JBL GTx10

[Alex2507]

Alex - If TLS Guy said to use polyfill in those cabinets, do what the man says.

The problem was that I couldn't remember what he had told me.

It would not be a bad idea to place mineral wool behind the driver, if you crossover is not fourth order at 80 Hz or below.

For now my crossover is 12 db/oct on the system I plan to use those subs with so I'll be itchin' and scratchin' before it's all over.

As far as I can tell from the data in Bass Box Pro, the volume displaced by that driver with flush mounting is 0.078 cu. ft, which you could round off to 0.1 cu. ft if you want.

Cool. That's easy enough. I still wonder what 'P-Vd = 0.35 liters' refers to and what annunaki's term 'critically damp' means but it's not a stumbling block.

BTW Dr. Carter, the fractions to decimal equivalents you have at the bottom of page 1 on the alignment has been incredibly helpful so far ... very nice touch.

btw. dampening and bracing are 2 different things.

The article I linked from JL Audio states:

"Any standing waves that might be generated by upper order harmonics in the enclosure can be readily absorbed with the addition of damping material such as polyfill or they can be broken up with strategically placed bracing within the enclosure."

... so the damping and bracing in the case of standing waves can work toward the same goal.

 

[TLS Guy]

Cool. That's easy enough. I still wonder what 'P-Vd = 0.35 liters' refers to and what annunaki's term 'critically damp' means but it's not a stumbling block.

0.35 lt is the volume of air displaced by a stroke of the cone at full power. (xmax not exceeded).

A ported enclosure is critically damped, when you start to kill Fb. This obviously reduces output, but makes the bass tighter.

Quite honestly I don't like the resonant reproduction of Qb4 boxes, and I admit I over damp mine when I do build them. It is just that TLs have spoiled me. You can and should critically damp a TL in my view, but even then you still get decent bass augmentation from the port.

The article I linked from JL Audio states:

"Any standing waves that might be generated by upper order harmonics in the enclosure can be readily absorbed with the addition of damping material such as polyfill or they can be broken up with strategically placed bracing within the enclosure."

... so the damping and bracing in the case of standing waves can work toward the same goal.

Polyfill is very good for taming Fb, but no so good for reducing reflections from the structure behind the Polyfill, mineral wool does a better job here.

You won't break up resonant waves with strut bracing like 2 X 4s. You need strategically placed braces, like figure of 8 braces, especially interlocking ones.

Unfortunately I was in a rush and never took pictures of the construction of the three way Qb4 enclosures in my downstairs system, but those speakers have obsessional interlocking bracing.

 

[Swerd]

The article I linked from JL Audio states:

"Any standing waves that might be generated by upper order harmonics in the enclosure can be readily absorbed with the addition of damping material such as polyfill or they can be broken up with strategically placed bracing within the enclosure."

... so the damping and bracing in the case of standing waves can work toward the same goal.

It is my understanding that damping with cabinet fill and cabinet bracing do quite different things.

Damping materials minimize the reflected standing waves inside the air space of the cabinet. It has little or no effect on the vibration of the cabinet walls.

Bracing adds stiffness to the cabinet walls, minimizing resonant vibration of the cabinet structure and the resulting audible coloration it can make.

If internal bracing also has an effect on standing waves in the air space of the cabinet, as TLS Guy also seems to say, I'm not aware of that.

Bracing also works better if it is not built symmetrically. An unbraced cabinet wall has an inherent resonant frequency. The larger the area, the lower the frequency. Bracing breaks up these large areas into smaller areas with higher resonant frequencies that each are quieter. Symmetric bracing looks nicer (especially in build thread photos on internet forums), but it breaks up the unbraced panel surface areas into equal sizes that can each resonate at the same frequency and add their sound together. If the unbraced areas are different sizes, each area has a different resonance frequency and are less likely to add up to a louder resonant sound.

 

[TLS Guy]

It is my understanding that damping with cabinet fill and cabinet bracing do quite different things.

Damping materials minimize the reflected standing waves inside the air space of the cabinet. It has little or no effect on the vibration of the cabinet walls.

Bracing adds stiffness to the cabinet walls, minimizing resonant vibration of the cabinet structure and the resulting audible coloration it can make.

If internal bracing also has an effect on standing waves in the air space of the cabinet, as TLS Guy also seems to say, I'm not aware of that.

