Ways of reducing Floor Cancellation Notch with a subjective improvement?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
"Floor bounce" refers specifically to the sound bouncing off the floor in the same vertical plane as the speaker and listener, which is usually the first (earliest), and almost always strongest, non-direct source. If you had a gaping hole in the floor that prevented this reflection from occurring, you would absolutely prevent the measurable null (and progressively weaker comb filtering) that happens in bass or mid-bass from it.

Sure, maybe a futon is not going to fully absorb the floor bounce, but it sure as heck is the right idea. None of the other room reflections are going to cause the floor bounce null. That's why it's specifically referred to as "floor bounce".

Do you want to explain why the math behind this is wrong: Floor/Ceiling Reflection Calculator

That calculator is for above room modes. Untill you understand the different room axoustics at differnt freqs. youll never get it. Gedlee posts here sometimes why don't you ask him the difference?
 
So I said below 200 or 300hz Gedlee used 100- 200hz. We SAY the same thing.

Referring to floor treatments to combat “floor bounce” as “not completely effective at 100-200 Hz, but it gets very effective above that” is quite different from what you said, which is “below 300 there is no “bounce,” room modes dominate the acoustics” which is an implication floor treatments are of no use below 300Hz.

Would you agree with a statement like “midway through the transitional region, boundary treatments cease to be effective”? Because that seems like a better way to put it.
 
Last edited:
I don't deny energy bouncing of the floor at low freqs, I have a problem when people think its the same as high freq reflections, and the solutions are the same. Neither is true.
Actually, apart from medium and boundary losses, sound field behavior is frequency independent. You don't mention two things which are important regarding this. So I give it a try.

One: modal behavior has resonant characteristics. In plain language: the resonance has to build up in time and does decay in time. Thus, first reflections are different (in time) from the modal resonances. The resulting comb filtering is too. As a sideline: the Schröder frequency presupposes a steady state situation with broadband signal for the condition of modes going from individual recognizable ones to stochastic distributed ones. That is not the case with music. It actually only is an acoustic tool.

Two: our ears integrate sound pressure over time. We need some kind of sustain to notice. In essence low frequencies building up to room modes fall well in the 'integration time' of our hearing system.

Apart from that, most rooms have better damping at higher frequencies and room modes decay faster. That in turn means that the interference caused by nearby boundaries become more apparent.

Thinking a futton on the floor between you and the speakers will cure this low freq "bounce" is wrong, you can't think of the sound as a ray that only gets to you in straight lines. The low freqs "bounce" off all of every wall before reaching you. So a futton on the ceiling would have just as much effect, not much. Your absorbing 20sq feet of 1600sq feet of bounce.
With gated measurement one is able to choose. You can take the floor bounce into account or you can leave it out. Reducing the level of the floor reflection by using some kind of damping is done often. Because it gives a rough idea about the in room response which we perceive. I'd call that 'effective theory' ;)
 
Standing waves are caused because sound waves bounce off surfaces so there is no contradiction. The difference is that standing waves occur at discrete intervals connected to room dimensions. Each standing wave has two high pressure points - where they bounce off opposing surfaces - and at least one high velocity point.

Muddled and boomy bass are typically caused by standing waves and there is a simple way to mitigate them: mount your bass drivers at locations where the standing waves have their high velocity points.

The reason is simple: a resonance is much more efficienty driven from a high pressure point than from a high velocity point.

In other words: float your subwoofers. Putting them on a floor, against a wall or even two walls, increases the efficiency with which they will set off room modes. (In my own loudspeakers, the subwoofer is incorporated in the main cabinet, which floats at ear level, removed from side walls. Never had a problem with boomy bass in any room I played them.)
 
That calculator is for above room modes. Untill you understand the different room axoustics at differnt freqs. youll never get it. Gedlee posts here sometimes why don't you ask him the difference?
Wow. We're talking about a single reflection. The calculator is still correct even if you decide to empirically verify the results outdoors on a ground plane.

I'm done with you.
 
No, YOUR talking about a single reflection, Im talking about the reality of music in a small room, where theres always more than one cycle, and theres always room modes. Where not talking about outdoors. Last time I say this, its acoustics 101. At low freqs the room is a resonator. At high freqs its a reflector. Learn the difference.
 
What cbdb states is you will not notice floor bounce effects of frequencies below 200-300Hz. The floor bounce and the resulting comb filtering is there for sure. But the modal resonances dominate. I tend to think that is the case in most of the domestic situations.
 
There’s honestly a lot more to unpack than that and massive oversimplifications that emphasize the effect (which frequencies) over the cause (room dimensions and driver placement) are bordering on misinformation to all but those already versed on the subject.
 
Last edited:
The floor bounce and the resulting comb filtering is there for sure. But the modal resonances dominate

I'm not sure what you mean by dominate....we hear an accumulation of many different attributors...why is it we would want to say the "room modes dominate"? Dominate what? The floor to ceiling cancellation/floor bounce/comb filtering is just a function of room mode behavior ...because rooms have ceilings and floors.....
 
