A bit of
history..
In the past MTZ Audio had the
opportunity to gain a first-hand experience on Audax driver units. Three speaker projects,
sold as DIY kits, were designed and implemented with the famous aluminium dome TW025A20
tweeter driver and the HM170Z18, HM210Z12 woofer units.
copyright © AUDAX, www.audax.fr
Many greek DIYers constructed
these speakers. Their satisfaction was more than rewarding for the people of MTZ Audio.
Since September 2004 Audax has stopped OEM driver sales.
The Mylo
speaker project..
picture courtesy of an MTZ Audio friend who owns a
Mylo pair.
Selection of
drivers..
The initial idea behind Mylo was
to address the acoustic environment of a relatively small listening room. Although there
are a lot of opinions on the room area a speaker can 'load' effectively, MTZ Audio people
have come to the conclusion that the optimum room area a pair of 6.5'' woofer cones can
drive in the low frequency range, is about 9-15 m2.
Another initial intention was to
make Mylo achieve sonic perfection in the mid-frequency range where male and female voices
as well as wind and string instruments operate.
At that time (late 2003) MTZ Audio
staff decided to select the popular aerogel cones of Audax drivers for these difficult
tasks. Mylo was designed after the 6'' HM170Z18 driver.
The aerogel cone material made
Audax drivers famous for their naturalness, openness and transparency in the
mid-frequencies.
Many things are subjective in
audio; in that sense MTZ Audio people found aerogel drivers much better than many popular
and unexpectedly expensive kevlar- or carbon-fibre drivers manufactured by other
well-respected brands.
copyright © AUDAX, www.audax.fr
The enclosure
design..
An old audio proverb says :
'loudspeaker enclosures are difficult to design and hard to construct'. We wouldn't agree
more !
Many speaker designers tend to
choose increased volumes even for small 6.5'' woofers in order to achieve an extended low
frequency response (i.e. a very low cutoff frequency). In this way power handling capacity
of the speaker-under-design is severely compromised.
Mylo was given a 24lt net volume.
The reflex-port was tuned at 44Hz and the resulting cutoff frequency (-3dB) was
measured at 39-40 Hz.
The enclosure material selected,
was a high-density 22mm thick MDF.
picture courtesy of an MTZ Audio friend who owns a
Mylo pair.
Driver and cabinet data were input
to our simulation software (LFA v5.0) to derive the optimum driver and port positions over
the baffle board. Vent emissions were kept to a minimum outside the tuning frequency as
illustrated in the following picture:
Thus Mylo was enhanced with an
exceptional sonic purity in the frequency range 120-800 Hz where enclosure standing waves
and vent resonances dominate the vast majority of other speaker designs.
A near field SPL measurement in
the port's mouth verified LFA prediction with an very good accuracy:
The crossover
network..
We at MTZ Audio, believe that
crossover networks are intended to manipulate, compensate and align driver responses, not
just decorate the interior of a speaker's cabinet. We certainly do not promote minimalism
in this area of electronics. Although we respect other design approaches, we definitely do
not encourage the excitement of driver's nonlinearities and cone break-up waves that many
DIY designers induce through their oversimplified crossover network topologies.
The idea is simple :
Intermodulation distortion artifacts never appear in SPL measurements. Crossover networks
are not merely 'frequency dividing' circuits. It takes more than a desired SPL curve to
really design a speaker system.
The picture above depicts the
anechoic SPL response of a Mylo speaker on tweeter axis, at a distance of 1m, for 2.83Vrms
input (Valid measurement frequency range 200Hz-48kHz). No smoothing is applied to this
measurement.
Obviously the upper cutoff (-3dB)
frequency of Mylo is approx. 30kHz !
The small 'valley' in the 1-7kHz
range compensates for early reflections in typical living room environment and enables
really loud listening sessions. People that own Mylo are really proud of it !
The exceptional similarity of Mylo
speakers SPL response is due to the very low production tolerances of Audax drivers and
our careful selection of crossover components.
A hardwired sample crossover
network is shown in the following picture:
A detailed circuit schematic
follows right below:
A few words on
impedance..
MTZ Audio staff has got an
extensive experience on amplifier design hence regards the nature of a speaker's complex
impedance very critical for amplifier feedback operation. We all know that amplifier specs
are measured across laboratory resistive loads of 4 or 8 Ohms. IEC 268 standard was never
revised despite the strong criticism by many researchers and designers involved in the
amplification case.
A special impedance correction
circuit was engaged in parallel to Mylo's crossover network, to render the latter's
impedance as resistive as possible in a wide frequency range. This sub-circuit is shown
within the crossover network schematic just above. Its 'healing' properties can easily be
understood in the following impedance graph:
In a very wide frequency range
(100Hz to 30kHz) a nearly flat impedance for the Mylo speaker was achieved.
At lower frequencies where large
impedance resonant peaks occur to absolutely all loudspeaker systems (up to 40 or more
Ohms !) such correction circuits demand extremely large inductance and capacitance values
and therefore are not feasible. Mylo's impedance correction circuit is surely a decisive
step towards sonic perfection, especially for those who do not own highly expensive
amplifiers.
The assembly
procedure..
Sometimes small details make the
difference.
Sealing any removable cabinet
walls, securing the driver screws with special clips..
picture courtesy of an MTZ Audio friend who owns a
Mylo pair.
..using vibration dampeners and
placing high quality absorption lining,
picture courtesy of an MTZ Audio friend who owns a
Mylo pair.
..making robust welding joints on
the driver terminals..
picture courtesy of an MTZ Audio friend who owns a
Mylo pair.
..are some of Mylo's small
secrets.
picture courtesy of an MTZ Audio friend who owns a
Mylo pair.
..and perhaps of its popularity
among DIY enthousiasts.
picture courtesy of an MTZ Audio friend who owns a
Mylo pair.
Some useful links (in Greek) in
AVforum's discussions concerning the Mylo project:
http://www.avforum.gr/showarticles.php3?topic=11&subtopic=16350
Mylo / Technical
Specifications
two-way,
two-drivers' design,
vented-box
low frequency alignment, port tuned at 44Hz,
high freq.
driver: TW025A20, alum. 1'' dome by Audax,
bass-mid
driver: HM170Z18, aerogel 6.5'' cone by Audax,
enclosure
volume: 24lt net,
speaker
ext.dimensions in mm: 244x524x294 (WxHxD),
SPL
response cutoff frequencies (-3dB): 39Hz-30kHz,
sensitivity:
85dB SPL / 1m / 2.83Vrms input (anechoic),
power
handling capacity: 100W rms per amplification channel,
impedance:
8 Ohms,
crossover
frequency 2.5 kHz.
Drawings and Assembly
Instructions..
Hint : images below, link to
downloadable pdf files.
