Pondering the Effects of the B&W Top Mount Tweeter.

[RobP]

I have wondered for some time what the effect of the smooth hard reflective cabinet surface has on the sound and frequency response of the tube mounted tweeters on the 800 and Nautilus series speakers.
I know that B&W didn't skip over this in their design, they made a curved top and mounted the tweeter on a membrane to suppress cabinet resonance, as well as pushing the tweeter as far forward as possible, but it cannot be a perfect design.

Could any of this play a small role in the bright or sometime harsh sound that some people comment on when they hear these speakers? Do these cabinet tops cause some breakup in the frequency response?

I think I see an experiment coming on in my near future.

What do you guys think??

[RebelMan]

The tube loaded tweeter and Marlan sphere were designed with eliminating sound wave diffractions, influenced from adjacent flat surfaces, in mind. This concept, like the transmission line for internal resonances, was meant to absorb/deflect external resonances away from the listener. Thereby minimizing any coloration of sound. My guess is that the smooth glassy finish was done deliberately to assist in this process by keeping tainted noise from entering the listener's field.

I have noticed that the diamond tweeter, which is responsible for pushing the high frequency breakup beyond human hearing, to have a definite benefit of reducing that harshness. Think about it, if the shinny surface of the 802's and up was really responsible for making harsh sounds, then shouldn't I expect my 803S's to be free of this anomaly? Unfortunately, they are not. Agreed?

[audioqueso]

lol... I think if any of us fully understood the technology behind it, we could be engineers for B&W.

Good answer though, Rebelman. That's just as much as I'll understand.

[RobP]

Rebelman , I do agree that the Marlan head does help with the diffraction issue, but the 803's and 804 are not free from this. It would be interesting too see the response plots of the tweeter after its installation on the cabinet top.
I made a pair of pads to fit the top of my N803 cabinets that should absorb the reflection from the top of the cabinets somewhat for my "unscientific" experiment to see if there is any audible difference with them on. I will post a pic of the pads later.
I started my listening test last night, but at 2 A.M. I guess other people like to sleep. :lol: So it will have to wait until this weekend. I am going to try to find my RTA to see if there is any measurable difference as well.

[aphexist]

Could any of this play a small role in the bright or sometime harsh sound that some people comment on when they hear these speakers?

Maybe a small role, but I think that the tweeter material, in this case aluminum or diamond, plays a far more important role in resonances and speaker preference.

Even B&W (sort of) admitted that the tweeter-on-top was little more than brand recognition and aesthetic value when they moved the tweeter inside the cabinet on the new SCMS wall mounts.

Also, I'm pretty sure that the "smooth, glassy finish" was chosen to look cool rather than protect the listener from the "regular plastic" sound on the lower range models.

[stantheman2]

I believe the "open" tweeter mount has an audible as well as aesthetic value. I owned Dahlquist DQ-10s back in the day, which had open-mounted midrange and high frequency drivers, and those speakers were renowned (and still are) for their open, natural sound.

Dahlquist advertised a simple demo that still proves the point of the audible benefits of an open mount. Take a square piece of cardboard, say 12" x 12", and cut a hole in the middle. Have a friend stand across the room, and talk or sing to you with their mouth against the hole (simulating a mid/tweeter mounted in a typical speaker front plate) and then repeat the demo w/o the cardboard. The difference is immediately obvious.