A new surround TM - completing the HT

[cjd]

Hopefully this works out.

The intention is to partially mount these into the wall or ceiling as side or rear surrounds. I've not yet done measurements, just got the first box done. I have to mount well above ear level in my room even for the sides, so this is an attempt at managing directivity and dispersion.



RS180-4 and 27TDFC

Could be a glorious failure too.

C

[ch83575]

I have always been interested in how designs like this function. In your design, is the woofer oriented to be on the listening axis, or is the listener mildly off axis for the tweeter and way off axis for the woofer? I guess I cant tell if these get mounted: vertically with woofer up, vertically with woofer down, horizontal with woofer toward listener, or horizontal with woofer away from listener.

I am sure they will end up sounding great! I have heard commercial 5.1 setups with similar designs for the rears that sounded quite nice, so I expect yours to sound even better (but no pressure or anything :W ).

-Chad

[cjd]

Woofer toward the listener. Tweeter is off-axis somewhat, but is also expected to be near the ceiling boundary. It can also be ceiling mounted with the woofer toward the listener. Or wall mounted as a sideways TM I suppose, woofer toward the listener.

Proper surround setup (I'll be going 7.1) means the listener should essentially be on the listening axis. Top end will likely have a rise directly on-axis with the tweeter to vaguely combat changed SPL for the listener further away and the off-axis arrangement (it may not work this way... some experimentation will be required on my part).

As I said, this may be a glorious failure.

[---k---]

Interesting. Looking forward to hearing how you think it compares to a more traditional layout. How you take your measurements is going to be real interesting.

[PoorboyMike]

How you take your measurements is going to be real interesting.

It's a good thing he enjoys taking measurements so much isn't it? 8O

Looks like a cool project. :T

[cjd]

It's a good thing he enjoys taking measurements so much

:crazy: :gah:

[stgdz]

I will go ahead and ask the stupid question.

Why not MTM and make a dipole surround out of it?

[cjd]

Why completely undermine the intent of a surround track with a dipole MTM?

Surround encoding is very specifically set up - for best results, you want direct monopole radiation in all positions.

[stgdz]

Why completely undermine the intent of a surround track with a dipole MTM?

Surround encoding is very specifically set up - for best results, you want direct monopole radiation in all positions.

Well I figured I would ask it as many people seem to want a dipole surround setup. You could just angle the other side where the speaker terminals are and add a woofer.

THX specifies that the sides be bipole surround.
http://www.thx.com/home/setup/display.html


like you said in your first post could be a a glorious failure :W with the worst part of it being that people spent some extra money at PE and the best part is that people may now have a dipole surround to play around with.

[cjd]

Bipole is very very different from dipole, so they're not comparable. You seem perhaps confused on the subject since you point at a THX spec recommending bipole, then say I should be making a dipole...

If I'd made dipole I'd have a nice big null at the seating position - that's the intent, to be sure. It sorta diffuses the directionality. But it also makes any spatial cues that exist in the side channels worth far less, so you gain some atmospheric sense but lose positioning and directivity. They're usually monopole tweeter to try to gain some of this back. However, they're a holdover from the early home surround encoding where rear channel was pretty much all mono anyhow, so you had to fake some sense of spaciousness.

Bipole is, I believe, an attempt at solving the "surround really should have multiple side channels but you only have one in the home" problem - but the sound is intended to be heard largely as direct radiation. The second ("bipole") mid-woofer is usually opposite a side with both mid and tweeter, which are direct radiators, thus the bipole tries to add some sense of ambience or space. Small room and in-walls? Nowhere for this to fire. In my room I could put it firing to the back of the room but that'd be an exercise in silliness (and certainly useless for the rear surrounds). That extra space is provided by having 6 or 7 channels - the rear surrounds play a similar role to a bipole side-surround in a 5.1 channel setup.

A well encoded surround track still puts the best results in the hand of a monopole direct radiator. Most suggest aiming it over the listener's head - note that this design will do this - I could have simply done a trapezoid shape and aimed both woofer and tweeter slightly down, but I have some vague hope that I'll be able to manage the off-axis behavior to a more equal response from seat-to-seat - no seat will ever get the full range out of the tweeter (see off-axis beyond 30 degrees, unless it's a tiny little dome or something...) - however, if I'd aimed the tweeter down, seats near the opposite side would get a much more on-axis to the tweeter experience...

So, if you're still working with old Pro-Logic gear, you probably want a dipole surround. Otherwise, you don't.

C

[---k---]

Edit: CJD and I were typing at the same time. But yeah, what he said. But I think I continued the typical market confusion of calling a bipole a dipole.

Dipole is/was a compromise for a time before their was Dolby Digital with descrete surround sound channels and for systems with too few of speakers and poor placement. The prefered method is like CJD said, to have direct monopole radiation in all positions. With 7.1 we're getting very close to this. And, just recently with the annoucement of Dobly Digital DSX and Audessy implement new "wide" and "height" speakers, we're even closer to this.

