Low levels of bulk sound velocity (V_phi) variations below 2000 km depth and a prominent anti-correlation of V_phi to shear seismic wave velocity (V_S) near the core mantle boundary are generally taken to indicate the presence of compositional deep mantle heterogeneity. Using a thermodynamically self-consistent mantle mineralogy model based on Gibbs free energy minimization we show that such effects can arise from differences in the bulk modulus at high pressure and temperature and that it is possible to predict the observed V_S/V_phi anti-correlation in a chemically uniform mantle. The mineralogy model provides us with elastic constants and density for any given P,T condition. We take this density to compute convective buoyancy forces in a simple (2-D purely bottom heated isoviscous and isochemical) compressible mantle convection model. Our approach allows us to predict a number of seismic observables from the convection model, all of which agree remarkably well with observations from seismic tomography. Our results are fully compatible with other published mantle mineralogy models, which similar to our finding predict an increase of dV_phi/dT with temperature and pressure, and a pronounced V_S/V_phi anti-correlation in the lowermost mantle.