svs - front and center - what the heck??

McLoki · November 2004

I was charting my svs 25-31cs+ since I added some granite under it. I highly recommend it if you are using a cylinder on a carpeted floor. I was able to pick up a free scrap at a local store and just set it on my carpeted floor, and sub on it (15.5"x22" - not the ideal size, but it was free) - bass is much now much tighter and more distinct. (and I thought it was very good before)

Anyway, I have the test tones burned to a cd and normally play them through my DVD player. When I do this, unless the AVR is set to stereo, it plays only stereo signals through the front left and right, and all combined signals go to the center channel. Usually for the test tones, it plays only through the center. I decided to try and put it in stereo mode to see what happend to some of my room dips, and was shocked with what I found.

Keep in mind my front left and right speakers are LSi7's and they are set to small (so should be crossed over at 80hz. I did double check all the numbers to make sure I was not reading them wrong.

How could the front speakers start affecting performance at only 20hz? Especially LSi7's? The values in the chart are corrected. Any ideas? Doc? Anyone? what the heck is going on? It does explain why I dont hear the room dips as much as you would think. (only tested with center channel in the past) Anyone else have wierd issues like this from front stage to center?

McLoki · November 2004

chart didn't add......

Airplay355 · November 2004

that sure is one ugly chart

VR3 · November 2004

With only a 10db break between frequencies, its not as bad as it looks.

However it is pretty bad...

and I have a question...

Why on earth would you run test tones through your center???

McLoki · November 2004

Originally posted by Vr3MxStyler2k3
With only a 10db break between frequencies, its not as bad as it looks.

However it is pretty bad...

What do you recommend to fix it? (moving walls is not a good option - and the speakers are in about their best spot). Would a PEQ help much or is it just as good as I get until I build a room for music/theater?

Originally posted by Vr3MxStyler2k3
and I have a question...

Why on earth would you run test tones through your center???

Didn't really think about it. My AVR automatically selects THX when I play the DVD player. Since the tones are constant, they play through the center. With the LSi7 - LSiC there is not a big difference in sound between them. I just wondered what would happen if I put the AVR in stereo mode. I was expecting a change above 50hz (maybe with my 2nd major room dip). The confusing part to me was the changes below 50hz.

VR3 · November 2004

I...

Would mess with the Phase on your SVS...

run sweeps for 0, 180, 90, and anything you want *since it is a knob* just do it until you find the flattest curve.

Move it around, eff with the crossover, volume, etc etc

PolkThug · November 2004

McLoki,

I believe that different frequencies can effect each other, as shown in your chart. Think about noise cancellation headphones; this is the opposite of that.*

Regards,
PolkThug

*My logic comes with no guarantee.

kberg · November 2004

Not to hijack this thread, but I noticed in the initial post that it appears tighter bass may be achieved by placing the sub on a slab of granite, as opposed to just placing the sub directly on a carpeted floor? If this is true, is there typically a significant difference?

I was only used to seeing granite used between the sub and hard flooring to significantly reduce vibration, etc. But if much tighter bass can be achieved by using a granite slab even for carpeted floors, then I may go grab a hunk of it.

Comments anyone?

sowen010599 · November 2004

Think about it, if you have carpet over concrete, the subs already on a MASSIVE concrete block.

kberg · November 2004

Originally posted by sowen010599
Think about it, if you have carpet over concrete, the subs already on a MASSIVE concrete block.

So, being that I already have carpeting over a concrete slab, another piece of granite over the carpeting probably wouldn't make any difference?

McLoki · November 2004

If the carpet is very short I don't know if you would see much benifit. In my case the carpet was medium height and on the first floor (with a basement). I noticed the sub seems to vibrate less and the bass is much improved. (the lower the bass the better the improvement.)

An easy way to tell the differece was when I was calibrating the sub with the AVR test tones. With the SPL meter set to slow it would jump about 3 db with the bass tones. With the granite under the sub, it jumps only about 1 db. This difference is noticable to hear as well.

Like I said, I was able to go to a granite place and pick up a piece about the size I needed (uncut) and they let me have it for free. If you can find a similar deal, it would be worth the test, then you can always take it back in to have it cut if you would like. (edges polished, that sort of thing)

It made a big difference for me. (also keep in mind that my sub fires down - I doubt you would see that kind of change with a front firing sub)

Michael

Tour2ma · November 2004

Stabilizing any speaker, sub to full range, front-down-side-up... whatever firing will help. Any energy going into cabinet movement is energy not going into sound reproduction...

As to your tracings...
It seems clear that your room is playing hell with your curve. What level are you calibrated to? 85dB?

Did you take any readings at other listening spots? If not, move around some at a couple different frequencies and see what knid of variations you get.

Sid's sub phase suggestion is a good one. Might help that 71 Hz dip. Doc posted some phase adjustment tricks to minimize the effort around here somewhere. But before you do this I think you have some other needs to attend to....

Your mains also appear to be interacting badly with each other (the enormous dip at 100 Hz and boost at 142.5). Try sweeping the mains with the SVS out of the picture, but the dip will likely still be there. Since I now know your room well

, I know your placement options are limited, but you can try toeing the mains in or out a little and see if you can improve the situation. Until you get them to behave, I see little point in trying to blend in the SVS using its phase adjustment.

Other than blaming it on the room, I have no idea why the center dies in the 140 to 160 range... A single radiator should not have this big of an issue. Try taking readings very close to it to be sure the speaker is not an issue.