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Howitzer build - Page 9

post #241 of 452
9/26/11 at 8:36am
Quote:
Originally Posted by PassingInterest View Post



I don't understand what this is for? To reinforce the mounting screws I assume. But it looks like they protrude into the woofer.
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post #242 of 452
9/26/11 at 8:49am
Quote:
Originally Posted by tuxedocivic View Post

I don't understand what this is for? To reinforce the mounting screws I assume. But it looks like they protrude into the woofer.

The blocks push the router away from the edge so that he didn't remove too much material from the baffle where the screws will dig in. The blocks will be removed prior to woofer mounting.
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post #243 of 452
9/26/11 at 9:14am
Thread Starter 
dykz34 has it right.

Time to glue the baffles on.

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post #244 of 452
9/26/11 at 9:23am
Oh cool. First I've ever seen that. Thanks guys.
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post #245 of 452
9/26/11 at 9:50am
I really have to spend less time working and concentrate on what's important, DIY!

So I know I missed the discussion on why the driver cutouts have the 5 leaf clover design which the blocks are used for but what effect does this have?
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post #246 of 452
9/26/11 at 11:16am
Quote:
Originally Posted by tuxedocivic View Post

Oh cool. First I've ever seen that. Thanks guys.

yeah - i was wondering the same thing. very cool little trick. i try to eyeball it and generally end up going too close to at least one of the screw holes. gonna have to give this a shot.
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post #247 of 452
9/26/11 at 11:21am
Quote:
Originally Posted by mjaudio View Post

I really have to spend less time working and concentrate on what's important, DIY!

So I know I missed the discussion on why the driver cutouts have the 5 leaf clover design which the blocks are used for but what effect does this have?

my understanding is that this allows easier airflow behind the cone... a nice smooth surface continued in the radiating pattern instead of a restricting ring of wood and then a 90deg step. i assume it reduces distortion to some degree but have not seen any comparison curves - would be interesting to try to measure the difference. wonder if anyone has a link, it seems like something that must have been tested in this forum at some point.
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post #248 of 452
9/26/11 at 11:30am
Quote:
Originally Posted by lowpolyjoe View Post

my understanding is that this allows easier airflow behind the cone... a nice smooth surface continued in the radiating pattern instead of a restricting ring of wood and then a 90deg step. i assume it reduces distortion to some degree but have not seen any comparison curves - would be interesting to try to measure the difference. wonder if anyone has a link, it seems like something that must have been tested in this forum at some point.


"Chamfering" the back is more for mid range, higher frequencies and is pretty much useless in the lower bass regions. With a HUGE amount of respect for PI and his incredible builds this is one of those head scratching moments for me. 10" NHT woofers will not play high enough for this too matter.

I think there are some measurement studies over on HTGuide.com showing its importance. Its overall important as part of the actually response curve isn't apparent but they always say its better to have done and not worry about it

We also have to remember that we should also consider designs that ensure the rear-wave reflection is not directed back through the cone. If someone cares enough to "Chamfer" then they might want to consider, rear wave diffusion inside the box
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post #249 of 452
9/26/11 at 12:54pm
Quote:
Originally Posted by penngray View Post

We also have to remember that we should also consider designs that ensure the rear-wave reflection is not directed back through the cone. If someone cares enough to "Chamfer" then they might want to consider, rear wave diffusion inside the box

Funny you mention that - my buddy was over the other day. First time he's seen my diy ht stuff. He does custom car audio work. Immediately he asked if my next build would be non-symmetric to avoid standing waves in the box and the like...
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post #250 of 452
9/26/11 at 2:10pm
Thread Starter 
Quote:
Originally Posted by penngray View Post

this is one of those head scratching moments for me.

Scratch no further, my friend.
The baffle is 1.25" thick and it mounts to a 3/4" thick front panel on the box.
That's a full 2" thick for the 10" driver, minus the driver recess depth.
So, the back chamfering was to allow the driver to "breathe."


