Center Speaker Built Into Fireplace Mantel - AVS Forum
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post #1 of 59 Old 02-20-2012, 08:05 PM - Thread Starter
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Our renovation plans call for a TV above the fireplace. I'm an experienced woodworker and thought it would look nicer to hide the center channel in the mantel. The front left/right speakers can be standard enclosures placed in the bookshelves flanking the fireplace. The rear speakers will be in-wall.
I like high quality sound, but my significant other would rather have a discreet/inexpensive system. The living room is a 17 x 14 foot rectangle. The house is very open - the back wall of the living room is a half-wall with columns (there is a kind of colonnade entry).
Anyone have any ideas for this? I thought maybe I could find a suitable DIY design and make the volume within the mantel match the volume of the design but with different height/width/depth.

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post #2 of 59 Old 02-21-2012, 10:41 AM
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do a search on google images for...mantel speaker. :-) surprisingly, such things exist and if you find a form factor that you like, then perhaps somebody can help you select a speaker that will work.

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post #3 of 59 Old 02-21-2012, 10:47 AM
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I would buy pi speakers and then do no center channel... requires major toe in though which spouses probably think looks ugly. Plus theyre huge

http://www.pispeakers.com/catalog/pr...products_id/97
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post #4 of 59 Old 02-21-2012, 10:51 AM - Thread Starter
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I've searched this and haven't seen too much. Maybe the type of person who makes DIY speakers is too interested in high-quality sound to stuff one into a mantel! I called Madisound who recommended the HDS kit.
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post #5 of 59 Old 02-21-2012, 10:53 AM - Thread Starter
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This is my obligatory third post to enable me to post links and pictures.
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post #6 of 59 Old 02-21-2012, 10:56 AM
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post away until you can post.

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post #7 of 59 Old 02-21-2012, 10:58 AM - Thread Starter
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This is what Madisound recommended.

http://www.madisoundspeakerstore.com...it-parts-only/

Here is a picture of a similar mantel with speaker.



Here is the drawing of the room. House is brick. The elevation of the fireplace wall is at bottom the back wall with columns is shown at top.

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post #8 of 59 Old 02-21-2012, 11:04 AM
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well, a mid-tweeter-mid, so called mtm design isn't ideal when turned sideways if you sit far to one side or another because the different distances to the mids creates comb filtering, but that may or may not really matter depending on how good your ear is.

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post #9 of 59 Old 02-21-2012, 11:12 AM - Thread Starter
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What configuration would you suggest? Here are a few pics of the house (its demo day).




This link below shows the setup we have upstairs (halfway down the page). Jamo in-wall speakers with a Paradigm center channel. I'd like to have a higher quality system downstairs in the living room. Plus, as the preceding pics show - looks like I'll be building a mantle anyway...

http://greenrenovation.wordpress.com/home-automation/
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post #10 of 59 Old 02-21-2012, 11:47 AM
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If you're an experienced woodworker, you can make anything look good. The goal here is to make it sound good as part of an overall viewing experience. To that end, you may want to reconsider a couple elements.

Screen placement
Over the mantle is good for pictures, maybe moving pictures, but not long-term viewing. You want the screen eye level when seated, and you want to be 2-3 screen diagonals away when seated for optimum viewing. No hard and fast rules, of course, but expect the high placement to cause neck pain, and beyond 3.5 screen diagonals viewing distance, you can't resolve standard def, so your HD screen is just a big, low-res display.

Speaker placement
I have no issues with a CC in the mantle, under the screen, just treat it as an in-wall speaker. My biggest concern here is home value if you screw it up... but your a woodworker, and it's your house.

You will have audible issues with "standard enclosures placed in the bookshelves flanking the fireplace." The only locations where speakers have predictable response are free-standing and in-wall. If hung on a wall, or put on a bookcase shelf, the wall reflection is both strong and audible, causing unpredictable peaks and dips in response at frequencies corresponding to 1/4 wave and larger wall spacings. Toole has a great example.

Note this is nothing to do with bass, standing waves, etc., save for resulting form the same principles. It's all about edges and the distance to reflecting surfaces, and which surface is reflecting. And the effect will be in the upper bass, low midrange, so expect vocals and most instruments to be affected.

