7 speaker home theater DIY project with active crossover...would love discussion

[cobyh]

I’m currently in the process of figuring out the replacement/upgrade for my living room home theater setup.



The room: I’ve got a 9 ft wide screen I’m projecting onto, hanging from the ceiling. The screen is about three feet from the back wall, and directly above a halfwall about 3.5’ high (there’s a stairway heading downstairs behind the screen). Acoustically, the room is really, really bad. Vaulted ceiling (peak perpendicular to line of sight to screen, thankfully), open to kitchen and dining room to left, open hallway to bedrooms and bath on right, huge volume to fill, assymetrical reflecting surface profile. The living room area is about 15’ x 25’; the back wall has a fireplace in one corner and a baby grand piano in the other, so the seats are ahead of those. Currently, I’ve got a set of Acoustic Research 312HO’s as mains, with an AR center and little bookshelf AR’s as surrounds. There’s suckouts in the room and the bass has serious nulls in various places and the waf of room treatments isn’t high, but I’m working on that. (luckily she wasn’t too upset with the 7 foot tall 24” diameter subwoofer…but she doesn’t like her miniature piano collection flying off the shelves in her music studio several doors down because of the vibrations…that kinda annoyed her when they broke).



The project concept: I want to have 7 identical speakers (sonically anyway) in the living room, and they don’t have to have extension below 70hz because they’ll be crossed over into the sub.

Some of the constraints include:

1. Form Factor: there’s about 12 inches below the screen and above the halfwall, and it’s right around ear height when seated for a movie. The part of the speaker with the drivers needs to fit in that space.

2. Output: Lots of it. Design goal is to get to 110db cleanly. I like dynamics. I like something that sounds good low AND high. The AR’s were good for that, with a high sensitivity, but the towers just don’t fit into the layout for the room.

3. Cost: Like most folks, I’m not made of money. So, >$1000 per speaker is out. I’m trying to get under $300 per speaker if possible for materials, not including amplification.

4. Clarity: I’m looking to use drivers that are quick, and to minimize anything that’ll make them muddy

5. Voice intelligibility: I’ve heard that crossing over in the 300hz to 3600hz range is to be avoided in a setup that does a lot of HT, however, it’s tough to do a 2way without violating that rule. And for the #3 criteria, a 2way is more attractive.

6. Dispersion/Sweet Spot: I’m looking to have excellent off axis response so that more than one person can have excellent imaging for movies and multi channel music. This also makes it tough to do a 2way.

7. Phase coherency: A must. I want this acoustic lens to be sharp.



Current direction for the design: Unless I go with three centers across the front, it’s almost impossible to satisfy the criteria stated above, and using centers on the walls to the side and rear is impractical. So, I need to roll my own, as it were. I’ve looked and looked and looked at various DIY designs, and one thing has become apparent…it’s silly to go with passive crossovers. With the Behringer DCX2496 as inexpensive as it is, active electronics is the best fit to the criteria. So…we’re going active. I’m planning on some fairly nonstandard enclosures as well.

1. Active crossover: Using multiple DCX2496’s for the seven speakers. Either 3 if 2ways, or 4 if 3way design is chosen. This will buy me phase coherency, time alignment, 48db/octave slopes, static and dynamic equalization, EQ profiles for various recordings, and the ability to iterate changes to the crossover to decide on best voicing. Downside is massive amount of time spent dinking with it, and the learning curve for using it. Cost is about a wash; good crossovers (passive) are similar in their cost per speaker especially if going with a 2way setup, where I can use one DCX per three speakers. If I’m able to implement one of my secondary goals (keeping the signal digital from source to amplifier…hard to do inexpensively) then it’s only 2 speakers per DCX, as that unit has one stereo AES input. Also, this solution will enable me to get a fairly flat FR in room, instead of just anechoic, which is important given that my room isn’t ideal by any means…

2. Enclosures: 12” diameter, probably 18” long (driven by driver requirements), and haven’t decided between sealed or vented. Won’t tolerate large group delay numbers, and will likely go sealed, but not locked into that yet. The cylindrical enclosure will be capped by wood on either end, and will have a tube either coming out the bottom with a 90deg mandrel bend the diameter of the woofer or normal to the surface of the tube. Tweeter (and mid, if 3way) will be mounted on a ring faceplate around the tube holding the woofer and be rotateable to accommodate various orientations of the main enclosure tube. I’ll model it in Pro/E and put up pics if anyone’s interested and can offer criticisms. Risks of standing waves will be mitigated. Material for tube will either be aluminum, pvc, cardboard (sonotube) or carbon fiber…haven’t looked into resonance yet.

