# Amp advice



## gafftaper (Jun 10, 2008)

Disclaimer: I'm am a competent sound op but not an expert in the noise department. 

We were advised by a theater sound system designer to purchase a QSC CX502 to power a JBL ASB6118 Sub. 

Amp:
Bridged Mono at 8 ohms 1100 Watts

Sub Specs:
Transducer (AES) Power Rating:1200 W (4800 W peak), 2 hrs
Long-Term System Power Rating:800 W (3200 W peak), 100 hrs

We cranked it up and BAM distortion on all the big bass notes. The installer says theres not enough head room and it's distorting when it peaks, so I need a bigger amp. 

I'm hoping to return it and upgrade to a QSC CX902 which hits 2000 Watts at 8 ohms, bridged. Does this sound to you like it will fix the problem?


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## avare (Jun 10, 2008)

Looking at the specs for the speaker and into consideration you wrote about a theater sound system designer, I have one question immediately. How loud are you driving the system?

Going from 1,200 W to 2,000 W is less than a 3 dB increase. If 3 dB is the difference, try first reducing the output by 3 dB and see if stops the major distortion.

Andre


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## David Ashton (Jun 10, 2008)

You have to make sure the gain structure is set correctly all through the system, only then will you be sure where the distortion is entering the system.90+% of distortion problems I meet are gain structure related.


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## DaveySimps (Jun 10, 2008)

I agree that proper gain structure is key to a good sounding system. As a rule you want your amps to be 1.8 to 2x the watts of your speakers RMS rating. For instance, if you have a speakers rated at 500W than your amp should be at least 900W or 1000W so that you can handle the peaks in your program material. If you go to big with your amp, you greatly increase blowing your speaker.

Looking at your spicific case, I would inclined to get a QSC CX1102 (if you want to stay in that line of amps). It offers a wattage in the range I listed above. The CX902 might still be a little weak on those peak program signals. The 502 that was recommended to you is definately under sized for your usage in my opinion. This could definately cause the distorted sound you were hearing on the "big bass notes" since these represent more peaks in the program material you were sending to the speaker.

~Dave


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## avkid (Jun 10, 2008)

DaveySimps said:


> As a rule you want your amps to be 1.8 to 2x the watts of your speakers RMS rating.


I tend go on the lower end of the scale at 1.5-1.8 x RMS.


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## DaveySimps (Jun 10, 2008)

Even based on your preferred formula, that amp that was recommended is still undersized. If you go with the 1.8 value, he will find a workable solution.

~Dave


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## gafftaper (Jun 10, 2008)

Just got word that they will take it back with a 15% restocking fee but I need to upgrade within the QSC product line. I'm really happy because it's been sitting here waiting for install for 6 months so I was sure they wouldn't take it back. I'm checking on the price for that 1102... that's double the power and one of the most powerful amps QSC sells. Sounds like every watt helps.


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## DaveySimps (Jun 10, 2008)

gafftaper said:


> Sounds like every watt helps.




It especially makes a difference when you are talking about subs.

~Dave


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## museav (Jun 10, 2008)

As Andre noted, if you change to the CX1102 you are talking about a maximum 3dB increase and that is only relevant to the maimum peak level if you really push the sub.

Before you go getting a different amp, I would first verify some other potential factors. Are all the amp settings correct and is it wired correctly, especially in regards to the bridge mode operation? Has the installer set the system gain structure? Are you clipping the amp input or anywhere else in the signal chain? Have they tuned the system and can someone confirm that appropriate filtering and processing, including high pass filtering for the sub, has been applied? Any of these could also be related to the distortion you noted and you probably want to eliminate these potential causes before spending more money on a different amplifier.

Also, just because you can go potentially go that loud does not mean that was the intent. You might want to find out if there was some target level that was defined, it may be that the system is working exactly as intended.


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## gafftaper (Jun 10, 2008)

museav said:


> As Andre noted, if you change to the CX1102 you are talking about a maximum 3dB increase and that is only relevant to the maimum peak level if you really push the sub.
> 
> Before you go getting a different amp, I would first verify some other potential factors. Are all the amp settings correct and is it wired correctly, especially in regards to the bridge mode operation? Has the installer set the system gain structure? Are you clipping the amp input or anywhere else in the signal chain? Have they tuned the system and can someone confirm that appropriate filtering and processing, including high pass filtering for the sub, has been applied? Any of these could also be related to the distortion you noted and you probably want to eliminate these potential causes before spending more money on a different amplifier.
> 
> Also, just because you can go potentially go that loud does not mean that was the intent. You might want to find out if there was some target level that was defined, it may be that the system is working exactly as intended.



