Dayton RS squat tower CC

[Marzen]

If anyone has given any thought to Jon's comment on designing a squat tower center for fp usage I'd be interested in your comments. I'm looking to mate this with my Modula MTM's.
I'm having some trouble getting started as I'm not sure what driver alignment would work best given the fact the tweeter will be below ear level. I wouldn't think an mtm would be ideal given the large lobe on-center with the tweeter axis and subsequent close proximity to the ground.

Thanks,
Ward

[JonMarsh]

OK, it all comes down to size, efficiency, and bandwidth goals. If used as a true center, with low frequency duties handled by a sub, then we're only concerned with maybe 50 Hz up. Lots of possible ways to go. To do it seriously on the cheap, one could try something like a single RS225-4, with the RS150 on mids, and, say, just for some brand diversity, an H1283 for the treble.

I think when this was first discussed we were thinking more in terms of taking David Robert's WMTW center channel and converting it to a squatt CC. Now, that crossover could be applied with a little modification to the above, or one could do it keeping all the original drivers, if the baffle width in the front is maintained.

Or, we could get even wackier. If the Center would likely have to work "full range", as in my case, for a while, I'd consider dual 265HF in a sealed alignment, 8 ohm nominal in series, crossed at 300 Hz or so to the RS150 and your choice of tweeter. That would be easier to get the impedance amplifier friendly, but the sensitivity would suffer. Still, if it was back against a wall, you know, kind of Allison Acoustics style, then BSC wouldn't be an issue, and getting 86-87 dB should be a piece of cake. Then I'd go for something like I built back in the 70's; beveled lower cabinet in front, woofers loaded into florr boundary; midrange up around 2 feet, tweeter just over that in the waveguide. Oh, I didn't mention waveguide earlier, did I? Well, we'll see, that's one of my scheduled experiments, H1283 in a waveguide. Ought to be good for 2 kHz on the bottom. RS150 should be fair at 2 kHz on the top, yes?

Tweeter a little below ear level wouldn't be a serious issue with a layout like this:



You see where this is all going? Actually, have dipoles in the work using this layout, but more LF drivers. Sure wish I didn't need a day job...

[cjd]

Yes.

I just have other projects to build first (furniture and stuff, no speakers)

Because mine will be going under my screen, there is no sense in a "normal" CC layout.

My plans are tentatively RS180,RS125,Seas tweet. Not set in stone - I may consider something else as woofer (RS225 perhaps). My setup will be against the wall, and the mains require no wider than 6.5" boxes, 6" preferred, so little/no BSC is needed. IB for the bass, so 50-60Hz is sufficient.

I may also decide to trim the frames of RS150's (or RS125's) on two sides.

C

[Marzen]

I should point out some criteria on the design:
1) 20" height max
2) 8Ω nom load
3) flush to wall placement
4) 45° (total) horz dispersion w/ excellant intelligibility
5) LF not needed due to sub
*Given the height restriction you can see my dilemma. What driver allignments do I have as options??? Aside from a TM.

[Marzen]

Does a dome midrange act as suitable transition driver when used to alleviate some of the trade offs inherent with TM designs?

Jon - are you talking about the RS150S shielded version (45-3500hz)?
As for the wave guide - what benefit would I see in a cc app?
C & J - Why would either of you consider a Seas tweet for cc duty? The off axis response looks severly attenuated above 10K, what am I overlooking here?
h1283 FR graph
27TDFC FR graph
Regards,
Ward

[JonMarsh]

Huh? Compare the graphs and double check the scale. The H1283 is down about 5-6 dB at 18 kHz at 30 degrees off axis- the 27TDFC is down about 8 dB at the same point. Not surprising, because the H1283 is a 3/4" dome, while the 27TDFC is 1.08" or thereabouts. Note that the 27TDFC is measured up to 30 kHz, while the H1283 is measured up to 40 kHz.

That's not to say this isn't a free country and you can use the 27TDFC or any other tweeter you'd like. I was just talking about what I would/will do. From the bottom edge of my screen I've got about 26" to work with. Still kind of squatty.

I expect the waveguide to reduce the distortion in the 2kHz to 6 kHz area, where there's a lot of energy in music and HT, by about 10 dB. It will also control the directivity at the bottom end of the tweeter's range, where usually dome tweeters pretty much "flare" and have a lot wider dispersion than the woofer. The idea is to have as close to constant directivity through the widest range possible. Forward arc target would be 100-120 degrees total included angle.