3. Amplification: External, likely several 7 channel amps



Questions….man, I’ve got tons of them as I work through this exercise. Here’s a couple I’ve got right now that I’d love some feedback on:

1. Driver selection and orientation- I’ve looked at Peerless, Vifa, Hiquophon, Dayton, etc., etc. If there’s a two way setup that’ll work well, then that’d be my first choice. I just don’t know if that’ll work well…I need to settle that aspect before I can move on. And do I do dual woofers with the tweet in a 2way? Can I get away with a single woofer? Where do I put the crossover point….with the steep filtering the DCX provides, can I get away with putting that crossover point in the critical human voice range and not suffer deleterious effects? How about some open ended discussion on this?

2. Amplifier selection-I won’t need an uber expensive amplifier rack, as the load will be resistive due to the use of the active crossover. I’d love the LPA-1 from Emotiva if the last amp wasn’t split. Grr. For the tweets, I was thinking of something like a Panny receiver run in direct mode; they won’t need a ton of current to drive to high volumes cleanly. What are some suggestions for 7 channel amplification for low cost, given the modest requirements?



Once I settle on the drivers and layout, I can proceed with the rest of the design. I welcome any discussion on it; whether it’s in relation to the two questions posted, or anything else in the project described above. Thanks!



I may post this in several of the forums dedicated to DIY speaker design as well, so I apologize if you see this more than once. I'd love some discussion and feedback on this if you've the time.

[F1 fan]

Wow coby , it sounds like you want to build a very serious and complex system.I thought I was getting carried away by running fully active LCR's but you want 7 active channels.I can say from expirience that great gains in dynamic capabilities are possible when going with the active approach for the front 3 channels.But IMO it is not worth the effort or expense of doing active surrounds.

If I understand correctly you are limited vertically at 12" ?You might want to consider building a horizontally oriented 3way WMTW or a WCW using the SEAS COAX driver.( See discussion on AVS about this idea someone is considering).
The SEAS unit is nice because it has a controlled vertical and horizontal directivity which helps dialog intelligability as well as stereo imaging ,also the woofer and tweeter are time aligned regardless of listener axis,and with appropriate xover design the off axis response will be very good.All in all it is a great driver choice for HT.
Anyway thats my $.02

[cobyh]

I don't think it's all that much more complex than one with passive crossovers and I think the gains will be worth it, especially for 7 ch music. Tell me about your LCR setup; what was used, why, problems you ran into, design goals.... Which components did you use? (drivers, active crossover unit, signal processor...)

I'll look at that Seas unit...right now I'm leaning towards a TM in a vertical orientation, and I'm up in the air on something like dual 6.5's for woofs arrayed horizontally under the TM, or a 10 or 12" woof on the side of the TM array. The Morel mid is looking attractive, though it's pricey.

[F1 fan]

Here is an updated list of my setup and my almost completed centre channel.

http://www.hometheatershack.com/foru...html#post13925

http://www.hometheatershack.com/foru...html#post30271

[cobyh]

Ok....interesting setup. For curiosities sake, why did you choose to crossover as low as you did to the tweeter? Also, the active crossover you used...those are analog?
And where are your woofers in relation to the MTM setup you've got for the center channel?

[F1 fan]

I crossed the tweeter over at 2k for a couple reasons.

1. It has much better dispersion at 2k than the 6.5" midwoofer so the combined system off axis response will be better than if the xover was placed higher.

