Alpair 10.2 in 8 liter sealed - Too good to be true? - Page 2

planet10 · 17th January 2012, 08:18 PM

Quote:

Originally Posted by rongon

Are those little blocks of the same dark wood (walnut?) as the ring is made of?

They are fir like the main bulk of the box AFAIK.

dave

rongon · 20th January 2012, 01:01 AM

Fir, eh? Hmmm... That's different. Fir would be a softwood, like spruce, pine, etc?

I got my Alpair 10.2's today. They're a bigger driver than I imagined. Very impressive. Can't wait to hear 'em.

I have a pair of old B&W DM100 8.5 liter cabinets. I'll be happy to use them as a start, especially since I can't afford $200 for a pair of cabinets at the moment.

The B&W cabs are made of 14mm (approx 1/2") particle board. Not very beefy, no. Would it be useful to clamp and glue an additional 1/2" MDF board on the front, as an additional layer of baffle?

I have several project panels of 1/2" MDF from Home Depot, left over from making some shelves. I was thinking of making sandwich baffles out of the MDF. I could cut the 139mm mounting hole in the first 1/2" baffle layer, with the driver front mounted on that.

Then, I could make a second baffle layer, firmly glued to the first layer. In that second layer, I'd cut the 165mm hole to fit around the 139mm diameter hole, and around the driver mounting ring.

I see in the drawing that the driver mounting ring + basket total depth is 13/32". I wouldn't get away with another 1/2" MDF layer, would I? I could check to see if I can get a 3/8" thick sheet of birch ply, or maybe MDF.

So in the end, I'd have three 1/2" layers for the baffle, the original cabinet, the first 1/2" added baffle layer, and the second 1/2" added baffle layer.

Would it be better to have a constrained layer of damping in between two of the baffle layers?

It doesn't seem too difficult, even for me. It's the joinery that would cause me trouble. But I'm sure there's something I'm missing, because it seems there always is. OK, what am I missing?

Thanks...

--

planet10 · 20th January 2012, 04:24 AM

Quote:

Originally Posted by rongon

Fir, eh? Hmmm... That's different. Fir would be a softwood, like spruce, pine, etc?

Douglas Fir is a species of pine.

dave

phivates · 20th January 2012, 04:54 AM

Douglas fir is pine, upgraded.

fastbike1 · 20th January 2012, 01:54 PM

Fir is significantly upgraded compared to the commonly available pine.

rongon · 20th January 2012, 02:14 PM

No botanists in this thread, I see.

Fir and pine are both members of the pine family pinaceae, but different genera. Fir is abies, pine is pinus.

Douglas-fir is a crazy one. Its genus is pseudotsuga (false hemlock) and it's actually a member of the larch subfamily (Laricoideae)! Douglas-fir is not a member of the abies (fir) genus at all. The common name is totally misleading.

Common names are confusing enough, but I love how the lumber industry made up names for species that don't exist. For instance, Yellow Pine. What is that? Actually, it can be Black, Jack, Jersey, Longleaf, Loblolly, North Carolina, Oldfield, Slash, Shortleaf, or Virginia Pine. It basically means that it isn't Eastern white pine (pinus strobus).

Sorry for the thread drift... and that was a doozie. But my surprise was at why a softwood would be preferable to birch ply.

--

chrisb · 20th January 2012, 02:45 PM

Ron; unsolicited pedantry at DIY Audio? That's new. I think the suggestion of D Fir was to specifically take advantage of its softness to provide a mechanical impedance at each of the two changes of materials

Scottmoose · 03:12 PM

Of course, softwood doesn't necessarily mean 'soft' either. I well remember GM discussing some boxes he made a few years back from pine that had spent the best part of 150 years seasoning as part of a barn in Georgia. Stiffness-weight ratio was extremely high; apparantly getting on for aluminium / sheet metal levels from its resonant behaviour.

rongon · 20th January 2012, 03:10 PM

Quote:

Originally Posted by chrisb

Ron; unsolicited pedantry at DIY Audio? That's new.

Quote:

Originally Posted by chrisb

I think the suggestion of D Fir was to specifically take advantage of its softness to provide a mechanical impedance at each of the two changes of materials

So... A hard layer bonded to a softer layer. If I have a softer layer already (1/2" of particle board), then a harder MDF layer bonded to it might be a good thing.

