I've come to be the online resource / expert for the Koss CM Series of speakers (~1977-84). As described in the thread linked-to in my auto-sig, I own and use the CM/1030, CM/1020, and CM/1010 speakers. Love 'em to bits! BUT, there's another CM speaker in the Series and it's the baby / oddball of the group: the CM/530. It's not mentioned in the earliest CM Series brochure (1977) that I have; it is mentioned in the 1978 brochure. It's not covered in the two older versions of the owner's manuals that I have. (If anyone has a manual from 1978 onwards that includes the CM/530 I'd love to get a high-res scan!) It is mentioned in the Koss Loudspeaker Service Guide that I mentioned in another thread a few months back, and which I have posted online on a number of sites. All this to say that it was, and is still not, as visible as its bigger siblings. In fact, a search of this site for "Koss CM/530" only turns up my thread from a month ago, where I detailed a failed attempt to get a pair, since I had never heard them in action. In that thread I concluded with the line: "I'll try to find another pair of CM/530. Some day." Well that day was yesterday. Hi-fi Shark alerted me that morning to a Kijiji sale. And the seller lived just a five minute drive from my house! A deal was done and yesterday evening I brought them home. Functionally the pair is like-new. All the drivers are working great. As are the frequency shaping switches. I've inspected the crossovers and they showed none of the usual signs of deterioration. The cabinets have the usual signs of use that you'd expect from a 40 year old speaker (why do people put potted plants on top of speakers?!) but after two rubdowns with lemon oil they look pretty good. The grill cloth has a tatter or three. And the badges are missing. So I set them up in my main HT this morning. Not in an ideal position; but the best I had: horizontally (as designed) on top of isolating pads on top of a pair of CM/1020s tilted downwards a bit and slightly toed-in towards the prime listening position. That room is acoustically treated and should give them a chance to show their stuff. I pulled out an old recently-refurbished Sherwood receiver, that is known to be able to handle the close to 4 ohm load that the CM/530 presents, to drive them. And I used my iPod Touch as the source. I listened to them for an hour this morning, and another couple of hours this afternoon. They sound quite good on a wide variety of material. While I don't have a pair handy at the moment to do a direct comparison, I'd say that I like them almost as much as the CM/1010. Both sound very similar in the midrange, but the CM/530 probably images just a bit better. (The CM/530's woofer handles upper bass and all the mids up to 3 kHz, which is very similar to the 3.5 kHz for the CM/1010). The CM/530 does not have the bass extension that the CM/1010 does - at least not that I recall. (And of course neither is as good as the CM/1020 or CM/1030 in that regard.) The CM/530 shares none of its drivers with its siblings, whereas the CM/1010's tweeter is found in the CM/1030. Overall I can now say that the sound of the CM/530 does fit within the Koss CM Series family. However one aspect of its sound that struck me / stood out, was how good it is nearfield. I don't think it was designed for such an application but it just might work pretty well. In a small room with a listener sitting relatively close I think they'd sound very good. I only know of one trade pub review of the CM/530. Check out pages 47-48 here. Anyhow I post this in case someone out there is looking for some information on these somewhat-rare speakers. I can always be contacted at [email protected] by anyone seeking additional information. I'm now looking for a pair of badges to go with the new grill cloth that I will eventually install. I'll keep them in the main HT for a while longer, and after that I'll look for a good home to lend them to as I don't have storage space for them. Jeff
It's been a few weeks since I set them up in my main HT and I've found myself listening to the Koss CM/530 more often than I expected. Maybe it's because I replaced the damaged grill cloth which greatly improved their looks. It's more likely because they sound pretty good. While listening yesterday, I again noted that they do not handle really low bass as well as I normally like. Oh, they're way more capable than most "bookshelf" speakers; just not as capable as good floorstanders. So I decided to pair them up with an unused Yahama YST-SW150 sub that I had bought a month or so ago. I used speaker-level connections and the YST's controls to properly calibrate the set-up (using a test disc / RS SPL meter.) I played around with the crossover point and eventually settled on 70 Hz. At that setting there was no localization of the sub's output and it offloaded a good amount of content from the Koss, and seemed to tighten up their sound above that point. The system now reproduces all of the bass in every one of the "demo" tracks that I normally use. Not boomy. Not fat, or bloated, or any of those other characteristics one might use. "Neutral" would be the way I'd describe it. For anyone out there still using a pair of Koss CM/530s, I suggest you try using them with a properly set up subwoofer. The CM/530 cost me $60C for the pair. The Yamaha YST-SW150 was $40C. One would be hard-pressed to put together a better-sounding / more capable stereo speaker system for $100C. Jeff
An update to my OP, for anyone wandering by... I have since discovered another trade pub review of the Koss CM/530. This one is by Julian Hirsch in Popular Electronics (June 1979) and can be found on pages 31-32 here. If you couldn't guess by now, let me say that I completely agree with the review's closing sentence: In conclusion, Koss's CM/530 is a thoroughly exceptional speaker, and one is not likely to find another at its price with better sound. Jeff
