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Old 16th February 2015, 02:24 AM   #1
lanetim is offline lanetim  United States
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Default Curved Small Thor Redux

Hi Everyone!

Like several folks who have posted on DIYAudio, I decided to build a pair of the Joe D’Appolito Thor speakers years ago when the AudioXpress article came out, in May 2002. While the drivers weren’t inexpensive, the reputation of the designer and the well-written article seemed to make it a safe bet (if interested see the original article, courtesy Madisound’s website: http://www.madisound.com/loudspeaker...r%20Review.pdf).

Unfortunately I wasn’t all that happy with the speaker when I finished the project. I found it to be lean and dry in the bass, though the midrange and treble were pretty good. Wasn’t quite up to the glowing review in AudioXpress, though, which was disappointing to say the least.

So having invested in the SEAS drivers, I decided to build the Odin version, thinking the problem could be with the transmission line. My hope was a more conventional base reflex design would be an improvement. With a smaller speaker, I would be able to supplement bass response with a sub if bass quality and extension still fell short. And indeed, I did find the Odin’s to have better quality bass, though still on the lean side.

So then I built a pair of 10” subwoofers, w/10” passive radiators, exactly the same external size as the Odins, stacking the Odins on top the subs. As you might imagine that’s not such an easy trick to pull off, so while it worked I subsequently put the Odin’s on stands and moved the subs to the sidewalls. This turned out to be a pretty good setup, with the ability to dial in bass extension via the subs by modifying the low pass filter point and volume control in my electronic crossover.

More recently last year I retired and moved to Oregon, and built a house which has a dedicated listening room, designed to the Golden Ratio. (This new room is wonderful and if you ever have the luck to build a dedicated listening/media room, be sure and use Golden Ratio proportions).

In an effort to get even better bass and balance in my system, I decided to look around for a new speaker project, and began searching on DIYAudio – and low and behold, found out there were others who had the same problems I’d had with the original Thor design! So thanks to all the great threads and shared work by Scottmoose, Planet10, Renron and others (thanks tons, guys!!), I became inspired to go for another Thor build.

My design goals are:

1) The new speaker has to be esthetically pleasing! Design and quality of the woodworking are very important.
2) The furniture in my new listening room sits folks on the low side, so I didn’t want the speaker to be any higher than 50".
3) I also wanted a tower concept, so the small Thor is about right. I would be retaining my subwoofers so the ability to dial in supplemental deep bass would not be a problem.
4) My current speakers sit 28-30” from the back wall, and ~38” from the sidewalls of my media room. I wanted to keep the same positioning, more or less.

I’ve always found curved speakers visually appealing, so I decided to follow in Renron’s footsteps and build a curved version of the Small Thor. Thanks to his excellent thread and pictures, I spent several months thinking through the construction details and drafted up this version of what Ron did, attached. Thanks for the inspiration, Ron!


I solicited help during the design phase from Planet10 and got lots of great suggestions and feedback – thanks again for all your comments, Dave!!

One design issue was where to put the crossover. I originally though about putting them in a box on the back of the speaker, but going with a curved design is problematic, the back is not wide enough and it is hard to make that esthetically pleasing. If I put in a false base or false top I’d have to raise the speaker another 3+”, which would make it too tall.

One obvious solution is to put them in a box on my equipment stand and run the driver wires to the speaker, but I’d really rather have them inside the speaker to reduce clutter – my equipment stand is already overloaded. So I made provision to mount them on the inside front baffle, but plan to test if this makes a difference by performing listening tests with the xovers both in and out of the speaker, running the wires through the port for the external test.

The other main issue was where to put the port, since in this design it could be out the front, the bottom or the back. The front was eliminated because I needed access to the crossover mount point. Down-firing out the bottom would require lifting the speaker higher, and I didn’t want to do that – so the practical solution was to go with a rear firing port. My speakers will be positioned well away from the back and side-walls, so hopefully excessive boomy bass will not be a problem.

