I am looking at building a 3 way speaker but wish to change the bass cabinet to slightly smaller size.
The design I am looking at uses an LCR circuit on the midrange unit and on the bass unit due to a low point of crossover and I have been told that if I change the bass tuning ie box size and port tuning that the LCR circuit would have to be changed also.
I dont know much about that sort of thing and although I can see that it may change the LCR circuit on the bass unit I assume the mid circuit would stay the same.
Also if I were to build it sealed I assume that the LCR would still need to be changed or am I wrong.
The design I am looking at uses an LCR circuit on the midrange unit and on the bass unit due to a low point of crossover and I have been told that if I change the bass tuning ie box size and port tuning that the LCR circuit would have to be changed also.
I dont know much about that sort of thing and although I can see that it may change the LCR circuit on the bass unit I assume the mid circuit would stay the same.
Also if I were to build it sealed I assume that the LCR would still need to be changed or am I wrong.
Colmo,
Reducing box size would push the sealed box Fc and impedance peak up, changing ported box size and Fb will affect the impedance curve also. Depending on how much higher the crossover frequency is above the change, a "slightly smaller size" may have little effect on the impedance in the crossover region, so may not require different LCR component values for the woofer, and should have no effect on the mid circuit in most.
Reducing box size would push the sealed box Fc and impedance peak up, changing ported box size and Fb will affect the impedance curve also. Depending on how much higher the crossover frequency is above the change, a "slightly smaller size" may have little effect on the impedance in the crossover region, so may not require different LCR component values for the woofer, and should have no effect on the mid circuit in most.
Am I correct in assuming that if the new impedance peak is higher than before on the bass unit that the resistor should be decreased in value to comensate
Yes, the resistor is one of the three things you might need to change. Due to the fact that this kind of filter is centred on a particular frequency you usually want to measure these things.
Do you really know what is the purpose of the LCR circuit in that design? Can you share here the crossover and drivers used?
Ralf
Sim it in Boxsim. You’ll have the opportunity to calculate the impedance from the box tuning and correct the LCR so that it keeps tuned to the second impedance peak with ported or the impedance peak with closed enclosure.
I have win isd pro and can sim it there.
I can get the second peak at the same frequency as the original design but the peak is slightly higher. Guess I could leave it there but if I want to reduce the peak should I increase or decrease the resistor in the LCR circuit.
I can get the second peak at the same frequency as the original design but the peak is slightly higher. Guess I could leave it there but if I want to reduce the peak should I increase or decrease the resistor in the LCR circuit.
That isn't clear yet.
If you are going to do the sim version of this instead of the measured version, I'd want to make a list of needs.. this is what I'd expect to do.
If you are going to do the sim version of this instead of the measured version, I'd want to make a list of needs.. this is what I'd expect to do.
- View the crossover to verify what it's doing.
- Sim the current impedance peak.
- Import that into a crossover simulator.
- Verify that the current LCR values are right for it (checks both the purpose of the components, and whether you can trust your sims).
- Repeat with the new simmed box.
- Consider other crossover adjustments for the new response.
Thanks for all that information.
One thing I would like to know is how accurate is the frequency of an LCR circuit.
What I mean is if say the peak is at 48hz does the coil and capacitor actually target 48 hz or is it 48hz plus /minus say 5 hz
One thing I would like to know is how accurate is the frequency of an LCR circuit.
What I mean is if say the peak is at 48hz does the coil and capacitor actually target 48 hz or is it 48hz plus /minus say 5 hz
Need some clarification, there must be a plus / minus to the frequency of an LCR circuit otherwise if there was a difference in the res. freq. of 2 bass units the crossover would work on one speaker but not the other.
The design is the Troels Gravesen SBA10, I have not purchased it yet so obviously do not know values of xover components and will not be able to divulge them later either.
As I said at the start I want to build it in a slightly smaller cabinet and I will tune it lower also so 2nd peak will still be about the same from memory approx 46hz.
As I said at the start I want to build it in a slightly smaller cabinet and I will tune it lower also so 2nd peak will still be about the same from memory approx 46hz.
As a practical point of view, you don't know the values of the components until you buy the kit. Only at that point you can sim your mod and decide if the components have to be changed or not, this depends on the Q of the filter and how big is the difference you made in the impedance with your mod. Asking here before is sterile.
Ralf
I don't understand the mod you want to do. The width is dictated by the bass driver, you can only reduce the depth, but why? If you want to place the speaker against the wall, and level the speaker with the surrounding furniture, this is a very bad idea
Ralf
I don't understand the mod you want to do. The width is dictated by the bass driver, you can only reduce the depth, but why? If you want to place the speaker against the wall, and level the speaker with the surrounding furniture, this is a very bad idea
Maybe you ask Troels whether this can be done without the LCR, ask whether you can buy without the extras.
Maybe you ask Troels whether this is meant to make the woofer peak look resistive, so you know, then set yourself up for measurement and take it on yourself.
Maybe you ask Troels whether this is meant to make the woofer peak look resistive, so you know, then set yourself up for measurement and take it on yourself.
Allen, from the Troels' description of the design and the graphs shown, it is evident that the LCR filter for the mid is mandatory. No graph is shown however on the effect of the LCR filter for the bass, but it is written: "To manage the impedance bump at 80 Hz for the midrange we have the LCR circuit consisting of R7-C5-L5. The upper impedance peak of the bass driver at 80 Hz needs the same treatment, hence R11-C8-L7"
Ralf
Ralf
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