WMTW Cener Channel Discussion Thread

[JonMarsh]

OK guys, I see there's a number of folks interested in talking about center channel's using a three way configuration with WMTW; that's a vertical MT flanked by woofers.

I've done a couple of designs like that in the past for other people, but don't have one myself- ThomasW's center channel dipole is based on that concept using a speaker patterned after the legacy whisper.

I DON'T have a project like that of my own currently in the works, as for my CRT fornt projection setup in a smallish room, I'm hoping to get by with the new MTM design using the RS180's and ScanSpeak tweeter- an expensive tweeter to optimize that layout, but probably not so bad compared with the crossover cost of a good three way.

If I WAS going to do an WMTW center, what might it look like? What does your dream WMTW center channel look like? and Why?


The only reason I think I would consider a bigger center is if I needed greater output capability for a larger room. First idea that comes to mind, since the crossover will be expensive, we want to keep the drivers at moderate cost.

Woofers:

Price king is probably the RS225 8" driver. Only if you plan to use the center below 80 Hz would a bigger driver (like the RS270) make much sense). Probably just go sealed.

Still have a soft spot for the HiVi M8a- I've used this in a number of very nice sounding speakers, and in a three way, it's relatively low peak and smooth response up to 1.8 kHz might be easier to design a crossover for.

Mighty mite- if you have limitations in front panel space, the Extremis 6 might be the ticket- lots of cone travel, but still needs a fair amount of volume if you want to go really low. No getting around Hoffman's iron law.


Midrange:

Here's where there needs to be a lot of investigation and discusion. A lot of midwoofers and cone midrange drivers simply have too much energy storage to use them above 2 kHz. This applies to the Dayton RS series, even the 5"; the smaller ones aren't markedly better than the 7", other than off axis dispersion. Maybe a reasonable compromise would be a 1.8 kHz steep slope crossover, combined with a tweeter that handles the low end gracefully.

Of course, the well endowed financially could just opt for an Accuton...

Tweeter:

Well, how much do you want to spend? You can get most of the way there with a 27TDFC SEAS, but a big Morel, or a Millennium Excel might be fun...


~Jon

[TacoD]

Seas Excel midrange and Morel Supreme/Seas Millenium tweeter. To my ears Excel is nicer then Accuton. But I do not need a center speaker, I am a stereo kind of person.

[Captain Cojo]

Wmtw

Jon,
Speaking for myself, cost is no object. I have a 61" samsung DLP, so shielding is not an issue. I have a shelf built flush to the top of the Samsung, and will be building the speaker cabinets out of quilted maple. Wide and deep works, although a dipole might be nice. Gonna need some poobah advice on my mains(DQ-10+), but realize that your time is extremely valuable, so what ever works for the majority is fine with me. I do have a large room with a vaulted ceiling, and want to end up with a "no remorse" speaker system-with all your great help. Heck, i may even send you guys some U.S.D.A. Prime tri-tips for the trouble!!

[cjd]

This will be interesting. :T

I am (already mentioned) undertaking a pile of HT oriented designs based around the Dayton RS drivers. However, I guarantee that my approach will be focused on getting 80% of the way there (or 90%, or 95% - really not sure how to quantify that) while focusing on keeping cost in a little more reasonable range all around. That includes crossover parts, of course. I am gunning, in part, for the Audax HT package that so many folks like. Besides that, my HT has some interesting space limitations, so designing a flexible package will be important.

Right now I have a few ideas rolling around. In my happy little world where ears are only average, I can't justify even the cost of the Scan tweeter being used in the Modula MTM. I really like the sound of the 27TDFC but the size of the face plate means a taller CC would be needed. I may just live with that. The Morel MTD-39 has my eye except that it's not shielded - not important for me at all, but I can't say that everyone will be using FP. So, I'm looking still.

