Hello everyone! Brand new to the scene and excited to dive in. I've spent the last 2 months reading and re-reading Intro to Basic Electronics, Speaker Building 201 & The LDC 8th edition volumes I & II. I have also been learning Vituix CAD and playing with Xmachina. My next steps will be getting testing equipment. Any recommendations on a cost effective setup would be great! I have a good selection of old speakers from brands of varying quality that I plan on disassembling to use the drivers for experimentation. I have been playing with the half space responses of 2 MTM configurations. Both use the Dayton RS100-8 mid bass and I have experimented with the Morel CAT 308 dome and Aurum Cantus G2Si ribbon tweeters. After completing a few test builds with the drivers I currently have, these will most likely be my first real shot at a quality loudspeakers. I am currently using Cambridge Soundworks and Triad MTM speakers scattered around my house that I can use for reference. I understand that the half space responses are not indicative of what I will be working with in reality. I am going play with the simulated diffraction in Vituix now as practice but I have some concerns with my current designs that I could use some direction on. For both alignments I have good frequency response and the phase and group delay seem appropriate. My concern lies with the impedance. The first alignment using the G2Si tweeter shown below dips to 2.8 Ohm and hangs at 3 Ohm from 200-1200 Hz low point. The second alignment using Cat 308 in my next post runs 3 Ohm from basically 200-2000 Hz. The second alignment is more consistent and has far less circuitry but I would like to try and build both. In both configurations the problem seems to stem from the large parallel capacitor in the low pass section. However adjusting this drastically effects FR. I welcome any feedback on these designs! My questions are as follows.
Are these impedances going to cause problems for a lower end amplifier?
Is there an easy work around to raise the total impedance that wont affect efficiency to horribly?
How does the load phase affect the impedance? The peaks in phase correlate to higher impedance levels, when the impedance is at its lowest the phase is close to 0. This means it is mostly resistive correct? Does this present less of an issue for the amp?
How does the acoustic phase look? Configuration 1 is 90 degrees out of phase in the low pass stop band. Is this ok?
If I invert the tweeter I get a 6 dB drop at the crossover. Is that steep enough?
Does any of this matter as it uses half space responses not real world measurements?
Thank you all in advance! So glad there is a place where I can have access to the wealth of knowledge you all have to offer. I attached the Vituix project file as well as pictures of all the relevant graphs. Alignment 1 is crossover variant 1. and 2 is 2
Are these impedances going to cause problems for a lower end amplifier?
Is there an easy work around to raise the total impedance that wont affect efficiency to horribly?
How does the load phase affect the impedance? The peaks in phase correlate to higher impedance levels, when the impedance is at its lowest the phase is close to 0. This means it is mostly resistive correct? Does this present less of an issue for the amp?
How does the acoustic phase look? Configuration 1 is 90 degrees out of phase in the low pass stop band. Is this ok?
If I invert the tweeter I get a 6 dB drop at the crossover. Is that steep enough?
Does any of this matter as it uses half space responses not real world measurements?
Thank you all in advance! So glad there is a place where I can have access to the wealth of knowledge you all have to offer. I attached the Vituix project file as well as pictures of all the relevant graphs. Alignment 1 is crossover variant 1. and 2 is 2
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Possibly. If you are talking about something like a home theater receiver, many of those aren't rated below 6 ohms. It's going to depend on the amplifier though. Some cheaper ones are fine at lower impedances.
If you just plot the impedance of your two midbasses on their own with no crossover, you'll see the base case for the impedance you are dealing with. Anything you do to raise that in their intended passband is going to cause a loss of sensitivity in some way. If you include a baffle step correction of some kind, it will likely improve the minimum in the lower midrange and up.
In Case 1, the minimum at around 1200 Hz might improve a bit if you get closer to a target roll-off for the tweeter, but I'm speculating. Looking at the individual legs of the crossover to see where impedance is for each will help show some of this.
Correct.
Large capacitive phase angles are typically hardest on a transistor amplifier, and they are more problematic at high frequencies. This is highly amplifier specific though. Some are much better at handling difficult loads than others.
EPDR (equivalent peak dissipation resistance) is the newer calculation used to combine the effects of phase angle and basic impedance into an equivalent resistive value. You may want to look at that, since I think it's included in Vituix.
