With those ikea bowls, they probably aren't fully round, but flat on bottom so they stay standing. Would that defeat the idea of diffusion?
I'm a bit confused on how to pick the size of the cup/ hemisphere, If I'm using a 3.5 FR88 full range driver, what specs would I use to calculate what i would need?
I had my 6-channel amp's opamp and power supply upgraded to better quality parts / grades. The SQ turned out fantastic after some burn-in. Resolution was greatly improved with excellent transparency
With those ikea bowls, they probably aren't fully round, but flat on bottom so they stay standing. Would that defeat the idea of diffusion?
Your gonna have to make an edge somewhere to mount it. I think the main idea is to focus around the front part of the enclosure. The back part isnt as critical as the front edge.
Quote:
Originally Posted by storm
I had my 6-channel amp's opamp and power supply upgraded to better quality parts / grades. The SQ turned out fantastic after some burn-in. Resolution was greatly improved with excellent transparency
With those ikea bowls, they probably aren't fully round, but flat on bottom so they stay standing. Would that defeat the idea of diffusion?
I'm a bit confused on how to pick the size of the cup/ hemisphere, If I'm using a 3.5 FR88 full range driver, what specs would I use to calculate what i would need?
I believe they are talking about the outside of the enclosure not the inside.
You I was reading about this about a month or so ago. It now makes more sense. Great info and I had already been thinking of ways to make it work in my up coming build, now I have a better understand on how it works and I have a pretty good idea of how I'm going to do it now.
Except without the lip..because i dont think the ikea bowls have the lip, it just transitions into the flat part.
Quote:
Originally Posted by storm
I had my 6-channel amp's opamp and power supply upgraded to better quality parts / grades. The SQ turned out fantastic after some burn-in. Resolution was greatly improved with excellent transparency
With those ikea bowls, they probably aren't fully round, but flat on bottom so they stay standing. Would that defeat the idea of diffusion?
I'm a bit confused on how to pick the size of the cup/ hemisphere, If I'm using a 3.5 FR88 full range driver, what specs would I use to calculate what i would need?
for purposes of reducing diffraction, a larger sphere is always better. The idea is that for a given volume (which you need for an enclosure) it should be as smooth as possible. It does not need to be perfectly smooth but you definitely want to keep sharp edges quite a distance away from high frequency sources.
so how do you determine the necessary radius of the enclosure and after that peak points above and below the driver does it matter if the sphere is continued? or could it be flat?
Thanks for this Pat. I have a sheet somewhere that had the frequency response for a supra baffle somewhere around here, I'll see if I can find it.
Are those the Nathans or Summas?
Those are the big kahunas, a set of Summas handbuilt by Dr Geddes himself. If anyone is in the PNW I'm going to be bringing them up to Mercer Island for the PNW Audio Fest later this month.
Question, would the objects around a typical install location (ie dash, defrost vents, pillar angles, glass, ect.) affect the response the same way as baffle shape would? If so then couldn't the changes that a less then optimum baffle bring actually correct the overall response once the surrounding objects own changes are summed in?
In other words, what if my pillar creates a dip where the stock baffle steps it back up to where it sounds better?
Also I think B&W used Tapering Tubes more for the internal benefits then the added bonus of it having the same external shape.
"The sound of silence. Not all sound generated by speaker drive units is good sound. The kind that emerges from the back of a working driver, into a conventional box cabinet, can bounce around and make a mess of the good sound coming out of the front. B&W’s trailblazing Nautilus™ speaker found a way around boxes. Tapering tubes filled with absorbent wadding soaked up the wayward sound energy and reduced resonances to an insignificant minimum.
Nautilus™ Tapering Tubes are fitted to nearly all B&W speakers, even when they’re not visible to the eye. Sound is channeled through a hollow pole magnet, away from the diaphragm, and disappears into the tail.. So all the sound you hear is good sound."
"When a driver is loaded by a tube of a similar diameter to the diaphragm, sound propagates down the tube as a series of simple plane waves. When the sound reaches the other end of the tube it is reflected back up the tube towards the driver. If it reaches the driver it causes delayed radiation that time-smears the original signal, blurring the clarity of the sound. If, however, you fill the tube with absorbent material and the tube is long enough, you can dissipate the energy before it reaches the end of the tube. The sound from the driver then remains clean and true to the input signal. Tapering the tube enables you to make it shorter for the same level of absorption. It acts like a horn in reverse - reducing the sound level instead of increasing it.