Where space is not a premium I'm looking at RS225's or a single RS270 plus TM with RS150 and 27TDFC. CC, RS225's, RS150, 27TDFC. Surrounds have me thinking still. One crazy idea is a TMTWW using RS180's or even RS150's as the W's (top and bottom), tweeter on either end, mid in the middle facing the listener. Rears not sure at all yet but thinking similar to the surrounds but TM on the face, W's on the sides.

Scaled back in size it's looking like tweeter/RS125/RS180's TMWW and WTMW-CC, again not sure but thinking RS150/RS125 in a similar WTMTW... as above.

The MTMs I have now would drop in, and I'll probably do simple TM adaptations. I may do my own MTM with the RS180 also.

Jon's approach looks like it will be reaching for that 110%. Spare no expense to achieve the ultimate. Which is why I'm a little surprised that such a topology compromise such as a simple "on it's side" MTM for a CC is even getting design time.

At least I'll have something left to shoot for down the road. 8)

C

[Brian Bunge]

I personally would be interested in a 3-way using the 27TDFC, RS150 or 180, and dual RS225's in a sealed enclosure. I may be doing like Jon and building my center into an entertainment center/wall unit so sealed would definitely be the way for me to go. Also, I just built a center for someone that was 28"W x 11.5"H and that would work fine for me so I don't think I necessarily need a small faceplate tweeter.

[cjd]

I personally would be interested in a 3-way using the 27TDFC, RS150 or 180, and dual RS225's in a sealed enclosure. I may be doing like Jon and building my center into an entertainment center/wall unit so sealed would definitely be the way for me to go. Also, I just built a center for someone that was 28"W x 11.5"H and that would work fine for me so I don't think I necessarily need a small faceplate tweeter.

24x11 is a nice comfortable fit for a TDFC and RS125 stacked. I'm having some concerns about doing this without actually building though - I had to significantly tweak the high pass circuit on the mid to get things acceptable going from full baffle step integrated to no baffle step... so any in-betweens I just don't know. But I'm doing this using FRD tools and PE's measurements (fairly trustworthy - same process I did with my MTMs and subsequently measured). Of course, negating baffle step tends to add series resistance, which makes the box want to go bigger...

11.5" height would just fit an RS150/27TDFC. Those would slide in nicely with a pair of RS225's. I think the RS180 might have some trouble keeping up with the 225's - the RS150 does. The question still is, how much (if any) BSC. In this case, the 225's will need to be cut to allow the TM to keep up if there is none - not ideal at all. I already have a tentative crossover topology for a TMWW using those drivers, though it would take some tweaking to get it right for a CC.

Brian, how much depth do you have to work with? Of course, I'm still cutting my teeth on this crossover thing, so none of this blurb probably really matters. Just happen to be in the process and piggybacking Jon's efforts (hope ya don't mind Jon! if you do, I'll just watch.)

[Stevepaul]

Dome mids make sense for center channels. The Morel 2" mid from 800hz avoids the necessity of running 8" woofers into their 'ugly' zone....and the 'neo' Morel MDT41 tweeter brought in around 4K would meet the center to center spacing at xover point (3.5") while staying about 1/2 octave away from the 2" mids rolloff. Both Morel mid and tweet have the power handling and sensitivity to run with the RS225's......and they make the enclosure construction simple.

I would think a dose of Jon's steep slope xovers at 800hz would be required. The 4K xover point would probably be OK with a standard 4th order LR...but, I ain't the xover guru!

The only problem with the addition of the Dome mid is...if you don't have it in your "Main" speakers, it may cause a tonal problem between the CC and the mains.

Just my 2 cents....
Steve

[Steve Goff]

I've been thinking for some time that a WMTW is preferable for a center channel. I don't much care for dome mids in a three-way center channel, since I'd prefer to cross the midrange in lower than a domed mid allows. It is hard to find a 5 or 6 inch midrange/woofer that would work well in this situation, but that is what I'd porefer, even if it is an expensive driver like the SEAS Excel 5 inch metal cone drivers.

