more detailed sound in lower volumes - amp VS. speakers position ?

[Eliav]

Hi
I have recently noticed that when I listen to music late at night on a volume around 35-45 ( Rotel 1068) my 803s sound very accurate, detailed and pleasant. at higher volumes (65 and up) the nice spatial organization tends to smear and fade away. I know my room acoustics is far from perfect,however , I wonder, is it the rotel 1095 " shortness of breath", or room acoustics( too much deflections, echo?) , can it be speakers position?
Suggestions are welcome

PS the 803s are positioned according to Cardas's formula away from side and rear walls, equilinear triangle etc.
Gear: rotel 1095, 1060, 1068
803s, audioquest cables, biwired.

Thanks
Eliav

[georgev]

Combination of both perhaps?
I would first play around with the room acoustics, position of speakers before investing in a new amp.
Acoustics are probably the issue here. IMHO.
Alternatively audition a more powerful amp. and see.
The 1095 is no slouch. Yes there are better and more powerful, and your 803's also go down low(? >4ohms), and I,m not certain how stable the 1095 is at lower impedances.
George.

[george_k]

If I had to take a guess I would have to say that your room acoustics are to blame, here's why.

In acoustics there is the concept of reverberation and reverberation time (for a definition see here http://hyperphysics.phy-astr.gsu.edu...ic/revtim.html)

Reverberation time is directly proportional to SPL, as SPL increases so does the reverberation time. Next comes the whole concept of equi-level loudness curves. Basically at lower volumes the ear is less sensitive to lower frequencies, and so music at a lower volume might sound more detailed because your primarily hearing the mid to high frequencies. (see here http://hyperphysics.phy-astr.gsu.edu...nd/eqloud.html)

At higher volumes the lower frequencies become more pronounced added to the increased reverberation time is probably what is causing the smearing.

For a strictly HT setup you'd probably want a non-reverberant room but for music some reverberation is good. I can't remember what they aim for but if you look into some good concert halls it might give you an ideal.

One more thought, at this point (your gear considered )you'll get more value in improving sound quality by acoustically treating your room versus of spending more on your components.

[greggz]

Your problem is probably related to the RT60 for your room.

RT60 is a measurement of how long it takes for a soundwave to decay to -60dB. Rooms with a high RT60 experience all of the problems you describe.

http://www.csgnetwork.com/acousticreverbdelaycalc.html

The ideal RT60 for HT is around 0.35 to 0.40. I don't recall what a good RT60 is for stereo.

When you start out at a lower volume, the sound more quickly decays.

Spending more money on equipment or cables is just a waste until you get your rooms acoustics under control.

[Eliav]

Thnaks guys !
I apologize for not responding earlier, I was out for business for the whole last week.
I feel that the problem is with my room as you all indicated, It's just so complicated to analyze the exact problem and to eliminate it. I am currently working on convincingg my wife to agree for some rigid fiberglass sheets and some bass traps...
Are heavy curtains on the rear wall generally better than naked wall for stereo listening ?

Thanks
Eliav

[greggz]

Are heavy curtains on the rear wall generally better than naked wall for stereo listening ?

Not really. For stereo you want absorption behind your speakers and at the primary reflection points and diffusion on the back wall. This is called a "live-end, dead-end" setup.

Let’s use a rather hastily thrown together example to illustrate your problem

Let’s say your speakers are 5 feet out from the front wall, 5 feet from the side wall, you sit 5 feet from the speakers, and you are 5 feet from the back wall. And for this illustration, let’s just say the sound is coming from the left speaker. And let’s say that the note played is at 100 dB (pretty loud!).

As the sound travels it looses energy (dB), and each time it hits a wall loses more energy. Let’s say, again for illustration purposes, it looses 1 dB per 5 feet and 2 dB each time it is reflected.

Sound radiates from a speaker in all directions. The direct sound wave from the speaker will take 4.5 milliseconds (ms) to travel the 5 feet from the speaker to you. It will be at 99dB (100dB - 1dB per 5 feet).