Bracing also works better if it is not built symmetrically. An unbraced cabinet wall has an inherent resonant frequency. The larger the area, the lower the frequency. Bracing breaks up these large areas into smaller areas with higher resonant frequencies that each are quieter. Symmetric bracing looks nicer (especially in build thread photos on internet forums), but it breaks up the unbraced panel surface areas into equal sizes that can each resonate at the same frequency and add their sound together. If the unbraced areas are different sizes, each area has a different resonance frequency and are less likely to add up to a louder resonant sound.

If you use baffles and holes it will brace and break up standing waves also. This is the matrix type of system as described many years ago by B & W. This is very similar to what I do.

 

[Swerd]

If you use baffles and holes it will brace and break up standing waves also. This is the matrix type of system as described many years ago by B & W. This is very similar to what I do.

Thanks, that one picture is worth a 1000 words.

 

[Alex2507]

Thanks guys. You're doing a good job of bringing me along.
Just a couple of things I want to make sure I am clear on ...

kill Fb ... taming Fb

I take it this refers to reduction in amplitude of Fb and maybe a smoothing out of what the Fb would look like with an RTA? Try not to loose me here ... the waters are deepening rapidly.

Qb4 boxes

Quasi Butterworth 4th order ... describes the typical low end roll off of a ported box with that Q thing around 0.7? I had to look that up of course and even then Google took me back to some of your posts here on AH. That sniffing around got me wondering about QL and Qtc which appear in your alignment and my two mostly unread books. Then my mind seized up like a overheated lawnmower motor.

I'll get to that. The more simple subwoofer section in Rumreich's The Car Stereo Cookbook has practical examples that would give me a more intuitive understanding. I started going through that section again but my workbook is out in the car so now I'm unclear on the parts I understood and the parts I wondered about because I can't see my notes and am struggling to get this post ground out.

If internal bracing also has an effect on standing waves in the air space of the cabinet, as TLS Guy also seems to say, I'm not aware of that.

From the JL site quote, I edited out the part where they specified the origin of the standing waves they were talking about being distortion and not resonance from the cabinet. Maybe I shouldn't have done any editing of their writing.

They also talk about asymmetrically placed bracing. My bracing will follow the placement of port and driver of which neither are centered so it will start off not creating equal divisions. My box was already about a hundred sq. in. shy of my target. I am going to buy that and the displacement of my bracing back with the addition of a hollow base. Instead of doing a toe kick which I feel would make these boxes look like they were perched I am going with a larger platform to set the enclosures on. Once again it is a matter of incorporating an existing piece of millwork that I garbage picked.

Tomorrow will be another day at the boxes. After sealing the inside of the boxes I had to spend the next day sleeping and the day after that I drove all the way down there to assemble the 2nd port and give up for the day. It's probably a combination of my new progressive lenses and paint fumes but I stalled hard on something that I'm itching to work on. I blame Swerd.

 

[TLS Guy]

Qb4 boxes

The Q if a resonance defines its width.

A high Q is peaked and boomy. Lower Qs have a higher roll of point but a more gradual roll off.

In an optimal ported alignment you try and shoot for a Qtc of around 0.7. This generally gives the flattest output, but not the most extended response as a rule. As a rule you pay a lot of unnecessary penalties for tuning a box too low to extend the bass response too low.

If the Qts of the driver happens to equal 0.4, the optimum vented box will resemble a B4 (4th-order Butterworth) alignment. As the value of the driver Qts drops below 0.4 the optimum vented box will begin to resemble a QB3 (quasi 3rd-order Butterworth) alignment. As the value of the driver Qts rises above 0.4, the optimum vented box will begin to resemble a C4 (4th-order Chebychev) alignment.

However a box with drivers on an exterior face of one ported chamber are generally referred to a Qb4 boxes.

QL is the Q (shape of the resonance) from cumulative box losses.

I prefer a Qtc of around 0.5. I attend a lot of concerts especially this winter. I have to say that the bass of my rig is very realistic and is very close indeed to the sound of bass strings, tymps etc.

 

[Alex2507]

Here's some pic's.

This is what I'm going to use for bases.
Whatever volume I have in the bases is what I can use for braces.

The base further adds to the complexity of the build but that's the price of free lumber. On the bright side it will get me a look I am after. Instead of it being like a toe kick on kitchen cabinets these bases will protrude 3/4" from each side.

