Film-Tech Forum ARCHIVE: How common are blown speakers?

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Posted by Mike Blakesley (Member # 26) on 05-09-2009, 03:48 PM:

Bobby H.'s comment in the Imax thread about blown speakers not being replaced as often as they should got me wondering:

How frequently do speakers blow? We have never blown one here. Is it just from people cranking the sound too high or is it due to bad system design or low quality drivers?

Posted by Steve Guttag (Member # 268) on 05-09-2009, 05:48 PM:

Mike,

We got into the reconing business due to blown speakers and it comes/goes in spurts. Generally right before the big seasons (gee I wonder why [Wink]

).

We have specialized in Altec, JBL and EV repairs (factory certified and only use their genuine parts on those).

Altec drivers often come in from just plain age! Some have had the driver, from being in the same position so long, just sag and the voice coil rubs.

Others are over driven.

JBL's are a much rarer driver to fail, as a group. The bulk that we see are the 2245H as used in the original 4645 (as Scotty would say...no stinkin' A, B, C or D). Those recones fall into two categories...foam rot and overdriven (to the point the voice-coil leaves the gap).

Some recone the 2245H as a 2242H (pleated surround)...the bass will suffer if you do but you will not see foam rot again. Many folks do not appreciate just how much power is required to play subwoofers in a digital sound world (film or DCinema). One MUST use the continious PINK NOISE spec when figuring out subwoofer power handling since that most closely resembles what a subwoofer receives...unlike the other channels. In some films, it can be sustained for quite a long time too.

Well a JBL 2245H is really just a 350-watt driver. It plays down flatly to 20Hz though. In most typical 200-300 seat theatres...you best have 4-8 of them if you want them to survive. In fact, if your room is 60-feet deep (speaker to rear seat)...you would need 6 4645s to play at spec. It would be a very good subwoofer system if you did...and it would play deeper bass than most systems offered today...but most seem to think 1 or 2 subs is all you need...idiots.

The other JBL drivers we see are often from their "econo" line of speakers (3000 series)...they are low-cost for a reason...the parts are not up to the job nearly as much. Most folks though want to believe they can pay less and get everything. Net result...BLAMO....and it probably didn't sound too good either.

Lastly...there are the mechanical damage JBLs...something went through the cone...oh well...accidents do happen.

EVs almost always suffer from two things...cheapass construction/design or over driven.

EV's specs are probably the most accurate...if someone would read them. If driven within their range, they will do okay (they still will sound like EVs though). But seriously...some of their driver constructions really suck....pleats tear apart, insufficient adhesive area to hold the spider...you name it. Their voicecoils are also rather understated, except in the EVX line. Most of their drivers handle far less power than people seem to think they do. We have received numerious speakers from the "pro" world where some schmuck believe the salesperson and bought the cheapo speaker and can't figure out why it blew up (and some blew up real good too).

Ashley amps have contributed quite a bit to our recone business. You can always spot an Ashley failure...the voice coil burns completely off the voice coil former. I always make a point of telling the customer when I see that failure to "repair or replace" their Ashley amp...they are amazed that I know who made their amp....you see a few dozen failures like that...you see a trend.

Surround speakers are another story. I've had the odd one here and there fail for seemingly no reason. I think most are made on the cheap since when one adds up the total cost of the surround channel, it is likely the most expensive channel.

By and large, however, if you properly design a system, use good quality speakers (pick your favorite)...and design the system such that the speakers are driven within their actual power handling, failures are a very rare thing...just like any other component within the system.

Steve

Posted by Monte L Fullmer (Member # 2797) on 05-09-2009, 07:06 PM:

Another one is the tech's fault if he sets a system up wrong. One tech I remember of did such this.

When he installed DTS-6AD units, he didn't check the dip switches inside .. and they were still on factory set of "wideband" instead of "bi-amp".

Being in 'wideband' it sends all frequencies into both LF and HF circuitry .. and with some LF heading to the horns, it toasted the HF drivers - split the aluminum diaphrams in those drivers.

I had to replace 8 diaphram assemblies in those JBL's due to his small, but costly fubar..

-Monte

Posted by Joe Redifer (Member # 3) on 05-09-2009, 07:53 PM:

Blown surrounds are fairly common in my large giant screen auditorium. We have 8 JBL 8330's to cover the whole thing. Granted the room really isn't that big (medium-large-ish), but I don't think the 8330 is the right choice. 8340s or some form of QSC would probably be better. The problem is that I don't want to put in new mounts. I want to use the 8330 mounts so that the changeout is a breeze.

Posted by Tom Mundell (Member # 4555) on 05-09-2009, 08:15 PM:

I wonder how much money would be saved just by putting in decent speakers/amps...at the Loews I worked at briefly blown speakers were quite common; by this point it seems like they could have saved a fortune just putting in decent sound systems to begin with instead of frequently replacing things...(though in Loews later years it seems like they gave up replacing and just left things broken)

Posted by Bobby Henderson (Member # 840) on 05-09-2009, 08:26 PM:

quote: Steve Guttag
In fact, if your room is 60-feet deep (speaker to rear seat)...you would need 6 4645s to play at spec. It would be a very good subwoofer system if you did...and it would play deeper bass than most systems offered today...but most seem to think 1 or 2 subs is all you need...idiots.

