Let’s talk First Reflection Points

[JkSpinner]

Hi all

i have an old carpeted lounge dinning room (7.5 x 4.4m ) that is now used as a Home Theatre / 2 channel room.  I have about 2.5m behind my couch.  I am in the middle of some changes / upgrades but think it is time I to look at treatments.  I have upgraded a few interconnects, added some isoacoustic isolation products, built a TT plinth, an amp plinth etc.  I know should measure, but I think my room should be tamed a bit before I measure.  And I am not sure I want to measure yet.   Have read many posts here and elsewhere and watched many videos.  I must say, I never thought that the room would have so much impact on my SQ.  I have also experimented with hanging sleeping bags on walls, etc.  I have already spent some time playing with speaker placement, following several guides, the 1/3 rule, the 38% rule, the 1/3, 1/5, 1/7 rule etc and I think I am close.

i would like to start with the 1st reflection point.  I know many suggest starting with bass.  However, I do not have a bass problem in my listening position, I do have a bass problem around the back wall at volume, but not the listening position.  So the first reflection point it is.  My problem is that I do not really have a first reflection point.
1.  On one side, I have a large 3m double glass door, but with reasonably heavy drapes/ curtains closed when I am listening to music.  So, are curtains really sufficient to act as absorption.  Would it be of benefit for me to place a moveable acoustic panel at the first reflection point in front of the blind / window, or just leave it?

2.  On the other side, I have a 2.3m opening.  There is a 2m side wall from the front wall beside the speaker,  then a 2.3m floor to ceiling opening. The opening opens to a 2.5 x 2.5 tiled entrance which extends to a L shaped hall way than runs along side of the room, then around the back of the room.   The entrance and hall way are highly reflective echoey tiled rooms, with zero furnishings on the wall, a typical modern house.  I am sure I get reflection back from the entrance hallway.

is there any benefit to trying to keep the sound in the room, I could easily install a blind over the opening, or put an a moveable acoustic panel at the first reflection point here as well.

i will probably install some smaller panels on the front wall behind the speakers, and once we purchase some furniture such as bookshelf’s for behind the lounge, may add some back there as well.  
 

I have not used any scientific approach, but I have spent time walking around the room to determine where there appear to be problems, and have experimented with sleeping bags and blankets.  I actually think adding some acoustic panels to hall way will benefit the house.

 

anyway, please extend your wisdom for my First Reflection Points.

 

Edited July 5, 2024 by JkSpinner
Changed to be more relevant

[JkSpinner]

What - no opinions or guidence on first reflection points.  Surely there is some wisdom or knowledge that could be shared.

Are blinds on Windows sufficient for sound absorption, and should I try and absorb the sound before it leaves the listening room Into a highly reflective echoey entrance and hallway?

[Guest]

Here are some absorption  information on common materials 

https://www.acoustic-supplies.com/absorption-coefficient-chart/

It will give you an idea of how to handle reflections.

 

To help answer your question, I have large windows and blinds behind my speakers and I ended up with some absorption panels on the windows.

https://soundacoustics.com.au/product/acoustic-foam-panels/acoustic-panel-at600-40/

(mine is previous model)

 

I also place temporary panels in front of my TV (on left side of listening position).  I can hear the music slightly off centre without them. 

 

As for echo, do the clap test, and decide how much you can put up with versus treating the shared room.

 

[Steff]

On 24/06/2024 at 6:27 AM, JkSpinner said:

I have not used any scientific approach, but I have spent time walking around the room to determine where there appear to be problems, and have experimented with sleeping bags and blankets.  

 

Am I right in saying that it's best not to proceed off in-room ear tests? A measurement mic would be inexpensive (and REW free) and might give you more accurate information regarding acoustic dynamics in your complicated room.

AND there are several very knowledgeable members here on SNA who could advise how to respond to the data.

Whether it then comes down to adding physical room treamtents (costly, optics, bulky) or whether you can address the prevailing issues more easily and cost effectively through DSP might be a consideration?

