Speakers for NuForce

rustydoglim · « **on:** 11 Aug 2005, 02:38 am »

In general, we recommend Ref 8 for speakers with >89db sensitivity and 8 ohm impedance. Ref 9 has the power to drive all speakers except Apogee. [Update: we haven't done any test or measurement whether Ref 9 is capable of driving a 1 ohm load speaker and still performs well]

eg. Wilson Puppy 6 which is >90db sensitivity with 4 ohm impedance sounded awesome with Ref 8. For a 89db sensitivity and 4 ohm impedance speaker, it will be borderline case with Ref 8 (we recommend that you go with Ref 9 unless your musical preference and room size doesn't need Ref 9's power).

Use this topic for speaker discussions and recommendations.

matix · « **Reply #1 on:** 11 Aug 2005, 05:32 am »

I am thinking of the Ref 9 until see this post by Jason. The JM Lab has a sensititivity of >90db. Maybe I should just get the Ref 8 and save some money. I am however, worry about big orchestral Mahler music which I normally listen to... On the M8, my 100wpc power tube amp is strained to the pt. of distortion...

rustydoglim · « **Reply #2 on:** 11 Aug 2005, 07:45 am »

Check the impedance of your speaker too. Does it drop to 2 ohm?
We have 3 pairs of Ref 8 out for audition at all time now and it is easy to get on the queue. You can give Ref 8 a try. If you listen to big orchestral in a big room, to be on the safe side, go with Ref 9. You might be happy with Ref 8 99.9% of the time but then you hit one note on a track that clip and then you'll have flash back for the rest of your life until you upgrade your amp

silversurfer · « **Reply #3 on:** 13 Aug 2005, 06:01 am »

Jason,

You mean to say that the Ref 9 doesn't drive any Apogee? Wouldn't they even drive the Duetta's which are 86 db and 4 ohm panels?

Don't you mean they won't drive the Apogee Scintilla 1 ohm?

nuforce-casey · « **Reply #4 on:** 13 Aug 2005, 08:56 pm »

Quote from: silversurfer

Jason,

You mean to say that the Ref 9 doesn't drive any Apogee? Wouldn't they even drive the Duetta's which are 86 db and 4 ohm panels?

Don't you mean they won't drive the Apogee Scintilla 1 ohm?

Apogee speakers have been out of production for 20 years?? They should be used with the 1KW Class A amplifier like Mark Levinson ML-2, Krell KSA 100, etc, that heats the room like a fireplace and pumps out 1.2KW to 1 ohm load.

To be practical and sensible, today's modern speakers rarely have a less than 2-ohm load, and usually, with even >2 Ohm load, the trouble is with the LC swinging widely, that could become problematic. For example, a highly inductive load could oscillate the amplifiers, while a capacitive load could drain too much current.

So a purely resisitive 2-ohm or 1.5-ohm load is really not difficult to drive, and designing amplifiers to drive resisitors does not make a lot of sense. NuForce's unique switching topology is load invariant, meaning, it does not care if the load is inductive or capacitive. However, the power consumption is typically a constant based on the current limit of the design.

Ref9 is designed to put out 7-9AMP in a steady state, with a peak of >20A for music programs. With a 1-ohm load, it simply means that the amp will hit 300W much sooner than with 2-ohm load. The ability so supply huge current is an advantage of NuForce design. Class A/B amplifiers using linear supply (as well as switching amplifiers using linear power supplies) starts to stretched when the current requirement goes up, are not able to supply a lot of current, and the rail voltage will start sagging. That's why our Ref8 could even drive the Apogee 1-ohm load and Sound Lab speakers.

Whether 300W is enough to drive Apogee, is purely a mathematical question. What's the efficiency, how loud you need, how far away from the speakers, with all these number, the required wattage can be calculated.

dBW = Lreq - Lsens + 20 * Log (D2/Dref) + HR

W = 10 to the power of (dBW / 10)

Where:
Lreq = required SPL at listener
Lsens = loudspeaker sensitivity (1W/1M)
D2 = loudspeaker-to-listener distance
Dref = reference distance
HR = desired amplifier headroom
dBW = ratio of power referenced to 1 watt
W = power required

nuforce-casey · « **Reply #5 on:** 13 Aug 2005, 09:13 pm »

How much power is required:

The farthest listening position from the loudspeaker is 3 meters (10 ft), and the desired Sound Pressure Level is 85 dB SPL (very loud) The loudspeaker chosen for the job has a sensitivity rating of 81 dB. With the minimum recommended amplifier headroom of 3 dB, then you need to choose an amplifier that can supply 28 watts to the loudspeaker.

