T39 Slim Access panel flange question

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Think
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T39 Slim Access panel flange question

#1 Post by Think » Tue Feb 13, 2018 2:16 pm

While reading the plan and looking at the sketchup model (very nice) I noticed that the lower flange of the acces panel is restricting the horn path by about 3/8". In the wider single driver version of the T39 this is compensated for a good part by the horn being 1/8" wider at that point (the hornpath is extra wide for the parts without the flange) then the next section.

Next thing that I would like is the accespanel screws to have some more wood to screw in. So my idea is to make 3 instead of 1 flange braces (as small as posible and hollow) and screw the acess panel straight in the baffle, extending the driver anchor ring a bit so I have 2 layers to screw in.

As a bonus, this will also stiffen this part of the horn, where the pressure is the highest, a lot.

Problem is that it will probably narrow the hornpath a bit more with the 3 braces instead of 1.

Would it be a good idea to make the lowest baffle flange thinner to remove the obstruction in the horn path? I could make it out of 1/4" plywood or 1/8" of solid hard wood (or aluminium) to flatten out the hornpath completely.

Or is it better to compensate only a little for the 2 extra braces I use, by making the lower acces panel flange 3/8" instead of 1/2", because a little hornpath restriction is needed?

Grant Bunter
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Re: T39 Slim Access panel flange question

#2 Post by Grant Bunter » Tue Feb 13, 2018 3:53 pm

Think wrote:
Tue Feb 13, 2018 2:16 pm
While reading the plan and looking at the sketchup model (very nice) I noticed that the lower flange of the acces panel is restricting the horn path by about 3/8". In the wider single driver version of the T39 this is compensated for a good part by the horn being 1/8" wider at that point (the hornpath is extra wide for the parts without the flange) then the next section.

Next thing that I would like is the accespanel screws to have some more wood to screw in. So my idea is to make 3 instead of 1 flange braces (as small as posible and hollow) and screw the acess panel straight in the baffle, extending the driver anchor ring a bit so I have 2 layers to screw in.

As a bonus, this will also stiffen this part of the horn, where the pressure is the highest, a lot.

Problem is that it will probably narrow the hornpath a bit more with the 3 braces instead of 1.

Would it be a good idea to make the lowest baffle flange thinner to remove the obstruction in the horn path? I could make it out of 1/4" plywood or 1/8" of solid hard wood (or aluminium) to flatten out the hornpath completely.

Or is it better to compensate only a little for the 2 extra braces I use, by making the lower acces panel flange 3/8" instead of 1/2", because a little hornpath restriction is needed?
I thought you'd gone!

Follow the plans to the letter, for the cab type you're building. If it was necessary to do things differently when building, it would be in the plans!

1. If you extend the anchors, you reduce the chamber size. Chamber size is always critical, most critical in a super slim.
2. The access panels flanges in the plans are enough to hold the access panel. Don't over think the plans. Narrowing the mouth of the horn by adding extra material will increase throat pressure. If throat pressure is to high, this ends up with shredded driver cones.
Adequately securing the access panel to the flanges is more about the amount of screws you use to do that, rather than the material, or the amount of material, you're using to attach the access panel.
3. The bottom flange needs to be made with 1/2" ply. Follow the plans.

Do you not think that, given the amount of T39's that have already been built by other users, that if any of the "issues" you perceive were actual issues, that the plans would not have already been modified?
Built:
DR 250: x 2 (melded array) with March 2012 plans.
T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
WH8: x 3 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...

Think
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Re: T39 Slim Access panel flange question

#3 Post by Think » Tue Feb 13, 2018 5:15 pm

I get the whole FTP thing. But if they were perfect there wouldn't be any updates. (nothing is perfect).

@1 That difference is minimal if you would use a tiny bit thicker wood or build 1/2" wider cab, the volume difference will be more. And I have to reduce the chamber volume anyway because of the low fs driver.
@2 It is narrowed allready, wouldn't removing this obstruction (like in the old top loaded T39) be an improvement then? Maybe minimal, but I would like to know. Which plan is better the 'original' or the newer one?
@3 A little variation is fine (wood thickness) according to the plans. But what would be optimal?

I just don't want the wood to be stripped later after removing the panel a few times and be able to tighten it very well to prevent air leaks. How so you check for air leaks which only develop at half or full power? 1 by 1 and a dB meter? How often? This is just a part of the box I don't want to have any problems with later.

Have a look at a simulation of the flexing of an other horn. (probably 18" driver and 3/4" 18mm ply)
Image

This flexing will lower output and slowly destroy your sub. (just like with boats)

Having some more bracing in the first part of the T39 looks like an other fine idea to me.

Bruce Weldy
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Re: T39 Slim Access panel flange question

#4 Post by Bruce Weldy » Tue Feb 13, 2018 6:48 pm

Think wrote:
Tue Feb 13, 2018 5:15 pm

I just don't want the wood to be stripped later after removing the panel a few times and be able to tighten it very well to prevent air leaks.
My six T39s are between 4 and 6 years old. The access covers have been removed exactly one time for each cab in order to tighten the driver bolts. If you are concerned about stripping, then use T-nuts.