It's not hard to eliminate all this by building the L/R into the bookcase, rather than sitting them on a shelf. In most cases this will also require the in-wall design to get proper tonal balance.

Lots to think about, and not all in line with your wishes, but hopefully aligned with best practices and what works. To learn more, I recommend Floyd Toole's book, Sound Reproduction.

Have fun,
Frank

Oh, my! I was writing while you posted pictures...

And don't discount options like horizontal MTMs as there are some, a very few, that address all the issues properly.
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post #11 of 59 Old 02-21-2012, 11:50 AM - Thread Starter
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The horizontal MTM looks like the best bet to fit within the mantel - vertical orientation is out , and coax speakers require a bigger diameter to attain the cone area of two smaller mids. I'll hog the center position and relegate the wife to suffer the comb filtering! The Madisound kit is well under the budget. Are there any better options in the $300ish range?
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post #12 of 59 Old 02-21-2012, 11:51 AM
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i just read your bio on your site...you are a badass...and deserve a really nice sound system. let me see if i can find something...and tyfys.

edit: here is one possibility.
http://www.hometheaterhifi.com/volum...er-9-2001.html
sealed cab instead of ported.

with the tweeter and mid stacked vertically, there will be no comb filtering to the side and the crossover point to the woofers is low enough so that they will not comb filter either.

if you don't like this particular build, try to find something with a similar driver configuration.

also build the mains with the same drivers/crossovers so that all three speakers will have the same timbre.

fiberglass or recycled cotton absorption works much better than the egg crate style foam used in that build.

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post #13 of 59 Old 02-21-2012, 11:59 AM - Thread Starter
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Thanks Frank, very helpful. Its probably possible to build the L/R into the cabinetry - I didn't realize it would make that much of a difference. I'll get the book you suggest. I know the screen placement is a bit high, but can't be helped. I'll mount it as low as possible. The screen size will be 55" and viewing distance is about 12 ft so pretty good.
Also thanks, LTD02, I've got some self-promotional stuff up on my site because I'm job hunting! I had already looked at the Audax design but it seems the drivers aren't available.
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post #14 of 59 Old 02-21-2012, 12:26 PM
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If I had your room and I was a good wood worker, I'd build PI speaker corner horns(google pi speakers) into those corners flanking the fireplace and try to make them look like part of the book shelves you are planning. If you do, opt for the high end drivers. With those, the center channel would be optional. You might want one for clarity of dialog but you wouldn't use it for music listening.
Thanks for your service!
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post #15 of 59 Old 02-21-2012, 03:01 PM - Thread Starter
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Interesting that I've heard two votes for pi speakers. I'd never heard of them, but perhaps I should not rule them out. Especially since it looks like I'll have to do built-ins for L/R anyway. The house is an 1899 bungalow with dark stained fir trim. The bookshelves and fireplace will be built to match. I plan to use vintage-style open-weave grill cloth to make it look as if the system was installed in the late 50's.
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post #16 of 59 Old 02-21-2012, 03:12 PM
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Pi's are superb, however that doesn't mean they're right for you. I'm not saying one way or the other, just keep your options open.

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post #17 of 59 Old 02-21-2012, 04:27 PM
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i must have pulled too many g's because all the blood left my brain with my earlier post on the center channel.

something like the pi's are definitely the way to go and make the center channel optional.

member nichol1997 built the ones shown in the image below.

2226h drivers in the mains, 2242h drivers in the bass. this is what you are looking for. with black grill covers over the bass bins, your wife won't even be able to see them. not cheap, but a huge bang for the buck (if you can find the drivers at the old prices, jbl recently bumped them into low earth orbit).

after a year, this was his review, "For the first time in years, I have not had the urge to build new speakers. There is nothing that I feel that needs improvement upon."
LL

