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Old 17th August 2013, 11:59 PM   #11
phivates is offline phivates  United States
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So MJK will be dropping by. You live in an alternate reality.
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Old 18th August 2013, 01:09 AM   #12
xrk971 is offline xrk971  United States
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Originally Posted by phivates View Post
So MJK will be dropping by. You live in an alternate reality.
Ain't that the truth Or it means Jim lives somewhere near NY or NJ?
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Old 18th August 2013, 04:53 PM   #13
Jim Shearer is offline Jim Shearer  United States
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phivates,
Many people think I live in an alternate reality. My wife assists me in interfacing with other people.

X,
I live only about 30 min. from MJK.

Cheers, Jim
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Old 18th August 2013, 04:56 PM   #14
Jim Shearer is offline Jim Shearer  United States
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Side bar--
Simulating boundary loading:

We all know that rooms have a profound affect on how speakers sound. And thus we spend lots of time fiddling with speaker (and furniture) placement, optimizing things as best we can. I have felt that rooms with cathedral ceilings sound better than rooms with standard 8í ceilings. Using Martinís MathCAD worksheets, I can see at least part of what is going on.

The graphs below are from the second part of the worksheets. Speaker positioned as follows:
Distance from Room Corner of Baffle Center= 36Ē
Angular Position from Room Corner of Baffle Center= 45 deg.
Rotation of Baffle Towards Room Center= 35 deg.
SPL curves are shown for:
walls but no floor & no ceiling
walls & floor but no ceiling
walls, floor & 8í ceiling
walls, floor & 10í ceiling

There is no option for a slanted ceiling, but I think the sloping of a cathedral ceiling is beneficial. But I could be wrong... Whatever, I think the graphs show that having the ceiling a bit higher is better.


to be continued...
Attached Images
File Type: jpg room2.JPG (45.9 KB, 604 views)
File Type: jpg room1.jpg (45.8 KB, 596 views)
File Type: jpg room3.jpg (46.4 KB, 598 views)
File Type: jpg room4.jpg (45.5 KB, 604 views)
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Old 18th August 2013, 09:57 PM   #15
GM is offline GM  United States
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Right, ideally a room should have all walls expanding from the sound wall to minimize its Eigenmodes and 'slap' echo. The one room I built this way [converted half basement actually] combined a diffusor back wall in the form of a sloped 'peak' similar to the attached link was the next best thing to ~2pi outdoors with a pair of corner loaded, heavily modified Altec A7-500 small cinema speakers.

20,000 Watt Home Hi-Fi System

GM
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Old 19th August 2013, 04:04 AM   #16
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by Jim Shearer View Post
Side bar--
Simulating boundary loading:

We all know that rooms have a profound affect on how speakers sound. And thus we spend lots of time fiddling with speaker (and furniture) placement, optimizing things as best we can. I have felt that rooms with cathedral ceilings sound better than rooms with standard 8í ceilings. Using Martinís MathCAD worksheets, I can see at least part of what is going on.

The graphs below are from the second part of the worksheets. Speaker positioned as follows:
Distance from Room Corner of Baffle Center= 36Ē
Angular Position from Room Corner of Baffle Center= 45 deg.
Rotation of Baffle Towards Room Center= 35 deg.
SPL curves are shown for:
walls but no floor & no ceiling
walls & floor but no ceiling
walls, floor & 8í ceiling
walls, floor & 10í ceiling

There is no option for a slanted ceiling, but I think the sloping of a cathedral ceiling is beneficial. But I could be wrong... Whatever, I think the graphs show that having the ceiling a bit higher is better.


to be continued...
Here is what I get for a corner placement at 36 in from walls and 35 deg toe-in. Looks very similar - I just can't get the damping to smooth out like the MJK.
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File Type: png PappasTL-Freq-1m-Corner.png (23.5 KB, 562 views)
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Old 19th August 2013, 07:10 PM   #17
Jim Shearer is offline Jim Shearer  United States
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Satisfied that I have a design which will meet my goals, I ordered a pair of FF225wk. I also ordered a pair of Eminence APT-80 horn tweeters, as the FF225wk is reported to need help in the top octave. I put the FF225wk into cardboard boxes to break them in. They sounded very promising to me. Then my wife commented,ĒThey sound so good already in the cardboard boxes, I canít wait to hear what they sound like in proper cabinets.Ē Unsolicited support from SWMBO-- Oh yea, this is gonna be good!

Time to proceed--cautiously!
With a Met, I know what Iíll get. With this design, I was less certain, so I built a prototype in oriented strand board. OSB is cheap, both in terms of cost and quality. When this project is finished, I will have no qualms about tossing this ugly thing into the trash.

I usually spend about 2 months building a pair of speakers. I obsess about every detail of fit & finish. Not that I can produce anything close to the furniture quality cabinets of someone like Terry Cain, but I want it to be the very best I can make. Using crummy OSB, I saw no point in worrying about appearance: just cut the wood & glue it together. Why waste time cutting another piece of OSB just so that the bottom board extends all the way to the back of the side extensions? The piece thatís an inch short will work just fine for test purposes. Curvy bit on the sides like the FH3 is esthetically pleasing, but not worth it here. My one concession in this regard was sanding the edges & corners so that I wouldnít get splinters every time I got near it. Even so, I donít want to try moving it around without gloves. Iíll say it again: ugly, ugly, ugly! So, less than a week from start to completed speaker. From the front, it doesnít look too imposing. But from the side, itís a different story: this one hefty chunk of speaker!

