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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: 31 January 2017 at 10:15am
I expect if you stacked a few more cabs together that would smooth out a little. It's only a few dB, I wouldn't loose any sleep over that considering what can happen you site bass cabs indoors for a gig.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fatfreddiescat Quote  Post ReplyReply Direct Link To This Post Posted: 31 January 2017 at 11:24am
Originally posted by odc04r odc04r wrote:

I expect if you stacked a few more cabs together that would smooth out a little. It's only a few dB, I wouldn't loose any sleep over that considering what can happen you site bass cabs indoors for a gig.


I would agree re stacking multiple cabs and would go so far to say that in stacks of 6 - 8 the change would be BIG, I would expect to see the quarter and half wave modes of the pipe become more damped as it is not so much working as a horn with just one cab but as a quarter wave pipe and port combo. stacking multiples should get interesting, it makes one hell of a difference to the low end and smoothness on my cabs.

Going back to a previous thread about ported into the throat horns, I think you are right about the bootstraping, I also think there are similarities in this cab, the stays x v2 and my ported horns.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 31 January 2017 at 11:42am
If you reverse engineered the horn area vs length relationship, and then figured out what kind of expansion it best matched to (exponential, hypex etc) then figuring out how many cabs you'd need to hit a proper cut off is fairly easy.

I reckon 4 of them and you'll notice a big difference. Maybe even 3 as it is not the longest horn, but then it isn't the biggest mouth either. Where's Staiper when you want a comment :)

A port from chamber to mouth is interesting because it will model like a vented box, except one end is now seeing a radiation impedance of whatever is going on in the mouth as opposed to free air. Some similarities to tapped horns, except how there is a duct resonance involved rather than exposed back of driver.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fatfreddiescat Quote  Post ReplyReply Direct Link To This Post Posted: 31 January 2017 at 12:06pm
Originally posted by odc04r odc04r wrote:

If you reverse engineered the horn area vs length relationship, and then figured out what kind of expansion it best matched to (exponential, hypex etc) then figuring out how many cabs you'd need to hit a proper cut off is fairly easy.

I reckon 4 of them and you'll notice a big difference. Maybe even 3 as it is not the longest horn, but then it isn't the biggest mouth either. Where's Staiper when you want a comment :)

A port from chamber to mouth is interesting because it will model like a vented box, except one end is now seeing a radiation impedance of whatever is going on in the mouth as opposed to free air. Some similarities to tapped horns, except how there is a duct resonance involved rather than exposed back of driver.


I would agree with everything you say there.
Re tapped horn I wonder what effect would be if they were set up in a V config? I think it would be pushing any software a bit to model it but I think it may have a noticeable effect. I guess putting the cabs on their sides with drivers inboard and then try with the drivers outboard to adjust the tap point possibly with a board on top?

I think due to mouth size and ignoring the possible tapped horn effect a block of 4 would be where it really starts to work, block of eight would be a monster, but maybe if the tapped horn effect were constructive then less would still smoothen it out and combine nicely.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 31 January 2017 at 2:02pm
Not quite sure what you mean tbh. a diagram may be required :)

I have come to the opinion that sometimes pen, paper and circuit diagrams are need to model the more exotic enclosures. There is no real magic to it if you have ever done circuit filter theory. Once you have gone through the derivation of lumped models for the more basic alignments (sealed, vented, then 4th bandpass) it gives you a much better appreciation for what is really going on.

Then you can start looking more at horns which are really just sealed boxes with better impedance matching on the other side for a FLH, and with one side free radiating for the RLH concept and go from there. If you can draw the acoustical circuit on paper and do some algebra then you can derive the transfer function of the enclosure.

I don't know how HR models its segments, expect it depends based on the type of expansion selected. Akabak seems like a SPICE netlist for electro-acoustic models hence its flexibility. I think the 2 port matrix method could work well for basshorns comprised of conical segments. I have used the same method for optical thin film transfer in the past with stacks of films and it is very powerful there with a minimum of maths for computing reflection and transmission coefficients.

So much to think about, and not enough time to ever properly do it!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fatfreddiescat Quote  Post ReplyReply Direct Link To This Post Posted: 31 January 2017 at 11:29pm
I'm not surprised it doesn't make sense to you as doesn't to me now I'm re reading it, if you were to lay the cabs on their sides with the bottom of the cabs touching to form a 'V' with  the drivers near the tip of the 'V'  and a board over the top, it should appear acoustically more like a tapped horn - maybe, only thinking for test purposes.