The limit of this type of loading is reached when the wavelength gets small enough to be comparable with the diameter of the tube. Above a certain frequency, the sound ceases to propagate as a simple plane wave and a series of cross-mode resonances are set up which can re-radiate through the driver diaphragm. To maintain the effectiveness of tube loading, you must restrict the bandwidth of each driver. This is one reason why the Nautilus loudspeaker is divided into a 4-way system. A more complex type of loading is required to cover a wider bandwidth and the sphere/tube enclosure was developed for the Nautilus™ 800 Series."
With those ikea bowls, they probably aren't fully round, but flat on bottom so they stay standing. Would that defeat the idea of diffusion?
Check out the jpg that ItalynStalion posted; it's not the shape itself that's uber-important. It's the lack of sharp edges.
In the jpg he posted, you'll notice that the sphere and the hexagonal enclosure worked the best. The cylinder worked ok when the driver is mounted on the curved side, but the results are ATROCIOUS when mounted on the flat side. And that's the general theme:
sharp edge = lots of diffraction
Just make your enclosures look like a Ford Taurus and you'll be OK
Ideally the enclosure should be tear drop shape, like an airplane wing, or a B&W 801. But *anything* that you do to reduce sharp edges will reduce diffraction.
Quote:
Originally Posted by karpe
I'm a bit confused on how to pick the size of the cup/ hemisphere, If I'm using a 3.5 FR88 full range driver, what specs would I use to calculate what i would need?
If you're using a sphere, the radius of the sphere is calculated like this: required sphere radius = 13500 / lowest frequency / 2 / pi
If you're using a simple roundover, the radius of the roundover is calculated the exact same way. That's because we're basically taking a sphere and "quartering it." required roundover perimeter = 13500 / lowest frequency / 2 / pi
You can work from the other direction too. For instance, if you're at Home Depot, looking at PVC, and trying to figure out what size is adequate, here's the calculation.
Lowest frequency = 13500 / 2 / pi / radius of roundover
For instance, you're standing at Home Depot, and trying to figure out if 2" PVC pipe will do the job. First, you have to take that pipe and quarter it, so that it give you a roundover with a radius of 1". A PVC pipe with a diameter of 2", chopped into four pieces, will give you a roundover with a radius of 1" and a perimeter of 1.57. ( pi / radius / 2)
Plugging those numbers into our equation, we find that a 2" PVC pipe, quartered, will reduce diffraction down to 1368hz. (13500 inches per second / 2 / 3.14159 / 1.57"
Does that answer the question? You can approach it from either direction. Either purchase some PVC pipe, or some Ikea salad bowls, and calculate the lowest frequency that they'll diffuse the sound. Or calculate what size you require.
Psychoacoustic research demonstrates that the roundover is most effective at high frequencies. If you're not convinced, grab a tweeter, buy a sphere for a buck, stuff a sock in it, and listen to them.
I think you'll be pleased by how the tweeters "disappear" in a sphere.
I've been thinking a lot about how I want to shape the a-pillars for my closed back Dyn mids and F#1 tweets (they don't need enclosures). I think this thread has given me food for thought. I am thinking that since the tweets are crossed over from 4K up that they would be fine in a sphere a little over 1" and the mids would work in 4" sphere. somebody let me know if I am missing something. Is diffraction going to be as big an issue with the mids?
Question, would the objects around a typical install location (ie dash, defrost vents, pillar angles, glass, ect.) affect the response the same way as baffle shape would? If so then couldn't the changes that a less then optimum baffle bring actually correct the overall response once the surrounding objects own changes are summed in?
In other words, what if my pillar creates a dip where the stock baffle steps it back up to where it sounds better?
Yes, other objects will contribute to the frequency response but there are two important things to keep in consideration:
1. the closer the sharp edge is to the driver, the more it matters, especially at high frequencies.
2. diffraction doesn't just screw up the frequency response, it does it differently for each listening angle. That is why you can't effectively EQ out diffraction effects. If you EQ to make it better in one position, it makes it worse in another.
It is useful to think of this like water flowing in a stream or ripples in a pond. A smooth and large rock will have the water flow smoothly around it. One with lots of edges creates all kinds of turbulence. If you put a bunch of jagged rocks in the stream you may be able to create an area where the flow is smooth, but you can't do that without making it rough in other places.
I've been thinking a lot about how I want to shape the a-pillars for my closed back Dyn mids and F#1 tweets (they don't need enclosures). I think this thread has given me food for thought. I am thinking that since the tweets are crossed over from 4K up that they would be fine in a sphere a little over 1" and the mids would work in 4" sphere. somebody let me know if I am missing something. Is diffraction going to be as big an issue with the mids?
