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Old 25th July 2008, 09:43 PM   #11
Nuuk is offline Nuuk  United Kingdom
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In a similar situation I went for TL helper woofers that worked well at the cost of a lot of space!
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Old 27th July 2008, 02:39 AM   #12
ozziozzi is offline ozziozzi  Australia
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Thanks again guys for your interest, especially Scottmoose for the computations. You see what I meant about "ridiculous" size for BR design-about the size of a refridgerator!!

Nuuk, I have liked your design for "stealth" TL hidden behind OB baffle since I first saw it. Unlike you, I do have a significant other to please so every little bit of concealment of technology helps. I am trying to make my designs look more like furniture or modern sculpture rather than industrial equipment. See my latest effort below which uses 70's SEAS units-2X 16ohm mid/woofers + 38mm dome mid/tweet XO at about 1.5kHz. Woofers are U-frame open back. Bass is there to ~35Hz and smooth, but down in level, so I am considering activeXO and two amps.
SEAS drivers have good Xmax so can stand a bit of a boost at low freq.

Is there any reason why I couldn't Nuuk's design 90degrees and increase the TL width to achieve area suitable for 10" driver instead of 8"? That would hide more of TL enclosure behind the front baffle--especially from the side. BTW I love the glass side panels to increase baffle width without optical bulk. V nice.
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Old 27th July 2008, 02:59 AM   #13
ozziozzi is offline ozziozzi  Australia
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Thanks again guys for your interest, especially Scottmoose for the computations. You see what I meant about "ridiculous" size for BR design-about the size of a refridgerator!!

Nuuk, I have liked your design for "stealth" TL hidden behind OB baffle since I first saw it. I have a significant other to please so every little bit of concealment of technology helps. I am trying to make my designs look more like furniture or modern sculpture rather than industrial equipment. See my latest effort below which uses 70's SEAS units--2X 15ohm mid/woofers + 38mm dome mid/tweet XO at about 1.5kHz. Woofers are U-frame open back. Bass is there to ~35Hz and smooth, but down in level, so I am considering activeXO and two amps.
SEAS drivers have good Xmax so can stand a bit of a boost at low freq. The wooden "waveguides" are an attempt to time-align mid and tweeter physically with woofers. The wooden trim rings (photoshopped on, but now real) are my wife's idea to improve design.

Is there any reason why I couldn't turn Nuuk's design 90degrees and increase the TL width to achieve area suitable for 10" driver instead of 8"? That would hide more of TL enclosure behind the front baffle--especially from the side. BTW I love the glass side panels to increase baffle width without optical bulk. V nice. Scottmoose, I would probably go with non-tapered TL, but would like to fold it a bit. Are there any serious consequences of folding, esp if I keep input below 200Hz?
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Old 27th July 2008, 03:07 AM   #14
ozziozzi is offline ozziozzi  Australia
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Couldn't attach two pics to one reply-don't know why. Here is the SEAS driver box--a sort of test mule.

Front baffle ~260mm wide and sides about 280mm each for a total equivalent to flat baffle width of about 820mm wide. Top and bottom panels also 280mm wide and height between about 500mm so equivalent to baffle height of about 1080mm. If that makes sense. Front baffle is jointed blackwood planks 30mm thick. Side panels 25mm Tasmanian oak hardwood, top and bottom panels veneered MDF. I have easy option to fit different mid or fullrange in centre position and tweeter in top position and to go totally OB for FR driver and woofers.

Back of woofers is stuffed with a roll of polyester fill with rubber-backed carpet tiles glued to side, top and bottom walls to dampen panels. I have the option to convert present U-frame to sealed or aperiodic enclosure by screwing on a back and fitting vents.

In this present for I can't detect any midrange resonances due to cabinet standing waves or panel resonances. The sound is open and uncoloured, but bass levels are a bit low and require boosting of bass tone control on amp.
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Old 27th July 2008, 06:21 AM   #15
Nuuk is offline Nuuk  United Kingdom
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The reason that I didn't make my woofer TL vertical was that it would have obscured the rear of the open baffle driver(s). However, there is this commercial design that uses a vertical TL woofer placed a little way behind the main baffle.

Moving to the Hawthorne Audio Augies, I got the same performance in a fraction of the space, so the TL's sadly went to the recycling centre.
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Old 27th July 2008, 01:08 PM   #16
ozziozzi is offline ozziozzi  Australia
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Nuuk said "so the TL's sadly went to the recycling centre."

Dear Nuuk, what a strange coincidence, the recycling centre is where I source most of my drivers. But that's another thread...

Thanks for all helpful suggestions. Back to the workshop to start my OB + helper TL.
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Old 27th July 2008, 01:46 PM   #17
Scottmoose is offline Scottmoose  United Kingdom
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No, there's no real issues with folding a damped LF TL as the wavelengths involved are too long to be concerned about corners etc. Everything higher up which would be concerned about bends isn't wanted for your purposes & will be killed by the stuffing.

Re the width, a TL's cross section has nothing per se to do with the driver's cone area, so, for example, a simple increase in width of an existing cabinet won't really work very well (especially if the existing box was designed assuming the line area had something to do with Sd). It'd need designing from scratch based on the driver's parameters, like the one I did above.

I assume we're still talking about the Jaycar units here? The TL I did above is about the smallest you're going to be able to get away with, although as an alternative, GM suggested this one, based on the same math, but with a different nominal tuning frequency which will give similar results (actually, a touch more gain at the lowest frequencies).

L = 80.426"
CSA = 144.352"^2
1.152 lbs/ft^3 stuffing, end-load the driver for flattest impedance

Volume is similar to the one I did above, as you can see, but it might be a bit more practical for you to fold up as being longer, its cross section is somewhat smaller & it requires a lower stuffing density as a result.
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Old 28th July 2008, 08:17 AM   #18
ozziozzi is offline ozziozzi  Australia
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I think I will go with Scottmoose's first suggestion "Max flat impedance TL. 52.328in long, 228.17in^2 CSA, Zdriver 21.23in. Stuff 1.568lbs ft^3 of dacron or similar".

Scottmoose Can I please just have a reality check on quick calc of box dimensions

228.17inches^ CSA (Cross Section Area Yes? eg 15" x 15" is 225inch^ about right - Yes?)

Using that CSA, I end up with a box about 27"H x 30"D X 15"W (internal dimensions) with a partition down the middle that is approx 12" high. This gives a folded TL length of approx 54" with a CSA of 225 square inches. Would I then put a vent of the same dimensions in the back of the box- ie 15" x 15"?

The total volume of this box is about 6.7cuft or 190 litres less driver, partition and bracing.

Does all that sound about right?
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Old 28th July 2008, 08:30 AM   #19
Scottmoose is offline Scottmoose  United Kingdom
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Should do. It's so heavily damped that you won't need to worry about any standing wave issues caused by the square cross section.

BTW, you can mount the driver at the sealed end for the flattest impedance if you wanted.
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