Curved Small Thor Build

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Firstly I want to thank EVERYONE who has contributed their time and MEGA brainpower to make the Thor a competent platform.

I am building a curved small Thor gleaned from the hard work of many contributors. I have attached a few pictures of my progress.

Question(s) to those with experience in such things;

1) Is it necessary to compensate for the lost interior cabinet volume due to the semi curved back side? If so, can I increase the cabinet depth by adding another front baffle with the appropriate amount of material removed to equal the lost interior volume? (similar to cutting "H" braces) it's ~141 cu. inches

2) Should I add additional weight to the cabinet? What is the purpose of additional weight? Prevent speaker roaming? Ala Subwoofers?

3) I've called the owner of Piano-Lac and he no longer sells to us DIY'ers unless a commercial address is available for shipping. He stated he had a problem with liability issues. I don't know anyone with a commercial address where he can ship to COD. Any Ideas?

4) Any problems with rubber feet on the bottom of the cabinets instead of spikes? I have laminate floors on a raised foundation.

Man, That MDF makes a mess! :hot:

Thanks for your help.
Ron
 

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Some more pics of progress

Strappin' down those wild beasties....ummm no.
As expected I made a mistake here in this photo. Yep. It's not placing the straps directly over the internal bracing. Caused the cabinet sides to warp!:eek: I was able to correct this faux-pas by cutting spacer blocks 3/16 wider than the internal diameter and forcing (spreading) the sides apart. Learning as we go.

I have 2 layers of 3/8 bendy ply on the cabinets now and used copious amounts of gue on both sides of the lay-up. Shot the ply down with 1" pin nails ... a little long but will not bother anything down the road. The bendy ply was a touch on the rough side (looks like resawn lumber) so I am adding a 1/8" skin on top of the existing plywood sides. The 1/8 ply is also bendy ply buy has a VERY smooth exterior to mate with the cherry veneer that will 'Purdy -em up. I'll post more pics again when I complete the next stage(s).
Ron
 

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More pics

A knot in the verticle spine caused a slight bend in the cabinet shape near the top, this was cured by relieving some tension on the inside of the bend. This method works well, and straightened it out overnight. Wood is not ever perfect. So we do our best.

Ron
 

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Renron,

Looking good!

For your finish you might want to look into CrystaLac. They have a gloss & satin black system. I have not tried their black system, their gloss clear poly is very nice. Builds quickly, mistakes rework well, and the gloss is simply up to how much wet sand/polishing time you want to invest.

Mail order source:
http://www.mcfeelys.com/subcat.asp?sid=42

The CrystaLac system coms in both brushable and spray on types. The black system appears to be spray on only. Of course regardless of what you settle on some expermenting on something you have less time in is called for.
 
Thanks Norm,

I buy screws from McFeeleys' all the time, as I am a General Contractor and do a lot of repairs. I love their square drive cabinet screws, haven't broken one yet with my 18V Bosch !

Thanks for the Crystal Lac comments, I will either use that or Piano Lac. Any preference? Info?

Dave, where's my mail? :bawling:
I'm Sro Roanry (in Kim Jon Ill's best voice) :D

Dave, I cannot thank you enough for the hours and hours you have spent developing my project.:worship:
QWTL are cool. A local speaker designer who has been doing this for >30 years owns a very HI-end home theater business has let me pick his brain and has offered to let me try out my speakers (when completed) on his many many systems. Wahoo!

Any input is extremely welcome and appreciated.

Thanks, thanks,
Ron
 
frugal-phile™
Joined 2001
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Renron said:
Dave, where's my mail? :bawling:

Was i supposed to mail you? Have i got an unansered email in my inbox? (the comment a couple posts up was for Norm)

I cannot thank you enough for the hours and hours you have spent developing my project

Something bothered me about Thor since i 1st read the original article... this thread -- and the info generated for it -- validates my gut feeling. If it hadn't been for that gut feeling, i likely would have never gotten involved, because Thor is not something i'd likely ever build.

Now if we could get the time to write the aXp article "Revisiting the Thor" we could generate a nice donation to the forum. I have a start (which JackinNJ also has). And we'll need pictures & measures.

dave
 
Hello

I am curious about your Thor build, as I have always admired this design, and would love to build one if I could find an excuse.

I thought that the Thor was a transmission line design though?

If you are asking questions about maintaining internal volume in a bass reflex or sealed cabinet, this is worrying. If you are asking the same question with regard to a transmission line, have you missed the whole point? In a transmission line the cross-sectional area of the line is crucial and needs to match the design. You can change the shape of the cabinets as much as you like (baffles may need correction), but at the end of the day the cross-sectional area of the line needs to increase/decrease along the line according to the designers specification.

Have I missed something?
 
Well, the Short Thor box Dave and I designed is not a Bass Reflex cabinet. It's a Mass Loaded Quarter Wave Resonator (Or Mass Loaded Transmission Line). Having said that, yup, cross section needs to be maintained as per the design; MLTLs are no different to other boxes in this respect.

