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Old 18th March 2010, 05:19 PM   #771
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by LineArray View Post
Does that mean the Q of a closed box e.g. beeing
irrelevant for behaviour in time domain, when placed in an acoustical small room ?
Pretty much so, yes. BUT the Q has impact in the amplitude domain and as a result very much impact the overall percieved sound. And a Qt = 0.5 closed box is still a good choice in an acoustically small room and tends to provide a bass that is perceived as more accurate.

Quote:
Originally Posted by LineArray View Post
Do we all waste our time in finding alignments for
BR speakers e.g. which seem to be good compromise between time - and frequency domain behaviour ?
Not really.

Because while intending to work on a problem that you cannot fix because it does not actually exist in the way it is stated, you inadvertently address a different problem that is very real and is improved with such "compromises" over so-called "maximum flat" alignments.

Ciao T
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Old 18th March 2010, 05:30 PM   #772
graaf is offline graaf  Poland
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Great discussion

Gentlemen - You are all GREAT!
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Old 18th March 2010, 05:40 PM   #773
graaf is offline graaf  Poland
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Quote:
Originally Posted by el`Ol View Post
A small amount of Basotect or felt like in the Carlsson will solve the problem. The bigger problem is that the corner loading only works up to a certain frequency. Simulate the corner in Hornresp as a conical horn plus eigth-space option and you will see. The solution I proposed earlier in the thread would be a very small bass driver and a very low-crossed horn tweeter.
or we can choose suitable driver - woofer, midwoofer or full range - that gently rolls off below 200 Hz ca 6 dB per octave - just to match the room loading

best,
graaf
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Old 18th March 2010, 05:42 PM   #774
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Quote:
Originally Posted by ThorstenL View Post
...
And a Qt = 0.5 closed box is still a good choice in an acoustically small room and tends to provide a bass that is perceived as more accurate.
...
So you think it is all about compensation of room gain and
flat in room response ...

That would be an explanation why with open baffles a high Q system
can be tolerated very well, as long as open baffle rolloff and room
gain sum up to a flat frequency response of the
"speaker and room" system as a whole.

So we do not hear the bass "hanging over" in time domain but
in frequency domain solely if the in room response is bass heavy with
a high Q system ...

I will have to think about.
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Old 18th March 2010, 05:46 PM   #775
graaf is offline graaf  Poland
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Quote:
Originally Posted by ThorstenL View Post
Further it only accounts for three walls in open space, it does not account for ceiling and other walls, meaning it actually undercounts the amplification of low frequencies.
yes indeed, and these are actually good news

Quote:
Originally Posted by ThorstenL View Post
As for a tool that is at least reasonably useful for estimating speaker/room interactions, placement and accounts to a degree for off axis response is here:

hunecke.de | Loudspeakers Calculator
thank You so much for the link

best regards,
graaf
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Old 18th March 2010, 05:46 PM   #776
gedlee is offline gedlee  United States
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Quote:
Originally Posted by ThorstenL View Post
Dear Mr. Geddes,



Directivity as such does not, that is true. What does however is the nature of the transducer with respect to how it exited the sound waves.

Pressure mode transducers (sealed/vented boxes) indeed behave as you suggest.

Yet gradient (cardiode) or velocity (figure 8/dipole) transducers are a different story.

So while directivity itself has no meaning in the modal region, the way it is attained most certainly does.

Ciao T
I don't see you disagree with anything that I said.

There are only two basic types of excitation, pressure and pressure gradient, or velocity. All sources are composed of a various mixture of these two fundamental types. But if you think of a velocity type (pressure gardient) as simply being two out of phase pressure sources seperated by some distance in space then there really is only the one type. In modeling rooms we only ever use the one type of source and create everything out of those.

How each source then excites each mode is the issue and finally we sum over all the sources. In doing this we never see a "directional" pattern only a modal pattern. Since any discrete mode does not allow an arbitray wave direction, (it is fixed in space) as long as there are only a finite number of modes being excited then the wave propagation direction is not arbitrary either, but fixed by the modes being excited. Hence, there is no directivity until the modal density is sufficient to allow for an arbitary wave direction in space.

