Crown XTI Output

[dannyn]

Is there any way to measure the output of a Crown XTI amp in SystemArchitect. I built a Titan 48 and I do not want to over power the driver inside the cabinet.

Thanks,

Dan

 

[museav]

The simple answer, I don't think so. I believe that the Input and Output meters in System Architect for an XTi are showing the analog level hitting the amp input and the digital level after the digital signal processing but before the internal D/A and amp section.

Theoretically, the D/A and amp itself are fixed gain devices so ignoring non-linearities, distortion introduced, etc., there should be a direct relationship between the level into the D/A converter and the output voltage, however the associated current and power will be load dependent. That means that monitoring the actual output power would require monitoring the output voltage and current (or at least two of voltage, current and impedance), which gets more complex than just voltage.

Just for discussion, if you could monitor the output then to get the most effective use of that information you'd have to know what to monitor and the actual limits involved. What can the speaker can handle, not just the driver by itself but rather the speaker as an assembly, and what was used as the test stimulus to obtain those numbers? How does the live audio signal compare to the test signal used to obtain the speaker ratings and are you going to monitor RMS or average values that tend to relate to thermal failures, peak levels that might relate more closely to mechanical failures or both? While the amp output might potentially be very beneficial information, if you're going to use that information to determine how hard you can run a device then you would need to consider what you want to monitor and how that relates to the actual limits of the speaker.

This is why integrated systems like those from d&b and Nexo as well as the processing in some powered speakers can get so complex as they are often assessing multiple factors and applying potentially different actions based on each or on specific combinations. I recall one manufacturer commenting that the processing in some of their powered speaker products included over 20 compressors and/or limiters in order to address the multiple relevant factors for the multiple drivers.

 

[dannyn]

Thanks for the post! I really appreciate it! So per Crown USA you cannot do this unfortunately. If you could find the number of ohms the speaker is performing at you could set up a certain test to figure it out. He said if you set up a sine wave test(this would have to be done on an iTech) and set it to say 60hz for a subwoofer and measured the voltage and used system architect to measure the R value you could use p=v^2/r. So basically they said what you just said. There way for monitoring the impedance was if you have an iTech there is a way to monitor it in System Architect. Do you know of any other way?

I know the speaker can handle a lot more than the drive I put in it. The driver is incredibly hard to get out of the speaker and seeing I did not even know if the cabinet design would work, I did not want to go all out on purchasing a nice drive until I could perform some testing.

So I guess for this test I just wanted to see how far I could push the driver without over driving it seeing it is especially hard to tell with this seeing it is a folder horn design when the driver has reached its limit.

Thanks for the post!

 

[dannyn]

Does anyone know of any other way to do this on an XTi rather than having the impedance ratings on the iTech's? Is that just for extreme precision, rather than using the ohm rating provided by the speaker manufacturer, or is does the ohm rating change enough to make a large difference during use?

Thanks!

Dan

 

[museav]

Does anyone know of any other way to do this on an XTi rather than having the impedance ratings on the iTech's? Is that just for extreme precision, rather than using the ohm rating provided by the speaker manufacturer, or is does the ohm rating change enough to make a large difference during use?

The chart in http://eminence.com/pdf/kappalite-3015lf.pdf includes the impedance for the Eminance 3015 driver that is often used in the Titan 48. Note that it ranges from a low of less than 7 Ohms at just under 200Hz to around 100 Ohms at about 42Hz (the resonance frequency of the driver). Now that is not accounting for the affect of the enclosure but for music styles or effects that might include longer term, single frequency content then the frequency involved could pretty obviously make a significant difference in the impedance the amp sees.

The reality is that a) you should be able to hear when the speaker starts reaching its limits and b) without significant additional circuitry about the only thing you can realistically control to protect the speaker is the voltage or amplitude of the driving signal.

Especially if you are using the Eminence driver you may want to look at this, http://www.eminence.com/d-fend/. Their immediate goal is to license the technology to speaker manufacturers and I know some speaker manufacturers were looking at it (in fact it was a speaker manufacturer that had me join them when they first looked at it at InfoComm), I'll see if i can get an update of their assessment. However, they also seemed interested in developing standalone versions that could be implemented in existing systems or systems that did not integrate the technology in the speakers.

 

[dannyn]

I actually used this kit, Titan Horn Loaded Subwoofers, Titan 48 Kit | Speaker Hardware with the driver being the Delta 15lfa. I just wanted to see if I could actually build the thing first and how it performed with a cheap driver. Do you think I would see a notable difference with the performance of the sub woofer if I did decide to go with a better driver? I am going to stick with single loading them so they are a better size for me.

So for the test, I was thinking of using an 70Hz sine wave on the sine wave generator in the amp, then measuring the voltage, squaring it, and dividing by 10. Does that seem correct?

Bill says in the directions:

You cannot hear the driver distort when you push them too hard. So, most people do not know when to turn them down. They push them till they break. It takes a while to get used to the extra clean sound of this cabinet and learn how hard you can push it.

That is really what prompted this for me and why I wanted to find out just how far my driver can be pushed without blowing it so see if it is worth it to build more and if I should load them with something better.

The D-Fend looks like a very cool piece of equipment.Thanks for the link!