Yeah and if the foam is totally gone and been sitting that way for a while the cone weight would put torque on the spider, probably sagging it and taking set in that orientation.
Now I kinda feel bad for tossing my wife's Sony 8" + poly dome sealed bookshelvs. I had thought of refoaming them but figured I could probably build something better anyway. Would have been a good first try for refoaming.
Got the refoaming kit from SimplySpeakers.com. I decided to go with the non-shim method, leaving the dust caps in place, to see how it goes compared to the shim method. Here is how it went:
SETUP: Initial setup showing lazy susan, glue, new foam surrounds, and battery pack, ready to go:
Step 1: Flip foam upside down & apply 1/8" bead of glue along entire inside edge:
Step 2: Smooth out glue while rotating the lazy susan:
Step 3: Flip foam over and connect one AA battery to push cone up 1/4" into the wet glue:
Step 4: Rotate lazy susan & press foam edge into the glue:
Step 5: Put two more batteries into holder, boosting applied voltage up to 4 volts. This pushes the cone up to it mechanical limit (+ Xmech). I then applied a 1/8" bead of glue around the outer frame beneath the foam.
Step 6: I then removed the battery pack, causing the outer foam edge to drop into the fresh glue:
Step 7: This is the critical (make or break) step. As the glue began to set, I pressed the cone up and down along it full VC travel, which caused the VC to "self center" as the glue began to thicken and set up. I lightly tapped along the side of the cone to confirm alignment. After about 5 minutes, the VC self centered, and no more rubbing could be heard.
Step 8: Another 1/8" bead of glue along the top of outer edge to secure the gasket.
Both woofers done. No VC rubbing. Still need to pull a few small dents out of the dust caps:
@6thplanet said:
So no frequency generator usage to check for rubbing/voice coil alignment?
No, not during the glue up process. I was thinking about using a generator during the glue up process, but the hookup wires got in the way when trying to spin the lazy susan. So, I just went by feel, listening for scraping noises, as I tapped on the cone sides and then pushed the cone in and out to its mechanical limits. Later on, I ran frequency sweeps with my generator and they seem fine. I was following the below linked instructional video from simplyspeakers.com, where they show the non-shim, non-generator method:
I gave both woofers a 2 hour break-in (about 3/4" peek to peek at 20Hz), then let them rest/cool for 2 hours, then measured the T/S parameters. If these measurements are similar to what they measured when new, then the Jensen engineers were probably going for a somewhat "punchy" alignment. I orignally guessed Fs would be about 20-22Hz or so. I was way off. Boxes internally are 1.9 cu. ft and heavily stuffed with fiberglass, so the effective internal volume is probably about 2.5 cu.ft.
I'm somewhat disappointed in the high Qts figures; was hoping for something more in the .500 range to produce a flatter, less punchy alignment. Maybe I should try @Wolf s idea of gluing more magnets onto the existing ones, like he did on his Opaz speakers. Looks like this could help to reduce Qes a bit and flatten the curve. I have a few old 16 ounce magnets laying around that I pulled from burned out Goldwood and Philips woofers. I'll clamp these onto the existing magnets and see what happens..
Yeah, I don't think stuffing the box will change the effective volume (actually Qtc) 30%, but maybe going aperiodic will lower that high Q hump some, at the expense of some sensitivity and a resulting higher F3. Could still sound really nice though.
@Mitchell_Cote said:
How about turning the closed box into a aperiodic vent box?
That would be one way to lower the Qtc somewhat, but the problem with aperiodic is that this lowing of the Qtc comes at a huge price. With aperiodic, the deep bass response simply goes away due to direct cancellation through the aperiodic vent. I need a way to lower Qtc, yet retain the deep bass extension.
@jhollander said:
I would have thought the M(ms) would have been closer.
I think this difference in M(ms) is due to measurement error. Before I did the 2 hour break in & 2 hour cool down, I measured both drivers completely cold, with no break in. The below screen shots show the data. As you can see, M(ms) for woofer 11 was actually higher (42.42 grams) before break in whereas woofer 13 was just a tad lower (41.88 grams).
I conducting an experiment using Wolf's magnet mod procedures and found that it made quite a difference. I had two magnets, so I did two tests, stacking the magnets together and then sticking them on temporaily using Gorilla tape. I oriented the magnets to repulse and therefore lower Qes. Fs and VAS remained constant while Qts dropped quite a bit. The 1W/1M SPL increased a little bit with the added magnets. These results make me wonder whether or not the original magnets may have lost some or their original strength over the past 35 years!
Here is how I repaired the dented woofer dust caps. These dents probably occurred several years ago, so when I attempt to simply pull them out, they quickly pop back to the old, dented position.
So, I took some small beaded, pearl head positioning pins (used to hold dress shirts together), bent the needle end 90 degrees, and then tied strings to the needles at the beaded end. The dust caps were made of a woven fabric/plastic material, so I could poke the needle through the dust cap at any point without damaging it. I pulled the dents out and tensioned the string to the basket with masking tape. This held the dust cap in the new position for a few days, long enough so it did not pop back to the old position. Worked pretty good, but still have a few small dents. With time, I should be able to get them all worked out.
