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Main Speaker System:

4/9/09: 

Frequency response measurements:

  Click for larger view.  The measurement location is stated in the lower left.

One of the next things on the to do list is to start installing room treatment material.  I think maybe that can clean the above response data up some.  I've also ordered ARC for my Anthem D2 so it will be interesting to see what it can do for me.  Overall, the sound quality from seat to seat seems really uniform.  Also, standing or sitting seems to make little difference as is expected with a long, "line array" such as this.

The following data was taken a couple days earlier and the setup of the Behringer crossover was slightly different than in the measurements above but this shows the uniformity of the measurement comparing at a sitting level and a standing level.  Actually the standing level measurement was beyond standing, the mic was close to 6.5 ft off the floor.

Microphone placement for measurements.  One measurement taken at each seat of each row using Earthworks M30 microphone..

3/28/09:

The lines are playing and while not completely dialed in, I have to say they are sounding pretty spectaular!  I did make a major change in the design.  The original plan was to use drivers on both the front and the rear to operate as a dipole.  Instead, I have left off the rear drivers and inserted batting material and Owens Corning 703 fiberglass insulation so as to operate as a cardioid. 

To mount the 2" Aura drivers I just glued them in place with RTV.  The 6" drivers are compressed between foam tape gaskets and rubber grommets.  As you can see in one of the construction photos the grommets simply go between the driver flange and an aluminum bar that holds everything in place.  This actually worked out quite well! 

The dynamic capability of these things is astounding!  The Anthem P2 amplifier can deliver 325 watts into 8 and 500 into 4 ohms.  The forty two 2" drivers are wired in six series groups of 7 in parallel for a total of about 6.8 ohms.  So perhaps this works out to be about 350 watts/42 or 8.3 watts per driver.  Given the 84 dB/1 watt efficiency of the drivers and the 32 dB gain of having forty two of them playing, the total output will be about 116 dB at 1 watt per driver.  Add another 9 dB or so at 8 watts/driver and one line is exceeding 125 dB not including room gain.  So, output of over 130 dB is possible.  I would never want to hear it that loud!  The point however is that if you are listening to an average level of 90 dB, you have near 40 dB headroom for dynamics.

The 6" drivers are wired in three series groups of six in parallel for a total of 4 ohms.  Given the 500 watt into 4 ohm capability of the P2 amplifier this comes out to about 27.7 watts/driver.  Given the 87 dB sensitivity and about 25 dB gain from having eighteen of them we get about 112 dB with 1 watt/driver.  At 27.7 watts/driver that's about 126 dB not including room gain.

I got these playing on the day before leaving on this trip to New Mexico so I didn't have much time to enjoy them but I did listen to some music and I checked out a few movie scenes.  The gun fight scene in Open Range was pretty spectacular.  I use to own a .45 and fired it once without ear protection. (big mistake!) So, I have an idea how dynamic a gun shot like that can be.  At the level I was listening it wasn't that intense but it wasn't far from it and I had a lot of headroom to have cranked it up.  It seems Hollywood adds a little to the low end of the shots for more impact so that took away from my memory of the actual .45 shot but that's ok.  It was really intense and makes for a really intense experience to watch that gun fight scene.

Construction photos: 

1-27-09:  Parts cutting for the lines has begun...actually it began over Thanksgiving but I just now got around to posting photos.  

7/23/08:  The main speakers have not been built yet but the plan is an infinite line using the Dayton Reference truncated frame 6" Reference drivers.  It will be a symmetrical dipole with 18 of the 6" drivers in the front and another 18 in the back.  High frequency will be handled by 42 of the Aura 2" drivers in front and another 42 in the back.  This is the same 2" driver used in the Linkwitzlab "Pluto".

7/26/08:  Just sitting here drawing up ideas for this thing I'm considering truncating it a bit.  I would like to limit the height to match the top edge of the screen.  Also I don't really see a need to run especially the 2" drivers all the way down to the floor.  In the drawing below I have limited it to sixteen pairs of the 6" drivers and thirty six pairs of the Aura 2" drivers.  I really think this is probably adequate. 

7/27/08:  One note about the 2" Aura drivers.  These are little reverse domes with a very large pole vent being the only escape to the outside world in the rear of the driver.  This vent along with the air mass behind the reverse dome forms essentially a ported baffle tuned to about 1,7 KHz.  If used in open air this driver has a very large 1.7 KHz peak as a result.  I will be mounting them back to back in a very thin fiber filled enclosure.  This will effectively eliminate the peak.  For this project, I already have 100 of the Dayton 6" drivers on hand but I have not ordered the Aura 2" drivers.  I've continued instead to search for an alternate solution.  If I find something else better then this design may change.  It's just that right now these have proven the best solution for the 600 ~ 700 Hz range up to about the 2 ~ 3 KHz range.  Conventional conical drivers, even very small ones have too many issues with non pistonic cone motion in this range.  Also, the air mass between the cone and frame seems to be an issue.  I believe there are also some resonances going on with this air mass being partially captured by the frame causing frequency response irregularities and stored energy issues.