I stuffed the first third of the line with Parts Express Acousta-Stuf. To prevent reflections from sides, back & top, I lined the areas near the driver with 1.5Ē egg-crate foam from PE. Mounted the driver & gave it a listen. Not bad, but needs BSC. Calculator says 1 mH inductor and 2.5 ohms for 3 dB correction. I settled on 1 mH and 2.2 ohms. Listen again: nice! Except that cymbals sound dull/muffled. Of course I knew this would be the case; both from comments about the FF225wk and because I had been breaking them in in cardboard boxes for 220 hrs.

Time to add the Eminence APT-80 tweeters. The tweeter will be mounted in a separate box on top. This arrangement provides maximum flexibility: it can be facing the front wall or corner--as recommended by Bob Brines (and similar to other designs like Terry Cainís Super Abby). Or it could point toward the ceiling. Maybe even face the listener. During testing, I found that not all recordings are created equal: most sounded better with the tweeter facing away from the listener, while a few were better with the tweeter aimed toward the listener. And if you move the speaker around, then the tweeter might do better if positioned at a different angle. With the tweeter in a separate box, itís a tweekerís dream!

I couldnít find an impedance plot for the APT-80, so I am basing my calculations on its nominal impedance of 8 ohms. With a specified sensitivity of 106 dB, I guessed at a 0.47 uf capacitor, which should yield an XO point of 41 KHz. Connect it up & listen again: not bad, but not quite enough on some recordings. I havenít settled on a final value; itís a toss-up between 0.47 and 0.69 uf. If I change my mind, itís no problem to tweek it, since itís in the tweeterís enclosure up top and easily accessible.

For evaluation during extended listening, I put the FF225wk on the left channel and one of my FE167e Mets on the right channel. Result? Completely satisfied. Goals have been met, yea, exceeded! Large scale orchestral music sounds very good; sounds... well, large; doesnít get congested and can produce 90+ dB peaks with no problem. Whatís more, the bass has more extension than I expected. Using Stereophileís test CD and my trusty RS SPL meter, I get an F10 of about 40 Hz at the listening position, thanks in part to room reinforcement. I thought I would need to get down to 30 Hz for a satisfying experience, but so far, I havenít felt the need of a sub.

And what does SWMBO think? She describes the sound as sweet. Yes, itís bit clunky, but itís tolerable. Verdict: time to go buy plywood and order veneer!


to be continued....
Attached Images
File Type: jpg Prototype PTL.jpg (38.2 KB, 407 views)
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Old 19th August 2013, 09:17 PM   #18
xrk971 is offline xrk971  United States
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Very nice work Jim! Congrats on a successful speaker from scratch. OSB actually has a nice industrial look if you are into that. Do you have any side profile photos? You said the 0.47 uF gives a 41 kHz XO, so you mean 4.1 kHz?
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Old 19th August 2013, 10:27 PM   #19
Jim Shearer is offline Jim Shearer  United States
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Quote:
Originally Posted by xrk971 View Post
Very nice work Jim! Congrats on a successful speaker from scratch. OSB actually has a nice industrial look if you are into that. Do you have any side profile photos? You said the 0.47 uF gives a 41 kHz XO, so you mean 4.1 kHz?
Hi X,

There will be some side shots of the plywood build. And shots of the internals during build!

The cap on the tweeter is set to XO at 41KHz so that its level is down to match the 225 around 8 KHz. The alternative is to pad down the tweeter with a resister along with the cap.

Cheers, Jim
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Old 20th August 2013, 09:03 PM   #20
Jim Shearer is offline Jim Shearer  United States
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So I purchased two sheets of 3/4Ē plywood from Curtis Lumber. (The local Home Depot & Lowes donít have any 3/4Ē ply that I want to buy--too many voids, not flat, and/or just plain beaten up.)

The curved edge on the rear of the side pieces was done by having my wife sketch the curve on one piece; then I used a jig saw to cut it as well as I could. Sand paper and elbow grease smoothed the curve. That first piece was used to replicate the other three side pieces; after rough cutting with the jig saw, they were cut to final shape with a router & a pattern follower bit.

I mostly build using dowel pins (for alignment) and clamps. In this build, there are a couple points where I reverted back to screws (for alignment and hold) or 17 gauage wire brads slipped into 1/16Ē pilot holes (for alignment).

The back/divider board joint was done by cutting the divider slightly short, then making a suitably angled flat spot on the bottom edge with a sanding block. When clamped together with an abundance of wood glue, the result is a nice tight ĎVí joint.

to be continued...
Attached Images
File Type: jpg PTL-001.jpg (56.1 KB, 376 views)
File Type: jpg PTL-002.jpg (54.6 KB, 207 views)
File Type: jpg PTL-003.jpg (43.1 KB, 169 views)
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