Fill a room up with amps and buy stock in the local power company?

Sweet rack setup.

What exactly is the equipment in the rack?

Whoa, if you are really running 2 ohm load to that subwoofer with the amp bridged you probably haven't pushed it pretty hard. It isn't rated for anything under 8.

Crown's do a great job of protecting themselves, if you give them too little load they will just mute (and the IOC lights come on) on any of the older models (I have a DC300 Series II in my studio). The newer ones continue playing, but sound distorted as heck once you get below 1 ohm.

I would ask if you were sure they were parallel, but someone with that rack of amps should know the difference between parallel and series.

I just discovered Crown has the service manuals and schematics for all the discontinued amps for download on their site. That rocks.

gonk:

I hear 10 dB tossed around in some circles as well. I have a degree in sound design and in every class I have attended or taught, we have used 6 dB as the half/double. That matches up exactly to what you see on equipment. It is possible that if you take a measurement of actual air pressure coming off a cone it may line up more with 10dB being double, but that wouldn't correlate to what you see on your 990 display.

3 dB is considered the minimum amount of volume change to be noticed by most people with average hearing, although in my personal experience a great many people can hear smaller changes than that, even those often not discerning about what they are hearing (not mentioning my wife specifically....). This is a rule of thumb and depends on relative factors.

The rack houses 7 Crown PSA-2 amps. Spec's are here:

http://www.crownaudio.com/pdf/legacy/k1071-8.pdf

I like 'em. I've owned one of them for ~15 years, driving my main speakers, and just recently (after buying the 990), upgraded all of my amps to them... found a sweet deal on a group of used ones.

Even though I'm not pushing them very hard, they will warm up a room. Plus, they do elicit some cooling fan noise; so getting them into a separate room (storage room shares a wall with my theater room) has proven to be a good move. I ran 3 20amp circuits from my breaker box, and hooked up individual switched outlets for each amp (switches are near the 990 and other equipment- so I don't have to go back into the storage room to turn them on/off.

To help describe how I'm using them, here's the "front" side of my system:

http://tinyurl.com/en4ml

Amp 1: left main (915W into 8ohm)
Amp 2: right main (915W into 8ohm)
Amp 3: center (4 ohm, 2 8 ohm speakers in parallel; ~1400W)
Amp 4: sides (hanging speakers), stereo; 275W X2 @ 8ohm
Amp 5: rears (not visible in picture, on floor behind and to the side of love-seat: stereo; 275W X2 @ 8 ohm
Amp 6: Sub. It's the coffee table looking thing back in the corner with a lamp on it. Home built cabinet, using 2 4ohm 15" Cerwin Vega Drivers wired in parallel. Not sure exactly what the power for the amp is in this situation- somewhere around 1800W would be my guess.
Amp 7: spare. Not hooked up right now.

The top piece of equipment in the rack is a Perreaux PMF-1850 power amp. Also not in use at the moment. Might sell it. Might keep it as a backup. Might use it somewhere else. Haven't decided yet. It's way too nice of an amp for garage duty; but doesn't pack quite the punch that a PSA-2 does.

With the exception of the little rear speakers, all of the others are Klipsch Professional/Industrial models, with fuse protection, heavy duty drivers for increased power handling, etc.

We had our King Kong premier last night- good fun.

I have enjoyed and been informed by the previous posts and a couple of questions come to mind. When I calibrated my system I set the 990's volume at "0" and used the manual test tone function to set each channel at 75db. I have tweaked a couple of individual settings (up a db or two for example) but nothing drastic. Now the questions based upon a simple condition: playing a CD in 2 channel mode.

1. When I play a CD using Upsample at -30 on the 990 volume I get 80 to 85db at my prime listening position using my SPL meter C weighted and Fast. At -20 I get 90 to 95db; Discussions above about volume settings of -10 to 0 make me think noise induced hearing loss. I imagine there might be some variability due to individual systems but do my results when playing a cd seem reasonable to you guys?

2. When I adjust the left or right channel a db or two in stereo or other 2 channel mode I can hear a difference in the location of the stereo image. I can easily tell that it moves left or right. Since I can hear the change is the 990 truely changing the calibration for an indvidual channel by a single db or am I missing something?

1. your cd seems reasonable to me. how loud is -20 on your system? Do you like it loud or what?

2. Do you have your speakers toed in at all? A slight toeing in can improve the soundstage quite a bit. Not much toeing in is needed.. just a slight amount.