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post #18 of 59 Old 02-21-2012, 07:23 PM - Thread Starter
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The Pi three in a tower version might be good compromise between good performing (for me) and discreet/thrifty (for SWMBO). Might the front baffle be made narrower without horribly impacting the sound? Something like a 13" enclosure width for a 12" driver. I'm planning to use a subwoofer disguised as a side table placed next to the sofa on the back wall.
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post #19 of 59 Old 02-21-2012, 10:21 PM
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13" is a little tight. The cutout for the TD12S driver is only 11" but the OD is 12.62" No reason the mounting lip of the driver can't overlap the cabinet sides if you are willing to deal with the tight quarters. Narrowing the baffle can impact the sound by changing the frequency at which baffle step starts. Placing the speaker tight to the wall in the bookcase will also change the frequency response. This can be corrected but its more work and more cost. M You get into either redsesigning the crossover (over most of our heads) or buing an AMP with DSP to equalize it flat, which requires tools to measure the frequency response. Maybe there is a local forum member that could help you with that part. Doing this stuff is our hobby and we enjoy doing it ... This is the slippery slope down which projects like this can slide.

but the corner speakers are designed for the corner and you could just build them and have them work, provided you can integrate them into the bookshelves. you may not recall but in the 50's Klipsh corner horns were all the rage. Perhaps you might need glass doors on your bookshelves adjacent to the horn so that the glass would work as an extension of the horn as the walls of the corner are intended.
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post #20 of 59 Old 02-22-2012, 01:16 AM
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Corner loaded Pi's or other waveguide loaded speaker would be the way I'd approach this too. It's going to take some planning on your part to get it right. In doing so, the left and right baffles will be angled. Once the angles are calculated, you'll find the baffle wide enough for most 12" woofers.

I'm not sure that current Pi speakers would be the way I'd go though, as Acoustic Elegance drivers are not exactly readily available which might stall your project or worse if the drivers become Unobtanium. A call to Wayne would be in order either way as to the alternate JBL woofer as well as a modified baffle step compensated crossover as well as help with calculating the baffle angle. Joining the Pi forums and posting would be a good way to start as Wayne often posts and replies. The SEOS project is coming along here at AVS as well and the SEOS 12 would also work nicely in this application.
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post #21 of 59 Old 02-22-2012, 08:14 PM - Thread Starter
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I've been reading and trying to get some things straight. The Pi speaker is range of speaker designs by Wayne Parham. But I might want to look at other similar designs. I'm running into what seems to be a lot of buzzwords.
Constant directivity speakers.
Uniform directivity speakers.
Waveguide speakers.
Cornerhorns.
What is the general type of speaker I should research? What type of design makes the center channel redundant?
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post #22 of 59 Old 02-22-2012, 08:45 PM
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generally, the frequencies that provide most of the imaging cues are roughly above 1khz.

a good horn/waveguide/whatever you want to call it focuses these cues like a flashlight in a room vs. an uncovered lightbulb. the uncovered lightbulb bounces sound all over the place.

each time that the light hits a wall, ceiling, or floor, it will reflect and create another phantom source. kind of like if you had another speaker sitting in the phantom location.

for music, some like this effect, as it makes the sound more "ambient".

however, for dialog, you want to minimize wall refections, so the flashlight approach is better.

some people use uncovered lightbulb type speakers and then use acoustic absorbers all around the room.

either approach can produce good results.

search on: jbl k2
and: bowers and wilkens 800 diamonds

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post #23 of 59 Old 02-22-2012, 11:17 PM
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Quote:
Originally Posted by two.dogs View Post

I've been reading and trying to get some things straight. The Pi speaker is range of speaker designs by Wayne Parham. But I might want to look at other similar designs. I'm running into what seems to be a lot of buzzwords.
Constant directivity speakers.
Uniform directivity speakers.
Waveguide speakers.
Cornerhorns.
What is the general type of speaker I should research? What type of design makes the center channel redundant?

Constant/uniform directivity is the same thing.

Having that constant directivity allows you to toe the speakers in front of you, creating a huge sweet spot for imaging, which basically negates the need for a center channel.
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post #24 of 59 Old 02-23-2012, 09:59 PM
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No particular speaker design negates the need for a center channel. Regardless of the design, all phantom centers suffer from frequency response aberrations that affect our perception of timbre, and even the widest sweet spot will have less image stability as compared to a capable physical center channel.

That being said, there are certainly instances where due to construction of the room or placement of av equipment and/or other items within the room the center would be so compromised that a phantom might be a better alternative. In that case speakers allowing a wide sweet spot would be advantageous. Constant directive speakers might be useful in hat regard (and I like them for many other reasons as well).

