Steven's Alpair 10.2 Pensil Build Log - Page 3

planet10 · 19th April 2011, 06:29 PM

Steven,

With reference to the holey brace. How are you going to tightly fit the driver magnet againt the holey brace? The brace's primary purpose is to shunt driver energy across more panels. A direct path of solid material from driver magnet to back panel makes this more effective.

As well it looks like the hole-to-brace ratio is such that you won't gain most of the 3rd (small) benefit of the holey brace. (to disrupt side-to-side standing waves). Also, just a gut feeling, but i suspect a lot of stress at the corners of the cutouts. A much larger radius would help.

As pretty as they are, these holey braces are short of the design goals for them. I hate to say it, but it is worth considering doing them over again, if not too late (ie if you are going to do them, might as well do them right -- and with the CNC not hard)

dave

onebadmonte · 19th April 2011, 06:55 PM

Looking good. I envy the fact that you did this in two hrs. It takes me that long just to pull out the tools and the table saw just to get started. o_o I look forward to the opportunity to hear these.

StevenZ · 19th April 2011, 06:59 PM

I didn't plan on snugging the brace against the driver. I believe with the density and quality of the plywood I shouldn't have much of a problem shunting the driver's energy. As for the holey brace, it's 3/4" x 1" and should provide adequate panel stiffening. Each brace is offset 3/4" from the center of the panel allowing for the "side-to-side standing waves" to be disrupted. Also the braces are terminated in the middel of each adjacent opening. Trust me, the enclosure is rock solid and I don't see any practical way of making it more rigid other than by adding another layer of 3/4" material on the outside or increase the internal bracing to complete and utter overkill.

I've build high powered subwoofer cabinets (2000 watts+) with less bracing and cheaper material and never experienced ill-panel resonance problems or compromised structural integrity. I have serious doubt that such a small driver will come anywhere near to testing the structural integrity of this cabinet. Though if it does, I'll have no problem redesigning my bracing and starting from scratch.

planet10 · 19th April 2011, 07:10 PM

I don't doubt it satisfies the goal of bracing the cabinet... it misses out on the other 2. Subsequently you will loose some downward dynamic range, and the Alpairs are certainly capable.

Quote:

Also the braces are terminated in the middel of each adjacent opening

The middle of each adjacent opening is the weakest connection point.

I applaud the effort, but those that are following this thread as an example for their build need to know the short-comings of your execution of the holey brace.

Zia's execution takes full advantage.

dave

StevenZ · 19th April 2011, 07:19 PM

You're probably right, this project has failed. Maybe we should delete this thread as it appears I've wasted my time and money. I'd also hate to be "the example" for which dictates what not to do.

planet10 · 19th April 2011, 07:40 PM

The project hasn't failed. Lots of people are very happy with Pensils with no bracing at all. Yours will be, IMHO, a step up from that. You will have a great speaker.

But it is important to point out (for the thousands looking on) that your holey brace miss the full potential of its application.

dave

StevenZ · 19th April 2011, 07:49 PM

I would've thought the brace that I built would've distributed the panel forces evenly along the entire brace system by having them stepped in the manner that I did. Also increasing the width to a full 1-1/2" inch in the middle and 1" veins throughout it's entire construction. In my eyes at the time it was a superior way to brace the cabinet. I just thought the hole's that were used in the plans were a simple way to do bracing because not many people are willing to do a window pane type brace. It's easy to buy a 3" hole saw and go to town, thus catering to the entry level DIY people out there.

As for bracing the rear of the driver, I can CNC a sliver to match the arch of the half-circle cutout and glue it to the brace, giving me a flat edge to hold the driver with. Hopefully this helps to salvage the project.

planet10 · 19th April 2011, 07:55 PM

The circlular hole was choosen because it leaves the strongest brace, It also forces a maximum 35-45% holes. That means that 35-45% of the internal waveforms will reach side to side, and their distribution will be hetergeneous, so weaker. One also gets a conncurrent decrease in the standing wave energy being imparted into the side panels. The rest (55-65%) will form higher frequency standing waves, higher frequencies at which the damping is much more effective. With more panel volume the holey brace also has more capability to damp & dissipate energy inside the box where it is less objectionable than if the energy is dissapaited outside the box.

Quote:

As for bracing the rear of the driver, I can CNC a sliver to match the radius of the cutout and glue it to the brace, giving me a flat edge to hold the driver with. Hopefully this helps.

I would recommend that.

dave

chrisb · 08:04 PM

Quote:

Originally Posted by StevenZ

I actually didn't bother with alignment of the grain. Though it did take a few minutes to place by hand all of the parts on the sheet correctly. Here are a few more pics. I'll upload the completed photos in a couple of hours.

