This web site is dedicated to the famous Tannoy Autograph and GRF Horn
Loaded loudspeaker enclosures.
I have owned my 15" Monitor Gold drivers from new. Originally they were fitted to a small sealed enclosure and some years later I made the corner mounted
About 5 years ago I decided to build the GRF enclosure, as it looked simpler than the Autograph. After much head scratching I made a quarter size model and once satisfied that I fully understood how the enclosure went together, I made the real thing. I used 19mm Marine plywood (no air voids) for top and bottom panels and all other panels were made from 12.5mm ply.
The sound improvement was amazing---I really didn't think that a horn-loaded system would improve the sound THAT much. I used the GRF's for a number of years but it was always in the back of my mind that the ultimate enclosure was the front and rear horn loaded Autograph. I scratched around on the Internet, looked at the Tannoy plans for many hours and eventually had a go at building a quarter scale model. In March 2004 I began building one of the enclosures. I firstly cut out the side, top and bottom panels and temporarily put it together to see how large the enclosure was---these are BIG enclosures and I thought my wife would divorce me knowing that I wanted to put them in the living room. It took many days and long nights to finish one of these enclosures but the results were well worth the effort and expense.
After many hours of hard, but enjoyable work I have finally finished both enclosures. They have been glued and screwed and the only thing left to do is to apply a clear finish to the Marine Plywood.
I have mounted both enclosures in corner positions in the room. It is very important to make the enclosures as rigid as possible as unwanted resonances can cause significant coloration of the sound.
Having listened to both enclosures I can say the sound is much different to the GRF. The Autograph is noticeably more efficient than the GRF, especially in the mid frequency range. One of the weaknesses of the GRF is that it sounds a bit thin in the mid frequency range. The Autograph on the other hand has a very nice fast mid frequency response. Voices sound full and natural and instruments like Bongos have a fast transient response. These enclosures need to be corner mounted and in a large room in order to get good low frequency bass radiation.
The bass harmonics are very well defined.
Below are some observations made by my good friend Kelvin Fleming:
I have surmised that
the main difference between the sound of horns and conventional direct radiator
designs is not the amount of bass, or even the frequency response
characteristics as a whole, but more the ability to reproduce transients as
they occur in real life. The horn enables the speaker to couple to the air with
very high efficiency and very high damping. It is the coefficient of coupling
to the air that is so different from direct radiator speakers, and the reason
why inefficient speakers can never deliver realistic transient response. The
typical bass reflex design produces large amounts of "fake bass"
because the speaker in conjunction with the vent rings and smoothes
out transients into lumps or thumps of largely irrelevant low frequency
information. This pads out the sound and gives the impression of extended
response. Obviously this is an excellent and cheap way of enhancing the
performance of small speakers, but is totally off beam for large units. This
observation, by the way, is coming from a person who has been a fan of bass
reflex designs all his life! A good test for a speaker is to input a square
pulse - theoretically the output should be nothing because the pulse consists
of DC and infinitely high rise times. With an average speaker the output will
be a loud thump because the speaker acts as a low pass filter, and rings
excessively. With a good horn design, the output is minimal, due to the very
high damping and efficiency. The upshot of all this is the horn design has the
ability to separate bass and midrange information and produce an astounding 3D
sound stage. The less "produced" and gimmicky the recording is, the
better it sounds. Kick drums "kick" and stop, they don't thump. 10
watts per channel fills the room with concert like volume, and even at very
high volumes the cones barely move. Turn up the wick and they just keep getting
louder without stress or compression. Having heard these Tannoys in more
conventional enclosures I can say that the transformation is total. It also
shows that conventional measurements performed on loudspeakers such as swept
sine wave response curves are quite meaningless - there are simply too many
variables in complex musical waveforms.
Why are there so many people who don't like horn speakers? My guess is, for one thing they are large; incredibly expensive to buy (in
Tannoy has released a reissue of the vintage " GRF Memory HE " corner enclosures, but these are not the horn designs of which there were two. The ones shown below were the slightly less complicated design.
The builder used Corel Draw to calculate the missing bits of data from the plans, and print life size templates for routing the top and bottom pieces. He constructed a quarter size model from high density cardboard to proof build the design before going ahead with the real thing. The project took approximately 20 weeks to complete; working nights and weekends.
These enclosures were specified for the 'Monitor Gold' series for achieving the best possible results from these drivers with the technology of the period. It could be said that the best technology of the period probably surpasses many of the so-called 'state of the art computer based design' technologies which exist today in loudspeaker design, and thus opens up a whole debate on the validity of many of the so-called advancements of modern audio. Without being a technological rechabite (we all know how CD has brought immeasurable advantages to our audio lives!), any person who has read on subjects such as quantum physics, would appreciate that there appears to be is no such thing as absolute knowledge, and therefore (it follows) absolute advancement in any field of human endeavour or experience - modern "architecture" is a good example, with the less than outstanding designs failing to justify the destruction of the buildings they were purportedly designed to replace. Of course opinions are like pairs of speakers, everyone has at least at least one or two ...
Please note that Tannoy has since declined to supply these designs to further inquirers; although I am trying to convince the constructor Richard that it would not be such a sin to let other's see them! However they are now available at the premier site for vintage gear and Tannoy info: Kiewa Valley Stereo site.
The following links show photos of one of the enclosures during construction.
Do you need plans for the Autograph? There are several web sites that have Plans which can be used to construct the enclosure.
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