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Dual 18" reflex sub tuning

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    Posted: 03 March 2015 at 10:24am
Here are two alternate tunings for a high power 2 x 18 reflex sub box . Which would you choose and why?

A or B ?





Edited by Panda - 03 March 2015 at 10:25am
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Peter Jan View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Peter Jan Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2015 at 10:42am
Neither...

I don't know what speakers these eighteens are, but they seem to ask for a different tuning than the ones proposed here. On first sight too much internal volume and/or tuning too high for these speakers.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2015 at 10:54am
If I *had* to choose one or the other it would depend on a few factors - like how much headroom do you expect to have when using them, because both are going to need a boost on the low end for most applications, and also how does the different tuning effect driver excursion (xmax). If you've got plenty of headroom (like 4x or more than average input kind of headroom) then the right, if not then the left.

The one on the right is nearly -5dB in the 50 - 60Hz region which is crazy for a sub.


Edited by Hemisphere - 03 March 2015 at 10:56am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Panda Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2015 at 11:22am
I agree with both of the above posts. 2 x Eighteensound 18LW9601 in a 400 litre reflex enclosure...doesn't look right to me. Anyone kind enough to model this and check the response?
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Peter Jan Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2015 at 11:52am
400 litre is way too much for those speakers, unless you want a sub for home cinema that reaches down to 15-20 Hz, but has low efficiency.
Think along the lines of 250 litre net internal volume and tuned around 35 Hz, than a HP - LP at about 30 Hz - 80 Hz.
That would be my idea of a sub with smooth respons and good efficiency for allround PA duty.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Panda Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2015 at 12:00pm
Originally posted by Peter Jan Peter Jan wrote:

400 litre is way too much for those speakers, unless you want a sub for home cinema that reaches down to 15-20 Hz, but has low efficiency.
Think along the lines of 250 litre net internal volume and tuned around 35 Hz, than a HP - LP at about 30 Hz - 80 Hz.
That would be my idea of a sub with smooth respons and good efficiency for allround PA duty.

Winisd shows -4db across most of the usable HP/ LP band for this configuration. Is that considered acceptable or poor performance for a sub?
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2015 at 2:20pm

One must look at the first -3 dB point when using a simulator. It really doesn’t matter if the cabinet frequency response line peaks higher further down the frequency range. It appears that driver was designed for horn-loading due to its natural decline on both graphs at 100 Hz. I would guess the VAS of the driver is not large enough to take advantage of the enclosure space it has to work with why, the driver is -2.5 dB to -3 dB at 100 Hz.

 

As I do not have the TS Parameters of the EighteenSound 18LW9601 off hand, I am basing my analysis on the curvature of the frequency response.

 

Best Regards,

 

Elliot Thompson
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Peter Jan Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2015 at 2:21pm
-4 dB in WinISD's Transfer Function Magnitude tab is compared to the speaker's reference efficiency, not the net SPL, so this -4 dB has not all that much meaning in terms of how loud the combinations goes with one Watt and says nothing about what it can do when reaching it's mechanical or thermal limits.
It's not so much as considering it good, acceptable or poor, but rather this is simply what you have to deal with, because there is no (practical) way around this low efficiency when you need to keep for instance size within sensible limits. Speakers for sub duty need to have big and heavy voice coils to get rid of heat that comes with high amplitudes (= high power) in these frequencies. Sturdy, heavy cones that don't bent or crack while displacing serious amount of air and aal that makes them much less efficient by nature. Whatever property or properties you try to optimise in this triangle : size - low extension - power, will automatically make the other one or two properties less desirable or even impossible to deal with in the proces. It is possible to have a respons that runs from let's say 25-80 Hz almost ruler flat, with reasonable efficiency, but it will take a big cab, more and typical, for the job selected T/S parameter speakers and big power to get it. It is possible, but in most cases just not practical.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2015 at 2:31pm
Originally posted by Peter Jan Peter Jan wrote:

It is possible to have a respons that runs from let's say 25-80 Hz almost ruler flat, with reasonable efficiency, but it will take a big cab, more and typical, for the job selected T/S parameter speakers and big power to get it. It is possible, but in most cases just not practical.


It requires money which is why, many choose not to go that route.

Best Regards,
Elliot Thompson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Peter Jan Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2015 at 2:37pm
Yes... AND that takes more money of course, but I thought that's obvious when one talks about bigger this, more that and more of something else LOL.
But indeed, it could be this speaker is more horn oriented with it's low Q, high BL.
And that brings me to say something I have to say way too often... when designing a cab, it's better to set your goals (respons, SPL, size constraints, budget,.. ) and than search for speakers that do just that within these boundaries. It usually gets done the other way around...


Edited by Peter Jan - 03 March 2015 at 2:39pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2015 at 3:19pm

 

 

The other way around is based on experience which, a lot of new designers do not have. New designers either gravitate to wards the latest thing from the manufacture, which marketing perpetrates as the best driver available or, what their friend uses based on hype. And of course, not fully understanding what the TS Parameters are telling them embarks a lot of common mistakes.

 

Most of the designers that get exactly what they want have a minimum of 20 years of trial and error which, cannot be grasped in a few years of experience for those that never wasted money on wood/loudspeakers on designs that never met their expectations.

 

Best Regards,

Elliot Thompson
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