AV12 sonosub construction pics

burdette

Sorry, I don't know how to load more than one photo per post...

Here is the base of the unit... the tube, obviously, goes over the driver. The amp isn't in the box yet, but that is where the box can/will sit (it isn't attached). You can just sort of see the output terminals on the back of the amp box.. I'll use about a 8" jumper to connect the amp to the sub.

burdette

Here should be the bottom of the baffle board (without the bottom base of the unit) and the top of the baffle board without the amp box....

edit.. nope.. only one photo.. so putting a ; between two file names isn't how you load more than one...

anyway, this photo is the top of the baffle....

burdette

HERE is the bottom of the baffle.... the "scratches" you can see on the surface of the driver may be the same thing Gonzo was talking about on his AV15s... they are not actually scratches.. they are tiny cracks *within* the clear powdercoat on the cone. You can't feel them with your finger.. and Stryke/TC Sounds assures they're cosmetic only.. but obviously it isn't picture perfect, which is why this beauty was a b-stock unit.

The legs hold the baffle 4" off the base.. so the driver is about 3.5" up... I made the mounting board for the input terminal out of the same 100 year-old hardwood (taken from an Iowa barn) as the sides of the amp box.

gidrah

Lookin' good! Please post more!

Dr. Spec

Excellent workmanship! You really have some good building skills. I think you'll be proud of this unit when you're done. I bet it will sound very decent also. Can't wait to see the FR on the unit - we'll see if those hours we spent on the R&D phase pay off - I think they will :-).

goingganzo

that looks great. i bet it will knock your socks off when you get it done.

av12 at 14 feet dident find out the box size or tune.
20hz---105
21hz---105
22hz---106
23hz---107
24hz---107
25hz---107
26hz---110
27hz---111
28hz---113
29hz---114
30hz---115
32hz---112
34hz---110
36hz---110
40hz---114
46hz---111

Dr. Spec

Are these Burdette's finished FR numbers? Is this a house curve or ground plane or WinISD - I'm a little confused. I thought he only test fired it.

burdette

Not mine.. he must've picked those up somewhere else.. hence the comments about not knowing the tune, etc. I ended up with about 142-144 liters of usable volume, tuned to 18.1Hz, 19" long port (including the flared ends).

I got the batting glued into the tube last night. I'm at that stage where I'm ready to glue the tube to the top and bottom... but need a day or two to think it through and make sure I've not forgotten anything... plus my wife and kids are home again after a 10 day visit to inlaws.. so I'm not quite able to keep up the construction frenzy I was on last week.

tryrrthg

Lookin good! all this subwoofer talk is KILLING me! I want to build a Stryke sub SO BAD IT HURTS! I need mine for music so I was thinking a low Q sealed sub. Sure wish I could afford it!

Dr. Spec

Will you be using full length end cap compression threaded rod studs like Ron-P did? Or just glue, or glue/screws?

burdette

Nope, no uh.. compression threaded steel .. um, whatever you said.

The top has two layers of 5/8" MDF glued together that slide down in the tube (one is solid except for a hole for the port, one is a 2" 'ring'); on top of that is a 3/4" piece of plywood that is routed so half slides in the tube, half caps it. Topped off with another piece of finished AC plywood that will hold the port (same wood/stain as the base in the first photo). That gives me about an inch and a half of solid support going down in the tube.
The bottom (if you can't tell from the photos) has two layers of 5/8" MDF that slide into the tube, one with a driver cutout, the other a 1" 'ring'... so I've got about 1.25" there. I'm going to glue with an expanding glue and probably use some finish nails.

The base will come off by removing 4 screws, and the driver is mounted with 8 bolts and hurricane nuts, so it'll come out if it ever has to. I don't see any reason to have to get back into this thing if it is built correctly, and I am saving another piece of tube in case I ever decide to do a different design or tear this thing apart.

Actually, I'd already decided that if I was going to use some sort of additional support for the endcaps (like the rods you mentioned), they would be OUTSIDE the tube.. probably 3 or 4 wooden rods - spaced evenly around the tube - running from the top to the baffle board, stained to match the rest of the wood. If I get this thing done and I blow the top off... I suppose I'll add the rods.

Thanks for the comments on the craftsmanship. I really put a lot of prep time in on this project - both thinking through the design AND making sure I took my time when executing. I was quite happy that that entire amp box - while as solid as a tank - has only 4 visible nail holes, and those are on the back .. the rest of the assembly hardware is hidden.

