Moving the tweeter off center can help smoothen on axis frequency response. You can model this with programs such as The Edge or Baffle Diffraction Simulator. However, the effect on power response is much more difficult to predict.
In my experience, offsetting the tweeter does make the on axis response smoother. The difference has been at most 1db over an octave or two. It's not much, but it also tends to fall right in the crossover region, so it's useful.
As a starting point, try placing the tweeter so the distance to the left, right an top of the baffle is the same. Now offset the tweeter by the diameter of the diaphram to the left or right.
Dan
In my experience, offsetting the tweeter does make the on axis response smoother. The difference has been at most 1db over an octave or two. It's not much, but it also tends to fall right in the crossover region, so it's useful.
As a starting point, try placing the tweeter so the distance to the left, right an top of the baffle is the same. Now offset the tweeter by the diameter of the diaphram to the left or right.
Dan
vdi_nenna said:
I'll add to what Dan said. Drivers are offset to aid in diffraction control. This is the altered response due to reflections that occur at the baffle boundaries, primarily the edges. This usuallly results in driver non-linear response as measured on most axes. The nearby driver diffraction contribution will change little.
The reason that the offset helps is that the diffraction signature is directly related to the distance between the driver and the diffracting boundary. When the distance to all boundaries is close to the same, the diffraction effect is reinforced at the frequency related to that distance. Offsetting the driver creates a situation where the distances to the boundary points varies more, thus reducing reinforcement. This helps to spread out the effect, so-to-speak, reducing the perceived impact. In other words, it helps to smooth the response.
A secondary benefit is that the diffraction signature always changes with the listening position. Toe the box in or out and the response changes. An offset helps to reduce this variation, though each case is specific. There may be a particular axis that is worsened, but the overall change is an improvement.
I have to disagree on one of Dan's points. The power response will change very little. The power response of the tweeter itself won't change at all. However, the power response of the system will be slightly altered as a function of the distance between the tweeter and the nearby driver to which it is crossed and then only for non-Butterworth crossovers. (Ideal) Butterworth crossovers won't see much of a change in power response due to the fact that they are uncorrelated already in the crossover region, being in phase quadrature, that is, 90 degrees out-of-phase throughout the crossover.
dlr
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