Speakerlab 7 Crossover Re-cap and T350 Tweeter Upgrade

Speakerlab probably isn't a name that rings any bells for most people outside of the Pacific Northwest, which makes it even more weird that I found a pair of their speakers sitting in a Goodwill in the middle of Texas. Initially not knowing what the hell these things were, the Speakerlab 7s quickly stole my heart, and ruined every other speaker in the house for me. But, being close to fifty years old, they could use a little TLC, and perhaps a few upgrades while we're at it.

Source: Speakerlab

A bit of background first: Speakerlab is a boutique speaker company based out of Seattle, Washington. Founded in 1971, they've specialized in relatively affordable kit speakers capable of trading punches with some of the bigger names in the industry. Their lineup over the years is wildly diverse, even featuring a comparatively low-cost Klipschorn clone called - of all things, the Speakerlab "K". It's like they were begging to get sued, and I'm guessing they might've gotten close as their lineup underwent substantial changes from 1979 onwards that distanced themselves from being "Klipsch copycats".

Source: Speakerlab

My model 7s in particular come from that mid-to-late 70s period where the company was all in on loaded horn drivers - again, very much a Klipsch thing, though not exclusively. The first generation 7s used an Electro-Voice T35 horn tweeter (used by Klipsch as the K77) and a what's generally assumed to be either an EV or Atlas built midrange horn known internally as the HD700B. These are coupled with a phased arrangement of in-house built ten- and twelve-inch woofers in a sealed cabinet.

Source: Speakerlab

I was actually shopping for vintage Klipsch speakers at the time and no joke, when I saw these for the first time I could've sworn these were Cornwalls (this was before I knew just how freakishly big Cornwalls actually are). But when I saw the badge and pulled the grills off, it was a completely different story. There were also no model identifiers on the cabs, which probably explains why they were out on the floor for $20 a piece instead of the auction site like most of the more desirable items go nowadays. Goodwill: putting the "profit" in "non-profit" since 1902!

So I parted ways with $40 and crammed them into the back seat of my car. They weigh something like 85 pounds each and barely fit through the car door, but I managed to get them home and inside the house. The problem is that I have basically no space for speakers of this type. Since the most logical space - the living room, has more furniture in it than a Swedish meatball outlet, and since my receiver was all the way in my bedroom, I crammed them between the corner shelves in the adjacent game room. Not ideal acoustics, but it'll have to do.

Now, the only true passive speakers I've listened to through my receiver - an unrestored MCS 3275, has been a pair of Klipsch R-51Ms. Obviously it's not apples to apples, but I was not prepared for how comparatively insane the Speakerlab 7s were to my piddly little bookshelf speakers. The mids and highs were full of detail and the low end was rich, punchy, and utterly house shaking on more bass heavy genres. These were speakers that beckoned you to come and listen to them, not just for putting them on in the background while you did the dishes or something.

But, as I did more research into the realm of vintage speakers, there were a few things I wanted to explore now that I had gotten a taste of what these things are capable of. More to satisfy my own curiosity than to fix anything that I felt was seriously wrong with them.

Source: Speakerlab

The first object of attention was the capacitors. Like any other old electronics, the electrolytic caps in speaker crossovers can go bad over time and alter the sound in often less than desirable ways. This is a subject of wide debate among speaker enthusiasts: some say replacing caps makes a substantial difference in sound, others say it does not. 

I would assume, not everyone's speakers age the same, so it's hard to say which opinion has more merit. In that same regard, you don't really know what new caps might do for an old speaker's sound until you actually put them in. My Speakerlab 7s sounded great to my ear as they sat, but they are also roughly 47 years old. Enough time has passed where it's safe to assume some type of degradation has occurred, and I was very much not alive to hear what they are "supposed" to sound like when new. And even if I was the original owner, the changes could've been so gradual that I'd have never noticed them.

Source: Speakerlab

Secondly, I wanted to look at the tweeter. In 1978, Speakerlab came out with a new variant of the model 7 called the "Super 7". It was largely the exact same speaker; same woofers, same cabinet, same crossover - except they swapped out the HD700B midrange driver for a more powerful Atlas PD-5VH (also known as the Klipsch K55) used in the Klipschorn and Speakerlab K, and also the EV T35 tweeter for a substantially larger EV T350.

