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In Reply to: Re: Crossover Frequency vs. Slope Question for Ribbons posted by JP van Son on October 23, 2006 at 11:23:53:
Looking briefly at the schematic, I see that that bass and mid bass are 2nd order filters(12db slope) low pass filters. There is no mid-bass high pass filter, which means the mid-bass is not limited at its lower end and overlaps the bass. Usually the mid-bass would have a band pass filter (i.e a high-pass and low-pass defining the lower and upper limits). It may be that the mid-bass is inverted in order to produce a flat acoustic response in the area of overlap. Further analysis is not possible since the inductor values are not specified.You are correct that by using a 2nd order high pass filter, you could lower frequency. Interestingly Magnepan typically uses a 2nd order high pass filter on the tweeter but they employ a low Q (often <0.3) so the slope is closer to a 1st order curve. I assume they have a reason for this. Also whether you could lower the ribbon frequency may not depend on the ribbon responding at lower frequencies but more on its ability to move enough air to keep the response flat.
I may be an egoist but at least I don't talk about other people.
Follow Ups:
I don't have the original documentation for these speakers and the only other owner I've located didn't have them either. So, I must rely on Russ Novak's old Stereophile review on the pair he owned. In that review, he made a point to mention that the crossovers were 1st order and how odd it was to have the one cone connected in inverted phase (I've gone in there and flipped it around and they do sound better, sound now like they're in phase using a pair of phase coherent Tannoys as a reference, but not great). Now, I'm still have much to learn about crossovers and am working on it, but the schematic I drew looks to me like a 1st order crossover for the cone drivers with a Zobel network added on for impedance correction, not a second order alignment. The ribbon has a textbook 1st order crossover with a notch filter, though I've not yet figured out a way to calculate it's properties with much certainty.You're right about the HP with the midbass and it's something that really bothered me when I first checked out the crossovers. Thought I was overlooking something in there. These speakers are designed such that the woofer is side firing and the midbass is firing forward. So, I'm guessing that perhaps the designer, Lewis Muratori, figured that the cabinet design and driver positioning would make for a mechanical crossover of sorts to induce an effective high pass filter.
and living in Melbourne, Oz.If you want to get hold of him to ask him about your speakers, why don'tcha send Hugh Dean (the designer of my AKSA amps) an email. I know he has Lewis's address.
Hugh is at: aksa1@bigpond.com
Regards,
Yep, I saw that cable article at the AKSA site a few months back when I was doing major research on these speakers. I also saw that Hugh Dean had made a couple of posts at another forum mentioning him, so I did contact him. Unfortunately, Hugh didn't have his contact information, but was very friendly and willing to help. If his customer service is like that, I highly recommend looking into his products.Another AAer saw a post where I had made reference to the Flatlines and emailed me about them. Turns out he had heard a pair once, which was cool. He also mentioned that Muratori does some occasional repair work for Tom Manning at SpeakerBits and that I might obtain his email address that way. I'm thinking strongly about doing so, though I have some reservations. Just how does one tactfully approach a speaker designer and ask questions of him to the purpose of tearing apart one of his creations in an attempt to redesign and improve the design? When I figure that out, I'll definitely try.
Hi JP,Your email address implies USA but you have Aussie speakers and know about SpeakerBits in Melbourne!!?? R U located in Melbourne by any chance?
As to "Just how does one tactfully approach a speaker designer and ask questions of him to the purpose of tearing apart one of his creations in an attempt to redesign and improve the design?" ... haha, yes, this might be a problem - depending on what sort of person LM is!! :-))
Certainly Hugh Dean is always interested in getting good and bad feedback about AKSA amps ... all part of the "continuous improvement" process! I drive my 3-way active Maggie IIIAs with AKSA amps so I can't speak highly enough of them.
I suggest you could say "Lewis, I love your speakers but over the last X years I've owned them, I've come to the conclusion that a few simple things could be done which would make them sound much better. Can you tell me ..." etc!! :-))
Good luck,
Nope, I'm an American and live just a couple of hours east of Seattle. From what I've learned, the Flatlines were imported by ?Immedia? in Berkeley, CA, which is why the backplate lists that city. Surprisingly, another pair showed up for sale at Hawthorne Stereo in Seattle (made a point of going there to check them out), so mine aren't the only ones.I know about SpeakerBits from back when I was using a pair of Tannoys as my mains -- they claim to be the only supplier of authentic replacement surrounds for these Scottish built speakers.
I hope someday to try out an AKSA amp (a friend of mine was building one sometime back, but had to sell it before it was finished due to financial concerns) with the Flatlines and hear what they can do.
I will eventually try to get ahold of Muratori and I just might try your approach. Oh, and thanks for the lead on replacement ribbons. Mine appear to be in good condition, but it's nice to know that there are possible replacements should I damage these while playing around with them.
Yup, those are 1st order with Zobels not 2nd order crossovers - I just decided to ignore the series resistor. Since the components of the Zobel can be calculated from C=L/R^2 where L=speaker inductance, and R=nominal speaker impedance the L of your mid-bass is 2.9mH and that of the bass 1.14mH.
I may be an egoist but at least I don't talk about other people.
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