This is posted on CF as an extension of this thread.

I change loudspeakers often. Most of the time, they've been Vifa or Focal-based DIY systems. After noticing Seas' release of the L18, I began thinking about a new design. Because most of my testing of late has been related to a custom C6 2-way design, I haven't had the time to devote to the design of an entirely new home system. Instead of waiting to begin the project from scratch, I decided to reproduce Zaph's Seas all-metal system. If it showed enough promise, I might tweak the design to suit home theater use.

The raw drivers: Focal 6KF shown for scale (and shock factor relating to the L18's massive nature)







My Measurements:

Tweeter


Woofer


The average person looking at the L18 response curve might conclude this driver is not salvageable due to the cone breakup. On the contrary, throughout it's intended operating range it's very smooth. It only takes two crossover components to drill a hole in the response right where the first peak is at 7 kHz, and Zaph describes this well in his narrative. In car audio terms, this driver should not be used in an active system without some passive components because you can't get rid of the effects of that breakup without those passive parts. This is why I've always said that many (most) times, active car systems still need some passive parts to be done right.

It took a day to build the boxes and crossovers:





Impedance and frequency response curves:





I spent much of the second day listening in stereo-only. My initial impression was that they were very articulate but insensitive and might not hold up well for Home Theater use. It turns out they're very sensitive to placement. It took me about an hour to find a sweet spot and to decide which side the tweeters should be on. I settled on having the tweeters to the inside. This resulted in a greater sense of separation and stage spread compared to the reverse. This design suffers none of the feared 'metal' sound that scares many people away from metal cones or domes. This system excels at reproducing acoustic instruments. Close-mic'd recordings were breathtaking. Zaph certainly knows what he's doing, and in stereo this is a damn impressive system. Still, this design left a bit off the table when it came to Home Theater use.

A small side explanation... people generally have a Home Theater system that doubles as their 2-channel listening setup. It's a fortunate person who has the space to have a dedicated setup for each. Since I don't yet have the space for a dedicated stereo setup, I expect my Home Theater speakers to be capable of both styles, and to do both extremely well. The requirements of each are different, but the nature of stereo reproduction in most regards is more difficult (and less forgiving) than HT. With that in mind, my designs and/or adaptations are created to suit both. That leads me to the particular adaptation for this design.

While listening to compressed Dolby Digital or DTS soundtracks, the speakers as designed sound a bit thin. It's the nature of the compressed signal. At first I was disappointed enough that I was going to put these speakers on a shelf in the basement and maybe dig them back out when I had space and time to do a dedicated stereo. But it occurred to me that an MTM version of this same system might perform rather well . It became a simple issue (as a starting point) of scaling the design to suit my needs. The internal volume was doubled (with added volume for new bracing and a larger port, etc. The L18 portion of the crossover was electrically paralleled and recalculated to add the second L18, and the D27's output would have to rise slightly to mate with the additional mid. The padding portion of the D27 crossover was modified to increase the D27's output by about 2 dB. The L18 rose approximately 4 dB. The cumulative effect in listening terms was a system that now had all the articulation of Zaph's design and now the somewhat boosted midrange response that really helps an HT application. These adjustments were done with my personal tastes and environment in mind, so others might not care for the results. This is also an ongoing project that sits in a holding pattern at the moment.

Further tweaking is intended as time permits, as is the design of a center channel using these drivers.







The top trace in this plot shows the intended results of the adaptations compared to the original design.

 

Wow this is great. I'm glad to see that you were happy with his designs and also his original setup wasn't well suited for HT use. I'm going to digest your post a little more. thanks for this write up. I hope you don't mind if i pick your brain a bit.

 

I heard these speakers, the MTM version, in my home theater and we did a bit of A/B with my Focal Kevlar MTM's.. well before we had too much beer to care anymore. They are EXTREMELY smooth and detailed and wonderfully musical.

Much like spkrboy's initial impression mine was also that they weren't to my taste for home theater. However I didn't spend NEARLY enough time with them to consider that any sort of firm opinion, just a first blush impression really. For HT I really like the forward and razor-sharp edge of my Focal Kevlars and the Seas (by design) just don't have that. My buddy there would probably tell me that what I'm missing is distortion, but even if it is I like it.

