Austin 166MKII build, new builder questions.

[cwujek]

Hello, I am new to home built speakers, so sorry for the basic novice questions. I searched through the forum and found the answers to most of my questions, but I have a few more. First off, I am building a Austin 166 with a Fostex FE166E driver. I have access to a full woodworking shop, so tools shouldn't be a problem. I am looking off the 6 page PDF on the frugel-horn webpage. Now, for the questions:

1.) In the notes section, it mentioned that there is a two inch extension around the perimeter of the supra baffle, facing backwards. I'm having a hard time understanding what this means, as it doesn't look like the speaker on the left in the photo has that. Maybe I'm thinking about it wrong?? In the picture, it looks like it was just glued flush to the front of the main cabinet. But it sounds like there should also be a a section that is behind the front plane of the cabinet, instead of everything in front of the plane. Unless the extension around the perimeter simply mean an 1.7 inch extension outwards....Sorry if I made this really confusing, I'm just not quite sure.....

2.) Note number two mentions an error in the second horn turn, please see my attachment to make sure I got this right.

3.) Some of the rear deflectors I have seen in pictures are flat on top, some are angled upwards. Is this a big deal at all, or am I just nitpicking things.....

4.) I am going to build the rear deflector separate, and was wondering about the best method of doing this. I was thinking of having the bottom of the speaker extend backwards, which small dowel stubs sticking up from this extension. The bottom of the deflector would have holes these dowels would fit in (this way, if I have to move them, I can make them somewhat portable). Think there could be any problems with this?

Thanks, any other general comments welcome, I am quite excited to build my first speaker cabinet!

[ronc]

If you mass load the deflector the extension and dowels are not required. By mass loading i am referring to filling with sand or kitty litter. The 45 degree slope upwards helps the horn initial wave form develop, in reactance with the angled rear of the cab it forms a type of waveguide and allows a bit of further controlled wave expansion, this allows a rear firing horn to become more akin to a front/side firing horn and helps the exiting pulse from re-entering the mouth. Its an option. What you are looking at is not a thick baffle, but a 2-3 layer (.7"T/layer) with trailing extensions.
The suprabaffle (name coined by Dave) extensions are simple extensions glued onto the back of the baffle which allow the wave travelling over the surface to end up at an edge rearward so the edge diffraction is not broadcast forward.
The original dwgs were lost in a puter crash (windows) but several in various forums have built the A166, so perhaps they can chime in.

ron

[seanzozo]

Originally posted by cwujek

1.) In the notes section, it mentioned that there is a two inch extension around the perimeter of the supra baffle, facing backwards.

2.) Note number two mentions an error in the second horn turn, please see my attachment to make sure I got this right.

3.) Some of the rear deflectors I have seen in pictures are flat on top

4.) I am going to build the rear deflector separate

Thanks, any other general comments welcome, I am quite excited to build my first speaker cabinet!

1) Cut 2 inch wide strips of birch 12.72 inches long, miter the ends and attach along the back perimeter of the Suprabaffle. Does that clarify?

2) looks correct to me

3) I use sand-loaded boxes I had around that are flat on top - law school has kefp me out of the woodshed - the beveled top is theoretically superior

4) Provided it is mass-loaded you can make them as seperate pieces. You don't even need to extend the bottom base backwards (though make sure to extend it slightly forward for stability).


Sean

[ronc]

Gee Sean.....Law school? Sorry, i am letting my experiences from the past loose.

ron


(ron sees sean in a court room trying to sue him for someone turning up a horn that he designed and now is deaf)

[cwujek]

Thanks for the answers, thats just what I needed. More questions:

1.) With something as sensitive as a horn, where should the speaker binding posts be located? I was just thinking of getting THESE , but I just don't know where I should mount them. I'm just going to use a pair of individual CAT5 cable strands on the inside too btw. Should I maybe consider getting a binding post plate instead of mounting directly to the wood? I attached a picture of a side view of the cabinet for reference. I was thinking that right where the number 7 is would be good, and I would route the wire through the horn up to that point.....