We were running it loud, but speaking loudly, I could still be heard by someone three feet away. Yelling I could be heard 30 feet away in the booth. I would say it was no louder than you would hear in a movie theater. It was definitely not concert volume. The audio being played was a Blueman Group 5.1 audio DVD so it had some big bass in places, but also wasn't loose hip hop bass... we heard the "bad sound" while listening to "Hotel California" too. The technician doing the install was quite certain it wasn't his gain settings. 

The installers are bringing a bigger amp in to test in the next day or two. Just to verify what's wrong. 

Thanks guys.


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## Eboy87 (Jun 10, 2008)

I assume an RMX4050 is out of the question? If you're staying in the CX series, I'd go for the CX1102 if budget allows. Just to be sure, and I'm sorry if this sounds like it's from the department of Duh, but you are using a crossover for this, aren't you? 

I tend to go for the higher side on power for subs, so things like a Powerlight 6.0 or the 4050 are what I'd go for, though you most likely need a 20 or 30 amp circuit to use them to their full potential.


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## gafftaper (Jun 10, 2008)

It's all going through a Bi Amp Audia Flex DSP. The crossover is set to send everything from all channels below 100hz to the sub. The alternative amp should tell us a lot. The CX 1102 is what I'm going for... looks like it's going to add about $900 to my system cost. Which isn't as bad as it could have been.


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## SHARYNF (Jun 11, 2008)

Keep in mind that most consumer dvd units have a boost on the low end on the 5.1 dolby setups. It might be worth also looking at how the bass management of the LFE signal is set up. Again might not be the case, subs typically need lots of reserve power, so you might be on the right track, also it is worth checking the ac power feeding the amp.
Sharyn


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## museav (Jun 11, 2008)

SHARYNF said:


> Keep in mind that most consumer dvd units have a boost on the low end on the 5.1 dolby setups. It might be worth also looking at how the bass management of the LFE signal is set up.


Which goes back to the issue of the system configuration. If you are using an LFE output that typically already involves an 80Hz crossover, depending on how the system processing with the 100Hz crossover is configured, you might be applying two crossovers and creating a hole between 80 and 100Hz.

I do not know your Contractor and they may be completely right, but it seems worth verifying some things rather than just saying they're okay and suggesting you spend more money. Have they verified the amp wiring and settings, I have seen improper wiring or switch settings for bridge mode operation on more than one occasion? Do they have a high pass on the subs at maybe 25-30Hz to keep out very low frequency garbage? Is the distortion associated with any clipping? How are the subs mounted and might that be affecting them (e.g. not having the half space loading JBL assumes in their numbers or getting anomalies from nearby barrier reflections)?

Based on the ASB6118 98dB/1W/1m sensitivity, you should be getting around 100dB peaks 100' from with the existing CX502, which it sounds like you are not. And going from a CX502 (1,100W bridge mono into 8 Ohms) to a CX1102 (2,200W bridge mono into 8 Ohms) will net you at the most a 3dB gain in peak output while it sounds like you are missing a lot more than that. I would want to make sure you are getting what you should from the existing system before making any changes.


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## SHARYNF (Jun 11, 2008)

I agree with Brad, before paying to swap out to a new amp identify what is the current problem. Sure for max performance the 1.5-1.8 factor is a good guideline for amp power for subs BUT from your description this might not be the problem.

One common problem in addition to all of the above is back to gain structure. It is easy to forget that amps may have volume controls on the input BUT usually these are AFTER the input stage that can still overload. the problem could be simply that when you are raising the level you are sending a signal to the amp that is overloading the input stage. The degree of distortion would lead me to check this out carefully, the installer should have gotten this right but you know how it goes


Sharyn


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## gafftaper (Jun 13, 2008)

We tested the sub today with a 3400 watt amp and it worked perfectly so it was just a barking due to lack of headroom. Now to order the biggest amp I can afford.


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## SHARYNF (Jun 13, 2008)

gafftaper said:


> We tested the sub today with a 3400 watt amp and it worked perfectly so it was just a barking due to lack of headroom. Now to order the biggest amp I can afford.



possibly but not guaranteed, I still would go back and check the levels going INTO the amp and of course check another copy of the same amp. 

