You are here

Log in or register to post comments
Welshsox
Welshsox's picture
Offline
Last seen: 2 years 7 months ago
Joined: Dec 13 2006 - 7:27pm
Bass cone flap

Hi

I recently added PS audio phone stage to my system which has once and for all solved any front end gain issues !! this phono amp has added fantastic dynamics to the system. The problem is that it might have added a little to much !!

The problem i have now though is that on very heavy bass tracks im causing the speaker cones to bottom out and start basically flapping. This is happening at loudish but certainly not ridculous volume levels. It is admittedly severe tracks like 1812 cannons etc thats doing it.

Im not really concened about the audible effects, im concerned if im damaging my Dynaudio Focus 220 speakers.

Any thoughts ?

Alan

Jan Vigne
Jan Vigne's picture
Offline
Last seen: Never ago
Joined: Mar 18 2006 - 12:57pm
Re: Bass cone flap

Sounds like you are allowing subsonic information from the arm/cartridge combination or record warps to get through to the amplifier. Does the phono stage have any sort of subsonic filter?

Welshsox
Welshsox's picture
Offline
Last seen: 2 years 7 months ago
Joined: Dec 13 2006 - 7:27pm
Re: Bass cone flap

Jan

There doesnt appear to be any subsonic filter.

It could be some form of vibration, it doesnt happen on CD's or SACD's

Alan

Editor
Editor's picture
Offline
Last seen: 3 years 8 months ago
Joined: Sep 1 2005 - 8:56am
Re: Bass cone flap


Quote:
There doesnt appear to be any subsonic filter.

It could be some form of vibration, it doesnt happen on CD's or SACD's

What you are seeing is your woofers react to warp-induced infrasonics, perhaps amplified by your tonearm effective-mass/cartridge-compliance resonance, that is being passed through by the PS phono stage.

The woofers in a ported speaker are unloaded below resonance, meaning that they will undergo large excursions with infrasonic information.

This won't do any harm, unless the amplitude of the "flapping" is large enouth to cause the woofers to "bottom." But it does use up amplifier power and reduce your system's dynamic range capability.

John Atkinson
Editor, Stereophile

Jan Vigne
Jan Vigne's picture
Offline
Last seen: Never ago
Joined: Mar 18 2006 - 12:57pm
Re: Bass cone flap

The frequency your woofer is trying to reproduce is in the below 10Hz range. As John says, this won't really do any damage to the driver unless it begins to overdrive the allowable travel of the voice coil. However, it forces the vc out of its most effective operating range and it eats up tremendous amounts of amplifier power to move a woofer at 10Hz or lower. Virtually all LP's will have some amount of warp frequency reponse and a poor match between the tonearm's effective mass and the cartridge's compliance will make matters worse.

If you're running a new table with the Ortofon OM5 cartricge that comes packaged in too many systems, this would be the case here. The OM5 cartridge is a low mass, high complinace design from twenty years ago when lower mass arms were more popular. Paired with the medium mass arms of today, that cartridge is not a great match when it comes to hitting the proper combination to minimize arm/cartridge resonances.

Try one of these subsonic filters, they will gently roll of the bass response from the cartridge when plugged into your phono section's inputs so you're not wasting power at the pre amp end of the system. This should reduce if not all but eliminate the woofer flutter.

http://store.hlabs.com/pk4/store.pl?section=12

Call Harrison Labs and tell them your situation. It's possible you might prefer the straight 20Hz HP filter or, if you're running a subwoofer, you might do better to have your main speakers rolled off slightly higher and the subs rolled off lower.

Another step towards improving the situation would be a record clamp that could flatten slightly warped discs on the platter. This will also benefit all of your LP's.

Welshsox
Welshsox's picture
Offline
Last seen: 2 years 7 months ago
Joined: Dec 13 2006 - 7:27pm
Re: Bass cone flap

Jan

Thanks for the advice

Its not that big a deal and only happens on very few tracks, i was more concerned about damaging my VC than trying to correct it acoustically.

Alan

BillB
BillB's picture
Offline
Last seen: 2 years 2 months ago
Joined: Aug 15 2007 - 2:04pm
Re: Bass cone flap


Quote:

Quote:

What you are seeing is your woofers react to warp-induced infrasonics, perhaps amplified by your tonearm effective-mass/cartridge-compliance resonance, that is being passed through by the PS phono stage.

The woofers in a ported speaker are unloaded below resonance, meaning that they will undergo large excursions with infrasonic information.

This won't do any harm, unless the amplitude of the "flapping" is large enouth to cause the woofers to "bottom." But it does use up amplifier power and reduce your system's dynamic range capability.

John Atkinson
Editor, Stereophile

Hmm, good point about ported speakers being unloaded below their resonance point. I have a 3rd "ambient" speaker where I do see large woofer excursions when playing vinyl - but not when playing CD's, and I have indeed always presumed this is from infrasonics from the turntable and/or record warps. The large excursions are "silent" since they are below the speakers useful response and I guess below hearing threshold as well. If I used an acoustic suspension speaker in place of the ported one, the "flapping" problem should be less - right?

