15 inch woofers: which have low moving mass?

[CLS]

Hi freddi,

I happen to find another interesting woofer - MCM 55-1880. And surprisingly, I also found you and pano were asking opinions about it.

Sensitivity: 98dB (W/M)
Impedance: 8ohm
Re: 6.6ohm
Le: 1.2mH
Frequency response: 26Hz~3500Hz
Fs: 28Hz
Qts: 0.23
Qes: 0.27
Qms: 1.46
Vas: 463 (liters)
Xmax: 4.4mm

However in the pdf datasheet, some parameters are different:
http://www.mcmelectronics.com/content/ProductData/Spec Sheets/55-1880.pdf

fs= 32Hz
Qes= 0.3
Qts= 0.26
Mms= 49 g (!!! I'm wondering how a 15" cone with 4" VC and mega dust cap can be this light !!! )

And I can't put together the 4.4mm Xmax(p-p) and 18.8mm VC length. So the top plate should be more than 16mm thick (roughly) - I suppose such build can not be so cheap.

That massive looking 100oz magnet is only producing 15TM of BL (Re=6.9 Ohm), this is odd, too.

And except for the 'reviews' within MCM web page, there are barely any other experiences shared on the web.

Hmmmm....

 

[AndrewT]

what's the formula that relates Fs, Mms & Vas?
Something to do with a weight hanging on a spring?

 

[CLS]

Thiele/Small - Wikipedia, the free encyclopedia

 

[AndrewT]

is this right?

Fs = c * Sd / 2 / Pi / sqrt[ Mms * Vas / rho]

from:
Vas = rho * C^2 * Sd^2 * Cms
&
Fs = 1/[2 * Pi sqrt(Mms * Vas / rho / c^2 / Sd^2)]

 

[Bill F.]

And I can't put together the 4.4mm Xmax(p-p) and 18.8mm VC length. So the top plate should be more than 16mm thick (roughly) -

Top plate is spec'd at 10mm in the PDF, so xmax is a misprint--it's really 4.4mm one way, or 8.8 p-p.

Interesting driver. Likely a real bargain.

 

[Andrew Eckhardt]

I thought Xmax (linear) was always supposed to be indicated as peak excursion, not peak to peak. It seems only the parenthetical notation at that parameter is wrong.

 

[Pano]

That's an interesting driver, but one would want to know the real specs and if they match unit to unit.

From the specs on the web page Unibox calculates Mms as 72g and Bl as 17.5Tm
But from the PDF spec sheet we get a calculated Mms of 49g and Bl 15.2, very close to the spec sheet numbers.

23 grams have gone missing somewhere!

 

[Cal Weldon]

I thought Xmax (linear) was always supposed to be indicated as peak excursion, not peak to peak.

It is but some less scrupulous manufacturers realize that a lot of the young'ns like the numbers so they sneak in the larger number with a small p to p at the end

 

[GM]

Interesting driver. Likely a real bargain.

Indeed, Looks like it will work in Altec 416 or similar alignments, though this doesn't imply it's a suitable replacement except as a relatively inexpensive 'make do' repair.

GM

 

[freddi]

- got an 1880 buried somewhere in my pile - - not looked at it for ~5 years - Fs seemed ~1/2 octave higher than spec but it wasn't run-in hard but do remember running it at 20vrms in a Karlson -IIRC Sd looked lower than some 15 and unit made by Tangband. -didn't' sound special in K15 - I thought this unit was discontinued (?)

