PC
Ex Member
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Hi Guys,
As a bit of background to my project I have recently built to working stage a 4 foot long 1 foot diameter tube DB using 2 x 10" dual voice coil drivers in isobarik, based loosely between Steve's original square boxed DB10 and 212 designs. It differs because it is of a tube design, and also is tunable on-the-move - ie I dont have to disassemble the end/s to move the inner tube/drivers up and down - I tune via a 5/8" threaded rod (with a nut welded on the end) going through the top plate and threaded through another nut welded to struts connected to the inner tube/drivers . Anti clockwise (from top) pushes down, clockwise pulls up! The whole time it remains sealed thanks to self adhesive closed cell foam strips and a fine mist of silicon lube on the tube inner wall. I am very happy with the type of sound produced, and want to commend Steves on his rubber throat design idea - much more musical than a uniform cylindrical port in my experience! I am using 2 x 140W monblocks (1 for each 10" dual voicecoil driver) and can connect the drivers in any parallel series combination; I have connected each VC to a pair of terminals on the outside of the tube.
I am however unhappy with the performance of my project in one aspect.... I am querying as to how it seems best tuned- its lowest frequencys and smoothest band seems to be produced when the flange plate is only 20mm from the bottom plate - but is still annoyingly ringy/peaky around the 100Hz and above range- mainly evident with tracks containing these bass music notes? At low volumes it seems to benefit being even closer to the bottom plate with a smoother bandwidth (less peaky around 100Hz up) , but at the expense of chuffing when playing at higher levels.
I am worried that I may have chosen 10" drivers with parameters not suited to this design, or could there be a simple fix? Questions I have asked myself, but cannot exactly answer and hope you could help me with are:
1. Could I stuff more polyester fill tightly into the sealed chamber thus reducing effective volume? 2. Given the driver's parameters (see attached) and design of my tube, what would be better - wiring the drivers dual Voice Coils in series or parallel? 3. I am also worried that I may have made the flange plate opening rather small - I notice Steve's original flange covers around half the cross sectional area of the box - whereas mine covers 3/4 of the cross sectional distance across my tube- about 1/5 of the area - should I remove the flange plate and trim to half the distance across?
Specifications: * Nominal Impedance : 2 x 2 Ohm Voice Coils * Power Handling: 250 Watts RMS * Sensitivity: SPL - 87.2 db - 1 Watt @ 1 metre * Voice Coil Resistance (Re): 1.3 Ohms * Resonant Frequency (Fs): 23.7Hz * Mechanical Q Factor (Qms): 3.976 * Electrical Q Factor (Qes): 0.382 * Total Q Factor (Qts): 0.348 * Equivalent Volume (Vas): 66.085 litres * Voice Coil Diameter: 65mm BASV * Xmax: 10mm * Speaker Dimensions: A 274, B 250, C 235 Specifications are for 1 driven voice coil only
My Volumes for the tube are as follows – Upper sealed is 42L without Polyester fill. 12 litres is taken up by the flange plate/ throat volume when tuned to best listening position. The coupled isobaric driver chamber volume (irrelevant I suppose) is 16.5L.
I can email a Word doc for more pics and details for anyone curious!
Any informative help would be much appreciated!
Thanks Steve & guys
PC
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