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Some records cause my speaker woofer to go through large displacements

qec

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I finally have a place to setup my audio gear and just listen to it. This has allowed me to start going through the whole system and get things running/sounding as good as possible. My setup consists of:

Adcom 555 amp
Adcom GTP 500 preamp
Audio Technica at-120 turn table with vm-95e cartridge
C Note speaker (home built), begin replaced shortly with Elac DBR-62's and a sub
Topping EX5 DAC
Emotiva XPS-1 phone preamp

I also inherited a stack of albums from the 70's and which I have been going through. On several of these album and some that I already owned I can see the woofer driver on the speaker bouncing back and forth with a fairly large displacement even at low playing levels. The result does not seem to be very audible so I expect it is very low frequency. This never happens when the system is driven by the DAC. I tried 3 different phone preamps and they all do the same. If I turn on the low filter on the preamp the situation goes away. Any idea what is going on? I'm sure this is not something new but I never use to just sit and stare at the music in the past so it went unnoticed.

Thanks in advance
 

Jim Taylor

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If your preamp has a subsonic (high-pass) filter, you need to engage it. Sometimes it's labelled "rumble filter". Jim
 
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qec

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Jim I mentioned that I did that and noticed a change. I guess my real question is: Why is this happening? Any why on only certain records?
 

sergeauckland

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Firstly, some records have warps that set off the arm/cartridge resonance, so generate a lot of subsonic output. Others will be flatter, and/or have the warps at a different frequency. If there's a mismatch between the cartridge compliance and arm mass, this will be made worse.
Secondly, in all probability, your loudspeakers are vented, so below the bass resonant frequency, there is no control of cone motion, so large excursion very low frequencies result in exactly to motion you see. This is made worse if the power amp is valve-based as the output impedance at low frequencies goes high due to limited LF feedback.
The phono stage of the amplifier should have a subsonic filter, either switchable or fixed. This used to be common in the 1960-70s when turntables were the main source, these then fell out of fashion, and nowadays, few phono stages have them. In my view, ALL phono stages should have a steep cut-off below 20Hz, as there's nothing down there other than noise and excessive excursion due to LF resonance.
The mania for 'straight-through' amplification without filters or tone controls has a lot to answer for.

S.
 

abdo123

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To put you in perspective, this is what the groove noise (a quiet passage on a record) of a record looks like, substantial low frequency noise.

it's very possible that somewhere something is happening and you're reproducing a shit load of low frequency noise. I would honestly just let it be if it's only a visual concern and only on a particular record.

index.php

This is what the frequency response of my phono stage looks like

index.php
 
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qec

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Thank you for the excellent descriptions. This all makes sense. @sergeauckland was also correct that the speakers are ported (rear). I have been pondering selling the Adcom equiment and just getting something smaller like the Topping PA5 since it has 2 inputs and volume control but I have found uses for the tone and filter controls on the GTP-500 and frankly I love the looks of Adcom stuff so I think I will keep and and figure out where to mount everything. Turntable takes up too much room!
 

PipeOrganNorm

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The problem of turntable rumble and excessive speaker travel is exacerbated by the RIAA equalization that has approximately 20dB more gain at 20 Hz than 1 kHz. I can't speak authoritatively but the possibility of IM distortion exists as well as decreased dynamic range. There's a lot of power being expended that's not producing music -- just low frequency noise. A steep slope high-pass filter (as shown above) is highly recommended! The graph Abdo123 posted above is helpful, but it stops where the noise really takes off, below 20 Hz or so, and is greatest in (roughly) the 8 to 16 Hz range. Ah, vinyl.....
 

nothingman

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I can’t explain why on a technical level but it’s a well known thing called “woofer pumping’ and it’s especially prone to effect ported speaker designs as others mentioned. You can look for a cart-arm mismatch in terms of compliance and weight, but odds are it’s just some warping in the record and unavoidable outside of using a subsonic filter. I have one record that just sends my speakers into crazy slow but large excursion even at minimal signal level. The KAB fluid damper is powerless to stop it. Subsonic filter knocks it out. Other records are similar to a much smaller extent. Part of the joys of an entrancing but flawed medium.
 
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