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Old 6th September 2004, 01:40 PM   #1
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Default Was building Phoenix ... Now maybe Orion?

I've been getting a lot of good input from this site.

As a result, I've changed my original build plans.

I am building a combination Home Theater system and main music system. I was originally planning to build Phonix surround speakers (using Orion drivers w/ modifications to the crossovers) and Orion mains.

To start out, I ordered the Phoenix plans. I now have the Phoenix plans along with the Orion crossover PCBs.

Once I re-read a bit more and learned from folks on this site, I started planning on going with Phoenix panels for the speakers, with a couple of dipole woofers. Why? One of the main reasons is speaker/driver compatibility on all the speakers.

I am the proud owner of a room that I have never successfully been able to get usable rear surround effects from. I currently have Martin Logan speakers all the way around the room - the room layout and the radiation characteristics of the drivers just didin't work in my setup. I'm going to go with a more conventional driver setup now, and I think I'll have the best shot of surround working properly if the speaker drivers all match.

Now, I've been thinging about building the Orions for all the speakers, with full-up Orions for the fronts, and just the Orion upper MT panel for each of the three surround speakers. While it looks like this is the more obvious way to go for the sonic benefits, and because it should be cheaper, there's two problems:

(a) From what I can figure, I would now need 14 channels of amplification. I would have 5 MT panels that require 2 amp channels each, and 2 dipole subs (2 drivers in each sub) that that require an amp for each each driver. Thus, the ATI 6012 12-channel amp isn't usable - or, I would have to buy two ATI 6012 amps - now the Orion option is more expensive.

Using Phoenix MTM panels and two of their dipole woofers, I would require only 12 channels of amplification (3 channels for the 2 fronts, and 2 channels for the 3 surrounds), so the ATI 6012 amp would be sufficient - and the less expensive way to go.

(b) The Orion MT panels drop off at 24 dB/octave at 120 Hz. This isn't a problem for the two front speakers, but the 3 surrounds are supposed to have a usable response going down to 80 Hz, if I remember right.

So, I have a couple questions:

1) Can I use other options to get the 14 channels of amplification? Can I use the ATI 6012 and 2 channels from an existing amp if it has a line level adjustment. I susupect not - I think that gain factor matching between dissimilar amplifiers is impossible just by adjusting the line levels. Has anyone built the cheap amp listed on the Linkwitz Labs site (See here)? If so, how well did it work?

2) Is the somewhat limited LF response of the surround panels going to be a problem for good surround sound? Would it make more sense to lower the cutoff frequency to 80 Hz for these panels?

Thanks!
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Old 7th September 2004, 10:57 AM   #2
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I have fronts which are MTMs like thePhoenix, and a center and surrounds that are TM like the Orion. I cross them over to a monopole sub at 80Hz and haven't had any audible problems with over-stressing the woofers.

This setup means I use 12 channels of amplification since I use one amp for both woofers in my mains rather than one for each driver. I also replaced my $2K multichannel amps with the Panasonic XR25 receiver, using the 5.1 channel input. The two of them I use cost a total of $500 for 10 channels of amplification.

Your degree of amplifier worship may vary, but I can't hear a worthwhile difference between them an my old amps, and they have had raves elsewhere.

Cheers

Steve
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Old 7th September 2004, 11:52 AM   #3
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More amps for the Orion?
This doesn't sound right. It could only be true if the Phoenix uses an amp channel for 2 drivers where the Orion uses one each. Surely this would mean that the Phoenix would need double the power in that one channel. You could look into using chip amps for all the channels and build them all diy.

With your surrounds you will have to experiment. Going from 120 Hz to 80 Hz where you have to equalise 6db/octave for dipole cancellation means that you need 4db of eq. This means you need 66% more excursion (6dB ~ double). This might give you problems if you modify it in this way, but then again surround content is not as demanding so it might not be as much of a problem as you expect. You might do ok with pushing them down a little lower - say 100 Hz and not bothering with a slight dip from 80 - 100 Hz, such as are normally encountered in a room with much greater severity with room modes. Or you could just leave it as is and see what you think - you might not find that the loss of low end in the surround channels is not worth worrying about.
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Old 7th September 2004, 02:36 PM   #4
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Quote:
Originally posted by paulspencer
More amps for the Orion?
This doesn't sound right. It could only be true if the Phoenix uses an amp channel for 2 drivers where the Orion uses one each. Surely this would mean that the Phoenix would need double the power in that one channel. You could look into using chip amps for all the channels and build them all diy.
I didn't think it sounded right, either! But ...

See the 8 channels of amplification required for the Orions in the System Specifications

See #3 under "Each playback channel consists of: ..." on the Phoenix

Paul, thanks for recharging some burned-out old brain cells. Your information on the excursion requirement had me thinking for a minute ... and then I remembered the old basic equations / theory from about 20+ years ago. I love this site! Your help has been invaluable!

Based upon your info, I don't think that I'm going to push the crossover frequency down yet. I'll build the "stock" Orion crossover if I can get this project off the ground.

