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Mini Scoops - Reality check

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JR.junior View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JR.junior Quote  Post ReplyReply Direct Link To This Post Posted: 06 January 2017 at 12:31pm
Support the scoop technology, larger mouth plays louder!
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paulus View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote paulus Quote  Post ReplyReply Direct Link To This Post Posted: 06 January 2017 at 12:35pm
take 400 off for the pds so you paying 300 for a pair of very tidy larrys which is not bad, dont expect silly spl with them but they do play nice and deep indeed, just remember what ever you get/build to check chamber depth, by experience with that driver you have there?( 1851 and oberton 1600) would go for a minimum of 25mm behind the magnet Big smile minis with 1851s and oberton 1600 are about the place and not really heard  a bad word about them, 

Edited by paulus - 06 January 2017 at 12:43pm
secret is in the expansion!!!
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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: 06 January 2017 at 12:42pm
Originally posted by paulus paulus wrote:

t... just remember what ever you get/build to check chamber depth, by experience with that driver you have there?( 1851 and oberton 1600) would go for a minimum of 25mm behind the magnet Big smile minis with 1851s and oberton 1600 are about the place and not really heard  a bad word about them, 

paulus thank you for this tip. But to hear nothing also could mean nobody using such cabinets.

Anyhow thank you guys for your commitment to the Scoop topic but what i'm actually searching for are SMALL alternatives to full Scoops not full Scoops. I would have built some if that would have been an option...


Edited by Diaz - 06 January 2017 at 1:15pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 06 January 2017 at 2:14pm
Well you know what Hoffman says about small cabinets. Which of sensitivity or low frequency response would you sacrifice some of to reduce cabinet size? No free lunch in physics.

You can make a scoop less wide, keeping the horn path length and reducing cross sectional area. But then you cannot put as large a diameter driver in. And as they say if you want SPL, there is no replacement for displacement. Mouth area is probably going to be too small to ideally terminate horn length too so response is going to get lumpy.

You can make the horn part of a scoop shorter. But now you are affecting low end cut off of the horn.

You can shrink the rear chamber size, but that will increase driver damping and as many people will tell you some drivers just won't work like that because if intended to drive horns they are probably quite stiffly damped already via Qes. So you will need a driver with a less strong motor to compensate perhaps and that opens up other issues.

A small alternative to an 18" scoop is a single 18" reflex. But you're going to have to bring more of them to the party and a more expensive amp rack too.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Diaz Quote  Post ReplyReply Direct Link To This Post Posted: 06 January 2017 at 8:15pm
Originally posted by odc04r odc04r wrote:

Well you know what Hoffman says about small cabinets. Which of sensitivity or low frequency response would you sacrifice some of to reduce cabinet size? No free lunch in physics.

You can make a scoop less wide, keeping the horn path length and reducing cross sectional area. But then you cannot put as large a diameter driver in. And as they say if you want SPL, there is no replacement for displacement. Mouth area is probably going to be too small to ideally terminate horn length too so response is going to get lumpy.

You can make the horn part of a scoop shorter. But now you are affecting low end cut off of the horn.

You can shrink the rear chamber size, but that will increase driver damping and as many people will tell you some drivers just won't work like that because if intended to drive horns they are probably quite stiffly damped already via Qes. So you will need a driver with a less strong motor to compensate perhaps and that opens up other issues.

A small alternative to an 18" scoop is a single 18" reflex. But you're going to have to bring more of them to the party and a more expensive amp rack too.

I'm with you on all above but what makes me wonder is that the Mini is right in between of all that somehow. It has a short Horn (1/4) but the Mouth is to small so it acts more like a resonator.  I just wonder because volume wise its not much smaller than a full scoop 120/60/76. The Mini goes with 90/60/75 so its "just" 30cm lower than the full and i just don’t want to accept that this should have such a great effect on SPL like everybody’s saying.
All are sounding like a Mini is like only half as loud as a full. I just cant imagine that. It couldn't be that much. That's why i'm asking here about real world experiences in comparison of Minis with full Scoops or Hogs.

P.S..: And please no "yes m8, size does matter" answers, thx Wink


Edited by Diaz - 06 January 2017 at 8:33pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 06 January 2017 at 9:59pm
I don't really know a lot about the fashions and design of mini scoops, but from the few plans I have seen they seem to resemble a transmission line style design with a large cross sectional area port. Not sure if the ports tend to expand or stay a constant area, but if they do expand it doesn't seem like much. Certainly not like the quasi-exponential expansion of a full size scoop.

When you put a constant cross sectional area port on a chamber with driver, that's a transmission line enclosure or 1/4 wavelength line as some like to call them. It resonates at well defined harmonic frequencies (open pope resonant modes) and the near field response measured at the port should show that. If you open up the mouth to turn it into a horn eventually the peaks go away and you get SPL gain over a bandwidth.

Then some people say mini scoops act as reflex enclosures, which seems less likely to me although I can see how it might be seen that way.

The way they get decent SPL probably has a lot to do with the large radiating area of the port, which is acting as a way to get the reverse wave out of the driver and make it usefully combine with the wave from the front.

