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Saturday, December 17, 2016

LG's 2016 4k OLED TV : My Initial Impressions

After our 50" Pioneer Plasma TV died, we decided to replace it was an LG 55" 4K OLED purchased at a Black Friday discount plus 5% cash back via credit card, tax free and shipped free. This thing is amazing, as it's contrast ratio is infinite, producing true perfect black levels. Its pixels can turn off 100%, which even a plasma pixel cannot do. The perfect blacks combined with enough brightness give it a dynamic range able to properly display HDR content - unlike some current LCD HDR displays. The color capability is also impressive. Standard 8-bit panels, give you 256 color variations for each Red, Green and Blue subpixels, which totals 16.7 million possible colors. Tack on 2 more bits, and you get 1024 variations of each color for over a billion colors overall. I was also impressed with LG's WebOS GUI and gyro propelled remote control. I was never a fan of integrated smart TVs, but this is a pleasure to use. It will even natively stream local stations via my SiliconeDust HD HomeRun networked tuner, albeit not as fancy as the Apple TV STB. A small detail I later noticed was that the clear plastic base makes it appear as if it was floating above my sound bar. Slick.

I can't get a great screenshot with my iPhone. You have to see it in person to fully appreciate the details!

The screen itself is about as thick as a car's side window! Then halfway down the electronics enclosure adds maybe 2 inches of thickness.

As far as the poor Kuro plasma goes, I'll attempt a repair it at a later date and if successful I'll install it in my workshop, or try to sell it locally. I hear there are still Kuro fanatics out there willing to pay more than a penny for these displays. 

Tuesday, November 15, 2016

Panel Bracing the Main Cabinets

Here you can see this loudspeaker cabinet has the internal bracing in place just prior to glue up. You'll notice I'm using pocket screws. Pocket screws are an easy way to firmly hold the bracing in place while glue is drying therefore no clamps are needed. I decided to use panel bracing along with a cross brace which anchors the baffle between the woofer and the waveguide cutout.

The "glue" I'm using is called PL Premium. Its a polyurethane construction adhesive commonly found in home improvement stores, or here on Amazon. It expands as it cures which helps fill in gaps, unlike your typical wood glue which shrinks. Its very messy to work with however, so wear nitrile gloves and be careful. It has the consistency of peanut butter and sticks to whatever it touches. Once you get it on a surface, its very hard to remove.

Panel bracing is a bracing scheme which increases the resonant frequency of a panel by physically subdividing it so acoustically it appears as several smaller panels. Panels tend to vibrate at a frequency determined by a formula which takes in consideration the dimensions of the panel as well as its density, bending stiffness and a few constants.

Our goal is to attenuate these resonances enough that they won't color the sound of the loudspeaker's output. We do this by first pushing the panel's resonance frequencies up and out of the band used by the woofer by altering the panels apparent dimensions via bracing.  Second we then attenuate those resonances with mass and stiffness. One could write a book on this topic alone. I've studied cabinet construction of JBL's 4xxx line of classic studio monitors and note they have done a great deal of research in this department. Not trying to reinvent the wheel, I've chosen this tried and true method to quiet these enclosures, plus a few other considerations not seen here to add a degree of overkill.

If you're interested in pocket screws, I started out with this kit Kreg K4MS Jig Master System with Pocket Hole Screw Joinery Kit. If you're a DIY type, you'll be amazed how many uses you'll find for pocket screws!