fidelity.

The before-and-after comparison in the Trohet R frequency response below illustrates the effectiveness of the time correction filter, eliminating a significant dip at 3200 hertz caused by a mere 0.06-millisecond delay between the tweeter and woofer.

Focusing on the power response, the Trohet R boasts a natural in-room performance, with a gentle roll-off indicating a warm, non-fatiguing sound profile, as shown by looking at the blue line (power response). This deliberate design provides an auditory experience than can be characterized as warm, yet detailed. Something that allows for hours of enjoyable non-fatiguing listening.

On listening to the Trohet R's, I can safely say this is one of the best bookshelf speakers I have ever heard. I know I might sound biased saying this, but it's what I have heard from others listening to them as well.

The thing that really comes through is just how clear and detailed the speakers are; the separation between instruments and notes is astounding. And yet, the speakers still have this warmth about them, it kind of goes against the notion that only bright speakers can be detailed—not the Trohet R's, they're warm!

To read more about the Trohet R's please visit the kit page.

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