Calibrating Modular Towers

walter duque

walter duque

Audioholic Samurai
My modular towers are designed to be passive bi-amped. I can run them also with one amp (and they do sound better that way). Now my question is: I am using the RCA outputs (from pre-pro) to run the tops and the XLR out puts to run the bottoms. Now the Krell manual states that the XLR outputs put out 6 db more gain then the RCA out puts. My amps all have gain knobs. How can I calibrate these speakers properly. Turn gain knobs to the bottoms down (but how much), calibrate tops and bottoms individually or get a Y-splitter and run them all either off RCA or XLR outs.
 
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AcuDefTechGuy

AcuDefTechGuy

Audioholic Jedi
You're talking about hooking the pre-pro to the amp?

It depends on the modular tower.

Is your modular tower two completely separate speakers when you remove the jumper cables? This is how the RBH T-system and SX-6300/8300 towers are. When you remove the jumper cables, the bass is completely separated from the treble/midrange drivers. If this is the case, then it would not matter if the gain is different. You would just calibrate the top (treble/midrange) as speakers and calibrate the bottom (bass) as subwoofers.

But if the modular tower is designed so that it is just one full-range speaker (like the Phil3), then I would use splitters and do either all RCA or all XLR because of the gain difference.
 
walter duque

walter duque

Audioholic Samurai
You're talking about hooking the pre-pro to the amp?

It depends on the modular tower.

Is your modular tower two completely separate speakers when you remove the jumper cables? This is how the RBH T-system and SX-6300/8300 towers are. When you remove the jumper cables, the bass is completely separated from the treble/midrange drivers. If this is the case, then it would not matter if the gain is different. You would just calibrate the top (treble/midrange) as speakers and calibrate the bottom (bass) as subwoofers.

But if the modular tower is designed so that it is just one full-range speaker (like the Phil3), then I would use splitters and do either all RCA or all XLR because of the gain difference.
Like I said these are designed to be passive bi amped but can also be hooked up by just using one amp. There are no jumpers. When using full range hook up I have to use one of these


between the tops and bottoms and then run the speaker inputs to the bottoms and they work great that way, but since I got these extra channels I would like to make use of them.
 
AcuDefTechGuy

AcuDefTechGuy

Audioholic Jedi
Like I said these are designed to be passive bi amped but can also be hooked up by just using one amp. There are no jumpers. When using full range hook up I have to use one of these

between the tops and bottoms and then run the speaker inputs to the bottoms and they work great that way, but since I got these extra channels I would like to make use of them.
Then it appears your modular tower is designed to be just 1 full-range speaker. In this case, you would want to stick with either all RCA or all XLR (using splitters). You don't want to use different gains.
 
walter duque

walter duque

Audioholic Samurai
Then it appears your modular tower is designed to be just 1 full-range speaker. In this case, you would want to stick with either all RCA or all XLR (using splitters). You don't want to use different gains.
Thanks for you input, that's what I figured but wasn't sure. BTW your recommendation to set my crossover to 100 worked great.
 
AcuDefTechGuy

AcuDefTechGuy

Audioholic Jedi
Thanks for you input, that's what I figured but wasn't sure. BTW your recommendation to set my crossover to 100 worked great.
Yeah, XO point is so variable. You just have to try different settings and pick one that seems best. :D

When I get my new RBH, I will try 80Hz-150Hz. If I think it seems to sound best @ 100Hz, 120Hz, or 150Hz, then that's what I'll use even if 80Hz seems to sound best to most people. Every case is different. :D
 
slipperybidness

slipperybidness

Audioholic Warlord
I believe that even though the gain (Av) is higher on XLR vs. RCA, the actual output voltage will be the same. It has to do with the voltage on the input signal being different on the XLR vs. RCA, so the gain must be different, but the output is not.

I can look into this more, but I don't have time now. Perhaps TLS will chime in.
 
AcuDefTechGuy

AcuDefTechGuy

Audioholic Jedi
I believe that even though the gain (Av) is higher on XLR vs. RCA, the actual output voltage will be the same. It has to do with the voltage on the input signal being different on the XLR vs. RCA, so the gain must be different, but the output is not.

I can look into this more, but I don't have time now. Perhaps TLS will chime in.
On my ATI amps, the RCA is 34dB gain and XLR is 28dB gain. When I use RCA, the speaker SPL levels are definitely higher than when I switch to XLR (manual SPL meter check).
 
slipperybidness

slipperybidness

Audioholic Warlord
On my ATI amps, the RCA is 34dB gain and XLR is 28dB gain. When I use RCA, the speaker SPL levels are definitely higher than when I switch to XLR (manual SPL meter check).
Hmmmm.