Pretty good overview here about speaker loads
https://www.stereophile.com/reference/707heavy/index.html
The recommended minimum cross point on it is 2.5 kHz. Your acoustic result seems quite a bit lower than that since the initial roll-off is gradual, then it steepens. You may have issues on that front. Most true ribbons don't like being driven with lower frequencies than they are designed for.
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Thank you Matt!
The RS100 woofers stay pretty linear through 3.5 kHz so I will play with raising the cross point.
I have zero background in any of this so if my questions seam basic I apologize. I learn fast.
The RS100 woofers stay pretty linear through 3.5 kHz so I will play with raising the cross point.
I have zero background in any of this so if my questions seam basic I apologize. I learn fast.
No need to apologize. Everyone starts at the same point: not knowing any of it. There are lots of details involved in designing and measuring speakers, but there also many members here that are happy to help. And you don't have to understand all of it to enjoy the process.
I used the diffraction tool to get me realistic responses. While the response is not as smooth it is still plus or minus 2 db. I am getting better impedance response with a minimum at 4 Ohm. The EPDR shown in pink however drops down to 2 Ohm. I am reading up on this to better understand its affects now. I was able to get the phase alignment very close with the biggest variances happening deep in the stop bands. I sacrificed a bit of linearity to get the Phase to where it is but nothing major. I have posted the 2 variations below.
What are peoples opinions of witch takes more importance, mostly flat response or properly aligned phase?
Var3 has a pretty complicated XO design, besides cost how bad is it to have 5 inductors? All but 4 a fairly small.
I will take any feedback good or bad it will only help me learn!
What are peoples opinions of witch takes more importance, mostly flat response or properly aligned phase?
Var3 has a pretty complicated XO design, besides cost how bad is it to have 5 inductors? All but 4 a fairly small.
I will take any feedback good or bad it will only help me learn!
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After reading the article by Keith Howard it seems like the standard measure of impedance is basically irrelevant. All of the speakers he tested the EPDR came in significantly lower. It seems to me that designing for a flat as possible load phase is more is more effective at limiting the strain on an amplifier then a higher impedance minimum?
Is it also true the amplifiers must be designed to handle dips well below there rated limit?
My current amplifier is a cheapo pyleusa 8ch 4-16 Ohm. It gets the job done but I will definitely be upgrading as I build more and more speakers. It is powering 7 MTMs spread through out the house. It did not like powering my 4 Ohm triad speakers in a location that required a 50ft run of cable.
How how the extra cable play into the EPDR? I would think it would raise the impedance from all the added resistance.
Is it also true the amplifiers must be designed to handle dips well below there rated limit?
My current amplifier is a cheapo pyleusa 8ch 4-16 Ohm. It gets the job done but I will definitely be upgrading as I build more and more speakers. It is powering 7 MTMs spread through out the house. It did not like powering my 4 Ohm triad speakers in a location that required a 50ft run of cable.
How how the extra cable play into the EPDR? I would think it would raise the impedance from all the added resistance.
That's highly specific to the individual, but I think the majority would say very tight phase alignment is less important than frequency response.
That really comes down to how they are used, where they are in the circuit, and whether a simpler approach can accomplish nearly the same result. I generally try to simplify and eliminate very large resistances, very small inductances, etc. Some people are obsessed with ruler-flat response and will build very complex crossovers to achieve it though.
Also keep in mind that many crossovers are adjusted by ear in the end, so you may not wind up where your model suggests.
Looking at plots from a distance, I'd lean toward the simpler one (post #7 in this thread). Though I'd also look to see if further simplification is possible (that 270 ohm resistor caught my attention).
I'm also one that likes to get a speaker up and running as early as possible to get a feel for how it performs. I'm OK with modifying crossovers multiple times to get where I want to go. If you have a different approach, that should be kept in mind.
To me, it's more of a question of where you draw the line and how much complexity it takes to mitigate it. I'll generally try to keep phase angle from getting extreme when I can, but if there's a reason for letting it creep up, sometimes there's no easy answer to fix that.
Your comment that all the speakers he tested were significantly lower than their impedance modulus also tells you it's a pretty common issue. Stereophile has always commented on speakers that are particularly hard to drive, and it seems like there are more of those than there are ones that are really easy to drive. Many amps do OK with moderately difficult loads, so it's not a situation where you have to minimize the load at all costs (unless you have a very specific reason to do so, but that would not be typical).
The impedance plots in your two newer ones look reasonable given the use of two 8 ohm woofers in parallel.