 

Not a bit. Fire away.

For anyone wondering, these can be built for about $175 in 2-way or about $275 in MTM configuration per cabinet.

 

This is the first time I've heard anyone say that a good stereo pair is not good for HT or the other way around. To me, it's either good or it's not. It shouldn't matter what it's used for. I've always designed HT to accommodate both. Although I have also always used the same speaker for C as for L and R as opposed to some kind of variant. I don't like when it sounds different than L or R.

 

The frequency response plots look wicked and the boxes will look cool when they are finished. I expect those 2-ways would work as rears or side surrounds finishing your HT setup. Are you going to detail your crossover design and release it somewhere so that others can build them too?

Besides working well, I always though Seas had some good designs for their drivers so they look good in the box. That step in the basket for the surround makes the driver look good when mounted. They have some smaller composite baskets that look equally as good.

Peter

 

Peter... I agree the metal cones look great, especially against a black finish. These are among the finest drivers I've ever worked with. The ARE the best I've worked with in this price range. The original 2-way is a little large to act as a surround, but that would be a case-by-case condition. There are a couple response issues in the MTM version that need resolved in the crossover (and possibly the cabinet design) before I can make suggestions to others, and this particular project is second in line behind my C6 project for Komoman. As it sits though, It holds its own with some very expensive systems I've heard. I hope I don't mess it up later tweaking.

Rob... that's a very contentious issue. I used to be on your side and I defended that position quite vigorously, almost to the point of physical violence . I certainly agree that tonal balance should be maintained across the front stage, but it can be highly impractical to place a third speaker in the center. Laying a L/R MTM on it's side is not a valid answer. I still believe your position should be true, but reality is almost always different than the ideal. As time has passed, I've changed sides in that argument. Consider these factors:

1. Movie soundtracks are mastered and recorded in very different types of studios than is the typical 2-channel recording (I'll defer to your expertise there). The natures of the studio playback systems are different in much the same way that Pro Sound is different from home 2-channel. Intention and environment still count for a lot.

2. Movie soundtracks are typically excessively bright. This lead to the THX specification which goes a long way toward mitigating the problem but it's not perfect and requires the end user to engage or disengage processing as necessary. The degree to which THX needs to work varies from soundtrack to soundtrack. This MTM's response is an attempt to resolve that problem at the speaker instead of in the electronics by finding a happy medium where both sound very good. I know it's not perfect, but it's far better than the 2-way was. That slightly elevated midrange and modified directivity really did wonders for soundtracks and voice intelligibility, but it's not elevated to the extent that stereo took a significant hit. In your room, YMMV.

3. Home Theater speakers are generally designed with controlled vertical directivity. It aids in voice intelligibility and in a wider 'sweet spot' for listening.

4. The horizontal dispersion characteristics of these systems are different, as a stereo, again, has that single 'sweet spot' while Home Theaters are intended to provide wider coverage. In aiming for wider coverage, you inherently give up some resolution in 2-channel reproduction at that 'sweet spot.'

5. Relating back to the horizontal dispersion issue, the typical recommendation for 2-channel stereo is roughly a 60-degree spread. For home Theater, it's typically no more than 45 degrees. To move wider creates an unnatural separation of events compared to what's seen on-screen. Conversely, you don't want stereo channels too close together, or the stage becomes too narrow.

I realize these points vary in importance from room-to-room, and this design may work well in some rooms but not others. In fact, it sounds far better in my room than it did at Komoman's house. Such room effects are the case with ALL speakers. I guess my overall point is that few stereo speakers are suited to HT, and few HT speakers are suited to stereo. It's a rare few that can do both well, and is why truly good high-end HT designs are very expensive.

Rob

 

"It's a rare few that can do both well, and is why truly good high-end HT designs are very expensive.

Rob"

very true Rob. Speakers look good. I have been going through my own HT upgrades and what a pain. I finally finished my sub boxes for the room. I just have one issue with the subs and I think its just a placement problem. Have to move em around when I get a chance and see if that helps. keep us posted on any updates with the ht stuff. I'd be interested in hearing about em.