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Old 1st February 2012, 02:23 PM   #21
bjorno is offline bjorno  Sweden
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I'm trying to catch up with all your postings concerning to Kef B139:

Visit this Url:

Bass Units

Which Kef do you think match your drivers?

Are you sure we are using the correct T/S when simulating your enclosure?

b

PS: Sorry,My computer is erratic, cannot use quote when I'm replying to a post like this as when hitting a quote button the quoted text disappears within a fraction of a second and when I'm writing here ,sometimes all my typing is wiped out and cannot be recovered.So I have to write in off-line mode making it difficult to keep up the phase with all.
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Old 1st February 2012, 03:44 PM   #22
tb46 is offline tb46  United States
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Hi bjorno,

Hope your computer gets better soon.

Regards,
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Old 1st February 2012, 03:53 PM   #23
tb46 is offline tb46  United States
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Post #20

Hi TheBaronGroog,

In the spirit of your Post #11:

Once I have a Hornresp model it's time to get to the real work :-) :

To start I choose a set of external dimensions for the finished box: external volume: from earlier T-TQWT I guess at Hornresp V_net x 1.4 (181 L x 1.4 = 254 L), then I apply "environmental" factors, e.g.: what fits in the room, to get to the height, width, depth values, and pick a material thickness. Then I use a spreadsheet to calculate the constant duct dimension (in this case: height - 2x material thickness), and then the other duct dimension from the Hornresp data.

In AutoCAD I draw a wedge that represents the duct from S1 to S4 using the previously calculated duct heights and the Hornresp L12, etc. length. This gives me the angle between, e.g.: the front face and the driver mounting board. This "wedge" also is the standard against which all duct heights (cross-sectional areas) in the drawing are measured. Once you know the distance from, e.g.: S3 to the the corner labled "1", it's easy to measure the duct height on the wedge. The same method can be used with pencil and paper.

Then its time to lay out the enclosure in an iterative fashion. You have to have a general idea as to where you are going (that always helps :-)). The first one from Post #3 was relatively easy, as I already had a very similar design. The one from Post #19 was much tougher.

As to:

"...could the port be moved to that end/further down..." --- That's how I started, L23 gets to be too long. That's what I mean by iterative, once you got a layout it's time to measure the path length/duct heights, and enter that data into Hornresp to see what happens; and so on..... I'd stay with bjorno's original design (or, at least as close as possible).

"...the small section voided in at S1-could that be removed..." --- When I take a first stab at something like this I try to stay as close as possible to the design. That said, I also think it can be deleted. Actually, the whole section from "6" to "11" can be done with square cuts, I don't think there is any need for additional angulation here. This section will be filled with stuffing at the rate of 1/2 lbs. / ft^3.

"...how do I work out the figures for the values 1-11 on the unfolded horn so I can transpose them to the build..." --- I ran out of time last night. I'll provide additional dimensioned drawings, with a squared up "6 to 11" section if that's alright with you. The other way is to draw it, and measure it.

"...slot is one bit of wood cut in half-round = jigsaw trying to cut a perfect circle and I'm no Da Vinci..." --- I have no data to base this on, but my gut feel is that a round port couples better to the room than a narrow/long port. I'm sure you're understating your wood cutting skills, and it doesn't have to be "that" accurate; but, either way will work.

"...any comment on what the output would be like if I'd gone ahead with this..." --- That is a tapped horn with the drivers located close to the mouth, and a short L12. I would expect an output similar to the one bjorno showed in Post #7 "GM's 1xKefB139". But without a complete Hornresp model, I just don't know. I would expect the output to be quite peaky, having a narrower passband and less low end extension, but being overall louder.

"...What benefit would there be in the isobaric mounting..." --- I see two benefits in isobaric mounting, first the reduction of the enclosure volume, second the reduction of distortion; this holds true for any type of enclosure. The big drawbacks are the additional cost and the added building complexity. For a TL/T-TQWT design you can get into problems with the size of ducts. The lengths will be determined by the frequencies involved, but the cross-sections depend on the required loading/TS parameters.

Thanks for the driver dimensions, as so often the real dimensions don't quite look the same as the paper dimensions.

Regards,
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Old 1st February 2012, 04:04 PM   #24
tb46 is offline tb46  United States
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Hi TheBaronGroog,

You might also find my post and attachment in this thread (Post #8)useful:

T-TQWT Double Fold Question

Regards,
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Old 1st February 2012, 04:14 PM   #25
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e) B139 6171
I'm guessing all this work has been wasted!

I did pull the specs off them using wt3:
http://www.diyaudio.com/forums/attac...-b139-b139.jpg

One driver was very out from the other, as you can see in the above link-will try and re-measure them asap!

Apologies for your wasted efforts
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Old 1st February 2012, 04:45 PM   #26
tb46 is offline tb46  United States
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Hi TheBaronGroog,

Maybe it'll give you or someone else a starting point. That would be worth it to me. :-)

Regards,
Attached Files
File Type: pdf 2012_Jan31_revised_additional dimensions.pdf (19.3 KB, 32 views)
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Old 1st February 2012, 05:03 PM   #27
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Oliver, thanks for your detailed post #23 above has helped clarify things for me

RE the isobaric-how much smaller could it make the enclosure? I know for "common" encloures it's half the space for the same extension or the same space for doubl the extension (give or take)-so could I keep the enclosure sixe, increase the horn length and tune lower?

OT: I've been told on this forum that isobaric doesn't lower distortion as we'd all been told for years-infact it could increase it! I'm trying to prove/disprove this, but have no suitable test equipment-trying to get DIYMA onto the subject with their Klippel.
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Old 1st February 2012, 05:06 PM   #28
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Quote:
Originally Posted by tb46 View Post
Hi TheBaronGroog,

Maybe it'll give you or someone else a starting point. That would be worth it to me. :-)

Regards,
Oliver, you legend! I'll have to remodel the output 1st-hope this works as well with the TS I've got!
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Old 1st February 2012, 05:25 PM   #29
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Seems everyones efforts haven't been wasted

I've kept the enclosure the same and entered in the averaged TS from the two drivers I have-at this point it's the best way I can see of doing it-will add more SPL responses from the independant B139 TS spec too:
Attached Images
File Type: jpg B139 variant.JPG (119.7 KB, 101 views)
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Old 1st February 2012, 05:31 PM   #30
tb46 is offline tb46  United States
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Hi TheBaronGroog,

The single best investment for the loudspeaker design hobby may well be a woofer tester, e.g.: WT3 or so.

It's a while back, but I have build a number of isobaric enclosures, mainly because of woofers the T/S parameters of which seemed to have been invented by the sales department at MCM. Isobaric enclosures work, no doubt there. Manufacturers will usually not go there because of the added cost, and because they can have a driver build to suit their requirements.

I'll attach a spreadsheet I just updated. Don't take it for more than you paid for it :-). If you can: mount the drivers in clam shell format and measure the T/S parameters.

As to Post #29, only one way to find out.

Regards,
Attached Images
File Type: jpg Isobaric_spreadsheet.jpg (56.7 KB, 100 views)
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Last edited by tb46; 1st February 2012 at 05:34 PM.
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