Testing for a blown/damaged woofer?

[xyrium]

A month or so ago I assembled a sealed two way design. Today, I noticed some buzzing during music playback (sounds like plastic vibrating at the end of a each tone). I'm thinking I may have blown one of the woofers.

I found this thread, and in post #15, a process for determining a blown driver is mentioned. Is that process correct? Maybe the buzzing is enough to indicate the problem and no further testing really needs to be done. :boohoo:

http://htguide.com/forum/showthread.php4?t=30668&highlight=speaker+blown

Thanks!

Edit: Changed title slightly by adding "damaged" and removed design name to eliminate any perceived design implications.

[abNORMal]

Especially if it is a sealed (non-ported) cabinet, make sure the screws holding the woofer in place are tight and the gasket is sealed. I have found air by-passing around the speaker can make a buzzing noise. Actually got a great deal on a sealed sub that was on display because the audio shop didn't check this.

[numberoneoppa]

I think would would have blown your ears before blowing a woofer on that system. Sounds more likely that something else is askew, see the above post. :P

[evilskillit]

I'm not familiar with those scanspeak woofers too. Sometimes the tinsel leads slapping the back of the woofer can cause a buzzing noise. If thats the case its no big deal, just need to secure em somehow.

[xyrium]

Thanks for the ideas guys. The woofer is definitely secure, and I removed the entire baffle to take apeek behind it, only to find that the cone was not restricted by anything, including the leads.

Initially I was thinking that all of those early tests that I ran on them using REW just beat them up. However, I even have them high passed at 40Hz (24dB LR xover on my dbx 260). I also guess that both woofers would have been damaged if that was the case, but the other one appears fine. Would the T/S parameters indicate anything? I have a functional WT3 that I could use to remeasure them.

This is all rather interesting, because I was having some issues early on with this assembly. I wonder if I screwed something up, somehow. THere really isn't anything you can screw up with a kit though.... Some have mentioned that the 30l cabs I used are too big, but even then, that would just lead to an even more damped response. Maybe that places too much pressure on the driver though?

Maybe Scanspeak won't charge too much to repair them...

[Dave Bullet]

Are you sure with re-assembly the wires to the woofer are not being pressed against the cone by damping material?

Run the woofer unmounted sitting magnet side down on a desk. Increase volume (but not until xmax) at a 20Hz tone, increase the frequency if it doesn't buzz (you will need to slowly increase the volume as well to keep excursion up). When buzzing starts - try and track down where it is being generated from.

With everything disconnected, evenly press down on the cone (symetrically) and see if you have any voice coil rubbing. COmpare with the good woofer.

Measure DC resistance with a multimeter (Compare with the good woofer).

Definitely use your WT3 to do an impedance sweep - and also with the good woofer to compare.

[evilskillit]

Ah Xyrium, man its a bummer this has been giving you as much trouble as it has. Dave's advice is pretty sound. If you try that and its still messed up you might see about RMA, how long is the warranty on this stuff and how long have you had it?

My WG build is coming along. I'm slow as dirt but I might be able to hear them this week. When that happens I'll post more.

[xyrium]

Thanks guys, I'll test the two woofers today with both a MM and the WT3. Thanks goodness for these removable baffles from PE, and the fact that I didn't glue them yet (if ever!).

There's definitely nothing touching the woofer. I used OC703 as stuffing, and it's square shape remains quite a distance from even pressing against the frame.

I was going to take these to an active config this summer, but after a disappointing purchase of an Art SLA2 amp, I'm still shopping Ebay and Audiogon for a good amplifier with XLR inputs...

Edit: DC resistance looks good at 5.8 Ohms.
Edit 2: Here's an impedance plot, also, there's a definite voice coil rub sound compared to the good woofer. The good woofer has the same DC resistance, at 5.8 Ohms.

[xyrium]

Here's the impedance sweep for the good woofer. One thing I've noticed with both woofers, is that their Qes has increased over time.