Of course, I presume that this is what you meant .
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Old 18th March 2010, 05:53 PM   #777
gedlee is offline gedlee  United States
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Quote:
Originally Posted by LineArray View Post
So you think it is all about compensation of room gain and
flat in room response ...

That would be an explanation why with open baffles a high Q system
can be tolerated very well, as long as open baffle rolloff and room
gain sum up to a flat frequency response of the
"speaker and room" system as a whole.

So we do not hear the bass "hanging over" in time domain but
in frequency domain solely if the in room response is bass heavy with
a high Q system ...

I will have to think about.
The speakers resonances is just another resonance in the room and is no more nor no less important than any other resonance. Bass "hanging over" is probably a good thing if it is broadband, but certainly a bad thing if it is modal. Large rooms have very large "bass hangover" and the bass is usually quite good - but its broadband since the bass is well above the modal range in a large room.

It would be impossible to hear bass in the time domain in the same way that we hear HF. A 100 Hz. tone take several ms. for the brain to even register it - basicaly a several cycles. The ear is steady state by this time. Clearly below 100 Hz and everything is steady state.

Flat in room LF response spatially averaged is the key, and only multiple LF sources can do this in a small room. The Q, etc. of any individual source then becomes totally insignificant.
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Old 18th March 2010, 05:59 PM   #778
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by LineArray View Post
So you think it is all about compensation of room gain and flat in room response ...
Not quite as simple as this. The whole way speakers and room interact may be described as 'slightly tricky and difficult' if one has lived a long time in England, where extreme understatement is raised to an artform...

Quote:
Originally Posted by LineArray View Post
That would be an explanation why with open baffles a high Q system can be tolerated very well,
To a degree at least.

If the open baffle (dipole at low frequencies) is placed fairly close near walls (take care to absorb the midrange with some 4" thick basotect beheind though), it will not excite room modes very well. If we then couple the listner well to the air velocity (so don't sit him near walls) things come together nicely.

One may notice that the old Audio Physics setup conventional speakers is the exact opposite of this and tends to work about equally well...

In room we need to consider in the modal region how the transducers are coupled to the modes AND how the listener is coupled to them.

Quote:
Originally Posted by LineArray View Post
as long as open baffle rolloff and room gain sum up to a flat frequency response of the "speaker and room" system as a whole.
This certainly does not do any harm... ;-)

Quote:
Originally Posted by LineArray View Post
So we do not hear the bass "hanging over" in time domain but in frequency domain solely if the in room response is bass heavy with a high Q system ...
It is a major contributing factor, IMNSHO.

Just measure a "maximum flat" aligned bass reflex speaker (preferably also with full baffle step compensation) in a normal room with a "common" near wall placement from the listening position. Take care NOT to use pseudo-anechoic measurements (you can always window afterwards).

While you are at it, also measure RT20/40/60.

Then measure the Audio Physics setup of the same speaker.

Then place a "maximum flat" open baffle near side and rear walls (absorb the rear wave higher up) and place the listening position almost directly in the room center. Now measure again. What I find usually most interesting is the set of curves or RT20/40/60 against frequency.

In some ways I find these tell more about what a speaker sounds like (in the specific room) than even the on/off axis FR Curves and the Step/Impulse response.

In the end what matters is to enjoy the music though. And I have friends who enjoy theirs using a pair of Bose 901's.

My votes for speakers I enjoyed most in living (acoustically small) rooms go to corner loaded Tannoy Horns (which are actually pretty flat when placed thusly) and the JBL Everest and the relatives with the asymmetric horns and the MEG RL-901K and of course my own designs... ;-)

Ciao T
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Old 18th March 2010, 06:04 PM   #779
el`Ol is offline el`Ol  Germany
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Quote:
Originally Posted by graaf View Post
or we can choose suitable driver - woofer, midwoofer or full range - that gently rolls off below 200 Hz ca 6 dB per octave - just to match the room loading
The corner is a horn and doesn't roll off gently.
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Old 18th March 2010, 06:12 PM   #780
graaf is offline graaf  Poland
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Quote:
Originally Posted by el`Ol View Post
The corner is a horn and doesn't roll off gently.
I mean the case of near the corner placement which is illustrated in my previous post with a graph
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