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Multi-Way Conventional loudspeakers with crossovers

Sealed enclosure -- golden ratio?
Sealed enclosure -- golden ratio?
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Old 9th September 2017, 06:14 PM   #71
gedlee is offline gedlee  United States
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Originally Posted by 33Polkhigh View Post
There are a lot of different issues going on here. One key is stiffness of the box which acts as an impediment to absorbing energy. We want the box to be decoupled from the energy of the driver. I get this, see attached image.

But even if this is the case then you still have a lot of energy bouncing around inside. This can form standing waves, which using prime numbers and non parallel sides can somewhat help with (I hear different things from different people).
The idea that non-parallel walls removes the resonances is false. It changes them, but for a given volume there will always be the exact same number of resonances in a given bandwidth.
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But then even without standing waves or other additions you still have the energy itself to deal with that if not converted to heat will work its way out in some form.

Thus the energy needs to actually be converted and the usual advice is to use stuffing such as fiberglass and foam etc. I have to say that in all the builds I've done the stuffing aspect was the hardest to get right. The reason is that it always adds a dead muffled sound, I believe because it doesn't equally work on all frequencies. Additionally it can affect the motion of the driver by impeding the flow of energy off of it.

So I'm starting to think that maybe a design like the nautilus which actually draws the backwave out into a cavity so it can't reflect back is the best at least for anything handling higher frequencies.

I don't see why this couldn't be done in a normal square box by just using a brace to bisect and create triangle shape? Or why not just use a big triangle shaped foam wedge pointed at the driver magnet to divided and extinguish the back wave?
The nautilus idea does not cancel or dissipate the back wave, it absorbs it just like any other box stuffing does. The absorption will have almost no effect on the motion of the cone except that it tends to make the box look a little bigger and this has a small effect on the cones motion at resonance. But above resonance the cone motion is going to be relatively unaffected by absorption. And, yes, one does need some absorption inside the box to absorb the internal acoustic reflections, but the enclosures structural resonances are actually the bigger issue if they are not absorbed as well.
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Old 9th September 2017, 09:31 PM   #72
33Polkhigh is offline 33Polkhigh  United States
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Originally Posted by planet10 View Post
That is a common trick to make a highly tapered open or closed midTL. To be effective for bass it would still need to be long.

Foam is not that good an absorber, and certainly not at low frequencies.

dave
Hi Dave, thanks for the reply. So then the question is whether there is any advantage to a triangle or tube shape that terminates as opposed to just a regular speaker box?

IOW lets take two examples. One is just a big box with a a lot of lining and another is a long tube that terminates. Both are lined with the SAME amount and type of lining.

So then will the terminated line more efficiently sponge up (a scientific term) the back energy than a big box? Will the sound in the line still reflect back the way that it does with a typical box speaker? Does anyone have experience with a particular internal shape that is better?

Also something else I was wondering is that if a TL actually converts the back wave to longer wavelengths, then wouldn't this be better at removing the typical box sound since its actually converting the energy. Or is the amount that gets converted inconsequential or creating new problems?
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Old 9th September 2017, 09:53 PM   #73
planet10 is offline planet10  Canada
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Sealed enclosure -- golden ratio?
Given the same volume i would guess that a triangle with a terminus out the back would have an edge, fold that with a terminus out the front second, and just a rectangular box last. The waveform need sto pass thru a significant portion of a wavelength of damping to be absorbed. Don’t know for sure where a straight tube out the back would fit, better than a rectangular box i’d think.

We have never done a rectangular box but have used all 3 of the other variants for midTL boxes, all stuffed aperiodically, which one dependent on how it fits with the rest of the box design.

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Old 9th September 2017, 09:59 PM   #74
33Polkhigh is offline 33Polkhigh  United States
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Originally Posted by gedlee View Post
The idea that non-parallel walls removes the resonances is false. It changes them, but for a given volume there will always be the exact same number of resonances in a given bandwidth.


The nautilus idea does not cancel or dissipate the back wave, it absorbs it just like any other box stuffing does. The absorption will have almost no effect on the motion of the cone except that it tends to make the box look a little bigger and this has a small effect on the cones motion at resonance. But above resonance the cone motion is going to be relatively unaffected by absorption. And, yes, one does need some absorption inside the box to absorb the internal acoustic reflections, but the enclosures structural resonances are actually the bigger issue if they are not absorbed as well.
Hi, thanks for the reply. So let me ask a theoretical question. Let's say you have two bells. And you put one in a large room completely filled with loose stuffing but leave a small gap around the bell. So a stuffed room but the stuffing isn't physically touching the bell.

Then you put the other identical bell in another identical room with no stuffing. I would assume that the room with stuffing would effect the sound of the bell.

IOW the stuffing would allow certain lower frequencies to travel through it well, but certain higher ones would be impeded. This would change the decay times of the higher frequencies and create a muffling effect?

