[Brian Cheney]

I ran a long series of nearfield (room-independent) bass measurements on the RM/X (w/vitrified high-compliance PR) today and faxed them to John Casler with a request to post (something I have never figured out how to do).

For Scott and other owners let me say the measurements show very smooth response (within 2dB) from below 20Hz to above 200Hz where I stopped the measurement.

There are dramatic differences in THD with PR tuning.  As you will see, 2nd and 3rd harmonic distortion drops from max 10.57% 2nd at 20Hz before tuning the PR, to 1.35% 2nd at 20Hz after tuning (tuning also smooths overall frequency response and raises 20Hz output by about 0.2dB.)  I removed about 5 fingernail fulls of putty to tune.

If John can scan and post, I can supply measurements on all systems going back five years, plus bloopers (drivers with very good reps from famous manufacturers that measured like doggy-doo and which we rejected).

[JoshK]

Wow!  That's cool.

[ekovalsky]

Great idea, that should satisfy those who question the bass response of the big VMPS speakers.  

20-200Hz, +/- 2db, <2% 2nd harmonic distortion at 20Hz =   That just simply kicks ass, Big B.  There are plenty of tube amps that can't match those measurements!

I've always felt that much of the low bass output of many speakers with "good bass" is distortion.  Most speaker builders are happy to list their +/- 3db range, but there is a reason why distortion isn't mentioned  

[Ravi]

why just stop at bass, why not the whole speaker measurement?

[John Casler]

I ran a long series of nearfield (room-independent) bass measurements on the RM/X (w/vitrified high-compliance PR) today and faxed them to John Casler with a request to post (something I have never figured out how to do).

If John can scan and post, I can supply measurements on all systems going back five years, plus bloopers (drivers with very good reps from famous manufacturers that measured like doggy-doo and which we rejected).

  ...

Hi Guys, I just got in and since I don't have a scanner, I am trying to convert these files (I use an E-mail fax system) to Jpegs and see if I can up load them.

This is taking a bit of time, but I hope it works.

[John Casler]

OK,  I hope these come out OK.

B, I wasn't able to put these in any particular order and they were so small, I couldn't tell which was which so if you want them in any particular order let me know and I'll try to re-arrange them.

If you want to write comments on the individual graphs or anything, I beleive as a facilitator you can use the "edit" button to add comments (OK by me)

So here they are

#1



#2




#3




#4




#5




#6




#7

[Brian Cheney]

Please examine these curves carefully.

Scott wanted measurements on the bass system of the RM/X so I ran 10Hz to 200Hz sweeps with 1/24th octave resolution and a little less than one watt input.
The sensitivity (without room gain) is about 85dB at 48Hz where the system has its maximum output.  Room gain (which everybody uses when quoting bass sensitivity) adds about 6 dB.

Nearfield means the mic is basically almost touching the woofer cones and is flush with the center of the PR slot.

Good midrange  and HF measurements require an anechoic chamber.  Unfortunately there is no anechoic chamber in this hemisphere large enough to make good bass measurements below around 80Hz.  

In-room fullrange measurements are worse than useless, since the room plays such a large role in the outcome.  See my curves on the Quad 57 taken in-room some years back, as published by Stereophile.

The biggest surprise in the change in 2nd and 3rd harmonics when the PR is tuned.  From 10.57% 2nd harmonic at 20Hz, distortion drops to 1.31% (with 3rd harmonic even lower) merely by my removing a very small amount of putty from the PR.  Amplitude response at 20Hz can also be boosted about .2dB with the PR adjustment.
There is about a .5dB improvement in overall linearity when the PR is mass-optimized. The measurement degrades if another fingernailfull of putty is added or subtracted to the (vitrified, high-compliant) PR cone.

Note that the system meets its -3dB point at 20Hz precisely and is only minus 4.5dB (relative to 48Hz) at 17Hz.  If you neglect the 1.5dB rise between 30Hz and 60Hz the system is -3dB at 17Hz.  This is outstanding linearity and bass extension.

There are many more measurements that Clio and Sysid can make but this is your basic bass performance, i.e. better than any High Fidelity speaker I have encountered these past 27 years.

If you have questions feel free to ask.

[Brian Cheney]

Quick note: while the 20Hz 2nd and 3rd HD levels drop to 1.31% and 1.14%, respectively, above 100Hz the tuned system has distortion dropping off the chart, less than 0.1%.  As noted above, many amps can't do this.

[ScottMayo]

Quick note: while the 20Hz 2nd and 3rd HD levels drop to 1.31% and 1.14%, respectively, above 100Hz the tuned system has distortion dropping off the chart, less than 0.1%.  As noted above, many amps can't do this.

Well, Radio Shack clearance amps don't, I expect. Audiophiles generally run stuff better than that; Bryston claims:

Distortion < 0.005% 20Hz to 20kHz at 120 watts into 8 ohms,
IM or THD+noise < 0.007% 20Hz to 20kHz at 200 watts into 4 ohms

and they generally exceed their rated specs in real life.

These are fine numbers for speakers, but maybe short of using ionized hydrogen for drivers, I don't expect *any* speaker to approach the accuracy of a high end amp.

Thanks for the graphs. Upper range stuff would be interesting, but only because I'm curious; my ears already told me that there aren't any problems up there.

I'd like to run these same tests here on my existing speakers - what software and hardware did you use? Aside from a PC, what does a testing package like that cost?

[Brian Cheney]

Clio runs about $1500 including a full-length card that mounts inside the computer and a 1/4" mic.  These measurements were made with the stock package.

