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DB210 pedestal tube project - tuning troubles! (Read 2665 times)
PC
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DB210 pedestal tube project - tuning troubles!
10/18/07 at 08:16:31
 
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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Bart_West-VL.
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Re: DB210 pedestal tube project - tuning troubles!
Reply #1 - 10/18/07 at 16:50:25
 
1. Better put something solid in there, to reduce volume.
2. Both speakers MUST be connected parallel, each speaker can have the DVC wired in series. Now you have only 2 Ohm. (1 DVC in series = 4 Ohm ... both drivers in parallel = back to 2 Ohm)
Or if you're amp can take it, wire everything parallel → 0.5 Ohm  8-)
3.Yes, trim it.

I would like to see some pics now.  :D
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Bart_West-VL.
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Re: DB210 pedestal tube project - tuning troubles!
Reply #2 - 10/18/07 at 16:54:41
 
I forgot to say; The DB10" also has a second resonance, at 125hz.
Set you're crossover to maximum 80hz or less.

B.
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Adrian
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Re: DB210 pedestal tube project - tuning troubles!
Reply #3 - 10/18/07 at 17:08:29
 
the 125hz resonance is really nasty Sad
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Too much bass never hurts, or does it ?
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60_and_up
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Re: DB210 pedestal tube project - tuning troubles!
Reply #4 - 10/18/07 at 20:00:21
 
subwoofer - 60-80hrtz and down only.
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Peace hath higher tests of manhood than battle ever knew. ...
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PC
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Re: DB210 pedestal tube project - tuning troubles!
Reply #5 - 10/19/07 at 04:42:15
 
Thanks fellas.

Whats a good starting point to reduce the sealed chamber volume?

1.I will connect DVC in series, and then drivers in parallel - my amps are stable to 2 ohms, delivering then 200Wrms. Not stable below that load.

2.Can I hook up the two drivers each with their own amp? - Or not the same result?

3. I will trim the Duct flange.
[img][/img]
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PC
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Re: DB210 pedestal tube project - tuning troubles!
Reply #6 - 10/20/07 at 07:41:53
 
Here is a view of the duct on the outer Tube. Tube will be painted with iron oxide paint to make it look a rusty one piece cast iron pedestal.
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