Straight Line Array SB65WBAC25-4

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As a follow up to the impedance question: as it stands now with the speakers you presently use, how much of your volume do you *actually* need? Back that out and see how high of an impedance your speakers could be run to get your volume control near(er) to its max part of the dial.

Most systems have too much gain/sensitivity and output power for one's need. You'll have pretty good efficiency with that many drivers. Might as well present an easier load to your amp if you already have more than enough headroom and regain a bunch of your end-to-end signal to noise ratio (by turning the volume knob up). Modern amps will happily swing most of their rail-to-rail voltage, especially into a 16+ ohm load. Minimizes crossover distortion too. :)
 
It absolutely does not provide efficiency. Electrical watts in vs acoustic watts out will be lower with a resistor. It's a question of voltage sensitivity pure and simple.

I'm recommending the OP use this flexibility in setting the speaker impedance to be in the best band of his volume control. There's no point in setting up a 4 or 8 ohm array when, with the efficiency gains afforded by array make it such that he can't turn the volume knob much past it's minimum.
 
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DPh, yes my mistake - meant to say sensitivity in dB/V input. As Scott Moose pointed out it’s 1.6dB more and apart from extra bit of sensitivity - it makes it a proper square based 6x6 series parallel. I don’t believe one should ever purposely build a speaker to lose sensitivity per V on purpose to match the gain of a typical amp. Most Class A amps actually have more distortion as voltage drive goes up and they tend to have lower gain than Class AB amps.
 
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As a follow up to the impedance question: as it stands now with the speakers you presently use, how much of your volume do you *actually* need?

I don't actually need that much, want is another matter:D. hehe anyways kazap got me thinking. Going to pick up some 1/2" mdf to do some testing. Combined with reduced cutout size and 1mm reduction in CTC spacing I'm going to test if I can squeeze 36 drivers upright on my space. That seems like it might be the best compromise for the array I wish to build.

I would like some options for testing out differences in shading and a delayed type CBT. With a 6 section floor to ceiling array you could use the bottom 3/4 of the array to test/configure a delayed CBT as outlined in the keele paper. Since the wiring is long and intensive I'd like to minimize the number of times I have the array open. Will do some testing today:cheerful:.
 
Final layout and sectioning

All fears gone! Made a test baffle 94.5" high and 5.5" wide. Looks like it will go in without scraping the ceiling therefore:

Per side:
- 36 drivers
- 6 drivers per sealed section.
- 6 sections.
- 65mm Centre to Centre spacing.
- 1/2 inch front panel and 3/4 inch everywhere else. Euro Birch used.
- 1/2 inch internal section bracing and routed out near the openings.
- Rough outside dimensions, 5.5" wide by 12.5" in depth and 94" height with out base.
- Pressure fit top and bottom with foam/wood base OR mount to ceiling.

Per section:
- 2 drivers in parallel + 3 pairs in series = 6ohms nominal for each section.
- speaker terminals to the rear for each section.
- No rear access panels. I will use a tool to tighten rear speaker terminals to enclosure after finishing is complete.

Total line nominal impedance = 9 ohms or 4 ohms depending on wiring. If shading required then each section will be connected to its own amplifier. Section delays and level reduction done digitally or at the line level.

Time to start the enclosure! This will take some time as I'm slow and don't have a lot of extra time to work on it. Will be using quick connects (without the plastic ends) to connect wire to the speaker terminals. Thinking grey enclosure to match the silver/grey of the SB65 cones........maybe black.......
 
- Pressure fit top and bottom with foam/wood base


Brilliant idea. You wont need a base plate at all and it should be more rigid anyway.



Time to start the enclosure!


What do you think of the idea of building the enclosure from just one sheet of 1/4inch pre-sanded ply using Kerf bending and compound curves for rigidity and low resonance?
 
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- 2 drivers in parallel + 3 pairs in series = 6ohms nominal for each section.
- speaker terminals to the rear for each section.
- No rear access panels. I will use a tool to tighten rear speaker terminals to enclosure after finishing is complete.

Hmmm... not so sure I agree you should wire 2p/3s per box. You now have a mathematically perfect 6s/6p option and I would wire each box all series and connect all 6 with a solid 10ga copper bus that runs through the holes on a 5way binding post all in parallel.
 
What do you think of the idea of building the enclosure from just one sheet of 1/4inch pre-sanded ply using Kerf bending and compound curves for rigidity and low resonance?

Good idea and one I'd like to explore at a later date but way beyond my mechanical skill level. The garage is not big enough to rip the 4x8 sheets of BB properly nevermind kerf cuts. There are some really great woodworkers on this site but definitely not me.

I almost want to contract out the enclosure out but I've collected too much of the material already. If I really mess this up I might have to do that in the end. This will be my first and last enclosure of this size hehe (I hope). Most of my builds are prototypes as I don't enjoy woodworking that much :).
 
Hmmm... not so sure I agree you should wire 2p/3s per box. You now have a mathematically perfect 6s/6p option and I would wire each box all series and connect all 6 with a solid 10ga copper bus that runs through the holes on a 5way binding post all in parallel.

I agree with you 100% but I do want the option of driving each section individually which would put each section at 24 ohms nominal. Do you think most amplifiers would be ok driving this high impedance? I believe more voltage than usual would be required to drive each section at 24 vs 6 but I'm open to options before doing the final wiring.

I'd like to not open the array again to rewire. Also I don't want to run each driver out the back of the array as that would be too messy for me. If doing a straight, unshaded array I would do the 6s/6p as that just feels right.
 
Do some quick napkin math to find out where you have your volume knob now with your present speakers and, given the new setup, what impedance would work to have a similar output at roughly 75% of your volume knob. Almost (there's always an exception) all voltage-source amplifiers will be happier with a higher impedance load. Your global SNR will markedly improve as you turn the volume knob up.

I'm betting your 4/9 ohm configuration will work out just fine, with odds that the 9 ohm will be the winning proposition (maybe the 36 ohm option! ;)). You have a lot of efficiency on tap, so your amplifier needs will drop markedly.
 
I have a class D multichannel amplifier with an output stage tuned for 4 to 8 ohms. In the back of my mind 6s/6p seems like the way to go so initially I will do a straight array (4 ohms), if/when I get to a multichannel implementation I'll make up the rest of my boards for 24 ohms nominal or go with a different amplifier. Too many compromises :) but such is this hobby!!
 
Ug! That is a lot of holes!
 

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When I read the AudioMachina XTAC white paper today I thought about your baffle view photo. In fact the XTAC 2.4 m (93.75" high) system offers a total of 36 2" diameter drivers vs. your 36 2.5" diameter drivers. Of course your system will cost less than one hundredth of the XTAC's cost.
 
When I read the AudioMachina XTAC white paper today I thought about your baffle view photo. In fact the XTAC 2.4 m (93.75" high) system offers a total of 36 2" diameter drivers vs. your 36 2.5" diameter drivers. Of course your system will cost less than one hundredth of the XTAC's cost.

Thank you for the white paper resource. I took a cursory read of the paper and it does seem very similar to my proposed build, save the corner loading. I believe member RA7 did a corner array based on the TC9FD with positive results. Interesting to see a commercial build that is similar. Will do some more reading about the XTAC speaker. I'm guessing we are ahead in surface area by a tiny tiny bit.
 
(I did the comparison of a part of a music wave shape and actual acoustical response with my system too :D)

That would a fun test! Questions, wouldn't any speaker system with a flat phase and frequency response be able to do what the white paper is claiming? With FIR filter correction a great many systems can be made to have a flat frequency and flat (close to 0) phase shift over the 20-20khz range.
 
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