Replacement woofers for vintage Infinity tower

[Nathan Rieben]

Here's one for the Infinity lovers,

I recently upgraded my two channel setup to a pair of Infinity RS-IIb towers. Unfortunately one of the towers got DC current due to a component failure and the woofer VCs in that tower are toasted. I'm considering upgrading to modern woofers because I wonder if the original woofers in the RS series were the weak link in otherwise great speaker systems. These are NOT the legendary Watkins woofer just the standard 10" polypropylene clear drivers with the reddish looking spider and the clear bullet dust caps. They were used in many of the the Reference Standard models. I love the way they sound, but anytime I've got one on the bench they strike me as underbuilt in terms of the magnet size and general motor structure. They sure are light-weight when compared to any PA stuff. It might be nice to get something with a little more X-max and power handling capability as long as the musicality remains.
What do you guys think?
Are these original woofers truly exceptional for some reason or can I do better by looking to newer products? Am I missing something?

Thanks!

 

[TLS Guy]

Here's one for the Infinity lovers,

I recently upgraded my two channel setup to a pair of Infinity RS-IIb towers. Unfortunately one of the towers got DC current due to a component failure and the woofer VCs in that tower are toasted. I'm considering upgrading to modern woofers because I wonder if the original woofers in the RS series were the weak link in otherwise great speaker systems. These are NOT the legendary Watkins woofer just the standard 10" polypropylene clear drivers with the reddish looking spider and the clear bullet dust caps. They were used in many of the the Reference Standard models. I love the way they sound, but anytime I've got one on the bench they strike me as underbuilt in terms of the magnet size and general motor structure. They sure are light-weight when compared to any PA stuff. It might be nice to get something with a little more X-max and power handling capability as long as the musicality remains.
What do you guys think?
Are these original woofers truly exceptional for some reason or can I do better by looking to newer products? Am I missing something?

Thanks!

Yo can NOT swap woofers in a speaker. The box is tuned to the Thiel/Small parameters of the driver, and the crossover is designed to the drivers electrical and acoustic properties. There are so many variables that have to precisely match that you will never find a drop in replacement.

You only hope of salvaging those speakers is to see if there is a reconing kit available, so a reconing service could repair them. So likely those speakers are now useless. By the way, you must have used an amp that did not have DC offset protection. Never ever, do that.

 

[Nathan Rieben]

Thanks for the reply. Yes, I was using a Crown DC300A series II. The Crown amps can output all the way down to DC. Interestingly though I think the unit that ruined the speaker was the Infinity bass EQ contour box. It put the crown into IOC protection so I (quickly) removed that amp from the circuit and wired in a Grand Integra M508. It put this amp into protection mode as well. When I removed the contour box from the system everything was fine. I did some tests on the output of the Contour unit while running a signal into it from the pre-amp and nothing seemed amiss. It's got me scared of that EQ unit to tell the truth. Have you ever heard of a bad EQ unit sending a DC signal to an amp which the amp faithfully reproduced? The volume was so low I could heard the speaker separating inside. Sounded like a little mouse chewing on something and it was over before I figured out what was going on.

 

[TLS Guy]

That Eq box boosted the signal below 100 Hz, and was intended to go in the tape monitor loop. It certainly could have DC offset as any unit could.

However the villain is the Crown DC300 A amp. These are a dangerous amps and should NEVER be used. Yes, the amp will not only amplify DC, but has no DC offset protection at the output stage. So that means that if an output transistor fails, which back then they were prone to do, then the whole 100 plus volt rail voltage is sent straight to the speakers, destroying them right away.

I installed a pair of those DC 300A amps in monster system I designed and installed in a hall. It was bi-amped with two of those units. On opening night a power transistor failed and sent a whole bank of 8 expensive midrange drivers up in smoke. I sent both back, and replaced them with 1 BGW two channel amp, and a pair of Shure monoblocks.

Any Crown DC300 A amp, needs to go to the recycling center immediately. They have been known to set speakers on fire. They are definitely too hazardous to have in service of any description.

As far as your speakers are concerned I would bet the crossover in that speaker is either toast, and certainly not in spec. after that catastrophic event.

 

[fmw]

TLS Guy is right about random driver swaps. They will rarely produce the same quality of sound you had before. But, if you have some money you want to risk you could try to install a driver with similar specs and see how it goes. It might not restore the original sound but it may provide acceptable performance.

