Monitor 5jr project
dyche01
Posts: 8
After falling in love with an old pair of Monitor 7's, I decided to upgrade my office audio system (built around a sweet-sounding Sherwood S-7110B receiver) with a pair of Monitor 5jr's I found on eBay.
The speakers sounded pretty good from the beginning. I was surprised at the clarity of the bass. I generally judge bass clarity by playing Paul Robeson records at moderately high volume and these sounded great. The higher registers, however, sounded a bit harsh and, in reading around on the internet, I found that other people also disliked the sound of the SL-2000 tweeter. To see if I could improve them a bit, I bought a pair of RD-0198 tweeters on eBay and a few MPP capacitors from Dayton Audio so that I could swap out the SL-2000's. Initially, I also planned to damp the basket on the main driver with Dynamat but, upon inspection, I found that it was already painted with a pretty good sound-damping material, so I left it alone.
Based on the Monitor 5 crossover schematics from this forum, it looks like my speakers have an older (and simpler) variant, with only one capacitor (12 uF) and no poly-switch (just a fuse). The crossover components were not mounted on a board, but were simply soldered, taped together, and then epoxied (hot glued?) into the space in the middle of the large inductor (see photo). In one case the electrolytic capacitor was so deeply embedded in the glue that I wasn't able to extract it, so I just cut the connections and left it in place. Following advice from this forum, I replaced the old 12 uF electrolytics with 13.5 uF capacitors made from 12 and 1.5 uF components. I have seen this type of modification referred to as a "TL" mod and I am embarrassed to say that I do not know what the TL stands for. Anyone?
Finally, I hot glued the capacitors in place. This was no trouble, but the RD-0198 was a tight fit and caused me a few minutes of anxiety over whether this tweeter was meant to fit into the same sized hole as the SL-2000. With some jiggling, it eventually slid into place. Now, after having burned the speakers in for a few days, I can report that they sound amazing! To do an A/B comparison I actually modified one speaker before starting on the other and then listened to them together. Even without a burn-in the new tweeter gave the 5jr a much smoother (less 'jagged') and clearer sound. I spent last night listening to an old Columbia recording of Eileen Farrell singing Puccini arias through these speakers. I don't think I could have done this with the old tweeters but, with the RD-0198's, the sound was not just acceptable, it was transporting.
The speakers sounded pretty good from the beginning. I was surprised at the clarity of the bass. I generally judge bass clarity by playing Paul Robeson records at moderately high volume and these sounded great. The higher registers, however, sounded a bit harsh and, in reading around on the internet, I found that other people also disliked the sound of the SL-2000 tweeter. To see if I could improve them a bit, I bought a pair of RD-0198 tweeters on eBay and a few MPP capacitors from Dayton Audio so that I could swap out the SL-2000's. Initially, I also planned to damp the basket on the main driver with Dynamat but, upon inspection, I found that it was already painted with a pretty good sound-damping material, so I left it alone.
Based on the Monitor 5 crossover schematics from this forum, it looks like my speakers have an older (and simpler) variant, with only one capacitor (12 uF) and no poly-switch (just a fuse). The crossover components were not mounted on a board, but were simply soldered, taped together, and then epoxied (hot glued?) into the space in the middle of the large inductor (see photo). In one case the electrolytic capacitor was so deeply embedded in the glue that I wasn't able to extract it, so I just cut the connections and left it in place. Following advice from this forum, I replaced the old 12 uF electrolytics with 13.5 uF capacitors made from 12 and 1.5 uF components. I have seen this type of modification referred to as a "TL" mod and I am embarrassed to say that I do not know what the TL stands for. Anyone?
