Rawley Benefit - Rev 01

A friend and coworker is supporting his wife as she battles cancer a second time. Some friends of theirs threw a huge benefit party for them a few weeks ago. A couple coworkers joined in on donating a speaker package for the live auction that I designed - and now, built :-) No worries - I quoted the job to be complete mid-late June. [whew]

I decided to buy the cabinets for this project - one of my suppliers donated to the Rawley's as well and gave me some nice discounts on the cabinets. I had seen the new cabinets that they carry in person last fall at the most recent speaker nerd gathering in Iowa.

I chose the shaped/curved cherry finish. It's real wood veneer, so it looks really nice - not like those crummy vinyl "wood grained" overlays. Originally, the plan was to use different drivers. I talked to some other speaker nerd friends, and one of them was going to donate some nice ribbon tweeters. One thing lead to another, and I discovered that they wouldn't fit with the midbass driver I was planning to use - both physically and acoustically. I guess acoustically is physically too. Hmmm. Anyway. They were too big and they also turned out to required too high of a crossover frequency (the midbass just couldn't fill in the gap). So, I dug around my stash and found a pair of Seas aluminum dome tweeters.

Here, you can see the baffles all taped up (thank you, 3M for the most wonderful tape in the world). The tape prevents chipping from when I router out the holes for the drivers. The panels have a really nice finish to them that I didn't want to risk chipping. The other baffle is flipped over; I was laying out the driver positioning, exploring my options. "But Scott, those look like they're on top of each other..." - Patience, my young Padawan. "But... but..." Silence!


Here you can see the holes that I've routered out; one with tape, one with the tape peeled off. You'll notice the tweeter has a beveled step in it for flush mounting. When the face of the tweeter flange is flush with the baffle face, this helps to keep the frequency response nice and flat. Normally, this would be done for the midbass driver as well. But, well, you'll see...


There - now do you get it? The midbass actually overlaps the tweeter - they use the same hole for the screw. This allowed me to leave a little bit of flat edge left for the tweeter on top, and more importantly, allowed me to reduce the center-to-center spacing. Ideally, the center of the tweeter and midbass should be right on the same axis. Obviously, that creates great difficulty when it comes to multiple things occupying the same space. That said, typically, "rule of thumb" is to keep the spacing less than 1/2 the wavelength of the crossover frequency. There I go, giving away those marvelous nerdy secrets.


This one's a bit more on top for better understanding. The drivers were just dropped in for a fit check, so the midbass isn't quite centered.


And this is the "Table-o-fun." (Thanks for the naming idea, Christina). Parts parts parts parts parts... and that glorious bottle of blue Mountain Dew. I'm a fan of this new flavor; hopefully, it stays around for a while. It's a little sweet for normal drinking, but I was working and sweating my tail off today. The extra sugar was earned. So, here, I was just laying out some parts, trying to see what I had in my bin for testing. These are just test sample boards for listening - us audio geeks are never done tweaking...


So, here's Rev 01 of the crossover. Prior to desiging this, I made a rather drastic design change last minute. I decided that the aluminum dome tweeter I had planned on using might not be the best for this project. In analyzing the numbers and sound timbre in my memory, I didn't think it'd match well with the sonic signature of the midbass and sub. So, I decided to change to a soft dome tweeter from Seas. I'm so glad I did - great move, Scott.


Here's the cabinets with the baffles removed. You can't see it, but there's acoustic "stuffing" in the back half of the boxes. This helps to eliminate standing waves and reduce distortion. It also affects the acoustic properties of the box "alignment" in how the midbass plays low frequencies.


Here's the back side, prior to the binding posts being installed. If you look closely, you can see the holes about a third of the way up on the back face for them.


And here's the beginning of assembly, the preliminary crossover mounted (temporarily) to the middle brace. There's a ring of closed cell foam used as gasket material to help seal the cabinet - NO AIR LEAKS.


And the final assembly...


Here's a picture of them playing one of my favorites, Alison Krauss. I know, I know - it's a totally sweet TV. Yes, my center channel is bigger than the sub I just built for these speakers (see left side)... FYI, my center channel weighs in at ~80 lbs.


Right, back to the Rawley Benefit speakers.


Yes, that's my socks - the left stand has a bolt that sticks up a bit past the surface of the stand shelf. I didn't want to risk scratching these new pretty cabinets.


I wasn't able to play much other some "light" female vocals tonight - downstairs neighbors are sleeping. I'll be sure to give them a good run in the morning while I get ready for work. In a word, they are remarkable. I'm really pleased with them - this one might not go much beyond Rev 03 for the crossover. I almost nailed it the first time. I'll have to have those that helped make these possible over for a night to listen to them a bit before we have to give them away. These speaker projects are really hard to let go of, even when I get paid for a set. Lots of blood and sweat go into these little buggars, even when I don't make the cabinets.

Stay tuned for more. Time for me to collapse into bed.