# Amp clipping?



## Drudge (Sep 1, 2008)

I have a Mackie HRS120 subwoofer and I've become convinced that the amp is clipping and causing subwoofer distress on certain intense low bass scenes in movies.I had the gain on the back of the sub set to the 12 o'clock position and the Audyssey Pro/Sound Equalizer told me to set the processor trim to +1dB.I tried setting the sub gain to it's normal setting,which on the Mackie is all the way up and I lowered the trim on the processor (to get the correct SPL level)to -9dB.It did not seem to solve the problem.

Looking back over the sensitivity setting section of the Mackie manual it says:









Do I need to purchase a unbalanced to balanced converter to get pro levels of +4dBu into the Mackie?
I assumed that since the Mackie had RCA inputs along with the XLR's that it would accept a consumer level signal as well.Could this be the reason the amp is clipping?

Being that the Mackie is a studio grade subwoofer capable of outputing 117dB peaks it seems that it should be able to handle the MV listening level of -13dB that I use for movie watching.Do I need to just purchase a new sub?I've been looking into an Epik Empire,but I'm not yet sure that the Mackie is not adequate.

Here is the link to the Mackie manual for the specifications:http://www.mackie.com/pdf/hrs120_om.pdf


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## torceador (Sep 8, 2010)

Your Mackie has a Peak Limiter built in at the final stage. It is doubtful that you are clipping the output, as it has a circuit immediately before the power amp that automatically reduces gain to a safe level. The input stages, however, look like they can be overdriven, according to the schematic.

That said, your +4dBu translates to 1.22 Volts RMS, which is probably the MAXIMUM it wants to see on a fully modulated LOUD sound, not average program level. If you try to get normal program level up that far, explosions will indeed overdrive the inputs.

Play a test tone at 0dB that is in the subwoofer range of frequencies (LFE) with the cabinet disconnected and measure AC voltage at the SUB output port to see the amount of signal you have. 

If you have been clipping the Mackie's inputs, it will sound wierd, I promise.

Carl


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## Drudge (Sep 1, 2008)

torceador said:


> Your Mackie has a Peak Limiter built in at the final stage. It is doubtful that you are clipping the output, as it has a circuit immediately before the power amp that automatically reduces gain to a safe level. The input stages, however, look like they can be overdriven, according to the schematic.
> 
> That said, your +4dBu translates to 1.22 Volts RMS, which is probably the MAXIMUM it wants to see on a fully modulated LOUD sound, not average program level. If you try to get normal program level up that far, explosions will indeed overdrive the inputs.
> 
> ...


Hi Carl,

I don't have a multimeter to do any kind of voltage testing.The sub makes a clanging/rattling sound on deep high output level bass scenes.So,using the RCA jacks and a consumer level signal is fine and no need to use pro levels into the sub?


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## Mike P. (Apr 6, 2007)

Do you have the 15 hz subsonic filter engaged?


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## bambino (Feb 21, 2010)

I would say the crossover or filter is not set properly.:dontknow:


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## recruit (May 9, 2009)

I would say the trim on the processor needs to be around -5db and no less, then throttle back on the gain of the sub, but also agree with the above posts.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Drudge said:


> Do I need to purchase a unbalanced to balanced converter to get pro levels of +4dBu into the Mackie?


Like Carl said, +4 dBu is only 1.22 vRMS. The sub outputs of most receivers will put out way more than 1.2 vRMS with a 0 dBVFS signal. (0dBFS is the maximum input signal level that your receiver will see.) Assuming yours does too, there’s no reason to get a signal booster. In fact, you may well be overdriving the Mackie’s input.

Are you using any outboard equalization? That will decrease headroom.




> Being that the Mackie is a studio grade subwoofer capable of outputing 117dB peaks it seems that it should be able to handle the MV listening level of -13dB that I use for movie watching. Do I need to just purchase a new sub?


Keep in mind that the typical studio will be much smaller than the average home listening room. Depending on the size of your room, you may well need an additional sub.

Regards,
Wayne


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## Drudge (Sep 1, 2008)

I have the subsonic filter engaged and I'm using an Audyssey Sound Equalizer for EQ.Once I set up the Audyssey the sub was less prone to overload than it did before using the Sound Equalizer unit.My room is a small 15'x11'x8' space and the sub should still be able to put out over 110dB with room gain from what I've been told.

Are you guys saying that the sub would have a problem with consumer levels and they could be over driving the sub's inputs:scratch:?My processor will put out 6 volts at full +12dB over reference level,but I could never listen that loud!The max that I turn up the volume is -13db from reference.