In order to understand how much room I needed for the crossover, I decided to build it first. In researching the numerous Thor threads, jimangie1973 has spent a lot of time and effort redesigning and tweaking his crossover design. Jim is clearly another hero in the efforts to improve on the original D’Appolito design. Attached is Jim’s last and final? design.

According to Jim in a PM, the latest crossover “…has slopes closest to LR4. The added RLC on tweeter is there to counter the tweeter resonance impedance spike to keep the response LR4. Without, there is less attenuation around the resonance. Power handling is improved as a result of the added attenuation.” Jim will hopefully comment further on this post.


“The earlier designs had slightly too much baffle step compensation. The result was over time I perceived the sound as slightly bass heavy. This is the main change in the woofer section.”

Here are some pics of my crossover – I built it using ” phenolic board, and routed out depressions for the caps and inductors, which were subsequently mounted on thin rubber sheet glued in with RTV and held in place with cable-ties.

Enough for now - more later - your comments welcome! ;~)
Attached Images
File Type: jpg xover1.jpg (792.9 KB, 437 views)
File Type: jpg xover2.jpg (932.6 KB, 425 views)
File Type: jpg xover3.jpg (526.9 KB, 406 views)
Attached Files
File Type: pdf Thor Xover.pdf (317.4 KB, 24 views)
File Type: pdf CurvedThorPlan.pdf (281.0 KB, 44 views)
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Old 17th February 2015, 01:50 AM   #2
lanetim is offline lanetim  United States
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Having previously used MDF for speaker projects, I'm making the switch to baltic birch for the front, back, and internal braces after researching materials on the forum. I've got to say it is a lot nicer to work with than MDF. The exterior will be finished in cherry, and I'm cutting my own veneers on the bandsaw. The front baffle will have 1/8" cherry laminated to 3/4" & 1/2" BB. The edges of the baffles are trimmed with 1"x1" cherry, which will have a 1" roundover applied once the internal braces and ribs have been fitted.

The back is built up to 1" thickness. The sides will be 5mm bendy plywood, supported by ribs rabbeted into the internal braces, and will also be built up to 1" thickness by laminating multiple sheets, ending with 3/32" cherry veneers with the grain laying horizontally.

This pic shows one of the front baffles after machining the driver cutouts, with the back prior to cutting the port etc.
speaker1.jpg

These show the beginning construction of the internal braces. On the back of the front baffle is a recess fitted for the crossover - will show a detailed pic of that later.
speaker4.jpgspeaker-2.jpg
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Old 17th February 2015, 02:02 AM   #3
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Quote:
Originally Posted by lanetim View Post
... switch to baltic birch... I've got to say it is a lot nicer to work with than MDF.
And it should sound better

dave
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Old 19th February 2015, 03:45 AM   #4
lanetim is offline lanetim  United States
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Progress pics. The back of the front baffle:

BaffleBack.jpg

The internal braces have been 'swiss-cheesed' and other support pieces and the ribs are being fitted in. The support pieces and ribs all slide into the rabbets. My dog Duke closely supervises all steps.

InternalBottomRight.jpg InternalFrontRight.jpg

These are the ribs - they slide into the dado joints, and once glued in place will hopefully form strong null points, providing additional bracing of the side panels to the internal structure.

Ribs.jpg

A pic of the jig I used to make the curved sections. Very simple, used 1/16" drill bits to scribe the curve into the wood.

Jig.jpg

Still need more sanding and fitting of individual parts. Next step is fitting the back, installing the port tubes and the binding post plates. Should be able to start gluing parts together this weekend.
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Old 24th February 2015, 01:00 AM   #5
lanetim is offline lanetim  United States
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Here's a pic of the Odins the new speaker is destined to replace. One of the subwoofers is in the background.
Odins.jpg
The front baffles after rounding the edges with a 1" round-over bit. Just rough sanding at this point.
frontbaffles.jpg
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Old 24th February 2015, 05:47 PM   #6
lanetim is offline lanetim  United States
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Default Top Design - opinions needed!

