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Frequently Asked Questions
When a new loudspeaker looks different from what is
conventionally expected or what experts in loudspeaker design consider to be
reasonable, then this raises questions, expectations and conclusions based on
speculation, previous experience, understanding or a personal agenda.
I consider the LX521 to be my best design in a long search
for an electro-acoustic transducer, which can set up in a domestic size room a
realistic seeming illusion of an acoustic scene, while perceptually moving the
loudspeakers, the room's resonances, reflections and reverberation beyond one's
acoustic horizon. The LX521 was designed for easy construction and low cost in
keeping with its acoustic performance goals. Only in a few areas could I have
made different design choices, but I had my reasons for not doing so. Your
questions may bring these to light.
As DIY loudspeaker builders you may have your own ideas.
Pursue them and not just in your mind. Design, build, listen and compare to
live, unamplified sounds. Learn from the LX521 by building it as designed first
and then modifying it. I have learned from my previous work, which you can study
on this website. There are also ORION FAQ and PHOENIX FAQ pages with relevant questions about dipole
speakers. I have learned from what I heard at shows, from what others have
demonstrated to me or talked about on the web, at conferences, in books and
publications. To that I add my own thoughts and experiences. The LX521 is the
result.
I strongly recommend to build the LX521 per instruction.
Set up the monitors in your home for enjoyment or in the recording studio for
work. I very much hope that these transducers will be used by recording, mixing
and mastering engineers to further the quality of recordings.
Q1 - How do they sound?
A1 - They render the phantom acoustic scene with greater
clarity, presence and realism than the ORION. Monitors and room readily
disappear. Microphone techniques and spatial rendering consequences show up
clearly. Sound-wise they are completely neutral from top to bottom. They
emotionally engage the listener with the music, the instruments, the performers
and their acoustic surroundings, making music listening more effortless and
pleasurable.
Q2 - I do not like the appearance
of the top baffle and want to change it slightly
A2 - Don't change it. Try to get used to it. The
midrange/tweeter baffle is an essential acoustic design element. It controls the
interference between between front and rear radiated sound waves in order to
obtain a dipolar radiation pattern over the whole frequency range. Thus baffle
dimensions must be measured in fractions of radiated wavelength and how much
phase shift is produced. For example, at 7 kHz the wavelength is 49 mm. Every mm
causes 3600/49mm = 7.350 of phase shift . The 19 mm thick
baffle introduces 1400 of phase shift between front and rear
radiation on-axis. At increasing off-axis angles this phase shift becomes less,
but the varying width of the baffle also contributes to the total phase shift
and to the summation of front and rear radiated waves at points in space around
the monitors.
Q3 - I want to use a 1 inch thick
top baffle and recess the midrange drivers
A3 - The top baffle was not designed for this and ideally should be
even thinner than the 3/4" wood chosen for mechanical strength and ease of
construction. The upper midrange part of the baffle has the most critical
dimensions. See A2. The driver mounting hole should not be chamfered, because it
could affect the polar response and baffle strength. The baffle could be milled
out of 1" thick wood or other material according to its 3-dimensionally
specified dimensions.
Q4 - I think eliminating the
passive crossover and driving lower and upper midranges separately and from an
active crossover of higher order might yield
higher performance
A4 - Maybe, maybe not. I have not tried it. When I
started the design I was looking for a midrange driver and baffle combination
that would extend dipole behavior into the kHz frequency range and still allow
for a 3-way design with a dipole woofer below 150 Hz. Furthermore I wanted a
dipolar tweeter with wide vertical dispersion. I could not find a midrange drive
unit that met my needs at low and high frequencies simultaneously. Thus the two
chosen drivers. They provide a wide frequency overlap range, conducive to a
first order crossover, to gradually merge the two midrange dipoles into one. In
essence I turn the two into a single, very broadband midrange dipole with low
group delay variation. The smaller driver does not show signs of stress at its
low end, nor does the larger driver show signs of harshness at its high end. A
passive crossover network brings with it the convenience of not having to
redesign the ORION ASP printed circuit board, which I now also use for the LX521
ASP.
At some point in the future I might do a new layout of the board and add a first
order (or higher?) crossover to have the option of a fully active 4-way monitor.
But right now I am totally unmotivated, because I have no evidence of practical
benefits and only of further work. For example, the frequency response due to
the passive crossover is determined by the driver and network impedances and
would require modification of the midrange equalization for an active crossover.
Also, there is no 10-pole Speakon connector available or a 5-conductor-pair
speaker cable.
Q5 - Will you offer a DSP based
crossover/equalizer?
A5 - A DSP based xo/eq makes a lot of sense for manufacturing
and cost reasons. For the DSP to become the sonic equivalent of the LX521 ASP
will require a lot of attention to design and performance details in the digital
and analogue bowels of the beast. I am not an expert in DSP application
programming or even know how to chose the most suitable DSP engine. It is not on
my priority list at this time.
