OPEN BAFFLE SPEAKER PROJECT
I've probably mentioned in early parts of this paper,
when designing something new like this, I like for it
to take a long time. Between each step in development
I like to put the project on ice for at least several
months. I like to do this because each time I
thaw it out and get back into it, I see it as if I was
a different person. This eliminates infatuation
and proud papa syndrome and breaks any desire to stay
on the same road I was on when I stopped. You
know, things in motion tend to want to stay in motion.
Part 3 of this paper I had reached a point where
I was happy enough with the results for myself but worried
about making it user friendly enough to publish or sell.
So after Part 3 was written I put the project on
ice. Above is a photo taken in my then unfinished
listening room with the speakers set up as they
were in Part 3. The broadcast speakers (HDTs)
are just out of the frame on either side of the Open
I had a listening room to complete before I could continue
any honest evaluations. (I also had to bring the
listening room to near completion because it's been
on ice since last year's DECFEST). My plan was
simple. Get the room done, and during Decfest, set
the system up and demo it. It will be the first
time I've heard it since I put it on ice after part
3. That should put some substantial pressure on
me, and an excellent real world test. It's either
going to bomb badly or it's not.
did happen to the speakers themselves while they were
on ice. I robbed one of the drivers to help a
desperate audiophile out in a time of need. I
had been using our DFR8 full range driver but wanted
to try the shielded version of the DFR8 in these cabinets
since it has a much more streamline magnet assembly
since the speakers were on ice, and I'm a man cursed
with having to wear too many hats, I waited until a
few nights before the DECFEST and built a new pair of
shielded DFR8s. I then bench-tested them and
that was it. Yes, believe it or not I'm going
to present the ZOB at the fest using brand new drivers
with a total burn in of 10 minutes. I figure if
the ZOB impresses with these handicaps in place then
I'm solidly on track with the design.
fest finally came and I set up ZOB just as it had been
before, only the room around it has been largely finished.
BTW, I didn't get to complete the room until
three nights before the fest so I had no idea what to expect
from anything we heard in there.
a room packed full of onlookers, I set up the microphones
and was concerned about trying very hard NOT to set
the gain too high so as to spare us all the horrible
sound of low frequency feedback. So by the time
I had music playing so that I could blend in the broadcast
speakers - and I remember thinking how odd it was
that I was already hearing plenty of bass and hadn't
yet turned the broadcast on! Well, no time to process
that so I turned on the broadcast speakers with less
gain than I recall from before, putting me farther away
from the yellow zone of potential feedback or booming. That
was a good thing, I could relax.
listening to them was only brief enough to make sure that
nothing sounded bad, and then I continued to mingle with
everyone. It did sound really good. Smooth
with nice weight. The broadcast was completely
transparent. The frequency balance seemed better
than before. I noticed they remained set up and
in use for a very long time meaning they were able to
hold peoples attention better than other speakers. In
a fest environment holding anyone's attention more than
several minutes is hard to do if you're a speaker
or an amplifier!
I considered the first real world test a success. I
set the ZOB up exactly as I had it at the end of part
3 of this paper and let about 40 people listen to it
without my intervention or presence in the room.
ZOB was put
on ice directly after the fest until some three weeks later
when I decided to use them one evening at the other
end of the listening room... shown above. I wanted
to hear them by themselves again - without the broadcast
system. So I set them up at the other end of the
room and there it was again - body! Way more than
I remembered at the end of Part 3. I spent an evening
with them rotating amps and sources. There was
far less of a gap between the resonant chamber and the
driver roll off. In fact, the holes that were there
in the past (that were so nicely filled in with broadcast
speakers) were filled in enough that I'll have to perform
it to see if they are still there at all. The
overall Q of the chamber has lowered (flattened) too.
I'm getting plenty of usable bass at 40 cycles. After two more repeat nights of conformational
listening on good recordings and some daytime listening
on horrible recordings I can conclude the following
The speaker is now usable on its own - something I
had given up on for the most part.
