Subwoofer out Clipping Tests.

[micb3rd]

Something we have discussed before is that some AV Recievers/Processors will clip the subwoofer output when turned up.

This clipping from an AVR is low level signal level clipping and thus while sounds bad is not dangerous at all.

High level clipping i.e the clipping you get from overdriving an amplifier past it clean limtis is a very different thing and is dangerous due to the increaced power.

As I just got a new portable scope I set to testing the subwoofer output on my Denon AVR-1802.

To test you need 0db test tones to unsure you can drive the system to its maxumim level.

I disconneted the RCA from my subwoofer amplifer and connected the scope to it.

I set the Subwoofer level to 0 and AVR the master volume to 00.

I played a 20hz tone and observed...no clipping.

Next I upped my subwoofer trim level on the Denon till it read +12db result....no clipping.

That is good news. I also tested in Stereo and Prologic II just to check...yes all fine.

I then upped the master volume to 02 and it was clear that the output was starting to clip as I upped it to 06 the output clipped hard.

I then backed the master volume back to 00 and tested at 30hz, 50hz and 80hz to enure it was clean. They were all clean, at 80hz it was clear on the scopes trace that the onboard crossover was starting to attenuate the output.

So to conclude my old Denon 1802 does not clip the subwoofer output at all unless you push the master volume past 00 and have the subwoofer trim level at +12. They have done a good job in setting up this classic AVR.

I wonder if your AVR/Processor also do not clip? I may have to test some more!

Here are some pictures.

AVR Master level 00 (and subwoofer trim level +12).

19hz on the edge of clean.

20hz clipping.

20 hz clipped hard.

50 HZ starting to clip.

50hz Clipping.

50 hz Clipping hard.

 

[Member 639844]

Where did you get your meter from, it could be useful . I have noticed my AVR's volume doesnt really increase once you pass 00, so I'm pretty sure the 875 does certain things on board to help prevent stuff like clipping happening ( I know in some cases it certainly does, 7 channels driven for eg and the Onkyo engages a power management that reduces output a fair bit to protect the power supply and keep everything running smooth). I have clipped the EP4000 during testing, but Ive never noticed any issues I thought were related to the AVR.

 

[HiFiRuss71]

I've struggled to get any of my AVRs to clip their output in normal use, but found it quite easy to get them to force the input ADCs of an EQ device to clip. BFDs and SMS-1s are a case in point, the latter being very sensitive to clipping.

I thought the Aerial Acoustics SW12 was running out of puff earlier in it's stay, but latterly realised that the SMS-1 wouldn't accept any signal above reference -6dB without some fairly obvious artifacts creeping in. To compensate, you just turned the SMS-1s analogue output gain up by 6dB, but it just illustrates that you have to be going fairly mental to clip an analogue output, but troubling digitized inputs are a damn site easier.

Russell

 

[micb3rd]

Where did you get your meter from, it could be useful . I have noticed my AVR's volume doesnt really increase once you pass 00, so I'm pretty sure the 875 does certain things on board to help prevent stuff like clipping happening ( I know in some cases it certainly does, 7 channels driven for eg and the Onkyo engages a power management that reduces output a fair bit to protect the power supply and keep everything running smooth). I have clipped the EP4000 during testing, but Ive never noticed any issues I thought were related to the AVR.

I tested my subwoofer amplifier I get about 37.5 volts before I clip, I don't haver a decent true RMS clamp meter so can't test its real power yet.

I did a couple of 30hz and 50hz tones to full clipping with the subwoofers hooked up, it was loud. I did not have my SPL meter to hand but my room was complaining in various places. I'll need to do some bracing before I put more bass in this room.

Here is the one.

ARM DSO Portable Digital Storage Oscilloscope DIY Kit on eBay (end time 12-Jul-10 16:16:57 BST)

It does not come with a manual but this one is exactly the same.

http://www.seeedstudio.com/depot/images/product/dsomanual.pdf

I've struggled to get any of my AVRs to clip their output in normal use, but found it quite easy to get them to force the input ADCs of an EQ device to clip. BFDs and SMS-1s are a case in point, the latter being very sensitive to clipping.

I thought the Aerial Acoustics SW12 was running out of puff earlier in it's stay, but latterly realised that the SMS-1 wouldn't accept any signal above reference -6dB without some fairly obvious artifacts creeping in. To compensate, you just turned the SMS-1s analogue output gain up by 6dB, but it just illustrates that you have to be going fairly mental to clip an analogue output, but troubling digitized inputs are a damn site easier.

Russell

Yep! I often try to explain to people even though their signal output may be clean as a wistle it can end up at so high voltage that the inputs are clipped on the other devices in the signal chain.