[Enrico]

Are there any impedance curves available for any of the current VMPS line, especially the 626R, RM40 and RM/X?

[Brian Cheney]

For all three systems, the impedance is 3.6 Ohms minimum to 200Hz, then rises to 4.6 Ohms till about 7kHz, then falls to about 3.8 Ohms up to 25 kHz and beyond.  With the FST the impedance stays around 6 Ohms starting at 7 kHz.

[Enrico]

Thanks Brian.

[Dunedain]

Brian,

What is the efficiency rating of the Neo mids and also
the spiral tweeters vs the FST (taking into account and
adjusting for the enhanced output from the two identical
spiral tweeters working together on the RM2 and RM40 speakers)?

Thanks for the info.!  

[Brian Cheney]

Each Neo panel 86dB.  Two spiral ribbon tweeters 90dB, one FST 96 dB (all 1W/1m SPL). Doubling up on the panels adds 3dB, and there is additional sensitivity gain from the array effect.

[Dunedain]

Hmm, very interesting.  That FST has an extremely high sensitivity.

89dB if you have two Neo panels, like the RM2 has, add to that another
speaker (the left and right main speakers working together) and I think
that adds another 3dB.  So now we're at 92dB effective sensitivity for
an RM2 (mid-range freq.'s).  Add in, say, 2dB for natural room gain,
plus another maybe 2dB gain for this array effect you mentioned (just a
guess on that array 2dB gain).  And we're looking at an effective 96dB
efficiency for the mid-range frequencies (handled by the Neo's) on an RM2.  

Do I have that right, Brian?  Or did I miscalculate something?

[ekovalsky]

So with the array of six neo panels in the X their combined sensitivity (excluding any radiation pattern augmentation from the linear array) is just under 94db, a pretty close match for the 96db on the FST.

What is the sensitivity of the bass system on the X?  If I remember is was in the high 80's on the RM-40's.  Is it higher with the X because of the larger woofer and passive radiator and slightly higher cabinet volume?

If the bass sensitivity is well below the mid/tweeter section, won't there be significant amp power dissipated as heat by the mid/high crossover to attenuate levels to match the less efficient bass section?  Or does in-room bass gain make up for most of the difference?  

If it doesn't, this may be a good reason to try active biamping so the gain levels can be set independantly for the bass and mid/tweeter sections before  the amplifiers.  This would probably be most worthwhile if lower powered tube amps were to be used for the mid/tweeter section.

[wshuff]

Brian wrote:

"For all three systems, the impedance is 3.6 Ohms minimum to 200Hz, then rises to 4.6 Ohms till about 7kHz, then falls to about 3.8 Ohms up to 25 kHz and beyond. With the FST the impedance stays around 6 Ohms starting at 7 kHz."

Is this really the case for the 626R?  I ask because the price sheet on the website lists it as an 8 ohm speaker, and the sticker on the back of my 626R says, "Impedance:  4 Ohms nominal, 3.6 Ohms minimum (RM2, RM40) 8 Ohms nominal, 5.6 Ohms min (RM1, 626R)."  

All this time I've thought that the 626R was an 8 ohm speaker.  And does it really have a sensitivity of 90db/1W/1m, or is it lower?  I've never felt like I've had to push my amp to drive it at all, so whatever the sensitivity, and whether it is 4 or 8 ohms, it hasn't made any difference.  I'm just curious.

[Brian Cheney]

The 626R is available in 4 or 8 Ohms (5.6 min) and is standard in the 8 Ohm version.  However it does dip to 4.6 Ohms to 5.2 Ohms in the mids depending on the panel.

[BrunoB]

Brian wrote:

With the FST the impedance stays around 6 Ohms starting at 7 kHz

 ...

I am trying to understand how the variable L-PAD works and how it affects impedance. A L- pad is made of two resistances, one in series and one in parallel that let you adjust the relative volume of individual drivers  while maintaining a constant  impedance.  I think that the variable L-Pad's in my 626R are designed to maintain  a 8 Ohms impedance (I measured a 8 Ohms resistance between two contacts of the L-Pad).  Is this correct?
If the FST tweeter has an impedance of 6 Ohms, should the speaker then have an 8 Ohms impedance above 7 KHz because of the L-Pad?

This is just a curiosity question - I purchased my speakers as a kit and wonder how it works.

Bruno

[Brian Cheney]

The Lpad has two windings and two wipers.  As the resistance to the load decreases the resistance to ground increases, maintaining constant impedance.  The FST is a very flat 8 Ohms impedance.

[BrunoB]

With the FST the impedance stays around 6 Ohms starting at 7 kHz.

The FST is a very flat 8 Ohms impedance.

Ok, this is newbie question. How is it possible that the speaker has a smaller impedance than the driver ?  Is it because of the crossover?

Thanks,

Bruno

[John Casler]

With the FST the impedance stays around 6 Ohms starting at 7 kHz.

The FST is a very flat 8 Ohms impedance.

Ok, this is newbie question. How is it possible that the speaker has a smaller impedance than the driver ?  Is it because of the crossover?

Thanks,

Bruno

Hi Bruno,

Generally if you use two 8 ohm drivers in  speaker the impedance drops to the 4 ohm region.

Not a hard and fast rule, but multiple drivers in combination, are usually lower in impedance than single drivers.

[ekovalsky]

Ok, this is newbie question. How is it possible that the speaker has a smaller impedance than the driver ?  Is it because of the crossover?

Thanks,

Bruno

Drivers in series...

8 ohm + 8 ohm = 16 ohm
(driver1 + driver2 = total)

Drivers in parallel...

8 ohm + 8 ohm = 4 ohm
(1/driver1 + 1/driver2 = 1/total)

Most complex multi-way speakers using multiple drivers per section use a a combination of parallel and serial connections.  

For example, in a line array of ten drivers you can wire in parallel four groups, two of three drivers in series and two of two drivers in series.  Assuming each driver is 8 ohms, the total impedance for the array will be 4.8 ohms.

[ctviggen]

Plus, that's only an approximation -- as the above discussion illustrates, most impedances vary with frequency, at least to some degree.  When we discuss impedance, are we talking a value for complex impedance (capacitance, resistance, and inductance), or just resistance?

[BrunoB]

Hi Bruno,

Generally if you use two 8 ohm drivers in  speaker the impedance drops to the 4 ohm region.

Not a hard and fast rule, but multiple drivers in combination, are usually lower in impedance than single drivers.

Hi John,

Yes, at first that makes sense. In a 626R, the tweeter and the midrange are connected in parallel, so the combined impedance should be lower. But, because of the crossover, the tweeter and the midrange do not see the same frequency range. Where the two drivers overlap, I can see why the impedance would decrease. My understanding is that in the frequency range where the drivers do not overlap (e.g. above 7KHz for the tweeter), we would have only the contribution of one driver to the impedance. Is this correct?

Thanks,

Bruno

[John Casler]

Hi John,

Yes, at first that makes sense. In a 626R, the tweeter and the midrange are connected in parallel, so the combined impedance should be lower. But, because of the crossover, the tweeter and the midrange do not see the same frequency range. Where the two drivers overlap, I can see why the impedance would decrease. My understanding is that in the frequency range where the drivers do not overlap (e.g. above 7KHz for the tweeter), we would have only the contribution of one driver to the impedance. Is this correct?

Thanks,

Bruno

There are those much more qualified to answer that than I, but once the "circuit" is created, any impedance changes at various frequencies, by any of the drivers, affects the electrical demands/conditions of the circuit as a whole as far as the amp is concerned.

The amp sees the circuit as a "whole" at the binding posts (including the speaker cable)