The bass is largely absent below 40 Hz, but above this
it is full and incredibly flat sounding. It's hard,
if not impossible, to aggravate it with complex bass
lines. This is absolutely the cleanest bass I've ever
heard next to my Acoustats.
Imaging varies with sources and recordings more than
it does with other speakers.
Imaging ranges from one to six feet outside the speakers
and between eight and 30 feet to the back limit of
the sound stage. Presence and detail are almost
in a new league, may even be a benchmark.
Good recordings sound good. Great recordings sound
completely real depending on the source used. Bad recordings
get thin sounding, making the speakers seem too present.
A foam tile was temporarily placed below the driver
on the face of the baffle. This produced a noticeable
improvement in midrange smoothness. (The room
presently has a concrete floor with a small area rug.)
A foam tile was temporarily placed behind the driver
on top of the adjustable slot panel to create more division
between the port and the rear wave of the speaker. It
seemed to improve the coupling between the driver and
the chamber below.
A two watt Zen Triode amplifier has a much weight as the
25 watt Torii MK II with these speakers, or put another
way, the bass (frequency balance) of each sounds about
the same. On the box speakers, a Torii MK II will
usually develop noticeably more visceral bass than a
Zen Triode. Also for most of my listening, the
playback level was the same for both amps. I used
the TORII MK II for the majority of my listening simply
because it is a less forgiving amplifier and also because
it is capable of complex feats of effortlessness in
classical music at louder playback levels. A great
amplifier to judge how good a speaker really is.
With the exception of my Acoustats, never before had
I experienced such a wide gap between the sound quality of
different sources and recordings. This is consistent
with past experiences in that when an audio system gets
too transparent, the contrast between good and great recordings
becomes so huge that you can only bear to listen to
your best recordings, substantially reducing the content
of your music library.
CAME THE IMPERIAL BROADCAST
spending a week with the open baffles all by themselves,
I wanted to hear what they would do with the broadcast
system added again. However, this time after some
study of the room I realized I might be able to use my
Imperial SO horns at the opposite end of the room to
effect a similar wave front at the arc of the speakers
by just jacking with the phase angle.
set up a two-watt Zen amp to drive the Imperials (shown
above) and re-installed the microphones in the
open baffle cabinets. Remember, now more than
ever, the broadcast system is an ambience tool with
the added benefit of introducing a controllable amount of
weight and scale to the playback. (Before, it was
almost a requirement just to have a usable frequency
balance.) The broadcast has shifted from a requirement
to a luxury.
got lucky with the phase angle and the wavefront from
the Imperial SO cabinets, and if you study the room
shape you may be able to see why this worked so
well. The broadcast system is turned on but just
to the point of being detectable no more. I
don't want to be aware of the broadcast speakers in
the listening position or anywhere in the room as I
walk around. This is how it was set up in part
3 when I used the HDT MK IIs as the broadcast speakers.
is a picture of the the right Open Baffle speaker and to right the
HDT used as the broadcast speaker. The unused
Imperial SO is the large cabinet that looks as
if it is built
into the wall behind the open baffle speaker. This is
how I set it up for the show, and this is the back of
the room. When the time came to demo the ZOB all I had
to do was turn the couch around.
the Imperial SOs in this way with speakers at the opposing
end of the room has a wonderful effect on the rooms
acoustics, creating a flat bass response throughout
the dead center of the room with no holes and even all
the way out to the boundaries. This acoustic correction
effect makes the open baffles appear to have better bass,
as you might expect, so a very symbiotic relationship
results between the driver in the open baffle and the
HOW DOES IT SOUND?
sound stage has pushed back to whatever the recording
sets it to. The Imperials are completely undetectable. The scale, weight, dynamic impact and control
are so good I'm unsure if I've ever heard
better. Everything about this speaker sounds right;
imaging is lucid, the music breathes and you physically
feel each note, even when it's just a delicately soft
piano stroke it still has a physical sensation. The
most complex piano works played at live volumes hold
together with grace and seem to have no flaws. On
music that has a bodacious bass line it just thrills
your spirit and achieves a power and authority that seem
to be impossible from such small speakers. This
is with everything set dead flat. The microphones are
no longer EQ'ed, everything seems very forgiving,
there are zero feedback problems, and we are still using a cheap $200
Behringer mixer with some drum mics.