The question is does a mini's port act as a Helmholtz resonator (port) or a 1/4 length transmission line?

Easy enough to measure with a near field measurement. Stick a mic very close to the driver (1cm) and measure the SPL response at low level. Then put it 1cm away from the centre of the port. At the wavelengths involved ground bounce is probably not going to matter a lot.

If it as acting as a reflex the SPL from the port will peak at the resonant frequency and fall off either side. If it is a 1/4 length pipe you'll see lots of spiky resonant frequencies.

I don't know where I am going with this, but if you want to have a crack at a mini scoop 1/4 line transmission theory is probably your friend Tongue
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Post Options Post Options   Thanks (2) Thanks(2)   Quote Aman Gebru Quote  Post ReplyReply Direct Link To This Post Posted: 07 January 2017 at 5:48am
Lets clear this up once and for all.

A mini scoop is a reflex design. It's not a transmission line or a rear loaded horn (scoop).



This is a transmission line. It's the complete opposite of a mini scoop. In a classic transmission line the beginning of the tapered port should roughly be equal to the radiating area of the driver. The port then decreases down its length until it terminates with an area around 1/4 of its starting area. Not all transmission lines are of this design, it is possible to use a port of constant area thought its length. The port or resonant pipe as its know is tuned to 1/4 wavelength of the required operating frequency of the design. If you want to hit 40Hz then the port is going to have to be 2.15 meters long. For 35Hz the port will need to be 2.46 meters long and for 30Hz will need to be 2.87 meters long.

A mini scoops port gets larger, not smaller and if it were a transmission line would not have the required length to load it anywhere near low enough. The longest port paths found in mini scoops are in the 1.4 to 1.5 meter range, and if they acted like a transmission line would be tuned to around 60Hz. Many have ports that are around 1.2 meters long, which would be a tuning frequency of 72Hz if you believe they are a transmission line. Users of mini scoops are reporting hearing notes from their speakers lower than 60Hz, so something else is going on.

The truth is that if you reverse engineer a mini scoop you can calculate it as a reflex design. You have a driver in a rear chamber that is ported to the outside. The only difference is that the port is tapered and larger than normal. As the port has a large cross sectional area it will need to be longer for a given tuning frequency, hence why the ports are between 1.2 and 1.5 meters in length. Most mini scoops are tuned between 35 to 40Hz and because of the large port (that can be equal to the drivers Sd), will have more output at the tuning frequency compared with much smaller ports with an identical tuning. If you sim a mini scoop as a rear loaded horn then you start to see what's going on. And that is that the horn acts as a port and the important thing is the rear chamber volume. If you sim with a 1.4 meter horn with a rear chamber volume of 30 litres you get an f3 of 58Hz. If you now make the rear chamber 200 litres all that changers is the f3, which now goes down to 29Hz. This is not what happens in a true horn, as it's the horn length that dedicates the cutoff. The impedance plot is also very revealing when comparing a mini scoop with normal scoop. The mini scoop only has 2 peaks, which is the same as a reflex design, the normal scoop adds a third higher peak around 100Hz that is associated with a rear loaded horn.

So a mini scoop is a reflex design with a larger tapered port. People on here say they play as heavy as normal scoops, yeah they will, in fact they could play more heavier as some are tuned around 35Hz or lower. If the track you are playing has a lot of content between 32 - 45Hz then the mini scoop could outperform or be equal to a normal scoop because it can be more efficient below 40Hz.

The grunt people talk about from normal scoops is the rising output with frequency. The 60 to 80Hz output of a normal scoop can be very high and it's this that gives the impression of grunt and edge to the sound. A mini scoop plays flat as its a reflex and so while can be as loud as a normal scoop low down, doesn't have that 60 - 80Hz bite that gives the impression of raw SPL. It explains when people say, yeah the scoops at the dance were louder but the minis played heavy that night.




Edited by Aman Gebru - 07 January 2017 at 5:53am
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Post Options Post Options   Thanks (2) Thanks(2)   Quote Aman Gebru Quote  Post ReplyReply Direct Link To This Post Posted: 07 January 2017 at 6:54am
Here are 2 examples.



This design has a large average cross-sectional area of port because of the large throat and has a tuning frequency of 53Hz.




This design has a smaller throat, so smaller average port cross-sectional area, the average height of the port is 210 mm, giving this design a tuning frequency of 41Hz.

Both designs used 600 mm as the internal enclosure width and tunings were calculated using BassBox Pro 6.



Edited by Aman Gebru - 07 January 2017 at 6:59am
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Post Options Post Options   Thanks (2) Thanks(2)   Quote Aman Gebru Quote  Post ReplyReply Direct Link To This Post Posted: 07 January 2017 at 7:25am
Plots for the 41Hz design.



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Post Options Post Options   Thanks (2) Thanks(2)   Quote Aman Gebru Quote  Post ReplyReply Direct Link To This Post Posted: 07 January 2017 at 8:03am
Here's the impedance and what I deduce from all the plots.



