Actually, the "gut shot" looks quite nicely built. Solid wood sides, honecomb laminates for the baffles, angle iron braces, PVC pipe, real wool, what's not to like? A wire mesh screen on the vent can probably keep the moths at bay. Never tried wool, I have plenty of old pillows to scavenge polyfill from. I would probably use less stuffing too, just go up to driver but no more than 2 in beyond with stuffing. If the response looks anything like this, you are golden.
I'm just in the middle of reading that Cornu thread - bit of a marathon! Interesting stuff but I'll probably stick with this for the time being. The Alpairs sound as nice in these cabs as they do in Frugel Horns, maybe a fraction down on bass but sweet and very detailed. I've actually moved the speakers in a bit since I took the picture, still experimenting with placement, stuffing etc.
Cheers, Ian
Cheers, Ian
A question: wife has returned and seen the speakers in situ. She likes them but wants to know if they can be a bit lower so they don't come over the line between the wall and the sloping ceiling. Stop laughing at the back!
OK, I know what she means and to be honest I prefer the looks of a rectangle to a square. So is it possible to change the aspect ratio of the cabinets - e.g. have a height of 14 inches and a length of something above 15"?
OK, I know what she means and to be honest I prefer the looks of a rectangle to a square. So is it possible to change the aspect ratio of the cabinets - e.g. have a height of 14 inches and a length of something above 15"?
That is a nice finding indeed because the FH3's are known to be one of the nicest sounding speakers out there for the A7.3.
The Cornu's are a fun speaker to make - not hard at all and have a magical "BIG" sound. They have some coloration bit the character is very nice and can be impressive sounding from such a small low profile box. If you have access to foam core then building the Cornu with hot melt glue is easy. The bendability of the foam core and the instant bonding of the hot melt glue is what makes it possible.
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You can reformat the speaker to anything you want - just preserve the cross sectional area, the length, the vent, and the approximate position of the driver relative to the closed end (that can vary from 0.2x to 0.33x). So stretch it out to a long "stick" 45 in long x 5in wide, or fold once for 22.5in long x 10in wide speaker. Or fold it into a 3d cube 11.25in on an edge (not kidding, I have done it). You can make it curved or non rectangular and parallelipd or trapezoidal. Have fun.
Keep in mind though, if it is flat and against the wall you have 3dB boost in bass vs no flat and sitting on a stand.
OK, please bear with me while I try and understand this. In the diagram below the volume of the vent above and to the right side of the driver is 15*2.75*5 = 206.25 cubic inches. So presumably this volume is what we have to preserve when altering the proportions
So, if the dimensions are changed to a 10*22.5" box then the distance of the right vent wall and across top would have to be approx 3.3" to give the same volume of vent (10*22.5*3.3333 = 206.25) Is this correct?
I don't really understand the role of the 5" wall to the left of the driver but I assume this would be also 3.3333 from left edge and 22.5/3 up from bottom.
Then there is the position of the driver. Do I tuck it under the bend of the right hand vent as in the above diagram or in the middle of the new baffle?
XRK, your help is much appreciated!
Yes, preserve the volume but more importantly, the cross sectional area (2.75in x 5.0in=circa 88cm^2). So fold it differently but you will always end up with 45in total path. CSA can be some other dimension to get same as 88cm^2 but you will see that because the driver bezel is about 5in wide you have to have a minimum width of 5in. So really all you can do is fold differently.
I had an hour to spare and here is where I am so far with the wall mounted MLTL for the A7.3. In order to make it fit on a standard 20x30in sheet of 3/16in $1 store foam core, the size was reduced a tiny bit to allow both front and rear baffle panels to be cut from a single sheet of foam core. Internal widths for channels ended up at 4.8in instead of 5.0in. I got bracing in place, foam behind driver, and paper towel tube port installed. Note shown is the spring-loaded terminal cup mounted on same side as port. I am now waiting for glue to dry on capping operation. When I return from travel in a few days it should be set - I used Liquid Nails (low VoC) to cap the front baffle on this time. The adhesive is nice in that it is a great gap filler like caulking but is very strong and a light putty color that blends well with white foam core.
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Very clever and quick! So if I've got this right, because you've narrowed the channels you will have to build the box a little deeper to maintain the cross-sectional area? For my build I'm assuming that if I keep to a cross-sectional area of 13.75 sq inches for a vent 45" long with the driver around a third from the closed end then I can make the vent more or less any shape I like. Is this correct?
Thanks, Ian
Thanks, Ian
Yes. Just keep vent CSA and length the same. For my box, I will raise tuning to about 60Hz to increase bass SPL to compensate for any baffle step losses. So I will keep box depth at 2.75in.