At 45-60 degrees off axis, good results are getting the system pretty smooth to 10 kHz before the tweeter drops out. The waveguide may actually help the upper range directivity also. We'll see.

~Jon

[cjd]

Er... you know of a (dome) tweeter that doesn't drop off like that?

8ohm means either 4ohm drivers in series or single 8ohm drivers. So a simple TMW if you like, or a TM. I still believe that there is value in alleviating the M of stuff up to ~250-300Hz such that a 3-way would be beneficial.

RS150 is good maybe up to 2100Hz or so - no way to 3500. Should do well crossed in a 3-way to a waveguided 3/4" dome as Jon is contemplating. I think you can cross higher if you go 3-way. I really like the 150, but it is probably too wide for me to use, and I want to have matched drivers all around (including surrounds).

C

[Marzen]

Huh? Compare the graphs and double check the scale.

I did, I can't help if they obfuscated it & I'm eliterate :W

From the bottom edge of my screen I've got about 26" to work with. Still kind of squatty.

...the Yoda CC with Wave Force™ Technology...
-Thanks for the explanation in shirt sleeve English. The benefits sound outstanding, but that may be a tough one for me to model; not sure where to even begin to come up with a base line for horn length & Sd. I need this one to be 90% diy & 10% cut-n-paste. If you should be sitting in an airport sometime & want to write a full primer on basic design ideology...

Er... you know of a (dome) tweeter that doesn't drop off like that?

Not since I learned to read...

I still believe that there is value in alleviating the M of stuff up to ~250-300Hz such that a 3-way would be beneficial.

I've listened to lot's of 2 ways & I'd have to agree...hence my question about dome mids. I'll plug in your RS180,RS125,Seas selections and see what I can do with that.
Thanks,
Ward

[JonMarsh]

Well, the waveguide, if used, will be a modified off the shelf part from MCM. The rest should be pretty straight forward. I'm still thinking (for the HT rig) in terms of a "squatty" Sophia Klone, most likely with the H1283, though there are some Focal TC120dx2's sitting around that probably would be good, but someone I know would like me to reserve them for "higher end" stereo systems, I'm sure.

Actually, I'm even thinking about a whole new front side array- three of these guys, just the outside two may be taller. I even have some RS150-4 and RS180-4 on order to test as midranges. (higher sensitivity, which may not matter a whit, but less rear masking sans the shielding pot, which I do like). Top modules might be separable, like a Watt Puppy, so I can build them in common.

Really, just thinking out loud right now.

[Dennis H]

Actually, I'm even thinking about a whole new front side array- three of these guys, just the outside two may be taller.

You need four speakers unless you want Yoda-sized images from your center. The dark side of the force is strong with two center speakers, above and below the screen, with the mains' tweeters mid-screen high. A vertical phantom center, if you will, that will image perfectly for anyone sitting down, even if they are way off to the side, and give perfect side-to-side pans with none of the down-up-down nasties favored by the rebels.

[cjd]

Ahh Dennis, if only it were possible. I have a heat duct drywalled in immediately above my screen - no room up there.

Compromises sometimes must be made. But I agree entirely. I may do some measuring, see if I can sneak a "corner" center (similar to what I have planned for surrounds) a bit further out and have it actually be about the same distance from the listeners as I place my on-the-floor center.

C

[Dennis H]

Chris, if you really cross to the dark side and use digital EQ/crossovers, you can align the timing of the top speaker and the bottom speaker. (erecting a force field around my throat to keep Evil Twin from crushing my larynx. )

[Marzen]

Well, the waveguide, if used, will be a modified off the shelf part from MCM. The rest should be pretty straight forward.

Glad to hear that, & it would be interesting to read how you go about selecting a horn for a particular driver.

[Landroval]

The dark side of the force is strong with two center speakers, above and below the screen, with the mains' tweeters mid-screen high.

Yes, definitely dark side. Might look tempting, but in reality it deceives you and consumes all the joy from your life. How will you ever get over with the combing from the two speakers which are so so far away from each other? There might be a tiny sweet spot, but that's all. How many times have you seen the left or right channel played from two separate fullrange speakers? No, no, the only way to do this properly is to have the center behind the (acoustically transparent of cource) screen, with the tweeter on the same level with the tweeters of the mains.

[cjd]

Chris, if you really cross to the dark side and use digital EQ/crossovers, you can align the timing of the top speaker and the bottom speaker. (erecting a force field around my throat to keep Evil Twin from crushing my larynx. )

I don't want that many sound cards in my HTPC. :P Besides the fact that it would compromise the sound.

