Westrex

[VolvoHeretic]

I think that I want to try the added mass to my bastard 418-8H II A8 clones, (but cheating with a graphic equalizer goes a long way to the bass junkie fix I want) and I have the math linked around here somewhere, just can?t link up with my too busy engineer son to run the math. What is that metal ring, copper wire, gold painted steel coat hanger? This 418 has no cooling venting front or back, I wonder if I need to cut out a quarter sized hole through the aluminum dust cover first, then glue on a 416 paper vented dust cover over that, and then add the wire ring, adjusting the wire gauge to fit the mass needed? Just how accurate does the added mass have to be, calculated weight of glue and actual globbed on are two different things?

[GM]

This 418 has no cooling venting front or back......Just how accurate does the added mass have to be, calculated weight of glue and actual globbed on are two different things?

It takes a considerable amount of added weight referenced to the driver's moving mass [Mms] to make any major change, so the more accurate the added mass, the closer to hitting a target set of specs. For example:

12" driver/40 Hz Fs/0.4 Qts/60 L Vas has a Mms = ~78.4028 g. Adding this amount reduces Fs/SQRT[2] = 28.28 Hz and Qts increases by SQRT[2] = 0.566, SPLeff. drops by a factor of 4 [~6 dB].

Since the motor will run hotter due to lower efficiency, adding a cooling vent seems a good plan, though if used in a MI app it may not sound 'right' anymore.

GM

[VolvoHeretic]

It takes a considerable amount of added weight referenced to the driver's moving mass [Mms] to make any major change, so the more accurate the added mass, the closer to hitting a target set of specs. For example:

12" driver/40 Hz Fs/0.4 Qts/60 L Vas has a Mms = ~78.4028 g. Adding this amount reduces Fs/SQRT[2] = 28.28 Hz and Qts increases by SQRT[2] = 0.566, SPLeff. drops by a factor of 4 [~6 dB].

Since the motor will run hotter due to lower efficiency, adding a cooling vent seems a good plan, though if used in a MI app it may not sound 'right' anymore.

GM

2.77 ounces? I don't know what MI app means, but it is a base reflex box.

[cradeldorf]

2.77 ounces? I don't know what MI app means, but it is a base reflex box.

MI app = Musical Instrument application. (Guitar Amplifier)

[GM]

2.77 ounces?

Right, not much in reality in this case, but I said 'referenced to the driver's moving mass [Mms]', which is a doubling of mass. Normally, mass loading is only done to [sub] woofers and of course passive radiators [PRs] where thousands of grams may be added. I've bonded 3/4" MDF discs to 15" woofers to get them down to below 20 Hz.

GM

[Andywin]

Yes there is always a trade off with any changes. In this case the reduction of resonant frequency also means a loss in efficiency. As Westrex have reversed the compression drivers in my speakers to use them as dome mid/hi's the loss of efficiency is not a problem. They still require padding down to match levels.

Below are some measured specs of the 2080E driver I found on the web. Specs are pretty good

Model: 2080.E
Thiele-Small Parameters:
Fs: 34.00 Hz
Vas: 149.27 l
Qms: 19.3111
Qes: 0.1998
Qts: 0.1978
Sd: 693.60 cm2
Vd: 0.0694 l
XMax: 1.00 ?mm
Revc: 12.0000 Ohms
ZMax: 1171.7574 Ohms
ZNom: 12.0 Ohms
Bl: 35.8684 N/A
Rms: 1.1093 kg/s
Cms: 0.2185 mm/N
Kms: 4.5767 N/mm
Mms: 100.2717 g
Mmd: 79.2648 g
Levc@1kHz: 2.5270 mH
Levc@5kHz: 1.0722 mH
Levc@10kHz: 1.3017 mH
Levc (Ave): 1.0793 mH
no: 2.8480 %
SPL @ 1W,1m: 96.56 dB
SPL @ 2.83V,1m: 94.80 dB
Measurement Info:
Method: Delta Mass
Added weight: 32.00 g

[kjs]

Adding mass to the cone does not only alter T/S parameters and efficiency. Of course it alters sound also. And in case of changing a 2080 by adding the 32g mass ring one will change its attack and sustain tremendously. The hole in the dust cap has not much to do with cooling in case of 2080 instead it prevents compression of air and stiffening of the suspension due to movement.

[Andywin]

Adding mass to the cone does not only alter T/S parameters and efficiency. Of course it alters sound also. And in case of changing a 2080 by adding the 32g mass ring one will change its attack and sustain tremendously. The hole in the dust cap has not much to do with cooling in case of 2080 instead it prevents compression of air and stiffening of the suspension due to movement.

I don't think the 32g applies to the mass ring but then I'm no expert on Theil SM measurments.

Any alteration to the sound will be dependent on where the extra mass is added. The JBL solution is the most elegant but placing the added mass around the dust cap gives minimal change. If the mass was added across the entire cone then there would most likey be a more noticable change.

The trade off between deeper (very taught) bass and a little loss in sensitivity works very well in this application. The lower bass is very articulate and certainly gives my JBL array 1400's a run for their money and the upper bass seems to reveal slightly more detail than my BTH K10A dual concentrics that use the same cone Western Electric 4181a.