Ricci's dual B&C 21SW152 build thread. - Page 7 - AVS Forum
Forum Jump: 
 
Thread Tools
Old 04-29-2010, 03:54 PM
AVS Special Member
 
vasyachkin's Avatar
 
Join Date: Jan 2008
Location: DIY-AV.NET
Posts: 2,134
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by Ricci View Post

Port is too close to the internal walls, the exit is compromised due to such a tiny worthless flare and proximity to the edge of the baffle also compromises it. How about since both exits are asymetrically loaded? Not enough baffle surrounding the port too.

you gain like an inch of baffle dimension reduction by squeezing it in the corner - which is nothing. but you lose a lot by cramping it up in the back.

you should either have it centered IMO or have two smaller round ports left and right. either of these alternatives will allow you to fit longer ports into same depth box because the exit will be less constrained.

centered port will be vented to 3 sides in the back ( left top and right ) versus 2 sides ( top and right ) that you have now - which means you will not need as much clearance behind it.

two small ports will be vented on 2 sides each or 4 sides total - so they could be brought even closer to the back wall and at the same time they would make the front baffle smaller - but they would not be as efficient as a single port.

either way out of these 3 possibilities the one you have drafted so far i think is the worst one.
vasyachkin is offline  
Sponsored Links
Advertisement
 
Old 04-29-2010, 07:33 PM
Advanced Member
 
Vinculum's Avatar
 
Join Date: Dec 2001
Location: York, Pa
Posts: 944
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 12
Quote:
Originally Posted by Ricci View Post

21's from Kevin.

Last I heard, Kevin was not selling 21" PRs by themselves and was saving them for finished subwoofers he was building. If this has changed, let me know because I'd take 4 myself.

Dr V
Vinculum is online now  
Old 04-29-2010, 08:18 PM
AVS Addicted Member
 
LTD02's Avatar
 
Join Date: Oct 2003
Posts: 16,852
Mentioned: 26 Post(s)
Tagged: 0 Thread(s)
Quoted: 565 Post(s)
Liked: 1170
"My calculations show that it does."

you are right. i was wrong.

i still think that you need the mark of the beast on your subs. how about 666? ;-)


LL

Listen. It's All Good.
LTD02 is offline  
Old 04-30-2010, 06:16 AM
AVS Special Member
 
vasyachkin's Avatar
 
Join Date: Jan 2008
Location: DIY-AV.NET
Posts: 2,134
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Just so u know Ricci designing a subwoofer is a lot easier than picking a blender. At least you have total control over all design parameters - that makes it easy - i have to choose between models that exist and decide which one is going to blend food better by looking at their friggin pictures

In my mind i have already reverse engineered both Blendtec's and Vitamix's design practices just as i have previously done for JBL, Infinity, Revel, Dynaudio, Genelec, Mackie, TC Sounds, Re etc

But i still can't pick one !
vasyachkin is offline  
Old 04-30-2010, 09:45 AM - Thread Starter
AVS Special Member
 
Ricci's Avatar
 
Join Date: Mar 2007
Location: Louisville KY
Posts: 5,131
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 42 Post(s)
Liked: 242
Quote:
Originally Posted by Vinculum View Post

Last I heard, Kevin was not selling 21" PRs by themselves and was saving them for finished subwoofers he was building. If this has changed, let me know because I'd take 4 myself.

Dr V

Look at you dropping in out of nowhere... You'd have to contact Kevin yourself.

Please tell me you have been using those ACP's this whole time.




Quote:
Originally Posted by LTD02 View Post

"My calculations show that it does."

you are right. i was wrong.
;-)

Neener neener.
Ricci is offline  
Old 04-30-2010, 10:59 AM
Advanced Member
 
MBentz's Avatar
 
Join Date: Jun 2006
Location: Chicago
Posts: 950
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 24 Post(s)
Liked: 41
Quote:
Originally Posted by Ricci View Post

Let me guess. Port is too close to the internal walls, the exit is compromised due to such a tiny worthless flare and proximity to the edge of the baffle also compromises it. How about since both exits are asymetrically loaded? Not enough baffle surrounding the port too.

If you can keep turbulence down in the port, then the corner placement might allow you to make it slightly shorter since it'll get extra internal loading...same goes with the floor actually. The downside is that the Q of the port is going to get a bit more narrow since you've effectively got more mass, but less inductance. This may not be a bad thing though because the Q of the port gets wider as it starts to overload.

