Infinity repairs

[Goldenblack440]

Hi all, this is my first post on this forum, i live in Perth, WA. I'm hoping someone has some experience in speaker driver replacement and compatibility. I have some Infinity SM-112's They are about 14 years old, i bought them from Singapore. I was never really that impressed with them- the best feature of them i thought were the cabinets! Very solid and well made with excellent veneering and nicely fitting grilles. However you don't buy speakers for the cabinets. Sure they have the Infinity hallmark of what they call "realism" but after listening a while, i realised that all they have done is made the midrange very prominent. They are very lacking in bass- embarrassingly so - and the overbright midrange frequencies start getting rather harsh and annoying at more than average listening levels. After many years of reading HiFi mag reviews and seeing them raving about the Infinity series (the RS series - Reference Standard), these were a let down- smacking of budget design. I opened them up and they didn't even bother to put damping inside- completely bare! The tweeters are the poly cell- not the EMIT ribbons unfortunately and they have an attenuator- the midrange do not on this model, which they do desperately need to balance the sound.

To get to the point, just recently i noticed the foam suspension on the bass drivers was completely rotten, crumbled away at the touch. So i thought this might be a good opportunity to give them a bass injection with some better drivers.

But are these old school Infinity's rated at 4ohms? That's what they measure at. And that's probably how they get such a high efficiency rating of 100db/w/m.

I tried putting in some old 10" Jensen drivers i had lying around (measured at around 5.6 ohms) and found that the amp cut out on even slight bass boost at low volume on both channels. Did this three times on some bassy Madonna tracks. So i am wondering if i should use some car woofers, which are usually rated at 4 ohms to try to get some sort of compatibility.

Any experience with compatibility like this would be appreciated and any recommendations on brands of driver to look out for also. I am considering some expensive (for me) Jaycar Kevlar cone drivers- around $150 each, but maybe these are just 'Made in China' stuff? THanks

[masoth]

Not here to help with your problem but to welcome you to the forums. I remember a few posts dealing with speakers so suspect there are a few knowledgeable members about the place.

soth

[Goldenblack440]

Thanks Masoth- you're up late (or early rather) - then again you're 2 hours in front of us. I'm off to bed now. Have a nice day.

[Rattrap]

goldenblack, you can't just measure the ohms on the speaker with a multimeter. With speakers we're talking impedeance thats rated in ohms. If its not stamped on the back of the speaker then it can be a problem. Normally its stamped or on a sticker on the large magnet on the back of the speaker. If your amp was cutting out with any bass at all then my guess would be that the Jensen speaker impedeance is too low. DON'T USE THEM!!! Not unless u want to see smoke come out of your amp. You can go higher impedeance & it won't effect your amp but not lower. It's important that u try to find out what impedeance the speakers are & match it. Lower & u'll damage your amp, higher & u'll loose some power output. Speakers are normally rated at 4, 8 or 16ohms with 8 ohms the most common.
If the ohms arn't stamped on the back & you can't find any more info on the net then my suggestion would be to try to find out what rating the Jensen speakers are & go to the next higher ohm rating.
I can't help you with brands of speakers, i've been out of the field for too many years now.

[Goldenblack440]

Thanks for your reply Rattrap. i went and had a look at both sets of drivers- nothing nowhere unfortun8ly. I was aware that total impedance consists of resistance, inductive reactance and capacitive reactance etc so i sort of knew that it was a rough way of measuring it, however as a baseline point of comparison only, the Jensens measured at 5.6ohm and the Infinity were a tiny 3.2 ohm. Now i gather from what you say that the impedance of a speaker will be determined from what the amp "sees" when it is powered up and active. Is this correct? So these figures will change. But i assumed that since the Jensens were statically a lot higher than the Infinity ones, they would increase the impedance and not reduce it, as it seems to be doing with the amp cutting out. I'm sure the answer will come after some more research and ringing around Perth

[Rattrap]

I wish i could say that is correct GB but a speakers ohm reading has very little to do with its actual impedeance. The reading u are getting is dependant on the diamater of the copper wire, the thickness of the copper wire & the quality of the wire. While these will all effect the actual impedeance they won't give you any guide.
With your amp cutting out like it was it tells me that the infinnity speaker is undoubtably a higher impedeance speaker. My guess would be that the Jensen is 4ohms & the infinity is 8ohm. But thats a wild guess but also based on 20 yrs experence in the industry. 4 & 8 ohms are by far the most common rattings.
If it was my stereo system tho i wouldn't be relying on guesses. Amps can go pop way too easily. & you'd be blowing up finals transistors/IC's - they are the most expensive by far.

[Goldenblack440]

Mmm, interesting- i'd say you are right there. Although, the Jensens i pulled the woofers out of are really nothing special. 3 simple paper cone speakers and a single capacitor and coil as a crossover. Its definitely old school, i'd guess 8 ohms myself but not sure. The crossovers in the Infinity's look fairly complex, so its also possible that the Jensen drivers could be upsetting the way the whole thing works, in effect, also reducing the total impedance. I really need to speak to someone who has a lot of experience with Infinity speakers, so i'll do some ringing around, might browse some dedicated Hifi Forums.

I wonder if Soundman has any thoughts or experience?