Diffraction is an issue at all frequencies, but it's particularly audible above 1khz. But listen for yourself; go to the craft store, buy some spheres for a buck, and cram a sock in there to seal it off. I think you'll be surprised how quickly the speakers "disappear."
If you want to go the extra mile, buy some rope caulk from Home Depot. It's $5. It's used to seal plumbing, it's in the insulation section. That will seal the sphere completely, and it's removable.
So you can experiment with the spheres, and see if they make an audible improvement.
I remember reading about how Biggs from Jbl used a diffraction ring on the mids in his kicks. is it just the exterior surrounding the driver that is most important with a particular angle on the edge or the actual sphere shape behind the speaker, or both?
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is it just the exterior surrounding the driver that is most important with a particular angle on the edge or the actual sphere shape behind the speaker, or both?
I'm guessing here but I think it has more to do with the area closest to the edge of the speaker. Reason being is that those edges will get more sound bouncing off them than the rear of the enclosures.
I remember reading about how Biggs from Jbl used a diffraction ring on the mids in his kicks. is it just the exterior surrounding the driver that is most important with a particular angle on the edge or the actual sphere shape behind the speaker, or both?
Just take a look at the pic, it should be obvious:
Diffraction off the rear of the enclosure is a bigger problem at low frequencies than at high frequencies. At 5khz a wavelength is 2.7" long. So diffraction off the front is a bigger problem than diffraction off the back. But at 500hz a wavelength is 27" long, so diffraction off the rear of the enclosure is a much bigger issue.
The solution that Biggs used achieves the same goal, the main difference is that the wooofers are flush-mounted. In my experience, a spherical enclosure "disappears" better than a baffle, because the baffle re-directs most of the energy towards you. A spherical enclosure diffuses the sound in all directions.
That's not a knock on Biggs; IMHO diffraction is more audible at high frequencies than at low frequencies.
I have wanted to do some type of spherical or egg shaped enclosure for awhile now. My thinking is....a spherical enclosure along with a mat might be about the best way to get a small mid on the dash.....as it has to be one of the toughest places in the car to put drivers....reflections everywhere. However, when you have a car with a wide and long dash it is worth a try to put speakers there as there are benefits to dash mounting as well.
I was looking at some of the Gallo and Orb sets to play with. However, I ended up picking up a set of the KEF KHT1000 "egg" speakers in the Picofote1 IPOD dock. Mated with a sub, these are some nice sounding small speakers. The enclosure and the Uni-Q driver do a nice job in these....even more so in the larger models.
Quote:
They may look cute - but they sound anything but. Experiencing a movie or favorite album through KHT1005.2 is like seeing an old friend after a makeover: fresh, involving, more intense.The centre and satellite speakers all have KEF’s stunning 75mm (3in.) Uni-Q driver - the smallest ever made, its 15mm (0.6in.) metal dome tweeter and double neodymium magnets deliver the extended bandwidth you normally get with much larger units.
The curvy die-cast aluminium enclosures eliminate the diffractions and internal resonances that so often blur the output of conventional small speakers, so the sound is cleaner and crisper.
I hope to do some type of sphere or egg shape enclosure for some 3" fullranges to be mounted on the dash...will see...
Yes, other objects will contribute to the frequency response but there are two important things to keep in consideration: 1. the closer the sharp edge is to the driver, the more it matters, especially at high frequencies.
2. diffraction doesn't just screw up the frequency response, it does it differently for each listening angle. That is why you can't effectively EQ out diffraction effects. If you EQ to make it better in one position, it makes it worse in another.
It is useful to think of this like water flowing in a stream or ripples in a pond. A smooth and large rock will have the water flow smoothly around it. One with lots of edges creates all kinds of turbulence. If you put a bunch of jagged rocks in the stream you may be able to create an area where the flow is smooth, but you can't do that without making it rough in other places.
I see, thanks.
Edit: Although, objects around the tweeter in almost every install location are going to be nearer in proximity then the edge of a standard width baffle would be to the tweeter and more diffracting even due to the crazy shapes.
Diffraction off the rear of the enclosure is a bigger problem at low frequencies than at high frequencies. At 5khz a wavelength is 2.7" long. So diffraction off the front is a bigger problem than diffraction off the back. But at 500hz a wavelength is 27" long, so diffraction off the rear of the enclosure is a much bigger issue.
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