I can't even imagine why you'd be removing the access panels a few times. Even then, there is no reason to strip a screw. Replace the weatherstripping each time you open it, space the screws only a couple of inches apart, and then you don't have to torque them down like it's the end of the world.

You are creating an issue that doesn't exist.

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

Grant Bunter
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Re: T39 Slim Access panel flange question

#5 Post by Grant Bunter » Wed Feb 14, 2018 2:15 am

Think wrote:
Tue Feb 13, 2018 5:15 pm
I get the whole FTP thing. But if they were perfect there wouldn't be any updates. (nothing is perfect).

@1 That difference is minimal if you would use a tiny bit thicker wood or build 1/2" wider cab, the volume difference will be more. And I have to reduce the chamber volume anyway because of the low fs driver.

Perhaps you could have given that information in the first place

@2 It is narrowed allready, wouldn't removing this obstruction (like in the old top loaded T39) be an improvement then? Maybe minimal, but I would like to know. Which plan is better the 'original' or the newer one?

The newer version is better. If not, Bill would not have released it.

@3 A little variation is fine (wood thickness) according to the plans. But what would be optimal?

Sheesh man. Optimal is 1/2" ply

I just don't want the wood to be stripped later after removing the panel a few times and be able to tighten it very well to prevent air leaks. How so you check for air leaks which only develop at half or full power? 1 by 1 and a dB meter? How often? This is just a part of the box I don't want to have any problems with later.

This seems kinda contrary to what you said earlier:
Think wrote:
Tue Feb 13, 2018 2:16 pm
Would it be a good idea to make the lowest baffle flange thinner to remove the obstruction in the horn path? I could make it out of 1/4" plywood or 1/8" of solid hard wood (or aluminium) to flatten out the hornpath completely.
You can't have it both ways. Thinner material will strip out more easily. 1/2" ply isn't an issue with the horn mouth, or stripping out screws, but you want to change it.

Have a look at a simulation of the flexing of an other horn. (probably 18" driver and 3/4" 18mm ply)
Image

Unfortunately this is almost useless in this discussion. It's not one of Bills designs and I can't see any bracing, it looks to be a tapped horn (none of Bill's pro sound subs are tapped horns), it's a sim, and there's no real details about the cab.

This flexing will lower output and slowly destroy your sub. (just like with boats)

Having some more bracing in the first part of the T39 looks like an other fine idea to me.
Built:
DR 250: x 2 (melded array) with March 2012 plans.
T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
WH8: x 3 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...

Think
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Re: T39 Slim Access panel flange question

#6 Post by Think » Wed Feb 14, 2018 8:44 am

"You can't have it both ways. Thinner material will strip out more easily. 1/2" ply isn't an issue with the horn mouth, or stripping out screws, but you want to change it."

You don't seem to get what I propose; my solution will have 1+" of wood to screw in by screwing throught the flange/brace (s) in the baffle and have less narrowing because the thinner flange does not have to hold the screws anymore, it's only use is to compress the gasket to the access panel as it will be supported by the braces.

Has anyone ever noticed this 3/8" narrowing at the accespanel flange? Which is quite a bit.
Has this been discussed ever?

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Tom Smit
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Re: T39 Slim Access panel flange question

#7 Post by Tom Smit » Wed Feb 14, 2018 10:11 am

I have gone through my plans, and through Sketchup, and have not found the 3/8" difference. The lower flange is the same width and the same length for a 10" driver regardless of cab width. All of the flanges are of the same thickness, some are wider, some are narrower depending on the location of the flange.

If it is a real concern for you, perhaps you could make 1/8" thick gussets, paired up, to be used instead of the 1/2" thick flange/baffle brace. This would allow you to do as you want by securing the access panel to the baffle. I don't see much to be gained by going this route.

In regards to narrow versus wide builds, my conclusion is that Bill found the best options available, and made the plans as such.
TomS

Bruce Weldy
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Re: T39 Slim Access panel flange question

#8 Post by Bruce Weldy » Wed Feb 14, 2018 10:42 am

Think wrote:
Wed Feb 14, 2018 8:44 am

You don't seem to get what I propose; my solution will have 1+" of wood to screw in by screwing throught the flange/brace (s) in the baffle and have less narrowing because the thinner flange does not have to hold the screws anymore, it's only use is to compress the gasket to the access panel as it will be supported by the braces.

Once again, you are trying to fix something that isn't broken. If you want to do it, then do it. But, if you are looking for someone to embrace your design changes among many who have built the designs, used the designs, and have an experienced opinion of said designs......you may be looking for quite a while.

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

Think
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Re: T39 Slim Access panel flange question

#9 Post by Think » Wed Feb 14, 2018 12:45 pm

Tom Smit wrote:
Wed Feb 14, 2018 10:11 am
I have gone through my plans, and through Sketchup, and have not found the 3/8" difference.
....
Maybe something changed in the newest plans which I have?

