Single Revel F208 with low midrange output

[Frgirard]

Stupid ideas :
Could you measure each mid the mic at 1 cm of the driver.

Could you invert the mid drivers between the speakers and measure them.

 

[puppet]

Have to pull that board out anyway then we can get a look at the circuit layout.

 

[MichaelJ]

Stupid ideas :
Could you measure each mid the mic at 1 cm of the driver.

Could you invert the mid drivers between the speakers and measure them.

I did measure each mid @ ~1" and posted those earlier in the thread. Not sure I quite understand what you mean about inverting "between the speakers". I had thought about there being a phase issue, but others earlier in the thread advised that probably was not the issue.

 

[Thomas_A]

I doubt that's it. Take a picture of the other midrange crossover.

I've never heard of an electrolytic cap failing in a crossover, it's not subjected to the constant thermal load that you'd see in a power supply or something.

To me the problem definitely looks like a resistive difference; the whole level drops off. If a cap failed or changed value you wouldn't see the whole response go down by 8db.

They can fail though. One of my prevous speakers had a measured deviation and crossover showed a swollen cap. Exchange fixed it.

 

[617]

They can fail though. One of my prevous speakers had a measured deviation and crossover showed a swollen cap. Exchange fixed it.

So, I just read up on cap failure modes. This was in the context of power supplies again. It turns out they can go out of spec in a number of ways. They can gain ESR, which would produce the effect seen here, and not change capacitance. Or, the ESR can remain fixed but the capicitance can change (probably go down).

It still seems unlikely to me that this is a capacitor, but it is possible. Having said that, it's unlikely for a crossover component to fail in the first place, but here we are.

 

[AnalogSteph]

A visibly bulging cap is almost certainly bad and likely to have high ESR, so that's one problem for sure. Surrounding components should be checked for signs of overloading as well... discolored insulation on coils, resistors that have gone out of spec. (If nothing found, the cap may have been bad out of the box.) Going by the size of the cap, I suppose it's in the midrange highpass, and high ESR may well cause a level drop.

Note that highish-voltage bipolar electrolytics like this one would likely have to be ordered from a parts distributor or at least a shop that specializes in speaker components, as the specs you need are not mainstream.

Too bad the board is so hard to access. The offending bass driver may be glued or siliconed in... one may have to find a way to get behind its rim, but not sure what sort of tool one might use that doesn't scratch things up. The venerable guitar pick or a spudger might be worth a try.

 

[Beave]

Sorry, I misled you about the location of the crossover. I assumed that the F208 would have separate crossover boards for the midrange and for the tweeter, because the F206 does. But now I see from your pictures that the F208 has a single crossover board for the midrange and tweeter crossovers combined.

I compared your crossover pic with some other pictures, and I can *mostly* tell which components are for the tweeter and which are for the midrange.

The top two Bennic yellow poly caps, along with the air coil inductor, the two white resistors on the left, and the inductor L2 and the small yellow poly cap C3 (behind the blue wires near the right side) comprise the tweeter crossover.

The three electrolytic caps and the three inductors at the bottom are for the midrange crossover.

I think that the F206 mid crossover has a couple of resistors for attenuation, but the F208, with its higher sensitivity, has no resistors in the midrange crossover.

That all makes it more likely that the bulging cap (pointed out by previous posters) is the likely suspect.

It could have been over-driven at some point, but I suspect it was a quality control issue from the get-go.

You would need to pull out the crossover board, unsolder that cap (from the back side), remove it, then buy a replacement cap of the same capacitance and voltage ratings, then install the new cap. (Or remove the crossover board and have a repair place do it for you, but you'd still need to unsolder the connecting wires.)

This is all best guesses and could be wrong.

 

[73hadd]

Good idea in theory, but if you don't have the ability to make 3d quasi anechoic measurements of each driver and then combine them accurately in software, the results will probably be worse than the passive crossover as it is.

Revel gets great performance with the passive crossover, I would stick with that.

I agree that troubleshooting/repairing the crossovers is a great idea, for ease of use and future resale.

I am confused by "Good idea in theory, but if you don't have the ability to make 3d quasi anechoic measurements of each driver and then combine them accurately in software, the results will probably be worse than the passive crossover as it is." We already know the crossover points from Revel spec sheet, or reverse eng by looking at component values. Yes we will need at least REW to adjust gain, but if we use a DSP xover with the same values and correct the phase/timing, what else is missing? The need for advanced measurements or T/S parameters would be choosing cabinets, drivers, and crossover points, which won't need revisiting correct?


Mostly I am interested in seeing if Revel can find a way to be more helpful here. Any updates on that point?

 

[restorer-john]

I'd lay money on the bulging top cap. As @AnalogSteph mentioned, they can stay close to capacitance spec, but the ESR goes very high and that could easily manifest as an overall level drop.

Don't rule out all the midrange related wiring as well. Check for low/no resistance on the driver terminals. I've had many spade connections to drivers go high. It's often caused by corrosion of the tin plating due to the adhesives/formaldehyde in the cabinet gassing-off over the years.

 

[MichaelJ]

Sorry, I misled you about the location of the crossover. I assumed that the F208 would have separate crossover boards for the midrange and for the tweeter, because the F206 does. But now I see from your pictures that the F208 has a single crossover board for the midrange and tweeter crossovers combined.

I compared your crossover pic with some other pictures, and I can *mostly* tell which components are for the tweeter and which are for the midrange.

The top two Bennic yellow poly caps, along with the air coil inductor, the two white resistors on the left, and the inductor L2 and the small yellow poly cap C3 (behind the blue wires near the right side) comprise the tweeter crossover.

The three electrolytic caps and the three inductors at the bottom are for the midrange crossover.

