Near or Midfield? Question.

[Valentin]

a great book on the importance of the directivity of a speaker system can be found here

http://www.amazon.com/Sound-Reproduc...8315432&sr=1-1

it is of great importance because the room sound

if you don't have a smooth and constant directivity (in the horizontal plane of most importance) the reflected sound will affect your perception in not a good way

if you have a 12" driver till 1.5khz this driver will have a very hi directivity and when crossed to the mid range the directivity will change to a wider dispersion

in the axis if you measure it can be flat but the spike produced by the hi xo point in 12" driver will be reflected from the room

the book explains it in more educated way (and with correct English)

this affects monitor and consumer designs
jbl has a paper which you can find in the Lansing library

[Beowulf57]

a great book on the importance of the directivity of a speaker system can be found here

http://www.amazon.com/Sound-Reproduc...8315432&sr=1-1

it is of great importance because the room sound

if you don't have a smooth and constant directivity (in the horizontal plane of most importance) the reflected sound will affect your perception in not a good way

if you have a 12" driver till 1.5khz this driver will have a very hi directivity and when crossed to the mid range the directivity will change to a wider dispersion

in the axis if you measure it can be flat but the spike produced by the hi xo point in 12" driver will be reflected from the room

the book explains it in more educated way (and with correct English)

this affects monitor and consumer designs
jbl has a paper which you can find in the Lansing library

Thanks Valentin...that's what I was looking for .

[Robh3606]

Here is what a 12" driver is doing above 640Hz

Rob

[Beowulf57]

Thanks Rob. So, between 1-4K, the "beaming" becomes significant(though somewhat mitigated by the 4" aluminum dome in the centre). With the 15" driver, likely even more so. So, this probably contributes a bit to the midrange over-emphasis...but the rising response curve of the D130/D131 between 1-4K is likely the greater culprit.

[Ti 5000]

Wow. So much Answers Now I have work for the next two hours to Translate all the thread with my bad Englisch
But thanks at all for Info...

[BMWCCA]

Here is what a 12" driver is doing above 640Hz

Just curious (again!).
Is this a generic plot from a handbook based on some irrefutable law of acoustics? Does it take into account basket depth? Cone angle? Cone material? Excursion? Aluminum dust domes? Do ALL 12" speakers necessarily behave exactly the same, or is this something like assuming all 2-D-cell flashlights, and all automotive 5-3/4" headlamps, put out the same pattern? :dont-know

[Beowulf57]

Just curious (again!).
Is this a generic plot from a handbook based on some irrefutable law of acoustics? Does it take into account basket depth? Cone angle? Cone material? Excursion? Aluminum dust domes? Do ALL 12" speakers necessarily behave exactly the same, or is this something like assuming all 2-D-cell flashlights, and all automotive 5-3/4" headlamps, put out the same pattern? :dont-know

Nope...I read 2206: http://www.jblproservice.com/pdf/Dis...els/2206HJ.pdf

So, not the same as a D130/D131...but what the hey, at least it gives an idea.

[BMWCCA]

Nope...I read 2206: http://www.jblproservice.com/pdf/Dis...els/2206HJ.pdf

I was talking about the dispersion graph above. What are you talking about? Frequency range as listed on the 2206 spec sheet?

[Robh3606]

Is this a generic plot from a handbook based on some irrefutable law of acoustics?

Hello BMWCCA


No

It's a 2206 mounted in a small reflex enclosure in 4Pi/free space. What you are seeing is the simulated resonse based on the on axis frequency response and the edge difraction as determined by the spacing on the baffle and the physical size of the box. Once you get above a certain frequency there is no significant baffle edge difraction so it really doesn't matter what box the driver is mounted in.

That was done in LEAP Enclosure Shop. Attached is a 2Pi simulation where the baffle board in infinite, like inwall mounting. You see the same trend above say 2k or so.