Well thanks again

[Rattrap]

The other option, tho the more expensive, is to completly replace all of the speakers, crossovers etc. Sounds to me like it wouldn't be a bad idea if the speaker boxes are of a good quality. That way you could get a full set of matching speakers with the correct overall impedeance for the amp.

[Goldenblack440]

yes that option passed through my head and then passed out again just as quickly- i like getting good results with what i have available- being budget minded. The Jensens also have attentuators on the tweeters so I am exploring the possibility of putting these on my Infinity's middle driver to curb the overly bright midrange. On the back of course, where they can't be seen. I also bid on some tweeters on Ebay a few days ago. They were some EMIT ribbon tweeters from the RS Series Infinities. Were supposed to be the world's best years ago (that's about 18 years ago!) They were at $37 for the pair- at the last 5 minutes, i bid $66- seemed i had won them, then 2 other bidders joined- they went for $82. Would have been a nice addition- if they were not damaged.

Anyway, if the situation comes about where i decide to get the Infin bass drivers' suspension redone, i can just put them back in and use a subwoofer which i just bought for $70. But its not the same really, as nice deep clear bass from a good pair of speakers.

[soundman]

Did I hear my name mentioned in vain

Id say the best option is to get the surrounds replaced on the existing drivers, you wont be upsetting anything then.

I would also be inserting L pads in the mids and tops.

you might have a chance of getting them to sound decent.

I'd stay away from the car HIFI speakers......the design assumptions are completly different.

If you want to replace the surrounds yourself it isnt all that hard, you should be able to get the parts from speakerbits.

you will need an appropriate surrouns and dust cap for each driver.

remove and clean up the from old surround
cut the dust cap out, shim up the voice coil with paper
fit the new surrounds with EVA glue, allow to dry
remove the shims
test the travel is clean
fit new dist cap.

cheers

[Goldenblack440]

Thanks very much for the advice Soundman- you are right, i can forget about the car drivers. I spoke to a fellow this arvo who has much experience on Infinitys. Told me a lot of interesting stuff about them. Mine it seems are 2nd generation (around 1990 vintage)- not as good as the expensive (and better) first generation, but still competant. He said to forget 3rd generation stuff: "Infinity" in name only apparently. He said to repair the existing drivers and put an L pad on the mid (the tweeter already has one), as i could be chasing for ages finding a suitable driver to match the cabinet and port specs. New drivers, BTW, are $300 each! He can do all this plus put some heavier damping in which he said should improve the bass (they had no damping at all when i bought them!) including pickup and delivery for around $200. Attenuating mid and high will of course give the bass more room to emerge. My Techinics Class A amp is also apparently considered very bright, so might have to look at that side as well. Also, some Infinitys suffer from poor room placement positions.

However, now you describe the re-foam process- it sounds like i could easily do it being a car restorer and an ex- RAAF av tech.,, But well, since this fellow was nice enough to give me the time and info, i'll give him the work.

Will let you know how it goes, he's picking up tomorrow.

[soundman]

I seem to remember that infinities always had a reputation for beeing a bit ...um....."bright".

But from what I know now, in a side by side sales situation that sells speakers because they seem louder.

cheers

[Goldenblack440]

True- one of the sound salesman's tricks, the louder speaker in a comparo gets more attention. similar to selling a used car: if it had a few noises- the salesman would usually try to get them to test drive it in the wet- they sound about 40% quieter.

the fellow picked up the Infinity's this arvo, can't wait to hear them when all done.

Just another quick question Soundman: My Technics SU-V4 Class A has switched speakers A and B or on mine, called Main and Remote. If i switch both pairs of speakers on together (and they are both rated at 8 ohms) will that reduce the load to 4 ohms that the amp sees, therefore increasing the load on it? Or has it been designed so that the amp still gets the 8 ohm load for each? A friend of mine said you shouldn't run all together as it puts too much strain on the amp, but i have never had anything blow up running them like this, even with a little extra bass boost.

Thanks

[soundman]

I cant tell you haow the amp is arranged or what the specs are.

If it is an ooold style amp from the early eighties or before most likely it will paralell the speaker outputs giving a 4 ohm laod with 2 8 ohm speakers per channel.

If it is a "modern" amp who knows you will have to look at the specs.

the whole HIFI speaker and amp impedance thing has gone pear shaped in the last 20 years.

at one stage all HIFI amps with drive 4ohms happily and speakers were either 4, 8 or 16 ohms.

these days amps can be 4 ohm ( rarely ), 6 ohms or 8 ohm.
speakers can be labeled 4, 6, 8 or whatever and the reality is anybodies guess.

and don't get me started with power ratings, speaker sensitivity and other foolishness we thaught got stamped out back in the eighties.

cheers

[Goldenblack440]

Thanks 4 that- its about 20 years old (and still in demand apparently from techo's- I often see Wanted ads in the classifieds for the SU-V series). When in doubt...read the instructions. I'll see if i can dig up the Operators manual and see what it says in there. I suspect though that it just internally parallels them.

Regards impedance of speakers- i just learnt, and you probably already know this... the rated impedance of a speaker is only nominal impedance and varies (up and down) with the source material and loads. Different speakers react to different loads and frquency demands in different ways, so some amps will have to work much harder with some brands of speaker due to the fact that the impedance can drop right down on certain areas of the material being played, whereas others migh remain at a more constant impedance.