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:
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The cabinet dimensions start to influence the sound radiation pattern and pass the radiation to 4π to 2π leading to a pressure increase in the forward direction due to a more focused radiation pattern (generaly +6dB SPL).
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Diffraction around the edges creates additional wavefronts at transition from 4π to 2π that interfere with the original waves from the driver. These interferences will causes cancellations or sommations at transition. Diffraction and Standing Waves article goes deep in these two concepts.
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.
This difference of front pressure is more a 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.
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.
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:
Baffle mistakes and solutions
For a tweeter without a waveguide, placing it in an asymmetrical position on the baffle is a good solution to distribute baffle diffraction (beaming), while keeping the midrange driver (if present) perfectly vertical to the tweeter.
The worst baffle step is caused by the “vintage” approach, which provokes a lot of diffraction affecting both on- and off-axis responses:
For horn versions, there is also a problem with the horn itself: it does not transition to flat at the baffle junction, and lacks a proper roundover to smoothly meet the cabinet sides. Creating significant midrange narrowing that negatively affects directivity.
As discussed in the midrange narrowing article, a large baffle will not solve the problem with a horn, its size only moves the edge diffraction problem further away. The profile must transition from the horn’s acceleration to a flat 180° surface and immediately include a proper roundover to the cabinet sides in a free-standing case. We still need to accelerate and then decelerate gradually.
For waveguides or horns, it is always better to have a continuous profile, avoiding flat areas between the horn and the edges, as seen here with the X-shape X25:
We can note the roundover with a reduced radius on the black cabinet, illustrating the advantage of midrange narrowing in this case for the woofer, while of course keeping a proper roundover for the horn.
This effect is also deeply explained in our Free-Standing vs In-Wall Mounting article.