An update of sorts, and as posted in another thread... To stave off an afternoon of Covid-19 self-isolation boredom, I decided to re-jig the Koss CM/530 set-up. As noted above, it consists of a Sherwood A/V receiver, the Koss CM/530 speakers, and a Yamaha YST-SW150 sub. I'm running speaker-level connections to the Yamaha, from there to the Koss, with the Yamaha's low-pass filter set around 55 Hz. The thing is, while it sounds very good, I really don't like any mains in any "2.1" system to be getting a full-range signal. For me it's counter-productive. I'd rather the sub handled all the deep bass - and avoid a "double bass" situation. Anyhow... That got me thinking that I should order another Rolls Stereo Crossover specifically for its high-pass filter capability. As I was noodling that idea the proverbial light bulb went off. Don't I own a perfectly good Outlaw Audio Model 950 Pre/Pro that has great bass management capabilities? And don't I have at least a few spare stereo power amps kicking around - including a just-refurbished beautiful NAD 2155? Yup! So out went the Sherwood receiver and in its place went the Outlaw/NAD combo. Set the Outlaw's bass management crossover to 60 Hz for the F L/R speakers. Connected the Outlaw to the Yamaha via RCA. Used the Outlaw's set-up capabilities and my trusty original RS analogue SPL meter to dial everything in. Worked like a charm. Noticeable improvement in the overall sound which I attribute, hopefully correctly, to the elimination of the double bass effect. Bass seems tighter. Jeff
A fellow CM/530 owner contacted me a couple of months ago looking for information that I could only provide by opening up the cabinet of one of the speakers. When I did I was very surprised to see that the spider on the passive radiator was torn and crumbling. While I could not hear its effect, clearly I was not going to leave it as is. I pulled the other one and confirmed that it had the same problem. So I boxed them both up, and what the heck, the crossovers as well, and sent it all off to The Speaker Exchange in Tampa Florida for a complete refurb. They were just re-opening when the parts got there but it still did not take very long for the work to be done and parts returned to me. As is always the case with The Speaker Exchange, they did a fabulous job at a terrific price! The speakers were re-assembled and they sound great. Do I think they sound different? Nope. But at least now I know for sure that what I'm hearing is as was intended when they were new. Jeff
Yet another update - and some advice to other Koss CM/530 owners... After enjoying a few months of listening to my refurbished Koss CM/530s, something weird started happening. At anything above casual listening levels the NAD amp that was driving them had its protection circuits start kicking in. After lots of troubleshooting and measurements it was determined that one of the speakers' crossover inductors was shorting. The coils were original and had not been replaced during the previous refurb. It's the first time I've ever known a coil to go bad. So both crossovers were sent back to The Speaker Exchange in Tampa, the coils replaced with new custom-made ones, and the crossovers returned - with a total roundtrip time of fourteen days, including shipping to Tampa and back from Ottawa. Impressive! I reinstalled them as soon as they arrived and put the speakers to the test, playing them at 10dB above my normal loud listening level for a couple of hours. No problems at all; they sounded just great. So my advice to other Koss CM/530 owners. With the shorted coil, the faulty speaker's measured resistance across the speaker terminals had dropped from a normal 5.3 ohms to 1.2 ohms. The NAD amp, like most of its era, can handle low impedances (like 2 ohms) but even it could not handle the 1.2 ohm resistance. And even then all that happened was its protection circuits cut in to prevent any problems. This might not be the case for all amps. I suggest that you, or a tech, check your crossovers to make sure everything is still within spec. (I can provide the Koss-original wiring diagram / Service Guide if you email me at [email protected].) Heck, if the crossovers are all-original, the resistors and caps probably need replacing by now anyhow, so why not have them refurbished. It's an easy job to R&R the crossover boards that even a non-tech like me could do. Contact me if you need help. Jeff
I should have updated this thread quite some time ago. As detailed in another thread last year, the Koss CM/530 are now paired up with a single SVS PC-13 Ultra sub. (Pic in the other thread.) I spent the better part of 2022 unable to use my main HT (and the CM/530-based system) because it needed to be turned into a storage room after a pipe burst on the other side of the basement. The repairs / rebuild was only completed a couple of months ago. I've since re-acquainted myself with the CM/530 / SVS system and it's really hard not to crack a smile every time I sit down to do some quality listening. One little thing has been nagging my OCD brain: my set have been missing their CM/530 grille badges. In the last month I've tried to find and buy a pair. Two messages to two promising possibilities went unanswered. But this evening, after yet more Google searching, I found one badge (and pins) for sale and snapped it up right away without even thinking of haggling over the asking price. Call it a little Christmas Eve present to myself! With a little luck, and more searching, I hope to find another one in the coming months. Jeff
Sorry for the tardy reply. Christmas and all that! Here's the front of my main HT. For this thread, you can ignore most of what's shown. What is apropos this thread are the pair of Koss CM/530 (horizontal, on top of Koss CM/1020s, which are on top of Velo subs), the SVS PC13-Ultra "tube" sub, and the Outlaw Audio Model 950 pre/pro with NAD 2200 power amp. The left CM/530 The right CM/530 The SVS PC13-Ultra sub and the Outlaw and NAD The source components are all in the main HT's gear racks and get sent to the Outlaw as a stereo analogue signal. If you'd like additional details / photos let me know. Jeff
An update to a previous post: after a lot of searching I finally obtained another Koss CM/530 grille badge. Actually two badges. A fellow I'd helped out with a pair of Koss CM/530, and then recently with a pair of Koss CM/1030, ended up giving away his CM/530s, but before he did he offered the badges to me. They arrived late last week - from Australia! Jeff