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## Wayne A. Pflughaupt (Apr 13, 2006)

> Once I set up the Audyssey the sub was less prone to overload than it did before using the Sound Equalizer unit.


That could certainly do it, if the bass equalizing was too severe. I guess you have no way of knowing what kind of equalization the Audyssey is sending to the sub, huh?

Regards,
Wayne


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## Drudge (Sep 1, 2008)

Wayne A. Pflughaupt said:


> That could certainly do it, if the bass equalizing was too severe. I guess you have no way of knowing what kind of equalization the Audyssey is sending to the sub, huh?
> 
> Regards,
> Wayne


The sub actually performs with less distress with the Audyssey.When I was using parametric EQ and REW the sub was misbehaving more frequently on bass heavy material than it is now using the Audyssey,but it only ever happens on about 1% of the movies I watch.I would have to take about 24 measurements with REW for before and after measurements and average each of the 12 measurements to get an accurate picture of what Audyssey is doing.Audyssey's graphs are 1/3 octave smoothed and the after graphs are not actual measurements,but theoretical results based on it's inverse filters if they correct the response perfectly to what it determines to fix the response to it's target curve.

I'm waiting till I get the rest of my final room treatments ordered and put in place before I attempt that though.I have to schedule a long period of quiet time in the late hours to pull that off.


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## Drudge (Sep 1, 2008)

These are the before and after graphs that Audyssey provides at 1/3 octave.I don't have the midrange compensation selected anymore,so the dip in the 2-5Khz range is not there on my current target curve setting,which is set to flat.The sub is in the best position that I can place it in.


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## acoustat6 (Mar 7, 2008)

Those graphs are useless, do yourself a favor and upload the FREE program REW available right here on the wonderful Home Theater Shack to see what your system is really doing.

Bob


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## lsiberian (Mar 24, 2009)

acoustat6 said:


> Those graphs are useless, do yourself a favor and upload the FREE program REW available right here on the wonderful Home Theater Shack to see what your system is really doing.
> 
> Bob


Why do you think they are useless? They are showing response measurements and indicating some of the problems he's had. For example a null in upper bass region explains why he has a less stressed sub after EQing than before. You can see that he's probably cranking the overall volume higher to compensate for the lack of midbass. Once that's fixed he doesn't need to crank the overall volume so high. 

REW is a very helpful and powerful program, but there is more than one way to measure a system.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Yeah, the sub graph does show some pretty radical EQ, but we can’t tell much beyond that due to the lack of frequency markings. I mean, it looks like it might have been EQd all the way up to 4-500 Hz.  REW could sure tell us a lot more!

Regards,
Wayne


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## Drudge (Sep 1, 2008)

acoustat6 said:


> Those graphs are useless, do yourself a favor and upload the FREE program REW available right here on the wonderful Home Theater Shack to see what your system is really doing.
> 
> Bob


Hi Bob,
Those graphs are designed to give full range target curve measurements that equate to what you are most likely hearing.It doesn't show the actual high resolution correction that Audyssey performs,but it gives you about the same graph resolution that REW would set at 1/3 octave smoothing which is often suggested to see the overall full range frequency trend without the comb filtering.

I have used REW for several years,I just haven't got around to using it to measure with Audyssey on vs. off.It requires a lot of measurements and quiet time and the mics from both REW and Audyssey have to be put in the same locations repeatably,otherwise you won't get any accurate measurements.The Audyssey Pro mic is actually more accurate than the ECM8000 due to it being referenced to a B&K reference mic.



Wayne A. Pflughaupt said:


> Yeah, the sub graph does show some pretty radical EQ, but we can’t tell much beyond that due to the lack of frequency markings. I mean, it looks like it might have been EQd all the way up to 4-500 Hz.  REW could sure tell us a lot more!
> 
> Regards,
> Wayne


 Wayne,the graphs are from 20Hz to 20Khz,but Audyssey's correction capability(if your speakers have the capability)is 10Hz to 24Khz.The 3 darker vertical lines indicate 100Hz,1000Hz and 10Khz and the vertical ticks are 5dB per division.

The Audyssey Pro software only corrects to the -3dB point of the speaker as it measures in the room and it finds the optimum crossover frequency based on the combined room and speaker interaction measurement results.It won't correct beyond the speakers measured capability to prevent speaker damage,but no room correction algorithm is perfect.