I was actually referring to what looks like quite decently aligned grain pattern on the parts labeled front and back.

Don't be dissuaded by commentary on the patterns used on your bracing - this likely won't be your last speaker project, and since they didn't take very long to whip up on your CNC, a new set could probably be produced before 3 or 4 more folks post about it on the forum. (and certainly a lot faster than cutting all those holes in Baltic Birch / Apple plywood with a hole saw )

Even when features of design or fabrication / joinery details on some of Dave & Scott's enclosures might appear to be intended to simplify construction, that's not always the case. And of course, there is no "absolutely right" way to design or build

anything

StevenZ · 19th April 2011, 08:10 PM

Maybe I should just stick to open baffle speakers next time

Hahahaha. Oh well, you live, you learn. I'm sure they'll sound fine in the end.

I've run out of this material so building more is out of the question right now. I'd have to order more, but at $275 USD per sheet it's not likely going to happen any time soon.

19th April 2011, 06:29 PM	#21
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 5	Steven, With reference to the holey brace. How are you going to tightly fit the driver magnet againt the holey brace? The brace's primary purpose is to shunt driver energy across more panels. A direct path of solid material from driver magnet to back panel makes this more effective. As well it looks like the hole-to-brace ratio is such that you won't gain most of the 3rd (small) benefit of the holey brace. (to disrupt side-to-side standing waves). Also, just a gut feeling, but i suspect a lot of stress at the corners of the cutouts. A much larger radius would help. As pretty as they are, these holey braces are short of the design goals for them. I hate to say it, but it is worth considering doing them over again, if not too late (ie if you are going to do them, might as well do them right -- and with the CNC not hard) dave __________________ community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

19th April 2011, 07:40 PM	#26
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 5	The project hasn't failed. Lots of people are very happy with Pensils with no bracing at all. Yours will be, IMHO, a step up from that. You will have a great speaker. But it is important to point out (for the thousands looking on) that your holey brace miss the full potential of its application. dave __________________ community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

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19th April 2011, 06:55 PM	#22
onebadmonte diyAudio Member Join Date: Jun 2007	Looking good. I envy the fact that you did this in two hrs. It takes me that long just to pull out the tools and the table saw just to get started. o_o I look forward to the opportunity to hear these.

19th April 2011, 06:59 PM	#23
StevenZ diyAudio Member Join Date: Jul 2010	I didn't plan on snugging the brace against the driver. I believe with the density and quality of the plywood I shouldn't have much of a problem shunting the driver's energy. As for the holey brace, it's 3/4" x 1" and should provide adequate panel stiffening. Each brace is offset 3/4" from the center of the panel allowing for the "side-to-side standing waves" to be disrupted. Also the braces are terminated in the middel of each adjacent opening. Trust me, the enclosure is rock solid and I don't see any practical way of making it more rigid other than by adding another layer of 3/4" material on the outside or increase the internal bracing to complete and utter overkill. I've build high powered subwoofer cabinets (2000 watts+) with less bracing and cheaper material and never experienced ill-panel resonance problems or compromised structural integrity. I have serious doubt that such a small driver will come anywhere near to testing the structural integrity of this cabinet. Though if it does, I'll have no problem redesigning my bracing and starting from scratch.

19th April 2011, 07:19 PM	#25
StevenZ diyAudio Member Join Date: Jul 2010	You're probably right, this project has failed. Maybe we should delete this thread as it appears I've wasted my time and money. I'd also hate to be "the example" for which dictates what not to do.

19th April 2011, 07:49 PM	#27
StevenZ diyAudio Member Join Date: Jul 2010	I would've thought the brace that I built would've distributed the panel forces evenly along the entire brace system by having them stepped in the manner that I did. Also increasing the width to a full 1-1/2" inch in the middle and 1" veins throughout it's entire construction. In my eyes at the time it was a superior way to brace the cabinet. I just thought the hole's that were used in the plans were a simple way to do bracing because not many people are willing to do a window pane type brace. It's easy to buy a 3" hole saw and go to town, thus catering to the entry level DIY people out there. As for bracing the rear of the driver, I can CNC a sliver to match the arch of the half-circle cutout and glue it to the brace, giving me a flat edge to hold the driver with. Hopefully this helps to salvage the project.

19th April 2011, 08:10 PM	#30
StevenZ diyAudio Member Join Date: Jul 2010	Maybe I should just stick to open baffle speakers next time Hahahaha. Oh well, you live, you learn. I'm sure they'll sound fine in the end. I've run out of this material so building more is out of the question right now. I'd have to order more, but at $275 USD per sheet it's not likely going to happen any time soon.