It will also travel the 5 feet behind the speaker to hit the front wall, bounce off that wall and travel the 10 feet to reach you. (total time 4.5 + 9 ms = 13.5 ms). It will be 95 db (15 feet of loss plus 1 reflection loss of 2dB)

It will also travel from the speaker the 10 feet to hit the back wall, bounce off it and travel 5 feet back to you. Elapsed time again 13.5 ms. It will be 95dB (15 feet travel loss and 1 reflection loss)

Its also going to hit the left and right walls, bounce off them, and travel to you. Since we are just talking about the left speaker, its going to hit the left wall first and to use a round number lets say the total travel distance is 10 feet (9 ms). Let’s say the total travel distance to hit the right wall and then you is 15 feet (13.5 ms). So from the left wall it will be 96dB (10 feet and 1 reflection) and from the right wall it will be 95 db (15 feet and 1 reflection).

(it’s also going to hit the ceiling and the floor in a similar fashion, but I think you get the point without me dragging this out)

So, now to wrap it all up you will have the same note hitting your ears arriving from...

in front of you at 99dB in 4.5ms (direct from speaker)
in front of you at 95dB in 13.5 ms (reflection off front wall)
from the left at 96dB in 9 ms (reflection off left wall)
from the right at 95dB in 13.5 ms (reflection off right wall)
and the rear at 95dB in 13.5 ms. (reflection off read wall)
(and the ceiling and the floor too)

This same note arriving at very small fractional time differences and at different intensities become “smear” and results in loss of detail and spaciousness.

And that example is just one note, one reflection. This same note is going to continue to travel and reflect and strike your ears until the distance and reflections (and incidental absorption) cause the sound wave to decay.

Now by treating the front wall and primary reflection points with sound absorbing panels, you are trying to mitigate the front reflection and the left and right reflection by sucking energy out of them and make them decay faster. With diffusion on the back wall, you are trying to retain some of that energy to keep the spaciousness, but prevent it from being directly reflected back at you.

Again, this all a vast oversimplification. There are all kinds of other things you have to take into account when treating a room (such as you treat for frequencies above 200 Hz different than you treat for frequencies below 200 Hz.) If you want to do it right, involve a pro. They will come in, take measurements for your room. Model it. Recommend speaker placement, types of treatments, quantity needed and placement. Then once the treatments are in place they will re-measure and tweak.

If you want to take the DIY approach, do a lot of reading and plan on some trial and error. Buy several 4’x8’ sheets of rigid insulation and cut them in to 2’x4’ strips. (Most commercial sound absorbing panels are really nothing more than either 6 pcf (pound per cubic foot) rigid fiberglass or melamine foam covered in Guildford of Maine FR701 fabric. You’re just paying a premium for them to do the labor to assemble them.) Avoid using the “egg crate” foam. It’s less effective than rigid fiberglass and can be highly flammable and toxic (remember that nightclub fire in Rhode Island a few years back that killed 100 people? It was the egg crate foam panels that caught fire).

Begin adding strips to the room in logical pairs (i.e. one on each side wall, or 1 behind each speaker, etc…). Then do some listening. Then add some more, and do more listening. Look for improvement but watch out for over-deadening of the room. If you’re technically inclined you could also look at purchasing something like EFT http://www.etfacoustic.com to do your own measurements.

[Eliav]

Hi Gregg !
Thanks for the detailed explanation. I think I understand the basic concept. with regards to the 2x4 rigid fiberglass (703 /705) sold in some construction stores, how many tiles would you recommend placing in corners, would you recommend blunting the whole rear corner from floor to ceiling or just up to a certain height ? what about side walls /ceiling corners, should they be treated the same ?
Btw, I checked on the Malmine foam on line- very expensive ( ~30 $ per piece).
How rigid shoul I be with the rules of speakers placement such as RW x .276 for side walls, RWx .447 for rear walls etc. I know it's my ears that should be the final judge, however I want it also to be acoustically right...

Thanks for your advice
Eliav

[greggz]

There are programs that you can use to model your room that will tell you exactly where to put your speakers (i.e. CARA CAD).

http://www.cara.de/ENU/index.html

http://www.positive-feedback.com/Issue8/cara.htm

In my room the ideal placement is partially in front of my screen... blocking the view. (CARA also allows you to set a 'zone' in which placement is acceptable and it will find the best position given that limitation)

Some, like Cardas, base his placement recommendation off of the "Golden Ratios." You can learn more about Golden Ratios and naturally occurring number patterns by Googling on "Fibonacci."