If you measure hornpath width at the point in between panels 3 and 4, it measures ~1 3/4". (to panel 6, not the flange)
At the lower side of the flange the hornpath is 1 1/4"
Just above the flange, at the acces panel, the hornpath is 1 3/8"
Above the flange, at the acces panel the hornpath is 1 3/4"

As far as I understand horns, this narrowing of about 3/8" on a total width of 1 7/8" is quite substancial. The horn being a bit wider at some point is no problem, but a narrowing is not so nice.

Bill is probably the only one able to give a theoretical estimation of the implication of this narrowing. Maybe he has made the old and new version and has measured them head to head in the same conditions. If nobody has done this so far, I can make both versions and do a comparison, but I first like to know what is know about this narrowing.
Last edited by Think on Wed Feb 14, 2018 1:39 pm, edited 1 time in total.

Think
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Re: T39 Slim Access panel flange question

#10 Post by Think » Wed Feb 14, 2018 1:23 pm

Bruce Weldy wrote:
Tue Feb 13, 2018 6:48 pm
...
My six T39s are between 4 and 6 years old. The access covers have been removed exactly one time for each cab in order to tighten the driver bolts. If you are concerned about stripping, then use T-nuts.

I can't even imagine why you'd be removing the access panels a few times. ...
I'm thinking of making the acces panels transparant, from Polycarbonate/Lexan which I allready have. Is has a scratch and UV resistant coating. Maybe some leds might go in there later. Maybe it is possible to light up some leds with the energy from a HPF, but I have to look into this. Yes, this is not in the plans but I like having a visual check on the driver and it provides something to look at for the people who hear with their eyes. Seeing a small driver in there will give them something to talk about.

I like to use wood bolts (hex or tork) over regular screws or T-nuts for the driver and acces panel. If you predrill with the right diameter drill in thick enough wood, they should not come lose and are easier, cheaper and faster to build with compared to T-nuts. T-nuts and loctite should work as well.

CoronaOperator
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Re: T39 Slim Access panel flange question

#11 Post by CoronaOperator » Wed Feb 14, 2018 1:35 pm

Think wrote:
Wed Feb 14, 2018 1:23 pm
T-nuts and loctite should work as well.
Don't ever do that, you will never be able to undo them. The T-nut will just spin and spin and if you ever have to replace the driver you will have to grind off the bolt heads. Use a lock washer instead.
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

Think
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Re: T39 Slim Access panel flange question

#12 Post by Think » Wed Feb 14, 2018 2:00 pm

CoronaOperator wrote:
Wed Feb 14, 2018 1:35 pm
Think wrote:
Wed Feb 14, 2018 1:23 pm
T-nuts and loctite should work as well.
Don't ever do that, you will never be able to undo them. The T-nut will just spin and spin and if you ever have to replace the driver you will have to grind off the bolt heads. Use a lock washer instead.
That is some great advice and an other reason not to go with t-nuts. Lock washers, don't do much is my experience and the star modelled ones are even more useless.

Very nice builds of your DR250's and T60's; very nice so see and read.
Last edited by Think on Wed Feb 14, 2018 2:16 pm, edited 1 time in total.

Bruce Weldy
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Re: T39 Slim Access panel flange question

#13 Post by Bruce Weldy » Wed Feb 14, 2018 2:08 pm

Think wrote:
Wed Feb 14, 2018 1:23 pm
Yes, this is not in the plans but I like having a visual check on the driver

You like having a visual check on the driver.......so, which subs have you been using that give you this visual check that you like having? I certainly don't know of any pro sound subs that offer such a visual aid. What exactly is the benefit of this visual check? To make sure the driver didn't sneak out when you weren't looking?

Partner, this is amateur stuff. You second guess the plans over and over, but then want to make ridiculous changes like this.

Read the plans. Cut wood. Put it together. Make noise. Use it on some gigs. Then come back and suggest changes based on your experience.

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

Rich4349
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Re: T39 Slim Access panel flange question

#14 Post by Rich4349 » Wed Feb 14, 2018 2:38 pm

Bruce Weldy wrote:
Wed Feb 14, 2018 2:08 pm
Think wrote:
Wed Feb 14, 2018 1:23 pm
I can make both versions and do a comparison

You like having a visual check on the driver.......so, which subs have you been using that give you this visual check that you like having? I certainly don't know of any pro sound subs that offer such a visual aid. What exactly is the benefit of this visual check? To make sure the driver didn't sneak out when you weren't looking?

Partner, this is amateur stuff. You second guess the plans over and over, but then want to make ridiculous changes like this.
Read the plans. Cut wood. Put it together. Make noise. Use it on some gigs. Then come back and suggest changes based on your experience.
NOOOO!!! Let him build both and compare! For science! For duty and humanity!
2 DR250s, 2 27" Lab15 T-60s, 2 30" Neo Titan 39s, 1 Autotuba...and looking for more!

Bruce Weldy
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Joined: Fri Nov 27, 2009 11:37 am
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Re: T39 Slim Access panel flange question

#15 Post by Bruce Weldy » Wed Feb 14, 2018 3:29 pm

Rich4349 wrote:
Wed Feb 14, 2018 2:38 pm


NOOOO!!! Let him build both and compare! For science! For duty and humanity!
You are absolutely right! I stand corrected.

For duty and humanity! And Beyond!

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

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