HTM-12 Build - beginner level

Erich's packing is well renowned. Now I know why.

It would take an extremely unlucky impact to do damage. All contents are held securely. The expanding foam is very secure.

Some nice poly caps and an assortment of resistors and inductors.


The compression driver is a heavy beast:


While the neo magnet on woofer is surprisingly light despite the nice basket:


Up close with the raison d'etre:


A couple clamp shots. I went and picked up 4 cheap clamps from harbor freight, which are fine for these precision cut panels. It's true, you can never have enough clamps. I could have used at least 4 more, which would probably have cut my glue up time down by 80%. It's not necessary, but probably worth it if you're short on time. I probably clamped down on the panels too hard and squeezed out 90% of the glue and warped the panels a bit.


A shot of the populated circuit board. I'll spare you from the nasty soldering hatchet job underneath.


And for the last pic for the time being, I didn't realize that Erich had included short screws and that they were supposed to screw right through the standoffs, so I gerry rigged these (much too large) conduit clamps with some wood glue with the intent to cable tie them to the circuit boards, since I didn't think I had any screws on hand short enough to not go straight through the cabinet wall. I'm still debating whether I should just screw the crossover boards in by hand. It'll be a tight fit now that I've glued the baffle on.

 

Sanding down the edges. I used 150 grit and it took a really long time. I'd probably go with 120 or 100 if there's a next time.


Drywall spackling the edges of the mdf


Sanded down again and primed with Kilz


Rolling on flat gray roof paint with foam roller


For beginners like me, a couple notes. In the past, painting with brushes, if I didn't seal the mdf edges, I could see it from across the room due to how much the edges would soak up primer/paint. This is the first time I've used a foam roller. In this case, I don't know if it's the rough texture on the "fine foam" roller or the ultralight mdf or the heavy roof paint but I don't think you could tell. My poor paint technique is probably more visible than any absorption from mdf edges (I forgot, I mean, I left an edge without spackle in order to test my theory.) Just make sure the mdf is sanded flush, and you'd be hard pressed to see the edges. If you're not looking to make fine furniture, and I'm most definitely not, then I'm not even sure primer is necessary - at least with this heavy roof paint. It's very viscous, and it was sometimes hard to get the roller to roll instead of smear the paint and destroy the texture. Also, painting outdoors at night probably played a factor. Make sure you have enough light to verify that the roller is rolling at all times...

 

If I had confidence I would/could tackle more home improvement projects, I would probably spring for a compressor and spray attachments, but my wife is a realist and told me it wasn't going to happen.

Any thoughts on whether I should just go with the zip ties on the crossover board, or if I should just bite the bullet (and my tendonitis) and try to screw the crossover boards in? I'm a little hesitant about how much stress the glued wire clamps will take, but it shouldn't see too much stress after I set the speakers into place.

 

One speaker assembled. I went with zip tying the crossovers, since I only found 4 stand offs. Not sure what happened there. The zip tie method seems stable enough for its sedentary lifestyle, though.

In the listening position, I can clearly see down the ports into the insulation and wire. I might have to get some spray paint and touch that up.


One more speaker to go. The final assembly takes a bit of time, if you are unfamiliar. In particular, it was a chore to cut the denim insulation.

 

Second speaker assembled. However, I realized that I forgot to apply the gasket tape on the waveguide. I removed the screws and turned the speaker over but the waveguide refused to come out. How likely will there be an air leak if I don't resolve this issue?

 

I decided not to be lazy and do things right. It's much easier to remove the woofer than the waveguide, so I went in through that hole. The cutout for the waveguide is so precise that I still had to pound on the compression driver with my fist to get it out of there. Gasket applied and both drivers reinstalled.

All's left is to get everything wired up and dsp set up.

 

The last post was actually supposed to be sent last night. Speakers are set up, and although the dsp chain seems to have a kink that needs to be worked out, the system is playing loud and clear.

