CAD plans will have to await Jennygirl's efforts -but she is fast. If you are anxious, you can build based on the Bwaslo spreadsheet and my sketch. There is enough info there to do it.
The SynTripP plans posted in #98 are quite accurate, I will post the missing dimensions after completion of the cabinets, which are going together well.
Art
Weltersys,
I put this into my Akabak model and I am getting some results that are different than your sketch in post 98: the BR vent lengths that I came up with need to be 7.5 inches, not 11.5 inches for a 3.09in dia port (equiv CSA). I am using 768cc for the driver volume and a 3.8in dia port (equiv CSA). It seems to work without a volume filler plug (although a plug will improve the funny business around 900Hz) with a 750Hz XO. Are you sure you set the BR vent correctly in HR for 2 drivers and 4 ports? I am using a 31 liter volume for the main chamber and only the short horn (no extension). Xmax is reached at 57 volts with a -24dB/oct HPF at 97Hz. This provides an SPL of 127dB at 1m. Sensitivity is 101dB at 2.83V at 1m.
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Yes, I did include the height of the foam gasket
As far as plans, I'm just waiting for someone to say the word "final" or for you guys to agree on the measurements. Adding the thickness is a big step for this one with all of the mitered cuts, so I'm waiting on the final dims to flush it out... and I'll be happy to do so!
JG,
I think we are converging on the design. I believe Weltersys is already in the midst of cutting wood/building so we will have more definite dimensions soon. I need to confirm the vent lengths between my sim and his estimates. Are you OK with the design as it currently stands with 83.5 deg H x 36 deg V for a 25.5in wide x 11.25 in high cabinet not including the extension? I think you were aiming for 130dB so you will probably have to go with 3 drivers per horn vs 2 as shown above.
Interestingly, I took this geometry and modified it to accept a 3in full range Faital Pro 3FE22 driver for the tweeter and a pair of Tang Band buyout 5.5in woofers W5-876SE (16ohm wired in parallel) XO at 500Hz, and here is what I was able to get when driven to xmax of 5mm with 38 volts:
This is using qnty 4 x 2.0 in BR ducts that are 7.0 in long and a 14 liter rear main chamber volume, with a 3 liter rear chamber for the 3FE22. The bass injection ports are 2.5in dia ea x qnty 2. The throat for the full range 3FE22 is 2in x 2in square.
For $70 worth of drivers per horn, this is very respectable performance for a home system. It is actually kind of attractive and I may have to try it out as I have the drivers already...
I think we are converging on the design. I believe Weltersys is already in the midst of cutting wood/building so we will have more definite dimensions soon. I need to confirm the vent lengths between my sim and his estimates. Are you OK with the design as it currently stands with 83.5 deg H x 36 deg V for a 25.5in wide x 11.25 in high cabinet not including the extension? I think you were aiming for 130dB so you will probably have to go with 3 drivers per horn vs 2 as shown above.
Interestingly, I took this geometry and modified it to accept a 3in full range Faital Pro 3FE22 driver for the tweeter and a pair of Tang Band buyout 5.5in woofers W5-876SE (16ohm wired in parallel) XO at 500Hz, and here is what I was able to get when driven to xmax of 5mm with 38 volts:
This is using qnty 4 x 2.0 in BR ducts that are 7.0 in long and a 14 liter rear main chamber volume, with a 3 liter rear chamber for the 3FE22. The bass injection ports are 2.5in dia ea x qnty 2. The throat for the full range 3FE22 is 2in x 2in square.
For $70 worth of drivers per horn, this is very respectable performance for a home system. It is actually kind of attractive and I may have to try it out as I have the drivers already...
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1) I am shooting for a box Fb of 70 Hz, sounds like you may be differing from my design goals. What is the excursion minma frequency in your sim? Hornresp predicts around 2.7 ohms for most of the 10" passband (1.64v for one watt), what are you getting?
1)I put this into my Akabak model and I am getting some results that are different than your sketch in post 98: the BR vent lengths that I came up with need to be 7.5 inches, not 11.5 inches for a 3.09in dia port (equiv CSA).
2)I am using 768cc for the driver volume and a 3.8in dia port (equiv CSA). It seems to work without a volume filler plug (although a plug will improve the funny business around 900Hz) with a 750Hz XO.
3)Are you sure you set the BR vent correctly in HR for 2 drivers and 4 ports?
2) Sounds encouraging.
3) My Hornresp port inputs show 194c square/6.4516 =30.07 inch square.
4 ports total 30.07/4=7.5 square inches per port with a length of 11.5" (2920 cm/2.54=11.49")
I expect that the port will end up being shorter than simmed or drawn to hit the desired Fb of 70Hz, but I always prefer to cut down port length rather than add, so that is OK. Because of the port location, parts "O" may not even be required to hit tuning. Also just realized that as drawn with parts "O" coming to an apex, they would island some air volume, they will have to be separated a bit to maintain the 31liter estimated net volume.
