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Surround Speaker Design for a Small Home Theater - Page 2

post #31 of 99
"How great a problem is this "coloration" in the surround channels and how audible/distracting is this likely to be.

Would a different speaker choice/configuration, such as dome tweeters or dipoles offer a better off-axis frequency response yet still allow for Time-Intensity Trading?"

that is specifically what constant directivity "waveguides" are designed to do--provide similar spectral content off axis as on axis. for a normal setup, where you are moving a little off axis to the side for a speaker in the upright position, the response off axis is pretty much the same as on axis albeit at a slightly reduced level. the on axis sound from the opposite speaker is arriving at a slightly reduced level too simply because it is further away. as a result, you have a match and the whole time/intensity thing works. when you turn the speakers sideways, that whole mechanism gets chucked out the window.
post #32 of 99
Even if you were to just rotate the waveguide, you'd still mess up the directivity - not to mention the crossover.
post #33 of 99
Quote:
Originally Posted by mhutchins View Post

The main problem I see with the above approach, is that the intensity falloff, as we go further off-axis, is quite frequency dependent (I am very new to waveguide speakers and thus have a very limited experience in this realm). Therefore, the near-side speaker, which is 20 or more degrees off axis to the listener, will have a gradual downward slope to the upper frequencies, whereas the far-side speaker will have a flat frequency response.

How great a problem is this "coloration" in the surround channels and how audible/distracting is this likely to be.

Would a different speaker choice/configuration, such as dome tweeters or dipoles offer a better off-axis frequency response yet still allow for Time-Intensity Trading?

I believe that with more and more discreet sound channels, sound engineers are moving away from broad/diffuse surround mixes to a surround sound stage with pinpoint localization and pans of surround sounds. Therefore, I want a set of surround speakers that can not only accomplish this feat, but do so in my little theater! biggrin.gif
Am I headed in the right direction or have I gotten lost in a blind canyon......

Mike
Dome tweeters will do the same thing but there will also be a discontinuity in the crossover region, because dome tweeters have very wide dispersion (approaching omni) at the bottom of their range while a woofer's dispersion will be narrowing ("beaming") before handing off to the tweeter. So things get whacky in the midrange off axis too. What makes time-intensity trading work at all is that the off-axis FR is smooth, if not perfectly flat and level.

edit: LTD02 is on the case, listen to him cool.gif
post #34 of 99
mhutchins, dunno what your budget is but a pro audio coax will have the best directivity control through a range of angles.

The B&C 8" are good and are used by Tom Danley and Mark Seaton, though I'm not sure which ones.

The bigger the better, though, for CD down to a lower freq.
post #35 of 99
Thread Starter 
Quote:
Originally Posted by LTD02 View Post

that is specifically what constant directivity "waveguides" are designed to do--provide similar spectral content off axis as on axis.

Now I am confused - all of the frequency response graphs I have seen show a distinct high frequency rolloff as you move further off axis. Many of these speakers are down 8-12 dB at 16-20 kHz at 40-60 degrees off axis yet at 1000 Hz and below there is no SPL loss. Clearly this is not linear response. Is it that I just don't have a broad enough experience to know that this is this still better than most other designs?

Quote:
Originally Posted by LTD02 View Post

for a normal setup, where you are moving a little off axis to the side for a speaker in the upright position, the response off axis is pretty much the same as on axis albeit at a slightly reduced level. the on axis sound from the opposite speaker is arriving at a slightly reduced level too simply because it is further away. as a result, you have a match and the whole time/intensity thing works. when you turn the speakers sideways, that whole mechanism gets chucked out the window.

Again I am confused - in a post above I thought we agreed that for my single row of seating we were attempting to perform Time-Intensity Trading in the vertical axis over a fairly narrow horizontal spread. If so, why does everything change so drastically when I lay a speaker on its side yet none of this occurs when the speaker is upright? Must I be concerned with what happens 30 degrees in front or behind my seating position (any more than 30 degrees above and below axis for my front speakers)?

I understand there will be lobing/interference as we move horizontally with horizontally aligned speakers, but is this any different from the vertical lobing encountered with vertically aligned drivers??

I don't mean to be argumentative, I just really want to understand these fundamental concepts. I really appreciate all of the instruction I receive.

Thanks again,
Mike
post #36 of 99
Thread Starter 
Quote:
Originally Posted by noah katz View Post

mhutchins, dunno what your budget is but a pro audio coax will have the best directivity control through a range of angles.

The B&C 8" are good and are used by Tom Danley and Mark Seaton, though I'm not sure which ones.

