Back in the 90s, I read Stereophile religiously, and there were a handful of speakers I wanted to own. The Infinity Preludes were particularly interesting to me, because they were highly regarded yet also affordable.
A few weeks ago I stumbled across a set on Craigslist. Typically they sell for close to $1000, but this set was only $200. I figured the owner didn't know any better, or perhaps they were in a hurry to sell.
So I hopped in my car and drove over a hundred miles to get them. When I arrived, I found out why they were so cheap: they were in terrible condition.
I probably should have just gone home, but I couldn't resist the urge to tinker with them.
A few weeks ago I stumbled across a set on Craigslist. Typically they sell for close to $1000, but this set was only $200. I figured the owner didn't know any better, or perhaps they were in a hurry to sell.
So I hopped in my car and drove over a hundred miles to get them. When I arrived, I found out why they were so cheap: they were in terrible condition.
I probably should have just gone home, but I couldn't resist the urge to tinker with them.
After messing around with audio for decades, I don't hang on every word that Stereophile writes. But this is what they said about the Preludes, twenty three years ago:
"Conclusion The Infinity Composition Prelude P-FR loudspeaker is a stunning musical, technical, and aesthetic achievement. Even without its high sensitivity, the Prelude's smooth and uncolored tonal balance, wide dynamic contrast, articulate bass, and wonderful soundstaging would make it a standout. But with its ability to be driven to satisfying levels using an 11W single-ended triode amplifier, the Prelude becomes the loudspeaker for such amplifiers. Indeed, the $6395 Cary CAD-300SEI/Prelude combination was one of the most musical-sounding systems I've heard—regardless of price."
To me, there were a couple other things of note:
1) One easy way to tell when Stereophile is laying it on thick is when the measurements look like garbage. But the Prelude measurements are very good, even competitive with the Revel speakers that sell for 2-3X as much. From what I can see, the Prelude is in many ways a Revel-style speaker in a much cheaper cabinet with drivers that are fairly pedestrian. Basically good engineering with cheap ingredients.
2) The author of the review, Robert Harley, bought the speakers. Incidentally, I met Harley earlier this year when he was listening to Kevin Voeck's latest design for Revel.
Infinity Composition Prelude P-FR loudspeaker | Stereophile.com
"Conclusion The Infinity Composition Prelude P-FR loudspeaker is a stunning musical, technical, and aesthetic achievement. Even without its high sensitivity, the Prelude's smooth and uncolored tonal balance, wide dynamic contrast, articulate bass, and wonderful soundstaging would make it a standout. But with its ability to be driven to satisfying levels using an 11W single-ended triode amplifier, the Prelude becomes the loudspeaker for such amplifiers. Indeed, the $6395 Cary CAD-300SEI/Prelude combination was one of the most musical-sounding systems I've heard—regardless of price."
To me, there were a couple other things of note:
1) One easy way to tell when Stereophile is laying it on thick is when the measurements look like garbage. But the Prelude measurements are very good, even competitive with the Revel speakers that sell for 2-3X as much. From what I can see, the Prelude is in many ways a Revel-style speaker in a much cheaper cabinet with drivers that are fairly pedestrian. Basically good engineering with cheap ingredients.
2) The author of the review, Robert Harley, bought the speakers. Incidentally, I met Harley earlier this year when he was listening to Kevin Voeck's latest design for Revel.
Infinity Composition Prelude P-FR loudspeaker | Stereophile.com
Here's what the speaker looks like. (These aren't mine.)
First order of the day is to replace all the woofers. I briefly considered re-foaming them, but it looks like way too much work. Re-foaming twelve drivers sounds dreadful.
I measured the woofers and here's what I found:
fs = 83
qes = 0.53
qms = 7.7
qts = 0.5
le = 0.42
It's almost a 'prosound' style of midrange, with fairly high FS for it's size, and a low QES. LE is kept low by using what appears to be a 1" or 1.25" voice coil. Excursion seems to be very low, about 1-2mm. Oddly enough, the woofers are vented but the built in subs are sealed.
Here's the measured horizontal polar response of my set. The rolled off bass is for two reasons:
1) The Infinity Prelude comes with an integrated powered sealed sub, and I didn't do the measurements with the sub enabled
2) The woofer alignment is ported and all the surrounds are rotted out, so the cabinet leaks
This measurement gives you the general idea: very wide directivity from a narrow cabinet with narrow drivers, along with some controlled directivity in the treble via a waveguide.
Here's Stereophile's measurement of the same
Here's my measurement of the vertical directivity. I know there's a ton of wiggles in my measurements and I think I had my gate set for way too long. Each speaker weighs over 100lbs, so elevating them is a real challenge.