My only real boo boo so far is visible in the photos... when I drilled the holes to mount the input terminal, I misjudged how much room I had and drilled right out the top of the board (you can see the nick on the black board over the input). Got that repaired... and then went to mount the input terminal and miscalculated AGAIN and didn't cut enough off the screw and popped right out the same damn hole I'd repaired. Haven't had a chance to work on it since, which is why it is so visible in the photo (plus digital photos seem extremely honest.. harsh almost). Fortunately, that nick will be sort of hidden behind the short speaker wire jumper. And if that is my worst boo boo... I mean, I've had visions of putting a screwdriver through the surround or something.

Dr. Spec

"I mean, I've had visions of putting a screwdriver through the surround or something."


That may yet happen - don't jinx yourself.

Sounds like it will be solid, regardless. That description was probably overly engineerese. Ron just used two threaded rods that run the length of the enclosure and pass through the endcaps and are secured with large washers and nuts. Might not be pretty but it sure is strong and rigid. If you use the right glue and vent it properly, I highly doubt you will "blow the end caps off". It's funny to think about, though. Again - GREAT work thus far.

Doc

burdette

Originally posted by Dr. Spec
That description was probably overly engineerese.

That would make sense given that 1) I are an engineer, at least by training if not profession... and 2) I make my living via analysis and legal technical writing. That is why my writing is usually 'complete' (i.e. long) and sentences cannot be taken two ways.

Originally posted by Dr. Spec
Ron just used two threaded rods that run the length of the enclosure and pass through the endcaps and are secured with large washers and nuts. Might not be pretty but it sure is strong and rigid. If you use the right glue and vent it properly, I highly doubt you will "blow the end caps off".
Doc

I found examples of sonosubs that used the rods.. others glued. Part of my goal was to purchase as little material as possible. I'd already had to pay $30 for 12' of tube when all I wanted was 4'. I agree that glue should work fine.. and if it doesn't, it'll take me about an hour to configure the 'rods' on the outside, as I'd mentioned. Plus, they would be aethetically interesting.

goingganzo

there is a thread over at the htf and a fellow with a av12 posted thoes # he was at 12 feet away. and dident say if it was rs corected or un corected.

i used my power drill with a screw guide to install the screws in my sub.

worked great but hen i was using the 2 in screws i kept snaping the heads off the screws. i went to a 1 1/2 screw and dident snap any more.

burdette

Are you drilling pilot holes? If not, do... if so, bump up a size on your drill bit and consider going just a little deeper. You just need to be able to see the threads a little on both sides if you hold the bit up in front of the screw - especially in MDF, you get hardly any compression.

I've got most of a very nice carbide 3/16" drill bit embedded in the two inches of MDF of the baffle. I had one hole I couldn't reach with the drill press.. used a cordless drill, tipped it a bit and snapped it right off. That is why the hole in one of the legs is off center - I had to move the screw over to avoid the bit. I know the credo of The Tools is "never leave a man behind"... but there was no way I could dig that bit out... RIP.

Dr. Spec

Originally posted by burdette
I know the credo of The Tools is "never leave a man behind"... but there was no way I could dig that bit out... RIP.

Seems like I'm not the only engineer around here with a sense of humor.

burdette

Based on what is in my "return to PE" box, I've answered my own question already, but thought I'd go ahead and throw it out there... I purchased a 6" speaker grill from PE to use on my port. It came with a rubber gasket that very nicely fit over the edge of the port - almost looked made for each other.

BUT... looking through the port from the bottom ... I came to the conclusion that the metal of the grill had to be 1) effectively reducing the port area... I'd say maybe 20-25%; and 2) obviously interfering with air flow.. neither of which are good.

Here is the grill:
http://www.partsexpress.com/pe/showdetl.cfm?&User_ID=12165972&St=2156&St2=37604807&St3=36960014&DS_ID=3&Product_ID=5722&DID=7

Does that sound reasonable to you... that a grill of this type (wide metal strips) would restrict air flow to the extent of effectively reducing the port area?

ALSO... have to ask this question again because I just today saw yet another reference to this.. opposite of what I thought... some guy on the HTF said that using flared ends *reduces* the length of port required. I've read that in other places, but thought someone here (Doc?) said that flaring actually requires a longer port (and I think the port-length forumulas I've seen support that). Just curious.

ALso.. anyone heard that WinISD incorrectly calculates port mach?

goingganzo

yes you must add a in to a flaired port to get the corect tune.
i dont know about the win isd thing but the alfa is a bit beter i hope. my sub sounds great and i have not herd any noise what so ever from my ports. aka bad noise.

burdette

Here is the *almost* finished sub, in the location that I hope to leave it. Yes, it is officially being held together with a 30lb bench grinder (gluing the tube to the ends is my only remaining step); it is not on the wooden base; and, the amp is sitting on the floor rather than on its perch.

The tube is spray painted ... I essentially emptied our paint shelf of any old cans of paint.. ended up with brown and a little flat black over that. The point was to hide the writing and break up any light that gets through an eventual cloth cover... but even if it doesn't look like it in the photo it came out looking pretty good.

