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Thread: time shift and the apollo s7

  1. #1
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    time shift and the apollo s7

    I am considering building a new passive crossover, if there is a better design than the LX5 (else replace the caps and check the resistors). In reading a paper on the Linkowitz-Riley (LR) filter, I see that there is a time shift for drivers not on the same vertical axis. This time shift causes a shift in the vertical acoustic radiation pattern, and if the time shift is not corrected in the speakers, the LR filter could be a bad choice. I presume that the time shift in the Apollo s7 in uncorrected, and as such the LR filter is a bad choice. Is that correct, and could you point me in the right direction?

    I thought I was on to the solution with the LR design, but it looks like it's not the proper solution. I will keep reading. I need to figure out what they were doing putting a cap in series with the resistor at the output end of the lowpass on the LX5.

    I was going to change from LE15A's to LE14A's after I generated the winISD comparison plot for the c51 cabinet, shown below. Then I decided that is a project that will have to wait until I get a house. The 15's are plenty of bass for an apartment. The new way of watching movies via the internet has led to a lot of what I call whisper/boom audio profile movies. I couldn't watch movies at all with a full range speaker. I will add the 3-3/4in port I came up with using the winISD tool. Need to recheck the volume before I trim it though.

    sidney, with new Apollo s7 set

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  2. #2
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    Rereading the paper on Linkowitz-Riley (LR), I missed that the shifting of the vertical propagation of sound, due to butterworth filter design was frequency dependent (see fig 1a).

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    From the paper:
    "Figure 1a represents a side view of the combined acoustic radiation pattern of the two drivers emitting the same single frequency. That is, a plot of what is going on at the single crossover frequency all along the vertical plane. The pattern shown is for the popular 18 dB/octave Butterworth all-pass design with a crossover frequency of 1700 Hz and drivers mounted 7 inches apart1."

    I was thinking that the shift of the vertical propagation of sound due to the Butterworth filter design would compensate (considerably) for the shift due to time shift in the Apollo s7, but the time shift affect on vertical propagation is not frequency dependent. Time shift figure:

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    The link to the paper: http://www.rane.com/note160.html

    So it looks like a Linkowitz-Riley solution would be a good one. The vertical propagation would still be shifted up (from the given, that the time shift from the vertically displaced drivers is uncorrected for in the Apollo s7), but there wouldn't be any funny shifts of the vertical propagation of sound near the crossover frequency. This shifts my question to: is the LR solution an excellent improvement to the LX5? Naturally I've got to figure out what order and what values, but at this point, I'm just asking to see if I am heading in the right direction towards a solution.

    Sorry about the confusion in the first post.

    sidney, with a new Apollo s7

  3. #3
    Administrator Mr. Widget's Avatar
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    Yes every passive network will introduce some phase shift and the drivers and horns themselves will also.

    Personally I would suggest that if working on a system without serious measurement equipment, dedicated testing facilities, and years of experience, I'd recommend you not get too far into the weeds. If you have a lot of free time and want to experiment, then by all means have at it and have fun, but if you want a fairly quick and satisfying solution, keep it simple and read up on other's journeys. Many have gone before you with varying degrees of success.


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    Administrator Mr. Widget's Avatar
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    Specifically on the topic of LR passive networks, there is the additional trade off of a LR 4th order network. They are literally twice as complex as a 2nd order butterworth filter which adds expense and more junk between the amp and driver. Every decision you make will lead you to needing to make new compromises.

    This complexity is one reason LR networks are often used in active multi-amp systems. I'm not one to blindly recommend going active to every experimenter, but if you are contemplating taking the deep dive down this path, a second great HF amp and an affordable LR active crossover will give you a lot of flexibility, likely better results, and get you there much more quickly than months of breadboarding passive networks.


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  5. #5
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    Hi Sidney

    I would follow Mr Widgets advice.

    You may wish to read the PI speaker document that explains the ins and out of vertical polar patterns.

    http://www.pispeakers.com/Pi_Speakers_Info.pdf

    If you want to pursue this l would consider obtaining some test equipment like a woofer tester

    http://www.woofertester.com

    You may find that the narrow dispersion of the HL91 is the dominant factor determining vertical lobes.

    It's also likely that a satisfactory improvement may require further re engineering than the crossover involving a more technically advanced horn but of course it won't end up being an Apollo S 7.

    In the early 1980's there was a movement towards R&D of horns that provide a dispersion that match the woofers st the crossover point as it found this was a significant factor limiting the audible improvement of monitors (see Jbl paper improvements to studio monitors)

    Even today system like the M2 utilise a wide dispersion wave guide.

    There are plenty of modern near field monitors that incorporate the LR filters with time alignment.

    It may be worthwhile auditioning this type of monitor to determine if you associate those characteristics with an improvement to the illusion of higher quality sound reproduction?

    Everyone has a different focus so that is something to explore before you embark on a long journey of diy loudspeaker improvement.

    I hope this provides a perspective on considering this type of project.

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