Dual voice coil sub, with active passive radiator? - diyAudio
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Old 30th June 2011, 12:45 PM   #1
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Default Dual voice coil sub, with active passive radiator?

Hi there, I am planning to build a home subwoofer and of the drivers I have at my disposal is a 12" dual voice coil sub. I have now started thinking about what I could use the second voice coil for rather than simply connecting it to the amp.

I thought about maybe installing the sub in a passive radiator style setup, only I would use a standard driver instead of the passive radiator, and connect its voice coil to the second voice coil on the main sub. That way it would be receiving the amplifiers direct induced signal, as well as the emf signal generated by the coils movement through the gap. I would need to have both drivers connected in this configuration to take the theil small paramters, as it will surely affect the parameters, namely through the changed damping characteristics and different inductance.

Do you guys think this idea could be worth pursuing further, or has it got fundamental flaws that I haven't thought of yet? I have seen some designs that simply use a ballast load over the second coil to provide an electrical adjustment to the drivers damping, I think my idea is taking this concept further. If anybody wants I can draw a schematic diagram in case my description wasn't very clear (it probably was't).

So, let me know your thoughts. Its just an idea I am toying with, and would like others opinions. There are folk out there who better understand these things better than I, and all input will be appreciated so long as its helpful, so I thank you in advance.
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Old 30th June 2011, 11:02 PM   #2
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diagram please
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Old 1st July 2011, 12:12 AM   #3
18Hurts is offline 18Hurts  United States
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OK, let me break this down

Dual voice coil sub with only one coil driven by the amplifer.

The second voice coil will generate electricity because it is a generator...

THAT coil generating a current and signal is fed to a second driver that will use the output to move?

If so, the second voice coil will be like regen braking in an electric car--in a way, if you hold your mouth right.

What will happen? Well, the second woofer will move according to the signal sent by the second voice coil. However, since the regen is not 100% efficient, it won't be that high of a signal strength and will drag down the efficiency of the first energized coil...

When I blew a microphone cable (back in my DJ days) I used my headphones as a microphone--not elegant but it did work. What you are doing WILL work...but not a very efficient way to do it. Sometimes you just gotta do it and see what happens. After all, that is what makes DIY Audio so entertaining and a cool hobby.

What happens if you take a dual-voice coil very inefficient car sub and feed the second coil to a very, very efficient PA sub? Will you gain output? Lose output? Get a really weird frequency response? Sounds like one of those cold beer experiments... why not? If you drink enough beer it might sound great!
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Old 1st July 2011, 12:26 AM   #4
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Location: Carlisle, England
The passive radiator will also be affected by the main driver via air pressure and will have a regen effect from this.
Murton-Pike Systems PCBCAD51 pcb design software. http://www.murtonpikesystems.co.uk

Last edited by nigelwright7557; 1st July 2011 at 12:32 AM.
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Old 1st July 2011, 03:18 AM   #5
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Originally Posted by nigelwright7557 View Post
The passive radiator will also be affected by the main driver via air pressure and will have a regen effect from this.
That was my thoughts. I know that a straight passive radiator will not have the same output as the speaker driving it. I also know that powering a second driver throught the induced voltage at the dvc subs second set of terminals will not have the same output either.

But I was curious as to what would happen if I combined the two? I could even include a choke in series between the driven sub and the secondary radiator, so that only the low frequencies will pass through, potentially increasing efficency by rejecting any induced frequencies out of the passive radiators range. I agree, it does sound like a cold beer experiment.
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Old 2nd July 2011, 12:52 AM   #6
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Location: Phoenix, AZ
Hello flyingtele, interesting idea. I would think that the response of the semi-passive radiator would be frequency dependent. Sometimes the mechanical coupling and electrical coupling would be in phase with each other, other times it would be out of phase. Thus some frequencies (in-phase) would be boosted, while other frequencies (out-of-phase) would be attenuated.
But as was observed, it's a ex-beer-iment type of thing, the only way to find out is to try it!


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Old 2nd July 2011, 12:57 AM   #7
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Location: Near Vancouver
What if the passive driver was wired out of phase?
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Old 2nd July 2011, 01:03 AM   #8
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Location: Phoenix, AZ
Hey Cal, I would suspect that you are still going to get some boost and attenuation, depending upon the frequency. This is because there are always going to be instances where the driving force of the electrical signal will be in phase with the driving force of the air pressure in the cabinet, thus causing a boost of the frequency, while at other times, these driving forces will be out of phase with each other.



P.S. Check your PM's Cal.

P.P.S Scratch that Cal, I see you already responded to my PM. Thanks!

Last edited by dave_gerecke; 2nd July 2011 at 01:06 AM.
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Old 2nd July 2011, 01:18 AM   #9
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Thanks for your input guys. I think the idea could work, but would need a lot of work to get it working correctly. It would be easy to wire some stuff up, but to do it properly I would have to test multiple drivers to use as the semi active radiator. Then likely have to tune that by adding/removing weights and then also trying to come up with a correct box volume. That way hopefully I can adjust the different areas of constructive/destructive interference between the drivers be be useful. In an ideal world, the frequencies within the units operating range would be boosted, while the upper frequencies where the unit is out of phase could help with the top end roll-off.

If there are instances where the electrical and acoustical driving forces acting on the radiator are out of phase, I could always try adding a 1st, 2nd, or 3rd order filter inline, as this will alter the phasing hopefully bringing the two inline maybe.

I think some investigating is in order, so watch this space folks. I am about to start work on some 3 way floor speakers, so once that's finished then I shall start ex-beer-imenting.
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Old 2nd July 2011, 01:23 AM   #10
Tliner is offline Tliner  Australia
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Try this. Connect left channel to one voice coil and the right channel to the other via a suitable crossover on each. This works very well when you don't want to run two subbies. Just position the subbie somewhere between the mains. Now this conniguration gives you the option of running a seperate power amp just to power the subbie. This gives the advantage of being able to alter the volume of the bass to suit your tastes. Keep in mind that some recordings are lacking in bass and may need that little extra help.

Have fun!
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