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Heeman's New DIY MTM Project

Flint,
Sorry to harp on this but I am wondering specifically how/why you chose Purifi Midrange drivers and Morel TSCT Tweeters. Previous use? Specs alone? Ability to source? You've heard them in other speakers?
Seems there must be a myriad of tweeters and drivers out there, so why these two brands?
Thanks,
Mike
Hmmm.... it is hard to explain as this is an area of expertise for me. So what makes me an expert in this area? I've worked with all of the Tweeters currently on the market selling for over $250 each, even these, and they are not dramatically different tweeters from the dozens of other Supreme tweeters Morel has manufactured in the past. With the Purifi midrange, I have heard two of the mid-woofer versions of the form factor from them and measured using my tools one of them in my space. I've also spent considerable time discussing them with people I've worked with in the past and are currently developing state of the art systems using them.

So, the choices were made based on:
  1. Experience
  2. Knowledge of loudspeaker design principles
  3. Research with subscriptions to half a dozen industry trade journals and J-AES and IEEE papers
  4. Understanding of how to read specifications
  5. Independent technical lab reviews by trusted loudspeakers engineers
  6. Discussions with loudspeakers I trust who have used them and other transducers of which I am intimately informed
    Understanding of how speaker characteristics translate to perceived loudspeaker tonality and performance

    And in this case
  7. Years of Heeman being my best friend and having tens of thousands of conversations about what he likes and doesn't like about speakers and sound in his home theater.
I don't know how else to answer the question. Did that cover it appropriately? I really want to be helpful.
 
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Coincidentally "Stumpy Nubs" just released a video today on working with MDF. I tend to agree more with Keith that properly-milled joints, plus lots of glue, is more secure for MDF than with adding fasteners, even if they get proper pilot holes; fasteners just seem to weaken the integrity of the sheet itself. ymmv.

EDIT: may help if I actually post the video, d'Oh!

MDF is merely sawdust with a weak resin in it to lightly hold it together then compressed significantly until the resin cures. It is NOT a structural martial which is capable of being fastened through the edge and being fastened into the face is not very strong at all. It isn't intended for use with fasteners and the very properties that make it inappropriate for fasteners are exactly why it is great for loudspeaker enclosures. The acoustical and mechanical vibration and flexing characteristics are a byproduct of the fact it is NOT a strong fibered material, like HDF, high grade plywood, and solid hardwood. You could use HDF or Plywood, but neither is remotely as effective as a loudspeaker enclosure material as MDF is, so it is a negative tradeoff to move to those materials. Plywood tends to be more ideal for portable, PA, outdoor, and more "rugged" enclosure, such as those used for PA speakers or Installed systems because it is more rugged, especially when being tossed around as a mobile system or mounted in an outdoor environment with widely varying temps and humidity levels which could rot MDF over time.

So, for home loudspeaker and recording studio loudspeaker systems, of the commonly available materials which are worked with standard common tools, MDF is by far the most ideal solution. If price is no object and you have access to the tools and skills, more advanced space-age materials like aluminum, steel, plastics, resins, and such can be more ideal in terms of acoustics and mechanics - not to mention any shape is potentially possible - but few home builders can work with raw metals and plastics. Consumer grade 3D Printers are also not very good as the plastic used is typically too flexible and the cost of using it in a way which comes close to matching MDF will cost 10x in filament as MDF and it could take weeks to print the components for one cabinet.
 
I guess that's what dust collection and air filtration is for!

This makes me want to do another speaker build really bad. Give that expensive dado set a workout.
 
I guess that's what dust collection and air filtration is for!

This makes me want to do another speaker build really bad. Give that expensive dado set a workout.
Yeah, while I have a make-shift dust collection capacity, I also wear a respirator mask most of the time I am machining the MDF. Seems to work well. Also, MDF dust is perfect for making wood filler by mixing it with standard PVA wood glue.
 
Weather in the area today.

Figured I'd get some paint on the bottom of the stands. This is the third coat on the rears. These are surfaces that will not be seen, so I am paying less attention to them.

20250213_171725.jpg
 
Yeah, while I have a make-shift dust collection capacity, I also wear a respirator mask most of the time I am machining the MDF. Seems to work well. Also, MDF dust is perfect for making wood filler by mixing it with standard PVA wood glue.
I have an 1100 CFM two stage dust collector and two shop vacs with cyclone separators and HEPA filtration. It cuts down on the dust a lot, but there is no way to entirely avoid those fine particulates. I generally wear a respirator or mask while cutting wood, but I don't like to wear one all the time. MDF seems to produce a lot more of those fine particulates than actual wood. That's why I have air filtration sufficient to clean all the air in the shop every 8-10 minutes. It uses a two stage filter, with activated carbon in the first stage and a HEPA fine particular filter inside.

I still have to dust. <sigh>
 
I didn't want to waste time during the Daytona 500 rain delay, so.........

I finished sanded (220) the stands and did some final filler work.

Ready for paint!

20250216_152814.jpg20250216_133607.jpg
 
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