Ok we have some people who think a perfect speakers should be a point source monopole, and that dipole is inherently inferior.
We have some who think a dipole is superior to monopole.
And we have some who think the devil is in the details. That issues like lobing are what kills a speaker.
So where does everybody stand ? I am including a poll. The poll asks which is the WORST PROBLEM for speaker radiation pattern.
We have some who think a dipole is superior to monopole.
And we have some who think the devil is in the details. That issues like lobing are what kills a speaker.
So where does everybody stand ? I am including a poll. The poll asks which is the WORST PROBLEM for speaker radiation pattern.
Your brain derives timbre from both direct sound and reflections. Things which cause the reflected spectrum to have sufficiently broad peaks and dips change the timbre and don't sound natural. While lobing (as on a planar "dipole" or MTM) is one such defect an acoustically large woofer crossing to an acoustically small tweeter causes similar problems.
More and less uniform have a bigger effect than intentional monopole approximation/intentional dipole approximation/conventional speaker/horn or waveguide.
Different directivity changes how the speakers interact with the room (image width/placement is less affected when speakers have less output towards nearby objects).
More and less uniform have a bigger effect than intentional monopole approximation/intentional dipole approximation/conventional speaker/horn or waveguide.
Different directivity changes how the speakers interact with the room (image width/placement is less affected when speakers have less output towards nearby objects).
Last edited:
that just made me realize that it isn't just the speaker that must have an even power response - the room must have an even ABSORPTION SPECTRUM too. no ?
when we talk about rooms we usually talk about room gain, eigenfrequency etc. but we never seem to talk about absorption spectrum ?
i mean if you plaster 1" thick foam everywhere in your room you will mostly kill everything up top without much effect below 300 hz or so. so could you in fact be making your room sound WORSE by applying room treatment ?
by absorption spectrum i mean room frequency response above eigenfrequency or whatever it is called.
Last edited:
Borat,
Floyd Toole has summarized a life time of object(aka double blind) tests to learn what listeners(trained and untrained, young, old, audiophiles, non-audiophiles, musicians, etc) like concerning frequency response and radiation patterns of loudspeakers, and reflective qualities of rooms, first reflections, total room power, etc.
This book would be a good starting point for your research on this topic.
Amazon.com: Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms (9780240520094): Floyd Toole: Books
Btw, almost forgot to mention, the tests DO include ESLs full range & hybrid in the mix with dynamic speakers.
Also shown are, comparisons of blind vs sighted tests for the same group of test speakers.
I've seen the comparisons through Chapter 9 and noted that in the Quad ESL/2-way/3-way comparison I didn't notice anything done to account for the differences in bass response (I could have been distracted switching between text and illustrations but will look again) in the form of low-frequency cut-off, total power from the speaker, or room gain for the pressure sources.
This is what I basically think happens. And I think it might be the cause of a lot of the CDs coming out really bright - but I am giving a lot of engineers the benefit of the doubt with that one.
It might be an over simplification of how we perceive things but I do think it gets overlooked that when you unevenly absorb reflections you effectively turn down the volume on the region you absorbed and not much else. I've heard it talked about here and there but for the most part speaker makers just stick to speakers and skip over the room part. Linkwitz is one of the first I heard explain it in a simple way like this about how turning down the reflection can be perceptually the same as turning down the volume. It's somewhere in this lecture
Linkwitz AESUK_lecture_0711.mp3 - 24.58MB
Here is a blurb about speakers from ATC although the article itself plays the fence and skips over absorption.
"4. Dispersion and Directivity
The relationship between direct and reverberant sound is
very important in high performance loudspeakers. It is clear that
not only must the on-axis magnitude response be accurate and
linear but also that the behavior off-axis must be both broad and
even with frequency exhibiting no abrupt dips in amplitude. The
aim should be to achieve a horizontal dispersion of +/-80 deg.
With a -6dB @ 10KHz and a vertical dispersion of at least
+/-10 deg. To ensure that in a well behaved room with a good
RT vs frequency characteristic, The reverberant sound will be
consistent with the direct sound in the listening area"
I assumed from the context of this forum, it was relating to listening/living rooms
Now if we're going to talk stage gear.... JBL has some cone/dustcap designs that can beam like a parabolic reflector!