Let's define floor bounce as the single sound wave that travels from the floor to the ear or microphone. The ear/microphone 'sees' the imaginary sound source as the reflection of the speaker on the floor surface. If you'd have a mirror as a floor, it would even be visible.
This floor bounce wave merges with the direct sound of the loudspeaker. Depending on the phase relationship the resulting sound pressure level will vary with altering frequencies. Since the level of the floor bounce will be lower than the direct sound (bigger distance, boundary losses) the resulting level fluctuations will be under +6dB and way above complete cancellation. And, due to the origin, this is only direct sound field related. When the direct sound stops, the floor bounce will be gone also (in -say- 3ms time).

Room modes however are the basics of reverberation. At low frequencies the individual modes are recognizable, at high frequencies they are more or less evenly spaced at small frequency intervals. Even in small rooms the decay of room modes (and thereby reverberation) can last up til a second or more. They (and the resulting reverb) contribute heavily to the sound pressure in any point of the room apart from near to the speaker. They do so not only in level, but also in the time domain: while the sound of the source is gone, the reverb lasts for several hundreds of ms.

Now what do we perceive? Our ears, just like sound pressure meters, integrate sound pressure level. So we will notice the strong variations of SPL over a frequency band if room modes dominate and are distinct. This is the case in most livings up to around 200Hz. The modal behavior masks the smaller level fluctuation effects in the direct (and first reflected) sound field. Even though we could be able to recognize the direct and first reflected sound (precedence effect), we likely won't notice the level differences in that sound field.

This all is not to say the floor bounce or any first reflection isn't important. In specific situations it will be, even at lower frequencies too. E.g. think of a speaker that not only 'sees' a floor but also an approximate equidistant side wall, as seen from the listening position.
 
Last edited:
Member
Joined 2003
Paid Member
I made measurements at 2m with 6 foot panels laid on the floor. They are made with 4 inch rockboard 60. 9 panels placed one at a time with a new measurement. Separated for clarity, Zero-2, 2-4,4-6,6-9. Then one showing all 9 vs zero panels. The last measurement is with all 9 panels with the mic resting on the top, near-field measurement and moving the mic with each take, ending up at 2m far-field plus adding the 2m zero panel measurement at the bottom.

I'm Still examining the measurements but much of it is clear. Except, the rise and dip from 200 hz to 600 is a little strange to me..
 

Attachments

  • Zero - 2.PNG
    Zero - 2.PNG
    42.8 KB · Views: 133
  • panels 2-4.PNG
    panels 2-4.PNG
    41.7 KB · Views: 140
  • Panels 4-6.PNG
    Panels 4-6.PNG
    42.1 KB · Views: 141
  • Panels 6-9.PNG
    Panels 6-9.PNG
    44.3 KB · Views: 133
  • Zero and 9panels.PNG
    Zero and 9panels.PNG
    39.8 KB · Views: 133
  • Nearfield Farfield.PNG
    Nearfield Farfield.PNG
    95.1 KB · Views: 54
  • thumbnail_20210118_124827.jpg
    thumbnail_20210118_124827.jpg
    173.3 KB · Views: 71
I'm not sure what you mean by dominate....we hear an accumulation of many different attributors...why is it we would want to say the "room modes dominate"? Dominate what? The floor to ceiling cancellation/floor bounce/comb filtering is just a function of room mode behavior ...because rooms have ceilings and floors.....

At low freq room modes dominate ( look up dominate) the room response which means reflections dont matter. But if you havnt realize youve been wrong all along dont bother, seems youll never learn anything you've already decided you've figured out for yourself , even when wrong.
 
What about measuring the speaker outside, there are no standing waves, the floor reflection is now isolated and can be measured.
If you do not want the reflection then you can still put the speaker flat with the surface in a hole.

Basically it makes no sense to measure the low frequency behaviour inside a room, only close-up measurements can be taken
 
Last edited:
At low freq room modes dominate ( look up dominate) the room response which means reflections dont matter. But if you havnt realize youve been wrong all along dont bother, seems youll never learn anything you've already decided you've figured out for yourself , even when wrong.
I don't see why you use this tone of voice. Maybe you should try to explain the phenomenon 'room mode' more explicit, instead of bloating about it.

For one, without the conceptual approach of a reflection (as an imaginary source), theory about room modes collapses quickly. And if so, and you state it's room modes, I state it's invisible bananas. Prove me wrong.
 
Last edited:
I cannot speak for cbdb but I believe his original statement was restricted to (and therefore only to applicable to) some hypothetical small, rectangular listening space. He has already dismissed other considerations as being immaterial.
Hate to break the news, but any space with boundaries will display 'room' modes. Be it a sphere, be it a cave. It's only that the solutions of the wave equation are quite simple in a rectangular room and the modes can be discriminated rather easily.
 
What about measuring the speaker outside, there are no standing waves, the floor reflection is now isolated and can be measured.
If you do not want the reflection then you can still put the speaker flat with the surface in a hole.
My favorite waste of time, measuring outside... but if you can keep the measurement window at about 8ms (side walls and ceiling essentially at more than 2,5m away at listening distance of 3m) the floor bounce is incorporated in your measurement. With all restrictions of the low resolution in frequency/time/amplitude the windowing brings along of course.
 
Hate to break the news, but any space with boundaries will display 'room' modes. Be it a sphere, be it a cave. It's only that the solutions of the wave equation are quite simple in a rectangular room and the modes can be discriminated rather easily.
Hate to break the news, but I was responding to a post about outside measurements and their relevance to the person whom the comment was directed to.
 
Last edited:
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.