About 20 years ago I spent some time crunching numbers with a college maths lecturer friend of mine looking at electro acoustic models, at the time I was playing with 6th order bandpass boxes and horn design and built my own crossovers etc - I'm not to hot on the maths - more a cut and try approach so I think I will be sticking with HR, Akabak, a mic, a saw. 
In the past I did work touring as systems tech with various systems including Flashlight, D&B C4/B2 and the EAW 850/750 systems as well as freelance FOH and Monitors on all sorts of systems, so any further study went out the window although got to look and listen to many different design approaches. I would love to go back to school but for now I'm trying to help my daughter through her degree and my son through his A levels with a view to studying engineering at uni. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 01 February 2017 at 8:13am
I think I see, arrange the cabs in a V and then add another coupling piece of wood (or whatever) between them to make a bifurcated mouth extension that the driver radiates into to make it like a tapped horn. Yeah might make an interesting difference. As the driver is radiating so close and directly into the large mouth it might not load it much more then free air but you never know until you try.

You're never ever going to get away from cut and try, but with a good model of a cab behind you at last you know what to cut for best effect. I just find that sort of working out quite interesting regardless of topic. Any kind of problem at all!

2 older kids is certainly not going to leave you with much time, one young one is enough for me. He will grow up to have a better workshop than I did, and will probably just want to paint instead Smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djkeet Quote  Post ReplyReply Direct Link To This Post Posted: 13 March 2017 at 9:29pm
Quote:
The Oberton 18NXB1600 sounded more harsh/rough and had a lot pressure.
The PD.1851 played more harmonic/melodic with more resolution but had less pressure.

Very interesting thread based on all the evidence provided I do feel natural justice should prevail and it can be summed up in a simple equation comprising of 6 of 1 and half dozen of the other as when the human element is introduced there appears to be a bias and really the conclusion should read BTW both drivers gone, looking for drivers with similar TS parameters which are powerful but waxed with musicality




Edited by djkeet - 13 March 2017 at 9:30pm
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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: 26 March 2017 at 8:02pm
Originally posted by odc04r odc04r wrote:

Originally posted by Diaz Diaz wrote:

Thank you odc04r for this usefull input and sorry for the late reply!
First, we didn't try it with a sweep but only with music.
My friend took the chance this weekend and made a measurement again.
It's a goundfloor
measurement like last time at 2m distance at a concrete floor.

It had -10°C so the Speaker was cold too but it's an outdoor
measurement this time.
So here we go: Oberton 18NXB1600 in an Staiper Mini Scoop MS18-MK2:


It seems we have been wrong with your estimated peak around 55, its obviously around 65. Tuning looks good for sub duties where 35Hz is just right. Underneath it falls like a typical bass reflex...
What also makes me wonder are the broad impedance peaks or to say it in other words the small/narrow valleys ;)
I'm not sure how to proceed?

How to get the 65Hz under control and perhaps the tuning a little deeper... 35Hz are quite ok obviously.
Should i got for a smaller rear chamber and a smaller horn throat? Could the MK3 Version be an option?

Btw. PD is gone...


You're not wrong about the tuning, clear impedance minima at 35Hz like you say. And I agree that at this point the cabinet is acting as a reflex enclosure. Could also be acting 1/4 wave to some extent, but I'm going to have to go with reflex as a 1/4 wave pipe at 35Hz would be 2.5m long and I don't think the horn path is that. Tuning is a touch peaky but I wouldn't worry about that personally. To be fair I said tuning of the port looked like it was about 40Hz from the nearfield SPL plot so I'm pretty happy with that guess!

The 30Hz peak is your driver, 65Hz peak is the sealed box resonance where the mass of air in the port makes it look effectively closed. Peaks after that are horn or transmission line related.

There doesn't seem to be any real region of horn gain, apart from perhaps 80Hz up. Which as you'd not typically use a box like this much higher does lend weight to the argument of it is effectively a reflex box with some extra port gain. Which makes sense as if it was a true horn I'd expect to see a more peaky lower response anyway due to low mouth area.

You can see that the second horn impedance peak is already very damped due to the sharp folding of the cabinet at about 150Hz. And around this region you have the classic 1/2 wave cancellation notch too.

Have you got any damping material in the rear chamber like the plan suggests? If not it would both lower the impedance peak at 65Hz, and shift the port tuning slightly lower. I'd definitely try that. Apart from that I don't think the cabinet really needs anything else. Experiment with different amounts of stuffing in the upper chamber until you find a measurement and sound that you like.

The 65Hz resonance is interesting, think of it as the box having some ability to store energy when operating at this frequency. The more damped the peak is the quicker it will release that energy when you stop driving it. There is a little peak in output that corresponds to it. I wonder if this is perhaps a good feature when it comes to rolling basslines which often tend to have a lot of content here. You may find that if you put too much stuffing in the chamber and the peak becomes damped that the box sounds a lot more dry maybe? Less fun?