old black Stereophile Test CD with the church organ
track, something I've heard at least several hundred times
over the past 15 years, came off so well that I was
able to construct the mechanism in my mind that opened
the air flow into each pipe of the organ, hearing
how each puff affects the initial attack profile of
the note. In other words, I had so much detail
that I could easily understand exactly what and how
the sound I heard was being created, as if it had
DOES THIS LEAVE US?
are probably wondering what the hell changed so much
between parts three and four, right? Two things; the room in fact got significantly better and
the driver was changed from the original DFR8 to the
shielded DFR8. The biggest difference was the
driver with respect to the bass response, but the room
helped to tip the frequency balance away from the top end. BTW, the
listening room is not yet finished.
There will be much work ahead once I start measuring
the room. And speaking
of measuring things, I'm anxious to spend more time
on the ZOB project, looking at the impedance and frequency
response of the ZOB.
summary, the results have changed dramatically from
part three, making this a product that will be viable for
the DIY market and user friendly for those who order
the speakers completely finished. The options are now to use them stand alone,
stand alone with a sub, or stand alone with a crossoverless
biggest thrill is that with this alternate shielded
efficiency of the coupling between the driver and the chambers
has increased sufficiently to make the speaker usuable
on its own for many
people. Even though the efficiency of the shielded
DFR8 is 2 dB less than that of the unshielded DFR8,
it is not noticeable. In fact, it seems louder now than
it did, and that's got to be because there is so much
more low frequency content than before. This validates my
original idea behind the design of the chamber now that
it works more efficiently. In my eyes,
that's one hell of a Zen speaker since frequencies below
100HZ are all passed to a driver that doesn't exist!
There's just an empty chamber. How cool is that?
to mention the purity and phase coherency of the bass
and if you add broadcast speakers, those characteristics
remain the same. No powered subwoofer can achieve
this seamless integration; with a line level input
and active crossover, it's impossible. Interestingly
enough, that means that no-one in the
world has ever heard bass this clean, textured, pitch
perfect and open from a moving coil speaker that
is a true full range point source because nothing
like this has ever existed, at least to my knowledge.
To get a single eight inch driver with no crossover to create a full balance of usable bass down to
40Hz without equalization in such a narrow baffle has
never been done either. It is the ultimate
in coherency, supporting the ideal that for a speaker
to accurately reproduce a kick drum accurately, it must be a point
source able to reproduce the whole range of that drum,
which is typically 40Hz out to 10kHz or more.
you reproduce the drum any other way, the subtle differences
in phase angle between the main driver and the second
driver are enough to alter the pitch definition and
smear the upper harmonics. The constsruction characteristics
of the drum can be
easily deduced and the type of heads used
and tuning if you're standing in front of it. On
a stereo, usually not but with this ZOB approach, it's
remember that this narrow baffle allows the speaker
to disappear completely without becoming a large room
reflector when compared with many other open baffle designs.
As a result, it images exceedingly well.
If you opt
for the crossoverless broadcast system, the source for
the broadcast amp is a pair of live microphones which
is a whole step better than live microphones recording
music and reproducing it back by CD player. So signal
quality is very high going to the broadcast system and
the system itself is reproducing the actual in-air sound
of the main driver you're listening to in the Open Baffle.
The harmonics are matched and the magic begins.
an absolute Zen approach to speaker design.
only real negative so far that I can see, is the low
xmax of our DFR8 drivers which makes them less than
ideal for open baffle use. Of course, this is the
challenge with all open baffle drivers since there is
nothing to load the driver at low frequencies. And
finding an eight-inch full range driver such as the DFR8
that has a high xmax and high efficiency is going to
be difficult, unless you want to spend over $500
we were to hi-pass the speaker at around 38 Hz we could
probably prevent this problem, but I'd like to work
with it for awhile and see what I can achieve with
the full range driver.
five will outline be whatever I've come up with to address this
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