AH - here's its basic Q's - I think somehow MCM confused it with something else -? its pretty much anti-Altec
;==================================================================
; Woofer Tester 2 Log File: 55-1880_Try1.log
;------------------------------------------------------------------
; 55-1880
;==================================================================
;==================================================================
Calibration test completed: Tue Apr 26 19:11:30 2005
Calibration drive current 3181.82 uA
;------------------------------------------------------------------
Calibration R = 10.000 ohms
Cable Resistance = 0.196 ohms
Cable Inductance = 0.000 micro-h
KResist = 1.015490 ohms/ohm
(internal R= = 223.408 ohms)
KPhase = -1.882435 microrads/Hz
;==================================================================
;==================================================================
Q test completed: Fri Apr 29 18:06:00 2005
Q drive current 3181.82 uA
;------------------------------------------------------------------
Revc= 6.5807 ohms
Fs = 38.1263 Hz
Zmax= 35.3349 ohms
Ro = 15.2489 ohms
F0 = 21.9715 Hz
F1 = 61.3508 Hz
Fmin= 182.9694 Hz
Qms = 2.2435
Qes = 0.5134
Qts = 0.4178
Le = 1.3208 mH @1kHz
XLe = 14.7362 impedance @1kHz
PLe = 34.2748 phase @1kHz
;------------------------------------------------------------------
Vas test completed: Fri Apr 29 18:18:28 2005
Vas drive current 3181.82 uA
;------------------------------------------------------------------
Revc = 6.5807 ohms
Fs = 38.1263 Hz
Zmax = 35.3349 ohms
Qes = 0.5134
Qms = 2.2435
Qts = 0.4178
Le = 1.3208 mH (at 1 kHz)
Diam = 308.0000 mm ( 12.1260 in )
ConeArea =74506.0071 mm^2(115.4845 in^2)
Vas = 175.6643 L ( 6.2035 ft^3)
BL = 15.4098 N/A
Mms = 77.3410 g
Cms = 225.3101 uM/N
Kms = 4438.3267 N/M
Rms = 8.2583 R mechanical
Efficiency = 1.8279 %
Sensitivity= 94.6194 dB @1W/1m
Sensitivity= 95.4676 dB @2.83Vrms/1m
;------------------------------------------------------------------
; When testing drivers with an up/down radiation (cone motion)
; enough weight should be used to get a decent resonance change
; without significantly altering the drivers suspension zero point.
; A typically good configuration is when Fs/Fsa=1.25.
; Horizontally mounted drivers are less susceptable but require
; a clay or soft caulk mass. The following may be of help
;------------------------------------------------------------------
Fs= 38.1263 Mms = 77.3410 g
Fsa= 29.4823 Mms+Ma=129.3410 g
Fs/Fsa = 1.2932
Ideal Test Mass = 43.5043 g
Test Mass used = 52.0000 g
Missed ideal by = 8.4957 g (too heavy)
Nickels used = 10.4000
Nickels desired = 8.7009
;-------------------------------------

 

[CLS]

to pano: It seems 72g is more like it.

to freddi: MCM is still selling it. So are many other on-line store. It's what I found yesterday. And, I got an impression that Karlson cabinet is very demanding. It seems only a few drivers 'pass the test'.

 

[freddi]

Karlson are very forgiving but in general low mass and strong motors work best on demanding transient passages

 

[CLS]

Ah~ that's not really "forgiving" Because the trend is heavy cone + low Vas + mega power, so light cones are getting rare. Sigh~

 

[freddi]

its probably the way I used it - I"m not real fond of heavy cones carrying a lot of vocal region in direct radiators but Dr. Geddes has lots of praise with the Summa

Franz Stolz has used heavier woofer in his K15 with success http://gainclone.com/Karlson/index.php?topic=826.0

 

[CLS]

EV DL15X

Thiele-Small Parameters (broken in),
fs: 42.0 Hz
VAS: 195 liters (6.89 ft3)
QES: 0.30
QMS: 4.55
QTS: 0.28
RE: 6.0 ohms
h0: 4.63%
SD: 0.086 m2 (132 in.2)
MMD: 0.062 kg (0.137 lb)
LE: 1.6 mH
CMS: 0.19 mm/N
RMS: 4.43 mechanical ohms
PE(max) (per ANSI/EIA RS-426-A 1980): 400 watts
Xmax: 4.1 mm (0.16 in.)

Somewhat old stuff. Still available, though.

 

[Pano]

Freddi - much mahalo for your measurements!

(if it seems to good to be true.....)

 

[ScottG]

Sica has some low mms 15's through Sica and also via Jensen:

S15-500

SL15B3P

NEO15-300

MOD15-200

 

[elac310]

This Jensen NEO15-300 looks awesome! Very low Mms, good BL for that weight, Qts and Vas are excellent for a BR enclosure which would not be of a US fridge size. Hmmm...I need to have a serious look at this one.
Thanks for the tip!
Chris.

 

[elac310]

Thanks. The GPA were mentioned in an earlier post and I managed to obtain parameters from them (especially Mms). The Iconic pages have been under construction for years and as I can see, there is still no data available but I could have missed something.
Chris

How silly of me; I never mentioned the data GPA sent me; here it is:

515-8G Mms = ~54g;
515-8LF Mms = ~73g;
515-8C Mms = ~74g;
416-8B(or 8C) Mms = ~71g;
3156 Mms = ~72g.

Chris.

 

[elac310]

To Freddi (and others):

The French audiophile community has a database at its disposal, which was created by a DIYer named Dominique Pétoin:

Since the menus are in French only, here is what you can get with Google Translate:

Google Translate

Under "Thiele and Small parameters of one or more HP, 1/3:" type the diameter of the woofer you're interested in, say 15", and you'll have the results for a large number of vintage and current speakers, it being understood that the feeding of the database being done manually by the author of the site and individual users, it is impossible to have all speakers in production.

Maybe you can find a few useful hints for your carlton application.

For those who read French, the link to the database in French: Les menus de la base de données et les logiciels de calculs des enceintes

Chris.