Probably shouldn't polute CJD's thread with a theoritical discussion of dipole surrounds. There are already enough of them at places like AVS. (In fact, about 1/2 way through "The Offical Audessy Thread" you can find a discussion about it with the CTO and founder of Audessy.)

[BeerParty]

Hopefully this works out.
<snip>
Could be a glorious failure too.

Either way, we end up with a win - we learn something from the people that are willing to try. You either get a cool DIY surround speaker or a funny looking box.

I am subscribed, and anxious to 'hear' your results...

[ibilisi]

I'll be keeping my eye out as well as I've been looking for a surround to pair with my dayton/seas front three. My surrounds will also likely have to be ceiling mounted, or close.

CJD, any thoughts on how these may work in the IIz system as front-height channels? Recent blurb in Sound & Vision suggested 7.1, using 5.1 + 2 height provided more "impact" in comparison to 7.1 +0 height. Marketing talk? Quite possibly.

Anyway, keep us updated :T

[jkrueger]

These would be easy to get approval from "the boss" for.

[cjd]

Still sitting on my desk awaiting freedom from yard work and house maintenance and such...

[Dennis H]

I think THX is still recommending dipole side surrounds with the null aimed at the listener. Basically trying to do with one speaker what a theater does with multiple speakers located along the side wall. But nobody listens to what THX has to say anymore.

[seattle_ice]

If these sound decent, could be a problem solver for my surrounds also. The seatting is too close to one of the side walls to have the speakers low. They have to mounted around 8' from the floor, against the bottom of the soffit.

[cjd]

I had a hunch that they'd turn out to be handy for more people than just me.

Now, if I can stop making my yard so I hate how it looks, but my neighbors stop being top rate jerks, I might find some time to measure and move forward!

[lexiphanic]

But nobody listens to what THX has to say anymore.

Probably a good thing.

[BeerParty]

Now, if I can stop making my yard so I hate how it looks, but my neighbors stop being top rate jerks...

I want to know how to do that! Can you post detailed instructions? And pictures? :roll:

[cjd]

Parts ordered.

I had stuff on hand to give an early variant a listen and give me a little proof that this was going to work.

They need to be at least 10 degrees off-axis for best results, so above the head - intended location is near (~8-12" down) the ceiling so that should almost always be the case. Tweeter polarity has to swap as you move closer to on-axis with it, and as you get into 15 degree and less vertically off-axis the tweeter level starts to go up also.

Hopefully the final version sounds better - it should, but... never know till it's all done.

[Txgrizzly]

very cool CJD, your prototype looks like something i built to house some speakers in a old 1970's Grand Torino station wagon back in the early 80's... i can almost guarantee that yours will sound a lot better than mine... then again the speakers were hooked to an old 8-track player at the time

[cjd]

I have crossover parts!

Unfortunately, PE decided to ship me a 50' roll of 10ga wire instead of a 100' roll of 14ga! Not sure if I'll have enough wire on hand to finish hook-up.

Whee!

[---k---]

That will suck if you run out of wire. But, hopefully they let you keep the 10ga?

[cjd]

Got two mounted up in the walls and one propped up behind me (I'll be ceiling mounting the two rears at a later date but that was just too much work for me today)

Got a movie tonight! We'll see how it goes.

[mackintire]

SO... what's the verdict?

[cjd]

They work. Not sure on how well yet - need to snag a movie with good use of surround and watch it, but before that I actually need to get out the SPL meter and balance output levels, not just by ear. I was out of town this past weekend (went up to see "Comedy of Errors" - superb performance) so if the usual Tuesday movie doesn't use surround it'll probably be this weekend before I get some time.

So far I'm not sure if they're too rolled off on the top end for my seating position or not - perhaps I should not have wall-mounted and should have ceiling mounted even the side surrounds, but that would run into the on-tweeter-axis null for two of the 3 seats... For folks with a little more space I think this won't be a problem whatsoever (nor will it be for me for the rears).

[fbov]

I find Master and Commander a great source of varying surround fields. The in-ship scenes are obvious candidates for subtle effects - creaks and groans that put you in the hold among the sailors. The initial battle scene (from the fog bank) is great for louder action, from the distance canon reports to the grape shot tearing through the ship, first in front, then beside, then behind. Close action canon shots really test LFE....

Plus I've read all 21.5 of O'Brian's Aubrey/Maturin books and generally like Russell Crowe's work (I hear they're working on Reverse of the Medal).

My other surround test source are SACDs, since it's easier to pin down the timbre of musical instruments than splintering wood. By the way, I'm finding I like the surround effect better with a simple omni tower, a la Linkwitz Pluto's than direct radiators (RB1's). It's also likely that YMMV.

HAve fun,
Frank

[cjd]

These are somewhere between omni and direct - crossover integration was NOT designed for on-tweeter-axis but rather, for off-axis (near-ceiling mounted in a space as small as mine puts one of these directly above two of the three seats in the house). I also tried to balance direct radiation at a longer distance such that SPL might be more even in any given seat.

To do SACD testing I'd have to haul the SACD player down, and I only have 3-channel stuff anyhow. I don't have Master and Commander either. But I do have some DVD's to use.