Cheers!
it´s a geometric problem, so not so easy at it seems. A speaker that beams and you listen at short distance crates a very sharp immage. An omni on the contrary creates a sound (at close distance) that is very "spacy". What is more natural sounding is also dependent on the recording process. I think this can not be resolved unless we agree on a certain distance in a certain room. It´s a never ending story. What bores me is the way the discussion goes. There is no "ideal" and nothing is "perfect" unless we agree on a mimal standart so this discussion will go on for ever. A waist of time if you ask me.
Depends, depends, depends...
I think there's not so much a problem with specific radiation patterns, but a personal preference for one or the other.
The recordings listened to can also give preference to high or low directivity.
This is why there are different ways to record and reproduce music and not 1 size fits all. Some prefer omnidirectional, others high directional eliminating reflections as much as possible.
Having read plenty of documentation on (psycho)acoustics and reviews on various types of speakers (besides the ones I've heard myself), the preference of people looking for a "live" preformance were omnidirectional and dipolar. One fine example is how audio engineers and orchestra members commented on the Linkwitz Orion during a high end show, according to them that was the way music was supposed to sound.
This is why I'm going to build a dipole design, create a flat as possible power response without the drawback of a resonating boxed design. Reflections will provide a complete sense of envelopment.
I think there's not so much a problem with specific radiation patterns, but a personal preference for one or the other.
The recordings listened to can also give preference to high or low directivity.
This is why there are different ways to record and reproduce music and not 1 size fits all. Some prefer omnidirectional, others high directional eliminating reflections as much as possible.
Having read plenty of documentation on (psycho)acoustics and reviews on various types of speakers (besides the ones I've heard myself), the preference of people looking for a "live" preformance were omnidirectional and dipolar. One fine example is how audio engineers and orchestra members commented on the Linkwitz Orion during a high end show, according to them that was the way music was supposed to sound.
This is why I'm going to build a dipole design, create a flat as possible power response without the drawback of a resonating boxed design. Reflections will provide a complete sense of envelopment.
People Like Bass
This is a good point, and one that Toole covers several times in the book. People like speakers with extended LF response. When comparing the same speaker with and without the LF response cut-off moved up in frequency with a LP filter, people invariably enjoyed the full bandwidth sound more.
This is a good point, and one that Toole covers several times in the book. People like speakers with extended LF response. When comparing the same speaker with and without the LF response cut-off moved up in frequency with a LP filter, people invariably enjoyed the full bandwidth sound more.
If the reflection does not possess the same spectral energy as the direct response, the brain may processes them as separate.
You are correct that the absorption spectrum should be flat. If you wish to approach the optimum, you must consider the loudspeaker and the room together as a total system.
As far as absorption, I would only worry about energy above the Schroeder frequency. The material should have a depth which approaches 1/4 wavelength of the desired frequency to properly damp the anti-node (maximum velocity).
well to merely provide damping 1/4 wavelength is too harsh. a very dense foam should be able to provide meaningful damping at significantly less thickness than that i think.
but to get FLAT ( with respect to frequency ) attenuation i think you will need 1/2 wavelength ( of the lowest frequency of interest ).
which really means that for flat absorption instead of using large surfaces of thin material we need to use individual blocks of foam. it also means we will have to accept less attenuation at high frequencies ( because it is impractical to cover the entire room with foam blocks ).
auralex makes some pretty gigantic foam blocks.
An externally hosted image should be here but it was not working when we last tested it.
the one in the pic above is classified as "bass trap" but in fact it is a perfect broadband absorber.
the one below is classified as "broadband absorber" which means it's almost as good as the one on top failing only as a bass trap:
for timbre purposes should work though.
An externally hosted image should be here but it was not working when we last tested it.
Last edited:
Foam operates by damping the velocity of the oscillating fluid (air), which occurs at the anti-nodes (maximum velocity, minimum pressure). As the thickness of the foam decreases, you approach the node (minimum velocity, maximum pressure), which results in dramatically reduced absorption.
A very dense foam may be reactive at high frequencies, which will result in a significant spectral imbalance. We want a material whose impedance approaches a constant value for resistance vs frequency and a minimum of reactance. I might advocate a foam which increases in density (as you approach the node) according to an exponential function. However, a variable density foam may be very difficult to achieve in practice.
Exactly
However, I wouldn't purchase commercial acoustic foam ($$$).
Being the brilliant man you are, why not cut out the middle man and design it yourself?
but how would i manufacture foam
sure Geddes says all foam is foam but i don't agree. foams are very different. i might get some cheap foam somewhere - but will it be even half as good acoustically ? i doubt it.
did you try laying down on a tempurpedic mattress ?
i think foam is better left to professionals
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.