I think that the F206 mid crossover has a couple of resistors for attenuation, but the F208, with its higher sensitivity, has no resistors in the midrange crossover.

That all makes it more likely that the bulging cap (pointed out by previous posters) is the likely suspect.

It could have been over-driven at some point, but I suspect it was a quality control issue from the get-go.

You would need to pull out the crossover board, unsolder that cap (from the back side), remove it, then buy a replacement cap of the same capacitance and voltage ratings, then install the new cap. (Or remove the crossover board and have a repair place do it for you, but you'd still need to unsolder the connecting wires.)

This is all best guesses and could be wrong.

Thanks for this!

The venerable guitar pick or a spudger might be worth a try.

Nice suggestion!

 

[MichaelJ]

Mostly I am interested in seeing if Revel can find a way to be more helpful here. Any updates on that point?

Nothing as yet...I didn't follow-up after the last exchange. But thanks to the advise and support I've received at ASR, I might do so now that I have a better idea what the issue might be.

 

[FrantzM]

Revel response leaves a bad taste in my mouth . Hope someone from here, is on this forum.. :

 

[MichaelJ]

My saga continue...

So remember how I couldn't remove the bass driver to access the crossover...? Well, no matter how hard I pushed the driver's magnet from behind, and despite my many attempts to slowly and gingerly loosen it using the screw holes—which I've done successfully on other stubbornly stuck drivers—the thing would not budge. I gave it a couple days hoping I would come up with a brilliant idea for how to do it. It came to me this afternoon in a moment of desperation: Install a wood screw into one of the holes such that it threads into the driver's baffle but not the cabinet and then pry it out with a small crowbar...

Well, the driver was so "wedged" in that the trim around the driver gave-out before the driver did, pulling portions of the gloss veneer around the trim clean off. If that's not enough, I can't even get the driver to fit back into the hole. (That single bass driver seems to be slightly too large for the hole; the other driver fits ever so slightly better.) So, now I have a single $2.5k speaker that has attenuated midrange and a chipped finish on the front face of the cabinet...ugh.

I guess now I'm just looking for sympathy folks

At this point, I'm seriously contemplating purchasing a single F208 to replace it or cut my losses and sell its pristine and perfectly performant twin. Does anyone have a line on a single F208? Alternatively, is anyone looking to pay top dollar for a single 208?

 

[Laserjock]

My saga continue...

So remember how I couldn't remove the bass driver to access the crossover...? Well, no matter how hard I pushed the driver's magnet from behind, and despite my many attempts to slowly and gingerly loosen it using the screw holes—which I've done successfully on other stubbornly stuck drivers—the thing would not budge. I gave it a couple days hoping I would come up with a brilliant idea for how to do it. It came to me this afternoon in a moment of desperation: Install a wood screw into one of the holes such that it threads into the driver's baffle but not the cabinet and then pry it out with a small crowbar...

Well, the driver was so "wedged" in that the trim around the driver gave-out before the driver did, pulling portions of the gloss veneer around the trim clean off. If that's not enough, I can't even get the driver to fit back into the hole. (That single bass driver seems to be slightly too large for the hole; the other driver fits ever so slightly better.) So, now I have a single $2.5k speaker that has attenuated midrange and a chipped finish on the front face of the cabinet...ugh.

I guess now I'm just looking for sympathy folks

At this point, I'm seriously contemplating purchasing a single F208 to replace it or cut my losses and sell its pristine and perfectly performant twin. Does anyone have a line on a single F208? Alternatively, is anyone looking to pay top dollar for a single 208?

View attachment 181754

Continue with fix and sell to someone for a center channel use in a projector/AT screen setup.

That totally sucks

 

[Thomas_A]

Bad luck there. There was no way of removing the crossover without further removing drivers?

 

[dominikz]

My saga continue...

So remember how I couldn't remove the bass driver to access the crossover...? Well, no matter how hard I pushed the driver's magnet from behind, and despite my many attempts to slowly and gingerly loosen it using the screw holes—which I've done successfully on other stubbornly stuck drivers—the thing would not budge. I gave it a couple days hoping I would come up with a brilliant idea for how to do it. It came to me this afternoon in a moment of desperation: Install a wood screw into one of the holes such that it threads into the driver's baffle but not the cabinet and then pry it out with a small crowbar...

Well, the driver was so "wedged" in that the trim around the driver gave-out before the driver did, pulling portions of the gloss veneer around the trim clean off. If that's not enough, I can't even get the driver to fit back into the hole. (That single bass driver seems to be slightly too large for the hole; the other driver fits ever so slightly better.) So, now I have a single $2.5k speaker that has attenuated midrange and a chipped finish on the front face of the cabinet...ugh.

I guess now I'm just looking for sympathy folks

At this point, I'm seriously contemplating purchasing a single F208 to replace it or cut my losses and sell its pristine and perfectly performant twin. Does anyone have a line on a single F208? Alternatively, is anyone looking to pay top dollar for a single 208?

View attachment 181754

Ouch, I can almost feel your pain!

However perhaps it might be possible to fix the cracks in the finish (here's an example of a chipped gloss finish fix) - perhaps it would be worth giving a call to local furniture makers and/or luthiers to see if it's a feasible fix.

Good luck and fingers crossed you find a satisfying solution!

 

[MichaelJ]

Bad luck there. There was no way of removing the crossover without further removing drivers?

Not as far as I could tell. The crossover was located directly behind the top bass driver. As such, I could not get a screwdriver back there to unscrew it. To attempt the fix, I had no choice but to try to remove it.

 

[617]

I assume you can't go through the back of the speaker?

Sorry to see the damage. I think you should be able to sell a single f208 though.

 

[dasdoing]

I can feel your pain. Lost an expensive device recently due to a stupid mistake.
Sorry

 

[JayGilb]

That sucks.
Sorry for your loss.