No?

Scottmoose · 20th January 2012, 03:12 PM

MDF is hard?

20th January 2012, 01:54 PM	#15
fastbike1 diyAudio Member Join Date: Aug 2009 Location: North Texas, USA	Fir is significantly upgraded compared to the commonly available pine. __________________ I was so much older then, I'm younger than that now.

20th January 2012, 02:45 PM	#17
chrisb diyAudio Member Join Date: Aug 2002 Location: victoria BC	Ron; unsolicited pedantry at DIY Audio? That's new. I think the suggestion of D Fir was to specifically take advantage of its softness to provide a mechanical impedance at each of the two changes of materials __________________ you don't really believe everything you think, do you? community sites t-linespeakers.org, frugal-horn.com commercial site planet10-HiFi

20th January 2012, 03:05 PM	#18
Scottmoose diyAudio Member Join Date: Mar 2005 Location: UK	Of course, softwood doesn't necessarily mean 'soft' either. I well remember GM discussing some boxes he made a few years back from pine that had spent the best part of 150 years seasoning as part of a barn in Georgia. Stiffness-weight ratio was extremely high; apparantly getting on for aluminium / sheet metal levels from its resonant behaviour. Last edited by Scottmoose; 20th January 2012 at 03:12 PM.

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20th January 2012, 01:01 AM	#12
rongon diyAudio Member Join Date: Jul 2009 Location: Across the river from Rip's big old tree...	Fir, eh? Hmmm... That's different. Fir would be a softwood, like spruce, pine, etc? I got my Alpair 10.2's today. They're a bigger driver than I imagined. Very impressive. Can't wait to hear 'em. I have a pair of old B&W DM100 8.5 liter cabinets. I'll be happy to use them as a start, especially since I can't afford $200 for a pair of cabinets at the moment. The B&W cabs are made of 14mm (approx 1/2") particle board. Not very beefy, no. Would it be useful to clamp and glue an additional 1/2" MDF board on the front, as an additional layer of baffle? I have several project panels of 1/2" MDF from Home Depot, left over from making some shelves. I was thinking of making sandwich baffles out of the MDF. I could cut the 139mm mounting hole in the first 1/2" baffle layer, with the driver front mounted on that. Then, I could make a second baffle layer, firmly glued to the first layer. In that second layer, I'd cut the 165mm hole to fit around the 139mm diameter hole, and around the driver mounting ring. I see in the drawing that the driver mounting ring + basket total depth is 13/32". I wouldn't get away with another 1/2" MDF layer, would I? I could check to see if I can get a 3/8" thick sheet of birch ply, or maybe MDF. So in the end, I'd have three 1/2" layers for the baffle, the original cabinet, the first 1/2" added baffle layer, and the second 1/2" added baffle layer. Would it be better to have a constrained layer of damping in between two of the baffle layers? It doesn't seem too difficult, even for me. It's the joinery that would cause me trouble. But I'm sure there's something I'm missing, because it seems there always is. OK, what am I missing? Thanks... --

20th January 2012, 04:54 AM	#14
phivates diyAudio Member Join Date: Jan 2011 Location: Willamette Valley	Douglas fir is pine, upgraded.

20th January 2012, 02:14 PM	#16
rongon diyAudio Member Join Date: Jul 2009 Location: Across the river from Rip's big old tree...	No botanists in this thread, I see. Fir and pine are both members of the pine family pinaceae, but different genera. Fir is abies, pine is pinus. Douglas-fir is a crazy one. Its genus is pseudotsuga (false hemlock) and it's actually a member of the larch subfamily (Laricoideae)! Douglas-fir is not a member of the abies (fir) genus at all. The common name is totally misleading. Common names are confusing enough, but I love how the lumber industry made up names for species that don't exist. For instance, Yellow Pine. What is that? Actually, it can be Black, Jack, Jersey, Longleaf, Loblolly, North Carolina, Oldfield, Slash, Shortleaf, or Virginia Pine. It basically means that it isn't Eastern white pine (pinus strobus). Sorry for the thread drift... and that was a doozie. But my surprise was at why a softwood would be preferable to birch ply. --

20th January 2012, 03:12 PM	#20
Scottmoose diyAudio Member Join Date: Mar 2005 Location: UK	MDF is hard?

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