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How much delayed sound comes through the cone from the inside of the loudspeaker in a closed box ?

Alexium

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View attachment 237354


Link to the thread where Duke and Perry Marshall discuss:

How well, do you think, do those open back speakers play into that corner? Doesn't look great to me, even though a bookshelf will provide some scattering (better than a bare wall).
I have one speaker very close to a corner myself, but at least it's in a closed box, costs around $200, and I don't go around telling everyone how awesome my setup is.
 
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Alexium

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"The sound coming through the cone test is completely invalid as in a real situation because the speaker would be playing and cone movement that is not in the signal would be strongly opposed by the amplifier. This is what the impedance, i.e. back emf is all about."
The question is, which is greater: parasitic sound via backpressure articulating the cone, or parasitic sound via backpressure actually passing through the cone, as any soundwave would? I can't imagine the cone being able to attenuate sound a lot, especially paper cone.
 

fineMen

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How well, do you think, do those open back speakers play into that corner? Doesn't look great to me, even though a bookshelf will provide some scattering (better than a bare wall).
I have one speaker very close to a corner myself, but at least it's in a closed box, costs around $200, I don't go around telling everyone how awesome my setup is.

So, what about the back-wave from the back-walls with an open back speaker instead of an enclosure's internal reflections come through cone -20dB destroying music (Mozart, Beethoven, US marching band) into a disgusting noisy mess? We need to review science to begin with: it didn't yet acknowledge the supersticious imagination of hifi enthusiasts of not mind but reality altering powers by as-if science talking.
 

sq225917

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The question is, which is greater: parasitic sound via backpressure articulating the cone, or parasitic sound via backpressure actually passing through the cone, as any soundwave would? I can't imagine the cone being able to attenuate sound a lot, especially paper cone.

Wouldn't a cone that was so thin as to be easily excited by the back wave be so flexible as to be totally unsuitable as cone material in the first place?

I wonder if the question shouldn't be- how audible is the backwave vs the damping factor of the amp?
 

fluid

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Thank you @fluid as always :)
Last question, I promise: would felt add to Vb or deduct from Vb? Meaning will it increase the cabinet size or decrease it? I am asking since I know that wad increases it but not sure if felt behaves in the same fashion when it comes to that
It does increase the apparent box volume to some extent but what is most obvious is the reduction of the Q of the combined driver and box. You can see that in the measurements I showed before. The resonance peak is reduced in height and spread out in width.
In the meantime I had this idea: why not combine all these? Like maybe use a thinner plywood, let's say 15mm + apply 4mm of vibrodamping material (like the one I linked above) that would act like an equivalent of a wall thickness of 19mm, right? And then add felt to the walls (10 or even 16mm) and then fill the box with wad
I don't know what the properties of the 4mm damping sheet are, so it is hard to speculate over that aspect. It is a pretty safe recipe to use a reasonable thickness panel, butyl type lining, felt and fibreglass. The wadding is good to create an apparent increase in box volume if that is all you want but fibreglass does the same job and is better at reducing cabinet resonance issues. Now if I wanted to use polyester I would buy the stuff from Bradford designed to go in walls to replace the fibreglass.

An impedance sweep is the best way to get an answer, it is such as useful measurement everyone should be doing it if they are designing speakers.
 

fluid

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The question is, which is greater: parasitic sound via backpressure articulating the cone, or parasitic sound via backpressure actually passing through the cone, as any soundwave would? I can't imagine the cone being able to attenuate sound a lot, especially paper cone.
Air pressure modulation in a sealed box produces some 2nd Harmonic distortion below the drivers resonance frequency but is overall pretty harmless.
If the box has a reasonable amount of stuffing in it, the rear sound has a hard time getting back to the cone and when it does it is still correlated and has a hard time overcoming the electrical damping of the amplifier. The cone is also moving which for any high frequencies makes it even harder. The basket and magnet of the driver creates a lowpass filter effect by itself, so any sound that comes through the cone is going to be quite low in frequency to still have enough oomf to get through all the barriers.

Conversely if you put a small speaker in a bare box and didn't connect the main box driver to an amplifier, you might hear a great deal of sound come through indeed.
 

DanielT

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How well, do you think, do those open back speakers play into that corner? Doesn't look great to me, even though a bookshelf will provide some scattering (better than a bare wall).
I have one speaker very close to a corner myself, but at least it's in a closed box, costs around $200, and I don't go around telling everyone how awesome my setup is.
They are probably location sensitive. It was a fair and such premises are what they are. Sometimes the exhibitors probably don't have much choice how to place the speakers.