[Brian Bunge]

Well, if I build this entertainment center/wall unit, it'll have to house my RPTV, so I'd basically have 2' of depth to work with. Center channel height could be whatever it needs to be as I'd probably do something similar to what Pete Mazz is talking about doing (center in soffit, angled down toward the listening position). So the center "enclosure" would be part of the unit. Of course, I haven't even started building this thing yet, but it may be the way I end up going.

Also, my wife just started taking stained glass classes so I might even incorporate that into doors on the sides, etc. and the cabinet would be built out of cherry plywood with solid cherry trim. That is, if I actually ever get around to doing this!

[cjd]

Brian: will the mains be built-in? Are you building those too, or just a CC? It sounds like you'll be best served by something somewhat tailored to your situation. I think it would also need no baffle step at all from the sound of things. And RS225/RS170 or RS150, 27TDFC or whatever else, absolutely do-able. I like the RS150 a lot for midrange - it's naturally nice and smooth, and the sound is just superb. Despite Jon's probable misgivings about my choice in crossover point. I also have some tentative crossover layouts already. Including some where I've been messing with those crazy elliptic-ish filter topologies.

I've been busy messing with cabinet ideas and sketching out crossovers. :B

C

[Brian Bunge]

Chris,

Yes, I will be building the mains, but no, they won't be built-in. I love building large floor-standing cabinets too much to do that! I still want to go with an MTMWW design using dual RS 10's (270's?) for the W's.

I'm starting to learn my way around LspCAD a bit, but don't have my measurement setup working properly nor have I had time to figure out the BDS software yet.

[cjd]

Ahh yes... hence the need for an efficient tweeter! I remember now.

In theory, a TMWW (27TDFC/RS150/RS225x2) hits 90-91dB efficiency. You may need active to match the RS270's to an MTM still. Sounds like fun!

[Brian Bunge]

Chris,

If you have anything worked up for that 3-way center please feel free to share!

[cjd]

It will be immediately obvious that I have a very different approach to this than Jon. At this point anyhow.

This is for a pair of RS180's, a RS125, and a 27TDFC. I haven't tweaked a CC with bigger woofers/drivers yet, but this may give you an idea of what's out there, what may be coming, and certainly give room for feedback and pointing out where I've gone wrong.

At the moment, my big issue is impedance. Not very amp friendly. It's less flat and less smooth than I would like. I think that a lot of the reason for that is the efficiency issues with using a single RS125 and the need for excessive overlap of the woofers and tweeter through the middle. It dips to about 2.9ohms as well.

Box volume should be about 30-35L sealed, for an F3 of 67Hz, F6 of 56Hz or so. Assuming the walls are covered. Separate sealed enclosure for the mid, target 3L or so. You could port this at 80L, tuned to 32Hz. F3 of 29.5Hz.

This is run using data I have on hand and a Hilbert transform run on the drivers. There is NO BSC, this is raw response (you may note a rising response on the tail end still). This is intended to be pretty much fully built-in. I do have versions with full baffle step (based on sims). In-between is where things get hairy using the simulations due to phase.

I used resistance values from the Jantzen 15ga air-core inductors at PE for the woofer circuit here, 18ga elsewhere. To negate the bump on the bottom use 18ga all around. 30dB reverse nulls, if that matters much.

You may note immediately that there is no zobel on the woofers - I found it was unnecessary - these drivers are quite well behaved through the range in which they are used.




It is possible to remove the bump on the top end if that is desired, but it takes a few value tweaks and hurts off-axis response. Having heard this tweeter with and without correction I'm not sure it matters - it's smooth enough without.

At this point I consider myself to have just about everything to learn still. Though I've built some speakers that sound quite good (and measure pretty good too).

Have at it!

