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In the Forum: Horn-Loaded Speakers
In the Thread: Jessie Dazzle Project
Post Subject: Cap dancingPosted by jessie.dazzle on: 7/8/2008
Romy wrote :
"...And with 1600 pound per channel you might forget about the DPOLS … -
..."
No, 1600 lbs per channel would be really serious!
1600 lbs is the total combined weight of the Left and Right channels, with frames, (the frames turned out to be kind of heavy). Then entire installation is on wheels (including electronics and lower bass enclosures), and is very easy to move, if one happens to be on smooth, level ground.
"...change the way you use RTA. You must not look at 80dB window...You need to found for yourself a reasonable resolution and stick to it... I personally use 1dB you might go higher or lower, but you need to see your .5-1dB very deistically. Use 10dB-16dB window... it is very important to found a convenient RTA window and resolution and never change it... go for 12dB window and .5dB horizontal markers..."
Yes I already do understand the importance of establishing a default resolution/sampling rate for RTA comparisons; I will take your advice on the range and resolution. If I get you correctly, the graph should display a range of around 12dB from top to bottom, in .5dB steps... Yes?
I don't have the RTA here with me, so can't refer to the all the possibilities it offers right now (will do it tonight). I do know that I had the sampling set for 1/6th octave, weighted for "White Noise"... I noticed that you use a non-logarithmic graph (in the previous post I used a graph that is supposed to correspond to the sensitivity of our hearing, exposing in greater detail the range where we hear best... I don't like this idea).
"...Your must to select for you’re a metal reference level – you must not balance the system abstractedly. The reference level in your case would be the main plot of your MF channel. I marked it Red on your TRA..."
I understand this to mean an average of the output of the MF horn, being subjected to a swept, and outputting at normal listening volume.
"...The MF is fine but it has quite strong bottom output down to 500Hz and rolls off too soon at HF. What distance you measured it and how much off axis the mic was? Was Mic calibrated at HF?..."
Measurement distance was about 6 feet back from the mouths of upper-bass horns and centered between the L and R stacks of horns (this is a plot of both upper-mid horns playing together... You will probably tell me that I should have tested a single horn, which is what I usually do). The mic is supposed to be calibrated, its not very old, and it has not been abused. The HF rolling off could be due to the fact that I was not on axis, or that both horns were playing; I also suspect the tone generator... I've been using a little computer program which seems to do ok until it hits the HF range, at which point I can hear it going a bit nuts. The computer sends the signal to the DAC, the same as if it were a music file. I also have a Tektronix tone generator, but have not dared connect it to either the preamp or directly to the power amps. I guess its just a question of measuring the strength of the output signal from the tone generator to make sure I don't fry something in the audio gear (any advice here would be very appreciated).
"...Since you have a dedicated Fundamental Channels I would cut the bottom response of MF Channels. Go for 2.7-3uF cap making the electrical crossover point around 4K. This will bring the acoustic crossover point of MF to ~ 1000Hz and would save a lot of necessary excursion at MF driver..."
Easy enough, I have the necessary caps.
"...Bring the Fundamental Channel 3-8dB lower - I do not see at your resolution how much – until the 500-900Hz region hit the Reference Level..."
"...Make the band-pass more narrow, decreasing the HF extension from the Fundamental Channel..."
"...It will be a coil around 2.7mH that would make 900Hz. Buy 3 or 4 of them, the cheapest ones, and then listen the MF and Fundamental Channels combined, while taking the turn out of the coil. Approximately around 2.3mH or 1000-1100Hz you might found it works better..."
That will have to wait until the weekend when I can get to the place where I buy coils.
"...a good 16R LPAD would help a lot..."
Up to now I have been superstitious about using anything with resistors directly in front of a driver; but I could maybe mix up a double martini and give it a try.
"...Find what to cross your Fundamental Channel at the bottom. It will depend how much your horn will tolerate without being choked with honk. Do not forget that at the range of the Fundamental Channel’s bottom knee the room maters..."
Yes, make that a tripple martini if I am going below 500Hz, 1st order...
Thanks Romy for all the help, I mean it; I know it takes time to respond.
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