The bigger the better, though, for CD down to a lower freq.

WAF is very cost sensitive in my household, so I have a self imposed limit of ~$200 per speaker excluding the enclosure. PE has two B&C pro coax drivers within my budget the 8CX21 and the 6FHX51

Would these work well for my application??
post #37 of 99
I can vouch for the 8CX21; I have 8 (11.1 system).

Note that you need XO's, and the B&C XO1's are $62 ea.

I got mine at Prousoundservice.com; $160 for 8CX21 and $68 for the XO.

If you go that route plan ahead because it seems they have to order them from Italy.
post #38 of 99
Quote:
Originally Posted by mhutchins View Post

The main problem I see with the above approach, is that the intensity falloff, as we go further off-axis, is quite frequency dependent (I am very new to waveguide speakers and thus have a very limited experience in this realm). Therefore, the near-side speaker, which is 20 or more degrees off axis to the listener, will have a gradual downward slope to the upper frequencies, whereas the far-side speaker will have a flat frequency response.

How great a problem is this "coloration" in the surround channels and how audible/distracting is this likely to be.

I run my theater like this (surrounds above and slightly behind first row) pointed at the opposite chair.

Personally, I prefer having this frequency dependent falloff you are concerned about. Nothing localizes the surround speaker worse than hearing the high frequency sounds coming straight at you. I prefer to be able to localize that off camera door knock, or bullet whizzing onto the screen, from "somewhere behind me on the right" I don't want to be able to localize it as "three feet back and four feet up on the right." If that makes sense.

Not saying that there are no better options, but if you're looking for a decent way to locate your surrounds in a WAF friendly way, mounting them high and pointing them across to the far side of the room is a good option.

-Suntan
post #39 of 99
Quote:
Originally Posted by mhutchins View Post

And this is what I am considering:




The enclosure face is 45 degrees from both vertical and horizontal, and the side panels are angled outward 30 degrees to increase the internal volume of the enclosure.

The acoustic discussion seems well underway, and it looks like you are now leaning toward a standard box. BUT, if you decide to proceed with a corner design like this, I thought I would make a few suggestions:
  1. Don't angle the side panels unless you have some serious woodworking skills. Getting the angle cuts to line up when the sides are not 90 degrees would make this a very difficult box to build.
  2. Make sure you have enough space behind the baffle for the waveguide, compression driver, and the rear of the box. The image you posted above is too small to say for sure, but it looks like there isn't room for the CD in that design.

Is there a small SEOS design that uses a sealed box? It seems like it would be easier designing this new box without ports, since you don't need these to go very low.
post #40 of 99
Thread Starter 
Quote:
Originally Posted by BeerParty View Post

  1. Don't angle the side panels unless you have some serious woodworking skills. Getting the angle cuts to line up when the sides are not 90 degrees would make this a very difficult box to build.
  2. Make sure you have enough space behind the baffle for the waveguide, compression driver, and the rear of the box. The image you posted above is too small to say for sure, but it looks like there isn't room for the CD in that design.

Is there a small SEOS design that uses a sealed box? It seems like it would be easier designing this new box without ports, since you don't need these to go very low.

Hey Chris, thanks for the tips.

1. I am not a very experienced woodworker, and I am indeed reluctant to do a design relying on compound mitered joints. What sent me off that direction was a belief (unfounded??) that I needed to keep the baffle as narrow as possible to minimize diffraction issues. In addition, I needed more volume than the straight sided design for extended bass response, but I did not want the box to protrude into the room any more than necessary.

2. Quite true. I may need to push the waveguide/CD more towards the center of the baffle or space the baffle further from the corner, or both...Part of my reason for using Sketchup is it allows me to model the driver mounting and check for just these sorts of clearance issues. Since I would be venturing off with an untested design, I planned to get a set of drivers in hand before building the first enclosure.

With regards to the low end extension, I was trying to achieve a -3 dB point around 80 Hz for better integration with my sub. The somewhat larger enclosure and port(s) would allow me to reach that goal. On the other hand, it may be overkill - I just don't know how critical this region is for an adequate surround sound stage.

Mike
post #41 of 99
Thread Starter 
Quote:
Originally Posted by Suntan View Post

I run my theater like this (surrounds above and slightly behind first row) pointed at the opposite chair.

Personally, I prefer having this frequency dependent falloff you are concerned about. Nothing localizes the surround speaker worse than hearing the high frequency sounds coming straight at you. I prefer to be able to localize that off camera door knock, or bullet whizzing onto the screen, from "somewhere behind me on the right" I don't want to be able to localize it as "three feet back and four feet up on the right." If that makes sense.

