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SVS Amp Question - Clipping


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9 replies to this topic

#1 of 10 Todd_Petersen

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Posted June 28 2004 - 03:51 AM

I have a CS - Ultra with the samson 1000 watt amp that comes with it. I have just moved a couple times in the last year and i have new speaker arangments. My speaker levels including my subwoofer are all the same and my subwoofer still sits in a corner. I have been watching movies at volumes i have watched before and i am seeing my amp clipping. What is this clipping caused from? Is this bad for the amp or the sub or both?

My main question is why is the amp clipping now at volumes 5 to 7 decibals from reference where i have played before with no clipping? For instance i was testing Toy Story 2 and the Haunting yesterday and i used to get 116 spl out of the Haunting at my old house with no clipping at about-2 "volume" on my B&K AVR - 507. Now with my speaker lvls exactly the same I am getting clipping on the haunting at or around -7 volume on my receiver and getting 112 SPl. I understand that different rooms will get different SPL but why is my receiver all of a sudden clipping on volumes it used to handle so easy.

I have all speakers calibrated at 75 on my SPL.


ALso my sub is closer to me now then previous rooms, about 10 or 12 feet away.

#2 of 10 Tom Vodhanel

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Posted June 28 2004 - 04:43 AM

Hi Todd,

You have to think in terms of system sensitivity. In room *A*, the Ultra might produce 100dB at the listening position with 4 watts of input from the amp. In room *B*, it may take 16 watts for the Ultra to do the same. Room size, number(and size) of openings into the room, subwoofer placement, seating placement, distance between the subwoofer and the seating positions, wall, ceiling and floor construction...all of these variable can affect the "system sensitivity". Going back to my example...it doesn't seem like 4 watts compared to 16 watts would be a big difference. But we are really looking at a 6dB reduction in system sensitivity. That is huge...it would be the same as adding a SECOND Ultra to your system(with the same amount of amp power). In other words, to enjoy the same bass performance in room *B* as you did in room *A*...may require a second Ultra. But before you consider that, experiment with alternate subwoofer positions(and alternate listening positions if possible).

Feel free to email me at techsupport@svsubwoofers.com if you would like to fax me a room layout or discuss any other possibilities in tweaking your system Todd,


Tom V.
SVS

#3 of 10 steve nn

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Posted June 28 2004 - 04:49 AM

I'm thinking you re-calibrated in your new larger room and it required a little more gain to achieve the same level.

Here is something for you to try. Cut your Samson back to 3/4 gain and then bump your gain up on your receiver accordingly to achieve proper calibration. Your SPL will increase with no clipping most likely but will not increase to the level your accustomed to. It might do the trick. It wont hurt your Samson to clip it a little but not a good long term practice.

EDIT I see Tom has answered also now. Hi Tom. Going the dual rout would definitely be optimal if other placement options don't materialize.

#4 of 10 Todd_Petersen

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Posted June 28 2004 - 05:52 AM

Thanks Guys,

I think when i get home from work I will get a layout of my apartment and show Tom where my sub is and where my listening position is. The room is not that big and i have it in a corner.


I just dont get how the Amp is clipping with all my settings the same as my old apartment. Even if the room size is a little different and what not why is the AMP straining more when i have the SUB setting -9 on the receiver for speaker level when it was the same before. The AMP doesnt no where my sub is, it just does what the receiver tells it and its telling it the same thing as it always has. I have never clipped so much so far from reference levels.


I am not using my Subsonic filter like i have before, maybe that helped alot. For some reason in this new apartment the SS filter makes my SUB HUM like you have never heard. I have tried everything to get rid of the hum but it doesnt work. 3 prong to 2 prong.

#5 of 10 steve nn

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Posted June 28 2004 - 06:10 AM

AH now I get it. I thought you moved to a bigger room and recalibrated. Not using your subsonic will definitely require more out of your amp and your sub. I think I would take Tom up on his offer and shoot him a mail.

Please try what I suggested earlier also. It really helped me when I was in a little db race in another Thread. The hum you speak of can really be a pain in the rump. There are so many things it can be. Yip! Give SVS a holler.

#6 of 10 Edward J M

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Posted June 28 2004 - 06:46 AM

Hi Todd:

Long time, no see! Posted Image

The last time I was at your place, your Ultra was in a very small apartment room, so it didn't take much power to reach the proper calibration level or to play at Reference Level.

We calibrated your system to 85 dB with Avia with the B&K AVR507 at Master Volume 0.0. I can't recall your exact sub level, but -5 sticks in my head. Anyway, we were able to play several DVDs (Atlantis, The Haunting) at/near Reference Level without the S1000 clipping. And we were hitting 116-117 dB (uncorrected) at the listening position. The SVS01 Marchand Bass Box was enabled at that time.

I recall a very slight hum placing my ear near the Ultra grill vent screen, but nothing major. If the box has gotten noisy, maybe you should return it to SVS for an exchange. An infrasonic high pass filter will definitely reduce the load on the amp, providing more headroom and less clipping, and also reducing the potential for bottoming the woofer.