I think I'm thinking about painting the whole thing.
I think I'm thinking about painting them ... green? ... yeah, green ...

 

[jeffsg4mac]

what are you going to power those with?

 

[Alex2507]

what are you going to power those with?

JBL MPC200

It's a rebadged QSC that I bought from tcarcio a few years back.
I used the amp for my mains before the great living room purge of 2010.

 

[annunaki]

Bracing also works better if it is not built symmetrically. An unbraced cabinet wall has an inherent resonant frequency. The larger the area, the lower the frequency. Bracing breaks up these large areas into smaller areas with higher resonant frequencies that each are quieter. Symmetric bracing looks nicer (especially in build thread photos on internet forums), but it breaks up the unbraced panel surface areas into equal sizes that can each resonate at the same frequency and add their sound together. If the unbraced areas are different sizes, each area has a different resonance frequency and are less likely to add up to a louder resonant sound.

It is very possible to have what appears to be symmetric bracing while in deed having asymmetrical bracing as well. You do have an important point though.

See most of my builds in that few panels internally ever end up at the same size, by design, though they may look the same in photos.


Also, if there is the choice over symmetrical bracing or no bracing, it is symmetrical all day long.


Alex:

Your vent is also acting as a brace currently. Adding more will further strengthen the enclosure.

 

[Alex2507]

Your vent is also acting as a brace currently. Adding more will further strengthen the enclosure.

Ah, yes ... the bracing. I have been waiting a long time to brace something ... anything. This is old growth Southern Yellow Pine. It comes from a 100 year old building. Check out how many annular rings there are in the 1-3/4" length. Another thing is that this piece is quarter sawn. As dense as it is there is no way to drive nails into this without pre-drilling. I dragged a few 4"x6" pieces to Eddie's a few years back and milled them all to this dimension to one day use as bracing in something ... anything.

This piece in particular is going to brace the vents along the back wall.

I cut the knot out and from the same piece made a brace for the left and right enclosure.

This is the part that I like. This is wood. There is still sap in these pieces. Even after 100 years it still smells like pine. There is evidence of life in this. In this next pic you can see where I cut a hole in the floor of the enclosure and a hole in the base to join the air spaces.

The base will get capped and clad with something ... probably Mahogany, real Mahogany, not the African stuff. I just can't get this worked up about MDF and veneered ply. Cutting that just gets dust and splinters everywhere not to mention chemicals but cutting into a nice wood species is different. Yeah, I know it's weird.

 

[Alex2507]

Seeing as how I'm getting all this positive feedback for the pic's here's some more.
I'm going to make a lattice of sorts, raise it up and anchor the top to it.
That should keep it from vibrating stuff off the top.

That plywood anchors the left and right walls.

See that writing? That's the way to dry land.
Water World rocks !!!

I threw a great big fat honkin' bead of silicone on top of the ply mostly because I had an open tube.

Bracing up the side of the box that didn't benefit from having the port run along it was incredibly complicated. It's isolated from the port so that I can still slide the port out the bottom but the pictures don't really help anything here. It just looks like a mess. At least I'm getting to burn up that wood. I think I only have to put another 84 linear inches of that brace stock in to get the Vb where I need it. The total I needed to cram in each box was like 380". That's the real reason for that ridiculous looking lattice on the top. That # was forced on me when I decided to use the existing millwork for the box and the base.

What are ya gonna do? *shrug*

Oh yeah, and with all that untreated pine in the box every time I play bass intensive music it will smell like someone is cleaning the toilet.

 

[ParadigmDawg]

Isn't this too big for a pocket sub....

 

[Alex2507]

Isn't this too big for a pocket sub....

10 inches is still just 10 inches.

This is an awful lot of work but Swerd and TLS say it's worthwhile.

I would have got more done today but I was dragging these things out into the light of day for picture time.

Here's that lattice.

Here's a peak at the bottom of the box. This is next in line for bracing.
It turns out that I need to stuff 100 linear inches of that brace material in there somewhere.

With the top all set it was time to separate the base and yank the ports to permanently attach the port to
the box bottom with glue and the right screws.

I don't understand why GO-NAD! thinks these ports are complicated.

It's the bracing that's kicking my @ss.

