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Hi!From the soundpractices article, the Hiraga xover attenuates 1k-5k about 12 db.
288G is rated about 109 db spl/1w/1m, while 288 16K is 115 db. a difference of 6 dB.
I was thinking to play around with the attenuation of the Hiraga x-over equalization section that had a 6.6 mH parallel 24 ohm parallel 0.82 uF and the entire section in series with the driver.
1. I interpret this equalization circuit as follows:
a.) 0.82 uf allows the high frequencies above ?? 12.5 kHz ?? to bypass attenuation
b.) 6.6 mH allows the lows below ?? 500Hz ?? to bypass attenuation.
To play with the attenuation, i will have to change the 24 ohm resistor. But if I do so the impedance presented to the crossover in the preceding section (10uf series, 6.6mH parallel with driver), will change and therefore the xover point will shift?Can anybody help?
Does this mean Ill have to learn Spice?
Angelo
Follow Ups:
Hi Angelo
I've not used SPICE but ECAP is very intuitive - you just draw a schematic on paper, number nodes ,describe line by line using R, L, C, etc with these nodes then plot - FET model with rp placed across cathode/anode is fine for simulating tube circuitsfor RTA - you can get a free one octave version of TrueRTA and details to upgrade at resonable cost here:http://www.trueaudio.com/
Hi Angelo, I built the 16 ohm version Hiragas several years ago, and used them happily for a while. My math is pretty shaky when it comes to the time constants, but it is possible to figure them using the formulae in the original SP article. There is also another way to determine what your crossover is doing. You can feed a constant voltage AC signal from an audio generator to the input, while terminating the driver outputs with the proper resistors- i.e. 16 ohm resistors for a 16 ohm network. Measure and plot the output voltages at various frequencies, and you can see what the network is actually doing as you make changes.Of course, the wild cards are still the drivers' varying sensitivity at different frequencies, plus the patterns of the horns used, so SPL testing in the listening room with the mic at your listening spot is really helpful if possible. I have found it necessary to potentiometers of several times the speaker impedance (50 ohms for 8 ohm driver, 100 ohm for 16 ohm driver) in series with the driver leads to permit final level matching- not the last word in impedance matching, but works well in practice.
Steve,The original SP article on the VOT A5 didnt have the formulas. Ill get my hands on an RTA and measure first to confirm what i think im hearing.
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