Quote:
Originally Posted by penngray View Post

We also have to remember that we should also consider designs that ensure the rear-wave reflection is not directed back through the cone. If someone cares enough to "Chamfer" then they might want to consider, rear wave diffusion inside the box

Great tip! How should I do this?
I was just planning on using some fiberglass insulation to line the inner walls. Or possibly some polyfil.
What's a better approach?
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post #251 of 452
9/26/11 at 2:22pm
On my current build, I was going to use wide (6") braces that are angled at various angles behind the driver. The idea is deflect the wave away from the region of the shortest distance between the woofer and panel. Again, possibly not necessary on a subwoofer playing with wavelengths longer than 4m. But in my case, the woofers are mid-woofers playing up to 1500hz, ~0.2m long.
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post #252 of 452
9/26/11 at 2:45pm
Thread Starter 
Quote:
Originally Posted by mjaudio View Post

So I know I missed the discussion on why the driver cutouts have the 5 leaf clover design which the blocks are used for but what effect does this have?

I'm sorry for the confusion, my friend.
Tomorrow I'll snap a couple of pictures to make things a bit more clear.
But again, basically I just wanted to chamfer the back of the driver cutout, because of the 2 inch thick wood the driver gets mounted to and I wanted to avoid chamfering away the wood that the screws need for driver mounting.

Speaking of pictures, I actually have some more, but I don't want to post them until I get a little farther along, or I may confuse somebody--which is not meant as an insult in any way. The next part will make more sense when you see a little more progress than where I am right now with it.
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post #253 of 452
9/26/11 at 2:51pm
Thread Starter 
Quote:
Originally Posted by tuxedocivic View Post

On my current build, I was going to use wide (6") braces that are angled at various angles behind the driver. The idea is deflect the wave away from the region of the shortest distance between the woofer and panel. Again, possibly not necessary on a subwoofer playing with wavelengths longer than 4m. But in my case, the woofers are mid-woofers playing up to 1500hz, ~0.2m long.

Oh, so fiberglass lining or polyfil is fine then? For a subwoofer, I mean.
Okay, now I get it. Penn meant to use rear-wave diffusion for mid-woofers, right?
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post #254 of 452
9/26/11 at 2:57pm
Quote:
Originally Posted by PassingInterest View Post

Scratch no further, my friend.
The baffle is 1.25" thick and it mounts to a 3/4" thick front panel on the box.
That's a full 2" thick for the 10" driver, minus the driver recess depth.
So, the back chamfering was to allow the driver to "breathe."

That is a lot of thickness,
That clears up my confusion

Quote:


Great tip! How should I do this?
I was just planning on using some fiberglass insulation to line the inner walls. Or possibly some polyfil.
What's a better approach?

Yeah stuffing it with polyfil is just fine. Im talking about mid range stuff, Subwoofer wavelengths are huge. Anyways, I have read about several techiniques, like using large PVC pipes (with holes) to redirect the waves to having non-parrellel walls or building some "V" internal bracing at the back.
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post #255 of 452
9/26/11 at 4:18pm
I remember John J. mentioning something about PVC pipes cut in half and glued to the back of the box.
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post #256 of 452
9/27/11 at 6:48am
Thread Starter 
Quote:
Originally Posted by tuxedocivic View Post

On my current build, I was going to use wide (6") braces that are angled at various angles behind the driver. The idea is deflect the wave away from the region of the shortest distance between the woofer and panel. Again, possibly not necessary on a subwoofer playing with wavelengths longer than 4m. But in my case, the woofers are mid-woofers playing up to 1500hz, ~0.2m long.

Link to build thread, please. I am interrested in following the progress.

Penn and LooneyBomber--Thanks for the info. That is interesting stuff.
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post #257 of 452
9/27/11 at 7:48am
Thread Starter 
I glued up two panels, but forgot to get a photo of the glue-up.
I took this shot right after planing.




I routed a recess on the backside to accommodate the lip that sticks up around the driver's edge.






I still need to round-over the edges.




Dry fit check.




The plan is to attach them with grill fasteners. I have some ordered. The plan might change, but I think it should work out okay.

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post #258 of 452
9/27/11 at 10:23am
I don't even want to show the L/C/R combo I just finished after following this thread...
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post #259 of 452
9/27/11 at 12:31pm
Thread Starter 
Quote:
Originally Posted by mrgfy6 View Post

I don't even want to show the L/C/R combo I just finished after following this thread...

