Hi,
I may have missed the point earlier in this thread so I'm probably repeating.
You said:-
ideal size for 2 side by side drivers = 600L.
then
ideal size for 1 driver = 300L.
and it follows that
ideal size for 2 isobaric drivers = 150L.
Is this what you meant when you said 150L would do?
A word of warning. Isobaric drivers are using the motors to help each other to drive the air load. Because of this you run out of Xmax very quickly. Keep the volume down!
The two isobaric voice coils give you a very flexible wiring arrangement.
Both drivers in parallel,
Both drivers with their own amp,
Both drivers in series (not normally recommended, but for a close coupled isobaric this should be acceptable.
I may have missed the point earlier in this thread so I'm probably repeating.
You said:-
ideal size for 2 side by side drivers = 600L.
then
ideal size for 1 driver = 300L.
and it follows that
ideal size for 2 isobaric drivers = 150L.
Is this what you meant when you said 150L would do?
A word of warning. Isobaric drivers are using the motors to help each other to drive the air load. Because of this you run out of Xmax very quickly. Keep the volume down!
The two isobaric voice coils give you a very flexible wiring arrangement.
Both drivers in parallel,
Both drivers with their own amp,
Both drivers in series (not normally recommended, but for a close coupled isobaric this should be acceptable.
"Isobaric drivers are using the motors to help each other to drive the air load. Because of this you run out of Xmax very quickly."
xmax is the same a sfor a singlr driver, so no more quickly than that.
xmax is the same a sfor a singlr driver, so no more quickly than that.
Hi Noah,
due to the extra motor power and the small back volume the speakers work hard to produce the low frequencies. You run out of piston travel much earlier.
I believe the effect is equivalent to half Xmax when using isobaric loading.
There is a way to model isobaric in most modelling systems, it's just a case of inputing the adjusted Thiel Small parameters. Some don't change, some are times two and some are halved. I have never needed to do it so don't know the numbers.
What I did was to discover that my actual cabinet was half the size of the optimum. So I tried isobaric as an experiment and sure enough it worked. But my speakers are big and efficient (Tannoy dual concentric) and were for domestic use and Xmax was never a problem.
due to the extra motor power and the small back volume the speakers work hard to produce the low frequencies. You run out of piston travel much earlier.
I believe the effect is equivalent to half Xmax when using isobaric loading.
There is a way to model isobaric in most modelling systems, it's just a case of inputing the adjusted Thiel Small parameters. Some don't change, some are times two and some are halved. I have never needed to do it so don't know the numbers.
What I did was to discover that my actual cabinet was half the size of the optimum. So I tried isobaric as an experiment and sure enough it worked. But my speakers are big and efficient (Tannoy dual concentric) and were for domestic use and Xmax was never a problem.
I understand that as you have twice the motor power, you get the excursion two times faster in the same volume. Hence the halved optimum volume.
In a sealed box, the sound is emitted excursion/pressure needed for a given SPL will not change with isobaric compared to single driver I assume.
Moreover, simulation tools don't show an increased in Xmax for a given SPL compared to single driver, which sounds logical.
I will power the sub with two paralleled LM4780, giving 100W per driver. It is pretty enouh for my purpose I think. The drivers are rated 300W, but driver ratings are not very "trustable"
I'm impatient to receive the extra drivers and measure them !
In a sealed box, the sound is emitted excursion/pressure needed for a given SPL will not change with isobaric compared to single driver I assume.
Moreover, simulation tools don't show an increased in Xmax for a given SPL compared to single driver, which sounds logical.
I will power the sub with two paralleled LM4780, giving 100W per driver. It is pretty enouh for my purpose I think. The drivers are rated 300W, but driver ratings are not very "trustable"
I'm impatient to receive the extra drivers and measure them !
"due to the extra motor power and the small back volume the speakers work hard to produce the low frequencies. You run out of piston travel much earlier."
The two motors in half of whatever volume work just as hard as one motor in that volume.
