From my point of view a first order on bass channels is uncontestable solution. The imaging, the ability to be integrated with room, the capacity of its second harmonics to cocoon the MF channels, the ability to be integrated with delay channel (if you advanced enough to use them), the imaging, the lessen sensitivity to phase mis-alignment, the imaging, the imaging … did I mention the imaging?
However, the first order on bass could not implemented everywhere just because you want it. Here is where the art of design come to existence: the playback system should be thought in a certain way where system’s ability handle the first order will logically flow from many other design decisions. Sure we all know that there are very-very many aspects how a playback system might be “thought”, and in some cases a first order on bass is not achievable, but still it is from my point of view is one of many ultimate objectives of what I call “well-thought design” or “Design for Sound”.
Below, I enumerated a few not necessary directly related points that people who would like to think about it the subject might use as starting points. What I will say is not a recipe but rather some moments that I discovered for myself while I was in pursuit my “first order discovery”:
1) With most of the bass drivers it is very difficult to roll them off properly with a coil between amps and the drivers as the bass drivers have own inductance that make the slope “immune” to increase of inductance in the filter’s coil.
2) With a full-range amp driving MF and bass practically all of the bids about first order bass are off.
3) With a full-range loudspeakers where MF and bass sections are not physically decoupled most bids about first order bass are off as well.
4) SS amplification is very-very complicated for first order bass as SS amps have very vulgarly sounding second harmonics.
5) Depends of the driver and the enclosure dumping of the driver with amplifier output is superbly critical. There are no objective or measurable mechanisms that would be indicative for proper damping. Each driver in a given enclosure, each amps and each interface are different and the only assessment available is use of the Proper Listening Evaluation Techniques ™.
6) The lowers order is “better”: the 1.5 order is ALWAYS better then 2nd order. A fraction of the order is made by implementation of two series first orders with a certain amount of octave between them.
7) It is better to have 2nd-Harmonic-affluent acoustic system and 2nd-Harmonic-leen electronics then wise-versa. It is always easer and less devastating to sound to reduce harmonic tail then to increase it.
8) The design of your bass section should be able to handle a room 2–3 time larger them yours. If in your room, at very high volume, you the bass section is stressed out then you have problems and you need to resolve the problem of power handling before thinking about the first order.
9) Drivers with low-mass cones and moderate flux are more preferable then high mass driver with high flux. Harmonics are written partially when the driver is rolling back and act as a generator… What car corners better: high mass or low mass if then have the same suspension, mass to HP ratio and the same mass allocation?
10) 30Hz and 120Hz are VERY different frequencies and in most of the cases they should be handled by different channels.
11) Electricity, electricity and one more time electricity! The subjective harmonics influence of your bass is HUGELY depending from quality of Electricity you have.
12) In many cases a bass driver is superbly sensitive to presence of any resistance between amp and voice coil, and this resistance is NOT a part of the amplifier output impedance. So, if you use a passive filter then keep the gage as high as you can and keep DCR as low as you can. Well, if you are in the world of air core coils (how it should be) and cross at 50hz then you looking at a large barrel of cupper in your room… that most likely will pick your local AM stations without any amplification. Read one more time the paragraph #1, #2, #5 and… How much more incentives you need to go multi-amping?
13) In some instances the contemporary recordings (or 99% of the re-mastered LPs from 60s) are made in a way that first order on bass will not sound properly – it is not the problem of your system but the problem of the Morons with diploma of electricians who believe that they are recording engineers.
14) Use Absolute Phase to check quality of your fist order crossover on your bass section.
15) In many cases a first order and a narrow-bandwidth lack of linearity at crossover point in better then a flat response and second order.
I could go on but I think it is enough for now. With a correct selection of the bass driver and it’s enclosure (this is 60% of success) to implement a proper low-pass first order on bass channels is not so difficult but once it is done and a person learn about auditable advantages then the person would never go for any sharper filters.
Rgs, Romy the Cat
> regardless though-- i do have a question about implementing the '1.5 order' crossover... how would one
> implement such a thing?
The 1.5 order is very easy. The “1.5 order” is not the order itself but rather it is a hype-name that I use. However, it is very simple to implement and very effective. The 0.5 order crossover based upon a phenomena that I discover that if I have at first-order crossover and then, for instants, after one octave another first-order crossover, then I of course have a second order crossover, however this type of “distributed” first-order crossover does less impact to Sound (imaging) then when I use full second-order crossover (I used religiously Bessel curve on second orders). That distributed crossover is a very interesting fruit, as it is allows a lot of flexibility. For instants you have the bass section that you would like to low-pass at 60 cycles with first-order. That frequency you'll found is necessary to integrate your base with your upperbass channel. The integration of bass is fine but you have an excessive HF “tail” from your low-frequency driver. If you go at 60 cycles with sharper order then you'll my gain some “issues” in imaging, so here is where you might employ the “distributed” first order. You'll keep your first order crossover at 60Hz and put in play and other first order crossover at, let say, 200Hz. The channel begins to write a full second order at 200 cycles, and does all typical for a second order phase spinning. However, the key in it is that subjectively, listening with that playback, this type of the arrangement screw up imaging less. The additional beauty is that you can move the second first-order crossover from (for instants) 100 cycles to 500 cycles, finding how much you would like to truncate the bass driver’s tail. There is even more very important benefit in this approach: the second first-order crossover might be not the actual crossover but rather roll-off from other means: enclosure, amplification, magnetics or whatever. The interesting part in that case is that if in place of the second first-order crossover is used a pure second-order crossover then the entire channel does not sound (imaging-wise) as a third order crossover.
You can NOT stack coils in series to get a “distributed half order crossover”. To make it “distributed” the first and the second first-order filters should be decupled. For instance the first filter might be at line-level and the second at the driver level. Or the first filter is at line-level and the second via a transformer or via plate filtering or feedback or whatever… You might also get the result loading the first filter to a proxy load and then write a second filter against the voice coil. As I said in order to have it working properly the entire channel should be thought from it's ground up…
Rgs, Romy the Cat