Also, AVRs can spontaneously alter their settings, especially if they have been powered down for an extended period of time. It would probably be prudent to go through the 507 set-up menu with a fine tooth comb and double check all the speaker size, bass management, PEQ, dynamic range compression circuits, THX II circuits, and bass limiter controls. Something could be going on there too.

Regards,

Ed Mullen
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#7 of 10 Todd_Petersen

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Posted June 28 2004 - 06:57 AM

Hey Ed

Its great to hear from you , i was hoping you would see this post.

I moved to Las Vegas about 8 months ago and just moved into a new apartment with the sub now in a corner.

The Sub is now at -9 on my receiver because the sub is alot closer to me now then when you saw it.

I cant get even near reference on those DVDs we demoed when you were over because the AMP is clipping.

And the SS Box is weird it hums on some outlets and not other. I moved to my mothers before i moved to Las Vegas and the box had 0 hum there. Now in this apartment it hums louder then the bass from the haunting, lol.

#8 of 10 Edward J M

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Posted June 28 2004 - 08:13 AM

Well, it's clearly NOT a defective SVS01 Bass Box if it hums on certain outlets and not on others. I'd say it's a ground loop, but you are using a cheater plug. Your new apartment might just have crappy electrical wiring and noisy voltage. I seem to remember you having a Monster Power Center; might want to run the SVS01 through that and see if things quiet down.

Also, remember that really bad null your old apartment had at 50 Hz? You could have something similar at Las Vegas where you are sitting in a null when you calibrate and this is requiring more power from the amp/sub to reach a given volume level. Mapping out the room acoustics is really the only way to see what is happening at the listening position.

Tom V has a good eye for room acoustics and should be able to bird dog potential problems and recommend the best sub placement. But room acoustics are weird (as you know), and sometimes running FR sweeps at the listening position is the only way to determine the best sub location. You could also try the "subwoofer crawl" where you place the Ultra at the listening position and crawl around the room, listening for the best/strongest bass response (with sound meter in hand too).

Good luck, hope you enjoy the new Vegas digs, and drop a line if you get back in town!

Ed
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Director - Technology and Customer Relations

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"What we do in life, echoes in eternity."


#9 of 10 Todd_Petersen

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Posted June 29 2004 - 05:12 AM

Ed or anyone else,

Here is a little update,

I hooked up the Black box and put the ground plus on the Samson amp and it got rid of the hum. I have always been putting the 3 to 2 prong plug on the SS Box and not amp.

So i got the Black box on my system again, not i went back and played the Haunting again and only getting 111 or 112 DBs compared to the 116 we got before. This is at -7 on the receiver so i think i might be able to get 114 or 116 again if i crank it to -1 or 0 like we had before but i am clipping at -7 so i dont want to push the amp further.

I checked all the settings in the AVR and they are all good and they match what we had before if not the speaker lvls are lower since im in a smaller room. I just dont understand why this AMP is clipping now and it didnt a year ago. Its not like im in a huge room compared to before and i have to stress the amp out, the settings are the same. Is it bad to have a little clipping, it just flashes at peaks. I want to go to like -2 or 3 on the receiver but I am afraid, do you think it would hurt the amp or the sub to try it if it clipped at -7?

#10 of 10 Edward J M

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Posted June 29 2004 - 06:12 AM

The only other variable I can think of is the SPL meter. I was using a B&K Model 2205 set to C-weighted Fast with a fresh battery when I was checking peak SPL's at your place.

I remember we had an RS meter there for comparison on the FR sweeps, but I don't think we were running it for SPL peaks (it's been a while though). The RS meter can tend toward the inaccurate side at high volumes, especially with a weak battery. Maybe the RS meter is starting to malfunction or the battery is dying?

The Haunting in DTS-ES 6.1 Discrete is recorded on the very hot side, and I don't know of anyone that can actually play it at Master Volume 0.0 (the Avia 85 dB calibration level) without wrecking something or it being just obscenely loud. I think you will hit Reference Level playback volumes on that particular DVD at around -10 Master Volume on a properly calibrated system.

Given how hot The Haunting DTS is, it doesn't surprise me that the Samson S1000 clip lights are flickering briefly at -7 Master Volume. Occasional brief flickering is not a problem, but if the light stays on for 1 second or longer, you are overloading the amp and you will eventually damage it and/or the Ultra.

I do recall you being able to play the Leviathan attack scene from Atlantis at MV 0.0 and we were hitting around 116-117 dB uncorrected (probably 120-121 dB actual) at the listening position. I recall you pushed it to +2 MV and the Ultra simply wouldn't play any louder, indicating the onset of dynamic compression and/or the amp running out of juice. Either way it was still a spectacular showing for a single Ultra.

It could be the RS SPL meter: 1) is reading low (compared to the B&K unit), 2) is becoming defective, or 3) has a weak battery. That, and I can't ever recall anyone playing The Haunting DTS-ES 6.1 at MV 0.0; it's simply mastered way too loud for that.

Hope this sheds some additional light, and do follow-up with Tom V at SVS Tech Support.

Regards,

Ed
Ed Mullen
Director - Technology and Customer Relations

SVS

www.svsound.com

"What we do in life, echoes in eternity."