Not saying that there are no better options, but if you're looking for a decent way to locate your surrounds in a WAF friendly way, mounting them high and pointing them across to the far side of the room is a good option.

-Suntan

That's good feedback, Suntan. Maybe I am worrying too much... tongue.gif
post #42 of 99
Thread Starter 
Quote:
Originally Posted by noah katz View Post

I can vouch for the 8CX21; I have 8 (11.1 system).

Note that you need XO's, and the B&C XO1's are $62 ea.

I got mine at Prousoundservice.com; $160 for 8CX21 and $68 for the XO.

If you go that route plan ahead because it seems they have to order them from Italy.

Thank's Noah.

These have just moved up higher on my list for consideration. What are you using for the mains in your system with these coaxial surrounds?
post #43 of 99
Quote:
Originally Posted by mhutchins View Post

What sent me off that direction was a belief (unfounded??) that I needed to keep the baffle as narrow as possible to minimize diffraction issues. In addition, I needed more volume than the straight sided design for extended bass response, but I did not want the box to protrude into the room any more than necessary.

Or you could go the other way and make the baffle very wide.

You could even make it an architectural feature and run the angled piece the full length of the wall and call it a molding; use speaker grille fabric the same color as the paint.
Quote:
Originally Posted by mhutchins View Post

What are you using for the mains in your system with these coaxial surrounds?

Currently 18Sound 12ND710 woofers and XT1086 horns/WG's with BMS 4552ND CD's; soon to be replaced with TD12M and SEOS-12/DNA360 CD's.
post #44 of 99
Quote:
Originally Posted by BeerParty View Post


Is there a small SEOS design that uses a sealed box? It seems like it would be easier designing this new box without ports, since you don't need these to go very low.

There is an EOS design coming that's in a small .35 cuft sealed enclosure. They can handle some serious power and put out plenty of volume.
post #45 of 99
Thread Starter 
Quote:
Originally Posted by noah katz View Post

Or you could go the other way and make the baffle very wide.

You could even make it an architectural feature and run the angled piece the full length of the wall and call it a molding; use speaker grille fabric the same color as the paint.

That is a fantastic idea! And it is well within my woodworking skills.

I am planning 2 layers of 5/8" drywall with Green Glue and isolation clips and hat channel for walls and ceiling. Would it be better to frame this out and dry wall in place or should I attach the "molding" after the walls and ceiling are in place?

If I did this after drywall, could I use the rest of the area behind the "molding" as a bass trap? Is the area/volume large enough to have any effect?

You've really got my wheels turning with this suggestion. Thanks Noah!

Mike
post #46 of 99
Thread Starter 
Quote:
Originally Posted by Erich H View Post

There is an EOS design coming that's in a small .35 cuft sealed enclosure. They can handle some serious power and put out plenty of volume.

Hi Erich,

Has this design been previewed in any of the forums yet? If so, do you have a link?

Thanks,
Mike
post #47 of 99
Quote:
Originally Posted by BeerParty View Post

Is there a small SEOS design that uses a sealed box?

There really doesn't need to be a different design for sealed vs. vented, as sealed vs. vented only affects response many octaves below the XO freq.
Quote:
Originally Posted by mhutchins View Post

Would it be better to frame this out and dry wall in place or should I attach the "molding" after the walls and ceiling are in place?

Sounds like sound isolation is important so you'd want to due the sheetrock first.

Also not sure what the net difference would be otherwise, as the speaker diameter determines the minimum width of the angled piece.
Quote:
Originally Posted by BeerParty View Post

If I did this after drywall, could I use the rest of the area behind the "molding" as a bass trap? Is the area/volume large enough to have any effect?

Maybe, but it would be the tricky kind; to be reasonably effective it would need to be one of the tuned types, where the panel resonance matches a room mode freq, or a Helmholz resonance type where it's essentially a driverless ported box with Fb a room mode freq that sucks up sound there.

Glad you like the idea, I hope it works out.
post #48 of 99
Thread Starter 
Quote:
Originally Posted by noah katz View Post

Glad you like the idea, I hope it works out.

I've been searching the net to try and find crossover schematics for the 8CX21, either Tom Danley's rumored design or the XO-1 offered by B&C. Best I could come up with was a picture of the B&C XO-1, but not all of the values are visible. I wanted to price out the cost of building my own vs. special ordering the B&C XO-1, but no such luck...