 

[JkSpinner]

Thanks Snoopy

I have done the clap test, i have a lot of echo in the music room, but the echo travels right through the entrance and hallway.  But what was most uncomfortable was when I did the Audesy speaker set up, I stood in the entrance and the reverb and echo was huge, I had to turn my head.  That's is the reason I thought of absorbing the sound before it got out of the music room.

I will check those other links out.  I am not sure I can place panels on the window, but I could place them in front

[JkSpinner]

Steff, I am not adverse into doing some measurements, although I think there are some basic things I can prior to taking measurements, hence why I posted specifically on first reflection point, and not on solutions for the entire room.  I have also seen how the measurment conversation goes down a rabit hole each time someone posts measurements, and I would like to avoid that before I get the basics sorted.

[Steff]

No worries of course, I appreciate your noting that measurements discussions can become...involving!

My concern was also about adding physical fixes that might produce other unwanted effects, cancellation of desired acoustics, e.g.

[JkSpinner]

Thanks Steff

I am comfortable in the fact that I will need to add something, especially at the rear of the room, but before I do, I wanted to address the first reflection point first.

Eg. Do prevent the sound from existing to room, or maybe I need to let it exit, and absorb it in the hallway, so that it does not bounce back. I don't know. 

For 2 channel, do I leave the blind open for natural acoustic, but intall a panel at the first reflection point to absorb it, but close the blinds for movies.

The first reflection point and bass seems to be the most important.  Since I do not have a bass problem in the listening position, I think I need to address the first reflection point, then maybe measure and go from there

[Steff]

We'll be interested to hear how you proceed!

Closing off the hallway opening, as you noted, might already yield a significant change in the room's acoustic dynamics.

 

[JkSpinner]

29 minutes ago, Steff said:

 measurements discussions can become...involving!

 

I have spent countless hours reading previous threads, and not sure I want to go there.  I am casing better sound, not perfect sound

[Willco]

 Hi there Jk,

To get into the Nitty Gritty of any type of solving room interaction conjures up plethora of problems some instantly correctable  some downright disturb and bothersome to dissect.

Without delving into any other setup procedures you have done --I shall host plus outline my version of my own setup --layman terms and from  what I gathered first after commencing the "adjustment bureau" in my sound room some 35 years ago.

 

Ok--First reflection points--see pic A.

Yes many and varied --I'd select the ones getting to the listening position first from the side walls.

items needed:

 

1 x Mirror hand held size OK> I x torch( or Bosch laser pointer) 1x helpful minion!

 

Get the  helpful minion to move along the walls holding mirror flat --position torch top of speaker (Tweeter close) Minion can align torch to reflect in mirror till it hits you in the listening chair.

 

I am solo so I cheat as I demo Dive first aid I use a Gentle Annie propped up in the chair!--you can use cushion/ blow up doll etc.

When the light is on you seated-  place diffusion there--side walls recommended--wall behind speaker absorption primarily.

 

Hmm- what to place in place--there are numerous items on the market locally available --some good some not so--experiment carefully there. Being old and not one up on the latest and greatest-I still use my ASC tube traps for the above --still proving their worth through thick and thin!

 

 As alternatives --Maybe Lps /books--curtains --not too heavy they would tend to absorb  if bulky.--fine for behind   speaker wall

 

Anyway like all suggestions take with care and let you ears decide--good luck!

 

Willco

 

 

 

 

 

 

[JkSpinner]

Thanks Wilco.  My question is what to do when you do not have  1st reflection point.  

Eg. One side is open to an entrance and hallway, the other is a window covered by a blind

[Guest]

2 hours ago, JkSpinner said:

I have done the clap test, i have a lot of echo in the music room, but the echo travels right through the entrance and hallway.  But what was most uncomfortable was when I did the Audesy speaker set up, I stood in the entrance and the reverb and echo was huge, I had to turn my head.  

Your priority must then be reducing the echo.  I suspect the entrance and halfway has lots of hard surfaces and few things in them.  Try hanging a blanket or two and see whether that helps. Put more things in them temporarily.  A narrow bookshelf with books, cushions, plants, rugs on floor etc can all help.  Or a blanket on the exit leading to these areas?