That depends on the cable. Normal speaker wire where the conductors run parallel is typically OK even in longer runs, but there are some cable types that are more capacitive or inductive. The longer they get the more it can become an issue with an amp that's borderline stable into the speaker load you're asking it to drive.
If the extra cable is mostly just adding resistance, that would make things easier for the amp in general, but that's not the only effect.
Another thing we haven't discussed is the driver locations in your models. They look to be at 0, 0, 0. To accurately model a speaker's response, you need to use real driver locations (including Z). Sometimes you get lucky with these on a flat baffle, and sometimes you don't. If you're trying to do the crossover right the first time, all of this becomes more critical.
Thank you again Matt! You have Givin me quite a lot to ponder as I continue to research.
As for driver location, are you referring to the xyz settings of the driver in the crossover section? I set a delay for the woofers in the drivers tab estimated by comparing driver schematics. Would changing the Z location further affect that delay?
I modeled the driver separation in the defraction tool. Will separating the Y coordinates in the xo schematic affect the modeled FR?
I want to pull the trigger on testing gear this week if finances allow. I feel that I need to get hands on and stop playing with hypotheticals. I am reading up on testing procedures to better understand the process before investing in gear.
The DATS seems like all you need for impedance, but there's so many microphones. And I need 2 of them to take proper time aligned measurements correct?
Any particular freesources for measurement procedures you would recomend?
As for driver location, are you referring to the xyz settings of the driver in the crossover section? I set a delay for the woofers in the drivers tab estimated by comparing driver schematics. Would changing the Z location further affect that delay?
I modeled the driver separation in the defraction tool. Will separating the Y coordinates in the xo schematic affect the modeled FR?
I want to pull the trigger on testing gear this week if finances allow. I feel that I need to get hands on and stop playing with hypotheticals. I am reading up on testing procedures to better understand the process before investing in gear.
The DATS seems like all you need for impedance, but there's so many microphones. And I need 2 of them to take proper time aligned measurements correct?
Any particular freesources for measurement procedures you would recomend?
Unfortunately, I don't use Vituix, so I can't give you specific instructions. I just wanted to make sure you were aware that how the drivers are "physically" laid out in the model matters if you want everything to be accurate for the off-axis behavior and the summation around the cross point. If done correctly, it will calculate the differences in arrival time based on how the baffle is laid out, what angle you are on, and for the acoustic origin of the individual drivers (Z offset).
As a broad overview of measurement techniques, the Stereophile series is pretty good:
Measuring Loudspeakers, Part One
https://www.stereophile.com/features/99/index.html
Measuring Loudspeakers, Part Two
https://www.stereophile.com/features/100/index.html
Measuring Loudspeakers, Part Three
https://www.stereophile.com/features/103/index.html
If you want a more in-depth look at it:
Testing Loudspeakers by Joseph D'Appolito
https://www.parts-express.com/Testing-Loudspeakers-Book-500-030
I use a hardware-based dedicated measurement system, so I also don't have experience with REW or any of the sound card based systems. There are threads here that discuss those though, and some other users might chime in if you need specific recommendations on them.
As a broad overview of measurement techniques, the Stereophile series is pretty good:
Measuring Loudspeakers, Part One
https://www.stereophile.com/features/99/index.html
Measuring Loudspeakers, Part Two
https://www.stereophile.com/features/100/index.html
Measuring Loudspeakers, Part Three
https://www.stereophile.com/features/103/index.html
If you want a more in-depth look at it:
Testing Loudspeakers by Joseph D'Appolito
https://www.parts-express.com/Testing-Loudspeakers-Book-500-030
I use a hardware-based dedicated measurement system, so I also don't have experience with REW or any of the sound card based systems. There are threads here that discuss those though, and some other users might chime in if you need specific recommendations on them.
I have read all of the sterophile articles and I have testing loudspeakers on the way! In the mean time I am reading through the REW manual to get a feel for it.
The REW manual seems to really like USB mics but i have read quit a few post here of people bagging on them.
Reading through it seems that if I get a 4 channel controller with 2 ins and 2 outs I only need 1 mic. And then just feed one of the outputs directly to an input for time reference.
If any one else who uses this style set up has any product recommendations I would love to hear your thoughts.
As for as taking gated measurements to try and capture an anechoic response. My garage is my largest room at approximately 25x30 ft. My back yard is much larger 40x60 ft but I live in Las Vegas valley and there is consistent ambient noise from planes, animals, fast and furious wanna he's and the steady hum of central ACs during the warmer months.
