[Mark Norman]

Hello all,


I really need some help. I am having a real problem with bass cancellation in my HT. Right in the main listing position I have a terrible bass null. It is big enough I cannot move my chairs out of the area. So I must relocate my sub (difficult but possible) or do some sound treatments?

Any information or reccomendations you could give me will help temendously.


Room Dimensions:


H=7'6" W=11'2" L=19'8"


Set up.: All descriptions are from seated position facing the screen(16').


Front projection using a 92 x 52 screen. Double doors in the rear of the theater, 2 doors on the left side if facing the screen. All doors are six panel solid. All walls and ceiling are drywall and heavily insulated for sound.

Wall to wall carpet. This room is in the basement with concrete foundation walls behind the front and right side walls.


Speaker setup:


Mains are approx 1" from back and side walls

Center is center 1" from back wall

Sub is between front left main and center approx 5" from back wall. Cross over is set to 80hz.

Surrounds are in back corners of room and are direct reflecting.

I have an additional sub that I am using with the Center channel so I have the center set to large with the sub high pass filter on 100hz.


I have the mains and the center set to "large" on the pre/pro set menu with the crossover set at 80hz.


The problem is like a square in the room that there is no bass at most frequencies. This area is 8' from the front wall, 3' from the side walls, and 2" from the back wall. THis forms a 5' wide by 9' long cancellation area. My seating position is between 14' and 16' from the front of the room.

The bass is set loud enough everything is readdy to shake off the walls, but you can't hear it in the null spot, but you can hear everything rattling.


I have tried moving the sub along the front wall and down the right side wall up to 12' from the front.



Please help me out....I'm ready to give up!



Mark

 

[John Ashman]

Ugh, that's weird. Your room sounds close to ideal. Have you tried inverting polarity on the sub? Should be a phase switch. It *could* be that the speakers/sub are out of phase and that causes the cancellation. What speakers and what sub? Have you tried shutting of the other sub? They could be out of phase. Are they the same sub? Can't form an opinon on this one yet without getting rid of the more obvious possibilities. What gear also and how is it attached? It may be an electronics issue. Have you tried just running the sub alone and seeing if the null still exists? I suppose your ceiling could be acting as a huge absorber.


John

 

[Mark Norman]

John,


Thanks for your reply.


My speakers are Paradigm Monitor Series, mains are 9's(towers), center is cc300, and surrounds are 3's(bookshelf).

The main LFE sub is the Paradigm PS1000 (10" forward firing) and the sub connected to the center channel is the Yamaha Active Servo 150.( dual 8" forward firing)


EQUIPMENT

Pre/Pro- Rotel 1066

5ch Amp- Rotel 1075

SACD- Sony SCD555ES

DVD/DVD-A -Samsung HD1000

DSS/HDTV-Zenith HD520

Projector- Sharp Z9000U

LD- Pioneer CLD 504

Outlaw and PA Audio Cables


I have not messed with the phase setting on either sub, but I have tried turning one sub off, it did not change anything.


My ceiling is drywall over 12" joists with R-30 insulation between the joists. The flooring above that is 1/2" cement board and 1/4" ceramic tile.


I am damn clueless on this one, what do you think or suggest John? I'll try anything at this point.


Thanks again


Mark

 

[hwc]

First of all, your subs aren't doing anything at all for the front and center speakers because you have them set to full range (LARGE). Therefore, NO bass is redirected from the front and center speakers to the sub. The only bass being played by either sub is redirected bass from the surrounds and the LFE channel. You essentially have five speakers trying to play low bass -- both subs, your front right, front left, and center. It is no wonder that you are getting cancellation out the wazoo.


Here's where to start:


Ditch the Yamaha subwoofer. Take it upstairs and hook it up to your computer or something. It is going to cause you nothing but grief. It is virtually impossible to balance two different subwoofers. With eight inch drivers, it's probably not playing anything below 40 Hz anyway.


Move the Paradigm subwoofer to the corner. You may want to move it around some more later, but let's start with a baseline setup. With a single 10, you will most likely need the 3 to 6 dB of free output from the corner location.


Set ALL of your speakers to high pass (SMALL).


Set the Subwoofer to ON in the pre-pro (not MAX).


Leave the RSP-1066's crossover at 80 Hz. Defeat or bypass the subwoofer's internal crossover if you can. If you can't, turn it as high as it can go as an interim measure until Paradigm's tech dept. will tell you how to jumper on the amp board to bypass it.