The restoration is now complete. I used Howard's Restor-A-Finish and Feed-N-Wax to refinish the woodwork. Didn't turn out too bad, I can still see a little of the water stain on top of one cabinet, but only up close. I have had a chance to listen to them for a while now and have taken a number of measurements. They can play loud and handle quite a bit of power. Just a tad on the bright side, which might be the crossover electroytics. It has two NPE electrolytics in the tweeter branch. In fact, all 4 xover parts ( 2 caps, 1 inductor, and 1 padding resistor) are in the tweeter branch. The woofer runs free on the top. Amazing how well the woofer measures and sounds with absolutely no xover parts!
Here are the tweeter free air Z curves. Kind of wonky looking, but sound is OK. The blue curve is the speaker (serial number ending in 13) with the crushed and restored tweeter dome. The yellow curve is the speaker (serial number ending in 11) with the good tweeter.
Here are the completed speaker Z curves, with xovers. Blue curve is speaker 13, yellow is speaker number 11:
Here is the 1 meter on-axis FR curve. These curves were generated individually for the tweeter and woofer with the xover in place. When measuring the tweeter, I substituted a 7.5 ohm resistor
for the woofer. When measuring the woofer, I substituted a 7.5 ohm resistor for the tweeter.
Here is the FR with the grill in place, but the mic 10" above the tweeter axis. This is how I think this speaker was designed, to be placed on the floor, with the ear about 10" above tweeter level.
Here are a couple more graphs, showing how the grill and ear height affects the overall frequency response. The sound is very bright on-axis, but softens quite a bit off-axis.
Thanks, everyone. They are very sensitive (seems like about 88dB/1W/1M or so) and they do not distort when you crank them up. A little bright sounding and a bit boomy in the 60-100Hz area. Deep bass, around 30Hz or so, is completely absent. All-in-all, not too bad for $30, a $27 refoam kit, and a small amount of labor.
Comments
Yeah and if the foam is totally gone and been sitting that way for a while the cone weight would put torque on the spider, probably sagging it and taking set in that orientation.
Now I kinda feel bad for tossing my wife's Sony 8" + poly dome sealed bookshelvs. I had thought of refoaming them but figured I could probably build something better anyway. Would have been a good first try for refoaming.
Got the refoaming kit from SimplySpeakers.com. I decided to go with the non-shim method, leaving the dust caps in place, to see how it goes compared to the shim method. Here is how it went:
SETUP: Initial setup showing lazy susan, glue, new foam surrounds, and battery pack, ready to go:
Step 1: Flip foam upside down & apply 1/8" bead of glue along entire inside edge:
Step 2: Smooth out glue while rotating the lazy susan:
Step 3: Flip foam over and connect one AA battery to push cone up 1/4" into the wet glue:
Step 4: Rotate lazy susan & press foam edge into the glue:
Step 5: Put two more batteries into holder, boosting applied voltage up to 4 volts. This pushes the cone up to it mechanical limit (+ Xmech). I then applied a 1/8" bead of glue around the outer frame beneath the foam.
Step 6: I then removed the battery pack, causing the outer foam edge to drop into the fresh glue:
Step 7: This is the critical (make or break) step. As the glue began to set, I pressed the cone up and down along it full VC travel, which caused the VC to "self center" as the glue began to thicken and set up. I lightly tapped along the side of the cone to confirm alignment. After about 5 minutes, the VC self centered, and no more rubbing could be heard.
Step 8: Another 1/8" bead of glue along the top of outer edge to secure the gasket.
Both woofers done. No VC rubbing. Still need to pull a few small dents out of the dust caps:
So no frequency generator usage to check for rubbing/voice coil alignment?
No, not during the glue up process. I was thinking about using a generator during the glue up process, but the hookup wires got in the way when trying to spin the lazy susan. So, I just went by feel, listening for scraping noises, as I tapped on the cone sides and then pushed the cone in and out to its mechanical limits. Later on, I ran frequency sweeps with my generator and they seem fine. I was following the below linked instructional video from simplyspeakers.com, where they show the non-shim, non-generator method:
I gave both woofers a 2 hour break-in (about 3/4" peek to peek at 20Hz), then let them rest/cool for 2 hours, then measured the T/S parameters. If these measurements are similar to what they measured when new, then the Jensen engineers were probably going for a somewhat "punchy" alignment. I orignally guessed Fs would be about 20-22Hz or so. I was way off. Boxes internally are 1.9 cu. ft and heavily stuffed with fiberglass, so the effective internal volume is probably about 2.5 cu.ft.
T/S parameters:
DATS V2 impedance curve:
WinISD model:
I would have thought the M(ms) would have been closer.