Here's the left vs right speaker. Clearly, one has a blown tweeter and possible a blown midrange and woofer
Good luck with those!
Back in the day, I had a buddy with Kappa 9's--think of the fun he was having 10 years later. By 1990, after the great 80's foam surround fiasco--I swore off purchasing anything with foam unless I could get off-the-shelf surrounds, I have an 18" PR with foam but not a problem getting a kit.
After the Preludes came the Overtures with rubber surrounds--I picked up a pair in 1999 and used them for 17 years. My needs changed to full HT and those Infinity amps are not known for longevity although I protected them with subwoofers. Now that they are 19 years old, I'm sure the ferro-fluid is starting to dry out along with the caps in the mid/tweet passive crossover. Actually pondered ripping them apart, replacing the ferro-fluid and caps then figuring out what passive crossover to use them with and adding woofers.
Still pondering! I get to it after my end table subs are done...some new surrounds and Atmos speakers--oh yeah, and a tapped horn sub... Presently they are museum pieces out in the garage gracing the likes of mini-disc and LD players.
I'm with you on Stereophile--I just look at the measurements. Their "recommended list" of green markers for CD's (17 years recommended!) multi-thousand dollar speaker wire and such shows their true colors. However, they do measure things so I just latch on to that.
For the Infinities, there is a place in Tampa that has kits for older speakers. Not sure if your drivers are included but a good place to start. If you have blown woofers/mids/tweets and can't get replacements--will you attempt to modify the preludes with different drivers? You are a greater man than me messing around with old Infinity foam... I've refoamed a few JBLs from back in the day but can't say I find it entertaining.
Good luck with the refurb, I refurbed a pair of 10" fully horn loaded two-ways from the '60's including new crossover builds--very educational and the owner was very happy that I improved the sound quality. Plenty of great speaker designs were murdered by foam rot in the 80/s/90's era--good to see you giving them a go.
Back in the day, I had a buddy with Kappa 9's--think of the fun he was having 10 years later. By 1990, after the great 80's foam surround fiasco--I swore off purchasing anything with foam unless I could get off-the-shelf surrounds, I have an 18" PR with foam but not a problem getting a kit.
After the Preludes came the Overtures with rubber surrounds--I picked up a pair in 1999 and used them for 17 years. My needs changed to full HT and those Infinity amps are not known for longevity although I protected them with subwoofers. Now that they are 19 years old, I'm sure the ferro-fluid is starting to dry out along with the caps in the mid/tweet passive crossover. Actually pondered ripping them apart, replacing the ferro-fluid and caps then figuring out what passive crossover to use them with and adding woofers.
Still pondering! I get to it after my end table subs are done...some new surrounds and Atmos speakers--oh yeah, and a tapped horn sub... Presently they are museum pieces out in the garage gracing the likes of mini-disc and LD players.
I'm with you on Stereophile--I just look at the measurements. Their "recommended list" of green markers for CD's (17 years recommended!) multi-thousand dollar speaker wire and such shows their true colors. However, they do measure things so I just latch on to that.
For the Infinities, there is a place in Tampa that has kits for older speakers. Not sure if your drivers are included but a good place to start. If you have blown woofers/mids/tweets and can't get replacements--will you attempt to modify the preludes with different drivers? You are a greater man than me messing around with old Infinity foam... I've refoamed a few JBLs from back in the day but can't say I find it entertaining.
Good luck with the refurb, I refurbed a pair of 10" fully horn loaded two-ways from the '60's including new crossover builds--very educational and the owner was very happy that I improved the sound quality. Plenty of great speaker designs were murdered by foam rot in the 80/s/90's era--good to see you giving them a go.
I think refoaming will be too much hassle.
My plan is to find drivers that are close to the Infinity specs, replace every last Infinity driver, and then measure the speaker.
Asuming the specs are "in the ballpark", I expect that there won't be any big peaks or nulls that will be impossible to deal with. There WILL be a difference in the efficiency of the drivers; some will be a decibel or two less efficient.
To address that, I intend to use a Mini DSP to tweak the over all response.
So basically Infinity Prelude Cabinet, Infinity Prelude subwoofers, Infinity Prelude passive xovers, and all new midranges, woofers and tweeters.
My plan is to find drivers that are close to the Infinity specs, replace every last Infinity driver, and then measure the speaker.
Asuming the specs are "in the ballpark", I expect that there won't be any big peaks or nulls that will be impossible to deal with. There WILL be a difference in the efficiency of the drivers; some will be a decibel or two less efficient.