Acoustically transparent screen, except at high frequencies you mean Landroval? :P

Ahh, the compromises we must make!

C

[Dennis H]

How will you ever get over with the combing from the two speakers which are so so far away from each other?

That's a conventional wisdom straw man. How many stereo fans do you ever hear complaining about comb filtering? And that's a much more extreme situation. The top/bottom speakers are closer together, reducing the tendancy to comb, and everybody's ears are about the same height sitting down so everybody is in the vertical sweet spot. In practice two centers above/below the screen sound very good.

Acoustically transparent screens are nice in theory but suck in practice. If you use a perf screen it will moire, kill the highs and create comb filtering of its own. If you use a fabric screen, it won't be very bright. When someone makes an acoustically transparent High Power that doesn't moire and doesn't kill the sound, call me.

[cjd]

I may be in luck Dennis. I think the actual distance to ear is going to be VERY close for a ceiling mounted vs. floor-squatting center, and I can always move the floor one around some to get it right. It sits in front of the IB manifold opening so can't go snug against the wall, regardless.

C

[Landroval]

That's a conventional wisdom straw man. How many stereo fans do you ever hear complaining about comb filtering?

Not many, but thats mostly because it's _stereo_. The center channel is one channel and should be played with one speaker. If we would have separate center-top and center-bottom channels, then it might make some sense.

Think about a situation where you would have big floorstanding speakers which would have one tweeter at the top of the speaker and one at the bottom. Why dont we have more amazing TMWWMT designs then? And that's exactly what you are doing with two center speakers.

Movie theaters are doing "okay" with the acoustic transparency. I can't say I truly enjoy the sound of most movie theaters, but at least the speakers behind the screen design seem to work.

I dont know if you have seen the ClearPix2 from Screen Research, but it should do quite well with moire, acoustic transparency and brightness.

[Dennis H]

Not many, but thats mostly because it's _stereo_. The center channel is one channel and should be played with one speaker.

So you're saying two stereo speakers can't accurately reproduce a soloist standing front and center? If you concede that phantom image, why can't it work the same in the vertical plane, especially when the spacing/angle is less than half as much?

For movies, you don't really need a large vertical sweet spot. Most people don't watch movies standing up because it casts a shadow on the screen.

I dont know if you have seen the ClearPix2 from Screen Research, but it should do quite well with moire, acoustic transparency and brightness.

Way overpriced and gain=1. To cut cost, you could DIY it with some blind fabric that has the same weave but gain=1 is still too dim (for me) unless you settle for a small image or spend big bucks for a light cannon.

Have you actually heard an over/under center arrangement or do you just "know" it won't work? It's not hard to experiment with if you have some small (identical) speakers you can prop up on a stepladder or whatever. Make sure the distances from the tweeters to your ears are the same when you're sitting down.

[Landroval]

I'm not a big fan of phantom center. It works somehow if you're precisely in the sweet spot, but anywhere else it sucks. And even in the sweet spot it doesn't work as well as a real center speaker. I have to admit that you're partly right about the phantom working in both vertical and horizontal setups, but it's so far from optimal designs that I could never live with it.

I've tried to split the center into two speakers, center-left and center-right, and it never worked well. Most of the same weaknesses applies to a top and bottom setup.

As I said, you're basically having a very high speaker with tweeters at both ends of the speaker. Two separate sources for one mono channel.

I agree that with a huge screen a single top or bottom center can place the soundstage too far from the image. If the only way to fix this is top and bottom centers, then one probably should try it.

[Marzen]

Recycling the Nat P as a TMM

If I wanted to recycle the Natalie P as a TMM, what should I be concerned with? My first thought was how do I factor c2c spacing between the tweeter and the 2 identical woofers as this isn't a 2.5 way & they're used at the same crossover point? I've run some models of the original design with the drivers rearranged as a TMM and I get some pretty odd polar responses, but that may be due to the fact I'm moving the simulators mic waaaaay back from the baffle as in the listening position.
Ward

[JonMarsh]

It will be strange- moving the mic back is what you need to do, but the polar response will be very goofy with the tweeter off to one side. It might be possible to convert the design to a 2.5 with some rework and an additional inductor (for the .5 woofer), but I'd have to think about that a bit.

Now I'm thinking a waveguide tweeter and something more like a midrange driver for this project idea- say, 1800-2000 Hz crossover on the top, and ~300 Hz on the bottom. Of course, for HT, I just might want to build three identical units like this...

