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pb2-ultra gain at the 1/2 way mark in a 12x 17 fully enclosed room. Is this ok?
15 replies to this topic
Posted October 23 2004 - 04:44 AM
Just got a pb2-ultra and I have somewhat of a bass null at my listening positon in a fully enclosed 12x17 room. I cant move my seating area. Moving the sub around helps a little but not anything significant. The bass in all the corners is considerably louder than in the middle open parts of the room (pretty normal right?). It is located in the front right corner of the theater right now. I also have a jbl s-38 on an open bar stool (used as speaker stands) next to the pb2 and then in the middle of the wall sits my 36" tube tv on stand. In the other front corner is my sanus equipment rack with a sherbourn 7/2100, sherbourn pt-7000. All speaks set to small w/ 80hz cross, sub on, night modes off, etc. Pb2 is at 25hz all ports open setting. With the subwoofer trim set to -4 I have to put the gain on the pb2-ultra at the 1/2 way point to get 2-3db hot over my mains. I am using avia and the pb2 ulta manual says to put the sub at 87-88 db vs 85 for the mains which is what I have. It sounds good in there, but it seems wierd to me that I have to have the gain at 1/2. Maybe it is just the characteristics of my room? My question is will this hurt the sub to have the gain this high when running at or near reference levels? I would assume not becaused everything is calibrated correctly according to Avia and my Rat Shack spl meter (c weighting, slow response). I think I need bass traps in the corners at this point. I tried calling SVS About this but they are closed today. I would really like to know if I am ok with this as I would like to fire up a few movies today, but I dont want to hurt the sub if the 1/2 gain thing is not right for some reason. Need help....
Posted October 23 2004 - 05:15 AM
According to the pb2-ultra manual, mains should be at 85 with avia and the sub at 87-88 in order to run 3db hot. Are you telling me the manual is wrong?
Posted October 23 2004 - 06:44 AM
Wow. Just got done reading that for the last hour or so. Thanks for the info as I had no idea. In one of Ed's last posts or so he says 83-84 for flat with avia and 86-87 to run hot which is about what I am at. So My original question still stands, will the pb2-ultral be ok with 1/2 gain in my room and conditions to run at or near reference?
Posted October 23 2004 - 08:35 AM
Seems to me that would be relative to what you have the output set to on the receiver wouldn't it. You can talk about where you've got the volume knob on your sub untill your face turns blue, but it also goes hand in hand with the sub output setting on the receiver. If you are testing with a sound meter and getting what people on here are saying for numbers, then I don't think you have a problem.
Posted October 23 2004 - 10:04 AM
The sub output setting on the pre/amp is at -4.
Posted October 23 2004 - 11:01 AM
When I had the PB2+ the gain was at half and phase at zero. come to find out the PB2+ and front were fighting eachother. After carefully and patiently adjusting the phase the gain ended up being less than half and with a much flatter response. just a thought
Posted October 23 2004 - 01:17 PM
Correct. The relative setting on the PB12-Ultra/2 gain is really meaningless. Proper calibration is all that matters, and you've done that. Don't give it a second thought; the manual suggestion is simply a starting point.
Posted October 25 2004 - 03:35 AM
Thanks for all the help guys. That is what I needed to know. These forums are awesome.
Posted October 26 2004 - 01:49 AM
I have my PB12-Ultra/2 gain at 50% too...no problems.
Posted October 26 2004 - 02:39 AM
FYI I had my sub gain in between the 3rd and 4th hash mark, receiver sub out at -8, calibrated about 4db hot. Periodicly the sub would not auto start and I would have to power off, then restart. Sub would work fine after that. At 1st it wasn't to often, but last month it happened 6 times. I contacted Tom@SVS, he had me lower the sub gain to half the amount that it was and increase the receiver sub out till the sub was calibrated to 4db hot again. Have not had any probroms with auto start since the change.
Posted October 27 2004 - 01:34 AM
My knowledge on the subject is miniscule compared to Tom V. and the good Dr., but I'll throw out my experience with my last two subs. While playing The Two Towers "Wall Breach" explosion at -12, my Velo CHT-15 would make a horrible, distorted "WHOOOM" sound. After turning the gain up from 1 1/2 to 3 1/2, and cutting the sub out from -0 to -5, the sub never made the sound again, and sounded much better overall. I was running my PB12+/2 just off the first hash mark (15%), -5 sub out on the receiver, +-0 on my Rane parametric, and the sub was 2db hot. I was happy with the extension of the SVS compared to the Velodyne, but didn't hear a big difference in sound quality. However, I kept fiddling. I now set the gain at 45%, -10 sub out on the receiver, and -6db on my eq. Still 2db hot, but the transformation in this sub is amazing. Much clearer with more detail. I was shocked at the difference. My wife, who couldn't care less about sound quality (until she hears better sound quality), said it was a big improvement. I can turn the volume way up without feeling like the sub is getting "muddy". Sure, the sub doesn't want to turn on if the volume is below -45, but if I'm trying to be that quiet, I don't want it on anyway. I am a believer in gain. (and SVS)
Posted October 27 2004 - 03:18 AM
The issue of sub pre-out distortion is documented. The hotter you run the pre-out, the more distortion it can generate. Why subwoofer pre-outs seem more prone (than speaker pre-outs) to this phenomenon is beyond me. Maybe with the newest generation of pre/pros and AVRs it's not a problem anymore. Nevertheless, THD levels of several percent and dynamic compression (clipping) of the pre-out signal wasn't unheard of in years past on certain AVRs. Because of these potential signal degradation issues, I always run the sub pre-out on the cool side (like -8 to -6 region). If I have problems with a sleepy auto-on circuit, I just bump the volume to get the circuit to initialize, and then it usually stays on. I have experienced sub shut-off at very low playback volumes, and in that case you can alwys just turn the switch to "on" instead of "auto". The plate amp won't draw more than a few watts from the line in "on" mode when the sub isn't being used.
Posted October 27 2004 - 06:23 PM
You may want to consider doing some kind of bass trapping in the corners. This can help minimize the cancellation at the listening spot. Properly done, it can make a dramatic improvement in the quality and articulation of the bass.
Posted October 28 2004 - 11:33 AM
I have considered bass trapping, but are there some good pro bass traps out there that can target the 40-60 hz range which is where my null seems to be? I have a big null in this range with the sub in the front corner. I found a better spot for the sub according to my FR charts, but I prefer the sub in the front corner because the low end is exagerated here.
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