I bought a pair of Totem Hawk speaker. However, one of the tweeter is blown. And I ordered a new tweeter from my local Totem dealer. I removed the old one and install the new one and found that the original circuit has the polarity reversed. The crossover is a simply first order design. Can anyone tell me why the tweeter polarity is reversed? Also in the tweeter circuit, why do they used three resisters in parallel along with one resister in series? Can them just use one resister? Is it because a specific resistance value that they want to achieve?
thanks a lot in advance
thanks a lot in advance
Polarity reversal may be the best thing in this case.. phase is not simple to predict just looking at the schematic. If you end up changing these values you may want to uncover the situation for your own benefit, or at least keep an open mind.
Probably. Some do this for power handling, some to deal with device parasitics.
It may have a fairly high crossover frequency such that the set back of the woofer voice coil relative to the tweeter causes a large enough phase shift that the reverse connection of the tweeter gives the best alignment. I'm not a big fan of first order crossovers as they don't protect the tweeter very well. If the power rating is sufficient one resistor will do the job. They may have got a good deal buying resistors in quantity or they tuned each speaker with a combination of resistors to match the speakers. Measuring the drivers magnitude / phase response with a microphone independently along with the impedance curves and you could model the crossover and drivers in a Xsim or other crossover design software and see exactly what the designer was doing.
Further thinking on this, there's a chance that your room response, desired levels and voicing choices might have you disagreeing with the choice of tweeter level. Not that this is necessarily the correct way to make such an adjustment, just saying that such precision is going to be within your own scope for adjustment.
Crossovers shift phase.
On both transducers, woofer and tweeter, and in opposite ways.
Phase difference can be high enough to cause a cancellation notch at crossover frequency, so a common cure is to invert phase on one of them.
Inverting tweeter phase is better than woofer, where if multiple woofers are used you can have Bass cancellation, over a wide band, very noticeable, while with tweeter inversion problems are subtle.
On both transducers, woofer and tweeter, and in opposite ways.
Phase difference can be high enough to cause a cancellation notch at crossover frequency, so a common cure is to invert phase on one of them.
Inverting tweeter phase is better than woofer, where if multiple woofers are used you can have Bass cancellation, over a wide band, very noticeable, while with tweeter inversion problems are subtle.
See post #3. A physical misalignment of the sound centres of woofer and tweeter in the horizontal plane can also introduce a phase difference at the crossover frequency.
The specs of the Totem Hawk say crossover frequency 2.5 kHz, 2nd order:
https://www.totemacoustic.com/pdf/spec_sheets/Totem_SpecSheet_ Hawk.pdf
So the makers must be taking into account the mechanical roll-offs of the drivers as well as the electrical roll-offs of the crossover components.
For comparison purposes, here is the crossover schematic for 2008's B&W CM5 speaker which has a higher crossover frequency of 4 kHz.
There appears to be no electrical phase reversal in this case. Gilbert Briggs led me to believe that phasing is less of an issue above 3 kHz!
The drivers in this speaker will have been engineered to work effectively with a minimalist crossover by incorporating their own mechanical roll-off slopes.
There appears to be no electrical phase reversal in this case. Gilbert Briggs led me to believe that phasing is less of an issue above 3 kHz!
The drivers in this speaker will have been engineered to work effectively with a minimalist crossover by incorporating their own mechanical roll-off slopes.
Talking of Gilbert Briggs of early Wharfedale fame, here is his (edited) take on electrical phase shift in a crossover network:
"The phase shift in a 1st order network is 90 degrees. Its effect is not serious but can be countered by pushing the upper frequency driver back a quarter of a wavelength at the crossover frequency.
With a 2nd order network, the phase shift is 180 degrees and it is well worthwhile to ensure that the bass and upper frequency driver are acoustically in phase (by way of anti-phase electrical connection)."
Briggs went on to say that "above 3 kHz phasing is of no importance in domestic listening". However, remember to regard that statement in the context of the 1960s!
Hope that helps a little, @hc167.
"The phase shift in a 1st order network is 90 degrees. Its effect is not serious but can be countered by pushing the upper frequency driver back a quarter of a wavelength at the crossover frequency.
With a 2nd order network, the phase shift is 180 degrees and it is well worthwhile to ensure that the bass and upper frequency driver are acoustically in phase (by way of anti-phase electrical connection)."
Briggs went on to say that "above 3 kHz phasing is of no importance in domestic listening". However, remember to regard that statement in the context of the 1960s!
Hope that helps a little, @hc167.
Anything else would be in contradiction to Totem's design philosopy: https://totemacoustic.com/totem-acoustic-our-story/
The spec said 2nd order but with single capacitor in tweeter circuit and single inductor in the woofer circuit, it looks to me a first order. Wrong?
It's electrically 1st order but overall, taking the drivers' mechanical characteristics into account, it's 2nd order.
The drivers each have their own mechanical roll-offs which, when added to the 1st order 6 dB/octave electrical roll-offs, result in overall 2nd orderl 12 dB/octave roll-offs.
The drivers each have their own mechanical roll-offs which, when added to the 1st order 6 dB/octave electrical roll-offs, result in overall 2nd orderl 12 dB/octave roll-offs.
I would not take this too seriously; It's boiler plate ad speak. Also don't all electrical engineers use and have extensive math backgrounds? And I'm willing to bet most (all) speaker designers employ their "ears".
Normally a tweeter (at least one with a closed backside) has a second-order roll-off at low frequencies, as it is a kind of closed box. An overdamped second-order response is equivalent to a cascade of two first order filters with different cut-off frequencies, so maybe they have a tweeter with a lot of damping and only take highest cut-off frequency into account?
Also, you invariably find with first order filters, that the difference of when tweeters are below ear height VS above ear height
a 180 degree phase shift is required to make the response 'sum' the same.
Capacitor shifts Tweeter phase 90 degrees one way.
Inductor shifts Woofer phase 90 degrees the other way.
But .. but .. but ... there is no woofer series inductor!
Oh yes there is, hidden in plain sight 😄
Start with voice coil inductance, and add heavy cone inductive behaviour.
Notice cone speakers impedance rises above, say, 1kHz ... that's why..