I've been looking at ways to control impedance swings as seen by the amplifier. Current state of the xovers.
The tweeter seems to be OK. I can play with the 10R0 as much as I like without any strange resonance problems 😉 So far anyway. Maybe be due to the 3R9 but the frequency response doesn't change so appears to be ok.
The woofer end was a bit different. Initial value of 10R0 there was 4R7 and no 100R across the L and C. The 4R7 was rather critical. Increase it and spikes down to 0R and peaks in the FR so wondered about how to damp the circuit, The 100R or some value across the L and C seem to be the best option.
The add ons are taking out the impedance rise from the cross overs. At the moment ignoring resonance humps it between 4 and any 6ohm up to 10Khz then a rise to 8 at 20Khz. Adding these bits has had no noticeable effect on phase from when I aligned it..
Some people say do not use these circuits across as they can result in short circuits. I don't see things quite like that but wonder how safe the above arrangement is likely to be.
No BS compensation. May be needed but Boxsim is too clever - as it is I might have more bass than I want due to room gain,
The tweeter seems to be OK. I can play with the 10R0 as much as I like without any strange resonance problems 😉 So far anyway. Maybe be due to the 3R9 but the frequency response doesn't change so appears to be ok.
The woofer end was a bit different. Initial value of 10R0 there was 4R7 and no 100R across the L and C. The 4R7 was rather critical. Increase it and spikes down to 0R and peaks in the FR so wondered about how to damp the circuit, The 100R or some value across the L and C seem to be the best option.
The add ons are taking out the impedance rise from the cross overs. At the moment ignoring resonance humps it between 4 and any 6ohm up to 10Khz then a rise to 8 at 20Khz. Adding these bits has had no noticeable effect on phase from when I aligned it..
Some people say do not use these circuits across as they can result in short circuits. I don't see things quite like that but wonder how safe the above arrangement is likely to be.
No BS compensation. May be needed but Boxsim is too clever - as it is I might have more bass than I want due to room gain,
How safe? Make sure the components won't fail under the worst possible conditions, and make sure the amplifier can handle them.
I went through a sample inductor thermal calculation here - https://www.diyaudio.com/community/threads/the-black-hole.349926/post-6864481
I went through a sample inductor thermal calculation here - https://www.diyaudio.com/community/threads/the-black-hole.349926/post-6864481
On the list to do. I think you responded to a question I asked about Boxsim's volt and amp meters. Not sure what to make of the results it shows on a project that pops up each time Boxsim is run but it uses a driver that has an average SPL with the usual drive voltage. It reports voltage changes in dB and not sure if the conversion to actual volts makes much sense.
The current driver does have a pretty constant SPL, quoted as 86dB. The FR trace shows 85dB, sort of indicating a 1dB loss in the entire xover circuit. Visaton could have chosen any dB SPL scaling to volts they wanted to. 😉 I'm not keen on dB's when I want to look at volts etc. I'll see what these indicate and also use some basic electronics for a rough idea. I may hook the xovers up to resistors and check that way as well. Heating rates etc calc's aren't on. Not for me anyway.
The components enclosed in red should have no effect on the acoustic output of the drivers (or voltage at the driver terminals) unless the amp has significant output impedance (like a tube amp) . They should only effect the impedance the amp sees. So, unless the amp's output is sensitive to the change in impedance load they should be otherwise passive.
They are buried in Boxsim's chassis data files. Also various aspects look fine as they are. 😉 There is also another problem - me. I don't want a complex solution. I've worked for too long in the design side of manufacture. I want to know how accurate the simulation is. I have 2 close to 2nd order LR xovers. Departures down to standard parts and the drivers but the phase alignment is better than others I have seen. The bass end driver may need changing but I'll have a cabinet I can fit something else to and measure the data that is needed. I'll also have fairly decent tweeter to match with what ever it turns out to be. 😉 I had hoped to use cheap.
it's not a solution I have seen, I started with networks on the drivers but that doesn't do anything about the xover impedance humps. I'm wondering about the 1mH on the tweeter. I vaguely remember there are rules of thumb concerning maintaining resonant F with changed values but have no idea what it is or that it exists.
The interest in keeping the impedance levels constant relates to class D amps. It will be going on one. Boxsim projects appear to play with xovers too to reduce them. Some of that goes on with this design. The hump without compensation is ~25ohm 😉 from memory so lets say not huge. I can build without the bits as it's an add on. The tweeter compensation method was stolen from a boxsim design. Just needed value change. 😉 Hope 50uH doesn't need many turns. Simplest way of reducing the lift once the the tweeter becomes the main speaker,
Other factors. Boxsim tells me I wont be driving the speaker with more than ~16vrms. Our av reciever does have a facility to limit volume. I assume this is to take care of problems in this area. This voltage starts me wondering about dc resistances. I'm having problems adding Boxsim's amp and volt meters. May be down to using the latest version and also a brand new design. I get it's red line of death and that tells me all sorts of data is missing when it's loaded. It expects the usual set that comes when a chassis is loaded.
Usually the simulated accuracy is good. Unless you provide quality data, it will easily be less accurate than the simulation itself.
In any case, accuracy isn't always the biggest concern.
Memory reset
More on Q here
https://ham.stackexchange.com/questions/12284/is-there-a-best-ratio-of-l-to-c-in-a-resonant-circuit
Might have something to offer rather than fiddling with 3 values. 1mH in the correction circuit seems rather high for the F's it functions at but 8ohm tweeter and 4ohm bass.
