Why the woofer moves badly when playing certain LPs

Hello starbusters,

That is a classic example of a bad record. If your problem is only with certain new records, and does not happen with old records, then very probably your system is ok. That to me looks like a pressing error of the record. On the video, towards the end, it is obvious that record is warped... Bad production of the record mechanically... Not much that you can do there...Subsonic filter may help, but only to a certain degree...
Hope this helps.. 

Audio Technica AT150Sa
Weight 8.0g,
Static Compliance 40 x 10-6 cm/dyne,
Dynamic Compliance 10 x 10-6 cm/dyne (100Hz)

Pro-Ject the classic turntable
Effective Arm Mass: 13.5 g

Resonant frequency of arm/cartridge: 7.5Hz

Look like arm/cartridge mismatch is the problem !

@imhififan


If AT’s compliance is 10cu @ 100Hz you have to convert it first to 10Hz and it will be about 17cu @ 10Hz (Mid Compliance).

13.5 (tonearm mass) + 8g (cartridge weight) = 21.5g and you can add hardware too, probably 23g total.

The you can cross the lines (17cu and 23g) and it will be around 8Hz which is OK according to Ortofon:

Resonance frequency can be calculated by using the formula

f = 1000 : (2 x π x √ (M x C)) where:
f - Cartridge resonance frequency in Hz
π - 3.14159265359...
C - Cartridge compliance lateral in µm/mN
M - Total tonearm system mass which is a sum of Mass of cartridge, Mass of headshell and screws and Effective mass of tone arm (all values in gram).

• Resonance frequency within 7-12Hz is optimal for the system.
• Resonance frequency slightly outside optimal interval 6,5-7Hz and 12-14Hz can be considered as a possible that probably can be used without problems.
• Resonance frequency outside the interval 6,5-7Hz and 12-14Hz is questionable, and the system might not work properly.

The OP could use the lightest possible mounting screws to reduce the mass slightly. Or to remove stylus protector on AT if it's possible (to reduce the weight of the cartridge). 

Or to find a slightly lower compliance cartridge for that tonearm, for example a cartridge with 15cu @ 10Hz like Pickering XSV/3000SP will be a perfect match if we will check this (the resonance will be in desired range for 15cu compliance and toneam/cartridge mass near 21-23g).

BUT some people does not care about resonance frequency at all, here is the thread about it.

If AT’s compliance is 10cu @ 100Hz you have to convert it first to 10Hz and it will be about 17cu @ 10Hz (Mid Compliance).

I just estimate and simply doubled it to 20 @ 10Hz for calculation.

Resonance frequency within 7-12Hz is optimal for the system.

I'd like to have 8-12Hz as optimal value.

As you can see even +/- 3cu is important, but it's not that bad with OP's tonearm and his cartridge

From viewing the YT video, it appears to me that the arm/cartridge combo is just barely outside of the optimal range and this is borne out by some of the posts above. The thing about this is a slight amount of record warp can really affect the setup a lot more- leading to some LPs being quiet and others not. This being a smaller speaker (I was unable to find if it was ported or not) the woofer is going to flop around quite a lot with out-of-band signals.


The idea of going to lower mass mounting screws is a good one (worth a try- its cheap; maybe also remove the stylus guard), better yet a cartridge with slightly lower compliance.