Small Room Open-Baffle Speaker

[The Shadow]

Today, I made a couple of prototypes, in MDF, of an open baffle design that
would work in a small room (mine is 12x12 feet).

Here is a front view of one of them



Each one is 30 inches tall, the same height as the Gilbert Briggs baffle
Width is 16.5 inches, approx half the width of the Brigg design. The drive unit is a Fostex FE207E.

Here is a pic of the rear of the baffle.
At the moment I am experimenting with different types and profiles of cardboard wing.



Here is how they look in situ with the rest of the system
The pic gives an idea of their size in relation to the rest of the room.



The Fostex driver qts is only 0.26, so not ideal but with the floor reinforcement, bass goes remarkably deep for the size of the baffles.

They have a very open, natural sound, but could do with a tweeter at some point. I'm very pleased with them so far and they certainly play music very well.

Steve

[alnewall]

Tis wonderful how something so simple can be so effective. When i knocked mine up, i never dreamt i'd still be using them 18 months on.

[The Shadow]

Hi Al

Yes they are very good indeed. This morning they sounded a bit lightweight on the big classical stuff, because of the lack of a bass helper so I switched the subwoofers back in and spent a bit of time tweaking the crossovers, levels etc.

Working from 200Hz downwards and operating at a low level, they give that little bit of extra reinforcement at the bottom end without adding any slowness to the sound. That's the beauty of "stereo" bass. It is so much easier to set up than a single sub. I don't think I could have kept the speed if I was only using a mono sub. Nobody was interested in the subs on eBay either, so I'm glad, in a way, that the subs didn't sell

Today I'm going to try using my Fostex FE 108ES drivers crossed over with a 3uF cap to act as an upward firing tweeter, in the same arrangement that Gilbert Briggs used in his open baffle design from the fifties. That should be very interesting.

[The Shadow]

Here's the FE108EZ configured as a tweeter, fitted to the rear of the baffle.



The tweeter is connected out of phase with the main driver to provide something approaching dipole treble. The argument is that although the main driver provides dipole mids and upper bass, it does not have a rear whizzer so is only providing monopole treble.

Siegfried Linkwitz argues that this discontinuity in the directivity of the treble compared to the midrange is audible and has begun fitting rear firing anti-phase tweeters to his baffles, with, he reckons, impressive results. Others have tried this of course especially the omni-directional fan club.

Of course monopole bass from a pair of subs is not ideal either but in my view, the problems related to this are easier to deal with and most open baffle builders using full range drivers don't consider the treble contradiction in directivity.

Whether Briggs thought about this with his upward firing tweeter in the fifties I'm not sure, but the results of fitting the FE108EZ as a tweeter firing at the ceiling are indeed audible. The tweeters have given an increase in height and space to the soundstage, very impressive on classical, live recordings and acoustic music; not so noticeable on multitracked pop recordings but nevertheless very useful, giving a good spread of sound across the end wall of the room. This despite the baffles being crammed into quite a small space.

Steve Back to top

[Richard]

Very nice just been reading of these (original) speakers in Peter's article in HFW this month, interesting stuff. The new WD's get a big thumbs up too.

Rich

[John T]

Originally Posted by The Shadow

Whether Briggs thought about this with his upward firing tweeter in the fifties I'm not sure,

Brigg's upward facing speakers may have resulted from necessity. I remember one of the first speakers I ever built was with one of his Warfedale 10" full range speakers fitted to the end of a spun concrete drainage pipe (standing on its end) Warfdale used to supply a kit comprising of a felt gasket for the speaker, a base for the pipe to stand on and form a base vent (and also to protect the floor!!) plus a conical deflector which was supported on a wire frame above the upward facing speaker which reflected the sound into the room. The pipe was filled with a roll of glass fibre loft insulation.

I'm afraid it didn't last long... My Mother said that under no circumstances would she have "a bloomin sewage pipe in the corner of her living room - even if it was a loudspeaker and her son had painted it to match the colour of the walls!"

Hey ho - those were the days!!

[The Shadow]

I moved the tweeter mounting plate today as last night I discovered a bit of a problem with them as they were positioned before.



The tweeter plate has been repositioned on a batten with a 10 degree offset on the top. This has brought the tweeter plate horizontal, with respect to the main baffle slope, so that the tweeter is firing straight up at the ceiling with no obstruction.

Closing the curtains and listening last night caused the soundstage height to reduce, treble levels to drop and the speakers to stop, "talking to each other", appearing as individual entities instead of being "invisible", as they had been during the day.

Examining the situation revealed, that with the curtains closed, the tweeters were firing straight into them, causing most of their sound to be absorbed. The baffles therefore reverted to monopole treble, causing beaming and a sweet spot, outside of which the image was not formed correctly, plus a very audible reduction in space and ambience was evident.

Having moved the tweeter plate so the HF unit is firing vertically has already led to an improvement in air and space over the sloping tweeter version. With the curtains closed there is no effect on the soundstage, treble levels or imaging. That's that bit sorted then. Looks like Briggs was on to a good thing with his upward firing tweeters.

Reading Peter's article on Briggs' baffles it certainly seems that, when he designed these speakers, he was thinking about every aspect of real room performance and how to get a realistic sound stage with width, depth and height whilst preserving domestic harmony.

These half-width Briggs inspired baffles I'm playing with, seem to illustrate very well and ultimately vindicate his "real rooms" approach to speaker design. Sadly as Peter says in his article, such important considerations have since been turned on their heads, and we have instead to put up with hideous plastic coned apparitions that need to be in the middle of the room to work properly.

Steve

[The Shadow]

Here is an idea of what the baffles might look like when the final models are built in proper birch ply.



Speaker grill slats off an old radiogram give a cross between Art Deco and Mackintosh.

I took the bottle tops off the backs of Andrew's phase plugs and replaced them with a couple of countersunk steel screws. This deadened the plug's interface with the motor magnet and removed a bit of ringing in the upper midrange.

All the same, I'll probably go for a pair of Planet10 phase plugs in the final model.

Steve

[david counter]

one wonders what what Mackintosh or perhaps Lutyens would have done with speaker design

[Cobblers]

Originally Posted by david counter

one wonders what what Macintosh or perhaps Lutyens would have done with speaker design

Apple Macintosh?

How about some Horny speakaz to go with the campy see through Mac models.

http://www.fergusonhill.co.uk/product_details.php?id=7