Also, turbulence generated at the exit of the port essentially comes down to the ratio of circumference to the port area. Going to two smaller ports increases the total circumference for the same area, which will introduce more turbulence than the one larger port.

The reason flaring works is that the transition to a smaller circumference/area ratio is slow enough that the air doesn't pull apart as quickly, making it easier to suck it back in on the rarefaction. However, flaring a 4" port to a 6" mouth is going to have more turbulence than a tube that is 6" the entire length. The reason is because the extra 2" of diameter acts like a soft flare, or at least that's how I've been led to understand it.

The biggest downside I see to having the port in the corner of the cabinet is that it guarantees the mouth is at a pressure maximum for all the internal standing waves...basically the same effect of standing in the corner of your room. This just means you'll need more stuffing inside the cabinet to keep the resonances sufficiently damped. The downside to stuffing is that it lowers the Q of the box capacitance, which makes the overall system less efficient...and combined with the higher Q of the port you're likely going to see a small dip in the frequency response just above the tuning point.

Btw, you can model all of this in WinISD by doing some manual manipulation. One saving grace might be the fact that heat on the voice coil might compensate for the dip above the tuning point when the system is driven harder. I personally like to adjust the tuning frequency and the box volume to minimize the amount of change seen between linear and fully non-linear operation. Sometimes you can keep it within a few dB and I've found that these boxes behave more consistently when EQ'd and tend to sound better overall because of it (it's easier to voice when things are more consistent).

Anyways, just some thoughts I had...I hope I'm not spreading any misinformation.

-Mike Bentz
~It's all about compromise~
MBentz is offline  
Old 05-01-2010, 09:31 AM - Thread Starter
AVS Special Member
 
Ricci's Avatar
 
Join Date: Mar 2007
Location: Louisville KY
Posts: 5,131
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 42 Post(s)
Liked: 242
You have some good thoughts there Mike. I had not thought about the internal cab resonances and how the inner port would terminate related to those. Too busy just trying to fit everything in there logistically without bending the port and providing adequate clearance. I had already decided against 2 or 3 smaller ports. They end up being a bit longer even with the same area and as you mentioned the surface air exposed to surface friction is greater so the core limit and chuffing effects start at lower speeds. I had thought about 3-6" or 2-8" ports but they ate up a lot of cab space and needed to be too long to maintain reasonable clearance. I'm going to have a bit of excess cab volume resulting in a slight resonance spike at tune (simulated at least), but with the 4th order LR HPF I'll be using it should flatten out well.

I think too much is being made of the port compromises made. How much of a difference in the real world performance are we looking at between having the port in the corner per the one model with 10" of clearance to the back wall and between a center mounted port that has an extra 6.25" of clearance from one wall but is only 9" from the back wall? For that matter Vas is convinced that the power port model I posted would be inferior due to the 2 90 degree turns involved, but I think this is overstated since the turns are a on 4.5" radius and the port area is expanding constantly as soon as the radius is entered resulting in a much larger final expansion on both ends. (We'll talk more on the power port later Vas. I've been busy.)


BTW in the newest May edition of the Voice Coil magazine the little brother of these drives the B&C 18SW115-4 is tested. Other than the parameters being different than the manufacturer's specs it did very impressively. They didn't have the 4ohm version specs finalized yet. The BL symmetry, suspension symmetry and inductance curves were beautiful. I believe the words were "text book", nearly perfect, etc. That gives me high hopes for these.
Ricci is offline  
Old 05-01-2010, 12:55 PM
AVS Special Member
 
vasyachkin's Avatar
 
Join Date: Jan 2008
Location: DIY-AV.NET
Posts: 2,134
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I think a slight spike in frequency response is OK because when the port begins to compress this spike will disappear.

The only real downside to big box is the weight.

Hey Ricci - i know you won't like this idea but i HAZ to pimp it. Do a single OVAL port centered below the woofer.



Oval ports are mentioned in the paper as superior - i think they randomize the formation of turbulence a bit.

