Passive Crossover Question... Power loss?

[Chr1]

I am using a pair of pro-audio Tannoy V12s designed for sound reinforcement which are intended for use with subs, which is currently what I am doing (3 x active). I am curious as to whether the crossovers within the Tannoys which presumably cut the frequencies below 70 Hz, merely dissipate the energy from the amplifier as heat, or whether something else is going on?
Apologies for the rather naive question. I am a bit of an electronics ignoramus!
Thanks in advance.

From the Tannoy manual...

Frequency response (1) +/- 3dB: 70Hz - 25kHz

(Have attached the manual from the earlier models... Essentially the same.)

 

[JayGilb]

The resistors in the passive crossovers (not sure of the components) are dissipating some heat, but the large majority of the heat is being dissipated by the magnet/basket structure of the speaker.

 

[Chr1]

This is confusing to me as I was under the impression that any energy bellow 70 Hz would not get beyond the crossover so would have to be dissipated as heat, no?

 

[Vincent Kars]

something else is going on?

Yes.
It is a high pass filter so blocking anything below 70 Hz.
All what is below 70 simply won't enter the wire hence no dissipation in the filter

 

[Chr1]

Yes.
It is a high pass filter so blocking anything below 70 Hz.
All what is below 70 simply won't enter the wire hence no dissipation in the filter

Thanks. Does this mean that the amplifier is not actually wasting power/energy on the frequencies below 70 Hz? I am curious as I am using two relatively low powered amplifiers which seem more than capable of providing the required SPL, but was under the impression that the Tannoy crossovers may be squandering some of the power.
Thanks again.

 

[YSDR]

Yes.
It is a high pass filter so blocking anything below 70 Hz.
All what is below 70 simply won't enter the wire hence no dissipation in the filter

No, it doesn't block, it only gradually reduces. So the signal below 70Hz enters to the wire, just reduced in level (with a properly executed high-pass), heating all elements in the loudspeaker that have DC resistance.

 

[Vini darko]

My possibly flawed understanding is that most of the filtered energy is shunted to ground/negetive with some being radiated as heat and electromagnetism.
So in answer to your question , yes the amp is wasting some energy.
To overcome this , moving to active crossovers in front of the amplifier will solve that. So the amplifier only amplifies the frequencies it needs to.

 

[YSDR]

My possibly flawed understanding is that most of the filtered energy is shunted to ground/negetive with some being radiated as heat and electromagnetism.

Only the parallel elements (in the passive filter) shunts the signal to ground, but if these parallel elements have series resistance (resistors, inductors, electrolytic capacitors) then they will heat up aswell.

 

[Chr1]

Only the parallel elements (in the passive filter) shunts the signal to ground, but if these parallel elements have series resistance (resistors, inductors, electrolytic capacitors) then they will heat up aswell.

Thanks. Presumably the crossover will be designed to shunt the signal to ground rather than waste energy? From what I can gather online the crossover is a good design with high quality components. Given that the speakers are designed for high power applications, I would assume that the crossover would be designed to waste as little energy as heat as possible?

 

[Vini darko]

Only the parallel elements (in the passive filter) shunts the signal to ground, but if these parallel elements have series resistance (resistors, inductors, electrolytic capacitors) then they will heat up aswell.

Yeah you're right I forgot about that.

 

[YSDR]

Thanks. Presumably the crossover will be designed to shunt the signal to ground rather than waste energy? From what I can gather online the crossover is a good design with high quality components. Given that the speakers are designed for high power applications, I would assume that the crossover would be designed to waste as little energy as heat as possible?

According to the manual, this speaker don't have a 70Hz high-pass filter. So, on it's own, the speaker takes all the power that comes from the amplifier. That 70Hz thing is where the anechoic frequency response drops to -3dB.
Moreover, the manual also says that, if you want to use this speaker with a subwoofer, the TX2 controller/active outboard crossover is recommended. Of course, you can use any outboard crossover if you know what you doing.