Once I can figure out what to do to get the required 14 channels of amplification taken care of, I'll start ordering all the parts. That's the only thing holding me up now.

sfdoddsy - Great info on the XR25! I will probably purchase 2 of those instead of the AT6012. Did you use Orion drivers throughout your system? If so, what crossover mods did you make to the MTM panels?

Arrg! ... I can't wait to get started on this!
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Old 7th September 2004, 03:33 PM   #5
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Quote:
Originally posted by ¿GotJazz?

Once I can figure out what to do to get the required 14 channels of amplification taken care of, I'll start ordering all the parts. That's the only thing holding me up now.
Some options to consider:

1. DIY chip amps - ok if you don't push them too hard, then they become ugly due to their protection system

2. DIY amp like ESP's 60/100w power amp - a little more expensive, excellent performance

3. An amp kit like Aksa

You may wish to have a go at one first to get it right, then duplicate with all the other remaining channels. Trying to get so many channels on a budget is quite a challenge. You might be able to pick up some cheap secondhand amps - you might find a power amp or an integrated amp which has inputs and outputs that let you get to the power amp with an amp like a nad, rotel etc and you can use the cheaper lower powered units for tweeters. Still, I expect if you manage to pull of a DIY amp, then that could well be the cheapest way to do it.

You might use lower powered chip amps for the tweeters, and more substantial amps for the woofers and mids.
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Old 7th September 2004, 04:49 PM   #6
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Look at this site:

www.hypex.nl

Not too expensive, even if you need a lot of channels.
There is a thread:

UCD180 questions

and

UCD180 or UCD400?

Want to sell the Phoenix plans and PCB's???
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Old 7th September 2004, 05:23 PM   #7
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Default Re: Was building Phoenix ... Now maybe Orion?

Quote:

1) Can I use other options to get the 14 channels of amplification? Can I use the ATI 6012 and 2 channels from an existing amp if it has a line level adjustment. I susupect not - I think that gain factor matching between dissimilar amplifiers is impossible just by adjusting the line levels.

2) Is the somewhat limited LF response of the surround panels going to be a problem for good surround sound? Would it make more sense to lower the cutoff frequency to 80 Hz for these panels?

Thanks!
1. Wired in parallel the Peerless XLS drivers (Orion or current Phoenix - the original Phoenix used different woofers) reach 2.5 Ohms. Your amplifiers' compatability with this load determines whether one or two channels are needed for each speaker's bass. I use a single Adcom 555ii for my Orions' bass. Matching between amplifiers is possible either with an input level adjustment or output attenuation (this raises the output impedance). AFAIK the 6012 recomendation comes from its inability to bottom the woofers above 22Hz, good turn-on manners, and gain which will provide good signal-to-noise performance with the cross-over.

2. A dipole requires about 5X more displacement to play 80Hz at the same level as 120Hz. Running the surround panels down to 80Hz will drop the maximum output level by nearly 12dB. With the Orions just approaching the output requirements for reference level home theater (0dBFS is calibrated to 105dB at the seats; but most sound tracks can't exceed 101dB) that could be marginal, although program content (I never looked at how loud the surround channels actually are) and your listening levels (I usually listen between reference -10dB to reference -5dB) can also make that a non-issue. A 120Hz 4th order acoustic XO between surround and main (stereo) bass seems to work well with other speakers. Given a surround sound decoder which provides a 120Hz 2nd order XO I'll just build one of the two main panel high pass filter sections for my center and run it that way. Steve Dodds has had good results crossing his MT pannel W22s to a monopole sub at 80Hz; perhaps he can shed light on his listening levels to match theory and practice.
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Old 7th September 2004, 05:25 PM   #8
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Quote:
Originally posted by paulspencer

With your surrounds you will have to experiment. Going from 120 Hz to 80 Hz where you have to equalise 6db/octave for dipole cancellation means that you need 4db of eq. This means you need 66% more excursion (6dB ~ double).
This is on top of the 4X / octave increase you have in a sealed system.
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Old 7th September 2004, 06:08 PM   #9
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Oops, I made a mistake.

For a monopole double the displacement/octave

Dipole cancellation below Fequal also requires double the displacement/ octave

120 - 80 Hz is two thirds of an octave so the extra displacement ~ 2.7x

This is equivalent to ~ 8dB of eq required

Drew, where did you get 5x displacement from? This sounds a little high.
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Old 7th September 2004, 07:44 PM   #10
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Quote:
Originally posted by paulspencer


For a monopole double the displacement/octave

Nope.

Monopole excursion limited output adds a 40 log f term, meaning excursion is quadrupling with each octave decrease in frequency. The additional compensation for dipole roll-off at 6dB/octave nets you an octupling of displacement requirements for each octave decrease in frequency.

2/3 * 8 = 5.3X displacement change

Or at constant displacement, maximum output decreases

2/3 * 18dB = 12dB

Sources:

Linkwitz spreadsheet
Linkwitz forumula
DIY subwoofers sealed forumula
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