 

Do the clap test and decide what is an acceptable level of echo versus what is practical in those places.  Even a few things against one or two walls may be enough?

[JkSpinner]

I have blocked the entrance with quilts and sleeping bags already.  Hence my original question.

Is it of any value to place a blind or acoustic panel at the first reflection point even though there is no wall ( no real 1st reflection point exists) to keep the sound in the music room and save for further reflections down the rd

[frednork]

At face value one side glass (even with curtains) and open on the other is near impossible to equalize the 2, so its more about reducing the audible difference between the 2.

 

Even though you will hear 1st reflection more the presence or absence of  wall will still have an impact beyond just the main reflection points as remember sound is spraying everywhere and bouncing of multiple surfaces before it hits your ear.  Next thing is that not all sound reflected is equal in terms of your brain processing it.  So sound that is at least 6ms after the main sound is perceived as "the sound of the room" and that is not as important to how we perceive the sound of the system as our brains automatically  tend to filter that out as background environment.  (microphones dont)

 

Next is the type of speakers you are using,  How widely do they spray the sound, Are they narrow or wide?  If you run dipoles then there is a huge amount less that may be hitting that 1st reflection point and may make trying to even them up less important. 

 

Another issue is how similar is the the response on axis and at angles. Without going into too much detail if the reflections are similar to the direct sound then that is considered better.

 

So back to your question.  Unless you build a glass wall similar in dimensions and characteristics to the other side then you will not have an equal starting point for treatment as symmetry in room characteristics is an advantage for stereo reproduction.  Another thing to remember is that room reflections are not only at (very) high frequencies which are easily absorbed by curtains or wall coverings etc., there are also reflections which still occur at lower frequencies which pass through these easily but may be affected/reduced by more robust treatment.  

 

So if we cant do a perfect acoustic symmetrical room  (and assuming you are unrestricted in what you can do) then we can only make one side more like the other so options are

a) "black out" the glass side to match the open side

b) add similar reflections on the open side to match the glass side

c) find some middle ground which is acceptable which involves treating both sides at probably first and second reflection points

 

How good this ends up being depends on the rest of the room.  If you currently have very long reverb times in that room then the things we are discussing are largely lost in the general noise of the reverb in the room.  However if the room is already reasonably damped then you will likely hear the effect of these strategies. 

 

If your room is extra large or the speakers dont "illuminate" the sides of the room much then less effort will be required. However if the opposite then more likely will be needed. 

 

As perfection is likely not achievable then you will need to make a call on what sounds better/best to youthat is acceptable (on all parameters) to achieve a least worst result.

 

[frednork]

Also would add that measuring will help you to figure out what treatment you may or may not need generally. You can think of the general "reverb" of the room as different to the issue of 1st reflection.  You can look at the effect of treatment generally in this thread I  posted a while back.

 

 

[Keith_W]

Sorry I did not see this thread earlier. It helps to think of your glass window on your right and the open hallway on your left as "reflection points" and analyse what is happening from an acoustics perspective. 

 

All surfaces have a "NRC" - Noise Reduction Coefficient - a measure of how much it will absorb or reflect the sound. An NRC of 0 means the surface is a perfect reflector, and NRC of 1 is a perfect absorber. A large opening in your room that opens to the outside has an NRC of 1, since all the sound escapes through the opening and does not get reflected back into the room. 

 

In addition, the NRC is not constant across the frequency range. For example, 10cm thick acoustic foam will have an NRC that approaches 0 at 20Hz, and an NRC that approaches 1 at 20kHz. A large window with a heavy curtain will selectively absorb high frequencies, but it will also have some low frequency absorption because glass acts like a membrane absorber. Your open hallway - who knows what it's doing. It is probably safe to say that it has a lower NRC than your window/curtain on the right. 

 

If you are hearing echoes in a clap test, it is likely NOT due to left/right bounce in your case. It is far more likely to be floor/ceiling or front wall/back wall. Echoes are caused by flat parallel surfaces with less than a 5° difference in angle between them. Treating just one of the surfaces with either an absorber or a diffuser will substantially reduce the echo. So will large pieces of furniture, especially shelves with lots of books in it. In addition, clap tests only tests a narrow band of upper frequencies and do not reveal all your room's acoustic problems. You are better off taking a sweep and comparing the ETC (Energy Time Curve) of your left and right speakers. 