CREATOR: gd-jpeg v1.0 (using IJG JPEG v80), quality = 90
post #49 of 99
Thread Starter 
The next question I have in this design process is how much intensity should I trade for a doubling in distance between the near speaker and the far speaker? Is 3 dB about right? If so, for which frequency? As you can see in the polar plot below, 4 kHz and 16 kHz are both 3 dB down around 15-20 degrees off axis, whereas 8 kHz, 2 kHz and 1 kHz don't fall below 3 dB until the listener is 40-50 degrees off axis. Which angle should give the best results, or do I need to build two small enclosures and experiment with down angles...

As it happens in my room, the near speaker is 52 degrees above the listener while the far speaker is 35 degrees above the listener.


The image above is excerpted from the 2013 B&C 8CX21 data sheet
post #50 of 99
Quote:
Originally Posted by mhutchins View Post

I've been searching the net to try and find crossover schematics for the 8CX21, either Tom Danley's rumored design or the XO-1 offered by B&C. Best I could come up with was a picture of the B&C XO-1, but not all of the values are visible. I wanted to price out the cost of building my own vs. special ordering the B&C XO-1, but no such luck...

CREATOR: gd-jpeg v1.0 (using IJG JPEG v80), quality = 90

Are you capable of crossover design? I would imagine that the stock B&C crossover is decent but not nearly as good as a properly designed crossover that was geared towards home usage. I have some of these drivers that I picked up several weeks ago, I was planning on building some coaxial surrounds but haven't been able to start in them yet. Are you using the 8CX21? I might be up for building some enclosures sometime soon, but I never got that far in the design process. Depending on your enclosure design, I may just copy it. Do you know what the optimal specs are for the enclosure using the 8CX21?
post #51 of 99
I did some reading on time-intensity trading a few months ago, and couldn't come up with an easy way to make those judgments - I know they're out there (in somebody's head), but I didn't come up with it. What I came away with though is that the later arriving sound must actually be higher level than the first arriving sound if a stereo image is to be maintained.
post #52 of 99
Quote:
Originally Posted by mhutchins View Post

Which angle should give the best results, or do I need to build two small enclosures and experiment with down angles...

It all comes down to the subjective effects, and you could spend a lot of time researching how to make that judgement, which I'd guess would be highly unlikely to give an optimal result for your particular room acoustics and system layout.

IMO you'll get a better answer in less time by building some boxes and experimenting.
post #53 of 99
Thread Starter 
The B&C 8CX21 plus XO-1 is just out of reach for my budget. mad.gif

Good news, though, Erich at DIY has done it again. I will order 2 of his surround kits as soon as they become available and probably add more for rear and height surrounds, maybe even wides... smile.gif

Mike
post #54 of 99
Quote:
Originally Posted by mhutchins View Post

The B&C 8CX21 plus XO-1 is just out of reach for my budget. mad.gif

Good news, though, Erich at DIY has done it again. I will order 2 of his surround kits as soon as they become available and probably add more for rear and height surrounds, maybe even wides... smile.gif

Mike

I just helped the project along. MTG90 did the hard work that requires the extra brain power. biggrin.gif
post #55 of 99
Thread Starter 
Kudos to both of you, then!! wink.gifcool.gif
post #56 of 99
Quote:
Originally Posted by Erich H View Post

I just helped the project along. MTG90 did the hard work that requires the extra brain power. biggrin.gif

We are all very lucky to have both you guys in our community!

When do you anticipate on having the flat pack or kits for this surround completed and ready to be ordered?
post #57 of 99
XLNT, looks like a great alternative.
post #58 of 99
Thread Starter 
I received the Eminence Beta 10CX and Denovo DNA-150 kit from Erich at DIY Sound Group this weekend!! Woohooo biggrin.gif

I'll start building test boxes next weekend, provided I get my chores done before then...mad.gif

Boy, those crossover PCBs are nice!!!

Mike
Edited by mhutchins - 1/13/14 at 1:21pm
post #59 of 99
Quote:
Originally Posted by mhutchins View Post

I received the Eminence Beta 10CX and Denovo DNA-150 kit from Erich at DIY Sound Group this weekend!! Woohooo:D

I'll start building test boxes next weekend, provided I get my chores done before then...mad.gif

Boy, those crossover PCBs are nice!!!

Mike

What are you going to use them for ?
post #60 of 99
Thread Starter 
Side and rear surrounds, plus wides. The rears I will probably mount at roughly a 45 degree down angle. The side surrounds, however, are probably more critical with regards to their angle, if I am going to achieve my goal of a reasonable stereo image. I want to try Time-Intensity trading for the side surrounds, without obvious source localization. This will be a real challenge since I sit so close to them in my small room....
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