# REW Connection and Cabling -no Amp to Speaker



## sawyer (Feb 10, 2013)

In the sticky: REW Connection and Cabling - I saw no mention of an Amp to Speaker connection

In the interest of performing measures at all staging locations why would that be omitted?

If a measure/capture is placed at that location. What would be the recommendation for the simplest, general, clean setup to have on hand to introduce the appropriate resistor value in that connection providing the correct level to the sound card? what guidelines should be observed in doing that. What impact would that have if any on speaker output if one also were to be observing speaker output (as well as speaker input/amplifier output which is what this setup would observe)


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## AudiocRaver (Jun 6, 2012)

sawyer said:


> In the sticky: REW Connection and Cabling - I saw no mention of an Amp to Speaker connection
> 
> In the interest of performing measures at all staging locations why would that be omitted?
> 
> If a measure/capture is placed at that location. What would be the recommendation for the simplest, general, clean setup to have on hand to introduce the appropriate resistor value in that connection providing the correct level to the sound card? what guidelines should be observed in doing that. What impact would that have if any on speaker output if one also were to be observing speaker output (as well as speaker input/amplifier output which is what this setup would observe)


Generally speaking, REW measurements for room correction are taken acoustically, and other than performing the sound card calibration, the electronic connections to AVR, to power amp (if separate), and to speaker are assumed to already be in place as they would be for normal system use, with no measurements taken at those points.

There is no reason that measurements cannot be taken at the amplifier output, just very little to be gained there compared to what is going on in the acoustical realm.

REW use for speaker designers/builders, with series R for measuring speaker impedance, is covered in the REW help files and in threads in our DIY Speakers and DIY Subwoofers forums.


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## sawyer (Feb 10, 2013)

Yes, there are large, safely, and easily obtained changes and gains to be made in the accoustical domain.

Since the soundcard or whatever capture device is used needs a specific voltage level input and the power is variable it involves obtaining/building a power amp load box which contains high power non inductive resistors. This needs to drop the voltage and it needs to do so without creating noise 

From a little googling, i see a suggestion that the power amp load box is connected across input speaker terminals with an additional parallel high-resistance voltage divider. The output to REW is taken across one leg of the divider.

I will have to check how the DIY speaker folks in another forum here approach the problem.


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## AudiocRaver (Jun 6, 2012)

If you decide to measure your amplifier output, use a voltage divider with values of 100Kohm and 1KOhm (both 1/4W), giving an output of 1/100th the speaker signal level to go into your sound card. With a 200W power amp into 8 ohms, you can have voltages of close to 60V pk at the amplifier output. With those divider values you would have 0.6Vpk into your sound card, assuming a line-level input.









I am a little surprised that you would be willing to go to the trouble for such measurements, did not mean to discourage it, just was not sure you were serious about doing them. While informative, they are beyond the scope of interest for most experimenters.

A very informative test would be measuring frequency response (or distortion) of the amplifier output voltage loaded by the actual speakers. Members have posted comparative frequency response curves of a speaker's output driven by different amplifiers, showing that they can be different. No one that I have seen has performed that test showing the amplifier's output voltage as loaded by different speakers - it should be easier to see variations at that measurement point. If you try it, it would be great to have you post your results.


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