For anyone thinking of addressing the lion's share of response anomalies with EQ who might be buying into this continuous stream of rubbish - I will present once again the counterpoint, fact checking view. Passive crossovers as most of us again with a reasonable amount of experience knowcan only absorb energy on a selective basis from that which is applied to the speaker terminals from the amplifier. EQ on the other hand has the potential to add energy to select bands. While the two methods can have essentially the same effect when subtracting energy, the same cannot be said for eliminating dips in a driver's response. And sometimes (some might argue often) when a dip occurs at one frequency, the energy "absorbed" at that frequency appears at a different frequency in the form of distortion. This behavior routinely occurs when drivers enter the breakup region. Hence when we add energy via EQ, we sometimes wind up with unintended consequences. Contrary to the above quoted ridiculous oversimplification, EQ is not equivalent to passive crossovers and the above claim - "any crossover is nothing more than EQ" - is patently false.
An often cited advantage of actively controlled speaker systems is the maintenance of sensitivity. The natural tendency is to boost dips rather than suppress peaks when it comes to "evening out" response. So the distinctions and the warnings by people like Linkwitz and myself about the limited usefulness of EQ as a high performance loudspeaker management tool should be at least considered if not fully heeded. Active speaker control is still a potential advantage but the end result needs to be carefully listened to and measured for increases in distortion that do in fact occur - contrary to assertions of others within this thread.
And now, hopefully the person who assured us he was going "to bail" earlier will live up to his promise and allow this particular thread to cease becoming yet another advertisement for JohnK's Sound Easy instructional download or some other plug for Sound Easy v17.
An externally hosted image should be here but it was not working when we last tested it.
Active or passive circuit?
Energy added or subtracted?
Does it make a difference?
If the voltage trasfer function across a driver's terminals is: Vd/Vo, does it make any different on how it was generated? Passive? Analog acitve? DSP? God?
The only real differences between active crossovers and passive are 1) with active the driver sees the output impedance of the amplifier as its driving point impedance. That might be an advantage, might not. 2) The transfer function of the filter is not dependent on the diver impedance, and possible variations thereof.
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This is what we typically call a quick and dirty run. Very time effecient for scanning through a batch of drivers when you don't have appropriate room available. From this you can end up with a short list of candidates for the nest round of tests with more sophisticated equipment.
Rather than continue to waste bandwidth I though it might be more instructive to post some measurements. I put a brief study together last night where I measured a driver's raw frequency response, CSD and burst response. Then I constructed a bandpass filter intender to be a 4th order 200 HP and a 2k Hz LP. In the first case a simple crossover was used which is representative of what might be accomplished using a passive approach at the design point, (this crossover was, however, emulated digitally). Then I applied the full power of DSP and constructed a filter for which the measured acoustic response at the design point would nearly perfectly match the target response. Along with that I also constructed an ideal electrical HP/LP filter to match the acoustic target of the full powered DSP crossover. The FR, CSD and Burst response of the electrical filter serve as the reference response which is the best than can be obtained in regards to FR, and linear/transient distortion of such a band pass. All cases were for minimum phase. No phase linearization was applied. Finally I measure the THD of the simple and full blown DSP crossover at a frequency where the most equalization was applied to see what effect the EQ had on THD. All measurement were taken in quick succession with identical setting. The results can be viewed HERE.
You may all draw you own conclusions from the study regarding the effects of EQ on linear and nonlinear distortion, and its usefulness with regard to designing a ZDL. The driver used was a Focal 5N411L.
You may all draw you own conclusions from the study regarding the effects of EQ on linear and nonlinear distortion, and its usefulness with regard to designing a ZDL. The driver used was a Focal 5N411L.
Nice work, John. Direct evidence that fully supports everything we've been saying.
Joachim, as a recent convert to DSP (primarily due to ease of development) I hope that you review this to see just some of the usefulness of the new DSP products available. The claimed negative effects are not a concern.
Dave
Joachim, as a recent convert to DSP (primarily due to ease of development) I hope that you review this to see just some of the usefulness of the new DSP products available. The claimed negative effects are not a concern.
Dave
I was out of the house for some days and got the oportunity to read the recent posts right now. Good work John, that is really helpfull. Still i am focussed to make a passive xover ZDL and then look into DSP options. I have a good RME Firewire Soundcard that should sound good enough and i will try to get the UE equaliser as soon as it is availlable.
Today i will remeasure the Scan wideband in a more stable, 50cm long PVC tube and then make a decission if i go for a sphere or a tube. I also will build the bass cabinet this week. Then a decission has to be made if a build a second Scan wideband in the sphere and look if i can build the ZDL as a 3 way or have to go to 4 way. Certainly i will continue my work as well as i can and when the speaker is ready i already organised a listening session with some of my German DIY fellows. I think i have to come up with some results now. Sorry, i can not dedicate as much time as i like to this project so my pace is rather slow.
Today i will remeasure the Scan wideband in a more stable, 50cm long PVC tube and then make a decission if i go for a sphere or a tube. I also will build the bass cabinet this week. Then a decission has to be made if a build a second Scan wideband in the sphere and look if i can build the ZDL as a 3 way or have to go to 4 way. Certainly i will continue my work as well as i can and when the speaker is ready i already organised a listening session with some of my German DIY fellows. I think i have to come up with some results now. Sorry, i can not dedicate as much time as i like to this project so my pace is rather slow.
