Dome Tweeters – Is Flush Mounting Just Hype?

Flush Mounting

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.

Peerless BC25TG15 Flush and Surfac Mount Response

Fig 1 – Peerless BC25TG15 Flush and Surface Mount Response

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.

So, Flush Mounting makes my speakers sound better

Technically, yes. But it is not the most important. What we should pay attention to first is the tweeter crossover because the destructive effects of diffraction caused by the baffle width falls exactly where we generally cross our tweeters (2.5kH ~ 3kHz).

There is an instance when flush mounting a tweeter is critical and that is when a super tweeter is used. Generally, we will cross a tweeter to a super tweeter at between 7kHz ~ 8kHz. Flush mounting a tweeter will definitely contribute to a smoother response.