Besides it will allow you to reduce the cabinet face dimension.

vasyachkin is offline  
Old 05-01-2010, 01:09 PM
Member
 
robseyes's Avatar
 
Join Date: Jan 2006
Location: Puyallup,Wa.
Posts: 102
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Ricci,
You mentioned earlier that you were going to test them in a spare sealed box.......were you ever able to do that? I'm curious to see the measurements & hear your your thoughts. Seems like a couple of those cubes with a basis & some juice would be fun.
robseyes is offline  
Old 05-01-2010, 01:13 PM
AVS Special Member
 
vasyachkin's Avatar
 
Join Date: Jan 2008
Location: DIY-AV.NET
Posts: 2,134
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
also i think you should go with square baffle and rear firing port. worst case scenario is 10% of the time the port will be blocked in actual use. with your designs the port is blocked by default 100% of the time.

rear firing port has 2 other huge advantages:

1 - it will cool the driver by blowing directly next to the motor.

2 - because internally port exit will be at the front of the cab the entire rear of the cab ( 2/3 of cab volume ) can be stuffed which will both reduce boominess, honkyness and increase effective box volume allowing for a shorter port to work at same frequency.

if you go this way you should use a single oval port in the corner with the oval rotated 45 degrees for better fit between the corner and the woofer motor.

You can also run the port itself diagonally ( in 2 dimensions ) across the box to make it considerably longer.

let me know if it aint clear i can draw a sketch.
vasyachkin is offline  
Old 05-01-2010, 05:43 PM
Advanced Member
 
MBentz's Avatar
 
Join Date: Jun 2006
Location: Chicago
Posts: 950
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 24 Post(s)
Liked: 41
Quote:
Originally Posted by Ricci View Post

Too busy just trying to fit everything in there logistically without bending the port and providing adequate clearance.

I think not bending the port is one of the more important goals. I totally feel ya when it comes down to actually implementing the theory...having the reserve to keep things practical demonstrates good engineering in my mind.

Quote:
Originally Posted by Ricci View Post

I'm going to have a bit of excess cab volume resulting in a slight resonance spike at tune (simulated at least), but with the 4th order LR HPF I'll be using it should flatten out well.

Is there any particular reason you're choosing to go with a 4th order LR HPF?

I would highly suggest trying a 2nd order Butterworth, if for no other reason than every time I've compared the two I've always preferred it.

I believe 2nd order should be steep enough to protect the driver from over-excursion and it's going to have less phase rotation at the corner, which means less group delay and tighter sounding bass. It also doesn't hurt to have that extra excursion below tuning because fundamentals in that region will create audible harmonics giving the impression of deeper extension (our minds fill in the fundamentals somewhat). At least that's what I've come to believe is the reason I prefer the sound of 2nd order. I've actually got a buddy at work who is running several EV MTL-4 cabs (quad manifolded 18's) and he was very impressed by the switch from 4th order LR to 2nd order Butterworth...

Quote:
Originally Posted by Ricci View Post

I think too much is being made of the port compromises made.

Agreed.

It ultimately doesn't matter until the SPL's get loud, but the crest factor is usually so high that the chuffing never really gets perceived (versus what it sounds like under steady state sine wave testing). If you take a look at pretty much all pro sound boxes, you'll notice that they're getting into some insane port velocities...even in higher end boxes.

Quote:
Originally Posted by Ricci View Post

BTW in the newest May edition of the Voice Coil magazine...

Interesting, I've not heard of Voice Coil magazine before...is this it?
http://www.audioxpress.com/magsdirx/voxcoil/index.htm

-Mike Bentz
~It's all about compromise~
MBentz is offline  
Old 05-01-2010, 05:47 PM
Advanced Member
 
MBentz's Avatar
 
Join Date: Jun 2006
Location: Chicago
Posts: 950
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 24 Post(s)
Liked: 41
Quote:
Originally Posted by vasyachkin View Post

also i think you should go with square baffle and rear firing port. worst case scenario is 10% of the time the port will be blocked in actual use. with your designs the port is blocked by default 100% of the time.

Obviously you've never done live sound before....rear firing port is a huge no-no for a million reasons...especially with such a large port.

But since you know everything, I'll leave it to you to come back and explain to us why that is the case...

Quote:
Originally Posted by vasyachkin View Post

2 - because internally port exit will be at the front of the cab the entire rear of the cab ( 2/3 of cab volume ) can be stuffed which will both reduce boominess, honkyness and increase effective box volume allowing for a shorter port to work at same frequency.

Stuffing the box does not increase the effective box volume and certainly doesn't allow for a shorter port. With the lower Q from the rear volume capacitance, I think many people mistake the slower roll off as behaving like a larger cabinet....but that's not how it works.

Quote:
Originally Posted by vasyachkin View Post

you should use a single oval port

Oval ports have more chuffing for a given cross-sectional area than a circular port...marketing hype is not physics.

