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ok guys, like usual, I have a question. I have 2 full marty's in my ranch style home and have had them co located in the front right corner of the room. unfortunately I have some suck outs in my room and have had to live with them for quite a while. however, I've moved my seating position back from the center of the room to 2/3rd back in the room and I've gained some SPL from that. now the "issue" I have is this. I'm using an IPR3000 to power both marty's with 890 watts per channel and have a yamaha 773 as the receiver. gains are maxed out on the IPR and I get no clipping on the amp with it calibrated 6-7 db's hot with my meter. HOWEVER my Yamaha 773 has a -10 to +10 range on the receiver LFE level... with them co-located in the front corner I can do about +4 on that range, but now I swapped them into different corners and I REALLY have smoothed out the nulls, but with them no longer co-located I had to bump the receiver to +7.5 to get the same spl level as them co-located (although now those nulls are VERY much better). the question I have is this. is the +7.5 on the LFE level on my receiver (out of a -10 to +10 range) actually clipping my sub output on the receiver or is that 2.5 I have left enough of a safety margin?
 

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Totally depends upon the volume level the AVR is set at.

For illustrative purposes, if sub out level was set at +0dB and you had the volume of the AVR at reference +0dB mv. This would be the same as the sub out set to +10dB and AVR at -10dB mv.

At some point the AVR's preamp will run out of voltage but usually there is plenty of headroom on the preamp outputs, likely more then enough to drive your IPR3000 to max output. Looked it up, 0.775v is needed to drive the IPR3000 to max output with a 4 ohm load. Usually any decent AVR will give a good 2+ volts on the preamp outputs and many will do much higher.
 

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Discussion Starter #3
Totally depends upon the volume level the AVR is set at.

For illustrative purposes, if sub out level was set at +0dB and you had the volume of the AVR at reference +0dB mv. This would be the same as the sub out set to +10dB and AVR at -10dB mv.

At some point the AVR's preamp will run out of voltage but usually there is plenty of headroom on the preamp outputs, likely more then enough to drive your IPR3000 to max output. Looked it up, 0.775v is needed to drive the IPR3000 to max output with a 4 ohm load. Usually any decent AVR will give a good 2+ volts on the preamp outputs and many will do much higher.
cool, I'm running it off an unbalanced MInidsp which is why I'm using the .775 volt IPR 3000 to pair with it. I normally don't turn the volume up UBER loud becuase of my SEOS cheap thrills sensitivity, - 19 is usually the MAX (and that was because the track on the battle of five armies is recorded UBER low...normally it's -30 to -25)... I haven't HEARD any clipping. I just wanted to make sure that going on the + side of the receivers LFE level trim was safe. I normally don't ever see the DDT light on my IPR 3000 even flicker more than once or twice, but I wanted to make sure the receiver wasn't gasping for air. hopefully this won't be an issue any more since I'm on the list for a pair of UXL 18's that will either supplement my two SI 18's in 2 more marty's or johnny cabs OR will be placed in a pair of Lowarhorns to replace them completely
 

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The unbalanced miniDSP is the weak link in that chain, however with 0.9 volts it should also have gust enough headroom for your IPR300. You can monitor output levels through the miniDSP software and see how high the peaks go.

I had an unbalanced miniDSP in my signal chain a while back (now use a balanced 2x4) and after hooking it up and I noticed that I the bass did not sound as dynamic as it did before placing in the chain, even when I bypassed all the EQ adjustments. Found out I had been clipping the outputs, it did not make any bad noises when that happened just the bass just sounded dull or less dynamic. Readjusted gains and all was well.
 

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Discussion Starter #5
The unbalanced miniDSP is the weak link in that chain, however with 0.9 volts it should also have gust enough headroom for your IPR300. You can monitor output levels through the miniDSP software and see how high the peaks go.

I had an unbalanced miniDSP in my signal chain a while back (now use a balanced 2x4) and after hooking it up and I noticed that I the bass did not sound as dynamic as it did before placing in the chain, even when I bypassed all the EQ adjustments. Found out I had been clipping the outputs, it did not make any bad noises when that happened just the bass just sounded dull or less dynamic. Readjusted gains and all was well.
yeah, I was wondering about the Mini... the unbalanced was my first entry into the pro amp world so it's been my mainstay for these martys.... normally I don't have a problem because I don't have the + level in my receiver boosted that far, but with seperating them I had to boost them to +7.5 and I'm maxed out on the IPR's gains. meaning I'm OUT of headroom (and I would even prefer to push it a bit higher If I have the chance). if, when I get my UXL's in I plan on getting the balanced 2x4 or just taking out the IPR 3000 and replacing it with an Inuke 6000DSP when I get them in. I'll take a look at the output levels on the mini when I have a chance with my wife's laptop (if it will hook up, I bought the mini dsp used and the 2x4 plugin software that came with it doesn't like anything but Win XP for some reason, Win 7 and 8 won't connect. )
 

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well, checking the minidsp's outputs is a no go. I forgot I got rid of my old XP laptop and for some reason the 2 way advanced plugin I have won't sync when using win 7 or win 8 for some reason. (probably because the plugin is like 3 years old and their most likely is an updated version that supports 7 and 8.... I bought the mini used with the plugin so I don't have access to an updated file. ).....

it's actually amusing that I'm running out of headroom with 2 SI 18s. my main room with the projector is 12x22 feet long, but it opens up to another 8x22 room on one side, a kichen near the back and a hallway right at the back so my room SUCKS up SPL like a hooker on friday night. I just pulled my old SVS PB-10 ISD from 10 billion years ago and put it in the 12x14 bedroom where it literally DESTROYS the room. like I have to have it -10 on the receiver and that's 8 DB's hot from the other 5 channels! I'm closing off that 8x22 room to the left side of my seating area with a french solid core doors, so hopefully that givs me some extra SPL from sealing up that area in the main room.
 

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great question. comes up all the time.
one method is to run a sine wave and put an oscilloscope on the output to see if the peaks are getting cut off or not. there are some low cost "mini" scopes for under a hundred bucks, but I'm not sure which one to suggest.
there is also a "kit" that includes a source disc and device that essentially does the same thing. smd dd1.
http://www.sonicelectronix.com/item...Detector-Analyzer-by-Steve-Meade-Designs.html
since it can be used to detect clipping, it can be used to set up gain structure fairly easily.
there are some good youtubes on that. essentially, you start with all the gear turned down. input a -0db signal. and turn each component up until just before it clips. by the time you get to the power amp, you have a good of gain structure as you are going to get.
eq complicates things greatly because now the gain structure is limited by the eq peak and it isn't always obvious precisely where that is. maybe with rew some sort of loopback after each device could identify the peak and then the gain structure could be set using a test tone at that frequency.
i would imagine most folks don't have enough rig for the gig though, so setting gain structure so as to never clip is going to result in an average spl that is too low.
so much for the scientific process. :)
 

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I did this by cutting an rca cable in half and wiring in a couple of resistors to make it into a voltage divider, record the output at each stage into audacity (or similar) and you then test for clipping with real output or sine waves. Resistors with about 40p each, the rest of the kit you may already have.

There is also zelscope if you want an actual software scope and you can also obviously do more complicated/capable wiring schemes but this does the job.

You can certainly measure preouts to get the shape of any EQ filter too. You can then just adjust trims accordingly if that adds any boost.
 
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