You are selling yourself short, Mr. G. You do good work.
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post #260 of 452
9/27/11 at 12:50pm
Wow I wish the stuff I build looked this nice.
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post #261 of 452
9/27/11 at 3:13pm
Thread Starter 
Thanks mtg90. You're very kind.
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post #262 of 452
9/27/11 at 3:32pm
Thread Starter 
Now for the bases.

Capture a footprint.




Ash in the foreground and Red Oak behind that.




The Oak is cupped. Begin by face jointing, crown up.
If the crown (peak) is down, the board will rock as you feed it through and you won't get a good flat reference side.




Now plane it, again crown up.




The board is perfectly flat.




Now you can joint the edges.

The Ash was cupped also, but at 2 inches thick, I was sure the surface planer's stock-feed rollers would not artificially flatten the board, as it would with the thinner Oak boards. Meaning, the feed rollers press down pretty firmly and temporarily flatten a board, before the cutters even contact the board. As the board exits the planer, it springs back into the cupped shape. Not so, for this thick Ash. Once you get a flat reference surface, you can joint the edges.




Joint the edges.




Re-Saw the Ash.




Re-Sawn Ash.




I'm ready for panel glue-up, but I'm out of time for today.

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post #263 of 452
9/27/11 at 6:45pm
Fantastic stuff PI. Even a planer!

Quote:
Originally Posted by PassingInterest View Post


Link to build thread, please. I am interrested in following the progress.

Penn and LooneyBomber--Thanks for the info. That is interesting stuff.

Ya, I might start a thread. It'll be more technical. But I could use some advice about waveguides, so I may do one. I'll link you
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post #264 of 452
9/28/11 at 8:16am
Thread Starter 
Bases continued...

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post #265 of 452
9/28/11 at 10:30am
Quote:
Originally Posted by mtg90 View Post

Wow I wish the stuff I build looked this nice.



2 reasons to read all of PI's threads.

1. The creativity, use of tools, building documenation is the highest standard you can find online. I mean this could be a freaking woodworking brochure PI should contact all those manufacturers because he has some nice tools and he is advertising them perfectly. I feel like its an episode of "Tim the tool man" but with real skills, real builds.

2. We have an reference point that is unmatched. Its important to know how far we have to go to come even close to PI's work. I wave a "white flag" evertime and accept my compromising skill set


I can read his threads 100 times and still simply shake my head in amazement the 101th time
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post #266 of 452
9/28/11 at 1:16pm
Thread Starter 
Wow! I don't know how to respond to that, Penn. I am deeply humbled.
Thank you.
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post #267 of 452
9/28/11 at 1:23pm
Thread Starter 
Bases continued...






I now have 2 out of 3 base templates.




Spray a few clear base coats.




Two unshaped risers in the foreground, glued together from scraps.

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post #268 of 452
9/28/11 at 2:46pm
Quote:
Originally Posted by penngray View Post

2 reasons to read all of PI's threads.

1. The creativity, use of tools, building documenation is the highest standard you can find online. I mean this could be a freaking woodworking brochure PI should contact all those manufacturers because he has some nice tools and he is advertising them perfectly. I feel like its an episode of "Tim the tool man" but with real skills, real builds.

2. We have an reference point that is unmatched. Its important to know how far we have to go to come even close to PI's work. I wave a "white flag" evertime and accept my compromising skill set


I can read his threads 100 times and still simply shake my head in amazement the 101th time

Amen brother!

I have learned so much from PI's thread's that I feel like I should be paying tuition
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post #269 of 452
9/28/11 at 4:03pm
Thread Starter 
You guys are way too kind. Thanks.
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post #270 of 452
9/28/11 at 9:07pm
Quote:
Originally Posted by PassingInterest View Post

You guys are way too kind. Thanks.

PI you are horrible!

your thread is horrible!
Your speaker is horrible!
Your ingenious templates and devices are horrible!
Your awesome vacuum pump is horrible!
Your breath stinks and is horrible!
All your base are belong to us and are horrible!
Your garage floor is horrible!
Your nifty little finishing triangle pyramid thingies are horrible!
Your perfectly flat board is horrible!
Your beautiful veneer job is horrible!
Your HVLP gun is horrible!

I like your truck though, more pics please.
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