Surround Sound Problem: Bass is weak in some areas.

[Rey-FD]

Hi all, I've come into a problem concerning my surround sound set up.. it's a Panasonic SA-HT65, the problem is that somebody in the family has touched the PS3/Amplifier and the bass doesn't reach the areas it used to.. 👎

I've recently connected the PS3 to the Amplifier via HDMI (due to being a spare cable) It worked perfectly, the sound was clear, the bass reached beyond where I was seated, everything was fine.. now it doesn't even go beyond half my rug.. note that everything was fine with the HDMI and all features were usable on my remote including the Dolby Digital etc.

I made a quick diagram:

Obviously, the before picture states that the bass is able to reach the majority of the living room without error, the after picture states that the bass is only limited to that confined space..

Green = Bass is Strong
Red = Bass is Weak

Here's some extra information:
1. I'm using a HDMI cable from the PS3 to the Amplifier (no HDMI port on TV(yet))
2. When I press the Dolby Digital button on the remote (which enhances sound, increases bass etc.) a message comes up on the amplifier saying "Not Possible for this PCM Source"
3. I've read through the manual
4. Using normal Red/White Cables (?) I'm able to activate the Dolby Digital but does not sound as good as how the HDMI set-up used to sound.
5. Subwoofer is facing forward (which is pointing down in picture)
6. No, please don't tell me to move my furniture closer together, because it was fine before and it should be now.
7. One step can make a large difference in bass levels.

 

[MatskiMonk]

Do you havea 180° phase shift switch on the sub... this is useful for moving around the inevitable dead spots from a sub...?

Using normal Red/White Cables (?) I'm able to activate the Dolby Digital but does not sound as good as how the HDMI set-up used to sound

If by Red/White cables you mean a phono lead (RCA jack) then that doesn't make much sense, you will only be getting a stereo signal into the amp so the best it will do is Dolby Pro-Logic IIx, which will not sound as good as Dolby Digital.

 

[Rey-FD]

Do you havea 180° phase shift switch on the sub... this is useful for moving around the inevitable dead spots from a sub...?

Thanks for your input

I doubt it, the manual doesn't specify anything about a 180° phase shift switch

If by Red/White cables you mean a phono lead (RCA jack) then that doesn't make much sense, you will only be getting a stereo signal into the amp so the best it will do is Dolby Pro-Logic IIx, which will not sound as good as Dolby Digital.

Sorry my bad, It's showing a Dolby PLII icon. which is yes, Dolby Pro Logic II

- -

I do however, have a microphone used for calibrating the sound, although I've tried numerous locations and they make little to no difference at all, this includes putting the microphone to ear level in the seating position as recommended.

Here's what it says from the manual:

Auto speaker setup allows you to achieve a satisfactory listening environment easily with the use of supplied calibration microphone as a detector of sound signals. the unit will first perform automatic speaker detection, then checks and adjust the following settings:

1. Detection *Checks which speakers you have connected.

2. Distance *Checks the distance of each speaker from the listening position and adjust the timing of each channel automatically.

3. Frequency *Makes any further corrections to the frequency response.

4. Level *Checks and adjust each speaker level automatically.

 

[maximumattack]

It could be something to do with the positioning of your sub in relation to the size of the room & the distance the low frequency can travel before it gets reflected. If the low frequency (or any frequency for that matter) is reflected back onto itself at a particular part of it's phase/cycle then you will not hear it as it effectively cancels itself out.

In the first picture it appears that there is another speaker directly in the line of travel between the sub & the corner of the room, this could have had enough of a surface area to reflect the bass back into the room before it reaches the point where it would be out of phase with itself. Even if you did have a Phase Invertion switch this might not make a difference here as it's possibly just the bass frequency cancelling itself out.

