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Mini Scoops - Reality check

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odc04r View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 04 April 2017 at 9:17am
Looking pretty good, if you're happy with it then great. At some point a swept response measurement is going to stop providing much help. It can't tell you anything about delay or harmonics for a start, the ears start to come into their own at that point. 

MEng always a sensible choice, opens up the door to CEng which is always a career winner if you're capable. It's not really that hard to get as long as you land a decent position out of Uni either. I did an MEng back in 2000, followed it with a PhD. In hindsight should have gone for the CEng instead but that's life for you. Things are going ok... And electronics/sound stays a hobby which keeps it fun.
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Diaz View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Diaz Quote  Post ReplyReply Direct Link To This Post Posted: 10 April 2017 at 12:53pm
Originally posted by fatfreddiescat fatfreddiescat wrote:

@DIAZ
The green plot looks like the lower tuned response from restricting the throat, it also looks like a more damped response but has more output? In the long run your ears are what counts in my book.
Adding some damping to the rear chamber will from my experience add to that lush deep bass sound by absorbing some of the upper harmonics etc, looking good Smile


Yes you are right. The green one is the one with the tighter throat.
We decided first to go with the more open/looser throat as the sound had less overtones/distortion.
After the last session i found that i can eliminate the 95Hz Peak causing the overtones quite good by using a steep filter around that frequency.
As the Measurement proclaims ~1db more in the tight throat version i will try the tighter version again and even try to make the throat even tighter. lets see what that does. I expect more damping, probably higher output and much more distortion around 80-90Hz but as we use them from 28Hz-65Hz this wont be a relevant factor.
Especially the damping is an issue as the cone movement around 65Hz is still very x-max touching.
I think that we can control the Excursion at 65Hz better by trying to tune the throat than to experiment with more wadding?
Anyhow it could be that we made a mistake at measuring at different volume levels and to prove that we do it again...
Lets see....
Stereofreezed Soundsystem rebuilding Pics: https://www.facebook.com/STEREOFREEZED/photos/?tab=album&album_id=1336346346387987
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Diaz View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Diaz Quote  Post ReplyReply Direct Link To This Post Posted: 03 December 2020 at 12:12pm
FYI. There is a worship group for Mini-Scoops on FB discussing Drivers for
Mini Scoops, Showoff Stacks, Share Plans etc...

Stereofreezed Soundsystem rebuilding Pics: https://www.facebook.com/STEREOFREEZED/photos/?tab=album&album_id=1336346346387987
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jan.i.am Quote  Post ReplyReply Direct Link To This Post Posted: 01 July 2021 at 10:09pm
Dear mini scoop experts, I need your help.

Inspired also by this thread, I've build a mini scoop. I designed one based on the Stiper MS-18 MK3 and have done some modifications on the plan. I've made some measurements and I'm really happy about the outcome. It's a success! Now I'm building the second one. Since I'm writing a thesis at a Technical University about the mini scoop, I have to dig deep into technical and mathematical details. I've already done a lot of research, but I still don't know exactly about the physics of a mini scoop.

My state of knowledge is that below the lambda/4 frequency of the horn of a mini scoop the bass reflex principle predominates and above that it works more or less like a rearloaded horn. The impedance plot has 3 peaks and even a little 4th one. So it can't be "just" a reflex design.

So, where is exactly the boundary between Helmholtz resonance and open pipe resonance? What's really the difference between a fullsize scoop and a mini scoop? What makes a mini scoop a mini scoop? Is it the throat chamber or the size of the bin? Who "invented" the mini scoop and do you know if there is some scientific paper or documentation about it somewhere in the web?

Thank you already in advance for your help.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 01 July 2021 at 11:01pm
You should be able to derive that analytically, using the one-parameter model maths and dividing the path into sections to make it easier to solve. Then join the sections together.

I believe the horn width is the same for the entire rear path? That removes some complexity, as you’ve only got one dimension to be concerned about when determining the areas of transition for each segment.

It can help to take the section view and lay out the segments as a straight horn to assess the profile, since that’s how Hornresp works. If you’re not so good with CAD tools, then doing it to scale on paper, scissors and glue works just fine too.

Once you can see or measure that, you can find the appropriate papers to base your working out from. Keele, Leach, Klipsch, Stewart, Webster & Rayleigh are the obvious places to start - aside from Beranek and Olson’s infamous textbooks, of course. You might also find use for Eargle’s Electroacoustic Reference and Frank Fahy’s Foundations…

Just be aware of the limitations of plane wave propagation assumptions if you’re doing it for a university thesis!

Thinking about ‘origins’ I doubt it’s easy to pin down an ‘inventor’ per se. The original 8” JBL Hartsfield might be a reasonable approximation from the mid ‘50s, if you removed the lens and final expansion.

Olson & Massa’s work on compound horns is worth a look too, particularly the use of a second throat chamber or lining to change the low pass behaviour of the horn section.

You could also measure the radiation impedance for the front & rear of the cone and also along the horn and at the mouth if you’ve got a box to analyse.

Edited by toastyghost - 01 July 2021 at 11:36pm
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jan.i.am View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jan.i.am Quote  Post ReplyReply Direct Link To This Post Posted: 15 July 2021 at 9:28am
Thank you toastyghost for your reply and for your hints.
But I'm still searching for answers about general facts of a mini scoop. If a mini scoop works like a bass reflex principle below the lambda/4 frequency of the horn, where is exactly the boundary between Helmholtz resonance and open pipe resonance? What's really the difference between a fullsize scoop and a mini scoop? What makes a mini scoop a mini scoop?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Contour Quote  Post ReplyReply Direct Link To This Post Posted: 15 July 2021 at 11:28am
It is smaller than a normal scoop… Big smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hi grade Quote  Post ReplyReply Direct Link To This Post Posted: 15 July 2021 at 7:31pm
LOLLOLLOLLOLLOLLOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 16 July 2021 at 12:20pm
Originally posted by jan.i.am jan.i.am wrote:

Thank you toastyghost for your reply and for your hints.
But I'm still searching for answers about general facts of a mini scoop. If a mini scoop works like a bass reflex principle <span style=": rgb251, 251, 253;">below the lambda/4 frequency of the horn, </span><span style=": rgb251, 251, 253;">where is exactly the boundary between Helmholtz resonance and open pipe resonance? What's really the difference between a fullsize scoop and a mini scoop? What makes a mini scoop a mini scoop?</span>


You can find that analytically, by doing what I suggested. The calculation of the flare rate, cross sectional area, and radiation impedance of each segment will let you determine where that transition happens. If you repeat the process for a given full size scoop design, you can show the difference yourself mathematically.

That’s not only the kind of thing that will get you good grades on a thesis paper for acoustics or audio engineering, but is also a good habit to get into. Testing things yourself is always worthwhile, since much of what you can find on Internet forums is Chinese whispers or twelfth hand information. If the papers or books don’t make sense, then making your own analysis will help bring them more into light and understanding.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 16 July 2021 at 6:04pm
Martin j kings papers come to mind....... very thorough rear loaded and quarter wave analysis, went above my head tbh.....



Edited by bob4 - 16 July 2021 at 6:13pm
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