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Zilch's AK Design Collaborative - Econowave Speaker

Steve O said:
But in most DA designs aren't the LF drivers in parallel? If so, each has the same voltage across it so power input to the LF section is doubled, thus the +3dB increase in (assumed) voltage sensitivity cited.

Thought experiment: Assume I have a speaker that produces 90dB with one watt of input under some set of specified conditions. By what's been offered so far, every doubling of the number of speakers results in +3dB increase in level (not sure if were talking sound power level or sound pressure level here). Now assume I have 1024 identical speakers each capable alone of 90 dB. 1024 is 10 doublings so now I have a system capable of 120dB @1W or taking it the other way 90dB @1mW. This doesn't seem reasonable. Taken to an admittedly absurd limit, an infinite number of speaker would be capable of 90dB with zero power input. What am I missing here?
Click to expand...

More than just the voltage. Regardless of the voltage, the woofer only has to use up 1/2 as much of its x-max to belt out the same level than it did with only one. Perhaps someone else can put this more "scientifically" than I.

Russellc
 
Not me, but the impedance goes down in parallel.
IIRC Dickason says 2 pairs of paralleled woofers in series gives 3dB more output acoustically, but compared to a single paralleled pair, the output is electrically halved. So that means no net gain.

:scratch2:
 
An increase in efficiency only occurs as a result of mutual coupling. As Russell says, two drivers in close proximity will behave as a single with twice the cone area. Since the electromagnetic driving force has also been doubled, we can mathematically relate this to a doubling in efficiency. (I am paraphrasing Eargle and Foreman here.) Thus, at VLF, (relative to the driver diameter,) the same power input (independent of the requisite voltage) will produce 3 dB greater output SPL. Above the region of mutual coupling, the output remains the same as with a single driver.... :yes:
 
Zilch said:
At very low frequencies, mutual coupling gives us an additional 3 dB; the pistons behave as one.... :yes:
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Like say, specifically near, or at, the resonant frequency? Has to be a 50% reduction in frictional losses to get 3dB with the same power. Otherwise we'd have cold fusion! :banana:
 
Zilch said:
An increase in efficiency only occurs as a result of mutual coupling. As Russell says, two drivers in close proximity will behave as a single with twice the cone area. Since the electromagnetic driving force has also been doubled, we can mathematically relate this to a doubling in efficiency. (I am paraphrasing Eargle and Foreman here.) Thus, at VLF, (relative to the driver diameter,) the same power input (independent of the requisite voltage) will produce 3 dB greater output SPL. Above the region of mutual coupling, the output remains the same as with a single driver.... :yes:
Click to expand...

I can't see this as a true increase in efficiency. I do see the plausibility of improved coupling or impedance match betw dirver and air but.......There are obviously subtlties here I'm not getting. If you've got some references you can point me to, I'll take this off line and figure it out on my own time.

Thanks
 
EWave NLA

My waveguides finally arrived today from JBL.

I have been very anxious to join the group listening to EWaves.

I have an old, beat on, set of New Larger Advents with the bull nose.

I thought I could fit the waveguide without too much grief.

After work, I went out to the garage and fired up the power tools. I was able to cut the correct opening in the Advents with my jigsaw. Now came the fun.

I very carefully removed 1/4" of the plastic from each side of the waveguide.

Lo and behold, it actually fit!

picture.php


One cabinet down. I'll work on the other tomorrow.

Of course, after not using the Advents for a few months, I discovered that the foam had rotted out in one woofer. I ordered a refoam kit last week.

More to come.
 
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Steve O said:
I can't see this as a true increase in efficiency. I do see the plausibility of improved coupling or impedance match betw dirver and air but.......There are obviously subtlties here I'm not getting. If you've got some references you can point me to, I'll take this off line and figure it out on my own time.

Thanks
Click to expand...

It's not an increase in efficiency of one of the woofers, but it is for a pair of them acting together. Two woofers also doubles the box size - so you're not getting your 3 dB more output for nothing! No rules of physics are broken ...
 
