LFM-1 Cabinet Resonance

After playing my sub at high levels over the weekend, it came to my attention that -- what I once thought was driver distortion / buzzing when pushing the LFM-1 hard -- was actually vibration from the top of the cabinet. I think it may be the plexiglass top. Anyway, when I pushed down on the top of the sub during playback, the noise stopped. I tried to think of some sort way to dampen the cabinet. I had three unused VPI magic bricks laying around, so I tried various placement of these along the top. After a few minutes experimentation, I found the trouble zone was the back end of the cabinet (toward the amp). I placed the VPI bricks three in a row at that location and now the buzzing / distortion is gone.

Now I'm a happy camper, but I am wondering if anyone else experience this issue???

Just to clarify, this is not a post pushing VPI Magic bricks. They're just basically big heavy blocks. Anything of similar weight would have had the same result.

I am not sure how the plexiglass top is secured but that shouldn't happen, I would give Outlaw a call. Never heard of the magic bricks but if you try putting them in a triangle I am sure you will here a difference

Don't think I didn't try that already

Anyway, I can live with it now that it is under control. Frankly, unless the problem reappears, I'd prefer not going through the hassle of a return. But I might give them a call just as an FYI.

It would be interesting to know, however, if other LFM-1 owners notice any changes / improvements by weighting the top of the cabinet.

My wife's 20+ pound persian cat likes to sit on the LFM-1, but usually not while it's really cranked up - I don't think that counts.

I just experienced this over the weekend on "my" father's day (Saturday) when the girls went last-minute shopping for the "actual" father's day. I was left alone (at last) for the first time since I got the LFM-1 and decided to put it through its paces.

I have two subs in my system, the LFM-1 and a Sunfire True Sub MK IV. I once had the Sunfire knock a sprinkler cover off the ceiling (before SMS-1), so I turned it down a bit this time.

I played Pink Floyd's Dark Side of the Moon SACD at -5db on the Outlaw 990 and thought I heard a faint rattle. My plasma monitor's attached speakers have been known to rattle, so I checked them and they were tight in place. I decided to really go for it and play the movie "Serenity" also at -5db. The beginning credits rumble is truly earth shaking and it did expose the LFM-1 as the source of the rattle.

I turned down the volume on the LFM-1 and kept replaying that scene until I had barely audible rattle (and before my ears started bleeding). Though I do not believe it is the plexiglass, since the rattle seemed to come from something "inside" the sub. Anyway, I rarely listen to anything at that level and other things start to rattle then anyway, so I can't blame the LFM-1 (too much). However, I am now even more impressed by the Sunfire True Sub.

Hey there garcianc2003 -- I just noticed your reply.

I wish I could say I'm glad I'm not the only one experiencing the rattle, but, unfortunately, your discovery only confirms there's a problem with some of the LFM-1's out in the field.

Harking back to when I first discovered the problem, I tried putting my ear up against the cabinet to see if I could locate a particular trouble spot on or in the sub. Like you, the noise seemed to come from inside the sub -- particularly near the amp side.

However, it invariably went away when I pushed down on the plexiglass top. And so, as my orignal post described, I was able to eliminate it by placing a few VPI Magic bricks in that area.

Since then, I wound up relocating one of the bricks toward the center of the sub top -- so the current configuration is two bricks at the rear, one roughly centerpoint.

If I have a chance this weekend, I'll snap a couple pics' of my sub so you can see exactly where they are located. If you feel inclined to experiment with some dampening, it would be interesting to see if your rattle points are in the same areas as mine.

Sorry I have been away from the forum for a while. I haven't had a good reason to post until now. I wanted to check if this LFM-1 resonance was a common problem. I really cannot listen to anything loud without the rattle coming in and I don't think it is the glass.
I ordered an auralex gramma isolator for the sub. I noticed that, despite the spikes, the sub has settled lower than I had anticipated into the carpet. Hopefully the extra clearance will help. If not, I will contact Outlaw support.

I got a reply from Outlaw support with some suggestions. I'll try those when I get a chance and post a follow-up. Thanks Outlaw Support for the quick reply!

garcianc2003:

Let us know what those suggestions were and how they worked out.

Interestingly, I don't seem to have the problems I once did with the rattle. One possible culprit I discovered some time ago: I recall repositioning the sub and noticed there was some play between one of the spikes and the spike "cup" (those discs that keep the spikes from marring the floor). It wasn't firmly seated. And I think this destablized the sub a bit at loud playback levels and caused it to teeter / vibrate. This would have exacerbated any vulnerable vibration points within the cabinet and/or plexiglass.

Anyway, I made the adjustment and things seems to be okay for the moment.

Regarding your sub's position relative to the carpet, what I first did was to use aftermarket spikes that had more clearance than those provided by Outlaw and were better able to pierce through to the subfloor. Later, I added a granite slab as a sub platform and that helped even more (view pictures 13 and 14 in my system pics album for a close up).

I think anyone who is using their LFM-1 on thick carpet should take a look at their ground-to-base clearance. It's pretty surprising how a thick carpet and pad can reduce the clearance compared to a hard surface.

I have to assume the proper distance between the bottom of the sub and the floor was based on a hard surface, not a thick layer of cloth.

One of the suggestions never occurred to me, which was to check that the binding posts were not loose. That was not the case but it never crossed my mind to check something so obvious.
The other was to unscrew the amplifier section and look for anything loose inside. I never got that far because, after accidentally bumping the cabinet with my knee in the process, I noticed that one of the vent ports was the cause of the vibration.
The Outlaws provided me some directions on how to apply adhesive but also offered to do the work for me. I am not the handiest person, so I opted to ship the sub for repair.

Thanks garcia:

I will check my ports next time I play the sub loud.

I have noticed distortion coming from that area before. I thought it was either the driver over-extending itself or excessive port chuffing. I will focus on the port vents next time.

BTW, there is one demo that makes the LFM-1 go plum crazy in this regard, it's the 4th track from Kraftwerk's "Aerodynamik." Though I doubt you or the Outlaw team own it, I would love to know if it causes problems with other LFM-1s.

Very odd, considering it can handle bass tracks like U571 with relative ease.

Best,

- Jim