The original Thor is an odd one -seemingly designed as a hybrid line, but because of the nature of the construction / drivers etc it can run into problems, particularly in terms of LF extension.
 
Dublin,
My reason for asking earlier about cabinet volume is because I read (somewhere...can't remember exactly where now) that 5%or less cabinet volume would not affect the way the drivers perform, as they are probably out of spec (with each other) by that amount or more. The speaker design is not sealed or bass reflex and I have kept the baffle cross-section area and size the same. I have kept the volume (as best as I could) to within 5% or less of the specs provided by Mr. Moose. The crossovers will be build to stock specs but with HI-End components, better than the parts used on the upgraded Xovers offered by Madisound / PE. In the end I hope they sound better than the original design by Joe D'Appolito.

Mr. Moose....
I hold you personally responsible for my intrest in the "Thor" project....well, you and Dave. :worship:
Your efforts are appreciated, especially by those of us who have taken on the construction of these wonderful speakers.
I have modified the cabinet to resemble the Volent floor standers as they have been approved by the highest power in the house....WAF. ;)
Cabinet volume was recovered by extending the rear of the cabinet 3/4" and not including some of the bracing in your original drawings of the "Small Thor". Hence my earlier photos of "Swiss Cheese". Bracing is accomplished by 5 ribs horizontally and 3 verticle "spines", the front baffle will aid in stablizing (sp?) the front between the ribs, the main spine contacts the rear wall as well as the rear of the front baffle, I will post picts.
If you see something I'm doing wrong please speak up.

Thank everyone for their intrest and input.
Ron
 
Oh yes. LF will not be a problem :devilr: Seriosuly though, extension, but no boom -I shaped the FR to roll off in step with average room gain. Expect grunt to the low 20Hz region from Short Thor providing the room supports frequencies that low. Re the difference between MLTLs and BRs, I've covered this a few times in other threads, but briefly:

An MLTL (or MLQWR to be more accurate) is a straight QWR. By restricting the area of the terminus by means of a port, you create an air-mass which resistively loads the quarter-wavelength resonances generated by the line. This does several things, the most significant of these being a) it lowers the fundamental resonance of the cabinet, and b) reduces ripple in the passband. There's more to it than that of course: for a full-dose of theory, go to my friend Martin King's site: www.quarter-wave.com and have a read of his white papers and projects. You'll find the documentation of his Project 2 ML TQWT particularly useful. Also, Bob Brines has some useful articles on his site: http://www.geocities.com/rbrines1/

Hope that helps
Scott
 
frugal-phile™
Joined 2001
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dublin78 said:
Hello
You can change the shape of the cabinets as much as you like (baffles may need correction), but at the end of the day the cross-sectional area of the line needs to increase/decrease along the line according to the designers specification.


And that is the problem with original Thor... the cab was designed using Augspurger's (scanty) alignment tables and then the cross-section was arbitrarily reduced by a 3rd which ended up giving a (properly) measured response only down to ~100 Hz.

dave
 
Another layer Another step closer

I purchased 1/8" bendy ply for the last layer as a base to adhere the cherry veneer. While scrounging around the mess I call my garage I came upon a roll of 1/16" bitumen, which in the trades we call Bitchathane. If you have ever tried working with this stuff in hot weather you know how it got it's name.:xeye: This particular version is sticky on one side only (some are both), so I tested a section to see how it would react to contact cement. I applied a thin layer to the non-sticky side and a thin layer to a scrap piece of wood I had just layin' around. After they both dried completely I clamped them together on my workbench. I came back and tested the adheasion about 15 minuites later. Oops. I should have put paper underneath the Bitchathane. I tore a layer of wood off the Bitchathane seperating the two and then spent the next 5 minuites with acetone removing the sticky tar mess that was stuck to my workbench! Well, at least I have a good seal. :)
It was 81* here yesterday, so I let the speakers sit in the sun after applying the Bitchathane and then gave them a good rub down with a scrap wooden block to ensure complete contact with the previous 2 layers of 3/8ths plywood. Man...that's some nasty stuff. I applied a healthy layer of contact cement on both the Bitchathane and the backside of the 1/8th bendy ply and let them dry. With the help of my neighbor we attached the smooth bendy ply over the Bitchathane and again pressed it down with a scrap block of wood to ensure reliable contact over the entire surface. At one point I (foolishly) attempted to remove the ply, only to crack it about 6" up, it was stuck back down with no problems again. OK, I guess everyone has to learn this lesson.......once.
I strapped the cabinets just for good measure and shot the 1/8 bendy with 5/8 pin nails just cause thats how I am. Overkill is my friend.
I have attached a couple of pics just to show progress. I must say that for only a 1/16th layer of Bitchathane the cabinets sound has changed to a thwump instead of a knock when struck with knuckles, I am impressed with the difference. Baffle width is now Exactly 9".
Ron
 

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