[BeerParty]

Any chance you could post a picture of these mounted on the wall? I'd like to see how they are positioned w/respect to the seating locations.

[Dave Bullet]

I like the compact design. How would these fare with a chapel / pitched ceiling? I suppose that would be too room specific to comment on?

[cjd]

Some impressions

They're subtle - not at all obvious, like my previous setup (which was not, to be truthful, all that ideally situated). The movie did not make particular use of surround but here and there there were little details.

I still need to watch something like one of Pixar's pieces where there is very specific use of surround.

Pitched ceiling I am sure they would do well enough - the design is a set of compromises in a very different direction from normal, so it's hard to be sure.

More impressions later.

Working on a formal webpage for the HT speakers.

[Brian Bunge]

Yes, we need pics of them mounted! I am building new speakers right now but have not nailed down what I'm doing for surrounds just yet. I'm also moving soon and will have a room with 8' ceilings and will have to mount surrounds on the back wall above the sofa. So something like this with the tweeter and/or woofer firing upwards might work well for me.

[cjd]

I'll get some pics. Should have the web-page up this weekend - if I don't, well... it's me. :P

[aduljr]

oh man these may just be perfect for my read and side needs. Sofa is up against the wall and I have no real other options for surrounds unless they are tiny.

[cjd]

*giggle*

:B

(testing surround, but I turned it up a bit... my wife came down to let me know I was shaking the whole house with The Incredibles... back to a couple other films to test surround more - nominal SPL is ~82dB but not quite sure where peaks are)

[cjd]

Mounted into the wall.



They seem to work quite well - subtle most times but they blend well with everything else - balance is quite good with me sitting quite a bit closer to one than the other. I watched most of the second half of The Return of the King - superb use of surround in this film.

The IB sub continues to elicit grins that make my face ache. It's just there, and then it's gone - no overhang, no ringing in the room.

[JonMarsh]

Yeah, IB's are pretty nice- makes anything in a box (unless it's a well damped LT) sound pretty "obvious" - "Hey, I'm a subwoofer!!"

[Brian Bunge]

Chris,

Those look great! Are you using them this way for both side and rear surrounds?

[cjd]

I will be ceiling mounting these for the rear surrounds - there's an 18" deep "shelf" behind/above the seats, so I'll still be off-axis on the tweeter enough.

[cjd]

Since I am having trouble finding the main in-wall schematics (must be on a different computer) I haven't finished yet - however, I thought it might be interesting to post up some images relating to this.

So here we have measurements from on-axis to about 45 degrees off-axis below the speaker (1/6 octave smoothing on the combined response) - you'll notice that there is fuzzy null present on-axis around the crossover point that disappears as you move off-axis - probably nearly impossible to avoid this while keeping the vertical TM arrangement - it probably IS avoidable if you instead horizontally mount surrounds such that the vertical off-axis is smooth and it's the horizontal off-axis that runs into these issues - for surround duty, horizontal positioning is probably quite fixed (for rooms like Ryan's I do not think this holds true, so his MTW's are better suited.) I'd probably design a nice 3-way with horizontally mounted TM were I to do this again - different driver selection is available now also - kinda wish I could start over, but... why. It works perfectly in my room.

It should be noted that on-axis response is nominally flat if you swap the tweeter polarity.

I tried to keep the same gate on all these, and these are not IB measurements - there is a "ceiling" about 12" above, which accounts in part for some of the less than ideal measurements. I have a whole pile of data but as these represent what you're more likely to encounter I decided to publish this set.

On-axis











Impedance is nothing surprising.

[cjd]

Nothing too fancy in the crossover either.

Dayton RS180-4 and Seas 27TDFC



Box design (assuming exact 3/4" material - my box is actually slightly less as I used 18mm birch ply)

[AlanH]

Hi Chris,

These look great for surround duty and would fit into my space perfectly. I love the idea of having them up on the wall and out of the way. Plus I already have two TDFCs and two RS180s sitting around!

I might have missed it, but have you posted a schematic with the box dimensions? How sensitive will these be to placement?

Thanks!

[cjd]

Note that this is the RS180-4 and NOT the RS180S-8.

Reflection interaction will change with placement - IMO this is a design that tries to make do with a huge set of compromises and a small amount of flexibility to try to smooth over the unknowns. What I'm trying to say is, I think they'll be consistently not-perfect no matter where you place them, and that's by design.

[AlanH]

Note that this is the RS180-4 and NOT the RS180S-8.

Oops! Thanks for pointing that out! I totally missed it. Okay, so I have the TDFCs and I'll have to buy a couple of the 4ohm Daytons.

Reflection interaction will change with placement - IMO this is a design that tries to make do with a huge set of compromises and a small amount of flexibility to try to smooth over the unknowns. What I'm trying to say is, I think they'll be consistently not-perfect no matter where you place them, and that's by design.

'Consistently not-perfect' sounds a lot better to me than perfectly inconsistent, which is what I feel I get when I try to wedge a regular TM box speaker into the corner of the room to serve as a surround. 8O