These speakers have great tone and can play loud and very clean. My system is used for music during the day. I had some apprehensions about using pro sound components in a home audio setting, but they were misplaced. To me, this sounds excellent. I've played a lot of live music, and these speakers remind me of that - clarity and dynamics of a great live performance. Let me clarify - a great sounding live performance. I EQ'd in a small q1 3db bump centered at 90db for an added kick, and there are no complaints from the speakers. Best of all, this is the first system I've had where I could kick the volume up and not want to turn it down because of the sound quality taking a nose dive, presumably due to lower distortion.

The downside is that the baby woke up and couldn't go back to sleep. Oops...

Well, the real downside is that it doesn't have the ultimate resolution 2 channel enthusiasts might crave, and imaging in my set up, which I'm choosing to optimize for tone/bass vs imaging, isn't as holographic as it could be. Speakers have tradeoffs - these are fantastic for a clean and smooth live sound.

I realize I'm still in the honeymoon phase, but it can't be helped. These are very fine speakers.

 

The imaging is excellent. Allow me to clarify and provide context. Please excuse the disaster zone below.

I am still tweaking my set up. The main problem (besides my untreated room full of hard surfaces) is that I have a tv between the speakers. When I made the imaging comments above, the TV was as you see it - the TV is well inside the beamwidth of the waveguide. After I posted those first impressions, I went around the side to take a look. You can't tell from this angle, but the TV is much farther from the wall than the speakers. I have since done what I could to push the TV as far back as I could against the wall. This, alone, has greatly improved imaging. At the same time as pushing the TV back, I also increased toe-in to a full 45 degrees. These two moves provided a wonderful improvement. Just pay attention to optimizing your setup and you will be fine. Leaving the TV firing into the speakers' dispersion pattern will destroy the imaging of any speaker.

I also have both speakers set on top of dual 10" dipole subwoofers, which vibrate to some extent. This is not a good thing. In my defense, I have them playing (I'm guessing here, I haven't measured yet) about 10-15db lower than the HTMs, so I'm not asking too much of it.

What remains are the consequences of not having a dedicated and treated room. To achieve the speaker's imaging potential, I would need to pull the speakers away from the wall. 5-6 feet+ would be the best. Not going to happen in my living room with small children running around. I think wall mounting the TV would probably also yield further improvement. If I could pull the speakers out into the room just a bit more to further reduce interference from the TV, that would also help, but at the expense of lower frequency speaker self-interference from the front wall. I would like to, one day, have a baffle wall, to see if any imaging improvements can be gained, but I consider that...unlikely. Perhaps in an alternative timeline where I don't have a family.

These are general issues that impact just about any speaker in an enclosed space.

My previous 2 channel setups had the speakers pulled out into the room by about 5 feet. You can see one of the speakers in the above photo. The LXmini/LXStudio designed by Siegfried Linkwitz has fantastic holographic imaging when I have them pulled out from every wall. In terms of dynamics and projecting a big clean sound, the HTM is in a different class. I would also say that the timbre on the HTMs is better, which is probably a result of the narrow controlled dispersion, as well as my placement very close to the wall. But the tradeoffs in these two speaker designs are completely different. I now need to place speakers close to the wall and out of the way of active small kids. The LXmini/LXStudio design doesn't work and image holographically against the wall. It also still doesn't compete in tone, timbre, and dynamics. I'm also sure that if I did pull the HTMs 5-6 feet out from the front wall, like I did with my LXmini/LXStudio, it would also greatly improve imaging. But you have to choose the solution that best fits your circumstances.

In case it's not clear, I have no regrets about building these speakers. I can't say that I've compared them directly to pro-audio solutions in the same price range in my room, but at the very least, it's somewhat unlikely that they will, in this price range, have a waveguide nearly as refined as the SEOS 15, nor will they use drivers as nice, and they will almost certainly use either molded plastic buckets for cabinets or an unbraced and undamped box. The top end of the HTM is smooth, refined, and uncolored - no harsh grain or spittiness. I'd speculate that it would take 1-2x more MSRP to get into the ballpark with a commercial product. A big reason for this is that in the commercial world, a huge portion of the BOM goes towards the cabinet and finishing details, never mind the marketing. The price has to go up tremendously before sound improvements can be justified - presentation and marketing come first. The drivers and engineering refinement are just a piece of the puzzle. DIYSG kits let those of us with different priorities absorb the cabinet and finishing costs through elbow grease. Just speculation, of course. And, I should add that I don't know how my HTM-12 experience would translate over to the 1099.

