Buy the LO7D if in good order and you can afford it.
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Here's a website all about the Kenwood L07D including the specs on the tonearm:
On that site you'll find:
"Tonearm effective mass is rather high at 17g. and will therefore be better suited to medium (between 10-µ/mN and 20-µ/mN) and low (less than 10-µ/mN) compliance cartridges."
When you examine specs of most cartridges today (anything from budget MM to cost-no-object LOMCs, you'll find that most compliance specs fall between 10 and 20µ/mN. For example, a $75 Grado Black has a compliance of 20; a $15,000 Clearaudio Goldfinger has a compliance of 15. According to the Kenwood specs and that website, both carts would be good compliance/resonance matches for the Kenwood L07D arm.
08-09-15: JagdzakuCompliance is how flexible the cartridge's suspension is. The higher compliance, the more readily it "wiggles," which should correspond to the effective mass of the tonearm. The higher the compliance, the less the tonearm's effective mass should be; the lower the compliance, the heavier the tonearm's effective mass should be.
The combination of tonarm effective mass and cartridge compliance always creates a resonant frequency. This resonance should be between 8 and 12 Hz, ideally 10 Hz. A lower resonant frequency can cause "woofer pumping" and rob the music of a good bass. It can also make the tonearm more prone to jumping the groove. A resonant frequency above 12 Hz starts to interfere with audible bass.
Here is a cartridge/arm calculator. For effective mass, you combine the effective mass of the tonearm plus the weight on the cartridge. In the case of your 17g Kenwood arm plus 8.2g Frog, that's an effective mass of 25.2g. Compliance is 35. Enter those numbers, click "Calculate" and you get a resonant frequency of 5.359Hz, which is way low.
Use the second calculator to find an ideal compliance for ideal resonant frequency: For example, if you have a 6g cart mounted to the Kenwood tonearm, you have 23g effective mass. For an ideal 10Hz resonant frequency, you'd want a compliance just above 11. Altogether, the "safe" 8-12 Hz range allows compatible compliance from 7.648 (@12Hz resonance) to 17.2 @8Hz resonance.
Jagdzaku, I wouldn't let the stock tonearm discourage purchase of an LO7D. It is a superb TT, even without the arm. If you have access to a machinist, it is feasible to devise a generic turntable mount that will clamp down into the stock tonearm pod collet and accept pretty much any surface mounted tonearm(e.g. Dynavector, Trans-Fi, Talea, Kuzma, Schroeder.) I've had great results with Trans-Fi on L07D.
Even if your phono preamp has a LF filter, an arm/cartridge combo with a native resonance of ~5-6Hz is asking for trouble. At a minimum, it would impair clean tracking and overexercise the suspension in the cartridge, possibly shortening its life.
Anyway, most LF filters do not operate as brickwall filters (unlike the HF filter in redbook CD players). SOME of that LF energy is going to make its way past the filter and into the amplification chain. At best, that adds sonic mud and raises your system sound floor. At worst, it may overstress amps or speakers.
Listen to Johnnyb53, he answered well.
Any and all low frequency "rumble filters" that I've tried robbed the musical presentation of a solid foundation and much of the life of the music.
Those LF filters were mostly for attenuating the "rumble" or motor noise of idler-driven turntables, and not for taming bad arm/cartridge mismatches, which can affect things (such as tracking) long before the result would reach the speakers.
09-27-15: JagdzakuNo it doesn't. The effective mass is the mass or weight of the tonearm from its pivot to the headshell.
The extra counterweight enables you to balance a heavier cartridge. The counterweight doesn't add effective mass, but the cartridge does.
You have to factor in the weight of the cartridge plus teh tonearm's effective mass to arrive at the total effective mass.
With all due respect to Johnny, and as Dave partly indicated, Johnny's response to the question about effective mass is incorrect on all counts. The effective mass is a function of the distribution of the mass of the tonearm from pivot to headshell, including the cartridge mass, (not just the total mass per se), which is why you cannot determine effective mass by simply weighing the tonearm, and the counter-weight also contributes to effective mass by a factor related to the square of the distance from the pivot point to the center of mass of the CW times the mass of the CW. Thus, the "subweight" increases effective mass on both counts; it shifts the center of mass of the total CW further away from the pivot and it adds to total mass. Apologies to Johnny...
To answer your question, almost. With mass behind the position of the cartridge, 100% of the weight difference does not subtract or add to eff mass. This is a trivial amount. The stock shell looks to be of very high quality, but it might be interesting to experiment.
To clear up some misconceptions, if you increase the weight of the counterweight and bring it closer to the pivot, eff mass will decrease with the change of distance.
I think too much emphasis is placed on resultant resonant frequency. IMO you'd be better off asking users which carts are a good match, which combination seems like it's made in heaven. Some carts seem to sound better with mass that puts them a little out of the recommended resonance range. While you don't want that undamped resonance approaching the audio band or excited by a warp, best results are not defined by "perfect" 10Hz resonance.
"To clear up some misconceptions, if you increase the weight of the counterweight and bring it closer to the pivot, eff mass will decrease with the change of distance."
That's only because eff mass will vary as the SQUARE of the distance between pivot and CW center of mass, whereas the relationship between eff mass and CW mass is first order. I'm writing this, because I don't know where there was a misconception. One interesting thing that falls out of the equation is that if you use a relatively low mass CW, you can have more control of eff mass simply by sliding the CW toward or away from the pivot vs using a "heavy" CW. I think this is what Technics (and other makers of vintage Japanese tonearms) had in mind with their design of the EPA100, which they claimed could be used with cartridges that vary widely in compliance. Modern tonearms have tended to go in the other direction, with heavy as possible CWs mounted close as possible to the pivot, to reduce inertia, I think. My Triplanar came with a variety of interchangeable CWs, so the CW can always be close to the pivot. But look at the very expensive Durand Telos tonearm; it has a rather long rear projection and a relatively light CW compared to some others and even to the Talea.