Bass anechoic vs in-room

[TurtlePaul]

Which suggests I’m missing something. How does “more 30hz” become 20hz?

Can you help me out? Cheers.

A room with room gain below 30 hz has flat-ish frequency response a above 30 hz and a +12 dB/octave gain below 30 hz. This means the lower the frequency the more gain you get. This nicely offsets the 12 dB/octave rolloff of a textbook ported speaker to create flat.

Every speaker benefits from this, but who cares about a speaker that rolls off at 70 hz in a room with gain below 30 hz. Yes the room will still produce this interaction but the speaker is ~20 dB down at the frequencies where the response levels out.

 

[sarumbear]

How does “more 30hz” become 20hz?

Who said that? It’s obviously wrong.

 

[Yorkshire Mouth]

A room with room gain below 30 hz has flat-ish frequency response a above 30 hz and a +12 dB/octave gain below 30 hz. This means the lower the frequency the more gain you get. This nicely offsets the 12 dB/octave rolloff of a textbook ported speaker to create flat.

Every speaker benefits from this, but who cares about a speaker that rolls off at 70 hz in a room with gain below 30 hz. Yes the room will still produce this interaction but the speaker is ~20 dB down at the frequencies where the response levels out.

Ah! Many thanks. Do I have this right?

A speaker that “goes down to 30hz” actually, and more accurately “only goes down to 30hz at +/-3db (or 6db). It still produces 20hz, just not very loud. The room boosts the “not very loud” bits. Is that right?

 

[Yorkshire Mouth]

Who said that? It’s obviously wrong.

I’m not saying anyone said that, I’m asking the question.

 

[sarumbear]

A room with room gain below 30 hz has flat-ish frequency response a above 30 hz and a +12 dB/octave gain below 30 hz. This means the lower the frequency the more gain you get. This nicely offsets the 12 dB/octave rolloff of a textbook ported speaker to create flat.

You are confusing closed box HP filter response with room gain. Room gain knee is almost never 12dB/oct. It varies with the room characteristics but often 6dB/octave.

 

[sarumbear]

I’m not saying anyone said that, I’m asking the question.

What makes you ask the question? If you study physics you will know that sound frequency does not change with reflections, unless you are moving the source.

BTW, if you haven’t studied physics, you will have problem grasping acoustics. I suggested having a crash course in physics.

 

[Purité Audio]

The room may add gain and or cancellation on all bass below the transition frequency.
Acoustically measure your room, see exactly what you are hearing, reduce any room gain peaks, really that is all you can do unless you are willing to invest in massive amounts of membrane traps/resonators etc etc.
Keith

 

[sarumbear]

The room may add gain and or cancellation on all bass below the transition frequency.
Acoustically measure your room, see exactly what you are hearing, reduce any room gain peaks, really that is all you can do unless you are willing to invest in massive amounts of membrane traps/resonators etc etc.
Keith

We don’t even know what does OP wants to achieve.

 

[abdo123]

For example, here is one of René's simulation plot. The red line represents a speaker with a perfectly flat anechoic response down to 1 Hz.

placed in a corner btw. very important for this topic.

 

[abdo123]

You are confusing closed box HP filter response with room gain. Room gain knee is almost never 12dB/oct. It varies with the room characteristics but often 6dB/octave.

my room behaves 12db/oct, but the subs have to be placed in a corner and the walls have to be really rigid just like the conditions in Rene's simulation.

(I live in a very tall building and my walls are basically really thick concrete and i still leak below 20 Hz)

 

[Yorkshire Mouth]

We don’t even know what does OP wants to achieve.

You’ve been asked a question.

If you can answer it, answer it.

If you can’t answer it, don’t.

You’ve chosen instead to second guess my reasons for asking it. A quick review of this thread will demonstrate why this has led the thread to becoming derailed.

You appear to have been backed into a corner, and subsequently defensive, by others answering the question I asked; a corner which has progressively left you looking aggressive and confrontational, because others have taken a different approach.