I'm somewhat disappointed in the high Qts figures; was hoping for something more in the .500 range to produce a flatter, less punchy alignment. Maybe I should try @Wolf s idea of gluing more magnets onto the existing ones, like he did on his Opaz speakers. Looks like this could help to reduce Qes a bit and flatten the curve. I have a few old 16 ounce magnets laying around that I pulled from burned out Goldwood and Philips woofers. I'll clamp these onto the existing magnets and see what happens..
How about turning the closed box into a aperiodic vent box?
Yeah, I don't think stuffing the box will change the effective volume (actually Qtc) 30%, but maybe going aperiodic will lower that high Q hump some, at the expense of some sensitivity and a resulting higher F3. Could still sound really nice though.
I vote aperiodic as well , if you dont mind cutting into those cabinets.
A couple smears of glue on the back of the lighter cone would probably fix that
That would be one way to lower the Qtc somewhat, but the problem with aperiodic is that this lowing of the Qtc comes at a huge price. With aperiodic, the deep bass response simply goes away due to direct cancellation through the aperiodic vent. I need a way to lower Qtc, yet retain the deep bass extension.
I think this difference in M(ms) is due to measurement error. Before I did the 2 hour break in & 2 hour cool down, I measured both drivers completely cold, with no break in. The below screen shots show the data. As you can see, M(ms) for woofer 11 was actually higher (42.42 grams) before break in whereas woofer 13 was just a tad lower (41.88 grams).
I wonder if this tuning was an evolution of the East Coast sound in response to the West Coast (JBL) sound?
Interesting stuff! You might be on to something here.
https://magazine.hometheaterhifi.com/issue/showcase-2022/now-a-word-from-the-east-coast/#:~:text=JBL, out of Los Angeles, became known as,that declined in the upper midrange and treble.
I conducting an experiment using Wolf's magnet mod procedures and found that it made quite a difference. I had two magnets, so I did two tests, stacking the magnets together and then sticking them on temporaily using Gorilla tape. I oriented the magnets to repulse and therefore lower Qes. Fs and VAS remained constant while Qts dropped quite a bit. The 1W/1M SPL increased a little bit with the added magnets. These results make me wonder whether or not the original magnets may have lost some or their original strength over the past 35 years!
Thanks for the results.
Nifty!
Here is how I repaired the dented woofer dust caps. These dents probably occurred several years ago, so when I attempt to simply pull them out, they quickly pop back to the old, dented position.
So, I took some small beaded, pearl head positioning pins (used to hold dress shirts together), bent the needle end 90 degrees, and then tied strings to the needles at the beaded end. The dust caps were made of a woven fabric/plastic material, so I could poke the needle through the dust cap at any point without damaging it. I pulled the dents out and tensioned the string to the basket with masking tape. This held the dust cap in the new position for a few days, long enough so it did not pop back to the old position. Worked pretty good, but still have a few small dents. With time, I should be able to get them all worked out.
Woofer needed acupuncture....
InDIYana Event Website
The restoration is now complete. I used Howard's Restor-A-Finish and Feed-N-Wax to refinish the woodwork. Didn't turn out too bad, I can still see a little of the water stain on top of one cabinet, but only up close. I have had a chance to listen to them for a while now and have taken a number of measurements. They can play loud and handle quite a bit of power. Just a tad on the bright side, which might be the crossover electroytics. It has two NPE electrolytics in the tweeter branch. In fact, all 4 xover parts ( 2 caps, 1 inductor, and 1 padding resistor) are in the tweeter branch. The woofer runs free on the top. Amazing how well the woofer measures and sounds with absolutely no xover parts!
Here are the tweeter free air Z curves. Kind of wonky looking, but sound is OK. The blue curve is the speaker (serial number ending in 13) with the crushed and restored tweeter dome. The yellow curve is the speaker (serial number ending in 11) with the good tweeter.
Here are the completed speaker Z curves, with xovers. Blue curve is speaker 13, yellow is speaker number 11:
Here is the 1 meter on-axis FR curve. These curves were generated individually for the tweeter and woofer with the xover in place. When measuring the tweeter, I substituted a 7.5 ohm resistor
for the woofer. When measuring the woofer, I substituted a 7.5 ohm resistor for the tweeter.
Here is the FR with the grill in place, but the mic 10" above the tweeter axis. This is how I think this speaker was designed, to be placed on the floor, with the ear about 10" above tweeter level.
Here are a couple more graphs, showing how the grill and ear height affects the overall frequency response. The sound is very bright on-axis, but softens quite a bit off-axis.
great project
Awesome! Hopefully someone will enjoy rocking them.
Those look great! I'm sure the previous owner would be amazed to see how you brought them back to nearly new condition.
Thanks, everyone. They are very sensitive (seems like about 88dB/1W/1M or so) and they do not distort when you crank them up. A little bright sounding and a bit boomy in the 60-100Hz area. Deep bass, around 30Hz or so, is completely absent. All-in-all, not too bad for $30, a $27 refoam kit, and a small amount of labor.