Sharyn


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## museav (Jun 13, 2008)

gafftaper said:


> We tested the sub today with a 3400 watt amp and it worked perfectly so it was just a barking due to lack of headroom. Now to order the biggest amp I can afford.




SHARYNF said:


> possibly but not guaranteed, I still would go back and check the levels going INTO the amp and of course check another copy of the same amp.


I agree Sharyn. Maybe the situation was misunderstood and the problem was not as extreme as it seemed but going from 1,100W to 3,400W should be a maximum 4.9dB increase and it at least sounded like you were looking for more than that. If you actually got more than a 5dB difference by swapping the amp then that that indicates there might be other factors involved such as a greater maximum input level on the other amp or something else. There are two other things that concern me.

It sounds like you may not be addressing headroom as much as normal operating level. Headroom is basically the difference between the average and peak levels, for systems headroom is the difference between the average operating level and the peak level possible. If the old amp did not work for normal use and the new amp provides a maximum 4.9dB greater output then you have a system headroom of less than 5dB, which is less than the 10-12dB that might be more typical and thus may indicate other problems.

Also, 3,400W is 4.25 times the 100 hour long term power handling and 2.8 times the AES rated power handling of your sub. Especially if you are running it that loud on a normal basis, every operator is going to have to be very careful or you are likely going to be replacing drivers regularly.

Overall it sounds like there may currently be a very fine line between "not enough" amp and "probably too much" amp. Again, this indicates that something may be wrong on a different level, be it gain structure or processing issues or simply the wrong speaker for the application.

That leads to the question of where is your Consultant? A Consultant is typically involved throughout the project including during the system installation, testing and training. They should also be responsible for their design. It sounds as though the Consultant has not been included in this and they probably should be involved, at least before any final decisions are made.

I really hope there is such a simple fix but it sounds like there may be more to a real solution than simply throwing the biggest amp you can find at it.


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## gafftaper (Jun 13, 2008)

museav said:


> That leads to the question of where is your Consultant? A Consultant is typically involved throughout the project including during the system installation, testing and training. They should also be responsible for their design. It sounds as though the Consultant has not been included in this and they probably should be involved, at least before any final decisions are made.
> 
> I really hope there is such a simple fix but it sounds like there may be more to a real solution than simply throwing the biggest amp you can find at it.



In their infinite wisdom, the college cut the sub and amp from the building budget to save $3,200. I'm currently out about $2200 for the amp and sub. I'm out $1900 for hanging (we wanted someone else to take the liability), resetting the DSP, and renting their own Genie lift (we can let them use ours due to liability). Now I've got a 15% restocking fee to pay and another $1000 to upgrade to the new amp which I hope will do it. 

Also when the college cut the amp from the system we also cut the support of the consultant. The current sub and amp were quickly suggested to me by the consultant but he wasn't paid for it, it was just a courtesy in a conversation during a site inspection. So I've been hosed on several levels to save $3,200 on a $4.5 million building.


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## gafftaper (Jun 13, 2008)

So Brad Sharyn and others... going back to the original speaker specs and Brad's comment about the amp needing to fit into a delicate balance with just the right amount of headroom without too much power...

Sub Specs:
Transducer (AES) Power Rating:1200 W (4800 W peak), 2 hrs
Long-Term System Power Rating:800 W (3200 W peak), 100 hrs

Does it sound to you guys like the QSC CX 1102 running 2200W at 8 ohms would hit in that middle sweet spot?


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## DaveySimps (Jun 13, 2008)

I think you are right on. 

I know where you are coming from with them "value engineering" items out of the project. We opened our space 4 years ago, and it is amazing the things that were cut out of a $12 million facility. 70% of the items I would say we have done ourselves since then. 

~Dave


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## museav (Jun 13, 2008)

gafftaper said:


> In their infinite wisdom, the college cut the sub and amp from the building budget to save $3,200. I'm currently out about $2200 for the amp and sub. I'm out $1900 for hanging (we wanted someone else to take the liability), resetting the DSP, and renting their own Genie lift (we can let them use ours due to liability). Now I've got a 15% restocking fee to pay and another $1000 to upgrade to the new amp which I hope will do it.
> 
> Also when the college cut the amp from the system we also cut the support of the consultant. The current sub and amp were quickly suggested to me by the consultant but he wasn't paid for it, it was just a courtesy in a conversation during a site inspection. So I've been hosed on several levels to save $3,200 on a $4.5 million building.