I'd suggest changing the angle of the sub as the distance the wave can travel looks like it can be changed quite alot from your pictures, then listening to a test tone whilst moving around the room. There's inevitably going to be some dead spots due to the room mode, through trial & error you should be able to position the sub in such a way that the dead zones aren't situated in any of the seating positions & you should feel the wall shaking bass that you are probably trying to achieve.

 

[Rey-FD]

It could be something to do with the positioning of your sub in relation to the size of the room & the distance the low frequency can travel before it gets reflected. If the low frequency (or any frequency for that matter) is reflected back onto itself at a particular part of it's phase/cycle then you will not hear it as it effectively cancels itself out.

In the first picture it appears that there is another speaker directly in the line of travel between the sub & the corner of the room, this could have had enough of a surface area to reflect the bass back into the room before it reaches the point where it would be out of phase with itself. Even if you did have a Phase Invertion switch this might not make a difference here as it's possibly just the bass frequency cancelling itself out.

I'd suggest changing the angle of the sub as the distance the wave can travel looks like it can be changed quite alot from your pictures, then listening to a test tone whilst moving around the room. There's inevitably going to be some dead spots due to the room mode, through trial & error you should be able to position the sub in such a way that the dead zones aren't situated in any of the seating positions & you should feel the wall shaking bass that you are probably trying to achieve.

Thanks for your in depth response , I tried changing the angle of the subwoofer and moving it to different locations in the room, it did make a difference, I'll do some more experimenting, although I'm still confused as why it's happening now and not before the problem arose.

 

[Anghammarad]

A classic solution is to place the sub in your normal listening position and then move around in the room while playing a test sound. The place in the room where your sub sounds best is also where you should place it.

 

[GilesGuthrie]

Yes, I think maximumattack is on the money. My assessment is that it's down to room reflections causing standing waves in the sound, leading to dead zones.

Also, my PS3 resets the config from time to time. Go into the sound settings on the PS3 and check that they're configured correctly, so it will only output what your amp can decode.

 

[Rey-FD]

Thank you both for your responses.

A classic solution is to place the sub in your normal listening position and then move around in the room while playing a test sound. The place in the room where your sub sounds best is also where you should place it.

I could do that, but I don't think there is many home-theater set ups out there with a subwoofer sitting in the middle of the room, I may be wrong.
Although it does seem to work more effectively. 👍

Yes, I think maximumattack is on the money. My assessment is that it's down to room reflections causing standing waves in the sound, leading to dead zones.

Also, my PS3 resets the config from time to time. Go into the sound settings on the PS3 and check that they're configured correctly, so it will only output what your amp can decode.

I've checked the PS3 settings numerous times, the audio output is auto configured, meaning Dolby Digital 5.1 etc. is activated etc. I've also tried un-checking all of the options leaving just Dolby Digital 5.1, with no improved results.
Right now, I'm putting the money on what maximumattack has said, just as you have.

 

[maximumattack]

Thanks for your in depth response , I tried changing the angle of the subwoofer and moving it to different locations in the room, it did make a difference, I'll do some more experimenting, although I'm still confused as why it's happening now and not before the problem arose.

No problem mate, good luck getting it all set up properly

 

[MatskiMonk]

Well 180° phase shift switches are designed to turn flat spots into hotspots, most subs have them.. but moving the sub is definatley a similar solution

 

[emacs]

the red region indicated in the first post is the valley (or null region) of several standing waves. it's tricky to minimise these null regions because subwoofers send out a broad range of frequencies.

an easy and unscientific way to reduce the occurrence of standing waves is to make your room non-symmetrical. chairs, couches and other types of furniture will not fix the problem. also, create bass traps if possible (place something cylindrical or irregular in shape at the corners of your room).

 

[Rey-FD]

the red region indicated in the first post is the valley (or null region) of several standing waves. it's tricky to minimise these null regions because subwoofers send out a broad range of frequencies.

an easy and unscientific way to reduce the occurrence of standing waves is to make your room non-symmetrical. chairs, couches and other types of furniture will not fix the problem. also, create bass traps if possible (place something cylindrical or irregular in shape at the corners of your room).