I believe this is what I noticed when I fully stuffed one of my builds. It wasn't crammed in there but certain frequencies sounded "sat on" for lack of a better term.

Maybe the recording studio method of using wedges and non parallel shapes is also applicable to speakers internally.
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Old 10th September 2017, 01:04 AM   #75
33Polkhigh is offline 33Polkhigh  United States
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I read through some of the posts again. It seems that the general consensus is that no "tear drop" or other magic shape will cancel out the backwave. Its just a matter of building solid and having the backwaves bounce around and dissipate with the help of sound absorbers.

I would think that if there was a clearly superior internal shape then all speakers would use it, even if the walls are made out of thin plastic it would still sound better. Dr G. and I think Linkwitz as well said that changing the shape doesn't reduce standing waves (I think this is the resonance being referred to here).

However, something like a t-line has the benefit of drawing some of the energy away from the cone and out as bass energy. How much better this is is debatable.
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Old 12th September 2017, 08:16 PM   #76
gedlee is offline gedlee  United States
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Originally Posted by 33Polkhigh View Post
Hi, thanks for the reply. So let me ask a theoretical question. Let's say you have two bells. And you put one in a large room completely filled with loose stuffing but leave a small gap around the bell. So a stuffed room but the stuffing isn't physically touching the bell.

Then you put the other identical bell in another identical room with no stuffing. I would assume that the room with stuffing would effect the sound of the bell.
The physical radiation of the sound would not be affected, but of course since a bell in a room has many refelcetion arriving at the ear the absorption would affect the reflections and change the sound that you heard, but not the direct wave.
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IOW the stuffing would allow certain lower frequencies to travel through it well, but certain higher ones would be impeded. This would change the decay times of the higher frequencies and create a muffling effect?

I believe this is what I noticed when I fully stuffed one of my builds. It wasn't crammed in there but certain frequencies sounded "sat on" for lack of a better term.

Maybe the recording studio method of using wedges and non parallel shapes is also applicable to speakers internally.
This is not too scientific of a study so I can't comment on your perceptions.
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Old 12th September 2017, 08:22 PM   #77
gedlee is offline gedlee  United States
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Shape and placement of the sound absorbing material will have a big effect on its effectiveness. This is because sound is absorbed only when there is particle velocity. At the walls the particle velocity goes to zero so absorption on the walls does little. I always place the absorption in the middle of the box, not on the walls. The box shape will affect the mode shape and move the locations of maximum particle velocity around. A long tube with absorption on the walls won't see so much sound attenuation because the wave motion is normal to the walls. Place it in the middle of the tube and it becomes very effective. So shape is a factor, but any shape can be optimized if you know what you are looking for - hence no shape is any better than any other. Only the implementations vary.
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Old 13th September 2017, 11:15 AM   #78
AllenB is offline AllenB  Australia
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Originally Posted by 33Polkhigh View Post
However, something like a t-line has the benefit of drawing some of the energy away from the cone and out as bass energy. How much better this is is debatable.
The aim is the same, keep the bass and get rid of the rest. Since it was discovered that an optimal transmission line gives a similar response to a closed box I've stopped building them.
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Old 13th September 2017, 06:36 PM   #79
gedlee is offline gedlee  United States
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because the wave motion is normal to the walls. Place it in the middle of the tube and it becomes very effective.
That should be "parallel to the walls" - getting too old for this.
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Old 13th September 2017, 10:43 PM   #80
33Polkhigh is offline 33Polkhigh  United States
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Originally Posted by gedlee View Post
The physical radiation of the sound would not be affected, but of course since a bell in a room has many refelcetion arriving at the ear the absorption would affect the reflections and change the sound that you heard, but not the direct wave.


This is not too scientific of a study so I can't comment on your perceptions.
Yeah, not a scientific study. I have to say that there is something less musical about a stuffed speaker. A lot of experienced builders use minimal stuffing. Maybe its just that the stuffing filters out higher frequencies so much better and so has a muffling effect on the sound emanating from the box.
I would assume that sound energy takes a path of least resistance and so something that blocks or slightly impedes the waves can affect the behavior of the source but idk.

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Originally Posted by gedlee View Post
This is because sound is absorbed only when there is particle velocity. At the walls the particle velocity goes to zero so absorption on the walls does little. I always place the absorption in the middle of the box, not on the walls. The box shape will affect the mode shape and move the locations of maximum particle velocity around.
This has been my experience. In my first build I tried foam on the walls and fully stuffed and liked neither. No stuffing was okay, but when I tried a flattened pancake of stuffing behind the drivers (horizontally) it was the best sound.

I would think a round beehive of stuffing or f-glass in the middle would break up the axial modes which I assume is a good thing. Then the internal sound would dissipate better with less distortions. Also a ball or slug in the middle would make the internal shape itself less important.
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