PureShape, Convex wavefront with cut circular-to-rectangular transition tweeter waveguide

Directivity polar plot

All measurements are real ones, performed with the ideal 25mm roundover return, taken at 1/24 resolution in a half-space presentation (±90°).

SPL

The loading effect provides from + 5 to 10 dB of sensitivity compared to direct radiation in the low end, allowing for a low crossover point with high SPL.

Distortion

Its loading capacity allows operation at very low frequencies. The radiation restriction, combined with the reactive loading effect, reduces the tweeter’s required excursion to achieve a given SPL after equalization to a flat response, leading to lower distortion.

Intermodulation distortion (IMD) is also reduced, since both harmonic and intermodulation distortions are strongly linked to driver nonlinearities, which generally increase with diaphragm excursion.

The driver becomes so efficient that most distortion components are buried in the measurement noise floor (around 0.01% here), making them effectively invisible on the 95 dB SPL distortion chart.

How it competes versus Direct Radiation (no WG)

Mounting

We recommend a round-over return of around 25mm radius on each exposed side to eliminate midrange narrowing and beaming.

Mounting is done with the baffle using M4 screws into a rebate 10 mm large, 8 mm high, with 4 mm radius corners.

Tweeter mounting is done as show here, users has to remove the face plate but reuse the screm and put it back in place, they will serve as a centering device

The fix system with his two M4 screw is provided too.

The waveguide is 3D-printed using PLA for indoor applications or PETG-HF (price on demand) for outdoor use.

It arrives raw unless you order the spray putty service. Layers of spray putty must be applied before primer for a smooth finish, as described in our dedicated article: How to Finish my Horn.

Roundover Kit

To reduce midrange narrowing and beaming, and to achieve the best directivity performance from your Pure Shape waveguide, we recommend using the roundover kit (equivalent to a 25 mm radius roundover) for users who are unable to machine the required roundover with their own tools or resources.

It can be bonded directly to your baffle, with the waveguide glued in place and finished flush inside. In this configuration, a rear access opening must be provided to allow installation of the tweeter.

For more adventurous users, it is also possible to install the tweeter directly through the woofer cutout below.

Passive crossover

PureShape brings the tweeter back closer to the mid-woofer in depth, making delay management easier in passive filtering.

Solutions for time alignment with passive filtering (no DSP delay):

• Asymmetrical Crossover: A steeper slope can be applied to the woofer to compensate for delay, by adding one more order to the woofer’s filter.
• Mechanically Time-Aligned Design: Alternatively, our medium waveguide solution positions the mid-woofer further back, achieving proper alignment without electronic delay.