There is a lot of 1/2" (nominally 15/32" for the ply I'm using) scrap between part "D" (Horn Top & Bottom) that will be doubled up and laminated for use in the parts "G & H" (Pole Box Front & Back, Pole Box Sides) rather than using 3/4", so 3/4" will just be used as cleats and grille frame parts, so could be lumber rather than plywood. If I had not made several (!!) cutting errors, it looks like the main cabinet is pretty close to a single 4x8 sheet of 1/2" for two cabinets. With the extensions, still should be under two sheets for a pair. Wish I had used "AA" ply, truing to figure all the parts to get the good side out with "AB" makes the build more complicated.
Back to the shop to compete preliminary assembly prior to testing the HF horn before port holes are cut, so we have a "before" version to see what kind of damage they do. I'll be doing some distortion tests also to see how much clean low output the driver has, which will determine whether it can "keep up" with the pair of 10".
Art
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1. The 7.5 in long vent excursion minima is at 91Hz and is about 2.8ohms. If I use 11.5 in long vents, the minima is at 72Hz. However, the longer vent has a resonance peak that generates significant out-of-phase velocity in the vent near 600Hz which results in a cancellation dip in the output - see plot.
2. Yes, it looks like a volume plug can only help and may not be needed.
3. & 4. Yes, I am using 7.5in2 CSA vents x qnty 4 too. The use of the longer vent causes the dip at 600Hz and reduces max SPL by not making the driver hit xmax at a lower voltage. The additional gain in bass output did not appear to be significant compared to the 7.5in long vent.
Here is predicted freq response with 11.5 in long BR vents - note sharp dip near 600Hz:
Here is the velocity at the driver face, the bass reflex ports, and the bandpass ports - note the velocity resonance peak near 600Hz:
Here is the Impedance for the 11.5in long BR port case:
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Dug through the trash just to answer your question
.There are some small voids, but the lamination seems pretty solid, unlike some of the stuff I have purchased at the big box stores that literally fell to pieces when cut into small parts.
Got this AC plywood last November at Lowe's or Home Depot, can't remember which, the brand is Rosewood Forest Products.
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X,
1. There are so many "moving parts" that very small physical changes result in rather large variances from the model. Testing the actual unit will tell the answer.
2. Pretty easy to make, so it will go in.
3) That's pretty close to the Hornresp prediction.The 70 Hz tuning should result in less excursion (and amplitude modulation distortion) in the usual pass band (>100 Hz) but allows more output in the 60-80 Hz range when used "stand alone". Since a pair will fit in the trunk of my Mustang, that's a consideration- there are events where not lugging the trailer with subs would be preferable.
4) As I have mentioned, I doubt that 11.5 length will be needed to achieve a 70Hz Fb with this port design, so the pipe resonances may be more like the shorter pipes you have modeled. We shall see when the drivers are mounted.
Back to the sawdust, still hoping to get some testing in today, but everything is taking longer than anticipated, last cabinets I built was almost a year ago, I'm getting old and rusty, not used to putting in "real" work anymore...
Art
No problem, after the wood scraps started filling in the trash, I regretted not having written down the details, the quality had surprised me, as other than the Aruco (sp?) they carried, most of the plywood has been garbage grade.
I was thinking of BB for this project, but with my wrists giving out want maximum portability, am willing to sacrifice a little solidity for weight.
As it is, with as much bracing the design imparts, I don't think there will be much sonic penalty.
I just finished 4 single sheet 18" BR subs from the same material. I went to a local lumber supply in NJ and priced 12 mm BB (not bad at $46), then I stopped by Home Depot on the way home to see what they had and found the Roseburg 23/32" ACX underlayment (I think it was $43) and it was the flattest, best looking plywood I have seen at HD in a long time and decided to go with it and less bracing.
I was surprised to see that resonance pop up too. Non linear systems, you got a love 'em. 11.5in corresponds to 585Hz half-wave pipe resonance so that explains it. I guess there is more energy there than at 900 Hz (7.5 in) as that is out of band for the woofer.
Measurements will be interesting - what I have seen so far is AkAbak does a decent job predicting the synergy from the band pass port standpoint.
Measurements will be interesting - what I have seen so far is AkAbak does a decent job predicting the synergy from the band pass port standpoint.
Not yet, lots of fiddly stuff around the throat, still have a little more filing, primer, sanding before it's ready for prime time, and have to assemble the grill frame, which completes the initial horn mouth.
Had to go into town for some hardware to finish the project, going to get back to it now.
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It does look very nice. Surprisingly compact that I worry how much of a gape will be in the sidewalls once you make the bass injection and bass reflex cutouts. That half inch ply looks great though. Probably no need for 3/4in ply here. Your CD throat looks to be non-square - was that by design? I seem to recall that Legis used a rectangular throat on his synergy and it may have caused some HF artifacts.
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