As you said, it's a matter of T-S parameters, and xmax doesn't change.
The two motors in half of whatever volume work just as hard as one motor in that volume.
As you said, it's a matter of T-S parameters, and xmax doesn't change.
Xmax doesnt change indeed I agree!
In fact Xmax might be slightly higher with clamshell isobaric and also a smoothing of the BL curve occurs!
The reason xmax why will increase is because sometimes (often) the center of the magnetic xmax is not the rest position of the voice coil's center. This may vary speaker to speaker even, and really only a dumax type test could interpret it to predict an accurate model.
The BL curve is also often not the same shape for positive and negitive excursions and when speakers are put isobarically the shape of the effective BL curve is the average of the two which is much smoother then either alone
In fact Xmax might be slightly higher with clamshell isobaric and also a smoothing of the BL curve occurs!
The reason xmax why will increase is because sometimes (often) the center of the magnetic xmax is not the rest position of the voice coil's center. This may vary speaker to speaker even, and really only a dumax type test could interpret it to predict an accurate model.
The BL curve is also often not the same shape for positive and negitive excursions and when speakers are put isobarically the shape of the effective BL curve is the average of the two which is much smoother then either alone
Sorry to relaunch the topic that late but some [10^91873917 censored 😡 ] thefts took my computer and my backup HDD away during the holidays (beautiful Christmas gift isn't it ? 
).
I fortunately didn't loose everything because I have backups at a friend's
Let's return to my project :
I received the second driver and it also causes me problems... ( Am I damned ???
)
Its aluminium cone isnt glued right on the coupling cone, and it actually shifts the suspension down on one side and up on the other side (it is not glued at the center and bends/stretches the suspension)
I told it to the online shop who gave me back the money, but let me the driver 😀
So I thought it wouldn't be a waste trying to repair it.
I took a hot air gun and removed the cone+suspension from the coupling cone.
Right now, I know how to remove it but placing it correctly again looks rather difficult :
the spider is a simple-type and it is very easy to make the coil touch the iron (it is a cheapo driver)
It is impossible to put the cone on it again without touching the iron !
I post some photos here if someone could help me
).I fortunately didn't loose everything because I have backups at a friend's
Let's return to my project :
I received the second driver and it also causes me problems... ( Am I damned ???
)Its aluminium cone isnt glued right on the coupling cone, and it actually shifts the suspension down on one side and up on the other side (it is not glued at the center and bends/stretches the suspension)
I told it to the online shop who gave me back the money, but let me the driver 😀
So I thought it wouldn't be a waste trying to repair it.
I took a hot air gun and removed the cone+suspension from the coupling cone.
An externally hosted image should be here but it was not working when we last tested it.
Right now, I know how to remove it but placing it correctly again looks rather difficult :
the spider is a simple-type and it is very easy to make the coil touch the iron (it is a cheapo driver)
It is impossible to put the cone on it again without touching the iron !
I post some photos here if someone could help me
An externally hosted image should be here but it was not working when we last tested it.
You need to take off the dome in the middle of the cone and shim the voice coil, (thin card or paper works fine), whilst you glue everything back together.
Hi,
you need to remove the dust dome from the middle of the cone to give you access to the magnetic gap from the front of the speaker.
Insert some thin paper or plastic shim into the gap to centralise the voice coil former. Try at least 4 around the circumference and use many thin sheets rather than a few thick but stiff sheets. They need to follow the curve of the gap as closely as possible.
Try to glue the cone back onto the former accurately and let it set.
Now recentre the cone surround to eliminate any pull on the voice coil. remove the shims and test.
Glue the dust dome back on to keep the gap clean.
I think speakerbits (or someone similar) has a video showing how it's done.
you need to remove the dust dome from the middle of the cone to give you access to the magnetic gap from the front of the speaker.
Insert some thin paper or plastic shim into the gap to centralise the voice coil former. Try at least 4 around the circumference and use many thin sheets rather than a few thick but stiff sheets. They need to follow the curve of the gap as closely as possible.
