Friday, March 6, 2009

DIY Horn speaker a.k.a. Kharma Horns

The Kharma Horns started out as a project driven by opportunity. I had the drivers left over from a pair of Einstein Rigoletto which were manufactured by Odeon for Einstein and Imported into the US By Lauermann Audio Imports. The speakers were damaged in shipping and I wound up with the hole mess. The original design was going to be a coaxial configuration using a Fostex FE164 modified by ACR and an Audax soft dome tweeter mounted in a horn flange. The toughest part of completing any speaker project for me is the cabinet. I found a guy on the web named Scott Stein from who built the cabinets to fostex specifications and gave me the port specs as well along with a Walnut wood veneer kit. As with all my speaker projects I try to employ some of my own ideas derived from designs I have seen or experienced. So in the case of the Kharma horns I wanted to deaden the cabinet vibration with a mixture of rubberized car undercoating and silica sand. Don't ask me how I came up with the combination. It just made sense to me. I applied the rubberized spray to the inside of the cabinets and then sprinkled the sticky rubber with sand. It took several coats of spray then sand, spray then more sand and eventually the cabinets became more and more inert. The treatment was easily tested by a light tap on the side of the cabinets. Resonance was lowered by 30% easily.
I also wanted to make the Kharma Horn crossoverless and direct coupled to the amplifier. To achieve this I ran the speaker cable directly into the cabinet through the port and soldered them directly to the driver input terminals. On the amplifier end of the cables I used a compression cold meld to avoid additional solder in the signal path.
Getting back to the driver. The fostex driver was originally modified by ACR. The only thing I know they did to the drivers were remove the wizzer cone. I on the other hand I dampened the basket with some duct seal, which lowered the basket vibration an amazing amount. I also coated the cone with a mixture of Mod podge and acrylic enamel paint. Two very light coated. The third driver mod was the removal of the dustcover and the addition of a phase plug purchased from planet 10 hifi The last problem was how to coaxially mount the tweeters. I would up finding some floral design wire and some epoxy to hold everything together.
At this point I had all the parts collected. The cabinets were ready for assembly. I assembled everything and sat back to listen and......tweeter on one side was toast. So I decided to go with just the fe-164 single driver. One thing I did not mention was the use of some sound anti-vibration flooring underlayment between the driver and the cabinet and inside the cabinet I used three different types of cabinet dampening materials two of which we pirated from the Einstein speakers that started this project.