Q6 - Are you done with designing
the LX521?
A6 - Yes. The LX521 has met and exceeded my expectations. I have
lived with it and used it now for nearly five months. Every visitor to my home,
whether trained listener or audiophile, is excited. I own the only monitor pair
in existence and I have not yet seen the production versions of the two midrange
drivers. Based on previous experience with SEAS I expect the drivers to be
duplicates of the prototypes, which I use. Thus no change to the design. I also
have not yet seen the baffle flat-pack, but it will meet all specified
dimensions and cause no changes to the ASP design. The ASP itself is documented
and parts are available to duplicate it.
I have heard loud voices on the Internet chiding me for presumed flaws in my
design or being late to some party. For whom should I feel sorry? I am free to
design as it pleases me, to change course and also to stop.
Q7 - Can the sound be improved by
using a different material for the top baffle?
A7 - I do not know since I have not tried, nor have I found a
reason for trying. A different material could mean using a material with
different mass, stiffness and damping properties, but preserving the outline
and thickness of the prototype baffle. In such case the acoustic wave launch
and guide properties of the baffle would remain unchanged, but the mechanical
vibration characteristics of the baffle might be different. Thus, any spurious
radiation due to baffle vibration might be different, but it is not known
whether there exists a problem to be solved or whether a problem would be
introduced. The dominant vibration mode for the top baffle is formed by the
upper midrange and tweeter section swinging back-and-forth relative to the lower
midrange section. The narrow neck above the lower midrange forms the pivot axis.
This is a low frequency bulk movement, which the bridge over the woofer baffle
largely prevents from becoming excited. I have no evidence that this
vibration mode has audible consequences, even when the top baffle rests directly
on the woofer baffle.
A baffle material with different thickness is highly likely to change the
acoustic wave launch and guide properties of the baffle, affecting particularly
the upper midrange and tweeter baffle section. Thus the optimum baffle contour
for the given drivers would have to be re-determined by acoustic free-field
measurements. Ideally the baffle would be very thin and the drivers would be
dipole point sources to minimize front-to-back distance. In reality the
drivers have too much physical depth and width relative to the wavelength they
are meant to radiate. Baffle outline and thickness are then used as parameters
for finding a practical solution for broadband dipolar radiation with a given
set of drivers. The LX521 top represents clearly not the only possible baffle
shape, but is an engineering and cosmetic trade-off that works well and is easy
to build. The whole speaker is not a piece of furniture but should be viewed as
an interesting, purpose-built sculpture that blends in visually, without
imposing its presence. Once the music plays it disappears from attention.
It should be obvious that changing to a different midrange or tweeter driver is
likely to also require a different baffle shape and equalization.
Click on ORION-FAQ
or PHOENIX-FAQ, if you did not find your answer above
Check out the ORION/PLUTO/LX521 Users
Group for knowledgeable
advise
CAUTION:
The content of any page may change without notice as
I learn new things or find better descriptions. The designs presented here may
change as I make new observations or gain more insight. I see myself as a seeker
of truth, though I now know that every person is, and ultimately truth is a
construct. There is only this. Maybe what has been done here points you to it.
Audio has overwhelmingly been a hobby for me, for my own pleasure and love of
music. I enjoy to share what I found and possibly to dispel a few
misconceptions. My interest is not on the business side, though I like that my
activities pay for my hobbies. You may not agree with some or all aspects of my
designs, the approach that I take to them, or the theories. I have no problem
with that. Just do not ask me "what would happen if ...". Changes that
you make to the designs are for your own pleasure and at your own risk. But if
you learn something worthwhile, then please let me know. My DIY projects are not
for beginners and it may be necessary for you to buy subassemblies or a turnkey
system from Wood Artistry. Please do not ask me for individual help with your
DIY difficulties. All my designs have a Support Page. It is listed on the cover
or inside of your project documentation. There is an ORION/PLUTO/LX521 Users
Group with people who can help you. I respond to every email eventually, but
you may not get the answer you want. I consider my writings in these web pages
as brief and to the point. I labor over every sentence and word and provide
little redundancy. Read thoroughly and maybe more than once. I do not write for
the rank beginner, but for those who have been around the block. You may need to
study up. The links in my text are for that. I have not been standing still
since I started this website in 1999 and with the idea of a brain dump of my
previous findings so they would not get lost to the audio community. In 2006,
after PLUTO, I thought I would go into a support and maintenance mode. No new
design. Stuff happened, more enjoyment to share. The recording and rendering
process interests me most at this time. Therefore the LX521. Let's see what it
will do. I could stop now and be content with what has been accomplished.
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