Try to glue the cone back onto the former accurately and let it set.
Now recentre the cone surround to eliminate any pull on the voice coil. remove the shims and test.
Glue the dust dome back on to keep the gap clean.
I think speakerbits (or someone similar) has a video showing how it's done.
Sorry I didn't post the photos so it is harder to understand what I mean 😀
The driver has no cap or dome in the middle. It looks like this
It has a decompression vent on the back : I thought puting paper sheets between the coil and the iron and trying to remove them through the vent once everything is glued.
I'm really curious to know how they assembled this thing in the factory...
The driver has no cap or dome in the middle. It looks like this
An externally hosted image should be here but it was not working when we last tested it.
It has a decompression vent on the back : I thought puting paper sheets between the coil and the iron and trying to remove them through the vent once everything is glued.
I'm really curious to know how they assembled this thing in the factory...
AndrewT said:
I have also heard that 33 hz happens to be the resonant frequency of a certain female unmentionable.
Would be a nice feature to have in a bed....
Arrange for a variable signal generator.
Conduct experiment (note: intervening/paricipating renders results invalid)
Record results.
Plot Curve, define Fr, Q.
Report here
Regards
George
Hi,
how do you manage to post pics way over the 100kb limit?
Pity the poor readers that do not have broadband or can't have as was my case until recently.
how do you manage to post pics way over the 100kb limit?
Pity the poor readers that do not have broadband or can't have as was my case until recently.
You can surpass the 100kb limit if you use another image hosting website than DIYaudio.
ImageShack
PhotoBucket
etc...
ImageShack
PhotoBucket
etc...
AndrewT and Tsimon5
Thank you both (AndrewT for the question and Tsimon5 for the supplied answer). This is very important and has to be made known (how?) to all members.
regards
George
Thank you both (AndrewT for the question and Tsimon5 for the supplied answer). This is very important and has to be made known (how?) to all members.
regards
George
LOLLLLLLLLLLLL 😀
That explains why female "toys" work on battery : if you plug them in the wall you can only get 50Hz 😉
Maybe 69Hz harmonics work fine too
Let's get back to the subject though, we may get censored 🙄
Sorry for that, I was too lazy to lower size & resolution 🙂
I didn't have time right now to look further at the driver. Got to manage to find time for this cheapo thing.
The fact is not that I'm sentimentaly linked to this driver, but it is the only way for me to have a working push//pull sub
AndrewT said:
That means exactly that.
DIYaudio will only store pics <100 kb. You need to store them elsewhere if you want to have something larger.
Back on topic...
You do seem to be in a hopeless situation there with reglueing the cone.
If it is to be done exactly correct the coil must be shimmed, yet it is impossible as the cone is a single peice and you would have no access to the shims once the cone was glued. However, if you cut a circle out of the center of the cone you could shim the coil and be able to remove the shims after the glueing is complete. Then you could glue the peice you cut out back in place, or just get an actual dustcap.
This might not be the best solution cosmetically, but its the best way I can think of to fix it.
You do seem to be in a hopeless situation there with reglueing the cone.
If it is to be done exactly correct the coil must be shimmed, yet it is impossible as the cone is a single peice and you would have no access to the shims once the cone was glued. However, if you cut a circle out of the center of the cone you could shim the coil and be able to remove the shims after the glueing is complete. Then you could glue the peice you cut out back in place, or just get an actual dustcap.
This might not be the best solution cosmetically, but its the best way I can think of to fix it.
Yep, I'll cut the alu membrane in the worst case. I'm right now testing the method I thought of : puting paper in the gap and trying to remove it through the decompression hole. It seems to be possible, though I hope nothing bad will happen during the "real" operation.
Concerning regluing : should I use the same kind of glue they used (hot melt glue) or something else could be more practical in this case (such as Neoprene, or cyanoacrylate) ?
Concerning regluing : should I use the same kind of glue they used (hot melt glue) or something else could be more practical in this case (such as Neoprene, or cyanoacrylate) ?
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