That sucks. Speakers are one if the last places I try to let Value Engineering touch as once something goes in it is often difficult, and more expensive, to change it later. You can pretty easily borrow and later add mics, stands and even things like effects and sources, but speakers systems and dimming systems (at least the core system) you may well end up stuck with if you cut initially.

I like the approach one client took. Late in the project it started going over budget. The budget issues were not with lighting or audio or video but because those were the system really left to go in, the Owner knew they would try to make up all the budget overages there, so they went on the offensive instead. They had the General Contractor VE out all the sinks, toilets, urinals, etc. instead and then went back to the Board and told them that unless they came up with more funding, they would not be able to get a Certificate of Occupancy for the project since the restrooms would be incomplete. To even further make the point, they held that meeting in the future Boardroom which was completely unfinished and without any systems and also told the Board that was also how the Boardroom would have to stay unless they got the funding. In no time at all they had all the funding needed to complete the building without anything being cut!

I think a CX1102 would be a good choice, my only concern is with the same maximum input level, etc. as the existing CX502, will the 3dB gain CX1102 represents solve your problem?


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## gafftaper (Jun 13, 2008)

I've done some more checking and it looks like with my state contract pricing I can choose from any of the big QSC amps. 

So I can chose from:
the CX 1102 
the PLX 3602
the PL 340
the RMX 4050HD

Suggestions? 


Second as long as we are at it I'm confused about the terminology from JBL on my sub. 
Transducer Power Rating (AES): 1200 W (4800 W peak), 2 hrs
Long-Term System Power Rating: 800 W (3200 W peak), 100 hrs

QSC has an amplifier selector tool but I need to put in RMS or Program rating and I'm not sure what those equate to in the JBL data.

*EDIT:* Ok, I've been doing some reading on AES and RMS... it sounds like they are similar but there is no real way to convert from one to the other as they are completely different standards. Program rating sounds like it's basicly useless. Is there an accurate way to convert AES to RMS? Can I just use the AES number in the handy QSC amp selector software as an approximation of RMS?


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## avare (Jun 14, 2008)

gafftaper said:


> We were running it loud, but speaking loudly, I could still be heard by someone three feet away. Yelling I could be heard 30 feet away in the booth. I would say it was no louder than you would hear in a movie theater. It was definitely not concert volume.



This is strange. Voice has frequency content down to 80 Hz, and that is for bass voices. Movie theater volume is based on a nominal 85 dB level 2/3 of the length back in the house. Assuming a 100 ft long theater, which is quite large for these days, and zero far field reinforcement of level, this works out to about 106 dB spl at 3 ft. Sound reinforcement speakers have typical efficiencies of 100 dB spl at 1 meter with one watt input. So the amp output is around 4 watts. Add a 10 dB crest factor and the amp output is still only 40 watts.

All the above is ignoring that voice has minimal, if any content at sub frequencies. Even with full range music, the amp is coasting.

What you are writing the symptoms are does not indicate insufficient power from the amp.

Andre


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## gafftaper (Jun 14, 2008)

avare said:


> This is strange. Voice has frequency content down to 80 Hz, and that is for bass voices. Movie theater volume is based on a nominal 85 dB level 2/3 of the length back in the house. Assuming a 100 ft long theater, which is quite large for these days, and zero far field reinforcement of level, this works out to about 106 dB spl at 3 ft. Sound reinforcement speakers have typical efficiencies of 100 dB spl at 1 meter with one watt input. So the amp output is around 4 watts. Add a 10 dB crest factor and the amp output is still only 40 watts.
> 
> All the above is ignoring that voice has minimal, if any content at sub frequencies. Even with full range music, the amp is coasting.
> 
> ...



I think you are misunderstanding what I was saying. The audio signal we were playing for testing was the Blueman Group 5.1 Audio DVD which has lots of Low bass notes in it well below 80hz. When I posted the message you are talking about I was trying to explain that we weren't running the system ridiculously loud causing the speaker to bark. I didn't have an SPL meter with me but it was about the same volume level as you would hear in a movie theater. Loud, but if you talk the person next to you can hear you. If you shout you can be heard a ways away.

