Hello! I am working on designing my first speaker, and man am I overwhelmed!
I am sure there are more to come, but for right now, I have one question:
(Please forgive me if I don't use the right terminology at times. I am very new to speaker design)
I am concerned about time alignment / phase coherence for my design. I have access to a CNC machine, and so I have been planning to design a baffle that is acoustically phase coherent. However, upon further research I came to find that this would only really work if I used a first order crossover, which is not my intention. The idea I stumbled across that I have no idea how to account for is crossover phase shifting. With higher order crossovers, I have read that the shifting would be substantial enough to cause issues. I have read that the simple solution is to just reverse the polarity of your mid range in a 3 way configuration to account for this crossover induced phase shift, but that just seems to me like a huge gamble. How do I account for this in my design? Thank you!
Another issue that comes to mind as I write this is: Just taking measurements off the internet and not taking into account z offset, I used PCD to design a theoretical 3 way speaker and found that the only way I could manage to create a frequency response I was pleased with indeed was to reverse the polarity of my mid range driver. Should I design my speaker offset in anticipation of reversing my mid's polarity? If so, how would I go about doing this?
I am sure there are more to come, but for right now, I have one question:
(Please forgive me if I don't use the right terminology at times. I am very new to speaker design)
I am concerned about time alignment / phase coherence for my design. I have access to a CNC machine, and so I have been planning to design a baffle that is acoustically phase coherent. However, upon further research I came to find that this would only really work if I used a first order crossover, which is not my intention. The idea I stumbled across that I have no idea how to account for is crossover phase shifting. With higher order crossovers, I have read that the shifting would be substantial enough to cause issues. I have read that the simple solution is to just reverse the polarity of your mid range in a 3 way configuration to account for this crossover induced phase shift, but that just seems to me like a huge gamble. How do I account for this in my design? Thank you!
Another issue that comes to mind as I write this is: Just taking measurements off the internet and not taking into account z offset, I used PCD to design a theoretical 3 way speaker and found that the only way I could manage to create a frequency response I was pleased with indeed was to reverse the polarity of my mid range driver. Should I design my speaker offset in anticipation of reversing my mid's polarity? If so, how would I go about doing this?
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I think you are talking about not introducing too much group delay. You've already touched on your own question by mentioning not using too high an order of rolloff. Simulators can show group delay.
Thank you for your response! I will look into that. I have not heard the term "group delay" before. If I used the same order crossover for both my mid and hi frequency drivers, would I rule crossover phase shift out as a variable? Or are the values of the components also big factors? Also, I updated my original post with another question haha so if you have any tips on that I would appreciate it.
Member
Joined 2003
You may notice that many successful speakers exist with flat baffles, how do they do it?
You see, phase is directly related to frequency response, so the shape of the response, rolloff and slope all have an equal effect on phase. For most speakers it doesn't take much to get phase alignment if the drivers, or I should say forward facing phase alignment. But your post is titled "time alignment" even though the discussion appears to be phase focus which is a bit different discussion.
In any case, at this point I probably wouldn't focus too much on a single aspect of speaker design, it sounds like you're a beginner and wanting to learn, so plan on gathering reliable data so you can input it to advanced design software like VituixCAD and get some hands on education for a better understanding of overall loudspeaker acoustics. So think about building a simple measurement jig, USB audio interface and XLR measurement mic. With a CNC you should be able to cut a simple box, take some real measurements and see the results for yourself in no time.
(group delay is just long phase/time shift predominately at lower frequencies. )
You see, phase is directly related to frequency response, so the shape of the response, rolloff and slope all have an equal effect on phase. For most speakers it doesn't take much to get phase alignment if the drivers, or I should say forward facing phase alignment. But your post is titled "time alignment" even though the discussion appears to be phase focus which is a bit different discussion.
In any case, at this point I probably wouldn't focus too much on a single aspect of speaker design, it sounds like you're a beginner and wanting to learn, so plan on gathering reliable data so you can input it to advanced design software like VituixCAD and get some hands on education for a better understanding of overall loudspeaker acoustics. So think about building a simple measurement jig, USB audio interface and XLR measurement mic. With a CNC you should be able to cut a simple box, take some real measurements and see the results for yourself in no time.
(group delay is just long phase/time shift predominately at lower frequencies. )
I appreciate you helping me out! You are probably right that I should just make a box and start the majority of my tinkering there, I am just afraid that if I commit to a box design before doing my due diligence, I will lock myself into a less than ideal design (which I know is inevitable, but I want to minimize this as much as I can). Time alignment / phase coherence honestly is not my main concern, so I wouldn't say that I am focusing on a single aspect of speaker design. I am trying my best to focus on every aspect that I can think of! Haha.
Being perfectly honest with you, I don't even know the distinction between phase coherence and time alignment. If two drivers are phase coherent, would they not be necessarily time aligned? I understand a "time aligned" speaker to mean that the tweeter and woofer signal would reach the listener at the same time, so if the crossover is phase coherent, and I design a baffle that takes into account the acoustic offset of my drivers, would there be anything keeping my speakers from being time aligned? Or am I just completely confused haha
This is a completely different topic than I answered in my previous post. Phase shift refers to difference in phase between the two ways. You'd be expected to manage this in a crossover so usually the term phase shift is used differently, but I can see where you're coming from.
