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Author Topic: Overpowering a horn on EV QRX 212/75  (Read 5935 times)

Chris Immanuel Hutagalung

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Overpowering a horn on EV QRX 212/75
« on: March 02, 2015, 03:21:09 AM »

Hi folks,

I have some newbie question here since I am a beginner in a live sound. So I have EV QRX 112/75 which rated,
HF Power Handling : 75W @ 8 Ohms
LF Power Handling : 300W @ 8 Ohms

And I have 2 Amps to drive them
CAMCO D-POWER 2 for the LF : 700W @ 8 Ohms
CAMCO D-POWER 1 for the HF : 250W @ 8 Ohms

My question here, would it be safe driving the HF with D-POWER 1 ? because its 3.3 times the power needed. A vendor here stated that since CAMCO D-POWER is a Class D amplifier, it is safe to drive the HF because Class D only supplies the power as much as the speaker needed automatically. Thanks again for the insights. I really appreciate it
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chuck clark

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Re: Overpowering a horn on EV QRX 212/75
« Reply #1 on: March 02, 2015, 03:44:46 AM »

Well Chris, your vendor is either ignorant or a liar.
The what if's are: what impedance are the drivers, what frequency are you crossing into them at, and what is the average energy content of the signal?  These are all real time variables that affect the real world power handling of your drivers.
   The short answer is your amp should be fine to drive your hi's. Just use comp/limiters to avoid unsafe peaks and don't clip your inputs on the mixer and don't clip the outputs of your amps. This should result in years of happy sailing.  Best of luck!
Chuck
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Steve Bradbury

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Re: Overpowering a horn on EV QRX 212/75
« Reply #2 on: March 03, 2015, 09:12:50 AM »

Chris,

The only thing that you have not mentioned is what crossover or loudspeaker management system you are using. However, as long as you stick to the recommended settings for the crossover frequency and filter slope, and don’t push the system too far, you should be fine.

It could be argued that the vendor is sort of correct about amplifiers only providing the necessary power. Not knowing what exactly what was said, I can’t judge whether he was being deliberately misleading, somewhat dishonest, or just ignorant. However since he qualified his comment with “because it was a class D amplifier” I tend to think at least one applies.

An eminent physicist (Lawrence Krauss I think) once said that every time he explained some aspect of physics using words he was lying a little, because the true language of physics is maths. Unfortunately most people don’t speak maths very well and discussion boards are not well equipped for it either. The explanation below is no exception to this. That is to say it is a very simplistic view of what is happening, and as you dig deeper things can be explained differently and seemingly contradictory to what I write. Hopefully it is adequate to allay you worries.

If you assume the loudspeaker is a simple fixed load connected to the amplifier, the output power varies relative to the input signal voltage of the amplifier, so the loudspeaker is automatically getting the right amount of power to follow the input signal. With no input signal the output should be zero, even if the amplifier is rated at a zillion Watts. As you turn up the input signal the output voltage, and hence power, increases until you hit the limit of the amplifier which is what gives the rating (250W @ 8 ohms in your case).

Unfortunately the amplifier won’t automatically know how much power will damage the drive unit, so if the maximum output of the amplifier exceeds the rating of your drive unit it has the potential to damage it if you turn the level up sufficiently. The onus is on the operator to make that decision.

In my experience, high frequency compression drivers are about 6dB to 12dB more sensitive than low/mid frequency cones. If we take 10dB as an example (it makes the figures easier) the compression driver only requires one tenth the power of the cone to give the same output. So sending 300W to the low frequency would require 30W to the high frequency.

Assuming that you have got everything set up correctly, that above ratio applies whatever the amplifier power. Even with a 1KW amplifier on the compression driver it would only be putting out 30W to match the 300W needed for the cone.

So somewhat tenuously, the amplifier is automatically only putting out what power is required and having a 250W amplifier doesn’t mean it will be putting out 250W, which is what some people think.

For what it’s worth I use four channel power amplifiers so that both the compression driver and cone use exactly the same amplifiers. In the last 15 years I have only damaged two compression drivers. That was the result of recalling the wrong settings on my crossover and putting a full range signal through them. I’ve never damaged anything simply because the rated output of the amplifier was much greater than the rating of the drive unit. However, I can’t say with 100% certainty that it won’t happen in the future, just that I am confident that it is unlikely.
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Ryan Grandusky

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Re: Overpowering a horn on EV QRX 212/75
« Reply #3 on: March 05, 2015, 09:49:26 AM »

Steve is on the money. You will ultimately need less signal to the HF (112db 1w/1m) to create the same sound level as the 12's (101db 1w/1m).