-Mike Bentz
~It's all about compromise~
MBentz is offline  
Old 05-01-2010, 06:28 PM
AVS Addicted Member
 
LTD02's Avatar
 
Join Date: Oct 2003
Posts: 16,852
Mentioned: 26 Post(s)
Tagged: 0 Thread(s)
Quoted: 565 Post(s)
Liked: 1170
"I think too much is being made of the port compromises made."

yeah, it's "audio theory gone wild". meyer sound uses a round corner port stategy on their 700hp. they use two round ports, but the idea is essentially the same.

http://www.meyersound.com/products/concertseries/700hp/

and, as you know, many of jbl's top of the line subs use triangular corner slot ports and other such 'terrible designs'. i think the key idea is that when you have 125db blasting in your face, a little port chuffing is way down the list of engineering concerns.

Listen. It's All Good.
LTD02 is offline  
Old 05-01-2010, 07:34 PM
 
mjg100's Avatar
 
Join Date: Dec 2006
Posts: 9,112
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 13
Quote:
Originally Posted by LTD02 View Post

"I think too much is being made of the port compromises made."

yeah, it's "audio theory gone wild". meyer sound uses a round corner port stategy on their 700hp. they use two round ports, but the idea is essentially the same.

http://www.meyersound.com/products/concertseries/700hp/

and, as you know, many of jbl's top of the line subs use triangular corner slot ports and other such 'terrible designs'. i think the key idea is that when you have 125db blasting in your face, a little port chuffing is way down the list of engineering concerns.

Made me laugh, thinking about somebody sticking their head to the port trying to hear chuffing with the sub playing 125db.
mjg100 is offline  
Old 05-01-2010, 08:14 PM
AVS Special Member
 
vasyachkin's Avatar
 
Join Date: Jan 2008
Location: DIY-AV.NET
Posts: 2,134
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by MBentz View Post

Obviously you've never done live sound before....rear firing port is a huge no-no for a million reasons...especially with such a large port.

good attempt at sounding smart Bentz. unfortunately it's a FAIL.

Ricci never said exactly what kind of setup he was going to use and where. All he said is that it wasn't going to be used in a home setting. He also said he "would like" to keep the port front firing. He didn't say it's a must.

i can think of reasons why rear port would be a problem. but i can also see that a front port is a problem as well.

Quote:
Originally Posted by MBentz View Post

Stuffing the box does not increase the effective box volume

EPIC FAIL.

Quote:
Originally Posted by MBentz View Post

Oval ports have more chuffing for a given cross-sectional area than a circular port...marketing hype is not physics.

i am not sure which one performs better - i don't have any data on that. intuitively it could go either way.

the reason i suggested it is purely out of packaging ( or as our friend Ricci says "logistics" ) considerations.
vasyachkin is offline  
Old 05-01-2010, 08:23 PM
AVS Special Member
 
vasyachkin's Avatar
 
Join Date: Jan 2008
Location: DIY-AV.NET
Posts: 2,134
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by LTD02 View Post

"I think too much is being made of the port compromises made."

yeah, it's "audio theory gone wild". meyer sound uses a round corner port stategy on their 700hp. they use two round ports, but the idea is essentially the same.

http://www.meyersound.com/products/concertseries/700hp/

and, as you know, many of jbl's top of the line subs use triangular corner slot ports and other such 'terrible designs'. i think the key idea is that when you have 125db blasting in your face, a little port chuffing is way down the list of engineering concerns.

i think there may be some sort of a point in multiple ports. maybe that makes the internal standing waves contribution partially cancel out.

but if we were to believe this is important we wold have to have several ports on every face of the cabinet

bottom line here Ricci is that the more u think about this stuff the more you don't get nowhere.

FLIP A COIN AND START CUTTING WOOD.
vasyachkin is offline  
Old 05-01-2010, 08:53 PM
AVS Special Member
 
soho54's Avatar
 
Join Date: Sep 2005
Posts: 3,329
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 17
Quote:
Originally Posted by JapanDave View Post

Ricci, here is a design I whipped up for you. I really think this is the final design , no question about it.

LOL, that is great! Thank you for that.
soho54 is offline  
Old 05-01-2010, 10:35 PM
Advanced Member
 
MBentz's Avatar
 
Join Date: Jun 2006
Location: Chicago
Posts: 950
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 24 Post(s)
Liked: 41
Quote:
Originally Posted by vasyachkin View Post

Ricci never said exactly what kind of setup he was going to use and where.

