Coytee Posted March 1, 2020 Share Posted March 1, 2020 Over on AK, I told someone they can balance their biamped speaker by using the 20*Log(V1/V2) where V1 and V2 are the respective input sensitivies of each amp. Calculate the difference and attenuate the more sensitive amp by that many db's. https://www.audiokarma.org/forums/index.php?threads/bi-amping-question.904938/page-2#post-13553036 Starts on page 2. I'm wondering if one of us (usually me) is a bit confused... so at the end I'm asking him for some real numbers so we can do a side by side... if I'm wrong, I want to know what/where so I don't mislead anyone. Quote Link to comment Share on other sites More sharing options...
glens Posted March 1, 2020 Share Posted March 1, 2020 I have a hard time remembering when/whether to use 20x or 10x, but an iteration usually clears it up. Looks right so far from here with the available info (none). Didn't follow the link... Add: would be easier to use the overall gain, in dB, of the amps, wouldn't it? Quote Link to comment Share on other sites More sharing options...
JohnA Posted March 2, 2020 Share Posted March 2, 2020 20*Log(V1/V2) is the equation for voltage ratios, but I think It is a little more complicated. In addition to input sensitivity, each amp will have its own gain and they are likely different. So, starting with your equation is fine, but may only get him close. No substitute for a SPL meter. 1 Quote Link to comment Share on other sites More sharing options...
efzauner Posted March 2, 2020 Share Posted March 2, 2020 This is not that complicated. I think we have to be careful what is meant by gain. Attached is the gain chart for my SA9500 amp. Note the input sensitivity at Power Amp IN is specified as 1 Volts to provide rated output power of 85 watts into 8 ohms. This is shown on the chart as 1V = 0dBv at the input of the PA OdBv is referenced to 0V so in this case dBv= 20 Log (V PAin/0V) This gives a Vout of the PA of 26.1V that corresponds to 85W into 8ohms if you use P= V^2/R Gain is Vout/Vin. In dB this is 20xLog (Vout/Vin). = 20 Log (26.1/1) = 28.3 dB. So when I mean be careful of what is meant by gain is that if gain is Vout/Vin to provide maximum rated power you are not going to match your levels. What you need to do is find gain for all your amps for an equal Vout given identical Vin. For example, you want all your amplifiers to provide the same output voltage for a given input voltage. If amp A (for you HF section for example) provides 10v out for 1V in, it is a voltage gain of 20dB If amp B (for your LF section for example) provides 20V out for 1V in, it is a voltage gain of 26dB and you would have to use 6dB of attenuation. Note that Amp B provides 2x the voltage. You could use a simple voltage divider circuit using 2 10Kohm resiistors in series. Voltage gain in dB works for any impedance. That is why the chart uses voltage gain because input and output inpedances change in the circuit. If you do not have such a chart then you could determine gain yourself with an audio generator (your laptop or phone and an online audio generater!) and voltmeter If you use power gain, which is 10 x Log Pout/Pin you have to calculate power using voltages and resistance. In this example, without using any attenuation to equalize the amps: Amp A at 10V out into 8 ohms gives you 12.5 watts Amp B at 20V into 8 ohms gives you 50 watts. the power difference between amp B and amp A is 10 x Log 50/12.5 = 6 dB the same as the voltage gain! now all of this assumes equal impedance and sensitivity drivers which is rarely the case! You would have to take both into account and back calculate the PA voltage into the drivers to provide same SPL, and then provide the right attenuation at the input of the PA to equalize them. Have fun! E Quote Link to comment Share on other sites More sharing options...
JohnA Posted March 2, 2020 Share Posted March 2, 2020 Yes, but, ........ Coytee stated he had input sensitivities and did not say he had amp gains. Quote Link to comment Share on other sites More sharing options...
babadono Posted March 2, 2020 Share Posted March 2, 2020 3 hours ago, JohnA said: No substitute for a SPL meter. Or a UMIK and REW with a computer. 1 Quote Link to comment Share on other sites More sharing options...
Coytee Posted March 2, 2020 Author Share Posted March 2, 2020 Not being an engineer.... I'm smiling and concluding that I indeed, was operating with half the picture. (can't say that was unexpected) Quote Link to comment Share on other sites More sharing options...