I replaced the Tweeters in my EMP towers as an experiment. The new drivers were of high quality and improved the sound of the speakers in my opinion. Perhaps I got lucky. If I hadn't I could just go back to the original drivers.
Your best bet is to have the woofers reconed and you may need to replace the crossover network. the new surrounds in a recone, however, may not have the same compliance and could well affect sound quality. There are tunable crossovers you can use to bring the speaker systems to a sound quality you like. Remember the sound of speakers is a totally subjective thing and their sound is affected meaningfully by the room acoustics. One man's triumph is another man's disaster.

I am the sort of person who would give it a shot but I have done a lot of speaker building and modification. I have done a few recone jobs as well. I don't recommend you do any of that. I just like to provide food for thought. I will just second TLS Guy's advice. Recone or replace the speaker systems.

 

[Nathan Rieben]

Thanks fmw I appreciate the response. If I understand you and TLS guy correctly its not so much that the woofers have unique Infinity magic, its just that they, together with the cabinet and crossover networks, are more or less a matched pair.
I looked into performing a re-cone myself but I have to agree it looks like a complex operation where more than a few things could go wrong. Unfortunately, the cost of a professional re-cone is more than an original driver. At this point I'm planning on purchasing some original used drivers in good shape. If I can find any. Worst case scenario I'll borrow from my RS-III but I really don't want to do that.
Just for fun, I contacted Infinity/Harmon this morning and surprisingly they were able to provide a modern driver they consider to be an acceptable substitute. I have to give them credit for not laughing me off the phone! These were discontinued in 1987! I don't think H/K had even purchased Infinity at that point! I would be happy to provide that model number if anyone is interested.
I ordered a pair and will be installing them in the damaged tower and then A/B testing them against the tower that was not damaged. (After repairing the cross-over of course ) If the sound quality is not at least equal, I'll just install original woofers again and return the modern "equivalents" or keep them for other projects.
I'll share how it turns out in my (subjective) opinion.

 

[Nathan Rieben]

TLS guy,

Thank you for the reply and the anecdote about the old Crown amps. I checked for DC voltage at the output this morning with a multimeter and there was a very small mV reading but nothing that alarmed me. Is it possible for an output transistor to fail intermittently?
In any case, I will be moving this amplifier along as I never really was too impressed with it's sound quality or the much hyped "authority" it allegedly has over bass drivers. My Integra M508 mops the floor with the Crown. The Integra is rated at 25 additional watts per channel but I don't feel it's enough of a disparity to explain the radical difference between the two.

 

[lovinthehd]

Thanks fmw I appreciate the response. If I understand you and TLS guy correctly its not so much that the woofers have unique Infinity magic, its just that they, together with the cabinet and crossover networks, are more or less a matched pair.
I looked into performing a re-cone myself but I have to agree it looks like a complex operation where more than a few things could go wrong. Unfortunately, the cost of a professional re-cone is more than an original driver. At this point I'm planning on purchasing some original used drivers in good shape. If I can find any. Worst case scenario I'll borrow from my RS-III but I really don't want to do that.
Just for fun, I contacted Infinity/Harmon this morning and surprisingly they were able to provide a modern driver they consider to be an acceptable substitute. I have to give them credit for not laughing me off the phone! These were discontinued in 1987! I don't think H/K had even purchased Infinity at that point! I would be happy to provide that model number if anyone is interested.
I ordered a pair and will be installing them in the damaged tower and then A/B testing them against the tower that was not damaged. (After repairing the cross-over of course ) If the sound quality is not at least equal, I'll just install original woofers again and return the modern "equivalents" or keep them for other projects.
I'll share how it turns out in my (subjective) opinion.

What particular drivers were recommended?

 

[TLS Guy]

TLS guy,

Thank you for the reply and the anecdote about the old Crown amps. I checked for DC voltage at the output this morning with a multimeter and there was a very small mV reading but nothing that alarmed me. Is it possible for an output transistor to fail intermittently?
In any case, I will be moving this amplifier along as I never really was too impressed with it's sound quality or the much hyped "authority" it allegedly has over bass drivers. My Integra M508 mops the floor with the Crown. The Integra is rated at 25 additional watts per channel but I don't feel it's enough of a disparity to explain the radical difference between the two.

My advice is never to hook a Crown DC 300 A amp, up to anything. If those replacement drivers are not satisfactory and they have recone kits, I can recone those drivers, as long as the kit comes with factory shims for centering the VC.

 

[lovinthehd]

My advice is never to hook a Crown DC 300 A amp, up to anything. If those replacement drivers are not satisfactory and they have recone kits, I can recone those drivers, as long as the kit comes with factory shims for centering the VC.