Often times home theater consultants will just use the rule of thirds or the rule of fifths for speaker placement. Divide the room horizontally and vertically into thirds or fifths and place the speaker at the intersecting points of these lines.

Only measurements and physics will tell you the best possible location. All other rules of thumb are just that, general rules with a high probability of being more right than wrong, but not exact.

Speaker placement primarily effects bass (frequencies below 200 Hz). For frequencies in the midrange and higher, its the sound panels that will effect this.

As for placement and quantity of sound panels, I couldn't even begin to tell you what you need (I don't even know what I need yet and I've been pondering this for over a year now).

If you're not willing to hire a pro, I suggest taking a look at the 5 example rooms on the RPG site and consider their recommendations as a starting point.

http://www.rpginc.com/products/cinemusic/index.htm

As for bass trapping, you really need to know what frequencies you have a problem with in your room. Those are pretty easy to find using a SPL meter and any of those room mode calc websites I have posted before. Some rooms benefit more from Helmholtz resonators to treat a specific frequency rather than broad low frequency absorption.

But to answer your question, bass wells up most where walls and ceilings or walls and floors intersect. A lot of pros when they design a room will use a special kind of soffit to treat those intersections.

What ever became of the experiment we discussed before with piling rolls of insulation in the corners to see if bass trapping even made a discernible difference in your room?

[Eliav]

hi gregg !
hve'nt done the experiment yet. I've got a friend coming over this weekend( i hope) to do some spl measurments in my room. he is using some rigid fiberglass sheets placed on wooden frames in his room based on his measurments. I will take the measurments with him and let you know
Thanks
Eliav
PS : I introduced him to this forum, hope he joins soon !

[SRT-10 Viper]

You can also do the mirror method... Sit in your listening seat and have another person run a mirror along the wall. Everytime you see your speaker in the mirror, that will be a reflection point. The reflection point is where you want to experiment with th rolls of insulation.

[dyazdani]

I found the forum!

I looked and listened to Eliav's room this afternoon - as well as took some quick 1/3rd octave measurements. It produced an expected response for a relatively untreated room. Actually, it looked very much like mine (I am also working to correct similar issues).

My recommendation is to start with a couple of 4-5" thick broadband absorbers in the two front corners to tame the bass, two 2" thick absorbers to catch some reflections off the rear wall (it is fairly close to the listening position), and a 2" thick absorber at each 1st reflection point. The front wall should remain "live" for now. You could argue as to which wall to keep live, but in his case, I would choose the rear over the front.

The above can be built for no more than $150 DIY style and I have found a local supplier for rigid fiberglass.

We have further plans to measure the room with 1Hz increment bass tones and see what happens. I do have the CARA software and will be modeling his room. I also have the ETF software, but no laptop, maybe I can find a way to make it work, for now just the trusty RS SPL meter.

[Eliav]

Not really. For stereo you want absorption behind your speakers and at the primary reflection points and diffusion on the back wall. This is called a "live-end, dead-end" setup.

Let’s use a rather hastily thrown together example to illustrate your problem

Let’s say your speakers are 5 feet out from the front wall, 5 feet from the side wall, you sit 5 feet from the speakers, and you are 5 feet from the back wall. And for this illustration, let’s just say the sound is coming from the left speaker. And let’s say that the note played is at 100 dB (pretty loud!).

As the sound travels it looses energy (dB), and each time it hits a wall loses more energy. Let’s say, again for illustration purposes, it looses 1 dB per 5 feet and 2 dB each time it is reflected.

Sound radiates from a speaker in all directions. The direct sound wave from the speaker will take 4.5 milliseconds (ms) to travel the 5 feet from the speaker to you. It will be at 99dB (100dB - 1dB per 5 feet).

