New 515s

**amh** · April 7th, 2005, 03:16 PM

Just received my new GPA built 515-8Gs. Very nice work. Well done Bill!

**RonSSS** · April 7th, 2005, 03:44 PM

And what are they going in?
Ron

**amh** · April 8th, 2005, 12:06 AM

I'm building a pair of stretch 828s. Probably another one of my "new ideas" that'll prove to be a been there done that for most guys here, but I gotta try.

I bought a ratty old pair of 828s that I'm going to knock the bottom out of. Then, by laminating some hardwood 14 ply no void to the sides, top and new bottom I'm going to increase the height of the reflex area by 9". This will give just over 10cu ft of box for the 2245Hs going in the bottom. Optimum size. I'm thinking about borrowing an idea from work and putting a layer of Ice Gaurd between the new ply and old box, then shooting screws around the outer perimeter to hold it together. For those of you not in the snow belt, Ice Guard is a VERY gooey sheet good that goes under the first course of roof shingles to prevent ice dam leaks. Hopefully this will act like the rubber cored sheet metal I design into cars, very quiet. Totally new front baffle on the reflex area to accept the 2245H. The added height will also allow some proper porting on the front baffle,a pair of 4-6" dia. GM has me thinking about bottom porting and slot loading as well.

Top horn area will be sealed off by installing a new horn bottom. I'm going to carry that angled board right to the back of the cab. Your numbers confirm suspicions that that volume is close to optimal for the 515-8Gs. I'm leaving this area sealed, no ports. Flares filled. XO is tentatively 120Hz bass to mid.

With the possibility that I'll use bottom slot loading, and I'm definitely adding casters under the cab, plus the extra 9" box height the whole affair will be about 12-13" taller than stock height. I'll slide the 511B on top forward to the edge of the cab to avoid any eclipsing of it's output when I align it to the seating position. Active XO will allow me to time align the 2245H and 511B with the 515-8G.

I'm thinking of pushing the mid to high XO up to 1200Hz. The A7 was originally intended for speech reproduction in theaters and they didn't want to XO in the speech frequency band, so they used 500 or 800Hz. The higher XO will broaden the range I'm putting through the 515-8G and perhaps suit music repro better. Just a matter of spinning knobs on the active XO to experiment at any rate.

With the arrival of the 515-8Gs I now have all the drivers for the project. Time to start cutting wood!

P.S. Thanks for the horn pics. Nice Job! They don't look bad at all.

**RonSSS** · April 11th, 2005, 04:59 AM

AMH,

Sounds like quite a project.
I'm not exactly sure how to use BoxPlot in the closed box config. But if I did it right, looks like the 515-8G is 3dB down at 100hz in a 3cuft sealed enclosure.
So it sounds to me like your plan will work. I like the idea because the A7 was never meant to go very low, and I think the front horn area is only good to around 100hz anyway.
So essentially what you will have is an A7/SubWoofer combination all in one BIG box. If it comes out well, and I'm sure you will be successful they ought to rock!

So you design cars? I see you are in Detroit.
Home of the muscle car. RonSS is because I'm a car guy and have had a few Chevelle SS cars, although I have a Nova now.

Keep us posted on the project.

Ron