More on Q here
https://ham.stackexchange.com/questions/12284/is-there-a-best-ratio-of-l-to-c-in-a-resonant-circuit
Might have something to offer rather than fiddling with 3 values. 1mH in the correction circuit seems rather high for the F's it functions at but 8ohm tweeter and 4ohm bass.
Find the -3dB points of the resonance peak and calculate it’s Q. Then adjust the notch circuit accordingly.
I admit that I'm not up to the latest in Class D amps, but the ones I have used (Class D Audio CDA 254) are not sensitive to impedance at lower frequency provided it is above the amp's specified impedance load for it's power response. At higher frequency they roll off if the impedance load drops due to the use of an series inductor in the amp's output filter. If the amp has a spec on frequency/power response it should say into what impedance. With the amps I have used as long as the impedance doesn't drop below that value at higher frequency there was no problem. But at some point above the audible range the amp's output will drop off. The woofer's low frequency resonance should not be a problem.
It's more of an aspect of interest. The data on the class D chips often indicate more distortion with increased speaker impedance. Maybe even different output filtering. The amp I will be using states the usual 4 to 8 ohm. I don't have to include the bits when I build. Also need to work out the power consumption in them. Bit of a problem at the moment.
Impedance is not constant across frequencies on speakers. With or without passive crossovers.
@thisusername
Not always. I'm listening to a set of two-way speakers right now that have a flat 4 ohm impedance across the full audio band. 🙂
For users who don't have amplifiers that are voltage sources, conjugates and various impedance-leveling techniques are a perfectly valid topic for DIYaudio.com
Dave.
Not always. I'm listening to a set of two-way speakers right now that have a flat 4 ohm impedance across the full audio band. 🙂
For users who don't have amplifiers that are voltage sources, conjugates and various impedance-leveling techniques are a perfectly valid topic for DIYaudio.com
Dave.
I just don't see the real world advantages of it other than a special case use with a certain amp that were not designed well for the use.
@thisusername The audio world is full of amps "not designed well for this use." 🙂
If you can't grasp the premise of this thread then maybe best to bow out???
Dave.
If you can't grasp the premise of this thread then maybe best to bow out???
Dave.
Amps with high output impedance (many tube amps) will have an output that varies with frequency if the load doesn't have flat impedance.
The relative power of an audio signal varies across the frequency range to begin with. But on a tube amp, its relative core loss comes into play as well as the inductance value of the primary of the output transformer.
I use an AV receiver rather than a separate amp. The distortion spec is pretty crap but relates to uW and max power. I've looked at changing to something similar with ARC etc. I found 3 units one still includes 5.1. Another stereo only. Decent distortion figures but there is an entry for loudspeaker impedance. One for instance assumes 6ohm. Higher - need to tell it. Data on class D chips show similar. More distortion the higher the speaker impedance. Maybe different output filtering. 😉 Worth worrying about - pass. Loads of small chinese boxes, all sorts of powers - when a spec is given it's with a specific load, Probably resistive,
Yes, certainly. But the point is that speakers are typically designed to be driver by a constant voltage source. If an amplifier had significant output impedance the applied voltage will not be constant constant. For example, the read line is the voltage applied to a woofer with the impedance shown in blue from a constant voltage source. The black line is the voltage applied to that woofer from a source with 1 ohm output impedance. Now consider a typical speaker with significant deeps and peaks in it's impedance curve. The SPL response can vary +/- a dB or more as the impedance changes and the speaker's response and voicing will be different form the design spec.
Speakers are just transducers. The common voice coil type are inductive loads. The chart above is the typical curve for a voice coil speaker not in a cabinet.
The voice coil's impedance is variable across frequency due to it being an inductive coil, and fallows a inductive reactance (XL) curve, which can be calculated by the formula XL=2 π fL L being the inductance of the speaker coil , and f being the frequency applied. When the frequency is applied at the point where the coil has the least reactance, the magnetic flux collapses, and the only impedance measured is the resistance, going lower in frequency, the polarity of the speaker's magnetic flux inverts which causes the phase of the transpose signal of the transducer to invert. The phase of the signal is not constantly transpose mechanically either due to the change in magnetic flux current and the internal impedance at that operational frequency.This correlation can be seen here in the free air resonance chart, with phase correlation plotted with the free air impedance curve.
When placed in an enclosure, the air resistance within the box poses mechanical induced impedance cause by the difference in air pressure. Here is the same type in a sealed enclosure:
When combined with other drivers to create a multi-way system, the impedance curve looks like this:
The resulting phase correlation on the output (which is measured with a microphone) is a result of the speaker acoustically transposing the signal into the air, and electrical loading is a result of the inductive loads and current returned from a filtering network, called a crossover.
Other speaker types have different characteristics. This is an example of an electrostatic speaker:
Is 'consistently constant' is what you mean?
There are two types of amplifiers: current output amplification and voltage output amplification. The variable that defines this type is the coupling method the amplifier uses to connect to the speaker. A voltage output is transformer coupled, that varies voltage in a fixed current circuit load created by the secondary of the output transformer and the connected speaker. A current out amplifier (dc coupled or capacitor coupled) varies the current and the speaker load develops the voltage across as the current return to the amp. This is without discussing what happens internally to the amplifier using either output methods and types of amplification device (tube vs. solid state) as well as amplifier topology (class A, AB, D, H, S, T etc).