How much power is enough for B&W Nautilus 804's?

i would go for 1 or 2. Personally, try 2 first...because my guess is that in the short run...properly set up you'll get loads of bass...and potentially in the long run, you'll change 804s for something (even if its 10 yrs from now)...but i would not be surprised if you kept the sub in any event. I still use mine, and i've got some pretty big speakers today...but i set the sub at below 41hz. Just my two cents. good luck!

3) makes no sense without 3a)remove built-in crossover.

Hi Ed,

I'm pretty certain that the output impedance of the Bryston preamp is low enough to be suitable for use with y-adapters, given the input impedances of your (and nearly all other) amps.

I would rule out course of action no. 3 in your list, though. Adding an electronic crossover would eliminate two of the potential issues I listed in my post (the last two), but would not make much if any difference with respect to the first. The somewhat limited current capability of the amp, as addressed in Bombaywalla's post, will assume increased significance in bridged mode as a result of the halved load impedance seen by the amp in that mode.

Good luck in your quest! Regards,
-- Al

Thanks all for the info! This was 1st post on AudiogoN. Took me a while to find where responses live.

Other details on my kit: low end Bryston preamp (.4B), only source is PS Audio DAC 3 w/ Cullen Phase 4 mod, RCA connectors thru out including Y adaptors from pre to amps for bi-amping, no electronic X-over

Seems to me I have 4 courses of action to consider:

1) get different, more bass-capable speakers
2) add a subwoofer (heard REL Stratus III is particularly well suited to 804)
3) add electronic Xover(s) to take advantage of possible bridged 4B-ST's
4) learn the electronics in play to REALLY understand / improve these system choices!

Again thanks all. Great stuff!

Ed

Exactly, if you want bass similar to open E string of double-bass Bowers will be your worst investment.

I haven't owned N804's, but I've owned several b&w's, inc. Matrix 802's. No matter HOW much power I fed the 802's, the bass was never tight or coherent enough.

I sold them & bought Totem Mani 2's, way better bass (& almost everything else). So you might want to check out other speakers, & not necessarily floor-standers IMO.

I run my system including the 804"s" with an anthem statement p5. works great.

Almarg,
excellent comments & observations esp. #1 as I was also thinking along the same lines. I've bashed B&W enough here (despite being a former B&W owner OR maybe because I was once a B&W owner) that I decided to stay away. ;-)
Then I noticed that you were thinking along the same lines & just had to pipe in..... :-)

One more thing - just because the Bryston amps are high wattage does not mean that they can source large amounts of current. I did not find any specs for the 4B-ST (tho' I did find a 1992 Stereophile review of the 4B). If the 4B-ST is anything like the former 4B then I read that the DC rails of the power amp are 85V! Meaning that the power transformer must be 60VAC. I have no idea what the VA rating of the power transformers are for the 4B-ST but that would have give some idea of the power delivery capacity. At any rate, the output transistors must be fantastically high voltage rated to run at 85V. IOW, at 85V the current handling capacity of some BJT power transistors is severely degraded i.e. they cannot handle much current while remaing inside their safe operating area (SOA). Thus, you have the high wattage of the 4B-ST but might not have the current delivery capability that B&W speakers so -l-o-v-e-. Hence a bass that is lacking heft.
Looking at the 4B-ST chassis leads me to believe that this thought process is on the correct track.
If the 4B-ST was a current delivery power-house the chassis would have looked like a Pass Labs 350 power amplifier Or a Plinius SA-250, for example.

Good comments by the others. Some additional thoughts:

1)If the impedance curve of the N804 is anything like curves I have seen for some of the other Nautilus models, such as the 801, the 4B-ST will most likely not be able to drive their woofer sections properly in bridged mono mode. Note that the power rating of the 4B-ST in bridged mono mode is only specified for an 8 ohm load, and not for a 4 ohm load. The reason for that is that in bridged mono mode the amp outputs "see" a load impedance equal to the speaker impedance divided by 2. Since the speaker's impedance in the mid-bass region (at least for the N801) is less than 4 ohms, it will be seen as less than 2 ohms, which the amp will probably not be able to handle, at least in an optimal manner.

2)I second the question about what preamp are you using to drive the amplifiers, and can you also describe how the preamp and amps are all connected together (e.g., with y-adapters)? Depending on the preamp design and the interconnection configuration, it's possible that bass is being reduced as a result of either impedance incompatibilities (due to the dual loading) or level mismatches (if perhaps you are using an RCA output for one amp and an XLR output for the other).

3)Assuming that you are biamping passively (without an electronic crossover between the preamp and the power amps), using the 4B-ST in bridged mono mode might result in a gain-matching issue between the low and high frequency amps.

4)Assuming that you are biamping passively, you would probably not be able to utilize a lot of the power capability of bridged mono 4B-ST's, because without an electronic crossover ahead of the amps all of the amps have to output a voltage range corresponding to the full frequency range of the signal. Therefore you would not be able to turn up the volume high enough to use much of the power capability of the higher powered amps without overdriving and clipping the lower powered amp.

Regards,
-- Al

No matter what you do to 804 they won't have bass even with kilowatt per side. Won't go anylower than 48Hz.
Running amps of different power puts them definitely out of tonal balance.
If you want to get bass the only way with 804's is by adding subwoofer

I love the 804. i have the 804"s" models... i use mine for mostly home theater so the low of the lows are from a sub... the 804 has really good highs and mids.... buy a good sub... Save the money on the new left and right speakers and just get the sub.

what are you running as the preamp? making the settings change might help as well...

my buddy is a bassist.... if you liked the sound from a commercial massive speaker then it will be hard to reproduce that same sound with anything but those types of speakers.

when it comes to bass size will play an important role... it is not the be all end all though.... but if you are used to a 15" black widow type speaker it will be hard to match it with something from ANY floor standing speaker.

Bill

Well, you have certainly proved power is not the problem. IME you have the wrong speaker to achieve the results you are looking for.

You've got loads of power in the 804s...loads. The 4B-ST is a mighty powerful amp, reknowned for its bass power. You're already bi-amped with another Bryston.

I would suggest if you wish for more powerful bass, other than room placement, you may wish to go for bigger speakers or a well-integrated sub option. If it is simply bass you seek, there are some very good options that will take time to integrate...but can be well worth it.

Aside from B&Ws own subs, you could try JL Audio, Velodyne DD-18, possibly REL.