Enter a new loudspeaker design – the Balanced Mode Radiator – to overcome this defect.
Before getting to that, let me first describe the CEAD BMR 4.5 speakers since context is important.
On one level, these are just straight forward ceiling loudspeakers. They are round and a designed to be inserted in 190mm holes. Each weighs 1.75kg and is supplied with a C-ring and a metal strut to act as a ‘tile bridge’, giving support in office-style ceilings. Those extra bits wouldn’t typically be required in the home, because there are fold-out lugs on the body of the speakers.
They come in pairs, with white metal grilles and white ABC surrounds for the part showing within the room. A powder-coated steel can protects the rear of the speaker from whatever dust, dirt and wildlife lurks in ceiling and wall cavities. Somewhat surprisingly, the powder coating is bright red and looks not dissimilar to a beautiful enamel red. It seems almost a pity that this part will end up out of sight.
A small rotary switch (located on the front baffle, behind the removable grille, so you can set it after installation) allows each to be set to either standard operation mode, with 4Ω impedance, or to 70 or 100V PA mode. Three power level transformer taps are provided for the higher voltage, and four for the lower.
Wiring is via a small terminal block which can be unplugged to make tightening its wire-gripping screws easier, and then plugged back in. This then hides in a cavity within the steel can, protecting it, while the cables can be secured in a clamp attached to the unit. The terminal blocks have two + and two – connections to ease daisy-chaining multiple units when deployed in fixed-voltage installations.
A strange driver
Once these are installed, they look entirely unremarkable – like just another couple of white ceiling speaker grilles. Normally behind such a thing you’d expect to find a single large cone, or possibly one with a small secondary cone affixed at the middle to assist with high frequencies. With a high end speaker the main cone might even be set back a bit and have a full tweeter in front of it.
The problem with these is that, as I said at the outset, such a loudspeaker is normally pointing in the wrong direction. It goes in a wall or a ceiling, and so it is ‘firing’ perpendicularly to that wall or ceiling. In the wall case, it is normally installed up high, perhaps as a surround speaker.
Now just about all loudspeakers produce quite directional sound, especially in the higher frequencies. The larger the driver, the more directional the treble. Those single-cone speakers might sound ok when they are firing directly at you, but if you listen at an angle they get pretty dull. Those passive ‘whizzer’ cones on the front can help somewhat, and active tweeters can help quite a bit. But even tweeters get more directional at the upper end of their range. Some models actually have the tweeter canted at an angle under the grille in recognition of the fact that few listeners will be directly in front of them.
All that’s well and good, but it still means that great care needs to be taken to place the speakers to have the tweeters pointing the right way.
These speakers are entirely different. Underneath the grille of each is a surprisingly small driver, mounted off-centre in order to make room for the transformer tap switch mentioned above. This appeared to be a 115mm class driver – the ‘4.5’ (inches) referred to in the model number. But rather than having the usual cone shape, the radiating part of the driver, which had a diameter of 80mm, was entirely flat. It looks very much like a flat disk, except for the soft rubber suspension around its edge.
Such a driver would normally be very much subject to directionality problems with treble, beaming the higher frequencies quite narrowly in a direction which was unlikely to be that of the listeners.
But this isn’t a standard driver. It is what CEAD calls a ‘Balanced Mode Radiator’. The lower frequencies are produced by the normal piston action of a voice coil pushing the cone to and fro. The upper frequencies by both this piston action, and by vibrations propagating through this flat disk. Calculated masses have been strategically added to this disk at various points to ensure that the timing is right to avoid the destructive interference between frequencies emerging from different parts of the piston surface, normally the source of high frequency beaming.
CEAD says that all this comes close to restoring the performance expected from a freely suspended, weightless disc, set to vibrate with music, except for a loss of sensitivity. The most important effect is the preservation of a wide dispersion of higher frequencies. Indeed, CEAD says that these speakers will produce a ‘coverage pattern’ of 140º. It adds that the speaker design lends itself to reduced falling off of sound levels at greater distances, allowing them to be run less forcefully for the same effect.
It rates the speakers’ frequency response from 80 to 26,000Hz, their power handling at 20W and their sensitivity at 85.7dB.
How did the system go?
Conducting listening tests with speakers such as these involved some rather different arrangements. While I started off simply putting them on stands as though they were regular speakers, that was obviously inappropriate for their general use. So I mostly put them here and there: hooked onto a wall up near the ceiling with the speakers at different levels, firing into the room with complete indifference as to the listeners’ locations. That, after all, is something like how they will be installed in real life.
The results were impressive. On the stands – used hi-fi style – they delivered beautifully dynamic sound, with drums particularly coherent. This is a marker of good timing and little phase shift, since all the frequencies produced by drum strokes sounded tied together into an integrated whole.
Except, of course, for the deepest one. The 80Hz minimum frequency response seemed to be pretty optimistic. There was simply not much mid-bass. I was thinking that the output extended to perhaps 120Hz, but I conducted a quick pink noise frequency response measurement and found that the response starts falling away at 144Hz quite rapidly, to be 12dB down by 100Hz. You will need a subwoofer for any kind of critical music listening, although as surround speakers in a home theatre system this will already be catered for by the rest of the system.
While on measurements, in my room their ability to project sound didn’t seem to differ significantly from regular satellite speakers. For both these and the satellites, the drop-off was about 4.5dB for midrange sound, and 3dB for broadband sound when measured at 2m compared to 1m.
There was also a nice airiness in their performance, attesting to the wide dispersion of the higher frequencies. I found that I could move the speakers so that my ears were 60º or more off axis without significant change in the tonal quality. In other words, they overcome the major problem with wall and ceiling speakers: they can be mounted flat yet still deliver the proper sound to you.
When I put them in a more representative position on wall hooks, their character changed little. They filled the room with reasonable levels of clean music that was, most importantly, even in character pretty much anywhere I stood in the room. There was no sense – even though they were being fed with stereo music – of the sound from one channel collapsing. They were in that way ideal lifestyle speakers – ones you can use to fill your room with fine music while moving around and living your life.
It looks like CEAD is onto something with its Balanced Mode Radiator technology. It is planning to release a larger 6.5 version (165mm) in the near future, with stronger bass extension.
Product: BMR 4.5 in-wall/in-ceiling speakers
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