Am I better off in the garage, a smaller but mostly silent room in side or out side?
Will taking the average of say 5 responses filter out the ambiance or only to a point?
The REW manual seems to really like USB mics but i have read quit a few post here of people bagging on them.
Reading through it seems that if I get a 4 channel controller with 2 ins and 2 outs I only need 1 mic. And then just feed one of the outputs directly to an input for time reference.
If any one else who uses this style set up has any product recommendations I would love to hear your thoughts.
As for as taking gated measurements to try and capture an anechoic response. My garage is my largest room at approximately 25x30 ft. My back yard is much larger 40x60 ft but I live in Las Vegas valley and there is consistent ambient noise from planes, animals, fast and furious wanna he's and the steady hum of central ACs during the warmer months.
Am I better off in the garage, a smaller but mostly silent room in side or out side?
Will taking the average of say 5 responses filter out the ambiance or only to a point?
Typically inside a house is going to be quieter and more absorptive than in a garage, so I would prefer that in a general sense. Ceiling height matters as well though. The first reflection point is what's going to limit the measurement. If the garage has a significant height advantage, that might make me lean toward it. Or if you can adequately absorb at the first reflection points and gain a lot of time window that way.
As long as your test signal is 20 dB or so above the ambient noise level, the noise will have minimal impact on the measurement. If you want to look at roll-off or deep notches, all of that will need to be similarly above background noise though. But don't get crazy with the levels trying to overcome very high background noise. Standard test levels are typically at 2.83 V or 86 dB at 1 meter, though many of my quick tests are below that level. Higher level testing for normal home audio is often done at 96 dB at 1 meter. The higher level testing is typically only done for distortion or compression testing, not general frequency response.
Averaging measurements helps, but the individual measurements have to be properly sync'd. Your REW setup has to be right to do that correctly. That's talked about in the manual.
https://www.roomeqwizard.com/help/help_en-GB/html/makingmeasurements.html
"REW allows multiple sweeps to be averaged, although best results are generally obtained by using single, longer sweeps rather than multiple, shorter sweeps. Multiple sweeps are offered when not using a Timing reference or when using a loopback as a timing reference. Do not use multiple sweeps if the input and output are on different devices (for example, if the input is a USB mic). If Repetitions is more than 1 REW uses synchronous pre-averaging, capturing the selected number of sweeps per measurement and averaging the results to reduce the effects of noise and interference. The pre-averaging can improve S/N by almost 3 dB for each doubling of the number of sweeps. Averaging can be useful if the measurements are contaminated by interference tones, whether electrical or acoustic, as they typically will not add coherently in the averaging and hence will be suppressed by the process."
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If you want to start an in-depth REW discussion, you may get more responses if you start a new thread with that in the title. I normally only read threads with titles that seem to be about something I'm interested in, and I'm probably not the only one doing that.
As long as your test signal is 20 dB or so above the ambient noise level, the noise will have minimal impact on the measurement. If you want to look at roll-off or deep notches, all of that will need to be similarly above background noise though. But don't get crazy with the levels trying to overcome very high background noise. Standard test levels are typically at 2.83 V or 86 dB at 1 meter, though many of my quick tests are below that level. Higher level testing for normal home audio is often done at 96 dB at 1 meter. The higher level testing is typically only done for distortion or compression testing, not general frequency response.
Averaging measurements helps, but the individual measurements have to be properly sync'd. Your REW setup has to be right to do that correctly. That's talked about in the manual.
https://www.roomeqwizard.com/help/help_en-GB/html/makingmeasurements.html
"REW allows multiple sweeps to be averaged, although best results are generally obtained by using single, longer sweeps rather than multiple, shorter sweeps. Multiple sweeps are offered when not using a Timing reference or when using a loopback as a timing reference. Do not use multiple sweeps if the input and output are on different devices (for example, if the input is a USB mic). If Repetitions is more than 1 REW uses synchronous pre-averaging, capturing the selected number of sweeps per measurement and averaging the results to reduce the effects of noise and interference. The pre-averaging can improve S/N by almost 3 dB for each doubling of the number of sweeps. Averaging can be useful if the measurements are contaminated by interference tones, whether electrical or acoustic, as they typically will not add coherently in the averaging and hence will be suppressed by the process."
*************
If you want to start an in-depth REW discussion, you may get more responses if you start a new thread with that in the title. I normally only read threads with titles that seem to be about something I'm interested in, and I'm probably not the only one doing that.
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