C

[ss396]

my .02 would like to see a speaker with better drivers to go beyond the performance of the adire LCC. i want to build this speaker to match up with my arial 10 T's which have a 5 inch focal kevlar midrange.

[JonMarsh]

This will be interesting. :T


Where space is not a premium I'm looking at RS225's or a single RS270 plus TM with RS150 and 27TDFC. CC, RS225's, RS150, 27TDFC. Surrounds have me thinking still. One crazy idea is a TMTWW using RS180's or even RS150's as the W's (top and bottom), tweeter on either end, mid in the middle facing the listener. Rears not sure at all yet but thinking similar to the surrounds but TM on the face, W's on the sides.

Scaled back in size it's looking like tweeter/RS125/RS180's TMWW and WTMW-CC, again not sure but thinking RS150/RS125 in a similar WTMTW... as above.

The MTMs I have now would drop in, and I'll probably do simple TM adaptations. I may do my own MTM with the RS180 also.

Jon's approach looks like it will be reaching for that 110%. Spare no expense to achieve the ultimate. Which is why I'm a little surprised that such a topology compromise such as a simple "on it's side" MTM for a CC is even getting design time.

At least I'll have something left to shoot for down the road. 8)

C

I understand your feelings about that. What's driving the attempt at a simpler MTM center is specific requirements at a friends for CT's for two systems (one in living room, one in bedroom), and my own situation, where I'm splitting HT and two chanel audio, and believe I can meet the HT requirements with a simpler set- full three ways are considerably more expensive and time consuming to design and build. If I had a system like ThomasW's or many others, for whom the HT was also the main two channel listening environment, then I'd probably want to step up to the plate that way. I've done a few WMTW designs for others, generally based just on what available drivers were convenient (for example, in one case, dual Eton 8-800 woofers, MB Quart 2" dome mid, and MB Quart tweeter).

The critical point for a center channel, I believe, is having good overall power response and off axis uniformity; this is more demanding than for the mains.

I could imagine doing a mini-Arvo Part as a CT, if I had the room, but how do you move a dipole speaker out from the wall sufficiently in a FPTV setup? A more practical setup might be two RS225 or two RS270, flanking a midrange and tweeter of one's choice- could be RS180, but I think I'd go with a Peerless HDS, for the addtional efficiency (about 2 dB) I've measured for the similarly rated drivers. So, perhaps an 850467 for the 7" midwoofer, any number of tweeter possibilities based on budget and taste, from 27TDFC to Millennium Excel or SS98000, and dual RS225? This might mate well with the ideas being kicked around for my high efficiency three way. A bit smaller, not the same bass extension, but likely to be similar tonally...

Your design looks interesting - I find even in a two way MTM the paralleled midwoofers present an impedance problem, because the RDC of the drivers is low, and making a three way with two woofers and a midwoofer makes it even more difficult. In the Arvo type three way I series the upper woofers, becuase I don't need the sensitivity. For cost reasons, as well as power handling, moving the LF crossover lower isn't so attractive, is it?

Do you think you'll build this up to try out?

~Jon

[cjd]

I'm not sure yet which direction I may go. I actually have room for a bigger CC but have size issues on mains - a 6" wide cabinet is ideal above 2 feet. Then too, it messes with baffle step in a big way. So, I'm pondering. But I think this may actually be a fairly ideal rig. I have TMWW towers with this driver combo that is modeling out almost too well. We'll see. I'm back to having "house" projects to do first, along with a looming "end of work" deadline with no new contract on the horizon yet.

I think before I go down this road I have some amp projects to look into. I'll probably be building an amp for the HT. Low impedance won't be an issue if I go this route - in fact, if it works it will pave the way for me to go with a 2ohm rig for more serious listening.

Who knows.

C

[Patrick Sun]

This thread brings back memories of 2002 for me.

[JonMarsh]

Yeah, Pat, I remember your projects from back then....

[Patrick Sun]

This thread had made to want to fiddle around with the XO a little bit, though...