grainy highs with spikes on 803s ?

[Eliav]

Hi
I have recently noticed some grainy highs with the metal spikes on.
The 803s are two weeks old, driven by a rotel 1095/ 1068 processor/ 1060 dvd.I use audioquest copperhead interconn. and speaker cables.
Since my room floor is covered with a very thin rug, i started with the rubber bottoms which produced some smeared lows. When I switched to the metal spikes, the speaker looked substentially taller ( the rug is very flat) and sound grainy in some cd's. It gives you a certain discomfort as if you want to ask the performer to clear his throat...Imaging is wide however hardly deep ( speakers 4 feet away from rear wall).
Any advice/ tip would be very much appreciated.
Eliav

[akhter]

Hi
I have recently noticed some grainy highs with the metal spikes on.
The 803s are two weeks old, driven by a rotel 1095/ 1068 processor/ 1060 dvd.I use audioquest copperhead interconn. and speaker cables.
Since my room floor is covered with a very thin rug, i started with the rubber bottoms which produced some smeared lows. When I switched to the metal spikes, the speaker looked substentially taller ( the rug is very flat) and sound grainy in some cd's. It gives you a certain discomfort as if you want to ask the performer to clear his throat...Imaging is wide however hardly deep ( speakers 4 feet away from rear wall).
Any advice/ tip would be very much appreciated.
Eliav

Taking a shot in the dark here, but is the floor very stable? I wonder if the sonic waves are causing something else in the room (the floor?) to vibrate. The rubber feet might have stablizied the floor with its weight.

[Eliav]

Thanks Akhter.
The floor it is concrete solid and stable..no wooden stuff. The side walls in both sides has big glass windows and big glass door, can this produce unwanted vibrations ?

[Djas_Puhr]

Hey Eliav,

I could see how your speakers, with the metal spikes on, might be transmitting vibrations through the concrete floor to the walls/glass, causing them to vibrate... but I would have thought this would have only been a problem with bass frequencies...

If this is the case then the probable reason you hadn't experienced the problem when using the rubber feet is that they would have been acting as a kind of decoupler between the speakers and the floor, reducing the amount of vibrational transfer...

???

Mj

[RobP]

It sounds like to me that having the speakers coupled with the floor caused a muddy bass response that covered up a problem that was already there. Those glass panels on each side of your speaker are highly reflective and can cause your problem with your upper end, just for giggles throw a couple of heavy blankets up on each of the glass panels and take a listen. I would almost bet your problem will be gone.

[Eliav]

Thanks soundgravy!
I have thought about this "too much glass" problem , I had hung a new heavy curtain on one side and will cover the other side soon. I hope the heavy curtains are not going to "swallow" the highs / kill the imaging. I will definitely keep the forum posted when I am finished.
your tip is very much appreciated.
Eliav

[Aussie Geoff]

I hope the heavy curtains are not going to "swallow" the highs / kill the imaging.

Not a chance - the best rooms are realitvely dead so that the imaging is not spoilt by reflections from the walls, floors etc...

Enjoy

Geoff

[greggz]

It sounds to me like the negative effect you are describing is "comb filtering" that is occurring due to all the hard surfaces in that room.

Here is pretty good overview of acoustical problems in rooms. http://www.asc-hifi.com/acoustic_basics.htm

What you need is a combination of absorption and diffusion at the right spots. Treating a room for stereo is different than treating a room for HT. With stereo you still want a rather live room in order for the stereo effect to convey the proper soundstage. For HT you want more deadening because you have 5 speakers rather than 2 responsible for creating the directional cues in the soundstage.

You'll need proper absorption at the primary reflection points in the room. You can find the primary reflection points by doing the old mirror trick. (One person sits in the primary listening spot and another moves a hand mirror along the walls and ceiling. When the listener can see the speaker in the hand mirror, that is a primary reflection point for that seating position. Each speaker has its own reflection point on each surface. So for stereo, there will be 2 spots on each wall, the ceiling and the floor. For HT most people just concentrate on the front 3).

The only thing you can do with the floor is thick carpet with thick padding under it.

On the walls, using something like drapes can help to a degree, but drapes have a very uneven absorption across the frequency spectrum. Its better to use something like Owens Corning 703 or 705 rigid fiberglass panels covered with Guilford of Maine acoustically transparent fabric.

http://www.owenscorning.com/comminsu...s700Series.pdf

http://www.acousticsfirst.com/gom/afc_GOM_Chart.pdf

Most people don’t do ceiling treatment because it has 0 spousal acceptance factor.

Directly to the side of your primary listening position and behind your listening position you need diffusion. Book cases filled with a variety of height and sized books make great inconspicuous diffusers. If you choose to go the pro route, look for something like the RPG Skyline three dimensional diffusers.

http://www.rpginc.com/products/skyline/

To learn more about acoustics, start with Ethan Winers great article. http://www.ethanwiner.com/acoustics.html

[Eliav]

Hi gregqz !
Excellent articles ! I would very much like to try some of these traps, especially the corner bass trap. How high should the 705 FRK corner trap should be ? should it reach all the way up to the ceiling?
Anybody mounted fiberglass on their room's walls without getting in trouble with their wives ????

Cheers
Eliav

[greggz]

I haven’t built my sound panels, diffusers, or bass traps yet. I'm still in the research stage (a.k.a. the procrastinating stage).

Here’s a quick and easy tip to determine how much you will benefit from bass traps.

- Go to Home Depot.
- Buy 16 rolls of pink insulation (R-factor doesn't matter. Faced/unfaced doesn't matter)
- DO NOT open/unwrap them. KEEP YOUR RECIPT.
- Stack 4 rolls in each corner.
- Calm your wife down. “This is just an experiment. This is just temporary.”
- Do some critical listening to your system.

If you hear an improvement, return all 16 rolls of insulation and purchase/build more esthetically pleasing looking traps.

If you hear no improvement, return all 16 rolls of insulation and take your wife out to eat with the refund money for being such a good sport about having 16 rolls of insulation stacked about the house.

[Eliav]

Hey Gregqz! /Geoff
Sounds like a plan, will do this week !
By the way, I have covered the big glass doors on my side walls with big, heavy ( and wife acceptable) curtains - gone are the grainy highs... !.
Why am i not yet hearing "deep" imaging ? it sounds like the speakers are wide open, infinitely open from side to side, almost nothing presented deep toward the rear. Is it my imagination ?

Thanks
Eliav