2.) On many fullrange designs, the front vertical panel (baffle) is usually the same width as all the interior boards, and the side panels surround all the inner panels. I noticed on this design, the baffle actually extends the full width of the cabinet. Was this for any specific reason? Any harm in doing it the conventional way with the front panel the same width as the interior panels, with the sides securing them?

Thanks again for all the help, I went down to a nice hardwood store and found some good American voidless baltic birch in 5x5 sheets for $54 a sheet....I should be able to build the whole thing using two sheets, I'll keep you posted with progress! Thanks again,

Chris

[seanzozo]

Originally posted by cwujek
Thanks for the answers, thats just what I needed. More questions:

1.) With something as sensitive as a horn, where should the speaker binding posts be located?

2.) On many fullrange designs, the front vertical panel (baffle) is usually the same width as all the interior boards, and the side panels surround all the inner panels.

1) I used these: http://www.partsexpress.com/pe/showd...umber=091-1247
and mounted them through panel 2 at the top with single strand cat5, it gives direct access to the driver and is hidden by the Supra-baffle. I wanted to go through panel 4+7 but couldnt find posts long enough. Routing through the horn should be fine too.

2) I did it the way it is indicated on the sheets - they way you describe should be fine. I can think of no reason is should be significantly different. If I did it again I might miter that join for looks

Can't wait to see another pair, I think it's one of the best designed back-horns out there. At some point I hope to do a pair of the layertone Austin's.

Sean

[serenechaos]

1) I'm still using cat 5 soldered to the drivers, and running clear throught the mouth of the horn to the amp...
Minimalist to the max.
I was thinking of putting the terminals in the bottom of 5 though, and hoping the wires would make the bend around 3 and back up to the drivers.

I had thought of putting the terminals on the top, but I'm glad I didn't. This weekend I was using a Heil AMT as a super tweeter, crossed in ~ 10k. Just set on top of the Austin 166, worked great.
Robert

[cwujek]

Originally posted by serenechaos
1) I'm still using cat 5 soldered to the drivers, and running clear throught the mouth of the horn to the amp...
Minimalist to the max.
I was thinking of putting the terminals in the bottom of 5 though, and hoping the wires would make the bend around 3 and back up to the drivers.

I had thought of putting the terminals on the top, but I'm glad I didn't. This weekend I was using a Heil AMT as a super tweeter, crossed in ~ 10k. Just set on top of the Austin 166, worked great.
Robert

Ah, good point. I want to leave the option open to add tweeters down the road. How did you like using the tweeter with the Austins? I was thinking of buying a pair of Fostex T90 super tweeters, but I'm going to build the speakers stock first, than see from there.

I think I figured out where the binding posts will be. Since the posts will not fit all the way through both 7 and 4, I will just go through the top of seven, and then drill two small holes in 4 for the speakers and the end of the posts to fit through. I will then fill the holes in 4 with some form of expanding glue (probably gorilla glue) to fill and space between the two.

I have started to trace out a cut sheet to begin building the cabinets. What is the measurement of the distance in my attachment? I will need that measurement to do the sides, and I wasn't sure exactly what it should be. Which brings me to my final question: How important is accuracy in these builds? I know that I will try to get the measurements as exact as possible, but can you REALLY build this down to 1/100th of an inch specs? Thanks again for all the great help, it has really helped me out,

Chris

[serenechaos]

Originally posted by cwujek
How did you like using the tweeter with the Austins?

How important is accuracy in these builds? I know that I will try to get the measurements as exact as possible, but can you REALLY build this down to 1/100th of an inch specs?

I liked what the tweeter added to the highs, but not something else added... Probably need to get better caps, I was just playing around with what I had. Maybe oil caps or teflons would help?

I don't know how important accuracy is, but since dimensions were specified that definitively, I tried to be at least that accurate in following the ‘print. I’m a prototype machinist by day, and I guess it’s habit…

[planet10]

We like using the binding posts with less metal in them...

our favorites (half-way down the page)

http://www.partsconnexion.com/catalog/connectors.html



We found mounting them on panel 8 was a good place.

dave