One speaker design I really admire is the Sonus Faber amati futura. They are an Italian work of art, and at $36k not cheap! Their base design is a complex form of what I'm planning for my speaker, also used by a lot of manufacturers:
SFTop-2.jpg

My plan is to use a modified version of this - here is a draft top view. I've found a metal worker in town who can transform my drawing into a CNC milled 1/4" powder coated steel plate (maybe brushed stainless?), from which I can mount my Parts Express cone footers. The plate would be easily attached using threaded brass insets, placed into the baltic birch bottom or side panels; screw bolts hidden underneath the speaker.
Base.jpg


Now I'm wrestling with how to finish off the top. I was going to finish it with a milled piece of solid cherry, but I'm attracted to using a steel or non-ferrous 1/4" plate. The simplest way to attach this would be to epoxy it into place on the top of the baltic birch - a permanent way to go with no room for error. Alternatively the steel plate could be mounted on a thin piece of cherry to provide a more layered finish. Here's a pic of the amati futura top:

SFTop.jpg

Any opinions?
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File Type: pdf base.pdf (98.2 KB, 6 views)
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Old 25th February 2015, 04:10 PM   #7
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Ideally, relatively lightweight [< ~40 lbs] speakers need to be mass loaded to the floor, so I used thick marble, slate tops held on with industrial grade Velcro because at the time it was cheap and later either used metal or Portland cement tops as a base under the finished top and/or recommended placing a large/heavy potted plant on top. Smoked tempered glass was real popular back then because speakers tended to do double duty as a place to put drinks, ashtrays, food. Looks good too or use clear to add that super depth to a wood/whatever finish.

How much weight required depended on at what point I heard the speaker 'tighten up', for lack of a better description and any more tended to 'dull' its 'tone'. Never did any comparisons, but this assumes that the driver[s] are mass loaded to the speaker as opposed to just baffle mounting them.

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Old 25th February 2015, 09:14 PM   #8
lanetim is offline lanetim  United States
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Thanks for your thoughts - BB does have a much lower density than MDF, so these speakers will likely finish in around 40-50 lbs, I guess. I hadn't thought too much about the mass loading issue, but a steel top would help.

From the Sonus Faber's website the Amati Futura has "a Tuned Mass Damper, with multiple tuning frequencies, like on record skyscrapers and F1 cars converts the residual vibrations into heat (thermkinetics) by out-of-phase vibrations."
MassDamper.jpg
Looks like it is in a sealed compartment in the top of the speaker - very interesting idea. Looks like they use BB or similar in construction of their cabinet frame.

Perhaps adding more mass than 1/4" of steel plate on top would be a good idea?
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Old 27th February 2015, 04:22 AM   #9
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Yeah, if I can easily lift it, it's probably too light, well, when I was younger anyway.

Regardless, at least when using 3/4" BB, apple, marine plywood or seasoned hardwood, there's a point where more weight is too much with relatively small speakers, so no set weight. For large cabs like my ~20 ft^3 mains, they still sound the right amount of inert at ~245 lbs on a 'floating' hardwood covered 1x8 pine board sub floor, so guessing I'm 'tuning' it more than the cab.

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Old 27th February 2015, 09:45 PM   #10
lanetim is offline lanetim  United States
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I'm thinking I'll go for the steel top, baring complications to ad more mass, thanks for the advice!

Currently gluing on the back and finishing gluing in the ribs. Can't have enough clamps!!
Glueup.jpgGlueup-2.jpg

Next step will be fine tuning the driver installations.

One question I have is how best to mount the drivers...with gaskets or without? It seems folks have done it both ways.

My current thought is to use a thin foam gasket on the front baffle, with hard felt on the internal brace. The SEAS drivers have a rubber boot, so there is already some give when mounting the driver frame right up against the internal brace, but I worry that a hard mount could produce rattles if the wood shrinks or expands during seasonal variations.

Seems prudent to use something like the hard felt that can absorb a bit of compression.

Any thoughts?

Thanks!
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