Maybe an RS270 on the bottom, if I want to go "cheap" and not to low, maybe an RS265HF, or even just a RS225. But given the cone modes in the RS midwoofers (at about 2.5 kHz for first major one), I'm considering other cone mids. Maybe this is just the sort of project I should turn over to Evil Twin.

[Marzen]

It will be strange- moving the mic back is what you need to do, but the polar response will be very goofy with the tweeter off to one side. It might be possible to convert the design to a 2.5 with some rework and an additional inductor (for the .5 woofer), but I'd have to think about that a bit.

Hi Jon, does it matter if you rearrange the drivers as a TMM w/ orig xo being the real question here.
I wouldn't waste any time on a 2.5 way, I was just looking for the short answer here in regard to how to handle the pair of 180's not being equidistant from the tweeter.

Now I'm thinking a waveguide tweeter and something more like a midrange driver for this project idea- say, 1800-2000 Hz crossover on the top, and ~300 Hz on the bottom. Of course, for HT, I just might want to build three identical units like this...

I've been anxiously awaiting the waveguide tweeter tests; hoping you'd post some details on you're selection criteria & methodology. But, that's a horse of another color entirely.

Maybe an RS270 on the bottom, if I want to go "cheap" and not to low, maybe an RS265HF, or even just a RS225. But given the cone modes in the RS midwoofers (at about 2.5 kHz for first major one), I'm considering other cone mids. Maybe this is just the sort of project I should turn over to Evil Twin.

(Sigh...where to start?) I started on this one as mentioned above. I wanted to stay with the RS driver family & try and retain some voice matching with the Modual MTM's but I ran into some problems with the driver combo & a friendly 8Ω load for my a/v rcvr. I even keystoned the pj so I'd have a few more inches of clearance beneath the screen to provide for a 3 way.
_So, I thought while I'm sitting on the fence waiting for the 8" shootout & tweeter waveguide tests to complete I would try & recycle my Nat P surround speaker into a cc. As far I know, I'm the only one interested in modifying an existing MTM design into a TMM cc. I'm also looking into recycling the Nat P surrounds from a point source spkr into a semi-dipole design for use as a null type surround. The latter due to my room layout & use of the surround channels for movies only.
_I think summoning the Dark Lord would be justified here. His ability to focus on the TMM target would be a benefit. Oh, and he wears a cape too.
Thanks,
Ward

[Brian Bunge]

Marzen,

Since you're basically talking about rebuilding several speakers, why not just go ahead with one of the 3-way center designs in dwaro's thread? It seems like it would fit your situation better.

[Marzen]

Hey Brian,
Here's the long explanation I probably should have posted further up:
1) I did that, at least in regard to using the different 3 way designs to help me muddle thru my own experiments with SoundEasy. Basically reverse engineer those designs & see if my results match theirs. That was an exercise to see if I could do my own 3 way design. Any of theirs would be a solid plan B. The TMM is nothing more than a desire to whip up something new from available parts while I wait on #2.
2) The Arvo incarnations...& Jon's waveguide/tweeter testing. Anxiously awaiting what comes of these. I'll be definitely be building something from these threads once the details are finalized.
__Until then, I can sit patiently on the sideline & continue redressing the Barbies I already have - the Modula MTM & Nat P. I started with the 1 cu/ft enclosures, then built the larger ported box, then the TL version, moving drivers & xo's to each new box. I'd like to measure all these now that I have the equipment to do it. There's a noob comfort level with rehashing the same core design in that it gives me a solid reference point for changes. Hence the desire to try a 2way TMM & the semi-dipole surrounds.
At the same time I'm learning to design, I'm learning what I prefer 'sound wise' as I progress. My tastes are changing. Because of that, I'm taking the same approach I use when brewing - copy an existing product you like, sample it for a while, and then tweak it so it's more to my taste. Perhaps several times before I realize what I really like.
Cheers,
Ward

[Marzen]

Well, after spending the majority of Sunday playing around with different simulated driver spacings & mic locations I discovered the TMM version doesn't work as well as the MTM layout, but it was a very close second. This was more evident with the on axis plots than off axis. I hope to get around to measuring this soon so I can compare the simulated vertical MTM to my physical one. I'll have to take a day off for this. Saturday morning I learned it's impossible to get a low noise floor with my familay at home :lol:
Ward

[Dotay]

I started with the 1 cu/ft enclosures, then built the larger ported box, then the TL version, moving drivers & xo's to each new box.

Ooooh, I'd be really interested in hearing your impressions about the differences of these designs. I'm really interested in the TL design of the Natalie P but to my knowledge no one had made it yet. Measurements would be great as well, but your listening impressions would be a great start. Which TL design did you use btw? Fat Thor?