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post #25 of 59 Old 02-24-2012, 12:55 AM
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"No particular speaker design negates the need for a center channel."

with respect, that is wrong.

the center channel is for listeners who are off the main axis and need some help pulling the voices back onto the screen. for most practical purposes, a center is not needed.

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post #26 of 59 Old 02-24-2012, 06:18 AM
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How much of a problem it would be, I'm not sure. However, even dead center, employing a phantom center can be problematic when playing back multichannel material. One encounters an un-avoidable, HRTF spectral issue (two octave wide 2k dip) when down-mixing and eliminating the center.

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post #27 of 59 Old 02-24-2012, 02:13 PM
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that's true, but taking that argument further, the only way to accurately reproduce music is first to use a binaural recording (a manican head with the microphones in the ears) and then play it back with both speakers for the tactile effect and noise cancelling headphones for the hearing effect. :-0 my point was that many folks find that phantom center is a sufficient solution, particularly with horn loaded speakers.

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post #28 of 59 Old 02-24-2012, 09:52 PM
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Quote:
Originally Posted by LTD02 View Post

the center channel is for listeners who are off the main axis and need some help pulling the voices back onto the screen. for most practical purposes, a center is not needed.

With respect, that is wrong. Phantom center imaging has unavoidable perceptual anomalies related to interaural crosstalk that generate differences in frequency, time, and spatial (hrtf) domains as compared to a physical center. The relative importance of each of these components is debatable, but in aggregate the result is nonequality of phantom and physical center speakers. The type of left and right speakers used does not change this, which was my point. There are of course other advantages to a physical center such ad image stability over a larger listening area, increased system headroom and dynamics, etc.

I don't deny that phantom imaging works surprisingly well, and for a smallish listening area the perceptual differences may not be so egregious. And there are cases where other constraints make the use of an equally capable physical center impractical, which I acknowledged. And then there is the reality that many people have listened to high quality phantom imaging on a great system for so long and in the absence of real, live music listening to establish a reference that they become so accustomed to the sound that a physical center no longer sounds right to them (which of course simply reinforces that there are in fact perceptual differences).

All that being said, in many systems the practical considerations make the use of a matched center impossible so from that point on its a crapshoot as to what will in the end sound the best.

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post #29 of 59 Old 02-24-2012, 11:48 PM
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bigus, i agree with your science, but question the practical ramifications of it.

as for the effects that you list, linkwitz has performed some a-b comparo's with and without the center channel. his conclusion, "...switching between actual and phantom center on recordings that used the center channel did not produce significant audible differences..." and "...at this point I am not convinced that a center speaker in my system is worth it..." might carry more weight with you than my opinion.
http://www.linkwitzlab.com/surround_system.htm

there is another problem with most center channels in that they are often located below (or sometimes above) the screen. this causes the sound to come from a point that is off the screen and to me and others seems very unnatural. for a-t screens, this aspect is not a problem. this factor seems to matter more if you sit closer up rather than further away, but i haven't quantified the effect. back when i was bouncing a 110" diag image off of a wall with and without a center located below and centered, but with mains where the tweets were about 25% up the screen, i always ended up turning the center off because with the voices located so low, it just sounded fake. i've heard others comment similarly and have mentioned before that perhaps we different sensitivities to the center channel's location.

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post #30 of 59 Old 02-25-2012, 10:08 AM - Thread Starter
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I've been over to the Pi Speaker forum and can't seem to find anything that will work. I thought the Pi 3 looked promising, so I sketched the attached layout. Unfortunately Wayne said they needed flanking subs a few feet behind, below and beside the mains, and WAF rules that out. Wayne said that if I moved from a bass reflex design (like the pi 3) to a corner horn like the pi 6 or 7, then flanking subs would not be needed. Unfortunately those are freakin ginormous and also fire out the back - so no way to incorporate into built in bookshelves.
So it looks like I'm back where I started. Does anyone know of a cornerhorn design of reasonable proportions that only fires out the front? If not, then I might be back to the L/R/mid design based upon maybe the econowave.
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