It's not exact per say but a generic 12" should be close. You have to remember that there is a full set of T/S data entered that includes cone area and piston diameter and this all comes into play. Maybe something like one of the older Altec BiFlex drivers, where there is a mechanical crossover in the driver cone, might be modeled incorectly. Based on what I have seen using Crossover Shop I would say that this is as close a simulation as you are going to get.

Rob

[BMWCCA]

No

It's a 2206 mounted in a small reflex enclosure in 4Pi/free space.

Ahh, thanks. I see the project title 2206 now. But it is computer modeled, so somewhat generic though based on known attributes of that particular driver. Thanks for clearing it up.

Back to the thread's wandering "midfield" question.

[4313B]

Back to the thread's wandering "midfield" question.

Page 2 Paragraph 2

http://ccrma.stanford.edu/courses/19...cture_7_06.pdf

[mini]

http://ccrma.stanford.edu/courses/19...cture_7_06.pdf

I might be arrogant to state such, but Stanford is obviously wrong:

"... near field, mid field, and far field.
These terms refer to the listener’s relative perception of the direct to
reflected sound ratio."

From here it starts to become a bit crazy ...

"Near field monitors are desirable in part because their sound is largely
independent of the room, ..."

The contrary is true. Near field monitors have a wide, not in every case regular directivity. The sound is swamped all over the place, and hence reverberated much. From that to stay within the near field is a must to mute the noise against the preferable direct field.

"Mid field monitors are designed to be heard from a longer distance, where the reflected sound and direct sound are about equal."

What for?

"Far-field speakers are designed to “throw” the sound a longer distance from the speaker, where the reverberant field may be stronger than the directly radiated sound."

Ah! What they try to say is: Far field monitors are used because of their narrow directivity pattern. In situations where a near field speaker otherwise would cause to much reverberation. That is the case if the listening position is farther away.

Ain't easy. A good source whilst starting to deal with the tropic of sonic excellence may be Dr. Earl Geddes, "Summa", "Home Theatre": www.gedlee.com

[4313B]

I might be arrogant

I think the general perception is that you're merely a troll, nothing more, nothing less...

[BMWCCA]

I know this is the DIY forum and I'm not a card-carrying member at this time, but the concept seems simple as stated in the Stanford link:

Speakers are also classified according to the distance at which they are designed to focus their sound output: near field, mid field, and far field. These terms refer to the listener’s relative perception of the direct to reflected sound ratio. Near-field speakers are designed to be heard in the near field, where the direct sound far exceeds the reflected sound intensity. Near field monitors are desirable in part because their sound is largely independent of the room, hence their popularity for home and project studios where acoustics are often less than perfect. Mid field monitors are designed to be heard from a longer distance, where the reflected sound and direct sound are about equal. Far-field speakers are designed to “throw” the sound a longer distance from the speaker, where the reverberant field may be stronger than the directly radiated sound. Far-field speakers are often soffit or wall mounted in large control rooms.

Nearfields are for listening up-close; at the board, straight ahead. Midfields for further back in the room; sitting around the conference table or on a couch in a group. I think the latter pretty much covers the Century Golds which was the original issue of this thread.

JBL adds this description in their 4400 material:

Dispersion (Polar Response Curves):
Like Frequency Response, this specification gives you a clear picture of how the loudspeaker system’s energy balance changes as you move off axis. In most monitoring environments, much of the sound you hear has been reflected at least once off of the various control room surfaces. When the loudspeaker's frequency response curve is smooth and free of significant peaks and dips, the ear will focus on the first arrival sound and hear it as an accurate reproduction of the signal source. However, reflections will also reach the ear, though fractions of a second later. Because of this, it is of equal concern that the energy balance off axis, that which is likely to be reflected, be as smooth and even as possible.

Depending on how you interpret this description, it would seem you're both correct!

[hjames]

I think the general perception is that you're merely a troll, nothing more, nothing less...

Ping ping ping!



basic internet rule:

Don't feed the troll!