3 Channel SET User meets SS Sub

[sfogg]

Erik,

Yup, the room 'singing along' can be a royal PITA. My last few rooms

had numberous rattles in the walls and such one the deepest loudest

material which was very distracting. New room is nice and quiet/solid

though so I'm loving that.

"I wonder if tennis balls would help, if I cut them in half and put

two under each front corner of the bass bin and one in back? Maybe it

would provide some isolation."

It might provide some isolation (if they can handle the weight) but if

the floor is resonating from the bass in the room itself and not

directly from contact with the K'Horns it probably wouldn't help much.

Shawn

[sfogg]

"

So would it be the bottom sub that should be wired out of phase?"

Maybe, maybe not. The bottom woofer should be wired in whichever manor

makes it *acoustically* the most in phase with the mains. And of course

the upper woofer should be the opposite phase of the bottom woofer.

To test acoustic phase with a sub and mains is fairly easy.... esp. if the sub amp has a phase control on it.

Turn up the crossovers on the sub amps as high as they will go as you

want the most overlap between the mains and the subs as you can get.

Play pink noise and with a SPL meter at the listening position invert

the subs phase (or adjust it if is is continually variable between

0-180 degrees) and find the phase which makes the meter read the

highest SPL. That would be the point the speakers are most in phase

with each other (summing best).

The other way of doing it is finding the point where SPL is lowest.....

most cancelation between sub and mains then inverting the phase to the

subwoofer from there.

You can also try the test with specific test tones instead of pink

noise. Pick a tone at or near the crossover frequency between the mains

and the sub.

Shawn

[edwinr]

My next door neighbor just bought a REL Strata 3. He's matched it with a pair of Epos M22 floorstanders. We've connected the sub via the high level speaker terminals at the back of the amp. When we got it hooked up, the first thing my neighbor did was to crank it up to horrible and unrealistic levels. He was in 7th Heaven with the sound - I was in torture.

Anyway a couple of days later he called me over. This time he thought the bass was a little boomy and one note. So we moved the sub a few inches out of the corner, set the phase from 0 to 180 degrees and bingo, we had some true low frequency response. The next thing to go was the unrealistic levels. We've tweaked it so that you can hardly notice it except where there's real bottom end.

My first comment is that some CD's have bottom end I didn't know was there. Awesome. The other thing I've noticed is that some CD's I thought had good bass - didn't. It was all mid frequency stuff. Maybe mixed for radio and boom boxes rather than hi-fi.

I reckon room nodes are only excessively excited when levels are set too high. The perceived one note bass problem cleared up when we dropped the levels down. Also I'm wondering that if the cross over level is set too high, there could be some over emphasis of low frequencies because the sub is competing with the main speakers, rather than working with them.

[sfogg]

Rel's are well regarded subs. Dialed in that should compliment a system nicely.

"I reckon room nodes are only excessively excited when levels are set too high. "

The room nodes act up any time material at their resonance is played.

The only difference when the sub is running hot is the nodes are that

much stronger. Room modes can *easily* cause +/- 15dB (or more) changes

in the amplitude response at specific points in the room. Next time you

are at your friends play pink noise in the system then walk around the

room. You might be suprised how much the sound of the bass changes

depending upon your place in the room.

The rooms resonances also cause problems in the time domain. The room

is literally ringing at all points in the room (excepting the nulls) at

the resonant frequencies in the room. You literally have certain notes

playing for longer then they should which obscures/masks music that

happens while the room is ringing. Time measurements will show these

sorts of problems pretty easily when looking at decay times.

For those that have never measured what their rooms do to bass playback

they may well be *shocked* at how much the room alters what your

speakers/subs are trying to do.

Shawn

[maxg]

Just 2 quick points:

1. The REL is an excellent SUB - certainly the most musical and most adjustable I ever came across. Why I ever sold mine is a mystery really. The only bad thing was it took so long to get the setup right - once it was there, however, I had Heresies that went from 20 to 20 and no-one could tell a sub was playing - until it wasn't.

2. The TT issues. The most likely cause of your problems is unsufficient isolation from the floor. When Tony setup his TT in a small room with a pair of B&W 802's the woofers flexed dramatically - and eventually actually broke and needed replacing. The problem was solved by the insertion under the TT of a sandwich of 2 harder materials with a foamlike insert in between. I dont know the details of its construction - but I can find out if you are interested.

I should add that this fix was massively successful. In comparison we had previously tried loading his stand with lead shot (the legs are hollow to allow this). We put in about 100 lbs of shot with no discernable benefit.