# EL70 Surround Speaker Show and Tell



## mwmkravchenko (Jul 11, 2009)

Hello gents.
Coolest thing was when I order Floyd Tooles book on sound reproduction and found that I could really learn something from the simple a coherent manner in which he explained what mattered in speaker design. It turns out that for a surround speaker they should create a controlled diffuse pattern. In other words there should be a pattern of sound reproduction that basically looks like two cantelopes back to back. A cardioid pattern. The only way I knew of approximating that was to mount drivers at an angle. To get the proper pattern it takes four of them. If we hang this on a wall near ear level we get a double cardioid pattern that looks like this:











I made a bunch of these in the winter for a lark. They turned out to be quite well designed.










There's a whole bunch of photos on http://s407.photobucket.com/albums/pp160/mwmkravchenko/SURROUND SOUND SPEAKER/?start=0

Hope you find it interesting.

Mark


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## johnnyfamous (Jan 21, 2009)

i like! what volume are you running each el in? it looks small:heehee:


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## mwmkravchenko (Jul 11, 2009)

> what volume are you running each el in? it looks small


About 2.5 litre gross. It rolls off a little high. But there are ways to help this out. First off there are 4 drivers. Second they are loaded into a true infinite baffle when they are hung on a wall. Third I tune the vent down to 40 hz and it actually sounds pretty good. You are off the speakers axis when listening to them. The resulting hump in the frequency response when listening on axis is attenuated to the point that it actually sounds rather flat. More neutral actually is a better term. All in all this is doing what it is supposed to. The great part of this pain in the butt design is that you cannot localize where the sound is coming from. That is according to Floyd Toole exactly what you want from a surround speaker.

Mark


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## Mike P. (Apr 6, 2007)

It's 2.5 liters tuned to 40 hz but the graph you posted is for sealed.


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## mwmkravchenko (Jul 11, 2009)

> It's 2.5 liters tuned to 40 hz but the graph you posted is for sealed.


To many EL70 boxes designed in WinISD. I picked the wrong one. The good news is that it looks the same except for the low end. The low end prop up was what I was writing about in the previous post but the graph does not support it. My whole day has been one long Doooh! Here is the right graph. Good catch Mike Thanks!

As mentioned the minus 10 db level is still respectable. Four drivers coupled together in a 1 Pi acoustical space and the low end will look a lot better. Not clean to 40 hz but at least 60hz. Should put together the last couple of boxes I still have and measure them for real. Time I only wish I had more time. MUhahhahahahaaa

Mark


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## mwmkravchenko (Jul 11, 2009)

I dug up the old impedance plot of the single driver measurement.










Away down near 30hz there is the second bump. I've been modeling this and I think if I push it up to 45hz which is still pretty low I will get almost flat response down to 50 with the 4 drivers and the hemispherical loading off the wall. Should sound a bit more punchy. We all like punchy right?

Mark


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## mwmkravchenko (Jul 11, 2009)

Can you tell I failed math a couple of times???

The volume for each section of the enclosure is 5.28 litres. The driver takes up the .28 and the stuffing medium weight makes up for the loss in the port volume. So I'm sticking with 5 liters. Some times I wonder where my brain goes :scratch:

But this measurement is verified with some actual number crunching I checked instead of relying on old WinISD files. To many of them. The response is below. It is tuned to 60 and the minus 3 db point is at 60 just like the doctor ordered. I knew my ears couldn't be that far off. 

Now a fine gentleman is working on some oh so cool sketchup renderings of this box. This will be a real treat to present.

When it gets a little warmer I will do some good measurements of this box for all to see.

Mark who can add when it counts :rofl2:


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