No, it wouldn't be enough because the two ways already have differences before you approach them with a filter.
Ok I'm getting confused haha. I will do some more learning before I ask my next question. Thank you anyways! I am eager to learn about this stuff. I'm just not a super technically oriented guy, so this stuff is pretty out of my depth. Have a good night 🙂
Simply the first one was about the behaviour of the combination of the two, and the second was about the way the two combine.
You too 🙂
Member
Joined 2003
My advice here is just don't expect your first to be perfect, just learn from your decisions good or bad and make your next speaker even better.
The basic principle to understand here is that audio is not a sine wave. Sine waves are ever repeating, so any phase alignment is a perfect alignment regaldless because every cycle of the wave is the same. In a dynamically changing signal like audio, phase aligned and time coherence are not the same. If a signal of a tweeter is 360 degrees out from the woofer, it is still phase aligned, but with a time delay of 1 cycle. Don't get too bogged down by it though, most speakers aren't time aligned and are still enjoyed by many. This time alignement part is likely why you've been given the recommendation for 1st order filters previously btw.
Ooooh I understand. That is a very good explanation. You say that time alignment is not a must, but do you reckon I would see any benefit from putting the work into getting it right? I am a college student, so I have pretty much the entire summer to get my design working. I am not necessarily sacrificing time I could spend working on the more important parts of speaker design by doing my due diligence here. You are probably right that my first attempt will not be satisfactory to me, but I don't take that to mean that I shouldn't still try my best.
If you have anymore spare time than you've already given me, I am also curious to know what aspects of speaker design participants in the DIY community most often find themselves needing to correct upon subsequent builds? I have heard this same idea from Paul Carmody on his overviews of the speakers he's made, and was curious then as well if he had anything particular in mind when he said it.
Member
Joined 2003
I don't speak for "the DIY community" but from my experience, most design problems come from designing with limited, incorrect, or inaccurate information, or simply from following bad advice (there's plenty on the internet and this forum). Following a good measurement and response processing practice, and understadning how to interpret the information is valuable, and the hands-on approach so you can hear what you are looking at first hand can really help. It has only been in recent years that loudspeaker design software that utilizes full 360 degrees of information has been readily and cheaply available. Prior to VituixCAD and CTA-2034 standard most design work was completed with single-axis information which is missing a lot of information of the overall speaker performance. I suggest reading through the CTA-2034 standard, the help file for VituixCAD under "how to get started", and of course the manual for ARTA is a good resource as well. Getting great results from the start has never been easier with the modern tools we have today, but still there is no replacement for education.
Phase/time alignment can be had in different ways:
1) Physical offsets using sloped / stepped or totally separate driver baffles.
2) Inverting polarity of one of the drivers (in some cases) solves the issue rather easily without extra effort / equipment.
3) Using all-pass filters to electrically correct the phase at the crossover frequency (analogue / digital methods available).
4) Using digital delay (memory) to adjust the arrival time for the relevant driver(s).
Basically, one needs to match the phase of one driver with that from the other driver at the crossing frequency. However, the phase of the second driver would also need to consider the physical misalignment (path difference) with respect to the first driver.
1) Physical offsets using sloped / stepped or totally separate driver baffles.
2) Inverting polarity of one of the drivers (in some cases) solves the issue rather easily without extra effort / equipment.
3) Using all-pass filters to electrically correct the phase at the crossover frequency (analogue / digital methods available).
4) Using digital delay (memory) to adjust the arrival time for the relevant driver(s).
Basically, one needs to match the phase of one driver with that from the other driver at the crossing frequency. However, the phase of the second driver would also need to consider the physical misalignment (path difference) with respect to the first driver.
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This is exactly the sort of answer I have been looking for. I will look into those resources you mention, and educate myself! Thanks!
This is exactly the sort of answer I have been looking for. I will look into those resources you mention, and educate myself!
I have been meaning to read through that, but I just haven't gotten around to it yet. I'll put that on the top of my list!
To make some clarification for @Bryguy there are really two different things here.
(1) Time alignment to me in a strict sense means the first arrival times from the drivers coincide. Like from an impulse response. The delay of the initial sound from amplifier to air sound pressure is affected by the driver construction and also by the crossover. Erm to make a kind of blanket statement that might not always be correct the higher order the crossover the more delay.
(2) Phase alignment to me means that in the crossover region the drivers' energies add constructively. The delay from (1) changes the phase across all the frequencies differently. The period of a 20 Hz wave is 50 mS; a 20 kHz wave 0.05 mS. So for example 1 mS of delay is only 1/50 of a 20 Hz wave (360/50=7.2° of phase shift) but is 20 cycles (7200°) of the 20 kHz wave. (Someone check those maths eh).
What did "time alignment" mean in the 70s? Probably not aligned arrival times, probably more like the physical thing. I feel unconvinced that aligning the voice coils or slanting the baffle can achieve aligned arrival times automatically as the drivers and crossover have such effect. Actually I'll start a thread about that https://www.diyaudio.com/community/...baffle-back-time-aligns-automatically.396602/
@Bryguy what did you end up building?