Now, if the speaker is Apogee Scintilla, 79dB/W sensitivity: to get 85 dB SPL, only 71W is needed, but to be able to attain a peak of orchestra peak/climax, say 100dB SPL, then a peak power of 2261W is needed.

NuForce Ref9 can supply peak power of 1300W/each, so they would allow Scintilla to attain a peak SPL of approx. 100dB, sitting 3-meters away. With 2 speakers driven by a pair of Ref9.

flintstone · « **Reply #6 on:** 13 Aug 2005, 09:49 pm »

We had a member of our forum (Apogee speaker users forum) try the Nuforce...I think 8's on his Scintillas.

He said they sounded fantastic...but, as noted above...a tad lite in the power department for the Scintilla so not a good match.

I'm an Centaur Minor and Duetta Signature owner...I would expect the Nuforce to do much better with my speakers which are (Maggie like) 3.6-4ohm load.

I did one day (just for the heck of it) hook-up my sub amp (Onkyo M-504) to my Duetta Sigs. While it sounded like an Onkyo...it did not peg the large power meters at loud SPL's as I thought it would.

Dave

silversurfer · « **Reply #7 on:** 13 Aug 2005, 10:09 pm »

Wouldn't that be 48 Watts for that 85 dBSPL? However it all comes down to if the Nuforce can supply enough ampere to the panels. In your example about the Scintilla you say that one Nuforce can peak with 1300 W. This does mean that they can supply 130 A assuming the Scintilla is a flat one ohm (which it isn't). If so then I do think they will drive Apogees except for the Scintilla.

Carlman · « **Reply #8 on:** 13 Aug 2005, 10:57 pm »

I'm using 86db Usher monitors (8ohms I think) and the Ref8's had NO problem driving them. In fact, it was quite nice.

Carlman · « **Reply #9 on:** 13 Aug 2005, 11:09 pm »

tvad, I thought about that too... And I'm not sure if the subject of this thread is truly indicative of the discussion... but if so... I would agree it's putting the cart before the horse... However, I have noticed with ALL digital amps so far, they really favor certain, specific combinations. I don't know what they are but some people love digital amps that have speaker X. If you go read all the early reviews of the digital amps, most people had a certain brand speaker that they loved it... then people like me that didn't have that specific speaker couldn't understand what all the fuss was about. I think VMPS likes digital amplification.. and there are others...

So, if that's the point of this thread, I think it's good to have a list of known 'good matches' to these amps.... and while it is techically backwards, it's helpful thinking forward.

John Casler · « **Reply #10 on:** 15 Aug 2005, 10:06 pm »

Quote from: Carlman

I think VMPS likes digital amplification.. and there are others...

So, if that's the point of this thread, I think it's good to have a list of known 'good matches' to these amps.... and while it is techically backwards, it's helpful thinking forward. ...

I decided to be a NuFORCE DEALER for that very reason (Thanks Jason)

Frank Alles who gave VMPS RM30s such a great review recently, tried his pair with the NuFORCE 8's and can't stop talking about them.

Look here for the review (of the AMP with the RM30s)

http://www.stereotimes.com/amp071505.shtm

rustydoglim · « **Reply #11 on:** 18 Aug 2005, 03:03 am »

FYI, we measured NuForce amp driving 16 ohm load and the result is just as good as on 8 ohm. We measured good results with 2,4,6,16 ohm.

vdm · « **Reply #12 on:** 21 Aug 2005, 12:17 pm »

Has anyone used the Nuforce with the Zu Cable Druid mk4 speakers? The Druids are characterized by their very high efficiency (101dB) and high impedance of 12ohm nominal, 7.5ohm minimum and 22ohm maximum.

They should be very easy to drive for most amplifiers, but maybe there is something in the design of the switching amplifiers that result in them not performing well at such high impedances. I guess many amplifier designers optimize their designs for loads in the range of 4ohm to 8ohm.

How small is the noise floor of the Nuforce amplifiers? High efficiency speakers tend to amplify the noise levels that may be inaudible for the less efficient speakers.

