upgrading my Tannoy Monitor Gold 15" drivers meant that I was ready to build
some enclosures. As an initial test, I put the drivers into
non-optimised 110 litres bass reflex cabinets. I was very
surprised when I played music for the first time. These drivers
went really low and sounded extremely good. I was surprised
because when I was simulating response using T&S parameters they
didn't look like they were going to cause an earthquake.
Following a rather promising initial tests, I
have decided to build replicas of Tannoy GRF horn-loaded
enclosures from 1960s. I always liked the look of them,
especially with the covers on - they are actually not many
speakers IMHO that look good with the grills on, but these do
indeed. I knew that it will not be easy due to internal panels
joining at 'funny' angles, but making GRF enclosures looked
much simpler than making Westminsters ;).
To save time and limit additional expenses I always try to follow the common proverb: "measure twice, cut once".
With fairly complicated constructions, such as GRF, it is
essential to plan everything and think about methods of doing
things before attempting any work. I have started from doing
research on the internet and downloading any available enclosure
plans. I have found some drawings with measurements that looked
like original Tannoy drawings. There were couple of measurements
that were unclear, therefore, I have drawn the enclosure
cross-section in 1:1 scale and calculated missing dimensions
using commonly know mathematical formulas. Drawings were then
re-scaled to allow for usage of 25mm plywood instead thinner ply used
in original drawings (length, width, depth and expansion of the
horn were kept as per original plans). Driver performance in GRF
enclosure was then simulated using HornResp software. The
results did not look too promising in terms of deep bass.
However they did not look too promising when I simulated the
Bass Reflex enclosure but sounded very nice, so I have decided
to progress with the project.
Methods of joining wood may have impact on the size of
the panels, so it is always important to consider these first.
Different methods were considered, but too keep it simple and to
avoid using screws, wooden dowels were chosen.
All cuts were planned to ensure most efficient use of the
Wood cutting proven to be a lot more difficult
than I originally thought. As I am not a carpenter, I was
intending to hire a professional to do the difficult angle cuts
for me. I have approached many different carpenters and wood
merchants in my town and none of them wanted to do it,
notwithstanding that they had really good equipment! Fed up with
that I have decided to do it myself. At the time I lived in a
small flat, so I had to do all the wood cutting in my friend's
back garden, using circular saw... Despite this inconvenience
and lack of table saw, the results were surprisingly good.
Router was used to cut flush mounts for the drivers and speaker
terminals. It was also used to round all of the internal horn
Thick cardboard jig was used to align the
dowel wholes on the enclosure sides with the dowel wholes on the
horn panels. What seemed to be a good idea in theory, proven
to be a little bit more tricky in practice (nothing that a bit
of sanding would not fixed though). Small neodymium magnets were
fitted into speaker front panels as well as the grills, to hold
them in place. All gaps were filled with silver sand. Enclosures
were glued together, leaving one side panel unglued, to allow
for adding or removing damping material. Initially damping
material was only placed in compression chamber and first part
of the horn.
Time to listen - very exciting stage. Well, I thought
it would be... my first impression was disappointment. The upper
bass was really boomy and there was very little of the really
deep bass. The tonal balance was just strange, and not right to
my ears. I have experimented with more damping, and ended up
with the whole horn throat (except the exit) dampen with felt.
This have greatly improved the total balance and speakers
started sounding more acceptable, more balanced. Nevertheless,
they were still lacking this very deep bass, which I knew well that
these drivers were capable of reproducing. Most of my favourite
recordings sounded ok but I was not blown away. The only time
when the GRF enclosures impressed me, was when I listed to Carl Orff - Carmina Burana.
The power and speed of the lower registers was just overwhelming
- never heard anything like this before.
However, I was not willing to keep these
refrigerator size enclosures and be unhappy with lack of deep
bass. For this reason I have decided to convert them into Bass
Reflex enclosures. I have calculated port size based on drivers'
T&S parameters, and converted the enclosures (Photos 16-30).
Time to listen again... On this occasion, the first
impression was totally opposite. Sound was nicely balanced, and
the deep bass was there when it needed to be . Please, don't
get me wrong, I can appreciate many more things than deep bass,
but I have had certain expectation from these massive
enclosures, and these expectations were met. Not only met, but
exceeded. The bass was deep but well controlled. Meaty but not boomy. Precisely how I wanted it! Tracks like Dire Straits -
Water of Love or Alice In Chains - No Excuses (Unplugged)
were taken to the whole new level. Enough about the bass though,
these speakers reproduce voices, saxophones and double bass like
no other speakers (if you are interested in my views on the
sound of these, please visit the Vintage Speakers section).
To sum it up - one of the best speakers I have
ever heard. Smooth and not fatiguing - well worth the investment
and all the hard work.
List of Components & Prices
Table below shows list of the parts together with prices,
necessary to build the enclosures as described
Total Time: 60h
Total Cost: £271.16
||Price Per Unit
|Plywood For Enclosures
|MDF For Grills
||M8 x 40mm
|Ronseal Wood Filler
|Van Dyck Crystals
||M6 x 50mm
||M6 x 12.3mm
|Brass Flat Washers
|Neodymium Magnets For Grills
|Vintage Speaker Cloth