What about the first post where Ricci says the following? :P

"These will be used in a PA type manner usually in a fixed location for drum reinforcement, some bass guitar and music playback, but they may ocassionally be dragged out for duty at local concerts, so they can be big but have to be manageable by just 2 guys."

Btw, I've already seen the data that verifies what I'm referring to about the stuffing in a cabinet. I would humbly suggest taking some of your own measurements to see it for yourself. Or if you prefer, we can continue propagating the misconception.

Changing the Q (or the losses) of the rear volume reactance is not the same thing as making the rear volume larger, which would actually increase the amount of reactance.

-Mike Bentz
~It's all about compromise~
MBentz is offline  
Old 05-01-2010, 10:54 PM
AVS Special Member
 
vasyachkin's Avatar
 
Join Date: Jan 2008
Location: DIY-AV.NET
Posts: 2,134
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by MBentz View Post

What about the first post where Ricci says the following? :P

"These will be used in a PA type manner usually in a fixed location for drum reinforcement, some bass guitar and music playback, but they may ocassionally be dragged out for duty at local concerts, so they can be big but have to be manageable by just 2 guys."

good job. you proved that i was wrong. you are better than i am. you win. congratulations.

now this place is associated with negative emotions for me so there is no longer any reason for me to be here.

enjoy.
vasyachkin is offline  
Old 05-02-2010, 10:13 AM - Thread Starter
AVS Special Member
 
Ricci's Avatar
 
Join Date: Mar 2007
Location: Louisville KY
Posts: 5,131
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 42 Post(s)
Liked: 242
Here we go...I'm about ready to buy wood this week. I'm tired of batting around ideas.

24.5w x 35.25h x 29.5d with 10" x 19.75" port







Ricci is offline  
Old 05-02-2010, 10:47 AM - Thread Starter
AVS Special Member
 
Ricci's Avatar
 
Join Date: Mar 2007
Location: Louisville KY
Posts: 5,131
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 42 Post(s)
Liked: 242
Quote:
Originally Posted by MBentz View Post

I would highly suggest trying a 2nd order Butterworth, if for no other reason than every time I've compared the two I've always preferred it.

I believe 2nd order should be steep enough to protect the driver from over-excursion and it's going to have less phase rotation at the corner, which means less group delay and tighter sounding bass. It also doesn't hurt to have that extra excursion below tuning because fundamentals in that region will create audible harmonics giving the impression of deeper extension (our minds fill in the fundamentals somewhat). At least that's what I've come to believe is the reason I prefer the sound of 2nd order. I've actually got a buddy at work who is running several EV MTL-4 cabs (quad manifolded 18's) and he was very impressed by the switch from 4th order LR to 2nd order Butterworth...

I'll give that a shot. I might need to raise the corner up a little from 20hz to 23 or 24 with a 2nd order, but that should be fine. I'll figure that out with real world testing. I know that the danley guys usually recommend a Butterworth filter.

Quote:
Originally Posted by MBentz View Post

Interesting, I've not heard of Voice Coil magazine before...is this it?
http://www.audioxpress.com/magsdirx/voxcoil/index.htm


Yes. That's it. It's a good read. All product testing, industry news, breaking technologies and patent reviews.


Quote:
Originally Posted by robseyes View Post

Ricci,
You mentioned earlier that you were going to test them in a spare sealed box.......were you ever able to do that? I'm curious to see the measurements & hear your your thoughts. Seems like a couple of those cubes with a basis & some juice would be fun.

Finished it last night. I won't be able to listen to it until sometime later this week. it's roughly 24x24x25.25 with both drivers in it mounted opposed. It'll probably take me a few months at-least to get the ported cabs done start to finish so It'll give me something to listen to the drivers in for the meantime.
Ricci is offline  
Old 05-02-2010, 11:58 AM - Thread Starter
AVS Special Member
 
Ricci's Avatar
 
Join Date: Mar 2007
Location: Louisville KY
Posts: 5,131
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 42 Post(s)
Liked: 242
Sealed dual opposed. This thing is actually a bit comical with the amount of cone area and motor jammed in there. There's about 4" of clearance between the 2 motors.