2.The midwoofer has some roughness in its response above 3k so the lower xover point and steep 24db slope will mean these irregularities will be much reduced in level.

Yes the active units are pure analog.I knew the exact xover response (slope and frequency)I wanted to achieve so other than level adjustments the need for tweaking crossover points etc.was not a necessity.
Also I like the fact that the signal stays in the analog domain instead of being sent through different stages of A-D and D-A conversion.But I will add that the Behringers are absolutely wonderfull units for those who want to do alot of tweaking.

Im now mixing the bass below 80hz of the center channel with the LFE subs.

[reed.hannebaum]

Coby,

If your goal is to create an "acoustic lens", then you probably want to use identical amps all the way around, or at least amps with the same circuit design. As I am sure you know, the phase/frequency response of amps can vary widely.

[cobyh]

reed.hannebaum wrote:

Coby,

If your goal is to create an "acoustic lens", then you probably want to use identical amps all the way around, or at least amps with the same circuit design. As I am sure you know, the phase/frequency response of amps can vary widely.

Absolutely. Intention is identical amps exactly for each level of driver, for all 7 channels. I'd love to use something like the Emotiva LPA-1 if it was actually a 7 channel amp instead of a 6 channel with the last channel being able to be a stereo amp at a much lower wattage.

I'm just starting the search for amplification. These will not be hard units to drive, since there will be no passive crossover. A rack of Audiosource amps might be an affordable way to go for the mids and lows, and still not sure about the tweets yet. Suggestions? I'm trying to keep the amplifier budget between $1500 and $2k tops...hopefully less. I"ll be scouring Ebay.
Gain control and balanced inputs would be a bonus.

[cobyh]

F1 fan wrote:

I crossed the tweeter over at 2k for a couple reasons.

1. It has much better dispersion at 2k than the 6.5" midwoofer so the combined system off axis response will be better than if the xover was placed higher.

2.The midwoofer has some roughness in its response above 3k so the lower xover point and steep 24db slope will mean these irregularities will be much reduced in level.

Yes the active units are pure analog.I knew the exact xover response (slope and frequency)I wanted to achieve so other than level adjustments the need for tweaking crossover points etc.was not a necessity.
Also I like the fact that the signal stays in the analog domain instead of being sent through different stages of A-D and D-A conversion.But I will add that the Behringers are absolutely wonderfull units for those who want to do alot of tweaking.

Im now mixing the bass below 80hz of the center channel with the LFE subs.

So you're extending the mids down to the 80hz point and then rolling off to the subs for a 3 way instead of a 4way?

Can you hear the difference if you crossover above 3500hz or well below it, in human voices? I guess if you match the dispersion, phase and have a flatish FR, you shouldn't be able to tell the difference, right? Life would be easier if I could live with a 2way (3way when the sub is taken into account)

[F1 fan]

cobyh wrote:

So you're extending the mids down to the 80hz point and then rolling off to the subs for a 3 way instead of a 4way?

Can you hear the difference if you crossover above 3500hz or well below it, in human voices? I guess if you match the dispersion, phase and have a flatish FR, you shouldn't be able to tell the difference, right? Life would be easier if I could live with a 2way (3way when the sub is taken into account)

It is only with the center channel that I let the midbass drivers extend down to 80hz because it has 2 of them therefore it has the volume displacement to handle it.So yes when combined with the sub it would be a 3 way.

My main speakers have only 1 midbass driver so I cross it over to an 8" woofer at 300hz then the 8" passes off to a 10'' woofer at 50hz to make it a 4way.


Generally it would not be advisable to crossover a 6.5" midbass to a 1" dome tweeter above 2500hz because the off axis response will be poor due to the narrowing dispersion pattern of the cone as frequency rises or in other words it becomes directional or beamy.And yes if the system has poor off axis response it will be audible.
A smaller diameter cone like a 4" or midrange dome could probably be successfully crossed over at 3600hz.

Most high performance 2way speakers on the market have crossovers that are well within the human voice range 1.8-2.5k so it is not a problem as long as it is done correctly.It depends on the actual drivers being used.

