Introduction: Upgrading a Linaeum Bookshelf Speaker
Radio shack produced a hidden gem of a speaker in the 90s that used a Lineaum tweeter that dispersed high frequency sound more evenly around the room. There are still many of these speakers on the used market. The Lineaum tweeters were commonly paired with a 5" woofer to reproduce low frequencies. The problem with these woofers is that after 25 or so years the foam surround (the part connecting the speaker cone to the frame) will rot away.
This project will replace the original woofer with a woofer with upgraded technology such as neodymium magnet and rubber surround. The model number of the speaker used in this instructable is RCA 40-5007.
Power drill with 1/8" drill bit
1/4" plywood and 1/2" plywood
Router is optional
Step 1: Removal of Old Woofer
Pull straight out on the grille to remove it.
Use a screw driver to pry out the four rubber socket screws that accept the grille as shown in the photo.
Take out the four screws underneath the rubber sockets.
Use a flat blade screwdriver or putty knife to separate the front (baffle) of the box.
Once the baffle is separate from the box. Remove the four mounting screws for the speaker and undo the two wire terminals.
Step 2: Choosing a New Woofer
The woofer I chose to replace the original is the Dayton Audio Nd-105-8.
The reason I chose this woofer is that it is a good match of the efficiency of the tweeter. In other words once the speaker is complete the bass, midrange and highs will sound balanced. Also the Dayton woofer has alot more throw than the original woofer so therefore it can move more air to create BASS! Well don't get too excited it is still a 4" woofer after all.
Here's a link to the woofer.
Step 3: Woofer Adapter Plate
The down side to the chosen woofer is that it is a little smaller than the original woofer so we will have to make a an adapter plate.
The adapter plate is made out of piece of 1/2" plywood glued to a piece of 1/4" plywood.
For a pair speakers you will need 4 pieces of plywood that are at least 5.5 inches square.
Start with a piece of 1/2" plywood and cut out a circle of 3-11/16" diameter. I used my router and a jig to cut out the circle but a jigsaw will do fine.
Lay the original woofer on the plywood and trace around the perimeter of woofer while trying to center the woofer frame on the circle.
Cut the outside perimeter line of the original woofer with a jigsaw.
The 1/4" plywood will have a trace of the perimeter of the Dayton woofer frame on the inside and the original woofer frame on the outside.
Cut out both lines and check that the 1/4" plywood slides over the frame of the Dayton woofer.
To summarize, you will end up with a piece of 1/2" plywood the Dayton woofer can screw into and a 1/4" plywood with the same outer size of the original woofer that slips over the Dayton woofer.
Glue and clamp the two pieces of plywood together after making sure the Dayton woofer fits.
Step 4: Sanding, Staining and Assembly
Once the glue has dried use a 1/8" drill and using the original woofer as a guide drill through the 4 woofer mounting holes through both layers of plywood.
At this point I used a tinted polyurethane to finish the plywood however this is probably overkill since very little of the plywood will be visible in the end, I mainly did this step to protect the wood from moisture as I will use this speaker in a humid basement.
I then drilled pilot holes and mounted the dayton woofer to the 1/2" plywood using these screws: https://www.parts-express.com/parts-express-8-x-1-...
Add weatherstripping between the enclosure and where the plywood adapter meets to help seal things up. Not very cosmetic but functional.In hindsight I could have looked for black weatherstripping instead of the grey I used.
Mount the plywood and woofer to the speaker baffle using #8 1-1/4 inch long sheet metal screws.
Install the two wire terminals. Assemble the enclosure with the four screws and you are done!
Step 5: Results
After breaking in the speakers for a couple of weeks. I measured the speakers using a special microphone.
I sent pink noise to the speaker and measured with an RTA. This gets technical but what we are looking for here is all the bar graphs should be about the same height. Some people have a preference towards having the bass a little louder which means the graphs on the far left will be higher than on the right.
The tweeter in this speaker is designed to play high frequencies from 4khz-20khz. The difference in the new and old woofer can be seen in the graphs. The original woofer on the left graph is louder (bar graph is higher) in the midrange from 250hz-4khz and therefore will overpower the tweeter that this speaker is famous for. The new Dayton woofer is quieter through the midrange, therefore achieving a proper balance with the tweeter. With the new Dayton despite a few peaks and dips a straight line could be drawn from 250hz-8hz. This is a decent result especially as this measurement was taken in my room where there are reflections that can negatively affect the graph. There is also more deep bass with the Dayton as shown by the bar graphs at 63 and 80 hz being higher.
Hopefully this is useful for someone, thanks for tuning in!
Participated in the
Audio Challenge 2020