First thing is wow, that is some very low vent air velocity. Peaking at 6 meters per second between 30 and 40Hz. This will never have any problems with vent noise.

The worrying thing can be seen from the cone displacement. The design unloads quite badly below 32Hz. You are going to need some good hi pass filtering. The maximum electric input also shows how the displacement and thermal effects how much input power you can apply before running into problems. Your limited to around 70 watts at 30Hz. The displacement plot also shows a peak at 60Hz, but at 9mm its well within the xmax of the driver and isn't likely to cause a problem.

Both group delay and phase look fine and the design is showing a max output of 128dB, although in reality this is 126dB as shown in the maximum acoustic power plot, which takes thermal and displacement constrictions into account.

The f3 is 41.3Hz and I think this would be a nice sounding speaker, but its not one for anyone who wants lots of output at 30Hz.

The impedance plot looks fine and will not give rise to any problems. It should be quite an easy load. You can also see the twin peaks, which is indicative of a reflex design. And yes, if I sim this design with horn simulation software, I still only get 2 impedance peaks.



Edited by Aman Gebru - 07 January 2017 at 8:10am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hi grade Quote  Post ReplyReply Direct Link To This Post Posted: 07 January 2017 at 8:29am
Can't see you getting the best results from shortman mini scoop using fk1 mid bass !
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 07 January 2017 at 9:35am
Originally posted by Aman Gebru Aman Gebru wrote:

Lets clear this up once and for all.

A mini scoop is a reflex design. It's not a transmission line or a rear loaded horn (scoop).



This is a transmission line. It's the complete opposite of a mini scoop. In a classic transmission line the beginning of the tapered port should roughly be equal to the radiating area of the driver. The port then decreases down its length until it terminates with an area around 1/4 of its starting area. Not all transmission lines are of this design, it is possible to use a port of constant area thought its length. The port or resonant pipe as its know is tuned to 1/4 wavelength of the required operating frequency of the design. If you want to hit 40Hz then the port is going to have to be 2.15 meters long. For 35Hz the port will need to be 2.46 meters long and for 30Hz will need to be 2.87 meters long.

A mini scoops port gets larger, not smaller and if it were a transmission line would not have the required length to load it anywhere near low enough. The longest port paths found in mini scoops are in the 1.4 to 1.5 meter range, and if they acted like a transmission line would be tuned to around 60Hz. Many have ports that are around 1.2 meters long, which would be a tuning frequency of 72Hz if you believe they are a transmission line. Users of mini scoops are reporting hearing notes from their speakers lower than 60Hz, so something else is going on.

The truth is that if you reverse engineer a mini scoop you can calculate it as a reflex design. You have a driver in a rear chamber that is ported to the outside. The only difference is that the port is tapered and larger than normal. As the port has a large cross sectional area it will need to be longer for a given tuning frequency, hence why the ports are between 1.2 and 1.5 meters in length. Most mini scoops are tuned between 35 to 40Hz and because of the large port (that can be equal to the drivers Sd), will have more output at the tuning frequency compared with much smaller ports with an identical tuning. If you sim a mini scoop as a rear loaded horn then you start to see what's going on. And that is that the horn acts as a port and the important thing is the rear chamber volume. If you sim with a 1.4 meter horn with a rear chamber volume of 30 litres you get an f3 of 58Hz. If you now make the rear chamber 200 litres all that changers is the f3, which now goes down to 29Hz. This is not what happens in a true horn, as it's the horn length that dedicates the cutoff. The impedance plot is also very revealing when comparing a mini scoop with normal scoop. The mini scoop only has 2 peaks, which is the same as a reflex design, the normal scoop adds a third higher peak around 100Hz that is associated with a rear loaded horn.

So a mini scoop is a reflex design with a larger tapered port. People on here say they play as heavy as normal scoops, yeah they will, in fact they could play more heavier as some are tuned around 35Hz or lower. If the track you are playing has a lot of content between 32 - 45Hz then the mini scoop could outperform or be equal to a normal scoop because it can be more efficient below 40Hz.

The grunt people talk about from normal scoops is the rising output with frequency. The 60 to 80Hz output of a normal scoop can be very high and it's this that gives the impression of grunt and edge to the sound. A mini scoop plays flat as its a reflex and so while can be as loud as a normal scoop low down, doesn't have that 60 - 80Hz bite that gives the impression of raw SPL. It explains when people say, yeah the scoops at the dance were louder but the minis played heavy that night.


Everything you say does make sense, I've never seen or heard one of these cabs for real and I haven't put the effort into measuring port lengths from any plans around.

It would still be nice to see a near field measurement of port output, that will leave no questions as to how the cabinet is acting. Or an impedance plot would do it.

The only reason I say that is because I wonder if it is possible for the port to act with both characteristics of Helmholtz resonance and open pipe resonance simultaneously? Does it have to be strictly one or the other? If the reflex port was 1/4 60Hz in length would it not necessarily do both? Usually it is a non issues I suppose as ports are far shorter, and any pipe resonances are going to shifted up into a range that the driver assisted by the port is unlikely to be asked to play?

If I have a bit of time later I might see what Akabak thinks about it.





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