[cobyh]

F1 fan wrote:

It is only with the center channel that I let the midbass drivers extend down to 80hz because it has 2 of them therefore it has the volume displacement to handle it.So yes when combined with the sub it would be a 3 way.

My main speakers have only 1 midbass driver so I cross it over to an 8" woofer at 300hz then the 8" passes off to a 10'' woofer at 50hz to make it a 4way.


Generally it would not be advisable to crossover a 6.5" midbass to a 1" dome tweeter above 2500hz because the off axis response will be poor due to the narrowing dispersion pattern of the cone as frequency rises or in other words it becomes directional or beamy.And yes if the system has poor off axis response it will be audible.
A smaller diameter cone like a 4" or midrange dome could probably be successfully crossed over at 3600hz.

Most high performance 2way speakers on the market have crossovers that are well within the human voice range 1.8-2.5k so it is not a problem as long as it is done correctly.It depends on the actual drivers being used.

Yea....I was assuming that poor offaxis response would be noticeable; I wouldn't try to use a 6.5" as a mid. I'm looking at the Morel dome unit right now as a midrange. My question was more along the lines of whether or not you could hear your crossover in that range; i.e., can you hear the effects of it when people are speaking through the speaker...

thanks for all the responses, btw

[cobyh]

thylantyr wrote:

You mentioned "The AR’s were good for that, with a high sensitivity, but the towers just don’t fit into the layout for the room."

If I understand correctly, you have space limitations and you want to build
smaller speakers than those?

Sort of....I've got space behind the screen and halfwall; the enclosure volume can go there, or in between the drivers. I'll model up the enclosure I'm thinking of and post it; it'll be a lot clearer then. I'm pretty sure I can best the AR design by a LONG shot in terms of dynamics, power handling and especially dispersion, as the dispersion on the AR's was not what I'd call adequate.

thylantyr wrote:

Have you considered building already published designs from cyberspace
using passive crossovers?

You should examine designs from here to give us a better idea on what
type of designs you see might work for you.

http://www.zaphaudio.com/




http://www.htguide.com/forum/forumdisplay.php4?f=39

http://www.partsexpress.com/projects.../homeaudio.cfm

http://www.humblehomemadehifi.com/

Actually, I've been to all those sites, and more. And I've looked at every project once, twice, 10 times. Had my heart set on the 340SE's for a while, but there's just too many compromises. About the only way I can satisfy my criteria is to roll my own. It's frustrating.

I'm really rather surprised that more folks aren't using active digital crossovers. As far as I can tell, they're comparable costwise with a good analog crossover, and have few of their compromises. Is it just that there's not as many folks out there already using them and they scare people? I don't get it....

Right now I'm looking at the Morel dome midrange for about $82 to do the bulk of the work, between 350ish and 3500ish, and the Dayton Quad 8" sub might work well for the 30 to 350 point, and I haven't decided on a tweet yet at all. One driver of each simplifies things a bit; I can likely do a vertical alignment of the TM and offset it's midrange center to the 2 Oclock position relative to the center of the 8" woofer. Any suggestions for a tweet (not a horn....I dislike the sound of those I've heard) that only has to do from 3500 up? 20k isn't even a necessity....my hearing goes to around 15k before almost completely losing the sensation (I'm 38).


What are some of your experiences with the DCX? Are you bringing in signal digitally or through analog? Have you made use of the dynamic EQ options?

[cobyh]

thylantyr wrote:

re: $1500 - $2000 amp budget

If passive crossover loudspeakers.

I'd use PLX3002 or PLX3402 for mains. My favorite bang for buck amp.
Buy them used on the auction site, average price for PLX3402 last year was
$765 each. That average price has dropped down to about $650 - $675 range,
I've seen some sell for $550 because PLX2 series came out and people are
selling old PLX to get the news ones unbeknowst them that very little has
changed from the old to the new series, mostly cosmetic and a basic crossover.
You don't need PLX2 series, save big bucks and use old PLX.