Flat A7.3 MLTL Completed
I added a second layer of foam core on the baffle with liquid nails for CLD, then added two more layers to rebate the bezel flush to reduce diffraction. The last two layers are a trapezoid with beveled edges to reduce diffraction to the maximum extent.
Completed speaker:
Impedance Measurement shows port is tuned at 44Hz (too low) - the min between the two peaks should be around 55Hz to 62Hz. I will have to surgically go inside and shorten the tube. Something is off with the tuning - maybe because I took off the secondary magnet cup to allow more breathing room behind driver and the higher Qts drove mass tuning lower?
Here are measurements with speaker flat on floor with mic 0.5m away. I added 1mH + 5R + 3.3uF BSC circuit I had lying around to flatten the mids some more. I think the excessively low tuning made the bass very low in SPL. Vent measurement is relative only (mic 1in away from vent with very low drive level). Th 700Hz hump is probably the baffle diffraction from a 16in square baffle. Maybe make the speaker a trapezoid the next time, or at least a rectangle to reduce diffraction bumps like this.
How does it sound: a bit bass challenged for now - so some tweaking will be in order. The overall sound is still very good for casual listening but a bit too much treble for me. Might need to remove that 3.3uF high pass cap.
I added a second layer of foam core on the baffle with liquid nails for CLD, then added two more layers to rebate the bezel flush to reduce diffraction. The last two layers are a trapezoid with beveled edges to reduce diffraction to the maximum extent.
Completed speaker:
Impedance Measurement shows port is tuned at 44Hz (too low) - the min between the two peaks should be around 55Hz to 62Hz. I will have to surgically go inside and shorten the tube. Something is off with the tuning - maybe because I took off the secondary magnet cup to allow more breathing room behind driver and the higher Qts drove mass tuning lower?
Here are measurements with speaker flat on floor with mic 0.5m away. I added 1mH + 5R + 3.3uF BSC circuit I had lying around to flatten the mids some more. I think the excessively low tuning made the bass very low in SPL. Vent measurement is relative only (mic 1in away from vent with very low drive level). Th 700Hz hump is probably the baffle diffraction from a 16in square baffle. Maybe make the speaker a trapezoid the next time, or at least a rectangle to reduce diffraction bumps like this.
How does it sound: a bit bass challenged for now - so some tweaking will be in order. The overall sound is still very good for casual listening but a bit too much treble for me. Might need to remove that 3.3uF high pass cap.
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Once mounted on the wall (40in high) and at listening position 1.5m away, the sound is a lot more balanced and the room gain boosted the bass somewhat - it sounds much better on the wall (green) than on the floor pointing up.
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Cool little project. Thanks for posting. Have you tried a shorter vent tube yet? IME ML-TL are very tune-able enclosures.
Based on the FR, perhaps losing the 3.3uF entirely would be a good idea. Maybe try a bigger choke and/or smaller R. Looks like about 6 ohm impedance at the start of that bump from 500-900, which would indicate ~2mH, but this might be too dull. Perhaps it'd be better to straight wire them and use digital EQ instead.
Based on the FR, perhaps losing the 3.3uF entirely would be a good idea. Maybe try a bigger choke and/or smaller R. Looks like about 6 ohm impedance at the start of that bump from 500-900, which would indicate ~2mH, but this might be too dull. Perhaps it'd be better to straight wire them and use digital EQ instead.
Yes, I cut down the vent to 1.0 inch and it is tuned to 50Hz now - much better. About 2.5dB more SPL at 60Hz which makes a difference. It's strange but I normally predict the vent lengths much more accurately than this. Not sure what is going on. I will lose the 3.3uF - just snip it off with wire cutters.
Like the trapezoidal baffle - adds something to the looks, a bit Art Deco
. I'm not sure about CLD using liquid nails, doesn't it dry hard? I was going to do a double skinned baffle and use green glue for the job which doesn't set.
I don't have the means to measure mine but in general I'm happy with the balance so I'll be sticking with original port size during rebuild.
. I'm not sure about CLD using liquid nails, doesn't it dry hard? I was going to do a double skinned baffle and use green glue for the job which doesn't set. I don't have the means to measure mine but in general I'm happy with the balance so I'll be sticking with original port size during rebuild.
Hi X,
Have you ever tried a Cornu with golden spirals made with foam ? Should be nice also
Yes, I actually invented the foam core spiral method to make a Cornu quickly and cheaply. That was basically how I got into DIY speaker building.
http://www.diyaudio.com/forums/full...e-board-speaker-enclosures-5.html#post3256043