Dipoles in themselves if you like that sound depends on taste. Many probably think or experiences sound too be not precise, or too much smeared, mushy sound. At least those are the words I've heard people who have listened to dipoles and didn't like their sound use to describe them. But the further they stand from the back wall, the more box speakers they start to sound, I think I read. I myself have not been testing dipoles and their placement in the listening space, I should add.:)
 

Alexium

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They are probably location sensitive. It was a fair and such premises are what they are.
I was just wondering whether in the case of the photo above one can conclude that open baffle speakers should not be used since it will be objectively (and subjectively) poor?
 

Burning Sounds

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They are probably location sensitive. It was a fair and such premises are what they are. Sometimes the exhibitors probably don't have much choice how to place the speakers.

Dipoles in themselves if you like that sound depends on taste. Many probably think or experiences sound too be not precise, or too much smeared, mushy sound. At least those are the words I've heard people who have listened to dipoles and didn't like their sound use to describe them. But the further they stand from the back wall, the more box speakers they start to sound, I think I read. I myself have not been testing dipoles and their placement in the listening space, I should add.:)
Just as not all box speakers sound the same, neither do all dipoles sound the same. Just like there are well designed and poorly designed box speakers, there are well designed and poorly designed dipoles. Well designed dipoles have precise, solid imaging and good dynamics. Unfortunately, I see the mushy, imprecise myth regularly repeated. Dipoles do need space to work well, though.
 

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I got a question and please excuse me, if this is obvious to some of you experts.

If there is a delayed signal coming back at -20dB, why do we not see higher distortion figures in the above mentioned frequency range (100 to 500Hz)? Wouldn’t the distortion be more in the order of 10% (-20dB) as opposed to around 1% (-40dB, at the tested SPL levels)?

Just some arbitrary example of a generally not too badly engineered speaker (Distortion over Frequency).
1666370267706.png

Thx.
 

NTK

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I got a question and please excuse me, if this is obvious to some of you experts.

If there is a delayed signal coming back at -20dB, why do we not see higher distortion figures in the above mentioned frequency range (100 to 500Hz)? Wouldn’t the distortion be more in the order of 10% (-20dB) as opposed to around 1% (-40dB, at the tested SPL levels)?

Just some arbitrary example of a generally not too badly engineered speaker (Distortion over Frequency).
View attachment 238664
Thx.
Simple reflections don't generate harmonics (they have the same frequency as the original signal). Thus, they are not "counted" as harmonic/non-linear distortions. They show up in frequency responses as comb filters.
 

Alexium

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Simple reflections don't generate harmonics (they have the same frequency as the original signal). Thus, they are not "counted" as harmonic/non-linear distortions. They show up in frequency responses as comb filters.
A great answer, I didn't realize it before you highlighted it. A distortion in the shape of the frequency response is not considered a distortion (not in the same sense that non-linear distortion is).
 

HarmonicTHD

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Simple reflections don't generate harmonics (they have the same frequency as the original signal). Thus, they are not "counted" as harmonic/non-linear distortions. They show up in frequency responses as comb filters.
Thanks a lot. Really appreciate it. Straight forward and simple explanation.
 

fluid

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A great answer, I didn't realize it before you highlighted it. A distortion in the shape of the frequency response is not considered a distortion (not in the same sense that non-linear distortion is).
There are two types of distortion, linear and non-linear. Frequency response problems are linear distortion, Harmonic distortion is non-linear. There are many other causes of both types. They both distort the original signal in some way but the perception of them is very different.
 

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Talking about how much of the backwave can leak through the cone is something I've also wondered about, actually even more so about large flimsy roll type surrounds that are pretty much acoustically transparent (no back emf to damp these out as well)...
 

fineMen

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... transparent (no back emf to damp these out as well)...

What the customer needs is a clear set of parameters to base the purchase on. It seems off-tracks to me to try to explain every detail in detail cleaning up sticky preconceptions given birth to by advertizing departments and fed to maturity by "the literature" aka glossy magazines and false friends in the internet.

I'm very unhappy that S. Linkwitz was cited with a minor concern that should back in the day support his ideal of a dipole speaker without cabinet. But one has to understand that his perspective was the reproduction of self-made in-ear recordings. I expect them to be done under not so ideal circumstances otherwise: less experienced orchestra--yep, just 'classic', and less sophisticated acoustics in the town hall. Let alone the difference between real in-ear and, what he used me thinks, besides-ear technology.

So, on the element of concern above, "EMF" namely, as part of the bigger concern regarding boxy harmonics whatever.