That T350 is the real star of the show. Almost every post I've read about it is dripping in praise, especially when compared to it's smaller sibling. It's substantially larger magnet allows higher frequencies than the T35, despite using the same diaphragm. This results in far more crisp and smooth sounding treble... allegedly. In general, a lot of folks seem to consider the T35 a pretty "mid-tier" tweeter, which is surprising to me considering that some of the nicest sounds I've ever heard out of a speaker up to this point have come from my own T35s. Only makes me more curious...

And that's what got me to this point. Not only did I get some shiny new Dayton Audio polypropylene capacitors to swap into the crossovers, but I also managed to bag a pair of T350s for a pretty decent price. The capacitors were definitely the main priority, but I really wanted to see how the bigger tweeters sounded against the factory set while I had the cabinets open - if the hype was real or not.

Not your typical speaker removal.

So without further ado, I started cracking the cabinets open on the right on the carpet. Speakerlab had a very curious way of assembling their speakers in that they just glued everything together with RTV silicone sealant. According to them, it provided an easy way of making the cabinets airtight and adding a bit of vibration dampening while still being removable if need be. As the 1977 catalog says, "There is no mistake so big it can't be filled with RTV. No kidding. Make a cut a little too big, just glob that shit on there and... well, it's inelegant, but problem solved.

For the at home DIYers which Speakerlab catered to - this was probably fine, but it's a bit baffling seeing a company that's capable of producing their own woofers not using something like gaskets and screws to accomplish the same task as the RTV. Perhaps I'm being a little too snobbish, but holy shit this stuff is a nerve-wracking mess to remove. The tweeters and their accompanying tongue depressors were easy enough to pop out with a bit of light leverage, but the woofers were like shucking the world's largest oysters. It made a pretty sizable mess and I managed to bang the cabinets up a bit in the process, but the interior was now accessible.

A quarter for comparison's sake.

Peeling back the fiberglass lining, we find Speakerlab's own X7 three-way crossover. As far as I can tell, there isn't anything too elaborate about the design of these: though the inclusion of L-pads for both the midrange and tweeter is apparently a nice luxury. There's also a pair of Zener diodes arranged in a waveform clipper configuration to protect the tweeter from unwanted voltage spikes.

The two paralleled 8 ohm woofers are what effectively make this a 4 ohm speaker, with the rest of the drivers arranged in 8 ohm configurations. Well, that's not exactly the case with the HD700B midrange, which is paralleled with a 16 ohm power resistor in order to effectively drop it's load down to ~8 ohms. This is an interesting design choice to me because paralleling a resistor to drop driver impendence in order to match a crossover's spec seems generally frowned upon, as you're just wasting power from the amp. I'm curious as to what their rationale was behind this.

The capacitor swap was pretty straightforward, though breaking the old electrolytics free from the weird resin-like glue was more of chore than I'm willing to admit. I also gave the L-pads a generous shot of Deoxit. It's worth noting that I've moved on from using CRC QD in favor of Deoxit because QD lacks lubricant, and I found it's effects to be only temporary at best even in the short term. Deoxit is way more expensive, but so far it seems be working better with what I've used it on.

That brings us to the T350s. I knew these things were going to be substantially bigger than the T35s but in person, they are absolutely gargantuan. A seven pound tweeter - versus the roughly two pound T35. There's entire speakers that weigh less than this goddamn thing. I was crossing my fingers that they sounded as impressive as they looked. Electro-Voice's documentation over the years is all over the place, but evidently the T350's hit peak frequency response of 23,000 Hz versus the T35's 15,000 Hz. Whether or not my ears can actually pick up on that is another question entirely.

That's... not normal.

But, there's a catch. It's important to point out that these T350s are labeled as 16 ohm models, yet they both ohm out at roughly 6 and 7 ohms respectively. Those are values you'd see out of an 8 ohm driver, not one rated at 16 ohms. Something like 10 - 12 ohms would have the expectation. Admittedly, these expected values were not something I was even aware of when I made the purchase. I just saw "tested pair of T350s!" and happily whipped out my credit card. 

For all I knew, the drop in expected resistance could have been the result of a damaged voice coil - though I could just as easily have seen a larger value as well, were that the case. I couldn't really say until I actually tried the tweeters out, which opens up another possibility: if they sounded fine, perhaps the original 16 ohm diaphragm was swapped out with an 8 ohm one? This is actually not unheard of, evidently because 16 ohm T35/T350 diaphragms became very hard to find for quite a while. And if an 8 ohm fits, well - you might as well make it work, or have a very expensive paperweight.

