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Discussion Starter #1
Greetings, Im in the process of building a pair of down firing sonotube subwoofers utilizing one Dayton Ultimax 15" driver per cabinet. I have a pair of Bryston 4B amplifiers that I was planning to use to drive each sub. I was hoping to run each in mono, providing 800w RMS x 8Ohm per sub. My question is, is it dangerous to run the Brystons in mono to provide a 4 ohm load for the Ultimax drivers? I'm not quite sure how stable these 4b's are built to be for 4 ohm loads when run in mono. Can anyone shed some light on the Bryston amplifiers when ran in mono for a 4ohm load?
 

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What year is your amp? Is it a newer SST model? The older ones, circa 90's NRB's are rated to do 800W bridged in to 8 Ohms and sound very powerful and tight. I think you have a wonderful amp set. I love lots of current for a big sub! This is a snippet of the specs of the NRB.

Description: Solid-state stereo power amplifier. Output power: 250W continuous into 8 ohms (24dBW), 400Wpc rms continuous into 4 ohms (23dBW); 800W continuous into 8 ohms in bridged mode (29dBW). Current delivery: 16A continuous, 48A peak, per channel. Frequency response: 1Hz–100kHz, ±3dB for 1W output. S/N Ratio: hum and noise, 108dB below rated output, 90dB IHF. Input sensitivity: 1.4V for 250Wpc into 8 ohms. Voltage gain: 30dB. THD+noise: 20Hz–20kHz, 0.01%. IM distortion (60Hz+7kHz, 4:1, SMPTE method): less than 0.01% at rated power. Damping factor: greater than 500 at 20Hz, at 8 ohms (equivalent to an output impedance of less than 0.016 ohms). Input impedance: 50k ohms unbalanced, 30k ohms balanced. Polarity: non-inverting.
Dimensions: 16 3/16" (411mm) W by 7 1/8" (181mm) H by 13½" (343mm) D. Weight: 40.1 lbs (20.2kg) net.
 

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You are correct, I have actually a pair of the 4BE's which were the earliest version of the NRB. It is essentially identical to the 4B NRB version. The name was quickly changed, which little to zero differences. I purchased these with a pair of Threshold SA/6e monoblocks for dirt cheap, ($200 for the pair of Brystons:unbelievable:), and knew right away I would be using them for driving a pair of subs down the road. I'm assuming you pulled those specs off the Stereophile review? This is the reason I question its operation in 4ohm, because as it lists its specs in stereo for both 4 & 8ohm, it does not list the specs for 4 ohm when bridged, so it leaves me curious, will these babies be unstable driving a 4 ohm load when bridged?
 

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Discussion Starter #5
Seriously? $200 for a pair of Brystons? In reality someone gave them to you. Lucky dog!

I don't think the 4BE is designed for a 4 ohm bridged load. It would be best for you to contact Bryston support to find out for sure.

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Thanks for the tip, I just sent them an e-mail and will wait to hear back from them. I read elsewhere on another forum that on two occassions, people ran the 4B NRB's bridged in mono to power a pair of Infinity RS-1b woofer towers, which I believe dip as low as 2ohm with great success, however I could be wrong. Thanks again.
 

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Discussion Starter #6
My fears were proved correct. Brian from Bryston already responded to a helpful response, the 4BE's are not safe bridged for a 4Ohm load, for others who might have the same question. Perhaps I'll change the scheme to dual opposed and drive each sub in stereo for a safe 4Ohm load, or wire them in series for a 8Ohm, or will that show the amp a 6Ohm load? correct me if I'm wrong, I'm still quite a "newbie" at wiring schemes and DIY's.
 

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You are correct, I have actually a pair of the 4BE's which were the earliest version of the NRB. It is essentially identical to the 4B NRB version. The name was quickly changed, which little to zero differences. I purchased these with a pair of Threshold SA/6e monoblocks for dirt cheap, ($200 for the pair of Brystons:unbelievable:), and knew right away I would be using them for driving a pair of subs down the road. I'm assuming you pulled those specs off the Stereophile review? This is the reason I question its operation in 4ohm, because as it lists its specs in stereo for both 4 & 8ohm, it does not list the specs for 4 ohm when bridged, so it leaves me curious, will these babies be unstable driving a 4 ohm load when bridged?
I just talked to a friend that had NRB’s and ran Apogee Duetta Signatures and they are a 4 Ohm Speaker. He said it worked well but he had to careful as he was also told it was not rated for it.

I have heard a dual 15 ported sub that was driven in 8 Ohms and it was very nice and tight. 800 watts and good current is deceivingly powerful.

Your right I got the info form Sterophile. I think you will have a killer amp set for your sub in any configuration!
 

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Discussion Starter #9
If a sub is a single coil 4 ohm or a dual coil 2 ohm then a pair of them can be wired for a 8 ohm load for a single 4BE in bridged mode.

Another option is a pair of dual coil 4 ohm drivers, each wired for a 8 ohm load and each fed by a 4BE in bridged mode.
Thanks for the reply. I think that dual 15's or dual 12's per sub run in series as you said, will be my best bet at this point, and though a little more costly, I'm not disappointed. A little more never hurt anyone :hsd:. I am hoping to use the Dayton UM's because of their high Xmax and I'd like to build them in smaller enclosures and then equalize them for deeper response. I spoke with a gentlement I met over craigslist who built his own 1' enclosures utilizing a JL 12W7-3AE driver per sub, and had great success equalizing them flat to 15hz because of their high Xmax. Hopefully I'll be able to accomplish a similar setup. http://minneapolis.craigslist.org/dak/ele/3742869261.html

Here are the ones I'm talking about. Forgive me if I'm breaking any Forum rules by adding the link, I'm not affiliated with the sale in anyway, just for reference.
 
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