Ricci is offline  
Old 05-02-2010, 01:05 PM
AVS Addicted Member
 
LTD02's Avatar
 
Join Date: Oct 2003
Posts: 16,852
Mentioned: 26 Post(s)
Tagged: 0 Thread(s)
Quoted: 565 Post(s)
Liked: 1170
looks cool.

just a couple random thoughts.

bottom port looks like a home for rodents, not sure if that is a concern.

might want to consider if/where you will put handles at this stage, as that might affect where you put the bracing.

the driver and the port are pretty closely spaced. might you need a little extra space to accomodate a grill?

how do they sound in the sealed enclosure?

Listen. It's All Good.
LTD02 is offline  
Old 05-02-2010, 04:34 PM
AVS Special Member
 
vasyachkin's Avatar
 
Join Date: Jan 2008
Location: DIY-AV.NET
Posts: 2,134
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by Ricci View Post

Here we go...I'm about ready to buy wood this week. I'm tired of batting around ideas.

24.5w x 35.25h x 29.5d with 10" x 19.75" port








Best news all day. Overall i am very pleased with this. I need to modify the bracing however.

Lemme sketch it up. I need a few seconds.
vasyachkin is offline  
Old 05-02-2010, 05:17 PM
AVS Special Member
 
vasyachkin's Avatar
 
Join Date: Jan 2008
Location: DIY-AV.NET
Posts: 2,134
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
ok here it is.






LL
LL
LL
vasyachkin is offline  
Old 05-02-2010, 05:54 PM
AVS Special Member
 
vasyachkin's Avatar
 
Join Date: Jan 2008
Location: DIY-AV.NET
Posts: 2,134
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Your bracing design leaves that thin part of the baffle between driver and port essentially unsupported.

Effective support must couple a vibrating plane to a perpendicular plane, not a parallel plane. Only perpendicular planes reinforce each other.

Unfortunately your design mostly consists of multiple planes that are all parallel to the baffle so there is no stiffness to support the baffle.

The bracing scheme i sketched up is basically as stiff it gets. It's all planes perpendicular to the baffle coupling to all of the walls perpendicular to the baffle at the same time.

This is basically a hybrid between a swiss cheese matrix design and simply tying the opposite walls with beams. It gives you most of the performance of the first and most of the simplicity of the second.
vasyachkin is offline  
Old 05-02-2010, 08:08 PM
AVS Addicted Member
 
LTD02's Avatar
 
Join Date: Oct 2003
Posts: 16,852
Mentioned: 26 Post(s)
Tagged: 0 Thread(s)
Quoted: 565 Post(s)
Liked: 1170
vas, i'd be curious to know which panels you think would vibrate in ricci's design. your design looks fine too, except that with more panel area, your design would be heavier.

Listen. It's All Good.
LTD02 is offline  
Old 05-02-2010, 08:25 PM
AVS Special Member
 
vasyachkin's Avatar
 
Join Date: Jan 2008
Location: DIY-AV.NET
Posts: 2,134
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by LTD02 View Post

vas, i'd be curious to know which panels you think would vibrate in ricci's design. your design looks fine too, except that with more panel area, your design would be heavier.

well i already pointed out that in Ricci's design the BAFFLE is one of the LEAST supported panels, even though it needs to be the most.

his bottom panel is the most supported even though it least needs it.

true his baffle is 2X to 3X thicker than other panels so there wouldn't be a problem but that's extra weight.

with proper bracing support between the driver and the port Ricci should be able to reduce the bottom part of the baffle from 3X thickness to 1X thickness without any loss in stiffness.

The horizontal "T" brace that i have sketched up could be upgraded to a SQUARE piece of plywood with some round holes cut out - that would marginally increase the amount of labor involved though.

Ricci if you don't want to generally follow my design you should figure out your own way to strengthen the baffle in the area between the driver and the port. What you have done so far with the triple thickness bottom part of the baffle is inefficient in terms of weight.

Once again i would keep the top section of the baffle at 2X thickness and reduce the bottom part to 1X thickness and use bracing rather than thickness for stiffness.

In fact in the top part you could go 3X thickness easily because it is like 80% a hole - so even at 3X you wouldn't be adding much weight. Not so on the bottom. Plus you need the stiffness on top more than u need it on the bottom. So 3X top 1X bottom.

