APRIL 2004

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PROJECT MAY
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April 9 - TimG

Now measuring MTM array. I'm computing a network for computer digital crossover simulation right now. I will simulate crossovers so that I can listen to the large, difficult to move, tower stack as an MTM and TMM, level match, and switch relatively quickly between the two simulated networks.

Horn is at 43.5 inches from floor currently. Each woofer edge starts at 1.875 inches from horn baffle edge. The horn is 11" high and you know the woofers measure 15.25". Woofers are currently 30" apart, but they will end up closer together when I have the H9800 horn. I wanted to get the 2380 flush with the front so 30" is what I have to work with for now.


 

 


April 22 - TimG

I began listening tests today on the mono prototype tower. It took me a while to get the digital crossover emulator working without problems, but now I am able to listen to the tower array with a variety of crossovers.

I will likely not be able to recruit a pair of arms to help set up the array in stereo until Sunday, but I do have some results to report. Just to remind everyone, the 1500AL woofers are each mounted in a 4 cu ft sealed box with baffle dimensions of 19" H x 21" W. Two woofer cabinets are stacked at the bottom with an 11" x 21" subcabinet for the horn placed above the woofers. A third woofer cabinet in placed on top. The center of the horn is 43.5" from the ground. If people are concerned about the horn height, I'm still looking into the horn throat at that height. The horn is a JBL 2380A and the compression driver is a BMS4590P with an attached network that crosses over from the midrange to the tweeter at around 6200Hz. The center to center distance on the woofers is 30" when the system is wired as an MTM. The two lower woofers are 19" apart when the cabinet is wired as a TMM.

On to listening tests. Dynamic range will not be a problem with the project May. The test amp produces 70watts into an 8ohm load and somewhere around 100watts for the 4ohm load presented by the system. I can't remember how much power Don has available, but I would think that 200watts per side should provide adequate headroom.

I did a quick and dirty crossover at first, using 3rd order electrical networks with 4th order LR acoustic crossovers at 800Hz, just to make sure the filter emulator was working. The second crossover included some notch filters to smooth out the response. I still need to work on smoothing the response above 12kHz.

The systems were auditioned with a variety of live and studio music from Van Morrison, Ben Harper, Diana Krall, Miles Davis, Smashing Pumpkins, Morcheeba, and Radiohead.

Based on initial listening, in mono remember, both the MTM and TMM arrays sound excellent. There was very little difference in the sound field when I was seated 7ft from the speaker. I could hear a difference between the two speakers when I did the sit-down stand-up test. Specifically, I could hear a recess in the response with the MTM, but I could not say that one array sounded significantly better than the other. When seated it was a toss up.

I will work on getting help moving the system to another room so that I can conduct stereo listening tests this weekend with a few more sets of ears. I have found at least 1 volunteer and I can hopefully convince his wife to listen as well. They are both music teachers. My wife says everything she hears sounds good, but she always objects to everything being too loud. I bet I'm not the only one who has heard that comment.

I will post images of the response graphs directly below this post. The images show screen captures of the crossover schematics and the response being produced by the crossover, at 1M, on the horn axis. The component values may be too small to view.

I think its time to start measuring the 435Be's. I have found a horn similar enough to the H9800 to at least start listening to them. If nobody objects I will order a pair from Parts Express, along with the port tubes, and some 1.5" to 1" throat adapters from JBL.

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=260-094


First 800Hz crossover before notch filters


Second 800Hz xover with notch filters


3rd attempt