Monitor & Monitor Series 2 (SL2500) crossover questions

pkquat

Searched but did not find a definitive answer for the first question. Is the stock M5 Series 2 crossover the same as the M7 Series 2, is it the SL3000 mod schematic? If it is the SL3000 mod schematic, does anyone know why they are that different? If the SL3000 mod schematic is just a mod, I assume the end result, crossover points and attenuation, are the same.

Does anyone know the reason for the low frequency crossover change? I would assume the PR tuning changed some, or maybe the cabinet. I'll search this later on today or the weekend, but if you know TIA.

Is the difference between the 5Jr, and the 5 & 7 high frequency crossovers lowering the crossover point for the 5Jr because the MW is working harder on the low frequencies, and maybe some attenuation differences (resistor change) because of the cabinet size? Am I correct in assuming the resistor in the high frequency path is for attenuation, or does it also effect the crossover frequency?

westmassguy

You're mixing apples, oranges and bananas. There is no Monitor 5 rev2 schematic.
All we have is the SL3000 revision for the Monitor 5, which I also use for Monitor 7 TL mods. The Monitor 7 rev2 is a complete re-design, while the SL3000 mod is just that, a modification to an existing crossover design. The 5jr is a whole different animal. It uses a 2nd order high-pass, inverted phase, with a 1st order low-pass. The Mon 5, 7, 10, and 12, all have 2nd order high and low-pass.

pkquat

There is a little fruit salad going on, and I wanted to see how they "peared". Seriously though, I thought I was more comparing apple varieties to stick with the theme. They all use the same MW, and tweeter combinations. For the SL2000 tweeter, they had similar high-pass crossovers for all three models. I would have thought the Series 2 with the SL2500 would again have a similar high-pass crossover for all three models. The available schematics for combos using the SL2500 tweeter are all quite different.

I was hoping an M5 Series 2 schematic existed somewhere or someone drew one up, but it didn't make it to the official schematic thread. The M5 Series 2 was made, so I was curious how the factory crossover compared to the M7 series 2.

The M5 and M7 B series with the SL2000 tweeter are almost identical except the M5 high-pass uses a 0.22mH inductor vs. a 0.23mH for the M7. (I'm not sure why they would be so close, yet different. They fall within a 5% tolerance band.) The high-pass for the M7 B and M7 Series 2 are similar except for the capacitor in parallel with the resistor. I would think the M5 series 2 crossover would be similar as well.

The low-pass crossover for the M7 changed when switching to Series 2, this made me wonder what the reason was for the change, and if the PR also changed. I think the PR may have changed in the M5 for the Series 2, but I still need to dig further. Since the low-pass changed for the M7 series 2, I wonder if the factory M5 Series 2 low pass also changed. The reason for bringing the 5Jr+ into the mix, was 2 fold. First, although the low-pass is a 1st order crossover, it and the PR stayed the same when it switched from the SL2000 to the SL2500. Second, the high pass crossover only changed by increasing the capacitor value. Similarly, the M7s and M5s had a capacitor added (although it is in parallel with the resistor).

I do need to refresh my memory better in simple terms how circuits are set up. I don't remember what effect the parallel RC circuit does vs. changing a capacitor or inductor value.

I thought the primary purpose of a resistor in series with a tweeter in a high-pass crossover essentially controlled the tweeter volume, like an old L-Pad. The resistor value was the resistance of L-Pad when they thought everything blended well and the level remaind the same between the tweeter and MW. Thus my attenuation speculation between the 5Jr and others.

westmassguy

A capacitor and resistor in parallel, form a contour network. The Monitor 5 SL3000 Mod does just that. There are two types:
If the response is rising with increasing frequency, a Resistor and Inductor in Parallel are used.
If the response is rising with decreasing frequency, a Resistor and Capacitor in Parallel are used.

pkquat

TY. It makes me wonder how or why the 5jr+ series 2 can get by without it. Maybe it blends well (enough) with the 6db slope of the MW, and it was a cost savings. The smaller box probably has an effect, but I would think it would effect the MW more. Then again, I would think there would be more similarities with the SL2000 tweeter versions.

As I've been digging into the differences further I see the similarities in the M10s, and RTA8's and 11's. Its interesting that a Zobel circuit was used for the RTA's with the SL2000. I think that is the name of the circuit across the tweeter.

I also find it funny and odd that no one has drawn up an M5 series 2 schematic, nor can I find any good and definitive pictures of the crossover.

pkquat

Well I came across a set of M5 Series 2 for a moving sale price to satisfy my curiosity. What are the odds . At this rate I need to find a reason for a peerless M7 and SRS 1.2 thread.

Attached is a picture of the crossover. It appears it uses the TL M7 high pass, and original M5 lowpass. The 8MFD Cap is in parallel with a 2.7 Ohm resistor. I am assuming the inductors are the same. When I rebuild the crossovers I will get the values. I should also note, these appear to have the older style MW6502 drivers. The dimples in the paper cone are more visible

Side note:
First listening impressions are, I am still not a fan of the SL2500. Its does not have the SL2000 spike, but it is not very detailed and almost a little quiet. Maybe its the crossovers but the uppers mids do not blend very well either. Overall they high end is a little better than my 5jr+ Series 2, but something still sounds off. The bass however is a little better than my 5A's (with the poly-fill behind the MW). My first guess is the roll off starts a little later and is less. What I really notice is that the MW and PR are moving much more for the same volume. I need to bump the bass up on the 5A's to get the same activity, but when I do, then the 5A's have much more bass.

westmassguy

The SL2500 is the less expensive version of the SL3000. The RDO-198-1s will be a vast improvement.

pkquat

Minor thread derailment - Passive radiators:

One of my original 5A PR's cracked and leaked. I have two spares that turned out to have leaks , and my current good spares. These are all from the same black basket era, ~'82-'84 I think. I have noticed that these surrounds are rather stiff. Much more stiff than what is in the Series 2. The series 2 is not far off in feel from the MW by comparison. I don't think it is just age. I vaguely recall the PR surrounds feeling much stiffer when new than the MW, but probably not as stiff as they are now. I am thinking the added stiffness (initially and now from age) has to effect the tuning.

For fun, I swapped out a PR from the Series 2 in to the 5A. The PR is more active, and maybe the MW is a little more at some frequencies, but I don't think the bass better after a quick listening test. The initial impression is they will be similar to a pair of early silver basket PR's with the additional paper gasket on the front side. I didn't look at movement at the time, but I felt they did not have a much bass as the black basket version. The surrounds on these are thinner and soft, similar to the Series 2.