These things are getting heavier by the day. I may not need a fork lift by the time it's over but a hand truck might be in order. I wanted to be shooting primer by the end of today but I wasn't even close. I still have to make a face and trim out the base after I get the bracing squared away and the cabinet screwed and glued. Maybe by Monday.

 

[GO-NAD!]

Here's a peak at the bottom of the box. This is next in line for bracing.
It turns out that I need to stuff 100 linear inches of that brace material in there somewhere.

With the top all set it was time to separate the base and yank the ports to permanently attach the port to
the box bottom with glue and the right screws.

I don't understand why GO-NAD! thinks these ports are complicated.

It's the bracing that's kicking my @ss.

It's apparent to me that you could've made these subs quite a bit smaller if you need to throw in all that bracing, in order to get the Vb you need. On the plus side, if they don't work well as subs, I'm sure they'll be strong enough to use as axle stands for working on your pick-up.

And yeah, that port design does look overly complicated (as in time consuming) to me. What's the reason for that? Honest question.

If it looks like I'm picking nits, I'm certainly not trying to. It's just that for me, the simpler a design, the better. However, that may just be a reflection of my skill level, rather than a deliberate philosophy....

I also noticed that you found a use for your telephone stand.

 

[sawzalot]

Ohhhh Noooo, Not the Telephone stand
Noooooooo.

Nice going with these boxes A , seems like they will be a tad on the heavy side but that's a good thing , yes ?

Thanks for the pics as well.

 

[Alex2507]

that port design does look overly complicated (as in time consuming) to me. What's the reason for that? D

I liked the look of the port having a more substantial boundary and being off center and vertical.

It's apparent to me that you could've made these subs quite a bit smaller if you need to throw in all that bracing, in order to get the Vb you need.

I could have made these a little smaller if I had the money to buy a few sheets of plywood and I could have made them much smaller still if I had gone with a much shorter 4" round port with a higher vent velocity. I wasn't shooting for small and simple. I was shooting for fun and free ... so far so good.

The base (an existing piece of millwork) determined the amount of bracing I would use as the unbraced box (an existing piece of millwork) was almost the perfect size but very resonant. I have been dieing to use up this material and now it's mostly gone so that's a good thing and the top of the box should be completely vibration free which it wasn't when I tested the drivers.

I also noticed that you found a use for your telephone stand.

Ohhhh Noooo, Not the Telephone stand
Noooooooo.

Not so my telephone table hating friends!

I was on my way out but this kind of telephone table hate can't go unchallenged!
Thanks for forcing me to make that corner presentable and I remembered that you like the cello.

Nice going with these boxes A , seems like they will be a tad on the heavy side but that's a good thing , yes ?

Thanks for the pics as well.

Thanks, Rob. I feel like posting pic's and making these boxes right is something I owe to the DIY guys that have helped me along. You have any idea what kind of patience that takes?

 

[GO-NAD!]

I could have made these a little smaller if I had the money to buy a few sheets of plywood and I could have made them much smaller still if I had gone with a much shorter 4" round port with a higher vent velocity. I wasn't shooting for small and simple. I was shooting for fun and free ... so far so good.

Gotcha.

Oh, I know it wasn't your telephone stand. I was just, as they say in England, "taking the pi$$".

...I remembered that you like the cello.

Thanks for that. Is it a good album? If so, do you know if it's avaiable on CD?

 

[TLS Guy]

10 inches is still just 10 inches.

This is an awful lot of work but Swerd and TLS say it's worthwhile.

I would have got more done today but I was dragging these things out into the light of day for picture time.

Here's that lattice.

Here's a peak at the bottom of the box. This is next in line for bracing.
It turns out that I need to stuff 100 linear inches of that brace material in there somewhere.

With the top all set it was time to separate the base and yank the ports to permanently attach the port to
the box bottom with glue and the right screws.

I don't understand why GO-NAD! thinks these ports are complicated.

It's the bracing that's kicking my @ss.

These things are getting heavier by the day. I may not need a fork lift by the time it's over but a hand truck might be in order. I wanted to be shooting primer by the end of today but I wasn't even close. I still have to make a face and trim out the base after I get the bracing squared away and the cabinet screwed and glued. Maybe by Monday.

It is nice to see this project coming along.

I will be surprised if you are not very happy with these.

Yes, it is a lot of work. But gear done right gives years of pleasure, and the work seems like nothing in the rear view mirror.