A tip for PMC owners

[jaxwired]

I recently tightened all the screws holding in the drivers on my PMC OB1i. And I'll be damned if they didn't sound better afterwards. And they needed to be tightened too.

If you try it, be sure not to over tighten and strip them. I was able to tighten them quite a bit, but I'm not sure how much torque they can take...

[BuffaloBill]

I checked all the screws in my OB1i. All tight as a drum. ( I did check the screws in my head and found some loose. I tightened them and sure enough the OB1i's do sound better.)

[gtubes]

cool tip

[jdebonth]

All, be very careful with this, I would not touch the screws if the speakers are performing well.

I had a slight buzzing coming from the midrange driver of one my EB1i's. Applying pressure to the plastic outside rim of the driver removed the buzzing, so I thought to adjust the screw tightness. I noticed the screws were not very tight and proceeded to tighten all screws on both speakers. The over-tightening resulted in buzzing from now both the tweeter and mid range units on both speakers. I have since over the period of months had to 'fine tune' the screw tightness to the point where the buzzing is no longer present.

The sweet spot is pretty much what the original somewhat loose tightness used to be (go figure). It's been an absolute nightmare getting back to this place as it is sometimes hard to detect the buzzing, the right track is needed with just the right low frequency energy to excite the vibration. Also mids and highs coming out of the drivers will mask the buzzing making it hard to hear but with certain music that contains sections with only low frequencies it is very much apparent. Sounds almost like a chest next to the speaker is vibrating due to low frequency excitation, it is extremely distracting.

[jaxwired]

Originally Posted by jdebonth

All, be very careful with this, I would not touch the screws if the speakers are performing well.

I had a slight buzzing coming from the midrange driver of one my EB1i's. Applying pressure to the plastic outside rim of the driver removed the buzzing, so I thought to adjust the screw tightness. I noticed the screws were not very tight and proceeded to tighten all screws on both speakers. The over-tightening resulted in buzzing from now both the tweeter and mid range units on both speakers. I have since over the period of months had to 'fine tune' the screw tightness to the point where the buzzing is no longer present.

The sweet spot is pretty much what the original somewhat loose tightness used to be (go figure). It's been an absolute nightmare getting back to this place as it is sometimes hard to detect the buzzing, the right track is needed with just the right low frequency energy to excite the vibration. Also mids and highs coming out of the drivers will mask the buzzing making it hard to hear but with certain music that contains sections with only low frequencies it is very much apparent. Sounds almost like a chest next to the speaker is vibrating due to low frequency excitation, it is extremely distracting.

Wow, that's terrible. But this sounds like a defect with the speakers. Seems to me the drivers should not "buzz" if they are tight. No "buzzing" on mine so far. I'd love to hear from PMC on this.

[jdebonth]

I am fairly sure the buzzing is due to the pressure fluctuations of the LF unit inside the speaker cabinet mechanically exciting the entire MF and HF drive assemblies if they are not screwed in correctly. Too loose or too tight = audible mechanical buzzing. The issue will be much more prominent with the EB's due to the low freq energy they exert. Infact it may be a non-issue with lower PMC models.

Also, I had not realised for weeks until I played a track that had only sub-100Hz content for a few bars. I then became very sensitive to it and noticed it more and more. As said I have now been able to eliminate it completely however it took alot of tinkering with the screw tightness.

I too would love to hear from PMC on this... although I guess the answer will be "dont touch the screws"

[chessman]

I have to believe there is a recommended torque setting for these screws. Loose drivers occur in many speakers and tightening them sometimes helps. As I just learned, it also sometimes hurts.

[jdandy]

Screws in wood or composite speaker cabinets will not hold a constant torque value as will machined threads into a threaded metal hole or a threaded nut. You have to be extremely careful when tightening screws into wood or composite materials. Snug is usually where you want to be, but not wrenched down to a higher torqued value like you would a threaded bolt. In addition, tightening screws should be done back and forth across the speaker frame from one side to the other rather than one screw to the next around the speaker frame. In this manner an even pressure is applied to the speaker frame as it is pressed to the cabinet mounting hole.

[MC352]

Maybe Ian from PMC should chime in here.

Ian, are you out there?

To me this kind of sounds like an accident waiting to happen. One turn too tight and the screw breaks loose from the wood.

How tight is tight? Hulk Hogan tight, or Popeye tight?

Maybe PMC can provide the specific amount of torque that should be used.

[ian@pmc]

Hello!

Leave sleeping dogs lie...

Info for you:
All bolts are torqued to a specific amount with shake proof washers to ensure they remain at the correct level. If over a long period they may need tightening. Finger tight and then 1/2 a turn is ideal.

Do so with the utmost caution. I would hate to have to see someones speakers need service after a most minuscule of tweaks...