We have tested it now with a larger amp without changing any other settings and that instantly solved the problem. So it was a headroom issue. The question now is which amp to replace it with.


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## avare (Jun 14, 2008)

gafftaper said:


> We have tested it now with a larger amp without changing any other settings and that instantly solved the problem. So it was a headroom issue. The question now is which amp to replace it with.



I am not doubting that changing the amp corrected the problem, but what you have described is not consistent with lack of power. One possibility that comes to mind is that the amp itself was defective. Nice thing if that is the case is zero additional expense for new equipment. Another thing that comes to mind is the gain structure of the system and amplifier input sensitivities.

Andre


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## SHARYNF (Jun 14, 2008)

avare said:


> I am not doubting that changing the amp corrected the problem, but what you have described is not consistent with lack of power. One possibility that comes to mind is that the amp itself was defective. Nice thing if that is the case is zero additional expense for new equipment. Another thing that comes to mind is the gain structure of the system and amplifier input sensitivities.
> 
> Andre



I'm with Andre, it is impossible to say no settings were changed when obviously the settings on the amp and the amp itself was changed. Certainly if you want to get a larger amp, that is no problem but from my experience you have not really gotten to the bottom of what actually happened. 
Sharyn


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## gafftaper (Jun 14, 2008)

Let's put it this way we unplugged the low power one and plugged in the higher power one and it worked perfectly without any adjustments to the DSP. 

Like I've said above I freely admit to not being an audio expert and so I mean what follows as a serious question not to be argumentative... The sub is rated between 1200 and 4800 watts and I was trying to power it with an 1100 watt amp. I replaced it with a 3400 watt amp and it works nice and clean. Why is lack of headroom not the clear problem?


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## avare (Jun 14, 2008)

gafftaper said:


> Why is lack of headroom not the clear problem?



Different gain levels on the different amps?
The first amp wasn't properly installed into the system? You are not the DSP programmer, the original consultant is no longer (sort of) on the job, the new consultant may not be completely knowledgeable about the system programming. The installer may have tweaked the system. The amp clip limiters may have been turned on.

Somethings going through my mind as I type this are: 

1. had the system been setup and tested by who ever, or whatever is the organization providing the sound system

2. as I understand the thread, the system was speced with a sub, then the sub was removed. Sometime after a sub was included again, the original consultant was terminated, and a new consultant brought in. Within these events did the new consultant change the DSP programing for the new, or old, or revised speaker components?

4. there should be at least documentation from the original consultant on the programming was intended to be.

3. what were the indicators on the amp doing when the distortion occurred?

Andre


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## gafftaper (Jun 15, 2008)

avare said:


> Different gain levels on the different amps?
> Just a hypothetical. Someone pointed out that even though we swapped amp for amp without changing any dsp settings there are still differences.
> 
> The first amp wasn't properly installed into the system?
> ...



Thanks, Andre. Again I don't want to debate I really want to learn something here. Just trying to lay out the facts. The current installers were certain from the moment they heard the barking the problem was headroom and they were satisfied that they proved it with the larger amp working. 

One other note, the amp was not purchased from the guys doing the install and the larger amp will not be purchased from them either so they've got no reason to be pulling a fast one on me.


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## museav (Jun 15, 2008)

avare said:


> This is strange. Voice has frequency content down to 80 Hz, and that is for bass voices. Movie theater volume is based on a nominal 85 dB level 2/3 of the length back in the house. Assuming a 100 ft long theater, which is quite large for these days, and zero far field reinforcement of level, this works out to about 106 dB spl at 3 ft. Sound reinforcement speakers have typical efficiencies of 100 dB spl at 1 meter with one watt input. So the amp output is around 4 watts. Add a 10 dB crest factor and the amp output is still only 40 watts.
> 
> All the above is ignoring that voice has minimal, if any content at sub frequencies. Even with full range music, the amp is coasting.
> 
> What you are writing the symptoms are does not indicate insufficient power from the amp.


I interpreted what was said differently, I took it that he was able to converse with somebody 3' away and yell back to the booth 30' away with the source playing at the highest volume they could achieve before the problems with the sub limited the overall system volume. So I don't think voice had anything to do with the source itself, it was only noted to provide an relative indication of the system level they were able to achieve.

