A second identical shorted loudspeaker as passive damped radiator

[ygg-it]

Hello, please help me to model and determine the behavior and distortion of adding a second shorted identical loudspeaker in a sealed box (vas 24l, fs 39hz, volume 20l) as passive radiator.

I tested because i had a spare identical loudspeaker around, and I like because I have very clean bass now, but not really sure how to model, and if I could damage the second speaker due to shorting its terminals.

I think it should be something like a sealed box with losses, something like a variovent, or a bass like air flow resistor.

 

[boswald]

Do not close(short) the voice coil. Leave it open(or remove it), and add mass to the passive cone to tune for your box volume.

 

[Galu]

I'll add that shorting the voice coil puts an electromagnetic brake on the cone's vibrations, and that's why you don't want to do it for your purposes.

 

[Galu]

I'll also add that it is usual to remove either the magnet assembly or the voice coil.

This is because the to and fro cone movement will be larger in amplitude in your passive radiator application and you don't want the voice coil to 'bottom out' on the back plate of the magnet assembly. (The passive radiator conversion requires to have around twice the to and fro movement of the working speaker.)

 

[Galu]

I think it should be something like a sealed box with losses, something like a variovent, or a bass like air flow resistor.

It's more like a reflex box where the mass of air in the port is replaced by the mass of the cone of the passive radiator.

 

[ygg-it]

Thanks, but everything sound better shorted. Why? Any issue?

 

[SpeakerBob]

I'd rather use the 2nd woofer powered in 0.5 way than use it as a PR. Might end up needing a bit of EQ after though.

Rob.

 

[ygg-it]

How to power in 0.5 way? In series?

 

[stv]

Thanks, but everything sound better shorted. Why? Any issue?

yes: you need to tune the passive radiator below the resonance frequency of the active loudspeaker, easiest done by adding weight. otherwise you will get sort of a boom box, with a rather high bass peak.
by shorting it you got a (nearly) closed box, which usually sounds good, but does not give deep bass. you disabled the passive radiator by shorting it.

 

[Galu]

Here's a useful link: AE Speakers --- Superb Quality, Unforgettable Performance, Definitely.

 

[Galu]

Thanks, but everything sound better shorted. Why? Any issue?

As I said, the cone won't vibrate with large amplitude as the shorted voice coil acts as a brake.

I can't understand how you are getting an improvement in this way unless you have removed the magnet system.

 

[Bromle]

Sonus Faber did this with the Extrema model. But they included a resistor network with varying resistance enabling the user to select his/her preference: less resistance = more damping (more «closed box»). In addition they added weight for proper tuning frequency.

 

[Galu]

Let's see if we're on the same page ygg-it.

By shorting the voice coil I understand it to mean you have connected a length of wire between the positive and negative terminals of the driver.

Is that correct?

 

[Galu]

That's interesting, Bromie! That Was Then... Sonus Faber Extrema | What Hi-Fi?

 

[stv]

I can't understand how you are getting an improvement in this way unless you have removed the magnet system.

I can: it is better to disable the passive radiator by shorting it and have a decent closed box rather than having a completely uncontrolled, mis-aligned passive radiator box.

 

[Galu]

 

[ygg-it]

Let's see if we're on the same page ygg-it.

By shorting the voice coil I understand it to mean you have connected a length of wire between the positive and negative terminals of the driver.

Is that correct?

Correct. Better with any resistor. And the speaker still move due to the coil resistance, so it doesn't act as a 100% sealed box, but maybe 80% sealed and 20% reflex?

 

[Galu]

If it sounds good to you, then fine.

However, going back to your original question, I don't know how you would model the behaviour.

 

[GM]

it doesn't act as a 100% sealed box

Right, a little lossy, similar to a heavily stuffed vented box [AKA aperiodic].

 

[phase_accurate]

It could probably behave like a variovent because it is a "damped leak".
And I would also try to play around with different resistor values across the passive's voice coil and not only with a short circuit just for curiosity and possible further improvement.
Maybe you will still like the shorted version best. If the excursion stays reasonable there should be no problem at all as long as you like the sonic result.

It would be interesting to know what happened if the circuit accross the voice-coil isn't just a short or a resistor but some resonant circuit.

A former workmate of mine did your trick with his DIY Manger boxes 25 years ago. He liked the sound with the second woofer shorted better than running both in parallel.

Regards

Charles