HT Front Stage Designs Using Markaudio Alpair 10.2 - Plans, Feedback and Build Log

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I had a previous thread over in the Markaudio forum where many excellent suggestions were made to improve my design. The initial idea was to build an LCR (identical speakers for the front three channels of a home theater) using the Markaudio Alpair 10.2. However, as I revised the design per the suggestions that I received, the project evolved away from that concept into a more traditional mains and center.

Some of the design goals of this project include:

- A traditional home theater form factor where the mains are taller and the center channel is of the horizontal persuasion.
- No stands required.
- Good bass response in case the speakers are used standalone without a subwoofer at a later time.
- Optimize driver height and baffle angle to aim high frequencies more directly toward listener's ears.
- Excellent dialog intelligibility from the center.
- The best possible voice matching between the mains and center necessitating the cabinets be as close as possible in design to one another.

Many hours of painstaking work later, I have drawn the latest designs in detail as follows:

Version 3, Center:

alpair-102-center-v3_zps4f5e4f36.png


External:
width: 30"
depth top: 7.15"
depth bottom: 8.1"
height: 9.5"

3/4" (19mm) plywood cabinet.

Internal:
width: 28.5"
depth top: 5.65"
depth bottom: 6.6"
height: 8"
depth, driver to back panel: ~ 3.7"

Total volume ~ 23 liters less bracing, ports, driver frame, magnet, cleats and hardware.

Off center horizontal holey brace shown in gray - 2" and 1" random holes. Bracing spars on either side of holey brace (only toward the ends, away from driver). Spars have 2" holes all along their length.

2 x slot ports, 5.6 long x 7" wide x 0.25". Tuning frequency ~ 38-40 Hz.

Version 8, Mains:

alpair-102-mains-v8_zpsc31506f7.png


External:
width: 9.5"
depth top: 6.15"
depth bottom: 10"
height: 39"
distance, center of driver to floor: 29"

3/4" (19mm) plywood cabinet.

Internal (sound chamber only):
width: 8"
depth top: 4.65"
depth bottom: 7.65"
height: 28.5"
depth, driver to back panel: ~ 3"

Total volume around 23 liters in the sound chamber. Void space at the bottom.

Off center holey brace shown in gray - 2" and 1" random holes. Bracing spars on either side of holey brace (only toward the bottom, away from driver, the side panel is widest here anyway). Spars have 2" holes all along their length.

2 x slot ports, 5.6 long x 7" wide x 0.25". Tuning frequency ~ 38-40 Hz.

Please let me know what you all think of these!
 
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Wow, nice! Just curious, is there a rationale for putting the slot vents very close to the driver?

Hi, thanks for your question. The ports are close to the driver so that the port scheme can be identical in the center and the mains, as per the design goals to keep them as close as possible to each other for matched voicing.

Also, it can't hurt to have more of a point source as the 40 Hz range is still quite within the audible range.
 
Nice designs! With the height and lengths you have you may have room for a MLTL, have you considered that approach? The vertical mains may need more clearance at top slot vent inlet as it is very close to edge and flow may get restricted.

Thanks for your question and comment.

Yes, I did consider the Pensils but rejected due to difficulty designing a truly voice matched (MLTL) horizontal center channel design that made sense. I'm sure the Pencils are nice and certainly much easier to build than my design.

The clearance of the top slot is intentional as the top panel becomes an extension of the port length to match the length of the lower port, it's just an elbow.

Keep the comments coming!
 
My local supplier had 5x5 foot pieces of quality 3/4" 13 layer Baltic Birch ply. I bought two for $120 USD with tax and had him rip them in half for transportation in a typical sedan trunk, yielding 4 30x60 inch pieces. That should provide plenty of extra for small mishaps.

The supplier had 4x8 as well but I could not fit everything on one sheet with the cuts required for transportation. So, two 5x5's were less costly than two 4x8's and everything fit fine. I think it looks like a good step up from the Home Depot "Birch" plywood I compared it with. The plys are a lot straighter with fewer voids and none of the 'twisted' areas in the layers (I don't know what else to call it).

Below are the cut sheet layouts for the four panels. I tried to arrange things efficiently, but I'm sure it could be better.

I decided to cut the slot port pieces from 1/2" "oak" Home Depot plywood I have on hand, so those pieces are not shown.

In case anyone is following this later, all of the drawings are somewhat accurate but not perfect, and are on a scale of 20 pixels = 1 inch.

I tried to allow for the Rabbet and Dado joints I plan to use when sizing the panels.

cut-list-5x5-sheet1_zps219e3459.png


cut-list-5x5-sheet2_zpsd0946f3d.png


cut-list-5x5-sheet3_zpsb3934169.png


cut-list-5x5-sheet4_zps269337af.png
 
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GM

Member
Joined 2003
Also, it can't hurt to have more of a point source as the 40 Hz range is still quite within the audible range.

A 1/4 WL of 40 Hz is ~85", so acoustically, this is how far away they can be and still couple as one.

What matters is that the closer the vent, the less noticeable its comb filtering harmonics will potentially be, which can be well up into the mids where the WLs have been shrinking exponentially in size down to < 12".

This can be minimized though by vent design as you have done and/or 'critically' damping the vent, so in scheme of things, not an issue unless maintaining peak vent system efficiency is a design priority, which is rarely the case in a HIFI/HT app.

GM
 
What a beautiful design. Since it's home theater what xover do you plan on using for subwoofer support? Am I right to assume that the 10.2's can crank on home theater levels if you relieve them of the low end as is typical with home theater processors? Looking forward to seeing pics and hearing your comments.
 