It will also travel the 5 feet behind the speaker to hit the front wall, bounce off that wall and travel the 10 feet to reach you. (total time 4.5 + 9 ms = 13.5 ms). It will be 95 db (15 feet of loss plus 1 reflection loss of 2dB)

It will also travel from the speaker the 10 feet to hit the back wall, bounce off it and travel 5 feet back to you. Elapsed time again 13.5 ms. It will be 95dB (15 feet travel loss and 1 reflection loss)

Its also going to hit the left and right walls, bounce off them, and travel to you. Since we are just talking about the left speaker, its going to hit the left wall first and to use a round number lets say the total travel distance is 10 feet (9 ms). Let’s say the total travel distance to hit the right wall and then you is 15 feet (13.5 ms). So from the left wall it will be 96dB (10 feet and 1 reflection) and from the right wall it will be 95 db (15 feet and 1 reflection).

(it’s also going to hit the ceiling and the floor in a similar fashion, but I think you get the point without me dragging this out)

So, now to wrap it all up you will have the same note hitting your ears arriving from...

in front of you at 99dB in 4.5ms (direct from speaker)
in front of you at 95dB in 13.5 ms (reflection off front wall)
from the left at 96dB in 9 ms (reflection off left wall)
from the right at 95dB in 13.5 ms (reflection off right wall)
and the rear at 95dB in 13.5 ms. (reflection off read wall)
(and the ceiling and the floor too)

This same note arriving at very small fractional time differences and at different intensities become “smear” and results in loss of detail and spaciousness.

And that example is just one note, one reflection. This same note is going to continue to travel and reflect and strike your ears until the distance and reflections (and incidental absorption) cause the sound wave to decay.

Now by treating the front wall and primary reflection points with sound absorbing panels, you are trying to mitigate the front reflection and the left and right reflection by sucking energy out of them and make them decay faster. With diffusion on the back wall, you are trying to retain some of that energy to keep the spaciousness, but prevent it from being directly reflected back at you.

Again, this all a vast oversimplification. There are all kinds of other things you have to take into account when treating a room (such as you treat for frequencies above 200 Hz different than you treat for frequencies below 200 Hz.) If you want to do it right, involve a pro. They will come in, take measurements for your room. Model it. Recommend speaker placement, types of treatments, quantity needed and placement. Then once the treatments are in place they will re-measure and tweak.

If you want to take the DIY approach, do a lot of reading and plan on some trial and error. Buy several 4’x8’ sheets of rigid insulation and cut them in to 2’x4’ strips. (Most commercial sound absorbing panels are really nothing more than either 6 pcf (pound per cubic foot) rigid fiberglass or melamine foam covered in Guildford of Maine FR701 fabric. You’re just paying a premium for them to do the labor to assemble them.) Avoid using the “egg crate” foam. It’s less effective than rigid fiberglass and can be highly flammable and toxic (remember that nightclub fire in Rhode Island a few years back that killed 100 people? It was the egg crate foam panels that caught fire).

Begin adding strips to the room in logical pairs (i.e. one on each side wall, or 1 behind each speaker, etc…). Then do some listening. Then add some more, and do more listening. Look for improvement but watch out for over-deadening of the room. If you’re technically inclined you could also look at purchasing something like EFT http://www.etfacoustic.com to do your own measurements.

Hi
I have done some spl measurements in my room, the spl meter was placed at my listenning position,baseline spl was 75dB.
I am sorry I cannot upload the excell graph.here is a summary of our findings
80 dB hump in the 50-80 hz range, at 30hz it went down to 70dB.
There were other 80 dB humps at 400, 800hz, and 3000-5000hz. the rest was oscillating around 75db( 72-77db range).
suggestions are welcome
Thanks
Eliav

[dyazdani]

I can upload the graph when I get home tonight, I should have done it in the first place.

The hump at the higher end (~5kHz) may be a measurement anomaly. I have almost an identical hump in my room. I also need to run a test at 1Hz increments to see the real peaks/nulls in the bass region.

Eliav, I have 3 sheets of rigid fiberglass being delivered tonight. You may come by and look at them if you wish.

[dyazdani]

Here are the room responses - 1/3rd octave increments. Now on to modeling his room in CARA...

[dyazdani]

I started a CARA model of Eliav's room. I had wanted to do a sound field calculation prior to adjusting the position, but my computer locked up in the middle. I will have to try again tomorrow.