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Old 22nd December 2012, 07:11 PM   #11
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You are probably right, Andrew. However, the way I justified that in my mind is that the Alpair 10.2 has been put in smaller cabinets than the distance between the slotted port components in these.

However, I'm thinking of a version 3 design already to address this.

As far as putting a single port at the bottom, that would turn it into a transmission line, which I am trying to avoid as it would be difficult to make a matching center channel design.
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Old 23rd December 2012, 12:20 AM   #12
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Here is version 3 of the mains:

Click the image to open in full size.

The specs are the same as in the OP, except the driver has been moved up on the baffle and the slot ports have been minimized internally to reduce reflections. The slots needed to be moved closer toward the driver as well to provide enough space at the top without folding the port to keep things simple.

Comments?
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Old 23rd December 2012, 07:18 PM   #13
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Quote:
Originally Posted by planet10 View Post
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
Dave, sorry to bring this up again, but what would you do to the version 3 design just above to improve the group delay issue? Make it shorter with a void at the bottom as a 'stand'?
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Old 23rd December 2012, 08:01 PM   #14
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I use macimum 20 litres for A10.2 (the large miniOnken for then are 16 litre). Do whatever you need to make them tall enuff -- try tilting them back 5 degees as well

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Old 23rd December 2012, 08:24 PM   #15
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Quote:
Originally Posted by planet10 View Post
I use maximum 20 litres for A10.2 (the large miniOnken for them are 16 litre). Do whatever you need to make them tall enuff -- try tilting them back 5 degrees as well

dave


even a little tilt helps a lot with enclosures that place the driver lower than we want or think they need to be - worked like a charm with several DIY designs that I can think of - Tysen, FH3, Vampyr, and commercial models as well - Terry Cain's Abby, various Thiels etc, etc
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Old 24th December 2012, 02:56 AM   #16
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Yes, I have built speakers with complex angles before - I'm a lazy woodworker, but not unskilled. I could make the front baffle sloped. However, in the version 3 design the driver is at the same height as other popular designs, like the Pensil. Are you saying it should still be sloped even though the driver is now at a very standard height? I mean, sure, it's still below ear height, so it makes sense, just wanted to double check.
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Old 24th December 2012, 03:11 AM   #17
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Of course, the goal of this project was to make three speakers as identical to each other as possible. That's usually what "LCR" implies in speaker vernacular. So, I think I'm inclined to keep the mains' front baffles at 90 degrees as the center would be at a different height anyway, and a slope on that might just make things more complicated. Sound reasoning?

Happy Holidays, by the way!
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Old 24th December 2012, 04:30 AM   #18
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by Ben_Tech View Post
Of course, the goal of this project was to make three speakers as identical to each other as possible. That's usually what "LCR" implies in speaker vernacular. So, I think I'm inclined to keep the mains' front baffles at 90 degrees as the center would be at a different height anyway, and a slope on that might just make things more complicated. Sound reasoning?

Happy Holidays, by the way!
No one questioned your woodworking skills, and even though I might build a dozen or more pairs a year, the laziest way possible is always appealing.

Unless you're blessed with a projection system, it's hard to avoid the placement / orientation constraints usually required to accommodate placing a center channel enclosure under or over the flat screen - and as the screens get bigger, this problem will only be exacerbated.



In my own system, the only possible configuration places the TV immediately in front of a large window, with the screen a bit lower than ideal, but it is what it is. With Alpair7s as LCR, ("mains" are Pensils) there's an approximately 5" difference in driver heights in the front row, but you can still understand what's happening, and the "discontinuity" is not as bad as might be expected. If I was to ever get off my lazy a$$, I'd probably build a new centre based on the existing design, but with a slanted front baffle.

There, I was looking for another project for the upcoming holiday weekend
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Old 24th December 2012, 05:44 AM   #19
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Thanks for the reply. Sorry, I was not thinking anyone was questioning me, sorry if it sounded that way. Hard to get the 'tone' across on the Internet! I do have an 85" front projection screen but it's permanently mounted to the wall. No such luck to have room for an AT screen with serious speakers behind it. Perhaps some day.

Below is version four of the mains. I shortened up the internal volume to 20 liters not counting the driver or port volume, so it would be a tad less in practice. There is now a void at the bottom. I also adjusted the ports to maintain the 40 Hz tuning and take advantage of the top panel as sort of an elbow extension of the port (why not... it was so close anyway it would have had some effect on the tuning).

Here it is:

Click the image to open in full size.

Specs again, as so much has changed since the OP:

0.75" ply
External dims:
Height: 39"
width: 9.5"
depth: 6.5"
Internal dims:
Height: 30.5"
width: 8"
depth: 5"
(1221 cubic inches / 20 liters)

ports: 2
port dims: 0.25" H x 7" W x 5.53" L
port tuning: 40 Hz
port mach: 0.04
Sim F3: ~ 40.5 Hz
Sim F10: ~ 31 Hz

Let me know what you think.
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Old 24th December 2012, 11:25 AM   #20
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With that enclosure aspect ratio, you'll get some QW behaviour; probably sufficient to shift Fb down; the vent aspect ratio will also do that through friction effects so you may end up with a near-aperiodic alignment (I don't have time to check at present).
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