I suppose the measurements don't tell the story, however, the faint voice coil rub does. Now I have to figure out how it happened, because if I do manage to obtain a replacement, I'd love to get a new pair, and NOT damage the new ones.

[bmaupin]

The woofers are fine.

I would mod the cabinet to include a screw on each side near the middle vertically of each baffle. I recently made a pair of 1" baffles like the originals for a 18W4531G02 and SB29 combo and the baffles vibrate and make noise. I have not had this happen with 18W4545 or 8945P. I will be making new cabinets for these and put the 8945P baffles back on.

Have you posted pictures of your construction?

[evilskillit]

Thanks guys, I'll test the two woofers today with both a MM and the WT3. Thanks goodness for these removable baffles from PE, and the fact that I didn't glue them yet (if ever!).

You might try gluing the baffles, or cutting a gasket and putting it between the box and baffles temporarily untill you glue them. The slightest little gap between to mating surfaces can cause some pretty nasty sounds to happen either due to surfaces vibrating against each other or air escaping. Happened to me on a sealed 8" woofer once.

Maybe just try going to a craft store and buying some felt or foam or something and cutting out the shape of the box, put it between the baffle and the box and tightening down the screws till its nice and squished.

Having said that I guess I should ask this clarifying question did the woofer still make the noise in free air outside of the cabinet? If you answered that question I didn't quite get it.

[bmaupin]

Having said that I guess I should ask this clarifying question did the woofer still make the noise in free air outside of the cabinet?

Good point.

[xyrium]

Once I heard the voice coil rub, I never bothered listening out of the box. I'll reconnect them to test that. I believe I've posted photos of the cabs, but I'll attach another for posterity.

Edit: Yup, still buzzes outside of the cabinet.

[xyrium]

Come on Evil! Get that thing done! I'm dying to hear your listening impressions.

My next project is definitely the L26ROY in a sealed cab. Then, once I sort out the driver issues with the mains, I can cross them over a bit higher, aiming for 60Hz...

Ah Xyrium, man its a bummer this has been giving you as much trouble as it has. Dave's advice is pretty sound. If you try that and its still messed up you might see about RMA, how long is the warranty on this stuff and how long have you had it?

My WG build is coming along. I'm slow as dirt but I might be able to hear them this week. When that happens I'll post more.

[evilskillit]

Come on Evil! Get that thing done! I'm dying to hear your listening impressions.

Heh, I'm trying. You can see where I'm at here if you want. I may actually be able to listen within the next few days. I'm so excited.

I've got a friend who is thinking of building the Zaph Revelators. Which are sort of a cousin to the ZRT, or something like that. I keep thinking of your build and then I think to myself "well, Xyrium has had so many little problems, he's not the guy to show if you're trying to talk someone into building these things" Its sucks that you've had so many little issues with the things. Hopefully you get it all ironed out, and they make you happy for years to come. Or till you get bored and do something else.

[xyrium]

Wow, nice work on the cabinet, it's shaping up nicely. I like how you even insulated the cross braces to absorb reflections. The waveguide and tweeter seems to have come out quite well. You're so close!

Honestly, John does such a fantastic job on his designs, one can only be happy to recommend them. The ZRT is a fantastic system, and I still highly recommend it, especially since it's perfect for noobs just getting into DIY since it's available in kit form. It may be one of the more expensive designs that he's done, but it's still a fantastic value.

Many of the problems I encountered were due to my own stupidity, and possibly even inadequate testing devices (the RS SPL meter). :roll:

[Not2Evil]

No insult intended, but sometimes the obvious eludes me.

Did you swap the speakers left to right to see if the problem tracks the speaker or the amp?

[xyrium]

No offense taken. Believe me, I'm hoping it's just something simple.

I'm trying to take everything into account. So, I've replaced the cables as well, even making new XLRs with some Mogami quad that I picked up from Markertek (and will never use again since they're a pain to prepare). In the end, I think that the voice coil rub is giving this one away unfortunately.