*although not a big deal at all.. use the "slow" on your SPL meter.

AVFan,

There are a couple reasons that you may see increased dB readings over your calibration. First off is that if calibration used a slow response (i.e. RMS or 'average') then that will show up a bit lower volume than fast response (i.e. peak). With sine waves RMS levels tend to be around 70% of peak levels.

This can be exacerbated by how CD's are mastered. Their average to peak values are reduced via limiting and compression. While the peak values should not get any higher, the average values do which makes them sound louder and puts more sound energy into the room.

For your second concern, slight volume changes are one of many clues the brain uses to figure out where sound is coming from. While a typical person may not usually be able to hear a 1dB change in volume from a single source they still will be able to interpret this change (and smaller) in the situation you tried.

When we discussed many people not discerning a 1dB change, you would have to change the level of all speakers that amount, or the inputs, to test that. The problem with testing that is that one becomes more sensitive when they are doing the adjustments, and they can lead themselves to believe they are hearing what they aren't. Basically when you adjust the levels you become more aware of it and it makes the test not as accurate. In some cases since you know you are adjusting things you will fool yourself into hearing a change that is imperceptible. To properly test this you would need someone else making changes where you couldn't see them.

Shawn,

I'll have to check the info that came with my SPL to see what the slow response setting actually does (e.g. RMS or average) versus the fast response setting. Regardless, I used the slow response setting for calibration and when I played the cds in stereo, so I'm not sure the fast/slow setting is a reason for the difference.

My sample of cds was pretty small when I made the measurements I noted above, but I don't recall their being a real significant difference in volume between cds. Yes, there is some variability (in particular one George Winston cd stands out as louder than others in my collection) in how loud cds sound.

I agree that if all the speaker volumes were increased 1db it would be hard to tell, but as I think you noted, when only one is changed it stands out. My second question was, or should have been, what volume change is noticable when only one speaker is adjusted? I notice the difference (e.g the "location" of the singer drum, specific instrument location) when a 1db (as noted on the setup screen) change is made to the left or right channel in stereo even when the master volume is at -30. Or another way:, When I make a 1db change on the setup screen do I really get a 1db change assuming -30 master volume that equates to 80 to 85db at my listening position? Sorry for the number of variables.

Something I just realized that would have greater bearing than what I said before is what level is being calibrated to 75dB at 0 on the display? For instance if you use Avia or DVE to calibrate a system, they output a pink noise and have you set it to 75dB. But that is not at full output, it allows for peaks well in excess of 100dB. Off the top of my head I don't know what output the 990 would use as its noise level, but it probably wouldn't be 0dBFS (decibels Full Scale, the loudest one can do in a digital signal). But likely there is some headroom involved.

As for what volume change can be detected when you adjust one of many channels, there is not an easy answer. It depends on the material you are listening to, and the person listening. It should be well under 1 dB, maybe as little as .3 dB, but there are a lot of variables involved.

The easiest to hear, and hence the smaller change needed to notice, would be a sound that is recorded well and the panning location can be heard, especially something like a vocal in the center of the image. As soon as a small amount of adjustment is made that sound will seem to move toward the louder speaker(s). Similarly if you add a slight amount of delay to one or the other the sound will seem to come more from the side without the delay. This is a function of how our brain works.

Now if you have a system that doesn't image very well, or a recording with issues so that the imaging is rather blurred, you can probably make a bigger change without noticing. Unfortunately I can't just say something like, 'oh, yeah, it is .564 dB.' Sorry.

Oh, and for the very last part of your post: If the 990 is truly working in dB (which it sounds like it is) then yes, no matter what the master level is set to, if you adjust 1 dB, that channel will change by 1 dB. It only gets weird with equipment that uses arbitrary and/or weird level indications. My current receiver behaves like the scale it shows is linear. That can lead to some real confusion!

Thanks, Shawn. When I calibrated my 990 I used its internal test tones. I have the DVE disk but I have not used pink noise from it to set the audio. M&K recommended using pink noise (one speaker at at time) to align the tweeter to the primary listening position; they said it would "snap" into place (Skyblazer noted something similar). Looks like I have two reasons, speaker alignment and volume to reference, to break out the DVE disk.

The ability to distinguish less than 1db changes between speakers is one of the reasons several gunslingers (including me) would like to have 0.5db versus 1db increments in the 990 speaker calibration. My old receiver had that ability and it was particularly helpful when fine tuning the center channel.