Jan Vigne
Jan Vigne's picture
Offline
Last seen: Never ago
Joined: Mar 18 2006 - 12:57pm
Re: Bass cone flap

The warp frequency is still beneath system resonance. They would pump more slowly due to the internal damping of the air but they must respond to the signal they are fed.

dbowker
dbowker's picture
Offline
Last seen: 1 month 2 days ago
Joined: May 8 2007 - 6:37am
Re: Bass cone flap

"Try one of these subsonic filters, they will gently roll of the bass response from the cartridge when plugged into your phono section's inputs so you're not wasting power at the pre amp end of the system. This should reduce if not all but eliminate the woofer flutter.

http://store.hlabs.com/pk4/store.pl?section=12"

Those things don't detract from the other sounds at all? I just mean, if you have all kinds of expensive wire, a nice phono-amp, and the like, and you throw those filters in the middle, in your opinion, it would not take away from the rest of the signal? Otherwise, they seem a very useful items. I have the Grado PH-1 BTW with a Grado Sonata MC on a Well-Tempered Classic.

Jan Vigne
Jan Vigne's picture
Offline
Last seen: Never ago
Joined: Mar 18 2006 - 12:57pm
Re: Bass cone flap

I've only tried a few of the Harrison Labs devices after being directed their way by a friend who builds speakers. The few I've tried are quite well made and exhibit at worst a minimal thumbprint on the sound quality. I use a pair of attenuators in my system and can say I've found no ill effects from their insertion into my system as would generally be expected with a high quality resistor in line with the signal coming from a low impedance source to a high impedance input. My volume controls probably have more effect on the sound quality than that pair of attenuators.

Obviously, some systems are more transparent to changes than others and some listeners are more sensitive to specific types of changes that are others. With that in mind I can't guarantee the results of any change you make to your system. But they are, IMO, worth trying and returning if you don't feel they are sufficiently transparent.

The Harrison Labs pieces are not cheap and they appear to employ the best materials available within what can be considered reasonable price ranges.


Quote:
Those things don't detract from the other sounds at all? I just mean, if you have all kinds of expensive wire, a nice phono-amp, and the like, and you throw those filters in the middle, in your opinion, it would not take away from the rest of the signal?

In this case we're talking about a HP filter that goes in line before the pre amp or amplifier. By removing the deepest bass energy from the incoming signal your electronics will actually have less work to do with less strain on the power supply and ps capacitors. That filtering in the case of a power amplifier will typically mean it is not struggling through some of the most difficult portions of a speaker's load. By filtering out the most demanding pasages from the amplifier you should hear a sense of greater cleanliness and more power on reserve. Those benefits should easily outweigh any effects of the filter itself.

I would make a bet with most listeners that the side-effects of this device are far less noticeable than the benefits of this device. How much can you hear from the HP filter in your present speakers? If you cannot identify the many problems associated with passive crossover filters, then you probably can't hear the downside to the subsonic filter. The speaker crossover is far more crude in its application, typically more complex and always placed at the worst possible location for its job compared to the Harrison Labs filter placed in front of the electronics.

It would require a very large inductor to filter the low frequency garbage from the phono signal if it were being done at the speaker end of the system and the amp and pre amp would still be struggling to reproduce subsonic information which has nothing to do with the music signal. The power amplifier would have to deal with the inductive load on its outputs. Such an inductor would be considerably more expensive and will have far more to do with the way the amplifier negatively performs - which will likely be much more audible - than will the positive effects of a subsonic filter placed in front of the pre amp.

Subsonic filters are one of those devices like mono switches that have disappeared from many pre amps. They both have tremendous advantages in any analog based system and they can be done exceptionally well with not a lot of effort. Unfortunately, the "straight wire with gain" crowd saw them as undesireable for the wrong reasons and they have disappeared from most pre amps. What that leaves is a problem - warp induced cone movement - that cannot easily be resolved.

The way I see it, you have a problem with warp resonance in any analog based system. Virtually all records will be slghtly warped and most will be off center. Today most turntable retailers have no idea how to match a cartridge to a tonearm - as evidenced by the preponderance of OM5's being packaged with Rega tonearms. This means most analog systems are generating resonance information constantly though these resonances are, like warp resonance, very low frequency signals. A tonearm with the effective mass of the WT arm is not meant for the higher mass and lower compliance of the Grado but there aren't many cartridges around today that do fit with the WT arm (fortuntately, the silicone damping of the WT arm provides a fair degree of latitude in this respect). You can ignore the problem of warp resonance and go ahead and spend your money on expensive cables and "nice" phono preamps but you'll still have a problem you are ignoring only because you cannot easily hear the downsides of your amplifier and speakers responding to an 8 Hz signal. This is a case where if you saw the effects displayed on an oscilloscope, you would, IMO, easily choose the subsonic filter over just ignoring the problem.

Other than an active circuit, which would be far more expensive and still not absolutely without effect, this is one of the the best solutions I know for solving this specific problem and well worth the investment in most systems. Another alternative would be to move to a table with either a good clamping system - preferrably a periphery clamp - or a vacuum hold down system. In most cases such clamping devices should make the effects of warp resonance minimal and you could probably dispense with any subsonic filters if the LP's were in a good shape to begin with. Short of that, I'd give the Harrison Labs pieces a try. I think you'll find most cables have a more audible effect than these filters do.

  • X
    Enter your Stereophile.com username.
    Enter the password that accompanies your username.
    Loading