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-   -   TH-18 Flat to 35hz! (Xoc1's design) (http://www.diyaudio.com/forums/subwoofers/190635-th-18-flat-35hz-xoc1s-design.html)

m R g S r 11th June 2011 06:23 AM

TH-18 Flat to 35hz! (Xoc1's design)
 
1 Attachment(s)
I just got my 18sound drivers from loudspeakersplus.com....ordered tuesday morning had them by friday evening! They are beasts!
http://img822.imageshack.us/img822/7979/photo15nh.jpg

(2) 18lw2400's which will be used in two TH-18 tapped horns, design courtesy of Xoc1 (Thanks again for all the info/effort you put into this!!) Also thanks to Djim for his help and patience through my questions with the design/corner bracing etc etc.

This thread is for anyone who builds his box. I figured I would start because I think I am one of the first to do so!

I will go pick up some good high quality 3/4" Birch tomorrow and get started on this. Pictures to follow asap!!

Here is the Sketch plus a nice cut list...
Attachment 226593

http://www.diyaudio.com/forums/attac...al-corners.jpg

Extra bracing which Djim suggested...
http://img864.imageshack.us/img864/7...gxoc1th183.jpg

Now I am pretty sure that the point of this design was for 4 cabinets to be Flat to 35hz. I am starting with only two because of cost, not just for drivers/wood but amp power needed to drive them as well. These are some powerful cabinets and depending on which driver you choose to load them with, they can take a serious amount of wattage!

There are a ton of different drivers which have been simmed for this design, I think most have been simmed for the cabinet without the corner reflectors, but still the same external volume cabinet.

Here is a sim for 4 cabs at xmax + with the 18 sound 2400 drivers...
http://img35.imageshack.us/img35/766...0vs18sw115.jpg

epa 11th June 2011 09:39 AM

i'll be following this one.:D
how much wood do you need for 1 box?

Xoc1 11th June 2011 03:35 PM

Background Info & Credits
 
This design owes a lot to all the people who have contributed their experience and knowledge on DIYaudio.
It’s an offshoot of the thread http://www.diyaudio.com/forums/subwo...esomeness.html. When I posted a T.H. that was more compact, and did not reach 30Hz flat, this generated a lot of interest.:)
The objective was to design and build a T.H. using an 18” driver in a reasonably compact package, that will have decent performance without any worries about speaker excursion when driven with high power (in excess of 1000W.) An extended HF response was one of the goals.
One significant contribution was Soho54’s technique for measuring the path length of a folded horn that was discussed in the thread http://www.diyaudio.com/forums/subwo...ht=spreadsheet
This allows the path length to be measured using segmented lines rather than offset curves. This method work very well with CAD setting out. I developed the technique of using the speaker path length and widths to generate an unfolded representation of the horn path, similar to the horn schematic diagram generated by David McBeans Hornresp software.
By using Parametric Cad the lines in the folded and unfolded layout are linked. It is then possible to adjust the shape of the folded horn and rebuild the sketches to immediately see how this affects the shape of the unfolded schematic. By an iterative process it is possible to optimise the shape of the horn with very good levels of accuracy.
I produced a folding scheme based on the same layout as J Bells SS15 speaker.http://www.diyaudio.com/forums/subwo...challenge.html. The SS15 is a very compact 15” T.H. that has been successfully built and tested by many forum members.
The overall size of the speaker I set out was rather shamefully almost a complete match of Tom Danley’s TH115 / TH118 :o– The theory being if the Danley subs work well at this size, it is ‘big enough’!:D

jbell 11th June 2011 04:11 PM

I applaud this design and effort as well.

This forum seems to be the one place that I've found with some serious thinking in terms of PA subs. No, not everyone needs pa 140db, but for those who do -- this seems to be the place where the thinking and DOING happens in regards to PA subs.

There are many forums where HT subs are the topic of the day, but very few places where PA is. Great discussions on power compression, what happens to suspensions as they approach limits, what happens in the 'real world' at 'real PA levels' as opposed to just simulations. (although we would be completely lost without David's wonderful hornresp, and for the brave... akabak for our simulations)

I look forward to the build, the testing, and eventually road show reports on how they worked in real life.

Xoc1 11th June 2011 04:12 PM

The Folding Process
 
1 Attachment(s)
As outlined above the horn fold is set out and then adjusted in the CAD model to optimise it. In fact I have almost given up on modelling up a speaker from scratch in Hornresp. Instead I now prefer to lay out a basic sketch model of the horn, and unfolded speaker and adjust it to shape. The unfolded sketch is used to create a Hornresp Sim. The horn wizard is then utilised to see which way the shape of the horn can be modified to improve the performance. The modified sim can then be used to help reshape the fold.
The CAD model can be easily copied and modified, so once a folding scheme is set out the work can be reused for another speaker design.
The original design omitted 3 of the internal reflectors.
These were added at Djims suggestion. The addition of the 3 reflectors shortened the path length slightly. The reflector lengths are optimised, but the overall folding was left as the original. The largest error in the horn taper widths introduced by the extra reflectors was 0.8mm, so I left the fold as it was.
At this point it might be good to mention that I made an error in my previous drawings :eek:the exit mouth internal dimension is 508 not 526. (Adjust S4 from 2814.1 to 2717.8)
Fortunately the effect on the sim is very minimal.

Xoc1 11th June 2011 04:54 PM

Updated Drawing with Internal Reflectors
 
2 Attachment(s)
Attached PDF is the latest drawing for the TH18
I have added the internal reflectors to the cut list and details.
I have also updated the unfolded schematic with the correct exit dimension.

I am currently looking at the design of the bracing. I had the un-braced cabinet analysed for resonances. The most significant result was the resonance of the exit mouth. This wobbles from side to side at about 61Hz.:eek:
The bracing as suggested by Djim seem to take care of the resonances that were found in the rest of the cabinet. It might even be possible to reduce the internal bracing, if I can get some more analysis done once I have added some bracing to the CAD model.
Primary concern at the moment is the horn exit mouth. I would like to add some reinforcement to this…..

m R g S r 11th June 2011 06:27 PM

Thanks! This is awesome! :D

I was about to go grab the Baltic Birch from my local supplier, and they want $80 per 5x5 sheet. I was figuring out a cut sheet for 4x8 wood then I found out that the real baltic birch only comes in 5x5. Anyway, I figure it will take 3-4 (5x5') sheets of wood per cabinet. Is the baltic birch really worth the $320 per cabinet? Or can I go with a high quality domestic or canadian Birch plywood (4x8 3/4" sheet is about $60)?

Thanks!

Xoc1 11th June 2011 07:52 PM

1 Attachment(s)
m R g R r
Baltic birch is the material to go for. I can't think of another material I have seen specified for decent Pro Cabs.
It is very strong - light and free from voids.
In a recent test I know of a single screw into the end of a piece of 18mm wide birch ply lifted 600kg!;)
I have put together a cut sheet and you can get 2 cabinets out of 5 off 5x5 sheets 1524 X 1524
So thats $200 per cab at your quoted price. :)
I checked it twice - I suggest you do the same!:scratch1:

m R g S r 11th June 2011 07:59 PM

Okay that sounds fine, about $200 per cabinet in wood, plus screws, glue, paint, handles etc etc it will be semi affordable.

You have helped so much on this project I appreciate it! I'm sure others will as well!

m R g S r 11th June 2011 08:02 PM

And for Bracing I'm assuming I can use a lesser quality ply correct?


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