Do you have a 6dB difference as measured with the SPL meter??? Or even 3dB difference?

Let's assume you are feeding an amp a single ended signal. Then, if you go to a differential signal, the peak-to-peak voltage will double. For a doubling of Voltage, that would be 6dB (a doubling of power is 3dB). So, it makes sense that XLR would have 6dB less gain, because the input is 6dB "hotter" on differential as compared to single ended.

So, I would expect that the output should be the same.
 
AcuDefTechGuy

AcuDefTechGuy

Audioholic Jedi
Hmmmm.

Do you have a 6dB difference as measured with the SPL meter??? Or even 3dB difference?

Let's assume you are feeding an amp a single ended signal. Then, if you go to a differential signal, the peak-to-peak voltage will double. For a doubling of Voltage, that would be 6dB (a doubling of power is 3dB). So, it makes sense that XLR would have 6dB less gain, because the input is 6dB "hotter" on differential as compared to single ended.

So, I would expect that the output should be the same.
It's been a while since I did manual calibration with trim levels. But it seemed like when I changed RCA vs XLR, I had to also adjust the trim levels on the same speakers. Perhaps it was something else. I just remember having to adjust the trims when I switched. :D


Now the Krell manual states that the XLR outputs put out 6 db more gain than the RCA outputs.
I wonder why the Krell XLR has 6dB more gain than RCA?

Shouldn't it be the other way around?

Perhaps Walter can measure the SPL between RCA and XLR. If they measure the same, then it would just fine to use both RCA & XLR. ;)
 
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slipperybidness

slipperybidness

Audioholic Warlord
I wonder why the Krell XLR has 6dB more gain than RCA?

Shouldn't it be the other way around?

Perhaps Walter can measure the SPL between RCA and XLR. If they measure the same, then it would just fine to use both RCA & XLR. ;)
Yeah, I was kinda scratching my head on that one too. I know that we had another really good thread on this exact same topic a while back.
 
walter duque

walter duque

Audioholic Samurai
from manual:

Balanced
A symmetrical input or output circuit that has equal impedance from
both input terminals to a common ground reference point. The industry
standard for professional and sound recording installations, balanced
connections have 6 dB more gain than single-ended connections
and allow the use of long interconnect cables. Balanced connections
are immune to induced noise from the system or the environment.
 
slipperybidness

slipperybidness

Audioholic Warlord
from manual:

Balanced
A symmetrical input or output circuit that has equal impedance from
both input terminals to a common ground reference point. The industry
standard for professional and sound recording installations, balanced
connections have 6 dB more gain than single-ended connections
and allow the use of long interconnect cables. Balanced connections
are immune to induced noise from the system or the environment.
Well, it wouldn't be the first time I have found a mistake in a manual or in a text book.

I think that isn't quite correct. I think it should read "balanced inputs have 6dB more voltage" and not "more gain".

I'll look into it a little more and try to dig up that thread from a few weeks ago too. In the meantime, maybe Gene or TLS will chime in on the topic.

What is the model of Krell we are discussing? The one in your sig? Do you have the spec sheet handy for it?

Edit: OK, you could also read that quote from the manual as "the balanced inputs have 6dB more gain", and that would make sense. That doesn't mean the output has 6dB more gain.
 
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slipperybidness

slipperybidness

Audioholic Warlord
Let's run through an example. The limit of an amp or pre-amp for the output before clipping is determined by the supply rail voltages, and not by the gain. The gain is just the ratio or Vout / Vin.

Let's assume the maximum output of an amp is 20V peak to peak, and the amplifier has a "very high" gain (meaning enough gain to drive it into saturation/clipping). If we feed the input a 1V peak to peak single-ended signal, then the output will be 20V peak to peak (the upper limit of Vout). Now, if we feed it a 2V peak to peak differential signal, the max output is still limited to 20V.

So, the gain of the single ended input = 20V/1V = 20 (or 26dB), and the gain of the differntial input = 20V/2V = 10 (or 20dB). Thus, the voltage gain of the differential input is 6dB lower than the single ended input.

On the other hand, the input equation would be 20log(2V/1V) = 6dB, thus the input is 6dB "hotter" for a diff input as compared to the single ended input, but the gain is 6dB lower.

I'm sure this will get peer-reviewed soon enough, but I believe this is all correct. BTW, I took solid state last semester and am currently taking Linear IC (Op-Amps) this semester. So, I'm still learning too.
 

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