Dome Tweeters – Is Flush Mounting Just Hype?

Much has been discussed about flush mounting drivers onto a speaker box. Is it just for looks or do speakers really sound better?

Before I proceed further, I should point out what flush mounting is.

The easy way to install a driver, whether it’s a woofer or a tweeter, is to simply cut a hole and screw the driver on. This is normally referred to as Surface Mount. When a driver is installed in this manner, the driver’s lip protrudes over the hole.

In Flush Mounting, the edge of the hole is rebated to accommodate the driver’s lips. After installation, the lip is flush with the surface of the cabinet panel.

To investigate whether there are any advantages with flush mounting, I surface mounted a Peerless BC25TG15 tweeter onto a baffle of 31″ x 24″ and did a response sweep. The Red Plot in Fig 1 shows a notch at 8kHz followed by a smaller one at about 16kHz.

After that, I did a sweep with the tweeter flush mounted (Black plot). Astonishingly, the roll-off is completely clean. What I got is a beautiful, linear slope.

From these plots, it is clear that flush mounting does indeed make a difference. When the tweeter is surface mounted, it resulted in a ripple effect at the higher frequencies. This is caused by Baffle Edge Diffraction.

Technically, yes. But flush mounting only removes the ripples at the higher frequencies. There exist a more destructive diffraction that is caused by the edge of the baffle. This is generally called Baffle Edge Diffraction. This is the one that should be addressed first. No amount of flush mounting can eliminate the diffraction that occurs at the edge of the front panel.

This page was last modified on 3 Mar, 2018.