I think the 100dB/1W/1m sensitivity rating may be a bit high, the JBL ASB6118 involved is rated at 98dB/1W/1m but that is with a half space loading and flown it could be closer to a whole space conditions. However, I do agree about the levels. Even accounting for potential loading losses, etc., with the 1,100W of the existing CX502, the sub should have been capable of over 120-125dB at 1m. So at 100' from the speaker, then the level from the sub would be expected to be at least 90-95dB and actually probably greater in a typical room. 

Gaff asked "Why is lack of headroom not the clear problem?" I think the biggest issue why some of us are not comfortable with the concept of just going to a larger amp fixing the problem is that it at least sounds like there were some problems with the initial system that are not explained and that would be resolved by simply more available amplifier output.

One example is that you said you thought you got around normal cinema levels from the system. It was noted above that your sub with the CX502 would be expected to be capable of over 90-95dB at 100' and if the sub was limiting your maximum levels, then the rest of the system should have been at those levels as well. So with the QSC CX502 the system would be expected to provide at least 5-10dB, and realistically more like 10-20dB, above the 85dB normally used for setting cinema levels and and that is assuming you were 100' away. So unless I misinterpreted what was presented, your comments on the initial situation indicate that you were not at all getting the results expected from the system.

Your comments regarding having intelligible conversation seem to reflect similar issues. Your statement that you could have a conversation at normal level at 3' and yelling at 30' would usually represent a level at the listener of about 60dBA. Again, your system, limited by the sub, should be capable of output at least 90-95dB, 30dB above the speech levels which would indicate that you should not have been able to communicate as you noted. And that is assuming you were 100' from the sub, if you were closer then the problem would be even greater.

At least adding to my concerns, I do not have a lot of the information I might look at if I were addressing such a problem on one of my systems. I don't know if the amps or anything else were clipping when the problems occurred. I don't know any of the actual levels (signal or sound pressure) or distances involved. No way of knowing if everything actually remained the same or not as maximum output is not the only potential difference between amps, there can also be differences in parameters such as input sensitivity and maximum input level as well as in any attenuator and other control settings. And so on.

All these factors may be why some of us are not comfortable with the concept of simply going to a larger amp fixing the problem. I think the biggest sticking point is just that it at least sounds like there were some problems with the initial system that are not explained, or that would be resolved, by the amp swap.


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## SHARYNF (Jun 15, 2008)

Could you provide more information on what was done exactly when you wrote: 
The new installer took the 8 amp outputs in the DSP and added a crossover point on all of them to feed the sub at 100hz. I'm not sure what else he did or didn't do. But the speaker was obviously barking immediately. They brought in the higher powered amp and it sounds great now. 

In my experience the obvious barking is a result of the amp amplifying a distorted signal, typically when an input stage is overloaded, and NOT a case fo the amp running out of head room.

While a lot of system designers like to fly the subs as a counter balance physically, typically the sub can be placed in a more convenient and less expensive location and be time aligned using the dsp

Sharyn


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## avare (Jun 15, 2008)

I am having difficulty quoting properly, so please refer to the reply to my previous post for proper quoting.


avare said:


> Different gain levels on the different amps?




gafftaper replied said:


> Just a hypothetical. Someone pointed out that even though we swapped amp for amp without changing any dsp settings there are still differences.



I have no ideas where on earth you got the hypothetical from. We on Controlbooth do not know what the other amp was or its gain. You referenced the QSC page on amps. Have a look at the voltage gains of the various amps IN THE SAME MODEL RANGE. The two amplifiers may have different gains, which if the DSP is not adjusted for, will make a direct plugin comparison meaningless. 

What is your background? Lighting? Imagine replacing a 120V nominal lamp with a 110V nominal but same wattage rating. To the unknowing, the lower voltage bulb is obviously brighter.


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## cutlunch (Jun 15, 2008)

If you look at the specs of the two amps there is a difference in the input sensitivity of about 120 MilliVolts. Normaly it shouldn't be a problem but if the DSP was setup wrongly it might have been enough that the input signal was slightly clipped on the earlier amp. Unlikely but possible. They only way would be to test it would be to put a low frequency sinewave into the system and check the output of the DSP.

What model DSP do you have? Sometimes you can get the software for these from the net and even if you don't change anything you can still read the settings.

Most DSP's have a number of program memories and if yours is not full you could add things like a mike input & volume control for speakers so you don't need an operator.


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## gafftaper (Jun 15, 2008)

avare said:


> What is your background? Lighting? Imagine replacing a 120V nominal lamp with a 110V nominal but same wattage rating. To the unknowing, the lower voltage bulb is obviously brighter.