Thank you

It's very weird, as I can take one step into that region and the bass will become very strong again, but once I step out it comes weak.

What do you mean by making the room non-symmetrical, does that mean I should place the speakers differently considering furniture doesn't really count, or change the layout?

 

[irnbrutwinturbo]

When i had the above problem i cheated, bought 2 considerably more powerful subwoofers!

 

[Rey-FD]

When i had the above problem i cheated, bought 2 considerably more powerful subwoofers!

Haha well there's only room for 1 sub on the amplifier!


- - -

On another note! It works now!

I placed the calibration microphone closer to the amp itself and for some reason the sub is more stronger where the main seating position is, thanks for the advice guys, I also have the proper dolby digital icon on the amplifier

http://www.dolby.com/consumer/setup/connectivity/game-console/ps3.html

I pretty much de-activated all of the sound encoding options and left Dolby Digital 5.1 and the last one which I could not un-check.

 

[emacs]

What do you mean by making the room non-symmetrical ... ?

most rooms are square or rectangular in shape with all walls (including floor and ceiling) that reflect sound similarly (due to same thickness, materials, construction, et cetera). you want to disrupt this similarity. changing how the vertical walls reflect sound, for example, can be accomplished by hanging a thick tapestry or heavy curtain.

standing waves occur whenever two waves of identical frequency interfere with each other while traveling in opposite directions (i.e., original sound wave from subwoofer smashes into soundwave that bounced off a wall).

you can calculate the actual frequencies that may exhibit weak bass issues if you know the dimensions of your room.

math


h = height of room
w = width of room
l = length of room

oblique length (D) = square root of (h*h + w*w + l*l)
fundamental frequency (F) = half the speed of sound / oblique length

calculate the harmonics for F. the nth harmonic is simply (n/2) * F

the frequencies that may exhibit weak bass in your room are these harmonics.


example

D = 6 metres
F = 170 metres per second / 6 = 28 Hz

first harmonic = 14 Hz
second harmonic = 28 Hz
third harmonic = 42 Hz
fourth harmonic = 56 Hz
fifth harmonic = 70 Hz
sixth harmonic = 84 Hz
seventh harmonic = 98 Hz
eighth harmonic = 112 Hz
ninth harmonic = 126 Hz
tenth harmonic = 140 Hz
et cetera ...

if your subwoofer is sending out frequencies at any of these harmonics, you may experience weak bass in the valley / null region of standing waves.

 

[Rey-FD]

Thanks Emac, the problem is resolved, but I might put use your physics/math equations if I want to try improve the sounds further, appreciate it.

 

[Dracwolley]

This might not make much of a difference, but try moving it just slightly so that it's up against a wall, with as much surface area as possible almost touching it. If it does touch it, you might hear some rattling, so try to get it close without touching. Also, put it against the weakest wall in the room.

I did this at a party once. We had two speakers which were rather light on bass, and we had a tiny subwoofer that we weren't originally going to use. When we turned it on it didn't make much of a difference, but then we put it next to a weak wall and the whole room became a subwoofer. It sounded perfect.

EDIT: I realized that your problem is resolved but I'm leaving this here for future reference for anyone else who stumbles upon this thread.

 

[Rey-FD]

This might not make much of a difference, but try moving it just slightly so that it's up against a wall, with as much surface area as possible almost touching it. If it does touch it, you might hear some rattling, so try to get it close without touching. Also, put it against the weakest wall in the room.

I did this at a party once. We had two speakers which were rather light on bass, and we had a tiny subwoofer that we weren't originally going to use. When we turned it on it didn't make much of a difference, but then we put it next to a weak wall and the whole room became a subwoofer. It sounded perfect.

EDIT: I realized that your problem is resolved but I'm leaving this here for future reference for anyone else who stumbles upon this thread.

Thanks Dracwolley! that's a interesting concept you got going on there, I'll try it out and see if it works sometime!