All - a little progress report from the hotrod garage. This past week I got first batch items of both the new terminals and the heatsinks. I think I mentioned the high purity copper bolts for terminals. But, heatsinks you ask? I know that heat is broadly everlooked as a problem in hi fi, since we’re not filling stadiums at 120dB. But, heat is a problem nonetheless, and it keeps showing up as audible.
I knew we replaced lots of burned voice coils at Thiel. I knew there were charred masonite crossover boards. I knew that styrene caps melted when too close to crossover resistors. And I knew that Jim actually goosed the Smart Sub output to compensate for VC heat to compensate for reduced output, with a thermistor feedback circuit to the amp. Good and fine remedies as far as they go. But it got really real when I was experimenting with crossover components hung by twine to mess with proximity and directionality for my new layouts.
Allow me an aside here. Over the years we explored feeding coils from ID or OD and gradually landed on OD feed and ID tap. That’s opposite from received wisdom; but my present experiments confirm. I like confirming experiments and conversely hate coming up with any different result than Jim did. So, I’m happy. But here’s an interesting thing: it seems that the coil orientation in geo-space seems to matter. I placed the coil under test quite distant from any interacting fields, and the sound changes as the coil is rotated and turned in space. I don’t know if I’ll gather actionable knowledge, but stuff does get weird. Everything is audible.
Back to business. All that handling with pink noise and music at 100dB, and guess what? The coil got hot enough to start unravelling when hung by a lead wire, and hot enough to burn my fingers when I caught it. That’s hot. Further experiments confirm serious heat in various places in the XO. This is fairly old news that I’ve reported before. But where it lead me is quite sweet. Both the speaker and the XO network will have heat sinks. The speaker’s 'hot snowflake' sink will be on the outside of the cabinet behind the drivers - which comes later. Now, I am building out various levels of XO and by a twist of fate, all will have spot heat sinks, rather than a hot snowflake on the top models only. The trick is scrap. The layout of the hexagonal trapezoids for the hot snowflake on the cabinet yields some offal which lends itself to individual small sinks near heat generators in the XO, which being outboard, can dissipate heat to room air. I had already decided to replace the final output solder lugs of each driver section with bolt-down terminations in conductive grease. Performance seems as good as solder, plus each board can come out without de-soldering. Each of those three bolt terminals (hot lead for each driver) now has a round pin heat sink on the opposite side of the board. Soon I’ll know if I can now touch those coils and resistors without getting burned. At any rate, we’ll dump considerable heat at the XO spot sources before sending the signal down the wire to the speakers.
The heat sinks and the pure copper bolts for terminals showed up this week.