AH... Now you are talking my language that makes perfect sense to me.


Thanks everyone. Lots of questions there that I just can't answer because I wasn't in the booth when the guy was setting up the DSP. I'll have some conversations with the installers and the consultant who picked the sub & amp in the first place and see if I can get to the bottom of any of this.


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## SHARYNF (Jun 16, 2008)

I guess my take on this is there is no problem with getting a more powerful amp, but getting to the bottom of what caused the problem is important since you could have a problem lurking in the background that will show up at a very inconvenient point in time, for instance, you could have a wiring problem with an intermittant short, a cold solder problem etc, again an underpowered sub tends to reveal it self a a lack of punch, more of a sloppy sound. Your description tends to be in my experience, an over driven input that is then amplified, a very low frequency noise signal that is getting into the signal or a wiring connection problem. 
TYPICALLY what is done that is different than how you describe the 100 hz crossover addition is to put it into the feed side of the dsp so that all the below 100 hz is fed to the sub, usually it is NOT taking the signal below 100 hz from each output and then combining them into a sub. In smaller home type systems there is an option to run the speakers a full range and then have an LFE sub, but typically this is not the approach taken with a large scale PAC PA system.

How was the DVD feed set up, was the DSP being fed a 5.1 signal split out so you were feeding 5 in put channels on the DPS and then creating a LFE .1` signal? Again typically PA systems are not set up in Dolby 5.1 format usually because this format creates a sweet spot location, that is not practical in an PAC size audience space

Sharyn


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## avare (Jun 16, 2008)

SHARYNF said:


> ...getting to the bottom of what caused the problem is important since you could have a problem lurking in the background that will show up at a very inconvenient point in time...



It is difficult in threads like this to sum up in simple terms why some people are going beyond what the simple fix is. Your quoted text does that very elegantly.

Thank you Sharynf

Admiringly,
Andre


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## gafftaper (Jun 16, 2008)

Hey a big thank you to all of you. I've learned a lot in this thread. I'm not sure what's going to happen as a lot of it is in hands of others who may or may not be as expert as this group... (unless Sharyn wants to stop in next time she flies north  ) 

Oh and to answer your question the DVD player has 5.1 outputs on the back that go directly into the DSP. On the output side when playing a DVD my patch panel amp output one is Front left, 2 is Center, 3 is Right, 4 surround left, and 5 surround right.


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## SHARYNF (Jun 16, 2008)

We could start a whole new thread on 5.1 vs surround in theater 

Just some thoughts on it:
Obviously surround has a real place in a theater where you are looking to be able to place sounds originating from locations other than from the stage. Problem is it is easy to confuse this with running 5.1

Dolby using a home dvd player in a PAC setting has all sorts of gotchas that you need to be aware of

First off, typically it assumes a speaker placement that is designed for a small space, if you look at a cinema install you will notice that the surround speakers go all down the sides, with multiples and typically NOT in the rear.

5.1 decoders on the higher end side of things have two options one for small speakers and one for large, with the difference being with small speakers, the low frequencies (dolby I believe uses 125 as the cutoff frequency) removed from the speakers and routed to the LFE channel. In the large speaker setup the LFC channel is used IN ADDITION to the low frequency content in the speakers. The LFE channel when you encode a mix if it is done knowlingly, has specific content that may or may not be present in the main mix. ALso keep in mind that all the placement is based on phase relationships of the various signals with reference to one another. 


In addition the spec for the lfe channel and Bass management from dolby has a 10 db higher level for the lfe channel which is a substantial boost.

When you put all this together in a home system it is one thing, but in a PAC system it can cause all sorts of issues. SO for instance in live sound while surround might be used, and aux fed subs for sound placement and better base management, typically 5.1 is not used

So in general for most PAC setups a typical install will just use the full range left and right outputs and not to a decode to 5.1. If I play a dvd in a real cinema with a dolby processor I let the processor decode the analog input using the traditional phase related algorithms. 

