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scoop for PD 1550

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rastim View Drop Down
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    Posted: 14 January 2017 at 6:59am
Hello there.

I have been using my PD 1550 in a cabin that was planned specially for that driver, a modified version of X1, somekind of a Letterbox. It really sounds nice and very very low.

But now I want to build a scoop and wondering would a Fane- scoop (for 15") or a Jbl 4530 suit best for this driver?

Will I be needing stuffing for scoop? Some are suggesting scoop needs it, someones opposite :)





or





Or would it be best just to scale down the original Superscoop plan for 18": s and stuck the 15" in?

Thank you!


Edited by rastim - 15 January 2017 at 5:06am
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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: 14 January 2017 at 7:38am
I've build some time ago JBL 4530 replicas for PD154, it has even stronger motor as PD1550, dimensional the same. They're now n a club Driven by Crest CA12, ipmprresive SPL at least to say.. Here the build.
http://forum.speakerplans.com/4530-replica_topic37990.html?KW=4530
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rastim Quote  Post ReplyReply Direct Link To This Post Posted: 14 January 2017 at 8:13am
Your build looks really good. Actually I´ve been staying on this Speakerplans many many years, not a member until now and have seen your post earlier too.

So you are voting for 4530? I was alittle worried of if the motor is too strong for this plan but in your experience it is not so.

So maybe I will build the 4530. But if anyone has an opinion, please write here!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 14 January 2017 at 9:30am
The answer to nearly all of your questions are, it depends Big smile

The 1550 looks like a pretty decent driver for a rear loaded horn. Good Bl, low ish Qes. Enough displacement to make some SPL. The 45Hz Fs says you will not get much lower then that out of any bin using it, so you might as well design a plan or look for one that has this has an intended cut off frequency from the start. It will not need to be as long, or have as large a mouth as a bin intended to get lower. Or you could have a largeish mouth with less bins together to approach an ideal horn situation from another direction.

Some wadding can help extend the length of horn that the air inside it sees, I recall reading somewhere that a typical transmission line length can be 80% of the theoretical length for cut off if you wad it properly. Wadding also helps damp higher frequency horn harmonics and resonances but if you have 180 degree bends in the folding they aren't a large concern anyway as they will naturally filter.

Definitely do not just put it in an 18" design. You will be wasting a lot of space and probably not get optimum performance because the volume of the chamber behind the driver will probably be too large to damp the driver motion well.

Have a read of this paper by Bruce Edgar. It contains the design process for a front loaded horn intended for 50Hz lower Fc cut off. With a rear loaded horn there is no sealed chamber on the front of the driver for damping as this box volume is the outside world and essentially infinite. This changes the design a little but a lot of the thoughts in there are relevant to both front and loaded horns.




Edited by odc04r - 14 January 2017 at 9:34am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rastim Quote  Post ReplyReply Direct Link To This Post Posted: 14 January 2017 at 10:14am
Thanks for the answers!

Putting a 1550 in a 18" design was not what I ment, I ment what about if one scales DOWN the plan to suit the 1550. I mean; in all the plans to 15" driver the angles inside (the roof of cabin) are 90 degr. and no any curves as you can see in a Mogales´Super Scoop design. So would it be good to do this plan(just smaller) or is it better to do for instance 4530- plan?
 And in the 15" plans some parts are not in same position as in Super Scooper, why is that? I realise it is easier to build that way but who cares about easy when speaking scoops :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 14 January 2017 at 10:58am
Ah right, sorry my mistake. Well you'd be more likely to get a result suited to the driver if you just downscaled a plan but it'd still be a crapshoot. Maybe you'll be lucky or maybe not. As all of the materials for a few cabinets and a decent driver start to cost £$ quite quickly it's worth trying to check some of your ideas with horn response or other methods before you cut wood to see if you're in the right ballpark. Personally I would not just downscale.

If you don't feel up to any maths then I'm sure you'd do ok building the 4530 scoop. The 154 and the 1550 are not such different beasts and if one works well the other probably will too. 154 will be a bit louder maybe. There isn't really any such thing as a driving force that is too strong for horns, it is a major contributor to mid band efficiency. You should get a nice strong 60Hz output with that design and you'll want to high pass with a fairly steep roll off at 45Hz or maybe a bit higher.

I'm not sure what you mean about corners, the 45 degree corner reflector pieces maybe in some designs? They are not strictly necessary for low frequency basshorns but as long as you maintain the horn area through the corner and do not shrink it they will be closer to the ideal horn expansion contour and they also add a bit of bracing to a cabinet. Maybe post a picture with an example?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JR.junior Quote  Post ReplyReply Direct Link To This Post Posted: 14 January 2017 at 11:49am
For PD154 I've modifide the throat oppening and made it tighter because of strong BL.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 14 January 2017 at 1:22pm
Paper I linked to has a formula for doing that if anyone is interested. Its for a front loaded horn but I have a sneaky suspicion it would translate well to a rear loaded. Haven't had time to do a full analysis yet, a project quite down the queue line.

Throat area is usually proportional to Qes which in turn is proportional to 1/(Bl^2). So yeah, as you put a stronger motor in there the throat is going to need to be a bit smaller for optimum performance.

These are the sort of sensible checks to do before putting any old driver in any old plan for a sanity check as to if it will work ok or not.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote luton_soundman Quote  Post ReplyReply Direct Link To This Post Posted: 14 January 2017 at 1:39pm
Sell it, buy a fane xb and build the eminence scoop. Had xbs in them and sounded amazing. Changed to 156 but prefered the xbs.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote knet94 Quote  Post ReplyReply Direct Link To This Post Posted: 14 January 2017 at 5:14pm
I had 1550s in 4 ASS 15" scoops. These were essentially 4530s without the plinth at the bottom. Sounded great to me.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rastim Quote  Post ReplyReply Direct Link To This Post Posted: 14 January 2017 at 6:50pm
Originally posted by odc04r odc04r wrote:


I'm not sure what you mean about corners, the 45 degree corner reflector pieces maybe in some designs? They are not strictly necessary for low frequency basshorns but as long as you maintain the horn area through the corner and do not shrink it they will be closer to the ideal horn expansion contour and they also add a bit of bracing to a cabinet. Maybe post a picture with an example?

That is exactly what I ment, the corner reflectors, thank you.

And the other pieces I ment were the inner panels, which are "tilted" in small scoop designs and in Super Scoop there are two panels (between the braces, 405 and 406 long) inside the box. Are those to add extra bracing, cause there are two of them and in the smaller box just one? I mean why is it planned with just one panel in small designs? Because in smaller box it is not needed to brace so much, so one panel is enough?

I hope someone can understand my prattle.... :D


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Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 14 January 2017 at 7:10pm
Originally posted by odc04r odc04r wrote:


Have a read of this paper by Bruce Edgar. It contains the design process for a front loaded horn intended for 50Hz lower Fc cut off. With a rear loaded horn there is no sealed chamber on the front of the driver for damping as this box volume is the outside world and essentially infinite. This changes the design a little but a lot of the thoughts in there are relevant to both front and loaded horns.

Erm, sorry I'm far from an expert, but that paper on FLHs is completely useless in this context…. 

Martin king has a long blurb about backloaded horn design on his page:


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