PLX2402 and PLX3002 is very close to the PLX3402, all class H with just a few
internal tweaks. I'd try to score a PLX3402 or PLX3002 for mains and
use at least PLX2402 for surround speakers and another PLX2402 in bridge
mode for the enter channel.

If you ever wanted to add more headroom to your design, score more PLX's
and bridged them for amazing performance, ie, dual PLX for mains in bridge mode is pretty sweet. Be patient and wait for good deals to show up on ebay.
These amps can drive mids and tweeters well way below rated impedance spec,
but subwoofers need to be driven no less than spec.

All you need is four proamps, play your cards right you can score those
amps for $2k.

If you do an active system using tweeters and midwoofers then you need
14 channels and many active crossovers. I don't know if this is worth the
trouble unless you built a really big system. For this job, you can use the
same PLX recipe and get 7 proamps but the budget is much higher. Id look
into the entry level proamps to do this job, perhaps Crown XLS 402/602/802,
or Behringer EP2500's....

Those are way more power than what's needed. What I'm looking for is 7 channels of 50-100w at 8ohm for the tweets (which should be an order of magnitude more than I need), 7 channels of 125w ish at 8 ohm for the mids (also likely much more than I'd need), and 7 channels of 300w ish for 4 ohm for the woofer (adequate). The amps for the tweets and mids don't need to be designed for 2 ohm loads; in fact, one of the advantages of not using a passive crossover is that it creates very easy to drive speakers...I'd like to take advantage of that fact and not pay more than is necessary for this system.

As far as many active crossovers....it'd require 4 DCX's for threeway all the way around and 3 DCX's if I went 2way all the way around. If I can find a pre/pro that has digital AES out, even better, though then I'll definately have to do 4 DCX's. The DCX can be had refurbed for $200....which is $100 per speaker for an active digital crossover. Definately not the major expense here. The amps are what make it pricier....but should provide gobs of headroom for 'effortless' dynamics (btw, I'm not a fan of flowery speech, hence the quotes)

Right now, the Audiosource 5.1's from Ebay look like a good deal for the tweets, and I think I can get 7 channels worth for less than $500 (possibly less than $400 but I doubt it. For the mids, either the Emotiva monoblocks or the Audiosource 5.2's or 5.3's. For the low end, the Emotiva 7ch or the Outlaw Audio 7ch units might do well.

Are there some good pro amp monoblocks I should be considering?

Love the pro amps as compared to the consumer amps...and a class D amp would probably work great for the woofer channel. I'm using a Mackie M-1400 bridged at some 1400watts for my LLT sonotube sub right now; worked out great.

[reed.hannebaum]

cobyh wrote:

Absolutely. Intention is identical amps exactly for each level of driver, for all 7 channels. I'd love to use something like the Emotiva LPA-1 if it was actually a 7 channel amp instead of a 6 channel with the last channel being able to be a stereo amp at a much lower wattage.

I'm just starting the search for amplification. These will not be hard units to drive, since there will be no passive crossover. A rack of Audiosource amps might be an affordable way to go for the mids and lows, and still not sure about the tweets yet. Suggestions? I'm trying to keep the amplifier budget between $1500 and $2k tops...hopefully less. I"ll be scouring Ebay.
Gain control and balanced inputs would be a bonus.

If you go 2-way at say 100 Watts/ch @ 8 ohms then you are talking about $1.40/watt. This is not very much. You definitely want to look at good used equipment and don't overlook professional equipment; its usually more band/buck, but you may have to put up with fan noise. I have a Carvin DMC600 that I use to drive (bridged) my sub and it works great. I bought it used/mint for $200 => $1.25/watt @ 8 ohm. It has great specs, gain control & balanced inputs, and the fan is very quiet. When I first got it I tried it on my main speakers and it sounded great. With a 100 db S/N this amp is quiet as a church mouse. Also, it runs very cool, so I keep it in a closed cabinet and no heat problems.

[reed.hannebaum]

Sorry, I just now noticed your post above. You are obviously aware of pro equipment. I agree with your comment of relegating class D equipment to low frequency assignments. I may be old school, but I can't help but believe that the switching noise of those mosfets would result in listener fatigue.