Ascent I crossover upgrade

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carl

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Hello everyone :)

This is one of my first posts on this great forum. I'm going to tell you a little about the upgrades I have done on my Ascent I speakers. First thing I would like to make clear, I am not a audio engineer nor do I proclaim to have an audiophile golden ear. I am simply someone that loves to listen music and would like to share my experiences.

I acquired a pair of Ascent I speakers about a year ago and loved them, but as time went by I got the upgrade bug. I figured the crossover would be a good place to start since manufactures are notorious for using 5 dollar caps or less on a pair of 10,000 dollar speakers. Not that there is anything wrong with them but you can do better IMHO.

View attachment ascent crossover schematic.pdf
http://www.humblehomemadehifi.com/Cap.html


First, I found the schematic for my speakers and made some decisions on what components had the highest priority to upgrade. In most cases, series circuits tend to have a large effect on the sound, while parallel circuits are less crucial. I decided to start with and change the 3.5mh wire wound air core inductor in the LF circuit with a foil one from erse. The schematic calls for 3.5 mh, but after checking the ones in my Ascent's(mounted) I found it to be more like 2.9mh. I found this to be strange, so I called Martin Logan and asked their service department, if this was a production change that was not documented. Their answer was "their suppliers machine must have been out of calibration that day"??? (my luck lol). I installed 3.5mh erse and checked the inductance (mounted) and found it to be more like 3.7mh. The increase in inductance was do to ferrous metal in close proximity of the inductor, not my meter playing games. I tried to relocate the inductor to reduce this effect, but to no avail (lack of room to work with). I replaced 3.5mh with a 3.3mh , mounted it and came up with a inductance of 3.47mh. This was good enough for me and much closer then factory. The DCR of this inductor is a little bit lower ( .5 ohm) and will increase the amplitude of the circuit by a small amount (more base). The cap in LF parallel circuit is a 270uf (electrolytic) and could be changed out with a polypropylene film type, (a lot bigger in size) but due to lack of working space and it being a parallel circuit I decided not to change it.

The HF circuit was much more straight forward. I changed all the caps and only one of the inductors (no space again). I used Mundorf Supremes ( a good compromise cost vs return). I needed to use multiples of caps to get the desired values I required and they took up a lot of real estate in the doing so.

How does it sound....well what I did to be sure of the results before and after the mod was done, I only did one. I listen for 3 weeks going back and fourth between the modified and factory ascent. The change was very pronounced, strings on the guitar were much more defined and the piano sounded a lot closer to the real thing. Female vocals seem to have more depth and definition to them. Hard rock seemed a little easier to listen to and I'm not saying the top end has been rolled off, far from it. Its just a more pleasing sound at the end of the day and there is no way I would go back ! I'm sure some of the mods I have done have altered the crossovers function a bit but most peoples room response is far from an anechoic type quality and would have a far greater impact on the output.

Thanks for reading MHO and enjoy the music because that's what its all about!

Carl.A ;)
 

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Carl, nice mods and great post. thanks for sharing.

A question though: for the bass, why would you not want the lowest inductance coil possible?
In the mid-bass, it's been established that the lower the inductance of the system (woofer + crossover components) the more accurate the impulse response.
 
Hi Jonathan

This is my limited understanding of it. The crossover is a fairly complex creature. Crossover networks use two types of filters to divide music frequency signals. A high-pass filter ignores, or passes, frequencies above a predetermined frequency but attenuates, or rolls off, those below it. Conversely, a low-pass filter passes frequencies below the predetermined frequency but attenuates those above it. High- and low-pass filters can also be combined (called "cascading") to form a band-pass filter, which passes only those frequencies (called a "pass-band") that aren't attenuated by the two filters. In each case, the predetermined frequency is called the "crossover point" or "cutoff frequency."

The key components in any passive crossover are its inductors and capacitors. An inductor (also known as a "coil" or "choke") is simply a coil of wire . Inductors are used in low-pass filters, since their impedance ( A/C resistance ) naturally increases as the frequency of incoming music signals increases. An increase in impedance always causes a decrease in amplitude or output, so the result is that high frequencies are attenuated determined by the filter's amount of inductance .

Capacitors consist of interleaved layers of a special foil and an insulating material such as polypropylene or Mylar. They are used in high-pass filters, since their impedance increases as the frequency of an incoming music signal decreases. Again, this increase in impedance lowers the output, and the result is that low frequencies are gradually filtered out.

The rate at which frequencies are attenuated is called the "crossover slope." Slopes are expressed in dB per octave, and typical figures are 6, 12, and 18 dB per octave. The higher the slope, the faster attenuation occurs. The number of inductors and capacitors used in a passive crossover determines its "order." A first-order crossover uses one component, a second-order two, a third-order crossover three. A crossover's order is also tied to its slope: First-order devices always have a slope of 6 dB per octave, second-order devices a slope of 12 dB per octave, third-order devices a slope of 18 dB per octave. Essentially, this physical use of extra inductors and/or capacitors causes higher-order networks to attenuate the signal more sharply.

Every component has a value, which indicates how much resistance the component will present to the amplifier and is largely responsible for determining the crossover point of a specific filter . An inductor's value is determined by the number of windings of wire around its core and the type of core used. A capacitor's value is determined by the number of layers of foil and insulating materials it has. The more layers, the higher the capacitance. The values of capacitors are expressed in microfarads (uF), and the values of inductors are expressed in microhenries (uH), and millihenries (mH).

Hope this helps
 
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