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Built the digital crossover block diagram today for the Megaliths. Will have to adjust the servo sub to line array levels with measurements.

Have an idea for speaker and room correction measurements.

The Boston Audio Society uses a measurement technique for measuring in room frequency response by making measurements at the listening position over a 1 foot cube. The mic is placed at the vertices of the cube and in the center position from what I have seen described. The idea is to do the same for the correction measurements.

Going to get some 1 foot rulers and make a measurement cube for repeatable mic placement for the measurements. Will need a mic clip to hold the mic on the rulers in position and have some ideas of how to do that.

The other idea is a measurement sphere of the same diameter, but harder to do unless the mics are imbedded into the sphere for minimize surface reflections.

The last batch of FPS planars arrived today from PE. They just put them in plastic bags in the boxes with no separators. The magnets stuck together and into the planar and surround. Three planars and surrounds were damaged. Sent an email to PE to ask for three replacements.

It's always something!

Very much not like PE. Let me know the outcome as I have some contacts there but I would like to see how they resolve it first.

Tom

Will do. Waiting on a response.

Thought for the day distributed amplification for a segmented line array.

Normally to drive a segmented line array, the drivers have to be connected as series/parallel combinations to make an impedance that stock amplifiers can drive. When two drivers are connected in series, the sensitivity of the pair is the same as one driver with increased power handling capability. When two drivers are connected in parallel, the sensitivity goes up by 6dB for the pair. This is at the expense of the impedance now being 1/2 the original value.

If I were to take 8 - BG Neo10 planars and put them all in parallel, the sensitivity would go up by 18dB if they are all well matched drivers. In real life, it will be less than that due to differences. The problem is the new impedance for the amp to drive is 1.33 Ohms. Not something most amplifiers like to see as a load.

Now if each BG Neo10 that has a 6 Ohm impedance has it's own amplifier, then the sensitivity increase is the theoretical 18dB increase at the expense of 8 amps. With today's solid state Class AB amps, that is not a great expense and can have great sound quality. The amps only have to be capable of driving one driver to full potential, not the entire array. Instead of one 600w rms amp capable of 1.33 Ohm load drive, you have 8 - 75watt rms amps driving 6 ohm loads. That is the approach I am using.

What would be problematic about doing a combination of series connected pair parallel connected to another series connected pair and so on

That is what is typically done, but you still loose the sensitivity by not having them all either in parallel or driven independently.

To give you an idea, 8 - Neo10, the standard sensitivity is 92dB/1w/1m. With all 8 in parallel or driven independently the sensitivity would be 110dB/1w/1m. That is theoretical, but they are pretty well matched drivers and should be close. If you series/parallel 2 or 4 drivers, you can get a 3 Ohm or a 12 Ohm load. Now the sensitivity is either 104dB or 100dB, not bad, but still not as good. The amp needs to be either 300w rms or 150 w rms now as well. Also that method is not as well suited for the beamforming crossover as with having an amp per driver.

Please remember that the sensitivity increases you're talking about only apply to VOLTAGE sensitivity, not power sensitivity....

Roscoe

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I can explain it to you, but I can’t understand it for you.

Not quite true on the sensitivity. The SPL goes up by 6db but the power consumed doubles so the actual sensitivity goes up 3 dB on a per watt basis. The common mistake today is to measure sensitivity at 2.93 volts but it should really be at 1W. That is done based on a marketing decision that all modern amps double their output when the impedance is halved which is rarely the case. The specs look better that way. Even for those amps that do, double the power does not give comparible sensitivity measurements.

Tom