Newb - First run with Passive Monitors - Crossovers, Bi-Amping, Power Needs

[Phantom48v]

Hey everyone, I'm new to home theater setups, but not to audio. Up until this point, I built my home theater using active studio monitors (Genelec), but after reading up on Don Keele's Constant Beamwidth Transducers, I'm seriously considering building the array kit as a surround sound system for my brother-in-laws Christmas present.

So far, I've got the subwoofers (Genelec 1094A x 3) and a plan for a pair of JBL CBT-70J's for the center channel (they use the same technology, and the kit isn't intended for surround sound, thus, no matching center channel available). These really aren't worrying me, the subs I've used for years, and the center doesn't require anything too special.

The speakers, on the other hand, have me asking questions. For an idea of what I'm doing, check out the kit at Audio Artistry. Each speaker uses 72 tweeters and 18 mid drivers, so it's not a simple task. I'm confident in my ability to build them, but beyond that, the necessary equipment is what I find myself questioning.

First up: Crossovers.

The build manual suggests a Behringer (a brand I despise) DCX2496. It goes into great detail about settings and all that, but I've tuned my fair share of studios, so this tech isn't new to me. Is there a better brand of DSP/Crossover hardware, for...let's say...under $2,000 each (I'll need 2)? Again, I'm new to any brand that's not recording-studio related.

Next: Equipment Chain.

First, an AV receiver with separate channel pre outs. This isn't a hugely important piece, as it'll basically be a video switcher with the ability to decode HDMI-embedded audio signals to individual analog outs (I'm thinking an Onkyo TX-NR709). The video will come from here directly to the TV Monitor, the audio will go out (RCA Analog to XLR) to the Crossover/DSP (we'll say the Behringer, for now).

The Crossover/DSP will be tuned once the equipment is installed in the room. This model provides 6 outputs via XLR: Right Front Tweeter Amp, Right Front Mid-Bass Amp, Right Front Subwoofer, Left Front Tweeter Amp, Left Front Mid-Bass Amp, Left Front Subwoofer (the second crossover will do the same for the Rear Channels). Subwoofer outputs go directly to the Genelecs...easy. The other outputs go to the Amps, which is where my questions get more ignorant.

The Amps the build manual suggests are a pair of Jeff Rowland Model 625 Power Amps (which means I'd need 4). These go for about $15,000-$20,000 each, which is NOT going to happen.

The power requirements, as noted by the build manual are: LF: 50-500watts HF: 50-150watts. My question is (first time passive, remember) is there an advantage to using higher/maximum wattage?

I found a single power amp which I believe will power all four speakers on its own. It's a Niles (brand I've never heard of...good?) SI-1260. First, it can take all 8 outputs from the Crossover using XLR to RCA cables. Each output provides 60 watt / 8 ohm, or 80 watt / 4 ohm. It can also be bridged to make 120 watts / 8 ohm.

What's the advantage of using the higher wattage with lower ohm? This unit has 12 channels of output, since these speakers need to be bi-amped, I need 8 outputs. Does bridging these channels cut the output capacity of this amp to 6, and since the speakers require bi-amping, only allow me to power 3 speakers at the 120 watt power range? Will the mid-bass drivers suffer being so far away from their load maximum of 500 watts?

I'm open to using 4 individual power amps, but I'm not familiar enough with what to look for that will work for this process. Is there any suggestions for alternatives that will bi-amp each speaker individually, and bring me higher up on the wattage range, while keeping price more reasonable (say, $500-$1,000 apiece)? The output of the amps should accommodate a pair of banana plugs, which will go to Speakon to the speakers.


I apologize for the length of my first post. I hope I've made my intentions clear, and provided enough references to let you what I'd like to achieve. Any help from people who have experience in this would be greatly appreciated. Thanks in advance for your time, I hope to hear from you with any suggestions you have to offer.

 

[fuzz092888]

First off, I'm no expert, and there are many more qualified people on here who can answer your question, and from the sounds of it you may know more about audio than I, but I can at least provide some suggestions for a few of your questions.

First, I haven't used one myself, but I've talked to a few people who have one and they seem pretty happy with this crossover:

Electro-Voice DC-One Two-in/six-out sound system processor

Second, the onkyo should be fine.

Third, to my knowledge, using a higher wattage will benefit you mainly during peaks, or if you are absolutely blasting whatever you are playing (someone can correct me if I've said something dumb). You shouldn't necessarily need all 500 watts, but something in the 100-200 range would probably be more than you'll ever need. The wpc rating is usually RMS, which means if something is rated 100 or 200 wpc it can takes peaks much higher than that (how much higher depends on build quality).