I have yet to measure a high-end tube amp that measured less than several % THD at 20Hz and full output.  The last one I checked was nearly 3dB down at 20Hz with about 5% THD at full power, and it complained audibly (transformer buzzing) in the process.

[ScottMayo]

I have yet to measure a high-end tube amp that measured less than several % THD at 20Hz and full output.  The last one I checked was nearly 3dB down at 20Hz with about 5% THD at full power, and it complained audibly (transformer buzzing) in the process.

Well, duh. Tube amp. That's what tube amps *do*, they distort in a pleasing fashion. Rolling off the high end, introducing even order harmonics and pouring in microphonic slurry by the pound, are why people buy them.  

[Parts of the above paragraph may be interpreted as playful humor and are in nowise intended to start off a flame-war, denigrate anyone's favorite amplifiers, make fun of equipment that heats your house and then goes pop after a year, or discount the Glorious Orange Glow of Goodness that are such an integral part of owning tube equipment.  No warranty is expressed or implied on this humor. Your mileage may vary. ]

[ctviggen]

One of the reasons I started looking toward non-tube-amp amps is because I used to live in Arizona, and the guys there said that tube amps are great except that they generated a ton of heat and could be finicky in terms of temperature ranges.  I couldn't take something that added more heat to a place that's 90+ for 7 months out of the year.  Having said that, though, I have to say that I took the glass fronts off of my electronics rack because 7 channels of amplification, several satellite receivers (at the time), a preamp, CD/DVD player, etc. really get hot after a while!  My Dish PVR would freak out after a time of being cooped up in there.  

Now, I joke that I've moved from 9 months of summer (AZ) to 9 months of winter (CT).  It's June, and I had to close the windows because it's too cold in the house and I don't want the heat to come on!  Now, I'm thinking of tube amps...if only to heat up my basement, where my gear is.

[ekovalsky]

Big B,

Since the THD drops so amazingly low with proper "tuning", is there a specific mass of putty that should be applied to the driver for optimum sound?  Obviously sound at the listening position will be affected by the room, but it seems the speaker should be set up to deliver the lowest distortion low bass possible.

In other words, by adding/subtracting putty from our speakers, are we trying to compensate for room bass irregularities by increasing?

I have spent lots of time adjusting the putty on the RM/X (and the RM-40's when I had them) but sometimes feel like a dog chasing its tail.  

If the driver performs best with, say 3gm of putty, knowing that amount was applied I could then tackle troublesome room modes with treatments or room EQ.  

By the way, were you able to send out the new passives (and grill fasteners) this week?  The graphs you posted were with the new passives, correct?  If so I guess I'll start with five fingernails from each  



By the way, I saw some great looking CLIO curves from the Selah Omegarray speaker.  Then I realied the x-axis was from 200-20kHz!  The 20-200 range wasn't included  

I'd like to hear that speaker someday.  It would be interesting to compare its Fountek panels to the Neo8 panels in the Alpha LS.  The built-in sub seems like a good idea too.

[ScottMayo]

Big B,

Since the THD drops so amazingly low with proper "tuning", is there a specific mass of putty that should be applied to the driver for optimum sound?  Obviously sound at the listening position will be affected by the room, but it seems the speaker should be set up to deliver the lowest distortion low bass possible.

Same question here. I'm on the edge of buying these things, and I'm on the edge of finalizing plans for an extension on my house, which includes a room for music. The room, in theory, will have good acoustics, at least that's the design goal (ok: the design goal is that the room acoustics won't suck, because rooms can't make things better, only worse.) If I know the speakers have arrived already tuned for minimum distortion and an ideal room, then that's (in theory) one less variable I have to fuss with. There are going to be enough things to mess with as it is...

[Brian Cheney]

While THD drops with proper tuning, the PR also compensates for amplifier output impedance (damping factor) and most importantly, series R of the speaker wire.  So, you'll still have to adjust the putty, just in a smaller range than before.

[nathanm]

Wouldn't it be great if there were a precise, repeatable method of adding\subtracting mass from the PR?  The putty thing seems like such a black art.  To me it would make more sense to have something like a threaded post with rubber washers on it so you could say, "Okay I liked the bass better with 14 washers instead of 20..."  Something that was consistent and not subject to people's fingernail dirt capacity. I've read so many posts about the putty and I still am not sure what the heck is going on.  Higher mass=lower resonant frequency?  Lower mass=higher resonant frequency?  The opposite?  Neither?  Personally I find the putty is a wonderful source of audiophillia nervosa, you just never know if it's right, if it could be better, is it too boomy, too dry...

[ScottMayo]

The opposite? Neither? Personally I find the putty is a wonderful source of audiophillia nervosa, you just never know if it's right, if it could be better, is it too boomy, too dry...

I find the audiophile hobby to be a wonderful source of nervosa. Would those speakers sound better 1/2" closer together? Angled 3 more degrees? Turned upside down? Was that click in the music, or am I hearing the first sign of very expensive thermal runaway? Cables don't really make a difference.... do they? Is my 20 year old speaker cable *still* oxygen-free? Those new digital amps aren't better than MY amp, are they? Maybe I should have stuck with vinyl after all. I'm a year older, have a lost another 250Hz of high frequency hearing? I know my wife likes big speakers, but are these *really* big enough? Will a green glowing disk *really* make my CD player sound better? That wasn't a resonance, was it...?

At some point you have to Let Go and Listen To The Music. When that point is, though, I don't know.  

[Marbles]

At some point you have to Let Go and Listen To The Music. When that point is, though, I don't know. ...

For me it was the exact moment I ran out of disposable cash....  

[John B]

For me it was the exact moment I ran out of disposable cash....

Ain't that the truth of it all!