Use a Radio Shack SPL meter to calibrate the system using the pre-pro's test tones. All speakers should read 75 dB with the meter pointed to the ceiling at a fixed location near your seating area.


To compensate for inaccuracies in the meter, start with the SUB calibrated to 72 dB on the meter. You may need to go up or down one dB from there, but don't touch it for at least a week and don't go chasing one particular recording trying to set it by ear. The idea is to get it set for a broad range of recordings.


Play a bunch of DVDs and CDs. Let us know what the results.


PS: This is covered in some detail in the RSP-1066's owners manual.

 

[Mark Norman]

HWC,


Thanks, I will do as you said today. I guess that concept does make sense.


I really notice a problem with SACD and DVD-A, which I am a ware of the double bass issue. How do you have your system stup for the multi-inputs?


Thanks again


Mark

 

[jmcomp124]

Quote:

Originally posted by hwc Move the Paradigm subwoofer to the corner. You may want to move it around some more later, but let's start with a baseline setup. With a single 10, you will most likely need the 3 to 6 dB of free output from the corner location. Set ALL of your speakers to high pass (SMALL). Set the Subwoofer to ON in the pre-pro (not MAX). Leave the RSP-1066's crossover at 80 Hz. Defeat or bypass the subwoofer's internal crossover if you can. If you can't, turn it as high as it can go as an interim measure until Paradigm's tech dept. will tell you how to jumper on the amp board to bypass it. Use a Radio Shack SPL meter to calibrate the system using the pre-pro's test tones. All speakers should read 75 dB with the meter pointed to the ceiling at a fixed location near your seating area.

Mark,

I suggest doing exactly what hwc recommended with an additional tweak for the phase. After you set the crossover at 80Hz, play an 80Hz test tone and try different phase settings at exactly the same location of the SPL meter. The phase setting that gives you the loudest SPL, is the correct setting. Since your mains can go pretty low, you can also try a 40Hz crossover for the mains, with the sub crossed over at 40Hz and your center crossed over at 80 or 120Hz. Try an AVIA sweep and let us know what you find.

-Jai

 

[hwc]

Quote:

Originally posted by Mark Norman How do you have your system stup for the multi-inputs?

I don't. I refuse to support a format with no standardization of channel usage, no bass management, limited title selection, and a disregard for the system configurations that make sense with every receiver or pre-pro sold in the last five years.


Using multi-channel analog inputs to bypass the system configuration options of a Dolby Digital 5.1 channel system makes no sense to me. Apparently, I'm no alone since a whopping total of only 300,000 DVD-A discs were sold last year in the United States.


The way I look at it is: DVD-Video discs work with my system. CDs work with my system. FM radio works with my system. My old Nak cassette deck works with my system. My Motorola digital cable box works with my system. Why should I buy recordings that don't work with my system? If they want me to buy another copy of Live at the Fillmore, remaster it in Dolby Digital 5.1, don't whip out the old quad mix from the 1970s and tell me it's the greatest thing since sliced bread.

 

[audioguy]

Mr Norman:


While I agree with hwc's recommendations, it still may not address your problem. While the sub in the corner will certainly give you more output, it will not necessarily solve the null issue. If it does not and if you are able to do so, try moving the sub much closer to your listening position (beside the sofa or behind it.


I have a huge null in my room followed by a huge peak if my subs are in the corner (or anywhere near the corner). I used a Real Time Analyzer to find a much more optimum position.


Good luck !!

 

[jmcomp124]

I started using ETF based on BruceD's recommendation and I am happy with it.

-Jai

 

[hwc]

Quote:

Originally posted by audioguy Mr Norman: While I agree with hwc's recommendations, it still may not address your problem. While the sub in the corner will certainly give you more output, it will not necessarily solve the null issue.

That is true.


However, there is really no way to know what you are up against until you get a good baseline setup, with proper bass management, and without multiple speakers trying to play the same bass in the system. He's got four different types of speakers in five different locations playing the same redirected bass and LFE channel. That's a recipe for a mess that nobody could possibly sort out because there are just too many variables. For example, lets say that the Yamaha sub is inverting the signal. You've just cancelled most of your bass from 40 Hz to 80 Hz.


Optimizing a nice simple logical system configuration is the only way to really evaluate other problems. Too many people start chasing down a tangential path with ever more complex schemes to try to band-aid a problem that fundamentally stems from their system configuration and calibration.