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Old 28th October 2005, 07:19 PM   #11
Ropie is offline Ropie  United Kingdom
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Scott, thanks for the tips! I might have another look at the mathcad sheets if I get time.

Quote:
Originally posted by Scottmoose
[B]So top tip -make sure the pointy[ish] bit directly below the driver has a bottom surface area equal to that of the Sd or surface area of the driver
Do you mean this bit?:

Click the image to open in full size.

Bjohannesen, that is an interesting history, I noticed it was a Danish HiFi magazine design. How was the bass response with your setup?
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Old 29th October 2005, 08:05 AM   #12
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Not quite. It does look like it though doesn't it! Look to the very bottom right of the cabinet directly under the driver -the dead-end bit that narrows toward the bottom: that's So.

All the best
Scott
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Old 30th October 2005, 04:05 PM   #13
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Hi Ropie, the bass was tight and clean. Of course, the very deep bass was missing with the small Fostex I used. The performance described in the articles you have found, is what i axeprenced as weel.

The drivers are now in my car, using the trunk as a cabinet. This is not doing very well, however, compared to the bass perfomance in the "minihorn".

I am not sure I would a 8 inch driver for this construction. Martin's MathCad will show this. I am familar with Martins work, and I might have the time to do some simulations in a week or so. This is not a promise, however
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Old 30th October 2005, 05:31 PM   #14
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Quote:
Originally posted by Bjohannesen
I am familar with Martins work
Guys... don't let him fool you... Bjorn has written a very good intro guide to Martin's worksheets that i have been unfortunatly too busy to get up on my website (i'm posting this as a kick in my own butt, becasue all you guys will be bugging me to get it up )

dave
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Old 1st November 2005, 01:56 AM   #15
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Quote:
Originally posted by s_zimble
I built a folded TQWT using the Rutter sheet as a guide for interier dimnetions. The position of the driver is at the fold, half in and half out, if you know what I mean. I have also thought that the top end of the tube might not be functioning as intended unless the driver is positioned further in the top end of the tube. As I have no equipment to take any comparitive measurments, does anyone here have a comment or advise on this idea? Also, I want to make a BLH using a single, small, full range driver and heard that BLH can be quite directional. Would designing an enclosure with a floor facing mouth eliminate some of the directionality?? would a folded TQWT act similarly to a BLH?

Thanks for your comments.
Stuart
Greets!

If you unfold the pipe you'll see that from a pressure POV, it doesn't matter whether the driver is in the bend or not. As frequency increases though, it reaches a point where standing waves (eigenmodes) begin comb filtering with the driver's response (actually it's modulating the diaphragm, AKA reflecting back through it) and due to the longer distances in the folded version, begins at a lower frequency, so some folks cut the internal baffle off at an angle and added more damping to reduce its effect on the FR at the expense of some pipe loading.

From the get-go, Weems made it clear that he didn't try to make a reference design, just a simple, inexpensive DIY pipe design that performed OK with cheap drivers. That was his 'thing'. For instance, somewhere around here I have a circa 1956 corner loaded folded pipe design of his for the cheap, high Qts/Vas 'IB' console drivers of the day. IIRC it was called the $3 baffle and made from the then just released Celotex insulation board. Worked surprisingly well too!

Anyway, for flattest response the driver needs to be positioned so that it suppresses the 3rd harmonic, ergo would ideally be closer to the vent than the throat, moving it farther down the baffle where there's lower amplitude comb filtering occurring. Moving the driver closer to the throat increases acoustic gain, but at the expense of increased 'ripple' in the pipe's harmonic BW.

A typical wide BW driven BLH is little more than a tapered TL, so yes, they perform similarly. Both can be quite directional over some portion of its BW, which normally is desirable, but yes, either corner or floor loading will 'fan' it out and the latter allows for adjusting it, turning it into a big vent ML-TL.

GM
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Old 2nd November 2005, 03:23 AM   #16
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Thanks GM for the complete answer. I have also been reading Martin King's horn theory. A bit chunky for the non engineer, but I am catching on, and what you say fits with it. From what I understand, when you begin to diminish the size of the mouth (for practical size reasons) you effect the horn impedence, making it act more and more like a TL, and introducing all of the standing wave and step baffle issues that should be resolved by a horn design. Is this about it??



Cheers, Stuart.
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Old 2nd November 2005, 03:49 AM   #17
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Greets!

You're welcome! Pretty much.

GM
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Old 2nd November 2005, 02:39 PM   #18
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Regarding the first post, your design thoughts somewhat remind me of Bert Doppenberg's Singular. Not the actual design, but the thought of the look of the piece.

May just be something further to consider...

http://www.diy-systems.com/index.htm...arget=d83.html

Note that there are drawings to download under the downloads section.

Best of luck!
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Old 2nd November 2005, 03:31 PM   #19
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Cheers for that, looks like an interesting design, though it is quite a bit bigger then I would want.

Quote:
Originally posted by BjohannesenI am not sure I would a 8 inch driver for this construction. Martin's MathCad will show this.
At the moment I am thinking about trying design in my orginal post but with a 6.5" driver, due to cost primarily.
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