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'Throbbing' Bass on MA Bronze

muckybucket

Established Member
I love my setup, but sometimes there seems to be a low 'throbbing' bassy sound. I don't always hear it, and my wife claims not to hear it...

I have my PS3 near my amp, could it be that causing the sound, or do I need to balance the bass better?
 

BlueWizard

Distinguished Member
There are typically three important things to consider -

1.) Are you speakers wired correctly (+) to (+) and (-) to (-). This is more a problem with weak bass though.

2.) Where and how are you speakers positioned? The closer they are to a boundary wall, meaning the side wall and/or the wall behind the speaker, the more bass re-enforcement you get. But, it the speakers are too close, yes the bass goes up, but it also can become overbearing and muddy the midrange.

Also, and this somewhat applies to the next item, is the postion of the speakers in relation to the room. Turning the speakers slightly inward toward the prime seating location can completely alter the nature of the reflections in the room.

3.) Room acoustics; is the room hard or soft? A hard room has lots of reflective surface. A soft room has lots of soft surfaces like cloth cover sofas and chairs, curtains, acoustical tile, carpets, etc... that absorb and diffuse the sound.

A room that is highly reflective will have substantial bass peaks and nulls in the room. When a reflected wave encountera on coming wave and they are in sync, they re-enforce. When the meet and are out of phase, they cancel each other out and create a void in the sound location.

Try moving around the room, and listening to the bass, is it better in some locations and worse in others?

You can get some test tones here, but you must use them with common sense to protect your speakers.

http://www.avforums.com/forums/speakers/925527-audio-test-tones-several-sources.html

When using tones like this, you can isolate a low frequency, and hear the bass without all the clutter. Play low notes in the 20hz to 80hz range, and you will be surprised at how different the bass sound as you move around the room.

Again, especially with the bass sweeps, you need to keep the volume modest; nothing over 1/3 volume. And you need to stop periodically to give you speaker time to cool off. This also works best if you keep the bass control on the amp set to flat or neutral.

Also, consider that it is just a difference in the recording, some recordings have the bass emphasized.

Also, and this is related to item #3 above, you could be experiencing some type of room resonance. If you have wooden floor, sound could be transmitted down into the wood, and this could make the hole room (or just the floor) resonate at one specific frequency.

The solution to this is to NOT couple the speakers to the floor. Rather, isolate them. To isolate, you create an artificial barrier between the speakers and the room. What that really means is you mount the speaker on rubber. The rubber feet isolate the speaker from the floor.

This can be done in a variety of ways.

1.) Simply don't use the speaker spike on the floor. Just setting the speaker flat without spike might be enough to stop the resonance.

2.) Many in the group have had good luck with using a granite or marble food chopping board for the local general merchandise store, and the putting Deflex feet under them.

Deflex Polyurethane

Some might cut squash ball in half or something similar, but the goal is the same. To stop the speaker from sending sound down into the floor.

3.) Variations on a theme. There are isolation platforms that accomplish the same thing. Some are very expensive, but some can be had for about £40 to £50.

Here is another thread where some of the possibilities were discussed -

http://www.avforums.com/forums/speakers/1176676-reducing-sound-vibration-passed-floor-below-me.html

The same principles apply, but this thread applies those principle for a slightly different reason.

Steve/bluewizard
 

muckybucket

Established Member
It is only slight, and I have only noticed it on occasion.

So you don't think it could be feedback from the PS3?

Wiring is fine, room is 'soft' with carpet and textured wallpaper (yuck!!).

Sub isn't spiked and sits on carpet. It is away from the wall and facing into the room, not in a corner.

Haven't heard it for a few days, sometimes wonder if I am imagining it as it is not there all the time!

Thanks for the advice, will try some sound tests when time permits! :smashin:
 

indus

Distinguished Member
BW, thanks for the link.

I have downloaded the real traps one under 'my music', but can't figure out how to burn it to CD.
The only time I have burnt music is via itunes, where there is an obvious option to do so.
Do I need to unzip the files first?

Thanks:)
 

indus

Distinguished Member
Don't worry I've figured it out:thumbsup:

BW, I have a bass issue at certain frequencies that sounds/feels like a pressure wave, it is very very audible. I've been looking into bass traps and was told if the problem is above 70hz I need a certain kind of bass trap and if below then a different kind.

If I play the test tones and just listen with my ears for the same unwanted effect, will I be able identify whether the problem is above or below 70hz, or am I barking up the wrong tree?
 
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BlueWizard

Distinguished Member
As the frequency sweeps (1hz every 10 seconds), you might be able to hear a resonance in the room or the speak, or in your hearing.

Especially at the very low frequencies, stop every two or three sweeps to give the speakers time to cool down (15 seconds or so). Likely your speaker can handle more time than that, but why take chances. Luckily the sweeps are in 10hz increments of 100 seconds each, and again, that results in 1hz increase for every 10 sconds.

Also, while you can try, there is really no need to run the sweeps in the 10hz and 20hz range, starting at 30hz more closely reflects what you can actually hear as a musical tone.

Keep the volume modest, at something approximating a casual listening levels. For me that was about 10 o'clock on the volume dial. I don't advise any volume setting higher than that.

Just a few thoughts.

Steve/bluewizard
 
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indus

Distinguished Member
Thanks.

I did that last night, and there are a number of peaks and troughs as you would expect. The test tone that replicates the offending effect I get (which is felt as much as heard, bit like a pressure) is 69-60hz.

As well as sounding/feeling like the problem, it also correlates with a peak on the spl meter (though there are plenty of other peaks).

From this can I assume that the problem I'm having when listening to music also comes from the 69-60hz range?

Apologies to op for slight hijack!:)
 

Rich9600

Established Member
MB

On the possibility of mains hum / radio frequency interferance...

Where is the sound coming from? Is it your speakers or sub?

Our house phone sits on top of the sub, normally on top of a huge pile of magazines. After a suitable period of nagging I got rid of the magazines and all of a sudden my sub started buzzing. This was simply interferance from the cordless phone. I moved the phone off to one side and all was quiet again.

Just a thought.
 

BlueWizard

Distinguished Member
Indus,

I'm guessing you have an acoustical problem.

As mentioned, this can be one of two things -

1.) sound bouncing around the room, and hitting a resonance of the room.

2.) sound radiating into the floors, and again hitting a resonance of the room.

If it is bouncing sound, then you need to soften the room, perhaps simply closing the curtain will make a difference. But one way or another, you need a way to absorb and/or diffuse bouncing sound.

if it is radiating into the floors, then you need to isolate the sub and/or speakers from the floor. Most wrongly assume that speaker Spikes isolate the speaker, but they don't, they couple the speaker to the floor.

You need something soft (more or less) between the speakers and the floors. One of the most popular solutions is marble or granite cutting board with Deflex poly-pod to isolate the platform.

Sometimes just substituting common rubber feet for the spikes is enough. You can buy threaded rubber feet at most hardware or building supply stores. Just make sure the threads match.

Of course, this is for hard floors. If you have carpet, the you already have a degree of isolation.

Just a few thoughts.

Steve/bluewizard
 

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