Hi All,
Been lurking with the idea of assembling a straight line array based on the Two Tower, Corner Full Range, Jim Griffin CBT and IDS-25. Thank you for starting and posting in those threads as the information is invaluable!
I originally was going to do a 3-way Open Baffle line array but that was too cost prohibitive with results unknown so straight fullrange line array it is.
After reading through the subjective 3-5inch test threads (also thank you) and based on Jim Griffins glowing recommendation for the SB65WBAC25-4.............just ordered 70 units for a straight line array. Trying to get 35 or so on 1 side.
Will post build and listening impressions with some rudimentary measurements and another endorsement of the full range line array.
Goals are wide dispersion in the upper range, usable down to at least 80hz and small footprint. Will assess the need for a bass array after listening tests performed. Onto the enclosure cutting!
21/2" SB65WBAC25-4 :: SB Acoustics
Been lurking with the idea of assembling a straight line array based on the Two Tower, Corner Full Range, Jim Griffin CBT and IDS-25. Thank you for starting and posting in those threads as the information is invaluable!
I originally was going to do a 3-way Open Baffle line array but that was too cost prohibitive with results unknown so straight fullrange line array it is.
After reading through the subjective 3-5inch test threads (also thank you) and based on Jim Griffins glowing recommendation for the SB65WBAC25-4.............just ordered 70 units for a straight line array. Trying to get 35 or so on 1 side.
Will post build and listening impressions with some rudimentary measurements and another endorsement of the full range line array.
Goals are wide dispersion in the upper range, usable down to at least 80hz and small footprint. Will assess the need for a bass array after listening tests performed. Onto the enclosure cutting!
21/2" SB65WBAC25-4 :: SB Acoustics
These are 3.6ohms DCR. 7 series and 5 parallel gives 5.0ohms (almost suitable for an 8 ohm amp) but you will take a slight hit in sensitivity. You may actually be better off making it a true 6 parallel x 6 series with a 3.6ohm 25w dummy resistor hidden in the cabinet to simulate one extra driver. The power you lose is now only 1/36 of the total vs a much more substantial loss from wiring as a 7x5.
Thanks! Dang it already ordered! I can't fit 36, ceiling too low. Seems like 7x5 it might have to be. Looking forward to sound testing.
A 4-ohm-capable amp will be fine with that.
Chris
Sure hope so, getting excited! Looks like 3/4 inch MDF. Looking at 91" inches for the front panel and 92.5" in total height. Might be close to scrapping the roof when standing this upright . That is with 66mm centre to centre spacing, this might be cutting it too close. Hope the frame tolerance for the SB65 is tight. Might have to relax to 32 drivers per side.
. That is with 66mm centre to centre spacing, this might be cutting it too close. Hope the frame tolerance for the SB65 is tight. Might have to relax to 32 drivers per side.
you should be able to get 4x8 sheets of murphy ply which is a high grade baltic birch with maple face veneers.
I’ll ping Chris who can tell you which distribs carry it. You should be able to get 12mm sheets which will be sufficient.
MDF is not a great speaker building material. The 12mm quality ply will outperform 3/4” MDF.
dave
You might think about making them in modular groups of six. With cabinets having positive mechanical connections to one another via brackets or maybe even rods that go through them. That simplifies construction and keeps is small and easy to manage. You can transport it too. Or if a talker ceiling is available add more?
Agreed. For perfect execution, put a bit of inductance in series with the resistor to simulate the same impedance as an SB65. Otherwise the ones in series with the resistor will have a slight rising response. About 0.05mH should do it.
Not sure I get it.
A line of 35 drivers will have a particular efficiency, and the wiring will determine the voltage sensitivity.
Ending up with a ~5ohm impedance will be fine for any 4ohm amp, and will still be way more sensitive than a single 4ohm driver.
Plus, resistors don't have impedance swings at low frequencies. A simple resistor will result in uneven power distribution to the rest of the drivers.
Chris
There isn't a great deal in it between either AFAIK. The 7x5 should have a minor drop in sensitivity vis-a-vis net efficiency (about 1.4dB) but purely keyed off the factory T/S data will still be around 98.7dB [nearly] in the array gain BW. A single power resistor substitution doesn't tend to have a massive impact in an array (I've done it with fewer units too when obliged) although in theory you're correct; since either work I'd probably do 7x5 myself as you've got a slightly higher impedance & it's (very slightly) simpler as no addional resistor is needed.
With my Modified CBT24 array background, I have a great deal of experience dealing with the SB65 drivers. My modified CBT24 units exhibit all the goodness of a long straight array yet add the benefit of constant beamwidth with near constant bandwidth to take things over the top. Inside my 32 feet long by 23 feet wide living room the CBT24s sound great with the 18 feet ceiling apex. I'm 6'3" tall and I have exceptional sound standing, sitting, or moving around the room.
I had help along the way with Kevin Kendrick's assistance on the enclosure construction as you can read in:
Jim's new CBT Arrays -
Techtalk Speaker Building, Audio, Video Discussion Forum
Notice the discussion and photos about the internal brace/nutplate. The nutplate provides an excellent way to attach the baseplate to the array towers. A substantial baseplate was essential for my arrays and will be for your straight array.
Mounting and attaching the SB65 drivers pose challenges which need some thinking to resolve before you cut wood. The SB65s are tiny! I specified 0.5 inch thick MDF for the cabinets which helps to improve the ability for the driver to have room to breathe within the mounting holes. You will need to improve the cutouts via reliefs around their rear exits and perhaps even chamfer cuts on the top mounting surface. With thicker material--say 0.75 inch--you will remove more wood around the holes.
I cover the assembly of my arrays in my Modified CBT24 thread on DIYaudio at:
My New Line Array--It's a Modified CBT24
Read about the discussion on soldering vs. crimp clip attachment of wiring to the drivers. I recommend the crimp clips (assemble with great care) and agree with Patrick Bateman's comments on soldering.
Good luck!
Jim
I had help along the way with Kevin Kendrick's assistance on the enclosure construction as you can read in:
Jim's new CBT Arrays -
Techtalk Speaker Building, Audio, Video Discussion Forum
Notice the discussion and photos about the internal brace/nutplate. The nutplate provides an excellent way to attach the baseplate to the array towers. A substantial baseplate was essential for my arrays and will be for your straight array.
Mounting and attaching the SB65 drivers pose challenges which need some thinking to resolve before you cut wood. The SB65s are tiny! I specified 0.5 inch thick MDF for the cabinets which helps to improve the ability for the driver to have room to breathe within the mounting holes. You will need to improve the cutouts via reliefs around their rear exits and perhaps even chamfer cuts on the top mounting surface. With thicker material--say 0.75 inch--you will remove more wood around the holes.
I cover the assembly of my arrays in my Modified CBT24 thread on DIYaudio at:
My New Line Array--It's a Modified CBT24
Read about the discussion on soldering vs. crimp clip attachment of wiring to the drivers. I recommend the crimp clips (assemble with great care) and agree with Patrick Bateman's comments on soldering.
Good luck!
Jim
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Probably right to skip it but getting extra +1.4dB extra sensitivity for cost of $1 resistor is quite a good value.
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