The Sennheiser HD 650 have a slightly warm profile. They lack a thumpy low-bass, but that's normal from open-back headphones. That said, a bump in the high-bass helps to balance their bass range with a touch of extra boom and warmth. They also have a very flat mid-range, so vocals and lead instruments are accurately reproduced. If you're looking for dynamic open-backs with more bass, then check out the Sennheiser HD 660S2.

These headphones are often compared to the Sennheiser HD 6XX. However, when we originally tested both headphones, we noticed that they differed in frequency response. After closer examination, we noticed our HD 650 model, which was originally tested in 2020, had lots of wear and tear on the ear cup padding. It can affect their audio delivery as they may not be able to create a good seal or fit. As a result, we purchased a new pair of padding to check for differences between this model and the HD 6XX. Note that this padding isn't the same as the original padding. It appears that Sennheiser altered their manufacturing in 2021, and there have been reports that the new padding is rounder and a bit stiffer. First, we compared the 6XX's original pass with a new pass using the same pads. It helps us identify if the headphones' padding has worn down enough over time to change their sound. Then we replaced the HD 650's pads and compared them to the HD 6XX, which still have their original pads. After this change, the frequency responses look much more similar. It suggests that wear and tear over time can result in a change in clamping force and, ultimately, frequency response. If you notice that your unit's padding is getting softer or flatter, you can replace them by purchasing a pair directly from the manufacturer.

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