To address that, I intend to use a Mini DSP to tweak the over all response.
So basically Infinity Prelude Cabinet, Infinity Prelude subwoofers, Infinity Prelude passive xovers, and all new midranges, woofers and tweeters.
The Dayton DC130AS is the obvious choice to replace the woofers. It's very very similar to the Infinity woofer, so close it might even be a clone. The diameter and basket shape is nearly identical, both are shielded, both are paper cone. The Dayton has a rubber surround and a treated cone, both of which are lowering the sensitivity and the FS. The Infinity is straight up untreated paper with an untreated foam surround. It's like someone at Infinity just designed this thing to be monstrously efficient.
The Infinity Prelude has a funky bass alignment, where all four woofers share a common enclosure, and it's ported very high. Around 100Hz, give or take 20Hz.
Here's the predicted response of the Infinity 902-7576 vs the Dayton DC130AS. The Infinity really walks all over the Dayton, unfortunately. Looks like the lower FS of the Dayton is hurting it's efficiency.
The Dayton isn't completely unusable but it would definitely take some tweaking with MiniDSP to get the spectral balance correct, and I'd have to tame that peak. The Infinity cabinet, though ported, is filled with polyfill. So that would certainly reduce the amplitude of that peak. Another odd feature is that it's a bit like a transmission line, because the ports are at the top and bottom of the cabinet but the woofers are staggered across the entire line. The woofer cabinet is basically a 6" cylinder that's three feet tall.
The MCM 55-1870 is an oddball choice to fix the Infinity. It has a heavy aluminum cone and it's a bit smaller than the Infinity. On the upside, it's cheap and there aren't many drivers in the range of $10-$15 that sound as good.
This looks like a much better match than the Dayton, and as a bonus, it's cheaper!
The clear downside, is that MCM's spec sheets are just completely fantasy. I've never seen a single driver from them that measured anywhere close to spec.
John Krutke measured the MCM 55-3870, which I'm nearly certain is the exact same driver as the 55-1870 but with a cast basket instead of a stamped frame. Using John's measurements, here's what I get.
Assuming John's measurements are more accurate than MCM's, it looks like what I would expect: the heavier aluminum cone drops the efficiency quite a bit and the higher qts exacerbates the low frequency peak.
Neither of these are insurmountable, I can smooth things out with DSP, but ideally I'd like to find a woofer with higher efficiency and a higher FS.
I think we have a winner. Here's the Pyle PDMW 5 versus the Infinity. Very very close.
I have some PDMR 5s here at the house, I used them in a Unity horn project. I believe the PDMR 5 is the same driver as the PDMW 5, but with a sealed off basket.
So I think I'll cut open the basket and see how it measures. My expectation is that the Pyle spec sheet is likely exaggerated; I wouldn't expect it to have such a high FS with a treated paper cone, but I'm willing to sacrifice one to find out...
I chopped up my PDMR 5s, to see if the published T/S is anywhere close to the "real" Thiele Small. Here's what I found:
published / measured
fs = 108hz / 125.8hz
qes = 0.8 / 1.43
qms = 8.32 / 3.78
qts = 0.77 / 1.04
le = not published / 0.42
re = not published / 7.1
Here's how the Infinity "stock" driver compare to the Pyle, using actual measured data
By design, the Infinity has a bump in the midbass
Here's how the "stock" driver compares to the Pyle woofer, if the woofers are run sealed instead of ported. This might be the best option; you lose some of that 'bump' but I don't know that I want it
published / measured
fs = 108hz / 125.8hz
qes = 0.8 / 1.43
qms = 8.32 / 3.78
qts = 0.77 / 1.04
le = not published / 0.42
re = not published / 7.1
Here's how the Infinity "stock" driver compare to the Pyle, using actual measured data
By design, the Infinity has a bump in the midbass
An externally hosted image should be here but it was not working when we last tested it.
Here's how the "stock" driver compares to the Pyle woofer, if the woofers are run sealed instead of ported. This might be the best option; you lose some of that 'bump' but I don't know that I want it
The "cheap side" of my personality tells me to drop a whopping $96 on eight Pyle midranges, but I have a few qualms:
1) they look dumb
2) I don't think "Q" is a huge factor in sound quality, but a "Q" of over one is fairly ridiculous. I worry it will be audible.
3) The high Q and heavier cone is lowering the efficiency, compared to the Infinity
Physically, Celestion's five inch midrange is a near-perfect fit.
The Celestion is the first woofer I've evaluated that exceeds the "stock" performance. It's about 3dB more efficient. Due to it's lower Q, it works in the "stock" ported box, but without such an excessive bump in the midbass.
