GR.V.P

GR.V.P Full Range 3-Way

Project Goals
My project goals were fairly simple for this project. The first set of speakers that I built were the Dayton III's. I liked these speakers very much, and they provided a great intro to building speakers. Within a couple weeks, I was finding some weaknesses with them, not to mention that the speaker building bug had bitten me. The things that I didnt like about the DIII's were that the midrange sounded thin, and blurry. I didnt think that they imaged particularly well either. Lastly, I would have liked somthing that sounded more effortless and tighter in the bass reigon.
To summarize:
1. Clearer Midrange
2. Better imaging
3. Higher quality, deeper bass

Driver Selection
Tweeter - I wanted somthing with a very flat frequency response, that wasnt too expensive. I had a few GR-T1's sitting around from my DIII project. I substituted these for a few weeks before I got the Dayton Silkies. I actually liked the GR-T1 tweeter better. It sounded slightly clearer and had better imaging abilities than the Dayton Silk Dome.
GR-T1 info

Midrange - I definitely wanted a smaller driver than the 6-1/2" on the DIII, I started to look at drivers around the 5" range. Since my tweeter was sheilded, I decided to stick with somthing sheilded so that if I ever wanted to make a HT system out of this I would be able to. These two design requirements left two obvious choices that were below $50.00; the GR Research GR130 and the Vifa M13SG-09-08. I am sure that there were some other drivers to look at, but these both had good reputations, and I noticed that both were used in various kits. Because of one simple reason, I decided to go with the vifa unit: The GR130 was going to be changed within the next few months, and I didnt want to be stuck with a driver that had been replaced. The sheilded version would have required a notch filter also, where as the Vifa unit had no visible resonances in the FR graph.
Vifa M13 SG-09-08 info

Woofer - After the midrange, the woofer was the second hardest decision to make. I definitely wanted to use somthing that would get into the lower 30's; the box would have to be 36" tall, in order to get the mid and tweeter at the correct height. I also wanted to keep the volume less than 3ft^3. I started by looking at 8 and 10 inch drivers from Vifa, Seas, and Peerless. After much simulation and research, I made the decision to switch to a sealed alignment bacause of the better transient response and group delay. With a 8 or 10" woofer in a sealed box, I definitely wasnt going to get into the lower 30's. I decided to look at 12" woofers, and finally decided on the Peerless 12"cc driver. It does well in a 90L sealed enclosure, it never exceeds it's xmax at 65W and has the nice slow roll-off of a sealed enclosure.
Peerless 12"cc info (last listing - 831857)

Design
I didnt want to do a standard 3-way enclosure, because I wanted to keep the baffle width at a minimum, I decided to use two separate enclosures. I also wanted somthing better than just plain boxes, so I used some chamfers on the front face of the mid/tweeter cabinet, and chamfers on the top face of the woofer cabinet.
I did some simulations (this was mainly done at the same time as driver simulations) and came up with the designs for the two enclosures. Because I didnt know how long I would be without the woofer cabinet, I decided to make the mid/tweeter enclosure ported for aditional bass response. I used UniBox to come up with .3ft^3 and the PE 2-1/8"x 5" port. For the woofer, again, i used UniBox to come up with a sealed enclosure of 90L.

This is a design of the speakers that I did before building them in 3D Studio Max Enclosures
Midrange and Tweeter - I made the front baffle out of .75"MDF, and the rest of the box from .5" MDF. I used one single cross brace between the midrange and tweeter from one side to the other. The baffle was cut with chamfers on the bottom, and one on each side. They get larger as you go up the baffle so that the baffle is the narrowest at the top near the tweeter. Both the woofer and tweeter are mounted in the center of the baffle. The port is located behind the tweeter, the terminal cup behind the midrange and the crossover on the bottom of the enclosure. Once it was complete, I used open cell foam on all faces besides the front and bottom, this audibaly reduced standing waves in the cabinet.

Here is a picture of the midrange and tweeter enclosure sitting on top of the woofer enclosure. Woofer - The woofer enclsure is made out of .75" MDF all around. It also uses very heavy bracing, and a top piece that is 3" thick. The box uses a type of bracing that I have never seen before; I used pieces that are aprox. 10" long. I cut 45* angles on each end so that they looked like trapezoids. These were then glued between the front and side or back and a side. There are 6 of these such braces in each enclosure, four of them bracing the front baffle and two bracing the rear baffle. These were used in the lower part of the enclosure, below the woofer. I also used a cross brace that went from one side to the other side directly behind the woofer. It is angled upward so as to not interfere with the back wave. Lastly, I used pieces of MDF glued to open spots on the cabinet. These make the weight of the pannel irregular, helping to reduce vibration. I also used open cell foam on the top bottom and upper section of the sides. I stuffed the remaining volume of the enclosure with 1.5lbs of acusta stuff. The top was made so thick in order to be able to chamfer it to get the style that I was looking for.

Crossover

This is a model showing the internal braces that were used, again modeled in 3D Studio Max The mid and tweeter crossover is the most important and went through many iterations, including first and second order parallel filters. In the end I ended up liking the sound of a series crossover the best, it seemed to add some warmth and musicality to the sound of the mid and tweeter. The first order series had some sevre nulls below the listening position, the second order sounded good but the series XO seemed to unify the drivers better. In the end the values that I thought sounded best came to 3000Hz. For the woofer I used a 2nd order parallel filter. It crossed from the woofer to the mid/tweet at 500Hz. I also used a 2nd order high pass at 500Hz before the series XO on the mid/tweeter. I put this crossover outside of the speakers in a separate box so that I could switch to an active crossover later if I wanted to. You will notice that there is no BSC built in. I decided to do this because I will be using these in rather small rooms for the next few years, so they will always be placed with the woofer within 18 to 24 inches of the rear wall (remember the depth of the cabinet is 16 inches).

This is the Crossover that is used, it may be a bit confusing to look at, but there is a 2nd order XO before a series XO for the mid/tweet.

This is the theoretical frequency response of each driver, and the overal response. I would agree with the upper midrange hump that you see, but not with the table from 9KHz on.

Finishing
I finished these in Honduras Mahogany, unfortunately, 4x8 wasnt quite enough to do the whole project, so I had to buy a second 2x8 sheet. The mahogany was glued on with 3M super 77. I used one coat of tung oil, followed by semi-gloss laquer. They look absolutely wonderful, and very expensive.

A picture of the left channel sitting in my room Final Thoughts
I thought this was a great project, in the end it took me 3 months to complete. They satisfied every one of my requirements, and get a big WOW from every single person that walks into the room, they then get an even bigger WOW from the sound. The best way to describe the bass is that it is silent, in that there are no cabinet noises. The lower mids are clean, and handled well by the peerles unit. The midranges are clear and solid, and very deep. The highs are clear and sharp. I do not have any measurement equipment so I dont know what the FR graph looks like, but it sounds nice and smooth to me. They are very easy to listen to for long periods of time. I do believe that it still needs a little BSC because bass is slightly lacking, this is a minor issue though, as they are still wonderful to listen to.