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Old 21st December 2012, 09:43 AM   #11
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Quote:
Originally Posted by sreten View Post
I know the territory and the consequences, clamshell
needs extra volume to clear one driver magnet, and
it cancels even harmonic distortion, so called doubling.
If you mean back-to-back mounting of the magnets, yes that cancels harmonics. For two 12" woofers you can assume 25-30 l of extra volume to just squeeze them in back-to-back. Seems to overcompensate somewhat for the 20 l you save on the rear volume.

Quote:
Originally Posted by sreten View Post
I'd expect the PR's tuning to moreorless fall into place,
Good luck with that.

Quote:
Originally Posted by chris661 View Post
Comparing 2x pair of isobaric vs 2x normal drivers isn't a fair comparison: the former will require half the box size, so of course will be less efficient.
It is a fairer comparison than comparing two pairs of isobaric to a single driver in post #4. The efficiency reduction due to the box volume is not the issue. Isobaric speakers need twice as much power, because the inner driver needs the same amount of power as the outer driver without increasing the SPL.

Quote:
Originally Posted by chris661 View Post
Designing an isobaric cabinet is as easy as a normal one, as is the construction.
It is not, because you have to design and build two chambers instead of only one. The difficult part is to mount the inner driver without affecting aesthetics, e.g. by fixing baffles with visible screws.
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Old 21st December 2012, 03:39 PM   #12
jerryo is offline jerryo  Isle of Man
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What I need is some help with the modelling, which I have only just dipped my toe into (so to speak) As I have said, it's a question of translating what modelled responses one can get using these available drivers ( active and passive) using experience into a useable design.
What I have so far using WINisd and Unibox, with Isobaric loaded active drivers in a ported and Passive radiator design is:

Three examples.

1: Vb = 40.0 litres; Port tuning = 46 Hz; Vent diameter = 0.102m; Vent length = 0.210m
Giving -3db at 47Hz. (vented design)
2: (using Unibox) Vb = 60 litres; Passive Mms = 509.00 grams; Fsp = 14.46 Hz; giving a
-6db at 30 Hz
3: (using Unibox) Vb = 135 litres; Passive Mms = 719.00 grams; Fsp = 12 Hz; giving a
-8db at 20 Hz
( all approx. )

There are many other results that obviously can be achieved with variations of Vb and Fsp and Passive Mms, many of which to my untutored eye look viable. The last example I realise is pushing the boundaries a bit, but is included to illustrate the post that I am making.
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Old 4th January 2013, 04:22 PM   #13
jerryo is offline jerryo  Isle of Man
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Well it looks like that I accidentally discovered EBS alignments, as you might know if you read my last post. I've subsequently read as much as I can about the subject and this has given me a new avenue of possibilities to explore; all very interesting!
So at the moment I am thinking along the lines of two sub's both with Isobarik loading and using passive radiators instead of vents with an EBS alignment, the degree of which is yet to be finalised. Wish me luck!

Happy New Year

And finally, please raise a glass to a friend of mine who died after a fall on New Years Eve just two days after after I saw him.
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Old 4th January 2013, 09:19 PM   #14
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I think the question you have not yet answered is what do you want to use the sub for?
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Old 5th January 2013, 11:25 AM   #15
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My sympathies for the loss of your friend.

Maybe you have already read Audio Innovation - by Dan Marx www.danmarx.org. If not, it may help you in your decision for or against EBS.

What are your size limitations? 40, 60 or 135 l are quite different conditions to base your design upon.

What are the lowest notes in the music you usually listen to? For pop music a -3 dB between 40 and 50 Hz is usually sufficient. If you listen to orchestra or grand piano you may want something around 30 Hz. Lower than that is only desirable for great church organs or synthesizers. If you want the subs for home theatre you can follow the THX standard with -6 dB at 20 Hz.
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Old 5th January 2013, 08:16 PM   #16
jerryo is offline jerryo  Isle of Man
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Hi pacificblue and thank you for your sympathies.
yes, I have read the Dan Marks website and did find it very interesting. With the drivers that I want to use I am not going to get too ambitious so I am not going to try and force them to produce high volumes at 20 Hz. as I realise that high excursion and power become more and more important. ( see my first post for driver specs) For a rough idea a -6db point at 30Hz would be nice. I don't listen to anything very load.
As for box volume, as small as I can get away with according to what degree of alignment I finally go for.
Cheers
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Old 20th January 2013, 03:55 PM   #17
jerryo is offline jerryo  Isle of Man
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Hi pacificblue,
I had to cut my last post short because I was rudely interrupted.
In answer to your question; I actually listen to a bit of everything and occasionally DVD's but music is the prime motivation for some decently deep bass.
Using Unibox I am getting good responses with box sizes around 80-90 litres with -3db points around 30-35 Hz which is looking good. With some careful room placement two boxes of this size should give me all the bass that I really need. Some degree of room lift and perhaps a little equalisation should remove the "bass shelf" almost completely.
I will continue to re-work the design on WINisd and UNIBOX before I finally settle on exact dimensions and tuning frequencies.
I have now got to work out a cunning way of persuading my wife that these to boxes are going to be "absolutely critical" to our musical enjoyment!

I'm actually quite surprised that there is relatively so little in the way of discussion regarding EBS alignments, especially since most of what I have read about them is on the whole very positive.
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Old 20th January 2013, 04:58 PM   #18
GM is offline GM  United States
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Most folks won't tolerate the large cabs required and if they will, then nowadays it's usually in the form of a tower/column design [aka MLTL, MLTQWT], which are sometimes folded to get a low tuning.

So, how big/tall can you 'afford'?

GM

edit: For when corners are available, you'll be hard pressed to get more bang-buck/square ft. than with a 'BIB' pipe horn.
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Last edited by GM; 20th January 2013 at 05:01 PM.
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Old 20th January 2013, 06:31 PM   #19
jerryo is offline jerryo  Isle of Man
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Hi GM,
I'm thinking about making the boxes long and low and hence visually unobtrusive if anything. At 27 litres per cubic foot they would only need to be around 48" long
(give or take) and 14" square to give the alignment that I might need or rather want.
Can you give me a linked example of a BIB pipe horn, out of interest.

Cheers
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Old 24th January 2013, 05:14 AM   #20
GM is offline GM  United States
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Greets!

Sounds like a plan! Many of the large pipe horns I did were mains speakers, equipment rack/TV platforms.

Hmm, 1.0 ft^3 = 28.31684659 L.

BIB basic layout attached.

BIB doc: http://www.quarter-wave.com/General/...BIB_Design.pdf

Main thread: Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks?

Plus you can search ‘BIB’ on the Loudspeaker forums link for some extra individual builds: Loudspeakers - diyAudio

Unfortunately, Godzilla’s consolidated BIB website is gone for the time being.

WRT the EBS, I’m assuming you still plan to make it isobaric and vent it with a PR. If so, making it a MLTL will acoustically lower its natural ‘shelf’ BW, ergo Fb. Using MJK’s MathCad software to accurately enough sim Ľ WL alignments, it’s down near 20 Hz.

This of course will increase the PR’s suspended mass and depending on the performance desired may cause it to easily bottom out due to the B139 theoretically not having enough usable excursion and piston area [Sd] even in pairs.

For my records: what is the driver’s make/model, Le, Xmax? Your available power and do you plan to wire them in parallel or in series?

GM
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