If the amplifier has a lower ohm rating it usually means that it is much more stable with difficult loads. No speaker stays at whatever ohm rating is has and generally swings up and down depending on what you're driving through it, so a lower ohm rating on the amp means it will handle those swings without it getting angry (again correct me if I said something dumb).

If you bridge it takes whatever impedance the amp sees and cuts it in half. 8 ohms becomes 4 ohms, 4 becomes 2 and so on. This also means it lessens the stability of the amp during those swings (unless your speakers are easy to drive, have better build quality, and stay flat).

As for amps,

Crown XLS2000 DriveCore Series Power Amp | Musician's Friend

These are just suggestions, and I may be wrong somewhere in there. If someone could verify/correct anything I've said that would be good.

 

[Phantom48v]

Thanks for the quick reply!

I'd never considered PA Amps for this setup, but from what little I know about passive monitors, I know Crown is the industry standard for power. The XLS2000, however, is waaaay above the power levels I need. The XLS1500 would be perfect for the mid-bass (300w/8Ω), however the smallest amp they offer at the lowest setting is still 65w over the maximum for the tweeters (at 215w RMS).

American Audio power amps has a model (VLP300) that will output 100w/8Ω, as well as one (VLP600) that will output 300w/8Ω, but I'm unaware of the brand, and it seems pretty cheap (around $150-$250, respectively), and I'd rather not go high-end on the speakers, and cheap on the other components. Does anyone know anything about this brand?

Going back to my original, the Niles SI-1260, are there any thoughts on using this piece? Is Niles a good brand? It has 12 channels, which can be bridged. My thought was to use the first 4 channels at 60w/8Ω (or, would 80w/4Ω be better for a tweeter with a 150w maximum load?) for the highs, then bridge the last 8 channels to run 120w/8Ω to power the 4 mid-bass.

Your response about power stability at higher Ω was really helpful, I think I'm understanding the change...I'm still just a little unaware what benefits come from either the loss of wattage or the loss of Ω. Is it always better to use less power at more Ω (which is the direction I'm leaning), especially when the power needs are so low (150w max to the tweeters)? Or better to push more power to the unit at the loss of Ω, especially since its driving 72 separate tweeters on each speaker?

Thanks again!

 

[fuzz092888]

I looked up the speakers in question and did not see anything about 150W max load, however unless I'm mistaken, putting more watts into than what the speaker is rated for won't necessarily harm the speaker. It really depends on how loud you are playing whatever it is you are playing and unless you are playing at reference levels or above you shouldn't be putting anywhere near 300 watts RMS (I could be wrong).

The speakers you mentioned are rated 8 ohms, so the 8 ohm rating is really what you're looking for when you look for an amp. If an amp is rated down to 6, 4, or 2 ohms it just means that it will deliver a higher current into the speakers. Again, unless the speakers you are driving are a particularly difficult load (low ohm rating, low sensitivity rating) this shouldn't be a big deal. The speakers you mentioned have a 90 something db sensitivity rating which is pretty good and they are rated 8 ohm, so they should be a fairly easy load to drive.

On an aside, the ohm rating speaks to what the impedance is. Or as Crutchfield says:

"A speaker's impedance rating refers to the amount of electrical resistance it presents against current flowing from your amplifier or receiver's powered outputs. Though impedance actually fluctuates as the speaker reproduces different frequencies, manufacturers usually publish a single, average figure, known as nominal impedance.

Most home speakers have a nominal impedance rating of 8 ohms; likewise, practically all home A/V receivers are designed to be stable when pushing an 8-ohm load. There are a number of higher-end receivers that are capable of handling a 4-ohm load (if you're not sure about your receiver, check the specs in your owner's manual). Speakers with significantly lower impedance (4 ohms or less) may cause problems with 8-ohm receivers by asking them to deliver more current than they are capable of producing.

When you drop from an 8-ohm to a 4-ohm load, you cut the electrical resistance in half, which usually causes your receiver to increase its total power output. Some people are tempted to mate their 8-ohm receivers with 4-ohm speakers, in order to get more wattage. It's wise to avoid this temptation, since it can lead to greater distortion, and cause the receiver to run hot or activate its protection circuitry and shut down."

There are better explanations out there, and somewhere I around here I saw a particularly good explanation with a good link or two, but for the life of me I can't find it.

