# Another choice from coaxes.



## Zene (Jan 13, 2007)

Hi .. I have a finite number of speakers (60 - 4" mids) to use in arrays for HT. 
I can use more for 5.1 (12) than I can 7.1 (8).
Question is, how important is 7.1 now or the near future?
I want discrete so each array would be identical. 
Super clean 5.1 or just **** clean 7.1? 
BTW ... I can either do OB or sealed arrays if someone cares to expound.
Zene (standing anxiously by table saw)


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## Bob in St. Louis (Oct 21, 2006)

Zene, There is a thread here on the Shack about the whole 7.1 mess.
In my opinion 5.1 (or less) is the way to go for HT. I tried 7.1 and it was horrible.

Regarding OB or sealed, I love my OB stuff. I can direct you to a thread or two where guys have gotten radical with small diameter drivers in OB arrays.

Bob


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## brucek (Apr 11, 2006)

> I tried 7.1 and it was horrible


Yeah, I guess everyones experience is different. 

My processor supports 7.1, and since I had an extra amp channel and speaker to go to 6.1, I decided to give it a try. It's a bit of a surprise, but I really like it. The back channel really seems to smooth the surround information out. I don't really have the room for 7.1, but my vote goes to 6.1...

brucek


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## Zene (Jan 13, 2007)

Bob ... Good stuff on your OB's, learning a lot. I'm getting a nagging feeling that a larger speaker for surrounds would do better than an array of smaller ones. I think the UB range is better handled by a 12" rather than 4"ers no matter how many. The typical 80hz crossover for surrounds is quite low. 4 inchers just ain't gonna get there without help. 
Just realized while doodling last night that one speaker in an OB IS a dipole. Sure might sound better/cleaner than two monopole speakers back to back. Converting to bipoles is not possible but aiming the speaker at listening position may give some kind of good direct/reflective combination. Gee, I wonder who does that? 

Brucek ... You lead me to a versatile system that will allow 2.1 to 7.1. Thx.


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## Zene (Jan 13, 2007)

Bob ... Sorry forgot to ask about thread on 7.1 you mentioned. Could you lead me to it?
Zene


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## Bob in St. Louis (Oct 21, 2006)

brucek - I don't think my room is big enough to support that many "points". It just sounded muddy.

Zene - I agree that a driver with more surface area (cone area) can handle the LF's better than a smaller one, regardless of configuration. Hawthorne audio will soon release a 10" coaxial (complete with XO) and a pair of those will be my rear surrounds, mounted in OB of course :bigsmile: 
Here's the link to the 7.1 thread:
http://www.hometheatershack.com/for...585-now-we-have-7-1-where-do-speakers-go.html

Bob


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## Zene (Jan 13, 2007)

Bob ... coaxes was my first choice as I have a pair of 12" P.Audios. I now plan to use them (ported so they will get low enough) as fronts, two ported 8" -10" coaxes for center, same reason. Both of these are PA speakers and even a 6 ohm resistor does not give me the lower frequency I need. The ported box behind panels will be removable to try as OB. 
I have two P.Audio 12" complimentary woofer/mids to the front coaxes to keep the overall system in the same family. The many many 4" was just a hope of getting by/buy cheap. The 4 rear surrounds will be OB but different than most. If using as dipoles a coax needs another identical (?) tweeter to face the opposite direction or two coax speakers (read expensive). One speaker can be used for each rear and it is automatically a dipole in OB, which I believe may be cleaner than two. Two tweeters firing in opposite directions, not necessarily as big as the coax horns. Advantage to this over coaxes is you have dozens of tweeters to choose from and if placed in a separate box on top of the OB they can be turned for experimenting. I doubt an elaborate crossover is necessary. If a variable L-pad is used get a good one. 
If the OB is not mounted to side/rear walls (I have no rear wall anyway) the panels can be turned more toward listener for a more mono effect and switch off the rear tweeter. Lots of variations for rears with this type OB. This is a better approach than anything I have seen or read about. (prejudice). Surround dipoles and tripoles are very expensive and usually have a few 5" woofers and tweeters.
I suggesting 12" or even 15" extended range OB speakers for surrounds. 
Whew! Hope any of this makes sense? If not would appreciate all the help I can get.
HT is tougher than stereo by 10 times for me. Yes, I will read all the link you sent, thx.
Zene


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## Bob in St. Louis (Oct 21, 2006)

Ok Zene, I'm as confused as ever.... I'm not sure what you've got going on.

I'll say this right off the bat: I'm not the most technical guy here. There, I said it.
_BUT_, I can help. Link me to the drivers you've got.

A couple questions for starters;
- Why the rear firing horns, are the drivers you have not capable of the HF's?
- If the link you have does not have driver specs, can you get them?
- Your comment, _"ported box behind panels will be removable to try as OB"_ is something I've never heard of. Are you wanting to build a speaker (traditional type enclosure) with a back that comes off to occationally open up to listen to your system as OB?
- This is interesting Zene (I've never heard of anyone doing your 'turning' idea), _"Two tweeters firing in opposite directions, not necessarily as big as the coax horns. Advantage to this over coaxes is you have dozens of tweeters to choose from and if placed in a separate box on top of the OB they can be turned for experimenting"_. Hmm...Reminds me of the revolving tornado warning siren horns... Very interesting idea. It sound bizzare, but I can't think of any reason it wouldn't be worth trying. Especially if you have a few horn tweeters laying around. Sounds like it might be fun to play with.
- Can you rephrase this sentence, I think you're saying something cool hear, but I don't understand: _"I suggesting 12" or even 15" extended range OB speakers for surrounds."_
- What kind of equipment are we working with here?
- Room specs. How big? Do you have pictures?