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## Wayne A. Pflughaupt (Apr 13, 2006)

> Wayne,the graphs are from 20Hz to 20Khz,but Audyssey's correction capability(if your speakers have the capability)is 10Hz to 24Khz.The 3 darker vertical lines indicate 100Hz,1000Hz and 10Khz and the vertical ticks are 5dB per division.


 If that’s the case, Audyssey flattened your sub’s response all the way up to 300+ Hz. I think you could do better with an outboard sub equalizer.

Also, why are there different crossover frequencies with the front L/R speakers? And no crossover frequency for the sub?

Regards,
Wayne


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## lsiberian (Mar 24, 2009)

Audyssey does some interesting things from what I can see. I've heard it's a great program for fixing crossover issues and isn't as good at addressing room issues from one of my speaker building friends.


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## Drudge (Sep 1, 2008)

Wayne A. Pflughaupt said:


> If that’s the case, Audyssey flattened your sub’s response all the way up to 300+ Hz. I think you could do better with an outboard sub equalizer.
> 
> Also, why are there different crossover frequencies with the front L/R speakers? And no crossover frequency for the sub?
> 
> ...


I was using an outboard parametric EQ previously with REW,but the Audyssey sounds better to me.The crossovers for the L&R are different because the right main is near an opening,so less boundary gain which results in the 70Hz crossover suggestion.My surround processor doesn't allow independent L&R settings.

It was suggested by Chris at Audyssey to choose 70Hz for both.You can change the crossover to a higher setting than what Audyssey suggests,but if you choose lower than that there will be no correction below the suggested crossover point.Audyssey Pro doesn't suggest a crossover for the sub.


You set the sub crossover to the lowest crossover selected for the other speakers,in my case 50Hz,since my rears are capable down to that range.I thought that was a little strange:scratch:,but after talking to Chris about it he said this is where the crossover is optimized based on the "real in room measurements" and said I should leave it where Audyssey suggests.


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## Drudge (Sep 1, 2008)

lsiberian said:


> Audyssey does some interesting things from what I can see. I've heard it's a great program for fixing crossover issues and isn't as good at addressing room issues from one of my speaker building friends.


It depends on what implementation of Audyssey you have that determines the measurement resolution and the results you get.The unit I have is the stand alone Sound Equalizer.It is more powerful than any of the current AVR implementations,at least until MultEQ XT32 equipped units come out.The sub equalizer and the SVS AE-EQ1 stepped up the correction resolution from 256x(which is what the Sound Equalizer is currently using)to 512x with firmware updates.The abilities are also limited to how much of the capabilities the AVR manufactures are willing to implement.

It also depends on how you take the measurements with regards to where you place the mic and how many measurement positions you take to get enough of a sampling of the room speaker interaction.If you give it bad measurements you get bad results.It can't change physics and it's been designed not to try,but nothings perfect.It's made an impovement in my room,but it is not a substitute for proper room treatments.I can only go so far with my room treatments,so the Audyssey helps correct the rest.

I'm starting to think that the amp clipping is a limitation of the subs amplifier.I think I need to just buy a new sub.The eD A7S-450 is looking mighty tempting:bigsmile:.


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## lsiberian (Mar 24, 2009)

Drudge said:


> It depends on what implementation of Audyssey you have that determines the measurement resolution and the results you get.The unit I have is the stand alone Sound Equalizer.It is more powerful than any of the current AVR implementations,at least until MultEQ XT32 equipped units come out.The sub equalizer and the SVS AE-EQ1 stepped up the correction resolution from 256x(which is what the Sound Equalizer is currently using)to 512x with firmware updates.The abilities are also limited to how much of the capabilities the AVR manufactures are willing to implement.
> 
> It also depends on how you take the measurements with regards to where you place the mic and how many measurement positions you take to get enough of a sampling of the room speaker interaction.If you give it bad measurements you get bad results.It can't change physics and it's been designed not to try,but nothings perfect.It's made an impovement in my room,but it is not a substitute for proper room treatments.I can only go so far with my room treatments,so the Audyssey helps correct the rest.
> 
> I'm starting to think that the amp clipping is a limitation of the subs amplifier.I think I need to just buy a new sub.The eD A7S-450 is looking mighty tempting:bigsmile:.


Just get an Ultra!:R


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## Drudge (Sep 1, 2008)

lsiberian said:


> Just get an Ultra!:R


I already spent enough money already:spend:!I really don't want to buy another sub.The Ultra is too much for my wallet.I'd have to go best bang for the buck!


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