The design and performance of the audio system are challenged, given the Roadster's open cockpit (convertible). You lose not only the walls and ceiling for reflection but, more importantly, introduce the ambient noise that can be as high as 95 dB on an interstate at 65 mph. The impact is a significant reduction in base and mid-range and the solutions to improve the performance range from picking different roads to drive on at a lower speed/less ambient noise , increasing the number of speakers and amps and competing with the 95 dB like a loud rock concert, develop aftermarket noise cancellation, wear noise canceling headphones or restore a removable hard top with sound deadening.
Road selection is not a viable option, and the off-interstate roads still have ambient noise that impacts the audio performance. In other words, the problem only goes away partially. Increasing the number of speakers and amps can help, but there is still a lack of contrast with the ambient noise, and you will reach unhealthy stereo dB levels. Noise cancellation in the entire cockpit is impossible, but it is possible in the headrest; note, I have not seen an aftermarket solution. I will return to this in future posts and see if the headrest option can be hand-crafted for an aftermarket solution. Lastly, wearing noise-canceling headphones works it is unfortunately not legal or safe, and you don't hear the engine which is a must, its part of the entertainment .
The ultimate solution is to restore an older hard top with sound deadening and other audio-compliant materials. It's not an authentic convertible experience when the hard top is on, but it would be superior to the soft top.
Working on the hard top, I found a vintage top made by Snug Top, probably in the 70s and resold and rebranded by Vilem B Haan in the Long Beach, CA area; Vilém B. Haan | Hemmings. The top is made from fiberglass; it needs new seals, a back window, restoring or replacing the latches, and has no sound treatment. Back to Hernan Lopez at Stuttgart Upholstery, where we worked out the planned restoration process, including re-sanding the outer top and applying canvas material. The inside ceiling will be treated with Dynamat (Butyl) and the headliner will be stitched leather.
Combining this sandwich of materials should reduce the ambient noise from the roof and provide a softer reflection source from within the cockpit. The seals and effectiveness of the latches will have to do the rest and when paired with the MG, which has had extensive sound deadening material applied throughout, should give us a shot at dB measurements below 70 dB at 65 mph on the interstate with overdrive engaged. If you are curious, the June 1976 Road and Track magazine showed the cockpit noise of an MGB with a soft top-up of:
61 Idle in neutral
87 Maximum, 1st gear.
70 Constant 30 mph
75 Constant 50 mph
82 Constant 70 mph
I will post an update once the top is restored; db measured at various speeds, including impact on audio performance. Till then, have fun and drive safe!