The question which remains is simple. Why could others clearly understand my question, and answer it clearly, but you cannot?

It has become increasingly clear that others have fundamentally understood what I was asking, whilst you have not. The fault is therefore not theirs, nor mine.

 

[DJBonoBobo]

Another school day for me.

You mean as a teacher?

 

[sarumbear]

my room behaves 12db/oct, but the subs have to be placed in a corner and the walls have to be really rigid just like the conditions in Rene's simulation.

(I live in a very tall building and my walls are basically really thick concrete and i still leak below 20 Hz)

How do you measure it and what is the f3?

 

[sarumbear]

How do you measure it and what is the f3?

If you haven’t measured it how do you know that it’s 12dB/oct?

F3 is the frequency at which the filter is at -3dB amplitude.

 

[sarumbear]

You’ve been asked a question.

If you can answer it, answer it.

If you can’t answer it, don’t.

I have answered your questions. You said so yourself that you are happy.

It has become increasingly clear that others have fundamentally understood what I was asking, whilst you have not. The fault is therefore not theirs, nor mine.

Is that why you were frustrated and said “I don’t know how to ask it more clearly.”

I don’t like argument for the sake of it.

 

[abdo123]

How do you measure it and what is the f3?

I equalise my subwoofers to 35 Hz Butterworth 12db/oct like Rene’s simulation suggests and it measures pretty “flat” in-room. With some losses.

 

[sarumbear]

I equalise my subwoofers to 35 Hz Butterworth 12db/oct like Rene’s simulation suggests and it measures pretty “flat” in-room. With some losses.

As the topic is the slope and as you cannot, understandably, cannot measure the response at 17.5Hz you do not know what the room gain slope is. You just used an EQ based on the 12dB/octave slope. The result maybe different and according to math should be different as there are not enough poles in the transfer function of the room effect to cause a 2nd order filter.

 

[MAB]

You’ve been asked a question.

If you can answer it, answer it.

If you can’t answer it, don’t.

You’ve chosen instead to second guess my reasons for asking it. A quick review of this thread will demonstrate why this has led the thread to becoming derailed.

You appear to have been backed into a corner, and subsequently defensive, by others answering the question I asked; a corner which has progressively left you looking aggressive and confrontational, because others have taken a different approach.

The question which remains is simple. Why could others clearly understand my question, and answer it clearly, but you cannot?

It has become increasingly clear that others have fundamentally understood what I was asking, whilst you have not. The fault is therefore not theirs, nor mine.

Yeah, he didn't understand your question. Happens so often online. I understood your question, and the answers you got.

 

[gnarly]

............... but the subs have to be placed in a corner and the walls have to be really rigid just like the conditions in Rene's simulation.

Yes, two crucial conditions for nearly every room-gain sim I've seen.
And to build on 'really rigid', that means all 6 box surfaces, walls floor and ceiling.
Oh, and let's not forget that means a box with no open hallways, openings to other rooms etc , and rigid doors and windows too.

Personally, once real world factors are taken into account, i think room-gain is most often wishful thinking.

 

[MAB]

Yes, two crucial conditions for nearly every room-gain sim I've seen.
And to build on 'really rigid', that means all 6 box surfaces, walls floor and ceiling.
Oh, and let's not forget that means a box with no open hallways, openings to other rooms etc , and rigid doors and windows too.

Personally, once real world factors are taken into account, i think room-gain is most often wishful thinking.

Totally agreed!
Also, to get 'room gain' at the listening position that actually takes their speaker's anechoic 30Hz roll-off down into the 20Hz range a couple other requirements:

1. The room needs to have an eigenmode in the ~20Hz region
2. That eigenmode needs to have a large positive value at the listening position
3. Extra credit - that mode's frequency and amplitude and Q should nicely compliment the roll-off of the mains

With multiple subs and a reasonable room that can often be arranged.
With a set of full-range speakers set up for listening in an arbitrary room, even more wishful thinking.

I think it's the anechoic response that matters. Everything else is room and placement.