Wayne1 said:
I very carefully removed 1/4" of the plastic from the sides of the waveguide.

Lo and behold, it actually fit!
Click to expand...
1/4" from each side, or total?

I looked at this recently and determined on the ones I had, at least, notching the vinyl bead at the baffle would reduce the interference to ~1/8" on each side, which could be relieved by undercutting. It'd have to be 1/4" on one side to allow an unmodified waveguide to slip easily into place.

As I recall, the bead stopped about 1/4" from the baffle on this particular pair, so even that step was unnecessary.

Are my calcs consistent with your measurements?
 
Zilch,

I cut away 1/4" on each side.

I did not measure under the beading. It is very probable that 1/8" per side would work.

I preferred to cut the waveguide rather than notch the beading. My tools and abilities are fairly clumsy.
 
I'm not criticizing your approach, rather, merely suggesting options. I suspect others may be wanting to do this once yours are complete, and we'll be linking them here for ideas as to how to accomplish it.

Anyone with a router table or access to a milling machine could easily shave the edges as well. I'll post a pic of the tool I'd use for the undercutting approach. There may be an appropriate router bit readily available, too.

It certainly tucks neatly in there, I must say.... :thmbsp:
 
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You are absolutely correct, Zilch.

A band saw or even a table saw could easily shave the plastic off the waveguide sides.

I will work on the other speaker tomorrow. I will try the 1/8" shaving first.

Thanks for all your help.
 
packrat said:
...No rules of physics are broken ...
Click to expand...

:D "We hold these truths to be self evident" Otherwise this would be witchcraft, not speakercraft!:thmbsp: Just trying to wrap my mechanical engineering background around a corner of the discipline where I have no professional experience. Certain principles - like conservation of energy - will serve you very well in practice. May not give you the answer you want, but it will tell you where the answer cannot be. Of course in loudspeaker design we cross the energy-conversion bridge from the dark art of electronic circuits into the complex issues of compressive fluid flow (air is a fluid to us :yes:) and resonant frequencies. Great stuff.
 
De-250:

Is:

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-6 dB at 1330 Hz. Where do Geddes and Parham run them?

What's 6.8 uF and 0.8 mH calc for nominal 8 Ohms?


Was:

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Wayne1 said:
My waveguides finally arrived today from JBL.

I have been very anxious to join the group listening to EWaves.

I have an old, beat on, set of New Larger Advents with the bull nose.

I thought I could fit the waveguide without too much grief.

After work, I went out to the garage and fired up the power tools. I was able to cut the correct opening in the Advents with my jigsaw. Now came the fun.

I very carefully removed 1/4" of the plastic from each side of the waveguide.

Lo and behold, it actually fit!

picture.php


One cabinet down. I'll work on the other tomorrow.

Of course, after not using the Advents for a few months, I discovered that the foam had rotted out in one woofer. I ordered a refoam kit last week.

More to come.
Click to expand...

You're going to love the way that sounds. I found that the bass on my converted LA's was 'loose' unless I loaded the cabinets pretty heavily, but YMMV.
I really like the way those WGs fit in the cabinet.
Personally, I'd have gone after the edge of the waveguide on a disk sander to take off just as much as material as necessary. It's quicker than a Bridgeport and you have quite a lot of control with zero setup except for taping off the surfaces.
Speaking of taping off surfaces, I had to cut the WG cutout really close to the rim of the cab. I worked out that I could do it with a jigsaw resting on top of the rim (rather than against the baffle surface) if the saw blade was more than 3" long. I taped up the edge to prevent scraping it. It takes a steady hand but it's totally doable. Works even better if you have an assistant vacuuming off the sawdust so you can see where you're going.
 
Z;
Regarding the charts in post 4878, what changes did you make to get from the 3/2 response to the 3/11 response?
Change to 6.8 uF and 0.8 mH?
 
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