Another concern I have is with the gain of the amplifier. A high gain may amplify the noise floor of source components. I understand the Nuforce has a gain of 26dB. Would that be too high for such high efficiency speakers? Is it possible to lower the gain of the Nuforce amps?

hometheaterdoc · « **Reply #13 on:** 21 Aug 2005, 12:30 pm »

I have now used the Nuforce amps with the following speakers:

Von Schweikert Audio VR-4SR, VR-4jr, LCR-15s, and VR-1s
Usher Audio Dancer II CP-8571, X-718, CP-727, S-520
Phase Technology PC 3.1 MKII

So, in essence, I have used them with a group of speakers ranging from $350 a pair to $10,000 a pair. In every single instance, the amps worked very well. It may not have been the exact kind of sound that everyone would like. But I've personally enjoyed every combo. Some have been downright fantastic!

rustydoglim · « **Reply #14 on:** 22 Aug 2005, 08:42 am »

Quote

They should be very easy to drive for most amplifiers, but maybe there is something in the design of the switching amplifiers that result in them not performing well at such high impedances. I guess many amplifier designers optimize their designs for loads in the range of 4ohm to 8ohm.

Don't speculate

Why do you think NuForce will not perform well at such high impedances? We tested it at 16 ohm and the spec is the same as that at 8 ohm.

Quote

How small is the noise floor of the Nuforce amplifiers? High efficiency speakers tend to amplify the noise levels that may be inaudible for the less efficient speakers.

Signal To Noise ratio is 120 db at 100W.

Yes, we can lower the gain from 26db to 23db if you custom order it but we'll have to charge you some extra labor to do that.

vdm · « **Reply #15 on:** 22 Aug 2005, 08:24 pm »

Quote from: nuforce-jason

Don't speculate Why do you think NuForce will not perform well at such high impedances? We tested it at 16 ohm and the spec is the same as that at 8 ohm.

My question alludes to a question I posted in the "Specs and other technical stuff" thread. When driving high efficiency and high impedance speakers the typical power output of the amplifier is around 5W, plus or minus a few Watts. At such low power outputs and driving of high impedance loads the efficiency of switching amplifiers can typically be in the region of 20% - four times lower than the typically quoted number. Since I don't want to speculate again,

my question is whether the Nuforce exhibits the same behaviour under such conditions, and whether it influences the sound quality when that happens.

Quote from: nuforce-jason

Signal To Noise ratio is 120 db at 100W.

Yes, but what is the S/N ratio at 1W, 5W, 10W and 20W? Those are the numbers that count for normal listening levels in quiet environments.

Please don't misunderstand me, I'm not trying to knock the Nuforce amplifiers. I do believe they are unique in their approach to switching amplification. For that exact reason I am very interested in them and may even buy a pair. But, before I do I'm really just trying to find out how they would behave with high efficiency and/or high impedance speakers.

rustydoglim · « **Reply #16 on:** 22 Aug 2005, 11:36 pm »

When we have time to provide some other technical information, we will consider. We have an audition program for those skeptics to participate. Instead of analysing everything to death, why don't you just listen to it?

NuForce amp has quiescent power around 5W, so in the case of high efficiency amp the max power consumption is about 10W, compared to 100’s of watts for class A amps. Efficiency for switching audio amps are not very important at such low power usage. It is the absolute number that counts.

referenceaudionz · « **Reply #17 on:** 2 Sep 2005, 06:32 am »

I've had great results powering Zu Druids with the Ref 8 via Crystal cable, Sonic Euphoria and Bluenote Stibbert tubed CDP.

In fact, I prefered the performance of NuForce (especially the added kick in the bass – Druids are great in this area) over my favorite & highly regarded low-watt triodes. Not to say the NuForce matches the quality of top valve amps, it's just that their virtues highlight the Druid's speed & dynamic ability. The game of system matching means you don't necessarily get that much better performance by spending alot more on tubes with these speakers (this obviously doesn't apply to the Definitions)

BTW, the switching amps have unheard potential – I modified mine early on by rewiring internally with Crystal cable. They're transformed by wire replacement on both the power side, speaker & input.

(FYI: I'm agent for NuForce, Zu, Crystal, Sonic Euphoria and KR!)

mmakshak · « **Reply #18 on:** 14 Sep 2005, 03:49 pm »

Remember Linn's philosophy? It disagrees with choosing speakers first. The sound of the speaker changes when the source changes(although you might have to drink the scotch supplied with their demonstration to fully understand this).

mmakshak · « **Reply #19 on:** 19 Sep 2005, 05:58 am »

Nobody ever answers what I say. It's obvious that speakers change how they sound, if the source changes, despite what Wilson says.