[JonMarsh]

Well, after spending the majority of Sunday playing around with different simulated driver spacings & mic locations I discovered the TMM version doesn't work as well as the MTM layout, but it was a very close second. This was more evident with the on axis plots than off axis. I hope to get around to measuring this soon so I can compare the simulated vertical MTM to my physical one. I'll have to take a day off for this. Saturday morning I learned it's impossible to get a low noise floor with my familay at home :lol:
Ward

Sounds like you're making progess AND having fun. :T

Yeah, families can be pretty tough on the noise floor....

With a TMM setup and the basic Natalie P crossover, you have the midrange radiating point at crossover strung over quite a distance, plus you won't get the center polar repsonse synergy of the 3rd order all pass with tweeter in the middle between the drivers. Beyond that, I'm not sure about the rest of the issues, it's probably a Jedai mind control thing, you'd have to ask Evil Twin.

[Marzen]

Ooooh, I'd be really interested in hearing your impressions about the differences of these designs. I'm really interested in the TL design of the Natalie P but to my knowledge no one had made it yet. Measurements would be great as well, but your listening impressions would be a great start. Which TL design did you use btw? Fat Thor?

I used the Modula version for the TL as these are my primary L/R spkrs now. I haven't really fiddled with the Nat P's except to put them in a 1 cu/ft box for a center channel vertical mtm. The TL model was from Paul Kittinger who was working with EdL. I don't know if anyone else has ever built these. I hope to update my website this weekend. I'll get back to you on construction and listening impressions. I don't think you'll find much difference with substituting the Nat P in the TL box compared to the Modula. If you run MathCAD I can send you the data for your perusal.

Sounds like you're making progess AND having fun.

Yeah, definately both! I really like the SoundEasy v.11 update. But, it's still all junk science until I can compare measurements with my sims.
I've been sidetracked recently with researching how to tweak the Z phase angle of the LP network at mimimus to appear more friendly to an 8Ω amp.
And I think the RS180/28 will morph easily into a wall mounted semi-dipole surround. Rough models look fair with (1) RS180 & (2)RS28's.

[jdybnis]

How big is your TL? I'm in the process of building an MLTL varient of the Modula MT. Internally it is about 63L. I considered a TL but I couldn't figure out anything anywhere near that size.

[Marzen]

How big is your TL? I'm in the process of building an MLTL varient of the Modula MT. Internally it is about 63L. I considered a TL but I couldn't figure out anything anywhere near that size.

Josh,
I'll get that info up this weekend on a new thread, I believe it was around 75L. I'd be really interested in you're MT variant for a wall hung surround.

[jdybnis]

Good I'll be watching for it.

I think my MT might be a little too big for wall hung surrounds. It's a floor stander with the same dimensions as the PE cabinet except the height is 53". It puts the tweeter just above my ear level when I'm sitting (I'm 6'5").

The interesting thing I discovered playing with Martin J. King's MathCAD worksheets is that the performance of a MLTL is not any better than a Bass Reflex design. Maybe plus one or two dB on the bottom. When you make a ported box that is tall and narrow you end up with quarter wave resonances whether you want them or not. His worksheets let you optimize the port placement to minimize the midrange junk coming out of the port (and also optimize driver placement if you're not already committed to a baffle layout).

[JonMarsh]

Good I'll be watching for it.

I think my MT might be a little too big for wall hung surrounds. It's a floor stander with the same dimensions as the PE cabinet except the height is 53". It puts the tweeter just above my ear level when I'm sitting (I'm 6'5").

The interesting thing I discovered playing with Martin J. King's MathCAD worksheets is that the performance of a MLTL is not any better than a Bass Reflex design. Maybe plus one or two dB on the bottom. When you make a ported box that is tall and narrow you end up with quarter wave resonances whether you want them or not. His worksheets let you optimize the port placement to minimize the midrange junk coming out of the port (and also optimize driver placement if you're not already committed to a baffle layout).

Yeah, isn't it funny how that works out? Then the TQWT concept sometimes "pops up" as a byproduct of the overall design, like my M8ta 8" towers. Driver positioning and the port positioning just happen to fall into that "formula".

[jdybnis]

Yeah it does seem to happen like that. It is reassuring when the designs derived from simulation correspond to the designs arrived at through experience. A couple other familliar things fall out of the models too. Stuffing is best at the top end of the enclosure, behind the driver. The top of any quarter-wave resonator should be braced the most strongly, it is the highest pressure region.