Thanks for making the measurements! I've not heard these cabs in the wild before but the SPL measurements suggest they could be fun. I expect with a few together crossed over at 80Hz they could do quite a bit of damage.

So, sorry for being quiet for some time but we had to finish some boxes.
I owe you some experiences with our MK2 experiment.
After my last post and with your feedback in mind i got a little help from a friend.
From there on we changed the whole building process and the plan.
Now we have a depth reduced cabinet with a lowered port/horn expansion rate but same port/horn length.

So we finally built 4 cabinets and already had a party with them. The Stack of 4 really performed heavy. No comparison to our X1's. Deep, heavy and with the lushness of a horn.
Now a direct comparison to other designs would be very interesting.
We also measured them. I couldn’t post the plots yet because they still on the comp of my friend who does the measurement.
btw. here the pics of our rebuilding sessions.
https://www.facebook.com/pg/STEREOFREEZED/photos/?tab=album&album_id=1336346346387987

What the measurements show is quite interesting. In comparison to the mk2 the impedance peaks are a little higher but the tuning didn't changed a lot, only a few Hz down.
But we won a few good litres of transportation volume (so much that we can close the door of our van now ;) ) and didn't loose on performance.
With wadding the back chamber there is still some room left for getting the damping at 65hz better.
Is there a max amount one can put in the chamber (besides putting that much in that it blocks the air stream of the driver)?

I have one more question to the more experienced developers in the forum.
As we changed the plan also the last section of the horn changed.
Now we have to problem that the last corner brace (Panel H in the MK2 Plan) is smaller/narrower than in the original Plan.
This effects our build in the way that we now cant fit wheels in the lower backward corner any more to drive the scoop like a pushcart.
If we expand/widen Panel H and therefore change the expansion rate of the last segment of the horn what will the effect be and how great will be the impacts?

Measurement Plots soon come...



Edited by Diaz - 26 March 2017 at 9:59pm
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 odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 27 March 2017 at 11:23am
Glad you're getting on with it and seeing results!

There is no hard and fast rule of what is too much damping, but when you hit that margin you will notice the output drop. Getting heat out of the driver must also be considered, an overdamped chamber is going to get warmer as that damped energy must be released somewhere else. The only real way to test this is empirically.

I can't comment on exactly what the change of moving the last segment would be, but because where you are running the enclosure it is behaving more like a reflex bin anyway if you make the change and your port tuning doesn't change for the worst I would not worry about it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Diaz Quote  Post ReplyReply Direct Link To This Post Posted: 03 April 2017 at 6:33pm
Thank you, ok, there is still enough space left for damping and we still have to do some tuning especially with the horn throat....

Here are the Measurements i owe you.
The two different Impedance and Frequency Measurement (green/red) are from the two different throat modulations.
Like you can see the Measurement didn't change a lot but the sound of the box did. With tighter throat it sounded more "honky" with more horn type overtones like i know them from our Elliminator 15" W-bins we once had.
With the more open throat it sounds more dry and a lot more lush and round...
But like you can see in the Measurements the measurable difference is not too big.
The only thing one can see is that we obviously got more narrower impedance peeks, what is quite fine.

So here we go:
Mini Scoops MS MK2 loaded with Oberton 18NXB1600 with different tuning/modulated. We call it the Hog Hunter version now ;)
Groundfloor Measurement at 1m.






Edited by Diaz - 03 April 2017 at 6:37pm
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 fatfreddiescat Quote  Post ReplyReply Direct Link To This Post Posted: 04 April 2017 at 9:11am
Originally posted by odc04r odc04r wrote:

I think I see, arrange the cabs in a V and then add another coupling piece of wood (or whatever) between them to make a bifurcated mouth extension that the driver radiates into to make it like a tapped horn. Yeah might make an interesting difference. As the driver is radiating so close and directly into the large mouth it might not load it much more then free air but you never know until you try.

You're never ever going to get away from cut and try, but with a good model of a cab behind you at last you know what to cut for best effect. I just find that sort of working out quite interesting regardless of topic. Any kind of problem at all!

2 older kids is certainly not going to leave you with much time, one young one is enough for me. He will grow up to have a better workshop than I did, and will probably just want to paint instead Smile

I somehow missed the last few posts on this topic, I nearly started a Uni course in Electronics Engineering 23 years ago - only popped in to find a lecturer at my local Uni who I had been told played with horn designs as a hobby, ended up having an hour discussion with the head of engineering who then tried to persuade me to sign up to the course - I got offered a tour soon after and my daughter is 22, needed the cash to put a roof over my head which it did do.
My son is now looking at which halls to choose at Bristol Uni, he's been offered a place on their MEng course so leaving home - Daughter will finish her final year in May so big changes here, possibly think about going back to school myself!

@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



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