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Old 22nd December 2012, 01:43 AM   #1
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Default Feedback: New LCR Design for Alpair 10.2

This design is specifically meant for home theater. I was thinking of a floor stander that could be rotated 90 degrees and used as a center channel without any changes to the cabinet in order to maintain identical voicing.

Here is a quick drawing:

Click the image to open in full size.

Specs:

0.75" ply
External dims:
Height: 39"
width: 9.5"
depth: 6.5"
(1500 cu in / 24.6 liters)

ports: 2
port dims: 0.25" H x 8" W x 4.59" L
port tuning: 40 Hz
port mach: 0.03
Sim F3: 38 Hz
Sim F10: ~ 30 Hz

The driver would only be 19.5" off of the floor, on center.

What do you guys think?
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Old 22nd December 2012, 03:44 AM   #2
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I think it looks like a cool idea. I do think the driver at 19.5" off the floor is far too low unless you're sitting in a bean bag chair. Are you planning on puttin the L/R on stands?

Scott
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Old 22nd December 2012, 03:52 AM   #3
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Bigger than i'd do. Look at the group delay (the dip above the liw frequency max is a give away). The high ratio vents will knock that back thou. F3 is gong to be in the neighborhood of 50 Hz, F10 about the same.

dave
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Old 22nd December 2012, 04:44 AM   #4
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Yes, I thought it might be too low to the floor... no, I won't be using stands. I've seen some small commercial floor standers with drivers not much higher than that, but still... it would cause main listening position to be off axis vertically (the driver will always be below ear height, but this would be a bit more so than typical). I could maybe raise the driver and ports nearer to the top for the LR. But then, it might sound a bit different than the center. Or, maybe not noticeably so.

Group delay, Dave? What am I looking at there? Sorry for my ignorance as to what group delay is.... I thought it was something to do with multi-driver systems? Or maybe you mean the sound emitting from the slot ports and the driver? Why is the F3 only 50 Hz whereas the sim shows it to be lower?

As to it being big, it is smaller than a Pensil.

Thank you in advance for the education.

Ben

Last edited by Ben_Tech; 22nd December 2012 at 04:51 AM.
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Old 22nd December 2012, 05:37 AM   #5
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So not REALLY trying to push you away from doing a matching LCR but if they're going to be on the floor I'd imagine that the imaging is going to be way off for music. Why not make your left and right with the drivers toward the top, at or near ear level then just adjust the port to be a single at the bottom, adjust its dimensions since you'll have just one port, and be done? The box dims could be the same so all your major cuts would be virtually identical making construction similar. I don't think you'd audibly hear a difference between them aligned this way with the center as you have designed vs them all being identical. Just my 2 cents.

Scott

PS I did SuperPensils with a custom Mar-Ken12 shallow that Dave designed and I beta'd. With some simple adjustment of the stuffing I was able to get an almost acoustically identical LCR. With the 80hz crossover the difference in bass is non-existent to my ears. It's a fantastic front stage. Just look at my SuperPensil build to see pictures and such.

Last edited by skeeter99; 22nd December 2012 at 05:45 AM.
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Old 22nd December 2012, 05:56 AM   #6
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Quote:
Originally Posted by Ben_Tech View Post
Group delay, Dave? What am I looking at there? ... Why is the F3 only 50 Hz whereas the sim shows it to be lower?
The blue curve that goes off the top of the graph... too high a group delay is one of the things that gives BR a bad name.

The sim does not account for the "R" added by the high aspect ratio slot port.

Quote:
As to it being big, it is smaller than a Pensil.
Pensil is a TL not a BR

dave
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Old 22nd December 2012, 05:59 AM   #7
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Quote:
Originally Posted by skeeter99 View Post
So not REALLY trying to push you away from doing a matching LCR but if they're going to be on the floor I'd imagine that the imaging is going to be way off for music. Why not make your left and right with the drivers toward the top, at or near ear level then just adjust the port to be a single at the bottom
With the vent at the bottom he will end up with an ML-TL. He has done most of what can be done with the current design to fight that.

dave
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Old 22nd December 2012, 06:47 AM   #8
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Ok, here is a revision to shift the drivers higher on the LR. The driver centerline will be around 29" off the floor, which is quite standard. I adjusted the ports a little bit to allow room at the top (the part after the elbow is shorter.)

LR:

Click the image to open in full size.

Center:

Click the image to open in full size.

The elbow in the ports is to prevent mids from escaping quite as much. Good idea?

Let me know what you fellows think of the revision.
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Old 22nd December 2012, 03:22 PM   #9
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Boxed in volume created by slotted port fixtures confine driver; reflections off of them and back panel increase amount of higher frequency energy bouncing back and re-radiating through driver. This is much bigger factor than mid radiation through slots. In pictured drawing the slotted port fixtures reduce distance that energy travels through damping material before bouncing back at/through driver.

Slotted ports break interior into three ported chambers, each alone and in combination with resonances.

Elbow in slotted port not much more effective in escape of mid frequencies than straight port; turbulent plus reflective properties at corner are complex and greatly influence behavior of port. At frequencies much above tuning of port/enclosure little energy enters port.

Critically lined and stuffed enclosure is route to controlling mid and high frequency energy without overly damping low end.

Regards,

Andrew
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Old 22nd December 2012, 05:28 PM   #10
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^^^

Maybe moving the ports on the center to the outside then moving the port to the bottom on the LR and making it one port would be better in this regard and help the internal reflection issues. That definitely is a big consideration with these thin cones. Good point for sure!

Scott
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