Even not glued together, the sub sounds good. I'm not pushing it very hard, but I get the idea.... I'll tell you what caught me off guard (just because it wasn't something I was going for) is how much better these Monitor 7Cs sound. I mean, honestly.. I've been financially able to replace these speakers for quite a few years, and the thought has never really crossed my mind... they are just... so.. nice.... Anyway.. I loved the Polk midrange before, but relieved of the baggage below 80 Hz has really freed these 6502s up.... acoustic guitars sound tighter, etc.

Edit: Yes, there are meeces on top of my speaker. The HT room was a billiards room before we sold the table (which is why the walls are painted the same color as the 6 ball). The mouses are playing pool; it is a music box from SF Music Box. Ahhh... the union of audio-as-hobby and fatherhood (the box was a 'gift' from my daughter when she was 3 and she liked to play pool).

goingganzo

looking good. i would install the top first so you can cauck the tube. or are you going to cauck?

burdette

The port can be dropped down in from the top. I don't think I'm going to use caulk, but I'm going to put *something* around the edge on top... either the high density weather-strip foam or I'm toying with the idea of using plumbers putty. Then I'll secure the port on the top with a couple of clips. The tube is also wrapped in batting which stuffs nicely into the batting attached to the inside of the top plate.

I think there is a good chance we're going go skip the cloth sock, unless my wife is especially keen on making it. We don't *need* it. I may also abandon the tube in the photo and use my backup... I'm not too happy with the way the batting is attached on this one.

Dr. Spec

Looks great! Nice job. Pretty noticeable difference for you on small vs. large?

Here is the equation for port length. The flanged end affects the "k" value as described below.

This factor is a part of a negative component in the denominator. So increasing "k" increases the size of the negative component, thereby making the overall denominator value smaller. A smaller denominator results in a larger value in any algebraic equation. So yes, adding flared ends will result in a longer port length in this equation.

Port Length
The port length required to tune a volume of air to a specific frequency can be calculated by using the following equation:

Lv = (23562.5*Dv^2*Np/(Fb^2*Vb))-(k*Dv)

where,

Dv = port diameter (cm)
Fb = tuning frequency (Hz)
Vb = net volume (litres)
Lv = length of each port (cm)
Np = number of ports
k = end correction (normally 0.732)

[port.gif (1467 bytes)]

The value for k, the end correction, can be fine-tuned by using the following values to derive the appropriate end correction figure for each end of the port, then adding them together

Flanged End: 0.425
Free End: 0.307

e.g. if both ends were flanged,
k = 0.425 + 0.425 = 0.850

if one flanged, one free,
k = 0.425 + 0.307 = 0.732

if both ends were free,
k = 0.307 + 0.307 = 0.614

Normally, k=0.732 is assumed

In practice, it's best to use ports that are slightly longer than predicted by the above equations, then adjust their length until the correct tuning is achieved. It is much easier to shorten a port than to lengthen it!

burdette

Yes, that information (equation and k values) is exactly what I have and have used in Excel. Given that I am unsure of *exactly* my internal volume, I sort of averaged. WinISD was giving me a port length of anywhere from 16+ to 17+ inches, depending on 142 vs. 144 liters, and depending on tune.. 18 vs. 18.1, etc. I included consideration of the volume taken up by the end caps, the port and the driver... and those could be off a half liter here, a quarter liter there, plus or minus.

So, I used a 19" port, including the flared ends. I figured that at most I'd add an inch for each flare, so I'm in the ballpark of what WinISD and the equation were giving me.

Frankly.. unless it sounds SO bad as to just slap me in the face, or I get port noise, I'll never have the equipment or resources to "fine" tune this anyway. And, given the level to which I sweated the design and didn't fudge volume or cut corners, etc, I think I'm well ahead of the game on many commercial subs (in the $400-$800 range), which I think tend to be under volumed and under ported.

What are your thoughts on the grill, Doc? The decision is made.. it is going back... and I think I am on solid ground as far as its potential negative effects (plus it saves me a little money). I suppose what I know for certain is that if I don't use a grill, I can't possibily have problems associated with a grill... So, I played it safe and I shot Bond in the head rather than leaving him tied to a table with a laser closing in on his nuts and me hoping he dies.

Dr. Spec

Yep, deep six the grill if no one will drop stuff down the port - that's the only drawback to not using one.

Get that bugger glued up and run a sweep!

RuSsMaN

Originally posted by Dr. Spec
Yep, deep six the grill if no one will drop stuff down the port - that's the only drawback to not using one.

Would it *really* matter if something did get dropped in? That Stryke could damn near blow it right back out.

Cheers,
Rooster

Christ, now I'm having visions of ports setup like a diesel stack on a rig, clank clank clank....