Thanks Zene
Bob


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## Zene (Jan 13, 2007)

Bob ... This is one of those designs better seen on paper. The written word is hard, but I will answer the best I can. 

-Link me to the drivers you've got. 
These http://www.paacoustic.com/Product_Detail.asp?CatalogID=0108&ProductID=BM-12CX38
for RL.
These for surrounds http://www.paacoustic.com/Product_Detail.asp?CatalogID=0112&ProductID=E12-200S
Horns to suit.

- Why the rear firing horns, are the drivers you have not capable of the HF's?
I do not want 12" speakers trying to go to high frequencies. One horn faces front and the other faces rear. This gives identical dipoles with just one cone speaker. 

- If the link you have does not have driver specs, can you get them? 
Yes, all the specs are there.

- Your comment, "ported box behind panels will be removable to try as OB" is something I've never heard of. Are you wanting to build a speaker (traditional type enclosure) with a back that comes off to occasionally open up to listen to your system as OB?"
No, the RL panels will be a standard OB design with a removable box on back to be able to try OB or ported. The speakers I'm using are PA and do not go very low and I may have to port. 

- Can you rephrase this sentence, I think you're saying something cool hear, but I don't understand: "I suggesting 12" or even 15" extended range OB speakers for surrounds."
This was comment referring to the conclusion I made that 4" would not do the job and bigger speakers would indeed be better for surrounds. One extended range with tweeters is cheaper than two coaxes.

- What kind of equipment are we working with here? 
Not sure I understand, but all my equipment will be just standard HT.

- Room specs. How big? Do you have pictures? No pics, yet, nothing to show. Room is 12 x 18 deep with open area behind the 18' dimension.

I will work on the quote thing. 

Thanks Zene


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## Bob in St. Louis (Oct 21, 2006)

Zene, sorry it took me so long to get back to you. The Q on those drivers confused me a bit. I have not heard of anybody using drivers with that low of a Q. Also thought it was strange the wieght of that 12" driver is 33 pounds!! That _MUST_ be a typo.
I enlisted the help of an OB guru on your driver choice. His responce was:
"To me any driver works better in an open alignment. That PAudio 12 is extremely low Q, so it would
need a lot of EQ to reach below 100hz, or better, a helper woofer."



> I will work on the quote thing.


You can click on "quote" on my post and see how I performed the above quote. You'll also see how I made the italics.

Bob


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## Zene (Jan 13, 2007)

Bob ... Weight is correct, they be heavy. I have had both pairs setting around for quite a while and bought the coaxes for stereo hi fi OB experiment, but returned to horns before I got a chance to do more than cardboard testing. 
I'm not sure of using OB's for HT as the reflective sound could affect front listening. Dr. Bose showed us how bad direct/reflect can be. I realize that dipoles are not as bad, but there is still scattering behind the speakers. I'm leaving that to your good experimenting. 
You are correct about not achieving low frequencies, however a 6 ohm resistor in line raises the Qes high enough to get it to -3dB at 48hz (ported) in UniBox. Not good enough for stereo as I do not like subwoofers for hi fi, but should be OK for HT LR. 
Nobody seems to like a low Q speakers because they cannot get bass from it. I would have no problem using a subwoofer for hi fi with it in HT applications only. In fact my HT will be able to do 2.0 to 7.1 with authority. Quality is yet to be determined.
To the real question of why to use PA? They are very efficient and most of us have no power from normal receivers. Mine is 50 watts and yours is 75. Limiting it to +10dB headroom gives us 5 and 7.5 watts to play with, and that may not be enough. 
The Xmax is very low meaning that cone travel is very limited and therefore should be less distorted than most speakers. 
Zene


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## Bob in St. Louis (Oct 21, 2006)

Zene said:


> I'm not sure of using OB's for HT as the reflective sound could affect front listening. Dr. Bose showed us how bad direct/reflect can be. I realize that dipoles are not as bad, but there is still scattering behind the speakers. I'm leaving that to your good experimenting.


OB will work very well in HT. Once you get the FR you're looking for, for 2 channel, HT is "just arouond the corner".




> You are correct about not achieving low frequencies, however a 6 ohm resistor............


I prefer mechanical means of getting the FR as close to what I want before I'd go with electrical/EQ adjustments. (cardboard baffles until you're resonably happy, then try cheap MDF/PLY for an "upgraded" temporary baffle.) _Then_ fine tune with electrical.




> They are very efficient and most of us have no power from normal receivers. Mine is 50 watts and yours is 75. Limiting it to +10dB headroom gives us 5 and 7.5 watts to play with, and that may not be enough.


