Karls 300L Tannoy cabinets.
Project by Karl Boyle:
Monitor Gold 300 Litres ported cabinets.
Picture 1 :Suspended-driver
Here is an account of my 300 LTR cabinets:In order to assist me with my design I used a piece of software called BassBox Pro..This is a very good package that has allowed me to achieve some very good results over the years with P.A. enclosures.The first step is always to determine the Thiel-Small parameters of the drivers, which are used to model their performance within the planned enclosure.Even if available, manufacturers specifications cannot be relied upon as they can vary by up to 25% even for new drivers.For vintage drivers, manufacturers specs. are of even less use, as the drivers properties will have changed with age. ( A bitumen impregnated surround may stiffen, raising the resonant frequency, wheras a rubber surround may become less stiff, lowering the resonant frequency.) ( The compliance of the driver will be similarly affected ).
The test procedure requires measurements to be taken with the driver in free-air, and also in a closed box of a known volume.
Picture 2 :Cabinet
Using the measured Thiel-Small parameters, I used the design programme to model a 300 LTR enclosure, tuned for a flat response down to approximately 40 Hz. ( This is obviously a very large cabinet size but necessary for the bass response I wished to achieve).I chose to construct the cabinet from 24mm birch-plywood which is nice and rigid, and good
to work with.
I included braces for extra stiffening.
Picture 3: Closed-boxI lined the cabinets with a minimum amount of damping material.
Picture 4:Damping materialThe driver connections are soldered directly, by-passing the standard connector
Picture 5:Driver-connectionsThere is a protection capacitor included, as I am using these drivers in an active setup.(I am using the active crossover designed by John Ridley, details of which are on this website).The leads are taken to 10A 4mm post connectors.
Picture 7:Plug-BreakIn my design I used a large square port for good linearity.
Picture 8:PortIt is necessary to measure the cabinets resonant frequency in order to check that the target cabinet frequency has been achieved. ( Some tuning was necessary ).
Picture 9:Final TuningThese cabinets are extremely large and heavy, and as my workshop is downstairs, that is where they will probably stay.( I think it would take 4 people to lift one ! ). It was necessary to fit 4 inch castors just to be able to move them around. I painted them battle-ship grey as I had a tin lying around and it seemed an appropriate colour. I would normally avoid using fronts, and would go along with removing the dust-caps, but as this is my workshop I thought it wise, as it would ony be a matter of time before I stuck something through one of the cones !.
I am very pleased with the results, as they produce the best effortless bass of any cabinets I have built previously, exhibiting both dynamism and subtlety.The following are some pictures of my present setup with Crown/Amcron amplifier on L.F. and Quad II amplifiers on H.F..C.D.player is connected directly to the active crossover input.
Picture 10:Final Setup1
Picture 11:Final Setup2Karl BoylePreston (UK)
The Tannoy Monitor Gold website
Hans Hilberink and Karl Boyle.
1970-1996-2005. update: 25-08-2006.