[fbov]

Good trouble shooting, but there's one suggestion I haven't seen; have you spoken with the vendor? Both Zaph and Madisound will stand behind their products and may have some definitive tests that point to mutual resolution. Nothing will fix a rubbing coil except a new driver....
Frank

[xyrium]

Hey Frank, thanks for your reply. Yes, I have. John has been fantastic throughout the assembly and measurements. He even noticed that the Qes was a little high on this pair. My concern is not only was it at .50 a month ago, but now both of them are at .60. So, I was hoping to have both replaced since they are only two months old Unfortunately, the vendor is not offering such. If the second driver goes, I will not be happy. Because at that point, I'll be rather tired of pulling drivers, shipping drivers, testing and retesting drivers, etc.

[jkrutke]

Good trouble shooting, but there's one suggestion I haven't seen; have you spoken with the vendor? Both Zaph and Madisound will stand behind their products and may have some definitive tests that point to mutual resolution. Nothing will fix a rubbing coil except a new driver....
Frank

Something to mention about this design: it was a public domain design that I allowed Madisound to sell as a kit, in much the same way I allowed Parts Express to sell the ZDT3.5 design. I wouldn't call it a Zaph "product", as I received no monetary payment for the design. (though in both of those cases, I did receive some parts for construction) So, it's mostly a non-profit venture that I don't provide support for.

And for clarity about actual Zaph products for which I am paid for, I only provide support to the buyer. In the case of the ZA14W08 woofer, my customer is Madisound. I provide support to them only and not end users. I am generally not a "people person", which is why I don't sell any products direct. Maybe someday I'll get some people skills and that will change. :B

All that said, I'll comment on the blown woofer. With the driver removed from the cabinet, hold it up to your ear and lightly push the driver in with your finger. If you hear any sort of scrape sound, that's a wrap on the driver. Rubbing coils may not show up in impedance measurements, but they will show up as tall order distortion in full spectrum plots. Most likely it is not "blown" assuming you have not abused them. A bigger likelihood is ferrous crap in the gap. Drivers with open spiders are highly susceptible to this issue usually from either a screw shaving or a magnet chip. The more you handle an open spider woofer, the more you are likely to get crap in the gap.

Now the bad news: there's not much you can do about it. You might get lucky if you run the driver at a low frequency just past Xmax for a while and hope the crap gets launched out or disintegrated. I've saved a couple woofers this way. On the other hand, the same operation may completely destroy the voice coil.

[xyrium]

John, you underestimate your abilities! You've always been excellent at conveying the facts, and I think the DIY community recognizes this, and truly appreciates your approach! Thanks again for commenting!

This said, that's exactly what I'm hearing with the woofer. There's a scraping sound, I called it rubbing, when I press the cone in lightly. I'm not an SPL guy, and that's why I went with the sealed design, so I can't admit to abusing them. However, the problem may have been the result of something faulty (or stuck in there like a magenet chip or the such as yuo've kindly explained) that I was hearing when certain passages seemed to cause compression in the drivers early on when I was doing all that testing, and then bought the WT3 to do more testing.

For now, I'll try to work with the vendor to have it repaired/replaced. They've always been good to me, so I'm hoping for that same continued support. I'm one of those neurotic audio guys though, and feel as if the pair is tainted now, and really wanted the pair of woofers replaced since they're only two months old. I'm going to have the other one tested at a local facility and have the T/S parms measured while I'm at it so I can compare the new woofer. Regardless, we'll see how it all pans out.

In the end, it's another fantastic design from you, and I look forward to putting them back in action, with the addition of a new sealed sub using the Seas L26ROY in the upcoming months!

[fbov]

My apologies, I had assumed you were actively associated with products carrying the Zaph Audio name. At the same time, you gave the response I had hoped you might.

A willingness to help others without compensation is a "people skill" I hope you don't change.

Frank