It's kinda spendy for a five inch woofer - it's $35 each and I need eight
I think I'll go this route though. Particularly if I opt to resell them in the future, the Celestion cosmetically looks like it "belongs" here, whereas the Pyle looks a bit rinky-dinky.
I could, I just don't want to refoam twelve drivers. Also, my initial measurements seem to indicate that at least one tweeter is blown, and possibly one mid and a woofer. The drivers are no longer available.
Yeah the last two Pyle woofers I bought went straight in the trash. Couldn't tell if they were built defective or just a terrible design, their Q was something like 1.6, right out of the box, and xmax seemed to be a fraction of an inch.
For $12, the PDMR5s are legit. I believe the PDMW 5 is the same drivers as the PDMR 5, but with an open basket. So I cracked open a PDMR 5 that I have here and measured the T/S. (on the previous page.)
From what I can see, the Celestion TF 0510 is the closest match for the Infiniti. It kind of sucks to have to purchase eight at $35 a pop, but it's about 3dB more efficient than the $12 Pyle PDMW 5.
The Faital four inch midranges are literally identical in dimensions. (4FE32 and 4FE35)
Here's the Infinity 902-7345 vs the Faital 4FE32. The Faital is quite a bit more efficient. The high Q of the Faital creates a big peak in the response
Increasing the volume of the cabinet from 0.14 liters to one liter smooths things out a lot, but I'm not sure if I have space to do that. (The speaker's crossover is right behind the midrange enclosure.
One option would be to share the enclosure with the woofer.
I've never rebuilt a speaker in my life, so if some of my comments are hopelessly noobish I apologize
I created the crossover in Bill Waslo's XSIM, using Kimmo's Saunista's spltrace to generate the FRD files. With that data in hand, I can plug in various drivers and see how they perform.
Here's the response using the Dayton RS125p paper cone reference woofer for the bass, and the ubiquitous Tymphany TC9 for the midrange. This wasn't a scientific choice, I basically wanted to see how the stock Infinity crossover would behave if I used a couple of drivers that DIDN'T closely match the "stock" drivers. To me, these results don't look too bad. Sure, there's a 3dB peak at 400Hz but I can EQ that out with MiniDSP, no problem.
Basically I'm trying to figure out if I can keep the stock enclosures, the stock passive crossovers, without having to find drivers that are exact matches for the Infinity drivers.
footnote : In the crossover simulation, the woofer section appears to be 3dB lower than the midrange section. This is because there are four woofers and two midranges. Once you factor in the additional woofers, the woofer section is basically the same efficiency as the midrange section.
I created the crossover in Bill Waslo's XSIM, using Kimmo's Saunista's spltrace to generate the FRD files. With that data in hand, I can plug in various drivers and see how they perform.
Here's the response using the Dayton RS125p paper cone reference woofer for the bass, and the ubiquitous Tymphany TC9 for the midrange. This wasn't a scientific choice, I basically wanted to see how the stock Infinity crossover would behave if I used a couple of drivers that DIDN'T closely match the "stock" drivers. To me, these results don't look too bad. Sure, there's a 3dB peak at 400Hz but I can EQ that out with MiniDSP, no problem.
Basically I'm trying to figure out if I can keep the stock enclosures, the stock passive crossovers, without having to find drivers that are exact matches for the Infinity drivers.
footnote : In the crossover simulation, the woofer section appears to be 3dB lower than the midrange section. This is because there are four woofers and two midranges. Once you factor in the additional woofers, the woofer section is basically the same efficiency as the midrange section.
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Agreed.
A few hours ago, my plan was to use four Celestion five inch woofers to replace the "stock" Infinity woofers, and possibly use a pair of Faitals to replace the "stock" midranges. This is an expensive proposition; $140 for four woofers and $80 for two midranges.
Quite a bit, considering I paid $100 for each speaker.
After trying a pile of different woofers, I think that four of the MCM 55-1870s will work nicely for the woofer section ($48) and two of the Peerless 830870s will work nicely for the midrange section. ($60).
That reduces the cost per side by about fifty percent, and I have a hunch the Peerless midrange will outperform the Faital midrange. The Faital mids are largely designed for maximum output, while it's clear that the Infinity midrange is engineered for a balance between smooth response and efficiency.
Here's how things look with the stock crossover, the Peerless 830870 midranges, and the MCM 55-1870 woofers. Not too shabby, especially for $108 per side. It still needs some EQ to reduce the bump at 400Hz, but nothing too difficult to fix with DSP.
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