With your drivers having 98 and 99 SPL, 50 watts should get you reasonably loud. Mine is actually 90 watts and my drivers are 96Db SPL. I've maxed the volume knob occationally, but it's very loud.

Bob


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## Zene (Jan 13, 2007)

Bob ... Getting anxious to try OB for HT, (you are winning the battle) but will get the P.Audios going first to get some fronts. I never use cardboard/cheap panels for testing. I just don't unless it's a 2' x 2' for a quick speaker evaluation. I would OK MDF as I live with it daily for testing, but never a finished product if you are after something good.
I use UniBox but WinISD should work, also. Put in a huge number for box size sealed and that should approximate an OB. You can see where it slopes off. Change Rs to see how it affects Qts and -3dB point/slope. Baffle configuration should have little, but can have a negative effect on FR. Then I use Edge Baffle Diffraction program and play with configurations in OB mode to get the flattest trace. Results are usually good. BTW, a speaker very close to the edge always shows the flattest response curve, i.e. lowest diffraction. If you already have a OB finished, model it and look at diffraction. You will be amazed. It should not take long to realize that the small, low, speaker in center, or tall narrow baffles suck. However, reserving my wrath for the staging gains with some of the designs. That is a tough balance, but I prefer flat frequency response first. 

I don't understand playing with baffle size and configurations. Just how many combinations are there, 10, 100, 1000? We don't do that anymore with sealed or ported, let alone bandpass. The only tweaking is a little stuffing and/or port size. Grabbing X size panel and cutting a hole in it is archaic.
My harshest criticism lately is from the response, "Well it sure sounds good to me and all I did was slap a speaker in any old board that pleased my eye".
That makes no sense. Comment should be, "How can I make it the best I possibly can with what I have to work with?"
That means computed, measured response and careful listening, of course. 
Zene


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## Bob in St. Louis (Oct 21, 2006)

> I never use cardboard/cheap panels for testing. I just don't unless it's a 2' x 2' for a quick speaker evaluation. I would OK MDF as I live with it daily for testing, but never a finished product if you are after something good.


I feel the same way. I don't like messing with cardboard, either. However, I'll mention it to guys in the hopes of showing them how easily OB experimenting can be performed.



> If you already have a OB finished, model it and look at diffraction. You will be amazed.


Yea Zene, there's Tolvan's "The Edge", ... MJK's got a diffraction program, there are a few good baffle design programs out there. But I just don't buy it for OB. Sure, if I was going to build a sealed/ported sub the first place I'd go would be a program. For baffle building though, find a program that models curves. I can show some pretty radical ideas in building an OB that can't be modeled (accurately). Modeling OB is futile (IMHO) Zene, Unless you're going to bolt the speaker to the floor of a anechoic chamber and have that be your listening room, it's a frustrating road you're going down. Zene, with OB, too many other factors will play such a huge role in the final (acoustic) outcome: Driver placement in room, toe placement, tilt angle, distance from side walls, distance from front walls, driver distance from floor..... You could spend hours and hours designing the perfect baffle shape, size, construction, material etc... and add to that the perfect driver which all models perfectly well together and then realize once you've built it the imaging/soundstage is dead. Oh, but it models "flat as a pancake". Have some passion Zene. Put the software away for one weekend, and play with it.



> It should not take long to realize that the small, low, speaker in center, or tall narrow baffles suck.


Pictures exist on the net of those very setups and the guys are perfectly happy with them. In the case of the tall thin one, the guy's even got numbers to back it up. If fact, he's got FR graphs from three different distances from the front wall. The graphs vary wildly.




> I don't understand playing with baffle size and configurations. Just how many combinations are there, 10, 100, 1000?


More than I could count. Infinite??? With so many driver choices, baffle design, shape, construction methods, room sizes, shapes the list would go on forever.



> Grabbing X size panel and cutting a hole in it is archaic.


That's how I got into OB. You described it perfectly.



> My harshest criticism lately is from the response, "Well it sure sounds good to me and all I did was slap a speaker in any old board that pleased my eye".


Try it!

Zene, after searching through the various OB forums, a fellow can get a good "feel" for what sized baffle should mate with a particular sized baffle. Let the saw dust fly. Spend $20 on a sheet of wood and come up with something that is appropriate for your sized driver. LISTEN TO IT!! Don't measure it. Maybe measure the LF roll off so you can add a sub, but don't graph it. Too many things can happen that make that graph useless. You could build it and EQ it perfectly and ruin it all by moving it away from the wall a few inches. OB is that "tweekable". It's a good thing!

Let me know if you want links/pictures to what I'm talking about.

Bob


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## Zene (Jan 13, 2007)

Bob ... Good input. As soon as I get HT up and running I will see if I can correlate scientific design vs. random design with my two favourite test pieces, True RTA and my ears. Speakers will probably be the Nirvana Super 12. Price is right and very curious about them. All tests will be with them in different baffle configurations. No woofers or tweeters. A very large baffle initially working my way down in size. I use MDF (yuk!) in my business so panels will be easy and cheap. I can recycle the ones I reject. 
BTW Edge can do 100 corners. That should be enough to simulate curved.
Zene


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