Strange partial driver failure? loss of bass in one speaker

[spice house]

I have a 3 way system using hds 810921, 830884, and sb34nrx75-6

I was listening to my speakers yesterday and I noticed one had quite a bit more low bass than the other. They have been fine for years.

I switched out everything I could - all cables, amp channels, ect, and narrowed it down to the drivers. Even switched the crossovers between boxes. I examined the drivers and did AC ohm measurements and everything seems to be in tact. Voice coils are shiny and uniform... no cracks or leaks...

When I played the subs by themselves the difference was huge - one was about 10db quieter and sounded like it had a strong rolloff at about 80. I though OK sub went bad - not sure why

Then I noticed one midwoofer plays lower than the other as well! How is this possible?

What sort of failure can lead to loss of low bass across a whole speaker, but leave the 100hz+ frequencies in tact? This also sucks because my midwoofer is no longer available! I don't suppose there is a way to fix this?

 

[DrDyna]

did you try flipping L/R on sources / preamp too?

 

[Arty]

before doing anythng else mesure impedance curve for the drivers.
that will tell more.

 

[weltersys]

Sometimes a layer of a voice coil can heat up, slough off and lodge in the gap, the speaker will play but have lack of bass.
A pinched coil due to a shifted magnet will have the same result.
In either case, pushing on the cone will have drag, usually a scraping sound.

You say "voice coils are shiny and uniform", that is interesting, I have not seen any speaker that the entire voice coil was visible without cutting the speaker open.

 

[DrDyna]

I have not seen any speaker that the entire voice coil was visible without cutting the speaker open.

Unless the motor is removable, I had a pair of old Tannoy dual concentric ages ago that you could unbolt.

Highly unlikely nowadays though.

 

[Cal Weldon]

Did you guys notice that he said two drivers in one box are doing this?

 

[DrDyna]

Did you guys notice that he said two drivers in one box are doing this?

Yeah, that's why my first thought was that it could be a source, but if he's moved the speakers from one side to the other and the problem follows the speaker, some measurements are probably going to have to be done to figure out what the culprit is.

 

[Cal Weldon]

Is that speaker near a source of heat that might have hardened up the suspensions somehow? Definitely do a mechanical test of cone movement to see of you can feel extra stiffness in those drivers. Can you pull the drivers put them on the bench and run a frequency generator through them to compare between units?

 

[weltersys]

Did you guys notice that he said two drivers in one box are doing this?

Yup, there are a lot of crazy mixes that put way to much energy in one side only now days..

 

[Cal Weldon]

I have a feeling that's not it. No problem with the tweeter.

 

[spice house]

before doing anythng else mesure impedance curve for the drivers.
that will tell more.

I took the midwoofers out and measured them -they measured the same..

I took the subs out - they measured the same

GOOD at least I dont have to spend $$$ - so i switched them between cabinets and it turns out it was due to failing silicone seal around BOTH boxes (mid + sub)? very wierd, not what I expected. Big bass must have pushed through the seal... I used a different tube for each speaker so perhaps one tube was bad? Still, they are only six years old... not what I expected

Good timing since I was in the midst of designing new boxes for them

Thanks for the help

 

[spice house]

It makes a bit more sense to me now, its been 90-100 degrees here the past 2 days and the speakers are in a room thats very poorly air conditioned, so there ya go

guess I should find a better sealant (and make straighter edges next time around)

I can't believe how much a little leak changes sound

 

[Cal Weldon]

silicone

Perhaps something other than silicone like urethane. Silicone's not intended for that.