My box has 3X plywood baffle

Ricci's current design is not bad, but i am a perfectionist
vasyachkin is offline  
Old 05-03-2010, 07:52 AM - Thread Starter
AVS Special Member
 
Ricci's Avatar
 
Join Date: Mar 2007
Location: Louisville KY
Posts: 5,131
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 42 Post(s)
Liked: 242
I already looked at adding a shelf brace there when I was doing the last model and I decided that the thin strip between the driver and port will not be a problem at all and neither will flex of the front baffle. Reason being is that I'm probably going to use 10" pvc pipe (yes I realize it's thick and quite heavy) for the port and this in itself will function as a brace due to the way it will be mounted into the baffle and internal cab baffle with a 3rd middle one. Not to mention that the baffle is 2x and 3x thick. There's also those 2 pillar type braces that will go all of the way from the front to the back of the enclosure. They are only placed relatively in the model. They will be spaced as close towards the center as possible while still clearing the woofer mounting screws. The top part of the baffle is 2x thick and as noted already it's 80% hole if not more. I don't see those 0.75" to 2" strips of double thickness wood flexing much. The area below the driver hole is a strip of about 1.5" thickness before it meets the port which will be coupled into 2 other braces and a 3x thick baffle with additional pillar braces. I just don't see it. Not a bad bracing scheme though Vas.




Call me crazy but i don't see flex as being a problem in this area of the front baffle.






BTW. Remember that you need to have close to an identical baffle for each side of the port to minimise distortion according to the Harman paper. Mine is. (As long as we are nit picking a bit here.)

The baffle is the thicknesses that it is for a reason. For stiffness is one, but really the driver section is 2x to flushmount the driver and move it back into the cab a bit. The entire driver baffle is also offset one panel thickness back into the cab to protect the driver further and allow clearance for some type of yet TBD grill system that will not protrude further than the front of the sub. I very briefly thought of back mounting the drives, but quickly threw that out. The port is 3X thickness mainly just to get an extra .75" of clearance from the back wall by mounting the port fully forward flush with the cabinet front. There is no worry of the port getting drinks spilled on it or a random object hitting it. That's the reason for the offset in the baffle. I'm not worried about an extra 5lbs of weight savings.




LTD02,

I can staple a chicken wire screen to the top of the inner port baffle and the bottom back shelf brace all of the way across to keep any curious rodents from getting to the driver at least. I'd have to imagine that the internal SPL in the cab should take care of the rest.

Handles are being considered. I left space on the sides and back for handles, but I'm not sure what style I'll be going with yet. I might go with casters too.
Ricci is offline  
Old 05-03-2010, 11:46 AM
AVS Special Member
 
vasyachkin's Avatar
 
Join Date: Jan 2008
Location: DIY-AV.NET
Posts: 2,134
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by Ricci View Post

I already looked at adding a shelf brace there when I was doing the last model and I decided that the thin strip between the driver and port will not be a problem at all and neither will flex of the front baffle. Reason being is that I'm probably going to use 10" pvc pipe (yes I realize it's thick and quite heavy) for the port and this in itself will function as a brace due to the way it will be mounted into the baffle and internal cab baffle with a 3rd middle one.

well PVC doesn't glue that well. i glued my PVC ports with silicon which wouldn't be a structural joint ( too flexy ). now if you can manage to use this PVC pipe as a structural member that's great - always more efficient to use EVERYTHING as a structural member. In Formula 1 cars and Ferrari Enzo the engine itself is part of the frame for example.

HOWEVER those two shelf braces on the bottom through which your pipe goes are not the best way to transfer the force from it. that's because as i already pointed out they are oriented parallel to the baffle. You should at least glue the bottom of that PVC pipe to the bottom of the enclosure directly.

Quote:
Originally Posted by Ricci View Post

BTW. Remember that you need to have close to an identical baffle for each side of the port to minimise distortion according to the Harman paper. Mine is. (As long as we are nit picking a bit here.)

no the paper used a 15 millimeter wide baffle i believe and it was enough. the point was to have SOME baffle, it didn't have to be "close to identical". my design did provide the required amount of baffle.

Quote:
Originally Posted by Ricci View Post

Call me crazy but i don't see flex as being a problem in this area of the front baffle.

well yeah you have something there but i like my design better.

Quote:
Originally Posted by Ricci View Post

The baffle is the thicknesses that it is for a reason. For stiffness is one, but really the driver section is 2x to flushmount the driver and move it back into the cab a bit. The entire driver baffle is also offset one panel thickness back into the cab to protect the driver further and allow clearance for some type of yet TBD grill system that will not protrude further than the front of the sub.

i knew that.
vasyachkin is offline  
 
Thread Tools


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off