| Search AudioEnz | |
| Articles | |
|
Current
reviews |
|
| News | |
| Community | |
| Buying | |
| About AudioEnz | |
About AudioEnz |
Kick back on tactiles
Or why tactile transducers make good sense.
By John Paul
December 2000
And
there's also the very affordable $NZ30 "Aura
shaker" from JayCar electronic hobbyist shops (pictured, right).
More on this unit later, but let me first elaborate a bit on Max's opinions.
Strong starts
Two points for audio purists about all these mechanical transducers are
first, from a scientific standpoint, it can be argued that you honestly
need response down to near DC to "accurately" reproduce the
initial strong leading pressure wave front edge plucked, struck or whatever
energy that starts the note going. I know while working as a sound operator
and dressing microphone cables near drummers warming-up there were real
trouser flapping breezes coming out of single headed kick drums.
Plenty of other examples of mechanical/pneumatic transfer functions are basic to music. Consider that double bass, cello and virtually all larger percussion instruments have legs, pegs or feet made of pointed steel. Proper concert halls have wood floors with the grain specifically running from stage into the audience to actually couple these instruments to listeners. Before amplification, bandleaders knew about resonant stage platforms and risers and often used them for maximum bass volume gain and percussion impact.
Of course a lot gets lost in the music recording process, so maybe something "physical" is or isn't there for the taking.
Movies are different as they are mostly built to spec and you can easily
second guess what Dolby and THX sound mixers are trying to do in most
scenes. But my point is that there are strong initial energy transients
that start highly compressible air moving and an easy way to get a similar
effect of lots and lots of moved air is to look at mechanical coupling
rather than pure air coupling.
My interest in floor shaker aspects started when I did a Kenwood and
Boston Acoustics THX system review here a few years back and questioned
readers "just how close do you really want to be to an exploding
petrol tanker" or something along those lines. Then I mentioned that
once in military training I was near some concussion grenades and it was
no fun at all. So how much boom and blast is necessary? And musically
just how much "attack" should start a note?
Personally, I hate exaggerated bass like all that dreadful one note crap
coming out of boom-box cars (Those fools will be deaf in their thirties!).
And a lot of home theatre I've heard simply has too much un-defined, sloppy
thick bass while the works have to be cranked up way too loud vis-a-vis
natural dialogue to get any real sense of impact. Max's car door is a
near perfect, easily observed live vs. precorded reference, of how and
what tactile sound is all about.
A legitimate shortcut
This to me, and my second point of this note, is the exact essence of
where the floor shakers really become useful and important for enjoying
both movies and music. Simply stated, they allow you to have dynamic impact
without the acoustic volume blowing your hearing out. Dynamic excitement
without giving you the all too frequent home theatre too-loud type headache.
Save your hearing but still get some honest programme (music or movie)
slam bang elements.
My own best example came one evening while my wife and I watched the
DVD of Tea With Mussolini.The volume level was at a comfortably
soft level for just following the emotive dialogue 'tween Maggie Smith,
Judi Dench, Joan Plowwright, Cher and the other "girls". Then
late in the piece, there was a sharp hard jolting thump that strongly
rattled the sofa and pictures plus antique bric-a-brac atop our piano
and a nearby side table. It was practically frightening, and my wife said
"Damn! What! Was that a trunk hit the house?". I twigged slightly
sooner and replied, virtually in unison with the movie script, "No,
that's the Germans (artillery reports) coming".
Perfect surprise, in place, giving appropriate enhancement to the story
right into the dramatic climax. I couldn't have planned it better. It
was fortunate because I had earlier subtly adjusted my thumpers for some
bass boost in old Rudy van Gelder recorded "purist" Blue Note
jazz music then forgot to do anything with them for the later DVD watching.
A cheap trial
I've got four Aura shakers from Jaycar configured together as two push
pull pairs. These Aura transducers are surplus video game vest body thumpers
where kids playing Mortal Kombat kung-fu get thumped thru game triggers
or whatever. They are heavy and one note, (actually one thump) so I'm
certain kids would quickly get bored with wearing a heavy jacket vest
that relentlessly hits them in the same place.