Is there a mod that can be applied to that amp to add such protection?

 

[TLS Guy]

Is there a mod that can be applied to that amp to add such protection?

Not that I know off. I suppose a thyristor clamp circuit could be applied to the output. When this circuits are triggered then the amp is destroyed. For the Crown 300 A that would be no loss.

 

[lovinthehd]

Not that I know off. I suppose a thyristor clamp circuit could be applied to the output. When this circuits are triggered then the amp is destroyed. For the Crown 300 A that would be no loss.

So what was the issue back then as far as not including such protection into designs?

 

[Nathan Rieben]

My advice is never to hook a Crown DC 300 A amp, up to anything. If those replacement drivers are not satisfactory and they have recone kits, I can recone those drivers, as long as the kit comes with factory shims for centering the VC.

Thank you I will keep that in mind and let you know if it comes to that

 

[Nathan Rieben]

What particular drivers were recommended?

Hi lovinthehd,

The Harmon audio specialists team recommended: Part #: 110250 (GGEC)

Based on the little bit of research I was able to do, it appears this woofer came stock on JBL ES100 speakers. I checked into reviews of that speaker and people were generally satisfied with the bass response even if they liked little else about it.
I'm a little disappointed that the drivers are coming from a Chinese manufacturer but I suppose nowadays that's to be expected. I don't know anything about GGEC, but I did find they build the drivers for Aperion Audio so I was a little encouraged. Perhaps they build a decent woofer. I found some specs online that claimed 100W RMS power handling capacity with 200W peaks. This concerns me as the RS-IIb woofers are wired in series causing the amplifier to see a 4 ohm load. My amp delivers peaks of 460W into 4 ohms and I will very occasionally tap into that realm. As nearly as I can tell, the cones are paper which also distresses me a little. Infinity had solid reasons for using polypropylene. In any case I'm reserving judgement until my ears give the final verdict.

 

[lovinthehd]

Search isn't bringing up anything particular for that. I'd think a large proportion of audio gear has Chinese origins these days, though, that's the way outsourcing manufacturing tends to have worked out Nothing particularly wrong with paper cones, but depends on particular makeup somewhat. Cone material and/or surrounds hopefully are suitable by design. Why is polypropylene for a cone material particularly important for Infinity speakers?

 

[highfigh]

Hi lovinthehd,

The Harmon audio specialists team recommended: Part #: 110250 (GGEC)

Based on the little bit of research I was able to do, it appears this woofer came stock on JBL ES100 speakers. I checked into reviews of that speaker and people were generally satisfied with the bass response even if they liked little else about it.
I'm a little disappointed that the drivers are coming from a Chinese manufacturer but I suppose nowadays that's to be expected. I don't know anything about GGEC, but I did find they build the drivers for Aperion Audio so I was a little encouraged. Perhaps they build a decent woofer. I found some specs online that claimed 100W RMS power handling capacity with 200W peaks. This concerns me as the RS-IIb woofers are wired in series causing the amplifier to see a 4 ohm load. My amp delivers peaks of 460W into 4 ohms and I will very occasionally tap into that realm. As nearly as I can tell, the cones are paper which also distresses me a little. Infinity had solid reasons for using polypropylene. In any case I'm reserving judgement until my ears give the final verdict.

If the impedance of each woofers is 8 Ohms, wiring in series would result in 16 Ohm total impedance, not 4 Ohms.

Match the amplifier output to the speaker's power handling limit more closely- you need to think in terms of 'worst case' scenarios and if something goes wrong and you can't stop it quickly, you'll be replacing drivers again. The 'problem' with some of the old Infinity speakers was their lack of sensitivity- they needed a bit of power to get going. Nice speakers, though.

When these Infinity speakers were made, poly woofers were new and they suffered from a problem where the cone would flex and release on hard bass impulses, which caused a kind of 'pop' sound. It only happened when they were being driven hard.

Not to pile on, but my initial reaction to seeing that you were using a DC-300 of any kind was "Well, there ya go". I think the only worse choice for an amplifier would be to use something like a Phase Linear 400.

I worked with someone who serviced electronics and he would say "They use those output transistors, to protect the fuses" when talking about a particular series of Sansui receivers, but it could apply to these Crown amps, too. I'm pretty sure the pro audio companies had modified versions when they used them for large concert venues- too bad they couldn't offer a safer model for consumers.

 

[TLS Guy]

So what was the issue back then as far as not including such protection into designs?