I measured the Scan wideband in a 50m long and 10cm diameter PVC tube. Again Mr.Stoll was right. The measurements turned out much better then in the mineral water bottle. Actually with the exception of the 90° measurement it looks slightly better then in the 6 liter sphere. Also the loss in the fundamental tone area is not more then in the sphere so this is an option too. i will now measure the tweeter on top of the tube.
Very interesting measurements. I have a pair of OX drivers due to arrive this week. Curious how early the measurement departs at 90 degrees from the others, I would expected it to be a bit higher. Thanks for showing that, I seldom see those. Most don't show beyond 60.
Dave
Hello,
I am sitting here thinking through the conversations here about the merits of DSP crossovers, active line stage crossovers, passive crossovers at the speaker and the stored energy thing (real or not)
First the stored energy and performance testing of a speaker / driver of any kind is done with the speaker installed in an enclosure and the electronics connected. The same speaker installed on an open baffle, in a PVC tube or mineral water bottle will perform differently. Any of the above configurations will change the performance of the same driver to the ear or measured with the test gear demonstrated here in this thread.
Dampening, electronic (feedback, electronic brakes) or mechanical (resistance, like applying the brakes) seems to be a key ingredient.
One example, remove all the passive crossover parts from between the speaker and the amplifier and the amplifier dampening ratio has much better control and ability to stop the motion of the speaker cone when the signal stops.
Lots of factors!
DT
All just for fun!
I am sitting here thinking through the conversations here about the merits of DSP crossovers, active line stage crossovers, passive crossovers at the speaker and the stored energy thing (real or not)
First the stored energy and performance testing of a speaker / driver of any kind is done with the speaker installed in an enclosure and the electronics connected. The same speaker installed on an open baffle, in a PVC tube or mineral water bottle will perform differently. Any of the above configurations will change the performance of the same driver to the ear or measured with the test gear demonstrated here in this thread.
Dampening, electronic (feedback, electronic brakes) or mechanical (resistance, like applying the brakes) seems to be a key ingredient.
One example, remove all the passive crossover parts from between the speaker and the amplifier and the amplifier dampening ratio has much better control and ability to stop the motion of the speaker cone when the signal stops.
Lots of factors!
DT
All just for fun!
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Hi Joachim,
This is one area where I found the first order series crossover is MUCH preferable to a first order parallel one. It is usually also quite possible to dispense with both LCR Traps for the resonance and the Zobel on HF part.
While this as such does not really make a difference in frequency response, it does mean we need way few crossover parts and can select higher quality ones in the same budget. My latest "messing about" speaker is 3-Way forst order and has 4 Pars for the whole crossover (two copper foil chokes, two capacitors) and two more parts to equalise the "CD-like" HF response of the circular Ribbon I use.
Of course, not a lot of drivers work successfully with first order crossovers, which limits the use in the end.
Ciao T
This is one area where I found the first order series crossover is MUCH preferable to a first order parallel one. It is usually also quite possible to dispense with both LCR Traps for the resonance and the Zobel on HF part.
While this as such does not really make a difference in frequency response, it does mean we need way few crossover parts and can select higher quality ones in the same budget. My latest "messing about" speaker is 3-Way forst order and has 4 Pars for the whole crossover (two copper foil chokes, two capacitors) and two more parts to equalise the "CD-like" HF response of the circular Ribbon I use.
Of course, not a lot of drivers work successfully with first order crossovers, which limits the use in the end.
Ciao T
Valid points. My experience with active configurations overall is very positive but in numerous instances, I've seen first hand the limitations of EQ when it comes to energy storage and breakup problems. The example Johnk just gave is a garden variety response anomaly (most likely a problem external to the driver like diffraction) that is well suited to correction with EQ. The lack of higher order distortion products from this dip suggests that it is unlikely to be a problem for EQ. None of this supports the earlier contention by DLR that frequency response anomalies represent distortion (even or odd ordered) and that they are eliminated with EQ. Aside from the fact that there was very little distortion to begin with in the case given, there was also no reduction in distortion after EQ as DLR suggested would happen earlier. The case given is not demonstrative in any significant way.
I've been busy laying out a new design, When I get back into the sound room, I will take and save some distortion plots that prove what I've been saying. No special isolated cases to prove a red herring - just garden variety situations in which EQ resulted in more distortion with less than expected improvement in frequency response.
That is not true Joachim. The LRC will make the load the passive crossover, or a directly connected amplifier sees more constant which makes the high pass passive filter easier to design but the damping of the driver is a function of the impedance the driver sees when looking back at the load prepresented by the LRC network, the crossover filter and the amplifier.
Depending on the Fs, Vas, and Q - I've found heavily damped tapered tubes useful in some cases for dealing with resonance without resorting to LCR traps. Considered mechanical damping instead of electrical damping?
Hello,
This thread is much like a speaker lab tutorial. The idea of separate / modular midrange, woofer and tweeter rather than a large square box that holds all the parts allows many possibilities that are not otherwise possible. Swapping in and out one mid for another or one XO variety for another is really interesting. Putting a pipe cap on the end of a midrange enclosure making it possible to swap in rock wool or raw sheep wool I never thought of before.
Joachim thanks for the eye opener.
DT
All just for fun!
This thread is much like a speaker lab tutorial. The idea of separate / modular midrange, woofer and tweeter rather than a large square box that holds all the parts allows many possibilities that are not otherwise possible. Swapping in and out one mid for another or one XO variety for another is really interesting. Putting a pipe cap on the end of a midrange enclosure making it possible to swap in rock wool or raw sheep wool I never thought of before.
Joachim thanks for the eye opener.
DT
All just for fun!
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