Hi there everyone.
I just bought 2 x Dibeisi 1208 speakers, one has no coil resistance (probably burnt) and the other has 8 ohms but coil is definitely overheated and makes noise above some watts.
It's written on them to be 300w but that's probably not true.
I bought them for $10 which is a bargain, thinking i'll use them for passive radiators.
Or i could repair them myself as a second, distant, option.
These are car speakers and the moving parts are very stiff.
The spider is relatively soft but the surround is quite stiff.
It's clear that they were made to burn lots of watts.
I don't think taking out the cone assembly and trying to remake the winding will yield good results as this probably was not a great speaker in the first place.
However, as a passive radiator (keep everything except the magnet) it will have a very high Fs due to stiffness.
I planned to build 2 subs with a 8" or 10" driver and these as passive radiators, with a f3 of 40Hz, less is ok but not mandatory.
And i don't think i could reach so low with these.
I could change the surround but these are wide types, for large excursion, and pretty darn expensive, even from aliexpress.
I could add mass but that will make it sluggish.
Any thoughts on this ?
I just bought 2 x Dibeisi 1208 speakers, one has no coil resistance (probably burnt) and the other has 8 ohms but coil is definitely overheated and makes noise above some watts.
It's written on them to be 300w but that's probably not true.
I bought them for $10 which is a bargain, thinking i'll use them for passive radiators.
Or i could repair them myself as a second, distant, option.
These are car speakers and the moving parts are very stiff.
The spider is relatively soft but the surround is quite stiff.
It's clear that they were made to burn lots of watts.
I don't think taking out the cone assembly and trying to remake the winding will yield good results as this probably was not a great speaker in the first place.
However, as a passive radiator (keep everything except the magnet) it will have a very high Fs due to stiffness.
I planned to build 2 subs with a 8" or 10" driver and these as passive radiators, with a f3 of 40Hz, less is ok but not mandatory.
And i don't think i could reach so low with these.
I could change the surround but these are wide types, for large excursion, and pretty darn expensive, even from aliexpress.
I could add mass but that will make it sluggish.
Any thoughts on this ?
Welcome to the forum. I'll give your thread my non-expert bump!
Do you have the Thiele/Small parameters for these speakers?
Adding mass is how you lower the free air resonance of a passive radiator cone in order to tune the speaker system to the way you like it.
I don't see how a passive radiator could be described as "sluggish" as it will vibrate freely at its resonance frequency.
Hi and thanks.
There are no TS parameters, i can't even find the speaker page ... most likely an older model and / or specific to a certain area of the globe.
I can't also measure the TS parameters since the coils are fried.
I could try to measure the fs as it is but i have to build a cabinet and buy another speaker to be the active part.
Regarding adding mass to tune a PR, yes, that's how you do it.
However, if the suspension is stiffer, you need to add more mass than for a softer one.
More mass means more inertia even if you reach the same fs.
We're not only trying to reproduce a constant hum but variations and transients as that's what music is.
So adding 300g instead of 100g may lead to the same fs but a slower impulse response from the PR.
All this is more academic actually until i measure the actual free air resonance of these speakers.
If measured fs is ~30Hz, all is good, however, i don't think it'll be that low.
From the surroud rigidity, i would expect fs to be in the high 50's ...
There are no TS parameters, i can't even find the speaker page ... most likely an older model and / or specific to a certain area of the globe.
I can't also measure the TS parameters since the coils are fried.
I could try to measure the fs as it is but i have to build a cabinet and buy another speaker to be the active part.
Regarding adding mass to tune a PR, yes, that's how you do it.
However, if the suspension is stiffer, you need to add more mass than for a softer one.
More mass means more inertia even if you reach the same fs.
We're not only trying to reproduce a constant hum but variations and transients as that's what music is.
So adding 300g instead of 100g may lead to the same fs but a slower impulse response from the PR.
All this is more academic actually until i measure the actual free air resonance of these speakers.
If measured fs is ~30Hz, all is good, however, i don't think it'll be that low.
From the surroud rigidity, i would expect fs to be in the high 50's ...
I had two fried but well conserved, old CANTON woofer, 8" with rubber surround and soft suspension for a closed box, German style, maybe 1990.
After removing the magnet and electrical wires, I glued a M5 bolt to it from the inside, by filling the dust cap and voice coil partially with epoxy.
Combined it with a 6" woofer (same as used in Adam A7) in a 25 liter box. I still had to use a thick washer and a nut to get them right.
With this woofer the port would have become quite long for the planed construction.
Tuning was quite simple, I temporarily fixed the PR inside out, so I could change weights in a second.
I took impedance plots and verified the tuning with some near field frequency measurements. The response drops quite steep, so you can see clearly what frequency you hit. The final added weight to reach 40Hz is quite significant, more than one might expect.
All passive radiator constructions I have seen used very soft suspensions, had high weight and where made extremely air tight. If the suspension of a donor seems too stiff, you may be able to carefully cut triangles from the spider. Not every defective woofer will make a usable passive radiator.
Things get interesting when you have many small bass chassis that drive a large PR. Another advantage is the absence of high frequency components from the inside, which,when you have to cross over quite high, would be audible through a port.
After removing the magnet and electrical wires, I glued a M5 bolt to it from the inside, by filling the dust cap and voice coil partially with epoxy.
Combined it with a 6" woofer (same as used in Adam A7) in a 25 liter box. I still had to use a thick washer and a nut to get them right.
With this woofer the port would have become quite long for the planed construction.
Tuning was quite simple, I temporarily fixed the PR inside out, so I could change weights in a second.
I took impedance plots and verified the tuning with some near field frequency measurements. The response drops quite steep, so you can see clearly what frequency you hit. The final added weight to reach 40Hz is quite significant, more than one might expect.
All passive radiator constructions I have seen used very soft suspensions, had high weight and where made extremely air tight. If the suspension of a donor seems too stiff, you may be able to carefully cut triangles from the spider. Not every defective woofer will make a usable passive radiator.
Things get interesting when you have many small bass chassis that drive a large PR. Another advantage is the absence of high frequency components from the inside, which,when you have to cross over quite high, would be audible through a port.