A 1/4 WL of 40 Hz is ~85", so acoustically, this is how far away they can be and still couple as one.

What matters is that the closer the vent, the less noticeable its comb filtering harmonics will potentially be, which can be well up into the mids where the WLs have been shrinking exponentially in size down to < 12".

This can be minimized though by vent design as you have done and/or 'critically' damping the vent, so in scheme of things, not an issue unless maintaining peak vent system efficiency is a design priority, which is rarely the case in a HIFI/HT app.

GM


Thank you, GM. I did not know all of that when designing these, I was simply following some of the experts in terms of what they sometimes do in these situations. It's good to know the real reason for this style of arrangement. :) All I knew is I needed front vents to place these near a wall (as do most HT setups) to avoid excessive bass reinforcement. I guess I also wanted to avoid elbows and their associated additional woodworking that may have been needed if the vents were at the top/bottom. And, of course, I thought two vents might balance things out a bit better, and also avoid these becoming a TL due to their shape. The vent pressure is low at Mach 0.04.
 
What a beautiful design. Since it's home theater what xover do you plan on using for subwoofer support? Am I right to assume that the 10.2's can crank on home theater levels if you relieve them of the low end as is typical with home theater processors? Looking forward to seeing pics and hearing your comments.

Thank you, Octavia.

I plan to cross over to a sub at 80Hz. This design should be somewhat full range on its own though, which is what I wanted in case they are ever used without a sub. My understanding is that the Alpair 10.2 is the best Alpair for home theater as it can do midbass with the most authority, after Mark's suggested break-in routine has been carefully observed. In my setup, these won't be driven very hard at all, but I'm sure they would have no trouble with 95 dB levels should one choose to listen at that slightly deafening level.
 
... they certainly look the part. Cosmetically reminds me of the Meadowlark loudspeakers. Obviously different bass loading, but a TL none the less. Click here to have a look at the Kestrel 2s. And here to look at the Shearwaters. I'm not sure whatever happened to Meadowlark.

Thank you, Stew. Yes, they do look similar to the Kestrel 2 now that you showed me a picture. I was only vaguely aware of Meadowlark. Good find.
 
Before you do an actual cut sheet measure the real thickness of your material. 5x5 sheets come in a nominal 18mm (+/- a couple tenths).If you just assume it is 3/4" you will be sad when you start putting it together.

dave

Thanks Dave! Good tip. Yes, I will get out the digital caliper and make sure I know the exact thickness of the material before I start marking on the actual wood.

Speaking of which, I took a quick snapshot of the Home Depot ply vs. the more expensive stuff I bought yesterday from the pro cabinetmaker supply.

Home Depot on left, expensive stuff on the right. You will see there are 13 layers vs. only 11 and the plys are lot straighter too. There are two sheets of each pictured.

An externally hosted image should be here but it was not working when we last tested it.
 
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Turns out Dave was right (surprise, surprise) and the material is just slightly over 18mm (.72 or .73 inches). :) I'll go ahead and err toward keeping the external dimensions the same and allow the internal volume to grow by that little bit. No problemo. Good to be aware of though!
 
I decided to build the center channel first.

Starting the layout on ply:

P1000764_zpsbaed7759.jpg


The cut pieces for the walls of the cabinet with some of the angles done:

P1000777_zpse1651093.jpg


The last thing I did was to switch blades in my table saw to a dadoe blade. I used it to cut some rabbets into the side edges of the top and bottom panels so that the side panels fit into that slot on each corner. The dadoe blade I have is the adjustable wobbling type. Maybe not the best as I'm seeing some slop in terms of the rabbets being square and true. Next time I get back to this I'll try squaring up the rabbets a little bit with a long file and see if that's good enough. If not, I'll buy the right router bit with a bearing and cut new top and bottom pieces and go from there.
 
A little progress finally.

Glued up the sides, top and bottom today:

P1000803_zps4aca9352.jpg


Hard to see in the pic, but the shot is showing the sloped side (roughly 6 degrees).

The bar clamps were plenty, the strap clamps were overkill.

The rabbet joints were quite a lot of work as the wobble blade did not produce perfect cuts. I tried cleaning them up with a flat file and a razor blade, but that took many hours to perfect one joint, so I decided to break out the router with a straight bit and just clamped a straight piece of wood across the workpiece and zipped out the high spots. Worked a treat. In fact, I'd be tempted to just use the router for any further rabbets and forgo the table saw.

Here's a pic of one of the finished joints -

P1000804_zpsb3e881e4.jpg


Next up - routing the driver cutout and slot vents in the front panel.
 
... they certainly look the part. Cosmetically reminds me of the Meadowlark loudspeakers. Obviously different bass loading, but a TL none the less. Click here to have a look at the Kestrel 2s. And here to look at the Shearwaters. I'm not sure whatever happened to Meadowlark.


I can tell you what happend to Meadowlark Audio. I heard they went over board on buying the cnc machines and all tracks of real wood. Just jumped the gun to quick and was not selling enough to pay the rent. So they have been gone for awhile now.I did heard the shearwater hot rods before they went under. Its a shame what a great little company gone to soon. I heard pat the designer is up in New York trying to start a new company? Who knows that was a few years ago? This is all the info I got from a dealer that use to carry Meadowlard Speakers. JM
 
What do you guys think as far as grain direction on a finished center channel speaker? Do you think the grain should run top to bottom on the front (vertically), considering its horizontal arrangement, or side to side (horizontally)?

All of the grain will be vertical on the mains, of course.

I'll be using real wood veneer or woodgrain laminate, I have not decided yet. In either case, the grain will be prominent.
 
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