Thanks for the detailed response.
I don't know tbh. Theoretically it seems like I should be able to generate a filter externally and then convolve the acourate XO with that filter before using it in the sweep. On the other hand, acourate has loads of features I don't remotely understand so perhaps it can be done in there instead. Can you describe how you would do this in RePhase?
There is a tab in rephase labelled "filters linearization"; it includes a column labelled crossovers which includes a large number of phase manipulation presets that effectively just reverse the phase wrap introduced by many conventional crossover filters without touching the FR.
I imported the impulse into holm and compared the two visually, I think it's actually more like 18-20 in acourate. Holm also indicates that the window is a symmetric window & is 20ms wide on the left and right at 1kHz. The shape looks like a Hann window but I'm not 100% sure about that. I think it's reasonable to argue that 12 in Holm is too big in this case given that I know the HF reflection arrives after 5ms or so.
That makes sense; I'll make a mental note of that for future comparability.
this sounds v promising. How do you translate the passive design into an active filter? I had noticed soundeasy had this capability but, from what I've read, it is rather pernickity about hardware and is a bear to learn.
The short answer is that I don't, I do the reverse. I'm not an EE and have limited skill with practical electronics, so I do all of my initial design empirically. I'm not good enough at circuit analysis to "work backwards" from an existing circuit layout to a filter bank unless the filters involved are textbook filters.
So I just work it out empirically; I measure the speaker elements separately, then figure out what filters and delay I need, dial them into JRiver, re-measure, etc. until I figure out the ideal combination. Once you know the actual filters you need, it's a matter of finding the right parts and layout, which is obviously non-trivial, but most of the PEQ filters in JRiver are textbook filters. So you can use the various calculators and design tools floating around the internet, like this one that will spit out a symmetrical crossover circuit complete with parts values:
http://www.diyaudioandvideo.com/Calculator/XOver/ Once you know what the ideal is, the real issue at that point is reducing complexity and trying to figure out to how to do the most with the fewest filters. I'll confess that if I were making a passive filter tomorrow, I'd want to huddle up with an EE friend of mine to make the translation from filters to an actual circuit to keep myself out of trouble. I tried doing one on my own many years back and the results were suboptimal
Delay will be a problem no matter what; doing fine delay in analog is brutally hard, which is why most speaker designers solve the problem mechanically instead: they just skip the issue of electronic delay entirely and try to get the drivers' voice coils physically aligned so delay isn't so important. There are obviously limits to that method, especially if you have horns, etc.
The main reason is that I have cables chased into a solid brick wall (my equipment rack is some distance away under the stairs) and running a 2nd pair is invasive work. The secondary reason is that I intend to remediate this in a few years when we have an extension built so I figured I would go passive for now and swap to active later. Finally, and slightly perversely, passive xo design seems like an interesting challenge.
Certainly interested in any and all links and/or adivce you have anyway. I suspect I'm going to need it
Fair enough; I enjoy a good challenge myself
. I'm happy to help to the extent I can, with the caveat that (as noted above) I'm pretty iffy at circuit design.
When you reach the point that you're thinking about active design, the first article I'd suggest is this famous one by Rod Elliot:
http://sound.westhost.com/bi-amp.htmIt does a very good job of laying out some of the major advantages of active crossovers and bi-amping, and contains links to a number of very good articles about crossover design.
To "amplify" and offer some observations of my own:
1) Delay is very challenging to get right in a passive crossover so your phase coherence will always be approximate (unless you're a very good EE or can get cm-tolerance driver alignment)
2) Because of the size and cost of electronic components (as well as power losses from passive components), you'll be limited in the amount of filtering that can be done with a passive crossover. For example, 4th Order crossover slopes are both parts-intensive and extremely power hungry, which makes them less practical in passive crossovers. Ditto for other types of parametric filtering.
3) This isn't the end of the world because we can dial in an arbitrary amount of electronic DSP in software,
but software DSP will be very limited in it's ability to correct any FR anomalies in the crossover region because both speakers won't be contributing to them equally, so you'll have some unresolvable lumps and dips in the crossover region. This is exacerbated because of the design limitations in 2) lead to most passive crossovers using lower-order crossover slopes (1st, 2nd, or 3rd), which means the effective "crossover region" could easily be three to five octaves!
4) Active crossovers with bi-amping significantly reduce intermodulation distortion
5) Because of the power losses mentioned in 2) and because passive crossovers require padding down the more sensitive of the two drivers, active crossovers allow for significantly better power efficiency.
6) Passive components change with temperature and age (i.e. the capacitance of a capacitor is not the same at all temperatures or after a few years). Because capacitance/inductance/etc. determine the frequencies/slopes of the filters, you may find that you get different speaker performance when playing music loud (because the parts heat up due to power flow, etc.). This can be mitigated to some extent by buying nicer components that have better temperature tolerance, but that raises cost, etc.
Obviously none of these issues is insurmountable, and there are many very high quality passively crossed speakers out there. It's just that passive crossovers necessarily involve making some compromises, especially for a DIYer. They can be close to perfect if you're a talented designer with a wide-open budget, but if you're trying to piece it together (or do it at low cost) it can be harder to get a good result.
By contrast, if you have the equipment to do active crossovers/bi-amping (a few extra amp channels and a multi-channel DAC) you can skip those compromises entirely, and just hack away until it's actually right (or let Acourate do it for you)