Mid-range beaming and narrowing

The Challenge of Midrange Response

In loudspeaker design, achieving a smooth and balanced frequency response across the entire spectrum is a continuous pursuit. One specific challenge lies in the midrange frequencies (typically around 1 kHz).

Here, two unwanted phenomena can significantly impact the sound and his power response: midrange narrowing and beaming.

Here we can see a not fully optimised end of profile resulting a narrowed mid-range in 1kHz region :

Whatever the horn, wageguide, integrated on baffle or not, the contour must be fluid in all directions.

Here is a very good elliptic waveguide with a slightly rounded traditional baffle where mid-range beaming and mid-range narrowing are still visible :

Then the same wave guide (but 0.5" tinier) integrated with a fluid profile :

Midrange Narrowing: A Dip Caused by Diffraction

Midrange narrowing refers to a decrease in sound pressure at specific midrange frequencies.

This occurs due to edge diffraction. When sound waves traveling from the driver encounter the sharp edges of the speaker baffle, they bend around these obstacles.

This bending disrupts the wavefront, causing destructive interference at certain wavelengths (frequencies). These wavelengths correspond to the dip observed in the midrange response of the speaker, affecting both on-axis and off-axis.

Here is an exemple about how to solve it:

Midrange Beaming: Uneven Radiation Due to Diffraction

While midrange narrowing represents a loss of sound pressure, another effect of edge diffraction is midrange beaming. This phenomenon describes the concentration of sound pressure in specific off-axis directions.

The bending of sound waves can lead to constructive interference at certain angles, resulting in peaks in the off-axis response. However, in other off-axis locations, destructive interference can occur, causing dips.

This creates an uneven sound radiation pattern, compromising the overall soundstage and affecting listeners at various positions.

The Impact on Listening Experience

The combined effects of midrange narrowing and beaming can significantly alter the way we perceive sound. Here’s how:

• Reduced Clarity: The dip in the midrange response, even on-axis, can weaken the presence of vocals, instruments playing in this frequency range (guitars, pianos), and essential details in the overall sound.

• Uneven Tonality: The variations in sound pressure across the entire response (on and off-axis) can lead to an unbalanced listening experience, where the sound might appear brighter or duller depending on the listener’s position relative to the speaker.

• Narrowed Soundstage: The uneven off-axis response can restrict the perceived width and depth of the soundstage, making the sound seem less immersive for listeners positioned off-axis.

• Compromised Power Response: The ideal combination of direct sound from the speaker and reflected sound from the room (reverberant field) at the critical distance (the distance where these two components are roughly equal) is crucial for a natural listening experience. Midrange narrowing and beaming can disrupt this balance, affecting the perceived loudness and fullness of the sound.

Optimizing Baffle Design for Smooth Midrange

To address these challenges and achieve a smooth midrange response, loudspeaker designers employ various strategies:

• Round-Over Returns and Sharp Edges removing: A smooth, curved transition where the horn profile meets the baffle minimizes disruptions to the wavefront, reducing both midrange narrowing and beaming. Finding the ideal radius for the round-over depends on the specific horn profile. It requires balancing diffraction reduction with practicality.

• Fluid Profile Integration: Seamless integration of the horn with the baffle is crucial. The combined profile should be continuous and avoid abrupt transitions on both the front and side of the baffle, minimizing opportunities for edge diffraction.

• Horn and Baffle as One: Ideally, the design strives for the horn and baffle to function as a single unit with a continuous profile. This ensures optimal wavefront propagation and minimizes diffraction effects.

For flat baffles, a simple round-over return might not be sufficient. In those cases, designers may employ profile acceleration and deceleration, this involves a gradual transition from the horn’s curvature to the flat surface of the baffle, minimizing the impact of abrupt changes on the wavefro

Advanced Design Techniques

Modern loudspeaker design tools like Finite Element Analysis (FEA) simulations allow for precise modeling of baffle shapes and their impact on sound radiation. This facilitates the optimization of baffle profiles to minimize diffraction effects and achieve a smooth, balanced midrange response.

Conclusion

Understanding midrange narrowing and beaming caused by edge diffraction is crucial for achieving optimal sound quality in loudspeakers. By employing careful baffle design techniques and advanced simulation tools, designers can create speakers that deliver a natural and detailed listening experience across the entire frequency spectrum, for both on-axis and off-axis listeners.