This is all, from the starting suspicion down to the ever deeper digging 'discussions' here of utter irrelevance:

- "EMF" is contained in the Thiele / Small model of a dynamic loudspeaker; every argument addressing the EMF is already eaten-up by theory
- beyond the range of the T/S model the cone's acceleration, hence its radiation is mostly determined by mass and drive force, not rigidity--NOT, take note, thank You
- the drive force is (a) motor strength x current and (b) to a relatively tiny degree backpressure; to emphasize motor ./. pressure just make the cone heavier, not stiffer and raise the motor strenghthaccordingly

Even if backpressure was of any concern it would only shift the GROUP DELAY by a tiny bit; the latter being out of the detection capabilities of human hearing

To understand the argument You should be able to understand the concept of group delay. If You do not exactly know what that is, please stop talking about stereo technology. It is absolutely hopeless. That is, why my early introduction of the argument was totally and not the least to say rudely ignored. Ignorance doesn't liberate from kindness.

Later reflections say at about 1ms with -20dB to -30dB level are of now concern, because they appear from the same source as the original, and just shift phase hence group delay which is in wider margins irrelevant for sound quality / fidelity.

In this S. Linkwitz, all honor to him, was plain wrong. Thank You.
 

Arnaudio

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@fineMen , while an interesting read, I did not catch what my quote had to do with your response except for that it has to be related to EMF word :). If you’re suggesting reaction forces on the driver from back EMF is irrelevant to sound leakage through the cone, tbh, I have no experience there myself but can only imagine it does damp out a but this driver (hence the Qes T&S parameter since you brought that up).

As for the comment about stiffness of a driver, the lumped parameter model for loudspeakers assumes piston motion from the cone so cone stiffness doesn’t even exist in that simplified world but I’m sure you‘re not suggesting cone break-up modes don’t affect radiation (I did not follow who’s comment you were trying to address with that).

Next, about irrelevance of back pressure on the driver behavior, that again leaves me puzzled as the acoustic loading from an enclosure on a driver behavior drastically changes its cone velocity response around the tuning frequency of the enclosure (and the group delay changes drastically depending on a sealed/ported/PR design etc, a lumped parameter model can estimate that).

Last, box internal acoustic resonances can be very clearly noticeable in undamped enclosure, even a sealed and very rigid/damped cabinet so, there’s no question to me that internal reflections in the midrange up leak through the surround and to some extent the cone as this isn’t a one way street for radiation (the internal acoustic, structure, external acoustic a fully coupled). In the world of vibro-acoustics, we don’t look at phase or group delay of the response but very simply characterize the Sound Transmission Loss of a partition (a dB value representing how much of incident acoustic energy is transmitted through something, 0dB being transparent, high positive value being low transmission, and negative values being amplification such as a double wall system). Per the earlier comment about people hearing each other screaming behind a wall, the STL of a cone and surround in particular are orders of magnitude smaller than the enclosure and thus likely much more critical to these midrange enclosure colorations than the box in general.

A long post to restate that … I wonder why sound bleeding though the cone and surround isn’t much talked about ;-).
 
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Tangband

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Thanks everybody for bringing some clarity to this subject . :)
 

fineMen

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@fineMen , while an interesting read, I did not catch what my quote had to do with ...
A long post to restate that … I wonder why sound bleeding though the cone and surround isn’t much talked about ;-).

This is all about mechanics, forces, counterforces, movement etc. Then it engages the concept of frequency. Yes, most audio-lovers do not know what that is--as a concept: frequency. Not a glance even. I'm serious with that. Which sense does it make to discuss?!
 
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Tangband

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Later reflections say at about 1ms with -20dB to -30dB level are of now concern, because they appear from the same source as the original, and just shift phase hence group delay which is in wider margins irrelevant for sound quality / fidelity.

In this S. Linkwitz, all honor to him, was plain wrong. Thank You.
Hmm…

Maybe Im calculating this wrong, but…

1ms soundtravel is 34,3 cm in 20 degree celsius. If one uses a box thats half the size of this, you get a 1 ms reflection, ie if one uses a box thats only about 17 cm on the inside of the cabinet. This is a very small box.
Its true that we humans cant hear 1 ms delay, we hear this as only one sound.

But:

In real life, we use bigger boxes. A standmount loudspeaker can easily be 34 cm big on the inside , and you get a reflection in this case thats 2 ms delayed. Can one hear this ?

A floorstander can be 1 meter high , delayed reflection through the cone would then be more than 5 ms delayed - clearly audible.
 
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