If you do want to keep running the outputs from the decode, I would recomment that you get a DVD player that allows you to select the "speaker size" setting this will allow the decoder to not place the low frequencies in the speakers, BUT typically you then need to select subwoofer, and this means that you would need to connect the lfe channel to your sub amp. It might be worth talking to the original DSP programming folks who originally speced the system as to how they were looking at setting up the system. In general when a system is value engineered to reduce cost and then an alternative is added back in later, it is worth having the original designer review and recommend exactly that device you add back in to the system, where it is placed and how the dsp settings are altered. These systems typically don't perform to optimum simply based on a lower cost plug and play approach. Again in general the high cost is not for the equipment put for the rigging to place the SUB and many times the original designer can come up with a lower cost location, but also re spec the dsp settings for time alignment, etc. 

Here are some links to dolby guides that might be of interest

http://www.dolby.com/assets/pdf/tech_library/L.mn.0002.5.1guide.pdf

http://www.dolby.com/assets/pdf/tech_library/4_Multichannel_Music_Mixing.pdf

Brad probably has a lot more experience in installs so it would be interesting to here his comments

In addition typically in a HOME environment the barking type sound is NOT from the sub from from the speakers which are being fed to high a level low frequency content which goes beyond the ability of the more limited range speakers to handle the signal.


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## gafftaper (Jun 16, 2008)

One thing I noticed, even though it's only a 200 seat black box, the 5.1 effect is highly localized. So it'll sound great to a half a dozen people but will be completely lost on the rest of the room.

For sound effects I'll be running them on SFX with an 8 channel Layla 3G into my sound board. So I'll be able to assign each effect to any or all of 8 speaker outs as you described... which is REALLY cool. I've been tinkering with SFX for two shows now and I'm in love. It's so cool and does things that just physically are not possible the old fashioned way.


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## avare (Jun 16, 2008)

gafftaper said:


> One thing I noticed, even though it's only a 200 seat black box, the 5.1 effect is highly localized. So it'll sound great to a half a dozen people but will be completely lost on the rest of the room.



What is the speaker setup? What is the assignment of the speakers to the DSP channels when in 5.1 mode?

Are you using a home DVD as source? It was probably remixed for home 5.1 etc sound. Movie theater sound systems have multiple speakers fed the same signal for surround left, right and rear channels. 

You are getting into the deep end again on sound. The The Recording Academy's Producers & Engineers Wing _Recommendations For Surround Sound Production_ describes several of environments used for surround sound and is the right price at free. Another good reference on movie theater speaker systems (and still free) is the JBL _CINEMA SOUND SYSTEM MANUAL_. These are in addition to the excellent documents SHARYNF linked.

Andre


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## gafftaper (Jun 17, 2008)

I have four EV ZX5's and two EV ZX1's It's Currently set with the 5's for the front and the 1's as surround (with one 5 not in use). As for the DVD player... can't remember what brand it is but it has 5.1 outputs on the back of it (no need for an encoder). So I've assumed it's from the pro-line... can't remember the brand but I believe it's a fairly major player. I haven't gotten into the DVD player menu at all but it does seem likely that if it has the decoder built in it probably also has some sort of equalizer or presets built in as well. The DVD goes directly into the DSP and I can only adjust it's volume by way of my "Biamp" rotary controller on the panel. 

Crap more reading! I seem to be swimming in the deep end a lot lately and there is a lot of reading involved.


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## SHARYNF (Jun 17, 2008)

Your experience re 5.1 in a PAC or even a small black box is very typical, and why most sound folks DON'T use it in this enviroment, it is as you are saying designed for a home type system with high a highly localised sweet spot. The theater systems while they can use a similar source, have a very different implimentation on how the speakers are placed and setup.

At least you are having fun with your new facility ;-)))

Sharyn


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## derekleffew (Jun 17, 2008)

<Lighting guy talking audio here, now I'm gonna get a buzz in my SourceFours> How exactly does one attempt to do 5.1 in a black box 3/4 thrust/arena configuration? Correct me if I'm wrong, but aren't movies presented in a "proscenium" audience configuration? 

Take a clue from CDS' _KÁ_ or _Love_ and put 5 speakers in every chair. Next time I talk with Jonathan Deans, I'll send him right over. The LCS system for your 200 seats shouldn't be *too* much more than the entire cost of your building, Gaff.

I have to get back to installing the 32" LCD in my sister's bedroom now. Haven't yet decided on 5.1 or 7.1, opinions?


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## gafftaper (Jun 17, 2008)

derekleffew said:


> I have to get back to installing the 32" LCD in my sister's bedroom now. Haven't yet decided on 5.1 or 7.1, opinions?



My vote is for 10.2!


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