I don't know much about Niles or American Audio, but what you're saying should work with the Niles. Personally if I was going to be doing the active bi-amping with those speakers I'd probably go with something a bit more substantial that the Niles, but thats just my personal preference.

 

[Phantom48v]

Well...it appears I didn't read far enough (or at least wasn't paying enough attention) but the speakers are rated to 4 ohm; from the AES Report/Assembly Manual:

13.1.5.8. Nominal Impedance:

4 Ohms (Not falling below 3.9 Ohms for LF and 3.6 Ohms for HF, see following section for graphs).

13.1.5.9. Amplifier Requirements:

LF: 50 to 500 Watts. HF: 50 to 150 Watts. Higher powered amps can be used to reproduce short-term transients without clipping for high crest-factor program material.

13.1.5.10. Maximum Continuous Input Voltage and Power:

LF: 45 Vrms (500 Watts in 4 Ohms). HF: 25 Vrms (150 Watts in 4 ohms).


I'm not sure where you're looking, but I suspect you're looking at the wrong speakers. Since I'm new, I'm not allowed to post links...I thought if I cited my source in the Trackback section below the post text window, they'd show up as a type of signature in my initial post. As I get past the introductory stage, I will re-edit my original post with the correct references. The speakers can be found at the AudioArtistry (dotcom) website, which provides all the information I've found, as well as the Parts-Express (dotcom) website selling the kits.

With this new knowledge, I'll have to reevaluate what I'd been looking at. I don't think I can bridge the channels and still run a 4Ω load with the amps I've been researching, and I'm assuming 8Ω would cause problems (these appear to be pretty picky speakers).

I'll do some more searching and get back to you, again, I appreciate the help.

 

[Phantom48v]

You may have a bit of noise with that one, because you'll need to use the Samson S-Convert to bump levels. I did, though keep in mind my Aurasound subwoofer drivers are flat on their own to over 1kHz.

Noise with what? Subwoofer? Amps? Center? Crossover?

 

[fuzz092888]

Ah- I see my error, I think I was looking at the JBL's you mentioned above. If you were planning on bridging to the 4 ohm speaker that wouldn't work at all. The Niles is only rated down to 4 ohms and if you have 4 ohm speakers and you bridged, the amp would effectively be seeing a 2 ohm load, which would not be good for any of your components. Plus I've been told that bridging is not recommended for anything below 8 ohms.

Its not that the speakers are picky per se, you just need to buy an amp that will run a 4 ohm load while still giving you enough power. You can either go with those stereo amps (the crown) for cheap, run the niles with less power, or figure on a different amp altogether. It really depends on what you want. Again the speakers aren't picky as long as you run something that is rated at 4 ohms.

As to the above, my guess is that he is talking about the amp, but that's just a guess. As to noise, that gets into more of a debate of what the noise actually is (ground loop hum, light fixtures on the same circuit, etc). He may be trying to say that they crown or whatever component he's talking about is especially sensitive to noise in the signal. Not really sure.

 

[Phantom48v]

Well, I've been doing research and found a pair of Creek amps that run 4Ω. An Evolution 5350 with 200w/4Ω, and an Evolution 2 with 110w/4Ω.

How do you select the ohm output? The amps I've looked at don't seem to have a switch...is it jumper settings or something? Just curious.

Got the JBL's today! Haven't had a chance to play with them yet, but it looks cool =). Reading instructions is important, otherwise you won't know the screen is bolted to the unit until you force the screen off only to discover 2 screw-sized holes in the metal =p.

 

[fuzz092888]

Ohms = impedance. This is more complicated than I feel comfortable trying to explain, but suffice it to say that impedance and resistance both have to do with acting in opposition to the current of electricity that is trying to be driven to your speakers. It's not a setting.

http://forums.audioholics.com/forums/loudspeakers/72894-6-ohm-speakers.html

This is a link to another thread here on audioholics that explains impedance (and in turn what the ohms rating means). Just read the whole thing so because other posters offer some corrections to the longer paragraph.

 

[Phantom48v]

Thanks for the link...it was really helpful. I talked to one of my electronic engineer friends and I think I'm ready to build. This is what I've decided on:

Emotiva XMC-1 Pre Amp/AV Switcher (when available)

(2) Deqx HDP-Express Crossover

Emotiva XPA-5 5 Channel Amp (Mid-Bass x 4, Center)

(2) Emotiva Mini-X A-100 (Tweeter x 4)


From what I've read, and what I've learned here, I think this is the best bang for the buck. If anyone can see any flaws in my plan that I may have overlooked, please let me know before I cut the check =p.