So that's why these 4 or 5 inch magnets & voice coils with a phenolic
PCB board type spider (and no basket or cone) are surplus merchandise.
They are cheap and nasty and offer about one half foot pound per watt
(20 watt max they say).
So I reckoned I could get much better kick by setting them up push-pull
driving each side of a board that's rigidly affixed (screwed and glued)
between two of the 8 by 2 studs between my speakers under the floorboards.
I've tapped off my REL Strata II crossover output driving an old Kenwood
80 watt integrated with a five band equalizer, with everything except
the 60 Hz band pulled out. On older musical (pre-80s, pre multi-tracked
& modern eq'd for car radio stuff) and nearly all movies I get honestly
great results.
No names, please
A few hard core audiophiles, who I won't dare name here, being un-informed
about the set-up remarked that my system seemed to have "very fast
bass" and "great dynamic attack". One keen ear asked, "what
did I do to the Image/Aerogel driver plus Linnaeum tweeter (via Plinius
M-16/SA-50) to make them so lively?". Truth is, the bass is actually
too fast as the mechanical conduction travels through the floor and armrests
quicker than thru the air, so they were actually feeling it before hearing
it. So in that sense it's a type of distortion as inaccurate (a few milliseconds)
"anticipated/delayed" wave timing. To their golden-eared (and
golden reared?) credit, they got the mis-timing right. So if you are very
rhythmically acute you've been warned.
Again with music, It's all extremely volume setting sensitive, but used
subtly it wonderful to not physically feel but just sense a good pianist
play the notes and have the thump from the pedals and dampers come thru
to simply present more of the instrument into the listening room. With
the sub-woof doing the upper bass and the shakers carrying on underneath
the aural illusion of a big "weighty and rich" Bosendorfer or
Steinway concert grand can be appreciably more convincing. This for me,
as a hard core music listener, says, run with it and refine it if possible.
Excellent cheap accessory
Jaycar and Dick Smith both have a brilliant little $35 kit-set that is
just the ideal thing for any of the shakers. It is listed as a sub-woofer
parametric equaliser, that offers variable low pass filtering (approx
40 to 200 Hz, 12dB/oct), frequency of ("Q") adjustment, gain/cut
there, and overall level, plus a switchable 20 Hz high pass filter to
protect vented boxes from over-flapping. Width of "Q" is adjustable
at assembly level and various options for powering it from existing components
or external power supplies make this a great little 3-chip, 4-knob electronic
device for "de-booming" and fine tuning any sub-woofer. It will
also obviously work on shakers which by being attached to 10 or 12 foot
studs, or platforms or whatever length room structure used, will resonate
at that wavelengths note.
Somewhat inconveniently, that 10 or 12 foot spacing between foundation
risers to studs carrying a shaker will produce very frisky 110 or 90 or
so Hz big noises when excited. So to avoid annoying and irritating one
note bass, I reckon equalisation is essential in this very physical domain
and happily these little Jaycar or Dick Smith kit-sets are perfect for
the job.
I've bought and built three for my system in that one will be used upstream
of my REL Strata II for a typical 75 Hz room boom problem. Then two of
these EQ modules will be cascaded (first output feeds input to second)
to either get a double bump/cut response modification as required, or
to use in a very deep notch filter as I fine tune my Aura shakers whilst
driving them with an old Bryston (bridged) 300 watt amp.
Test warble tones in MP-3 from 6 Hz on up to 200 Hz , plus 20-20k sweep
are available on the net at www.marchandelec.com
(plus some very nice electronic crossovers and amps etc). And the usual
test CD's with patience and trial and error will be interesting and cheap
fun for this project.
This madness (part II) all starts very soon and I'll let you kind folks
know what I've learned, but for the moment I'll just ask you if you would
like to enjoy the very desirable impact of dynamic movies and favourite
music without blasting the whole house (neighbourhood?) out? No new age
PC-correct touchy-feely nonsense allowed here, but seriously, do think
tactile!
Want to comment on this article? Click here for Feedback