So, I without really knowing any better, I wired them up and gave them a listen. I was fully expecting being 16 ohm drivers, that the T350s would run a little quieter than the 8 ohm T35. I even bought a pair of 16 ohm power resistors just to try the forbidden paralleling workaround. Color me surprised when not only they sounded roughly equal in volume to the T35s, they sounded great! That was how I concluded the diaphragms in these tweeters were probably replaced at some point, and thankfully - I wouldn't have any issues running them with the Speakerlab 7's existing crossover network.

What I really wanted to know though, was how the T35s stacked up, especially after the crossover recap. They actually sounded really pleasant to my ears, and the recap seemed to "lift" a kind of muddy veil that I had no idea even existed prior to the recap - it's just that the T350s still managed to sound even better. I don't even know how to describe it. The T35s did sound sharp and lively, but there was still just a kind of obvious "tint" to it that the T350s didn't have. Those things just sang, and I didn't feel like they left anything on the table. I was hooked, and that meant only one thing.

Source: Speakerlab

And that was to install them, of course! It was just a matter of figuring out how to place the super-sized T350 into the cabinet. On pre-1978 7s like mine, the tweeter was centered on the 10-inch woofer, but with the introduction of the Super 7, the tweeter was shifted right by about two inches. With the T350, it was butting right up against the midrange horn. 

I won't lie though, I'm not a big fan of how the offset tweeter looks. I get why they did it, as there's so little material between the 10-inch woofer and the top of the cabinet that it's a safer bet just moving the thing a little bit to the right to put more material between the tweeter and the woofer, but still. It just triggers my OCD. Plus, cutting an offset hole in my cabs would leave a pretty sizable gap to the left of the tweeter from the original hole that I would have to plug.

Notice how little material is left between the tweeter and the woofer holes.

I made a nice little paper template to help position the hole. Since the front of the cabinet rests on a slight lip, I first stuck the template under the front board, butting it up against the interior wall before making two horizontal marks next to the existing tweeter hole. Then I centered the template along those marks and traced it out. That way, I know I'm not going to accidentally cut into the hidden lip, which would also prevent me from inserting the tweeter along the top of the hole. I taped off the midrange horn (it's really a better idea just to remove the driver as well), peeled down the top insulation, and lined the inside of the cabinet with a trash bag. 

I still spent the better part of the next day vacuuming sawdust out of every nook and cranny in the room.

Honestly, this was a genuine hackjob that I'm not proud of. The cleanest way to go about doing this is by prying up the RTV'd front board and routing out the hole on a workbench. I couldn't get the boards out, and I learned the hard way that my router was simply too big to cover the entire hole because of it's proximity to the raised lip of the cabinet. So I had to drill perimeter holes along the top half of the tweeter hole and manually saw the pieces out before filing the edge. The cut looked like shit, but the tweeter fit and thankfully, the ugly bits were going to get covered up anyways.

Like nothing ever happened.

Keeping true to Speakerlab's mantra, I lined the edge of the hole with RTV, taking care to plug the T350's gaping screw holes to ensure an airtight fit. I reused the tongue depressors used in the original tweeter installation to cover up the remaining gaps on the top and bottom of the tweeter before sealing the edges with more RTV. I then sealed the woofer back in and let the whole thing dry for about two hours before scraping away the excess.

And one final touch: new labels. I re-created these from the ground up in Photoshop and printed them on adhesive backed vinyl. I also rechristened them "7+". They're not quite "Super", but they're definitely something a little more.

Repeat all that one more time, and...

...they're done!

I'm glad with how the finish turned out, in spite of that horrible cut job. It looks very factory, and that big chrome trimmed tweeter adds a pretty striking element to the speaker. But we're not doing this for looks; it's all about the sound, dammit! I can safely say that these speakers totally blew me away with just how ridiculously accurate they sound. It's gets thrown around a lot, but these literally sound - and feel like the band is playing right in front of you. Not a detail missed, and they're really easy to listen to - or loud enough to get the neighbors to call the cops on you, if you want.

That's probably all the work I'm going to end up doing to these Speakerlab 7s for a long time. As much as I want to replace the old scuffed and chipped veneer on the cabs, I'm anticipating moving in a few months and I really don't want to risk having all that fresh work damaged in the process. If and when I get around to it, I may also contemplate trying to mirror the front boards of both speakers as they're currently congruent and it looks a little funny with the grills off. Perhaps even drop some Atlas midranges into them while I'm at it - if I find them for a fair price and determine they're even worth it. 

But regardless, I'm extremely happy with these speakers. They're of an era and style I'm particularly fond of, and they just sound so incredibly sweet. It's way more speaker than I was expecting to ever get, and probably all I'll ever need.