 

The next question is whether you should go for absorption or diffusion. I don't know. It depends on your room's RT60 and your preferences for direct vs. reflected sound. Reflections should NOT be killed entirely, that is a common mistake that most people make. In general you should shoot for an RT60 between 250ms - 500ms. A 250ms RT60 will sound more "dead", and 500ms will sound more "lively". Some people like a more dead sound. I'm not a fan. 

 

Your goal is to achieve symmetry between left and right. You will not be able to do that without reconfiguring your room in some way. The cheapest option is to rotate your system along the long wall and place your listening position at the opening to the hallway. The room is all important - in some ways, it is even more important than the speaker itself. After all, the room dictates your choice of speaker, not the other way round. 

 

Would you be able to draw a diagram of your room? 

Edited July 9, 2024 by Keith_W

[parrasaw]

22 minutes ago, Keith_W said:

Would you be able to draw a diagram of your room? 

I agree with @Keith_W.

 

@JkSpinner, you are now getting great responses from some REALLY cluey members.

 

Your initial description of your room tells us a fair bit, but a digram (as requested by Keith) would give these guys much more to work with.

Hand drawn (to scale) would be all you need. 

Edited July 9, 2024 by parrasaw

[JkSpinner]

Here is one I completed earlier.  The speakers have been moved back a little, the front of the speakers are now 1.3m from the wall.  The speakers are .9m from the right wall, and 1.3m from the left glass door.  The room is a little offset due to the 45 degree brick wall.  It was a great idea at the time.

[JkSpinner]

4 hours ago, frednork said:

Also would add that measuring will help you to figure out what treatment you may or may not need generally. You can think of the general "reverb" of the room as different to the issue of 1st reflection.  You can look at the effect of treatment generally in this thread I  posted a while back.

 

 

I will take a look at this thread Frednork

[Keith_W]

Would you consider something like this? 

 

[JkSpinner]

14 minutes ago, Keith_W said:

Would you consider something like this? 

 

I assume you are referring to speakers?
the room is also a Home Theatre room, lounge room and my 2 channel room, so maybe not.  I have to work with what I have.  I have thought about about swapping it 180 degrees, gets rid of the window problem, the brick wall in front of the speaker problem. 

[Willco]

7 hours ago, JkSpinner said:

Thanks Wilco.  My question is what to do when you do not have  1st reflection point.  

Eg. One side is open to an entrance and hallway, the other is a window covered by a blind

My answer would be try this--using items you audition or Lps/ Bookcases/indoor Palm/Foliage /Bamboo/ light drapes ?

 

 

Or as Keith above suggested coming out of a semi corner setup--I used this myself, Placing items on the numbered spaces.

 

Whatever you decide don't over think it--just listen and place accordingly--it will snap into focus when you hear and feel it --

 

Good luck,

 

Willco

Edited July 9, 2024 by Willco

[frednork]

31 minutes ago, JkSpinner said:

I assume you are referring to speakers?
the room is also a Home Theatre room, lounge room and my 2 channel room, so maybe not.  I have to work with what I have.  I have thought about about swapping it 180 degrees, gets rid of the window problem, the brick wall in front of the speaker problem. 

The other side is probably better (reflection wise) as  one speaker will have none (as on the other side) but  the angles this way will lessen the first reflection for the speaker on the brick wall side.  As for whether everything else is improved , you will need to suck it and see.

[JkSpinner]

18 hours ago, Snoopy8 said:

Hi snoop

i do like the look of these, thinking a couple of these on my rear wall would do the trick.  But thought I would try and sort the 1st reflection point first, or lack there of.

Hybrid Absorber Diffuser HA600-75 mk11

https://soundacoustics.com.au/product/room-kits/hybrid-absorber-diffuser-ha600-75/

 

 

 

Edited July 9, 2024 by JkSpinner