I have pushed my QRX 115 horns (same HF) with the RMX 850 which is 200w at 8ohm for years and never had a problem. I use a Driverack 260 processor on my QRX setups with settings based off of EV's recommended DBX settings and have proper limiting setup although I have never had to push into limiting.

IIRC the EV settings for the HF crossover for the 212's output gain is -6db. With more amplifier power you may find you need to run this at -7db or more to maintain a properly balanced sound between the mids and the highs. As Steve explained this will help keep you from producing to much power to the HF as you will likely not drive a signal into the HF amp causing it to create its rated power. Of course you will still need to pay attention to ensure this is the case, limiters only go so far.


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Ryan "Squirrel" Grandusky
Sound Provider in Central Texas.
Speakers: RCF HDL6a, NX-L44a, 8006-AS, EV XLD281, QRX153, QRX115, ZX1, SB122, XSUBS, JBL PRX835w, SRX828SP, Yorkville LS2100P, EAW SM200, Macpherson M12P, Yamaha A12M.
Consoles: Digico SD12, SD11, Soundcraft Si Perf 1, Exp 3, Comp 24, Midas M32, Presonus SL 32SX, SL 16r, Mackie DL1608

Bob Leonard

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Re: Overpowering a horn on EV QRX 212/75
« Reply #4 on: March 05, 2015, 10:31:16 AM »

Chris,
Your key to success will have more to do with the proper installation, setup, and use of a crossover, regardless of power available. It is the crossover or DSPs job to limit the amount of power through gain settings that are allowed to power the compression driver. It is the crossover or DSPs job to provide that power to a frequency above the lower limit, and below the upper limit, of the compression drivers capability and manufactures recommended settings. Not only will the DSP or crossover settings be key to the sound of your system, but also critical to the longevity of the compression driver and other components that make up the system in it's entirety.

Keep in mind that the Camco amplifiers you purchased are great amplifiers, but they have NO DSP control other than low pass filters, and the filters provided as a feature of these amplifiers ARE NOT a replacement or substitute for a properly configured DSP.

Your first step, before powering these cabinets, should be to obtain a proper DSP capable of supporting the combination of amplifier/cabinets you have chosen, and properly configured using the manufacturers recommended or provided DSP settings.

Setting the sensitivity for the amplifier is not a factor in limiting power output of the amplifier.
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BOSTON STRONG........
Proud Vietnam Veteran

I did a gig for Otis Elevator once. Like every job, it had it's ups and downs.

Chris Immanuel Hutagalung

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Re: Overpowering a horn on EV QRX 212/75
« Reply #5 on: March 15, 2015, 10:54:19 PM »

Steve is on the money. You will ultimately need less signal to the HF (112db 1w/1m) to create the same sound level as the 12's (101db 1w/1m).

I have pushed my QRX 115 horns (same HF) with the RMX 850 which is 200w at 8ohm for years and never had a problem. I use a Driverack 260 processor on my QRX setups with settings based off of EV's recommended DBX settings and have proper limiting setup although I have never had to push into limiting.

IIRC the EV settings for the HF crossover for the 212's output gain is -6db. With more amplifier power you may find you need to run this at -7db or more to maintain a properly balanced sound between the mids and the highs. As Steve explained this will help keep you from producing to much power to the HF as you will likely not drive a signal into the HF amp causing it to create its rated power. Of course you will still need to pay attention to ensure this is the case, limiters only go so far.

Hey ryan im glad to see an EV user in this forum. I am planning to run this setup (QRX115/75 TOPS and QRX218S SUBS) at my church and I am biamping it with CAMCO D7 on SUBS, CAMCO d2 on the TOP LF and DAMCO D1 on the TOP HF. Do you have any crossover suggestion on this system? Btw I am using XTA DP448 as the Speaker Management System.
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Chris Immanuel Hutagalung

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Re: Overpowering a horn on EV QRX 212/75
« Reply #6 on: March 15, 2015, 10:55:43 PM »

Chris,

The only thing that you have not mentioned is what crossover or loudspeaker management system you are using. However, as long as you stick to the recommended settings for the crossover frequency and filter slope, and don’t push the system too far, you should be fine.

It could be argued that the vendor is sort of correct about amplifiers only providing the necessary power. Not knowing what exactly what was said, I can’t judge whether he was being deliberately misleading, somewhat dishonest, or just ignorant. However since he qualified his comment with “because it was a class D amplifier” I tend to think at least one applies.

An eminent physicist (Lawrence Krauss I think) once said that every time he explained some aspect of physics using words he was lying a little, because the true language of physics is maths. Unfortunately most people don’t speak maths very well and discussion boards are not well equipped for it either. The explanation below is no exception to this. That is to say it is a very simplistic view of what is happening, and as you dig deeper things can be explained differently and seemingly contradictory to what I write. Hopefully it is adequate to allay you worries.

