Baffle Step

Baffle Step as a Pressure Director, Not Booster:

While baffle step doesn’t create an overall gain in sound pressure, it acts like a pressure director, concentrating sound waves in the forward direction (towards the listener) for frequencies above the baffle step frequency. This can be visualized as:

At low frequencies the sound wavelength is large compared to the baffle size:
Sound from the driver radiates freely in all directions (think of a sphere),resulting in omnidirectional radiation (4π steradians).

When frequency increases and the wavelength becomes comparable to the baffle dimensions:

This combined effect leads to a global pressure increase in the forward axis from a frequency related to baffle dimensions and a beam of sound at transition.


The Energy point of view

While the baffle analogy is helpful, it’s important to remember that baffle step doesn’t create a uniform gain of +6dB SPL.

We take here as landmark the dB SPL (so in front of the speaker) in 4π, some parameters as woofer sensitivity are given in 2π on a big ISO baffle, so from this point of view, if we take SPL in 2π as landmark it’s no more +6dB SPL but -6dB SPL.

This difference of front pressure is in fact more a 6dB delta due to a difference in energy distribution than a plus or minus, to the energy point of view there is no loss or gain, the energy remain the same, only the his direction is changing, creating a energy focusing effect.

How to simulate it

The pressure increase in the forward direction is gradual and depends on the specific baffle size and frequency, as we can simulate it in VituixCAD with the Diffraction tool:


Analogy, Baffle Step as a 180-degree Horn:

The analogy of a 180-degree horn is apt. Similar to a horn, the baffle acts to channel and focus sound waves in a specific direction. However, unlike a true horn that uses its shape to progressively increase pressure by loading and acoustic loading, the baffle doesn’t create new energy. It simply redirects existing energy.

Addressing the Decrease in Other Directions:

The pressure increase in the forward direction comes at the expense of sound pressure radiating to the sides and back. This decrease happens because:

Analogy, The Water Fountain:

Imagine your speaker as a water fountain:

This is similar to what happens with baffle step:

Baffle mistakes and solutions

For tweeter without waveguide, put it in an asymetrical position in the baffle is a good solution for dispatch the baffle diffraction (beaming), but by keeping the medium (if there is one) perfectly vertical to the tweeter.

The worst baffle step is given by “vintage” way to do, provoking a lot of diffraction impacting both on and off-axis:

baffle-step-mistake 2
This way to do edge will be catastrophics on responses and wavefront propagation, for the horn version there is also a problem with the horn itself that does not return flat (180°) at junction to the baffle, creating a lot of midrange narrowing.

As seen in the midrange narrowing article, a big baffle will not necessarily solve the problem with a horn, as we have to pass from the profile acceleration of the horn to a 180° flat no acceleration surface, we have to accelerate then decelerate slowly for reach the big flat surface (it can be a wall in in-wall). The size of the panel, if he is not infinite (wall), will just put the problem further to the point of view of edge diffraction.

For waveguide or horns it’s always better to have an continuous profile to never create a flat area between the horn and the edges, as seen here with a X-shape X25:

wood return
wood return

Additional Considerations:

By understanding the interplay between diffraction, constructive interference, and radiation patterns, we gain a deeper appreciation for the complexities of baffle step and its impact on speaker performance.