 

[Robh3606]

I am using a pair of pro-audio Tannoy V12s designed for sound reinforcement which are intended for use with subs, which is currently what I am doing (3 x active). I am curious as to whether the crossovers within the Tannoys which presumably cut the frequencies below 70 Hz, merely dissipate the energy from the amplifier as heat, or whether something else is going on?
Apologies for the rather naive question. I am a bit of an electronics ignoramus!
Thanks in advance.

From the Tannoy manual...

Frequency response (1) +/- 3dB: 70Hz - 25kHz

(Have attached the manual from the earlier models... Essentially the same.)

The only crossover is the one @ 1.5K. Below 70Hz are not reduced by a crossover but rolls-off naturally due to the LF driver and box.

Rob

 

[Chr1]

The only crossover is the one @ 1.5K. Below 70Hz are not reduced by a crossover but rolls-off naturally due to the LF driver and box.

Rob

Thanks folks. My misunderstanding...Is this natural roll off preferable to a high pass @70 Hz? Presumably a 70 Hz passive crossover would be wasting more amplifier energy as heat?
Realise that a digital crossover is probably optimal but now just glad to hear that I'm not actually also merely heating components within my speakers as wasted amplifier bass energy!

 

[Robh3606]

Thanks folks. My misunderstanding...Is this natural roll off preferable to a high pass @70 Hz? Presumably a 70 Hz passive crossover would be wasting more amplifier energy as heat?
Realise that a digital crossover is probably optimal but now just glad to hear that I'm not actually also merely heating components within my speakers as wasted amplifier bass energy!

How are your active crossovers set-up?? They should have a summed output for subs as one of the options and should be able to select a high pass filter frequency and possibly the slope used figure 12dB or 24dB.

Rob

 

[YSDR]

Is this natural roll off preferable to a high pass @70 Hz? Presumably a 70 Hz passive crossover would be wasting more amplifier energy as heat?

The 70Hz natural rolloff it's just like that, not because it's "better" than a high-pass filter, but because the speaker is balanced that way. According to Hoffman's iron law, choose 2 from these 3 parameters, because you don't have all 3 at the same time: 1. small size, 2. high efficiency, 3. deep bass extension.
BTW a (proper) 70Hz passive filter needs very large value passive components that are large, heavy and expensive.

 

[TurtlePaul]

You seem obsessed with energy being dissipated as heat. You shouldn't be. That doesn't matter at all.

The crossover should be the one that sounds best. If you have a receiver with a high pass filter, you should use it and a sub with these speakers. Not because it saves energy, but because it sounds better to not have speakers producing notes below their roll-off and below the tuning frequency of their box.

 

[Chr1]

Thanks for the help. Should have explained that I am using high level connections from my amplifier to a pair of active 10" sealed subs underneath the two Tannoys and another active 12" sealed sub centered between these. The 12" central sub is crossed at 45 Hz and the two 10" @ 110 Hz. I am using MathAudio RoomEQ via Foobar to a Topping DX3 Pro. I am really just curious as to how much amp power is wasted in a passive crossover versus a speaker having a natural roll off. The MathAudio software has made a massive difference to my sound quality and hugely simplified the sub integration.

 

[TurtlePaul]

Not enough power is wasted to be meaningful. Any resistor would waste power, as would the resistive component of any inductor. That being said, the primary way that passive crossovers cut power is by increasing the impedance (the frequency dependent resistance) at certain frequencies by using capacitance and inductance. This reduces the current flow via Ohm's Law (V=IR) which then reduces the power via Watt's Law (P=IV). This isn't wasted power - if the amp sees an eight ohm load at one frequency and a 16 ohm load at another, it will naturally deliver half of the power at the 16 ohm frequency at the target voltage without wasting any power.

 

[Chr1]

Aha. Thanks for the explanations!

 

[Chr1]

PS I have previously used a Tannoy TDX-1 digital crossover in place of the DX3 Pro but though easier for sub integration, I found that the sound quality not quite as good.