Believe it or not, the hazard was not recognized until speakers started going up in smoke. They thought the fuses would do the job, but they did not. The very early versions of the Quad 405 had the same issue, which Peter Walker rapidly solved. He apologized and made the few customers whole. Crown could not have cared less and would not reimburse for the speaker destruction.

 

[TLS Guy]

Hi lovinthehd,

The Harmon audio specialists team recommended: Part #: 110250 (GGEC)

Based on the little bit of research I was able to do, it appears this woofer came stock on JBL ES100 speakers. I checked into reviews of that speaker and people were generally satisfied with the bass response even if they liked little else about it.
I'm a little disappointed that the drivers are coming from a Chinese manufacturer but I suppose nowadays that's to be expected. I don't know anything about GGEC, but I did find they build the drivers for Aperion Audio so I was a little encouraged. Perhaps they build a decent woofer. I found some specs online that claimed 100W RMS power handling capacity with 200W peaks. This concerns me as the RS-IIb woofers are wired in series causing the amplifier to see a 4 ohm load. My amp delivers peaks of 460W into 4 ohms and I will very occasionally tap into that realm. As nearly as I can tell, the cones are paper which also distresses me a little. Infinity had solid reasons for using polypropylene. In any case I'm reserving judgement until my ears give the final verdict.

Series wiring doubles the impedance, and parallel halves it. You need to make sure those drivers have the same impedance as the old, and that they are not lower.
Generally woofers should always be wired in parallel otherwise one tends to drive the other. I am highly skeptical you had good advice. I would say it is far more likely to be be rubbish. I have never seen a driver properly replace another as there are so many variables that have to match, and they never do. I am confident you were sold a bunch of BS.

 

[Nathan Rieben]

If the impedance of each woofers is 8 Ohms, wiring in series would result in 16 Ohm total impedance, not 4 Ohms.

Match the amplifier output to the speaker's power handling limit more closely- you need to think in terms of 'worst case' scenarios and if something goes wrong and you can't stop it quickly, you'll be replacing drivers again. The 'problem' with some of the old Infinity speakers was their lack of sensitivity- they needed a bit of power to get going. Nice speakers, though.

When these Infinity speakers were made, poly woofers were new and they suffered from a problem where the cone would flex and release on hard bass impulses, which caused a kind of 'pop' sound. It only happened when they were being driven hard.

Not to pile on, but my initial reaction to seeing that you were using a DC-300 of any kind was "Well, there ya go". I think the only worse choice for an amplifier would be to use something like a Phase Linear 400.

I worked with someone who serviced electronics and he would say "They use those output transistors, to protect the fuses" when talking about a particular series of Sansui receivers, but it could apply to these Crown amps, too. I'm pretty sure the pro audio companies had modified versions when they used them for large concert venues- too bad they couldn't offer a safer model for consumers.

Thanks for the correction, right you are about the total impedance. I was thinking the series circuit followed the inverse square law for some reason...those classes were a few years ago
I checked into the schematic for the speaker and the also the owners manual. The manual states that the amplifier driving the woofers will "see" a 4 ohm load. The wiring diagram does show the woofers to be in a series circuit. So I guess each driver must be two ohms. Not impossible I guess but kind of an anomaly in my experience.
Yeah, yeah I hear ya about the Crown and am well aware of their issue. It's not possible for an output transistor to fail intermittently is it? I've checked for DC offset at the speaker terminals on the Crown and everything seems fine. None-the-less that amp will be finding a new home. I still think the Infinity bass EQ box is suspicious because both amps popped into protection mode when it was in the circuit. I've got it on the bench now to check for anything obvious.

 

[Nathan Rieben]

Search isn't bringing up anything particular for that. I'd think a large proportion of audio gear has Chinese origins these days, though, that's the way outsourcing manufacturing tends to have worked out Nothing particularly wrong with paper cones, but depends on particular makeup somewhat. Cone material and/or surrounds hopefully are suitable by design. Why is polypropylene for a cone material particularly important for Infinity speakers?

You can search the part number on GGEC's site. Other than that you're best bet is searching JBL ES100. I searched for quite awhile before I found anything and what little I did find wasn't especially helpful.

As far as the polypropylene, I figure Infinity had access to paper cones and they would have kept production costs down. The engineering team at infinity chose the poly for a reason.

This video explains some of the reasoning behind Infinity's decision.

Start at approx 9:50

In my opinion, the weight/rigidity ratio tends to a theoretical advantage. Allowing fast transients while maintaining sufficient rigidity to keep the woofer more nearly a perfect piston.