If you assume the loudspeaker is a simple fixed load connected to the amplifier, the output power varies relative to the input signal voltage of the amplifier, so the loudspeaker is automatically getting the right amount of power to follow the input signal. With no input signal the output should be zero, even if the amplifier is rated at a zillion Watts. As you turn up the input signal the output voltage, and hence power, increases until you hit the limit of the amplifier which is what gives the rating (250W @ 8 ohms in your case).

Unfortunately the amplifier won’t automatically know how much power will damage the drive unit, so if the maximum output of the amplifier exceeds the rating of your drive unit it has the potential to damage it if you turn the level up sufficiently. The onus is on the operator to make that decision.

In my experience, high frequency compression drivers are about 6dB to 12dB more sensitive than low/mid frequency cones. If we take 10dB as an example (it makes the figures easier) the compression driver only requires one tenth the power of the cone to give the same output. So sending 300W to the low frequency would require 30W to the high frequency.

Assuming that you have got everything set up correctly, that above ratio applies whatever the amplifier power. Even with a 1KW amplifier on the compression driver it would only be putting out 30W to match the 300W needed for the cone.

So somewhat tenuously, the amplifier is automatically only putting out what power is required and having a 250W amplifier doesn’t mean it will be putting out 250W, which is what some people think.

For what it’s worth I use four channel power amplifiers so that both the compression driver and cone use exactly the same amplifiers. In the last 15 years I have only damaged two compression drivers. That was the result of recalling the wrong settings on my crossover and putting a full range signal through them. I’ve never damaged anything simply because the rated output of the amplifier was much greater than the rating of the drive unit. However, I can’t say with 100% certainty that it won’t happen in the future, just that I am confident that it is unlikely.

Thank you steve for your kind insights. it is really helpful
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Ryan Grandusky

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Re: Overpowering a horn on EV QRX 212/75
« Reply #7 on: March 16, 2015, 10:42:48 AM »

Hey ryan im glad to see an EV user in this forum. I am planning to run this setup (QRX115/75 TOPS and QRX218S SUBS) at my church and I am biamping it with CAMCO D7 on SUBS, CAMCO d2 on the TOP LF and DAMCO D1 on the TOP HF. Do you have any crossover suggestion on this system? Btw I am using XTA DP448 as the Speaker Management System.

As a crossover starting point:

The factory tunings I have seen from EV for the different QRX setups call for the horn to be crossed over around 1.3khz and low passed around 17khz with LR24 type filters and a -7db output gain.

The 15" mid is recommended to be crossover at 91hz with the 218 subs and 1.3khz with the HF with LR24 and a 0db output gain.

The 218 subs should be high passed at 35hz BW12 MINIMUM (I recommend a steeper slope and a high pass closer to 40hz) and crossed over at 91hz LR24 to the mids with a 0db output gain.

It may be worthwhile to contact EV (Bosch) to see if they have tunings for your model processor just in case they do.
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Ryan "Squirrel" Grandusky
Sound Provider in Central Texas.
Speakers: RCF HDL6a, NX-L44a, 8006-AS, EV XLD281, QRX153, QRX115, ZX1, SB122, XSUBS, JBL PRX835w, SRX828SP, Yorkville LS2100P, EAW SM200, Macpherson M12P, Yamaha A12M.
Consoles: Digico SD12, SD11, Soundcraft Si Perf 1, Exp 3, Comp 24, Midas M32, Presonus SL 32SX, SL 16r, Mackie DL1608

Chris Immanuel Hutagalung

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Re: Overpowering a horn on EV QRX 212/75
« Reply #8 on: March 17, 2015, 12:36:31 AM »

As a crossover starting point:

The factory tunings I have seen from EV for the different QRX setups call for the horn to be crossed over around 1.3khz and low passed around 17khz with LR24 type filters and a -7db output gain.

The 15" mid is recommended to be crossover at 91hz with the 218 subs and 1.3khz with the HF with LR24 and a 0db output gain.

The 218 subs should be high passed at 35hz BW12 MINIMUM (I recommend a steeper slope and a high pass closer to 40hz) and crossed over at 91hz LR24 to the mids with a 0db output gain.

It may be worthwhile to contact EV (Bosch) to see if they have tunings for your model processor just in case they do.

Awesome .. thanks a lot ryan...
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ProSoundWeb Community

Re: Overpowering a horn on EV QRX 212/75
« Reply #8 on: March 17, 2015, 12:36:31 AM »


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