This is a very common problem with commercial movie theaters. A house built for THX specs may have four or more subwoofer drivers. Then the non-THX houses merely have just one or two. Drivers fail or they're just turned way down so they don't fail. It's one thing that contributes to so much of the weak-ass sound often found in so many commercial theaters today.

Cost cutting with the surround array speakers also contributes to weak-ass sound syndrome.

quote: Monte L Fullmer
Being in 'wideband' it sends all frequencies into both LF and HF circuitry .. and with some LF heading to the horns, it toasted the HF drivers - split the aluminum diaphrams in those drivers.

The folks who did the original setup at our local Carmike theater when it opened in late 1994 made a similar error. When the theater finally started getting DTS prints like Braveheart the surround array sounded like it was going to tear itself apart. The speaker drivers were slapping against the speaker grilles in rapid fire fashion. I made calls to a few different people about the problem. Once they got the system fixed it sounded great.

Posted by Mark J. Marshall (Member # 1409) on 05-09-2009, 08:32 PM:

Blown speakers are pretty popular around here.

Posted by Steve Guttag (Member # 268) on 05-09-2009, 10:09 PM:

8 srrounds in a medimum/largish house? Way too few. 8 surrounds are about what we use a small room. Forgetting power handling for a moment...odds are the coverage is not uniform.

With digital soundtracks, the surrounds need to get much higher in level than they ever did with just optical sound.

The 8330A has finially come to the end of the line. JBL now has the 8350 to be their top surround...the 8340A is now priced like the 8330A was. The 8320 now is the baby surround.

Steve

Posted by Mark Gulbrandsen (Member # 72) on 05-10-2009, 09:04 AM:

Now JBL still does produce a few really good products HOWEVER... I feel that when JBL went with the plastic enclosure route they hit the end of the line for surrounds period. Ok, they are easy to hang, that perhaps the only obvious intention of the plastic cabs except higher profit for them. The QSC's are also as easy to hang. Go figure... The JBL's since going plastic have never sounded quite as good as the wood cabinet versions did. The plastic cabs have always had a strange honk and or thud type sound to them. It can be eq'd out to some extent but not completely and of course it costs extra to eq them. Funny that I had another large chain's head engineer bring this very same complaint up to me very recently...

QSC surrounds blow the present JBL stuff clean out of the water!! JBL surrounds have unfortunately become like Hollywood where only the bottom line is what matters and real performance is only a fart in the wind... their entire speaker line has slowly but surely become cheapened up to some degree. NOW no matter what minor changes they make to the plastic cab surrounds they are not going to equal the performance of a wood cabinet speaker. QSC has certainly shown thorugh their entire speaker line that the JBL philosophy doesn't necessarily hold true and indeed QSC speakers have left JBL in the dust.

Mark

Posted by Demetris Thoupis (Member # 833) on 05-10-2009, 11:06 AM:

Actually QSC "blows" about any other speaker so far! (no pun intended) We did an installation two years ago of a cineplex and we insisted on using the QSC range over the JBL to the client (although the client is very budget protective) and gave an extra discount so we could give the QSC range only because they rock the houses! No kidding.

Posted by Louis Bornwasser (Member # 3063) on 05-10-2009, 07:28 PM:

How common are blown speakers?

Except for foam surrounds on JBL subs, completely unknown around here. We use the Ashly amps which have had full protection for nearly 20 years.

Agreed that old Altec and JBL will sometimes fail due to dry rot: 50 years?? Electro Voice diaphragms fail around here 10 times more often than JBL and JBL outnumbers the EV by 50 to 1.

Whenever speakers fail, assuming proper "fit" (as described by Steve) look to the guy who maintains the system. Good stuff is really tough, but it is possible to destroy it if you try hard enough. Louis

Posted by Tony Bandiera Jr (Member # 2365) on 05-11-2009, 03:19 PM:

I'll bet there are a lot of blown speakers in West Hollywood. [Big Grin]

Seriously though, biggest issues I've seen so far:

Crown amps, when they let go they put the full DC power supply voltage on the outputs. (The old "D" series.)

As Steve said, misapplication (not enough subs or surrounds for the room).

Tampering by alleged "projectionist/techs" who think they can tune up a "B" Chain by ear.

In one extremely rare case, a 4-plex that lost all it's processors, several amps and a lot of speakers when the padmount transformer supplying the building burned out and put around 16,000 volts into the 120/208 system.

Lots of HF and surrounds blown out by using power amps of insufficient power output capability (usually because of a digital system added without upgrading speakers and/or amps).

Posted by Brad Miller (Member # 2) on 05-11-2009, 04:37 PM:

Assuming the system was properly designed with quality speakers (such as QSC and JBL...QSC being my favorite) and the system is properly calibrated and other factors have not interfered (B-chain tampering, kicked in drivers, trunks of cars, etc) blown speakers should be a very rare occurrence.

Most theaters however under-spec what is required to fill a room and end up seeing blown speakers as a common point of maintenance (and costs).

Posted by Tyler Potts (Member # 4952) on 05-11-2009, 04:47 PM:

The only issue that leaves me questioning if it's a more than rare occasion is our power supply/ignitor problem. We will get a blown speaker in one of our houses every now & then but I want to put it at maybe 1 a year if even that.