Another point I forgot to address - high end 2 channel has options like beryllium domes, ribbon tweeters, planar speakers, etc. They are generally available at a much higher price point, and offer further refinement in resolution and imaging - but they have their own set of compromises. Generally, you have to choose whether you want to pursue the high efficiency route or the small/slim route. Each has its advantages. It's pretty hard to have everything in one package, especially in the price range DIYers tend to be comfortable with.

 

If your priorities are for a clean effortless life-sized sound, these guys are a win. Midbass punch is excellent. Imaging is excellent, but more listening is in order. I've only had them set up for a day, after all. Key take away re: imaging: double check your tv is behind the plane of the speakers. They also sound great at low levels. Most of my listening is actually at lower levels when the kids are put to bed. It's just that, as others have commented, you can just keep turning them up, and they just play as loud as you tell them to play.

I think for further comments about the sound, it's probably a better bet to look at Matt's measurements and polar maps and marvel.

 

Greg, I probably overshared. You probably have more experience than I do.

I'm finding the compression driver very nice and smooth. No harshness to speak of. But my tastes are simple, and I'm not addicted to ribbon sound. IMO, ribbons sound amazing and if I were a dedicated 2 channel guy who sat in a single seat, maybe I would be more interested. However, in my experience with live sound, and though I'm still learning my tastes after these years, I find that the ribbon sound isn't necessarily encountered in the real world. For my living situation, I'm finding the HTMs to be the better solution for what I want out of this system. I played with a Q0.5 high shelf to lower the HF levels but ended up taking the filter off, for now. It's easy enough to implement, these days, should the need arise. If anything, I'm thinking I need to get my measurement mic out soon and flatten the bass out, as the placement up against the walls is slightly bass heavy for 2 channel. Movies would get 2 thumbs up, and could take more bass EQ'd in with ease.

Again, this is in relation to the HTM-12, I couldn't be sure how it would translate to the 1099.

Paul, I think they sound good at all levels, so far. Again, I'm just on day 2, and I've still got to measure room response and deal with any bass issues.

 

Here are some quick and dirty measurements of L+R channels from the MLP. The speakers are toed in 45 degrees and the MLP is equally off axis from both speakers. The speakers track very well above the transition from Schroeder. My room is asymmetrical on all 3 axes, so this is very nice. See the seos at work.

Here's the room response with both mains, two dipole bass cabs, and very old hsu research vtf-1 subwoofer firing.


1/12 octave smoothing. The speakers don't call attention to themselves; they sound natural. I'm very pleased.

 

You're welcome, hope you and others find it somewhat informative.

Next task, try to get an order for blank canvas frames approved by the CFO and line the backs with the leftover denim insulation. Hopefully that will help a bit with the upper bass dips.

 

My pleasure, thanks for making these designs available. When I first started reading Geddes' ideas over 10+ years ago, I never thought I'd be able to try them out, but thanks to diysg, it happened.

 

Quick follow up. I continue to be very pleased with these speakers. They allow me to enjoy the music. Instruments sound real. My favorite bit about the HTM-12 experience is that, after 20 years of interest in HiFi, it helped me better understand what my preferences are. I like the sound I'm hearing, and I need to petition the CFO for a pair of Flex-12s as stands for the HTM-12. Does this make sense?

 

Yes, these are keepers for me, and I am looking to continue down this DIY HT path. FWIW, I dialed in a very mild -1db first order high shelf filter at 1.4khz, and have been listening with this filter in place for the past 2 weeks. I have not been tempted to play with it and find this to be a very nice balance in my completely untreated room with a wall of windows. YMMV. I wish Matt would describe the transfer function of the HF pad on the crossover board, but this filter configuration works for me. I could also easily live with the original crossover setting, and imagine it would work extra well in a treated room or behind an AT screen.

 

I'm in the Los Angeles area.