Edgar Posted March 2, 2020 Share Posted March 2, 2020 13 hours ago, glens said: I have a hard time remembering when/whether to use 20x or 10x This will either clear things up, or make them even more confusing: Just remember that dB is always a ratio of powers: dB = 10 * log10(P2/P1) Also remember that power is equal to voltage squared divided by resistance: P = V²/R So P1 = V1²/R and P2 = V2²/R and dB = 10*log10(P2/P1) = 10*log10[(V2²/R)/(V1²/R)] = 10*log10(V2²/V1²) (the "R" cancel-out) = 10*log10[(V2/V1)²] Taking the logarithm of an exponent is equal to multiplying the logarithm by the exponent: 10*log10[(V2/V1)²] = 2*[10*log10(V2/V1)] = 20*log10(V2/V1) Quote Link to comment Share on other sites More sharing options...
Deang Posted March 2, 2020 Share Posted March 2, 2020 "There are three kinds of people in the world. Those who can do math and those who can't." 1 2 Quote Link to comment Share on other sites More sharing options...
ClaudeJ1 Posted March 2, 2020 Share Posted March 2, 2020 25 minutes ago, Deang said: "There are three kinds of people in the world. Those who can do math and those who can't." Actually there are 10 kinds of people in the world, those who understand BINARY and those who don't. 2 Quote Link to comment Share on other sites More sharing options...
glens Posted March 2, 2020 Share Posted March 2, 2020 6 hours ago, Edgar said: This will either clear things up, or make them even more confusing: Yep. It either will or it won't. Actually, the case of voltage vs. power is not terribly difficult (as I'd said, an iteration usually makes it obvious). Have you got a rule of thumb for sound pressure vs. sound power? Would it be safe to consider "power" involves "something squared" in all cases, as a rule of thumb? 1 hour ago, Deang said: "There are three kinds of people in the world. Those who can do math and those who can't." Too funny! Sounds like something Mark Twain would've said. Who was it? Quote Link to comment Share on other sites More sharing options...
Edgar Posted March 2, 2020 Share Posted March 2, 2020 2 hours ago, glens said: Have you got a rule of thumb for sound pressure vs. sound power? Yeah -- I always have to look it up. Quote Would it be safe to consider "power" involves "something squared" in all cases, as a rule of thumb? Well, "something times something"; voltage times voltage, voltage times current, current times current, etc. 1 Quote Link to comment Share on other sites More sharing options...
Deang Posted March 3, 2020 Share Posted March 3, 2020 19 hours ago, glens said: Too funny! Sounds like something Mark Twain would've said. Who was it? I honestly don't know, I heard it back in high school. I googled it once and came up with nothing. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted March 3, 2020 Share Posted March 3, 2020 1 hour ago, Deang said: I honestly don't know, I heard it back in high school. I googled it once and came up with nothing. I know it's not but it sounds like a Yogism (Yogi Berra). Quote Link to comment Share on other sites More sharing options...
ClaudeJ1 Posted March 3, 2020 Share Posted March 3, 2020 1 hour ago, CECAA850 said: I know it's not but it sounds like a Yogism (Yogi Berra). My favorite Yogiism quote: "It's amazing how much you can observe just by watching." To keep it relevant to Klipsch speakers..........................the more a cone moves, the more distortion it produces. You just can't watch it when it's in a horn! 1 Quote Link to comment Share on other sites More sharing options...
Dave A Posted March 3, 2020 Share Posted March 3, 2020 1 hour ago, ClaudeJ1 said: My favorite Yogiism quote: "It's amazing how much you can observe just by watching." To keep it relevant to Klipsch speakers..........................the more a cone moves, the more distortion it produces. You just can't watch it when it's in a horn! Why yes you can with a remote camera!! SAOTWU Quote Link to comment Share on other sites More sharing options...
ClaudeJ1 Posted March 3, 2020 Share Posted March 3, 2020 2 hours ago, Dave A said: Why yes you can with a remote camera!! SAOTWU PWK showed me the Khorn that was built out of plexiglas in the original Hope museum, across the street from the factory, back in 1985. They did Laser Interferometry measurements to show the K-33's motion to be within calculations' predictions of only about 0.060 (1.5 mm) Xmax when the horn was blowing out 120 db of output. This is why I never worry about recommending the Kappa 15C woofer (2.5mm Xmax) for LaScalas, Belles, and my own Quarter Pies bass horn as superior and more affordable than all the rest of the options. Quote Link to comment Share on other sites More sharing options...
Marvel Posted March 5, 2020 Share Posted March 5, 2020 On 3/1/2020 at 7:38 PM, JohnA said: Yes, but, ........ Coytee stated he had input sensitivities and did not say he had amp gains. He's a sensitive guy... 🙄 Quote Link to comment Share on other sites More sharing options...
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