Finally, I hot glued the capacitors in place. This was no trouble, but the RD-0198 was a tight fit and caused me a few minutes of anxiety over whether this tweeter was meant to fit into the same sized hole as the SL-2000. With some jiggling, it eventually slid into place. Now, after having burned the speakers in for a few days, I can report that they sound amazing! To do an A/B comparison I actually modified one speaker before starting on the other and then listened to them together. Even without a burn-in the new tweeter gave the 5jr a much smoother (less 'jagged') and clearer sound. I spent last night listening to an old Columbia recording of Eileen Farrell singing Puccini arias through these speakers. I don't think I could have done this with the old tweeters but, with the RD-0198's, the sound was not just acceptable, it was transporting.
Comments
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Now I have a question for the forum. Would there be any advantage to reshaping the bass port on these speakers? Specifically, I am wondering whether using a router to round off the edges on the inside and outside would improve anything. I have not noticed any 'chufffing' but my intuition says that rounding off the edges (and maybe epoxying and painting the inner surface to make it smoother) would decrease turbulence in the air flow. Most ported speakers I have seen have rounded rather than sharp edges but maybe some of this is for aesthetics.
Am I descending into 'tinfoil hat' territory here? -
None of MWxxxx drivers were painted with anything that could be called damping material. Ping the basket with your fingernail, it'll ring. If splitting cap values try to make them as even as possible otherwise the much smaller value acts as a bypass cap. To remove the original glue or modern hot glue use denatured alcohol. Rounding off the port would be a good idea.
BTW, you posted this in the wrong section. Contact Kenneth Swauger, the mod, to have it moved.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
>TL refers to tri-laminate.
Thanks for the info. I assume the RD-0198 is the same.
>Ping the basket with your fingernail, it'll ring.
I'll give the driver another look.
>If splitting cap values try to make them as even as possible otherwise the much smaller value acts as a bypass cap.
I don't see how this could be the case. I admit that my EE degree is a bit stale (thirty years old!) but I still remember that impedance goes as the inverse of capacitance: Z=1/jwC. The big guy will have a lower impedance (and therefore pass more current) than the little guy at all frequencies so I don't see how the little guy could ever act as a bypass.
>Rounding off the port would be a good idea.
Time to pull out the router!
>BTW, you posted this in the wrong section.
Oops! N00b mistake! Moderator contacted. -
In a crossover a small value bypass cap in parallel with a large value cap allows the high frequency component of the signal to move faster than it can in the larger cap. This is supposed to result in a more linear response. The only problem is this results in artifacts that at first sound kind of cool, but in short order become annoying as heck.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
> a small value bypass cap in parallel with a large value cap allows the high frequency component of the signal to move faster than it can in the larger cap.
When you add two capacitors in parallel their capacitance values sum. In other words, for C1 and C2 added in parallel the total impedance is:
1/Ztot= 1/Z1 +1/Z2 = 1/(1/jwC1) + 1(1/jwC2) = jw(C1+C2)
and
Ztot = 1/jw(C1+C2)
When you say that the "high frequency component of the signal" moves "faster" through the small value capacitor, it seems like you are saying that the small capacitor has a different phase angle from that of the large capacitor and that this difference is frequency dependent. In other words not all capacitors have a phase angle of pi/2? -
...or, to be explicit, it seems like you are saying that the impedance of the capacitors is more like:
Z1=1/jwC1 + delta1(w)
Z2=1/jwC2 + delta2(w)
and that delta1-delta2 increases with frequency? To induce a phase shift the deltas would have to be either resistive or inductive (additional capacitance would have no effect on phase shift) so I guess leakage current might have such an effect. My understanding of good mpp capacitors, however, is that they have very high leakage resistance (>>10^12 Ohms), so I am skeptical that I could hear a difference that was due to a difference in leakage resistance between 1.5 uF and 12 uF capacitors.Post edited by dyche01 on -
In theory, a bypass cap such as a silver mica is supposed to make a lesser quality electrolytic sound better. Polk did a lot of this in their crossovers. Maybe it helped, maybe it didn't. However, the general consensus is bypassing a film and foil cap should be avoided at all cost and from personal experience I agree. A different phase angle would certainly explain the artifact issue, but I'll leave the technical stuff up to you.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk
