Woofer Pumping--anything to worry about?

During a brief trial of a Thorens semi-auto turntable, I discovered that while footfalls didn't cause skipping, they did cause significant woofer pumping on my ported speakers. Which freaked me out, to the point that I returned the turntable. Still haven't replaced it with another one.

So here's my question. It's not about whether I could isolate the turntable better--I know I could. It's about whether woofer pumping is anything to worry about. After all, if I'd had the grills on the speakers, I'd have never seen that scary rapid in/out of the woofers, and might be listening in blissfully ignorant contentment to this day. On the other hand, maybe I was right to be concerned. If I can't locate the turntable in a place where it's more isolated, do I need a phono pre-amp that has a rumble filter? Do I need sealed-box speakers that won't pump? Or should I just relax and let the pumping begin?

 

Subsonic filter. http://www.hlabs.com/

http://www.hlabs.com/products/crossovers/index_files/Page395.htm

37 HZ 18 DB PER OCTAVE HIGH PASS FILTER PROTECTS YOUR SPEAKERS FROM VERY LOW RUMBLE THAT CAN DAMAGE YOUR WOOFER.

 

This looks like a very simple solution, one which I had no idea existed. Thanks, telemike.

 

KAB makes a great one as well - I'd be screwed without it.

 

I have the KAB version as well. I don't really like a filter in the source chain, but it's pretty transparent, and it frees you amp from having to produce that low end motor noise, record warps or whatever lives down in the depths.

 

Is it the KAB RF-1? (That's what I found on the website.) At $179, it's quite a bit pricier than the $29 Sub Bass Blocker from Harrison Labs, but if it's better, it's probably worth it.

 

I had a similar situation http://forums.stevehoffman.tv/threads/my-subwoofer-hates-my-turntable.405112/

When it was all said and done it was more of a ground loop issue that was resolved when I bought a turntable that had a three prong grounded outlet.

 

The KAB RF-1 seems nice and a good solution for some people. But it does the sum the bass below 140Hz. There are plenty of LPs that have stereo bass below that. You'd lose that stereo width on those LPs.

 

Very true. The sound reminds me of my old hybrid that had summed SS bass and tubes on top.

 

I don't worry about it.

 

I'd say definitely worry about it. A Cambridge 640p with a subsonic filter solved the problem for me. My understanding is that it taxes an amplifier more than you'd think.

 

Subsonic feedback will tax your woofers and degrade the sound as well. Luckily my receiver has a 15 Hz rumble filter.

 

Harrison Labs has other crossover points to choose from.

 

Does "tax" mean "permanently damage"?

I'm already convinced by the answers on this thread that I need a subsonic filter. But I want to know that I didn't do any irreparable harm. If I'm not hearing any obvious signs of malfunction (gross distortion, breakup, etc.), have I dodged a bullet?

 

No worries. It taxes your amp more than anything.

 

No damage to your woofers whatsoever; they're designed to do the job you witnessed. But glad you noticed before any long-term damage (although highly improbable) may have occurred.

How about shelf-mounting your TT and place sorbothane feet under it and see if the problem persists before shelling out your hard earned on an outboard subsonic filter ? It should do the trick as it has done it for me.

 

Subsonic filters are a great remedy for the symptom. But, ideally you should address the cause so you don't need a filter. Make sure your cartridge is matched for your tonearm (high compliance moving magnet cartridges - ones that track under 1.5g - should have a light weight tonearm). Or find a tonearm that has fluid damping. Don't let your woofers pump and use the rumble filter as a last resort.

 

True, to a certain extent. But one can have a perfectly matched arm and cartridge and very well set up and isolated table and still have problems with subsonics especially if one is using ported speakers. With sealed designs, not so much of an issue. Not an issue if you are playing all digital vinyl or digital media primarily.

Link below is to a discussion at Audiokarma which covers most of the bases.

http://www.audiokarma.org/forums/showthread.php?t=394426

I have seen some argue online that a good subsonic is not necessary even with ported designs. That may be possible but I think in the real world probability is much higher than not that a good subsonic is a good thing. On many all analog records, even perfectly flat ones, there is subsonic info cut into the record which will cause many ported designs problems as well as severely taxing the amplifier as others have mentioned.

Speakers, and amplifiers, are not meant to deal with this stuff so a subsonic makes very good sense. All subsonics are not created equal. Like many (but not all) things in audio you do sometimes get what you pay for. A $30 el-cheapo rumble filter is not going to be as transparent as the KAB (which I have used in the past, is very well built and quite transparent IMO) or an even more subtle/sophisticated design built into a high end stand alone phono preamp.

For most vinylphiles with ported speakers, I'd suggest that a good subsonic is a necessity. Personally (and I own a ported design) as someone who listens primarily to vinyl, I would not consider a phono stage without a good subsonic or using a high quality stand alone subsonic. I'd prefer (and use) the first option as the second entails yet another set of interconnects.

 

Great info. Thanks.

 

I use ported speakers with vinyl, tape, and digital. #nofilter. I don't have any issue with rumble and I don't see why I should. Let it be known that my speakers still have the original paper cones from the early 80's. They reproduce well down into the single-digits, even at higher volumes. I'm no speaker expert but I wouldn't stress it.

 

Just to fill in a detail, I wasn't getting woofer-pumping from rumble due to the turntable's playing of a record. I was getting woofer-pumping as I walked gently across the room to take the needle off the record! Music didn't make it happen--but the soft tread of my feet on the oriental rug over the wood floor did, transmitted from the wood floor to the platter to the cartridge. Maybe the turntable could have been better constructed, or had more isolating built-in feet, and this would have helped the problem (so in this sense the turntable was "to blame," despite that I could have isolated it better), but the problem wasn't from rumble generated by the turntable itself.

 

Any rigid platform turntable (and many suspension designs) with have issues with footfalls from a springy wooden floor. The only remedy is to isolate the turntable on a wall mount, or something similar.

jeff

 

I wouldn't worry about this unless you dance in front of the turntable while listening to your records.

The pumping isn't going to hurt either your amp or your speakers. Since it isn't effecting or caused by the music, don't sweat it. Unless the woofers are bottoming out, they are designed to move over the range you are seeing. They aren't being stressed at all.

But if you are still concerned, I have owned and used the Harrison Labs pieces for years, initially in car stereos but also in home systems. They aren't the most transparent pieces. I currently have one of their attenuators on my whole house music system but that's using in wall and in ceiling speakers. It isn't of the highest fidelity. If you do use one of theirs, and I have in the past, get either their 20 or 30 Hz filters. The 20 Hz one would be best.

The KAB piece looks better. There is a reason it costs five times as much.

riddlemay, you don't say if you are using an separate phono stage or the optional one for your NAD integrated. If you are using an external phono stage, then put the filter between it and your amp. Otherwise, if you are using NAD's phono stage, place the filter between Preamp 1 Out and Main In. Do not put it between the turntable and whatever you are using to boost up your phono level. It's not designed for the low impedance output of a phono cartridge and will screw up your frequency response if it comes right after the turntable.

 

If that's something you want to take care of then better isolation or a filter would do the trick, but if you're worried over whether or not it will hurt your speakers - in my opinion it won't. They're made to handle these frequencies. In reality it's only really demanding on your amplifier, which can likely handle the extra work without distorting unless it is extremely underpowered.

 

If you can get the woofers to oscillate by walking across the room while a record is playing your turntable is insufficiently isolated from floor borne vibration and even when you don't see pumping, any floor vibration, like what might be generated by the playing of music itself, is certainly smearing your sound, masking detail and having an effect at more than subsonic frequencies.

You should focus on proper table isolation via some scheme that works down to like 6 Hz or lower -- air bladder set ups, sprung suspension set ups, etc. And some kind of table stand that's rigid, inert and if necessary decoupled from the floor like a wall mounted shelf. The problem is not the sort of problem a subsonic filter is designed to address. The problem is one of insufficient environmental isolation and the table responding to a flexy floor to which it's been coupled.