MI app = Musical Instrument application. (Guitar Amplifier)Originally Posted by VolvoHeretic
2.77 ounces? I don't know what MI app means, but it is a base reflex box.
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MI app = Musical Instrument application. (Guitar Amplifier)
Last edited by cradeldorf; April 28th, 2012 at 12:39 AM.
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
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
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
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.
David I'm not sure how much I can add, as I have no familiarity with this particular system. It appears to be a later, lower cost, less efficient version of the Westrex 20/80 home system. I do know that the postwar Westrex/Western Electric London drivers used in both theatre and home systems were derivative of Altec Lansing driver designs, though often built to considerably higher standards with beautifully machined brass parts and other elaborate construction. I don't know if some licensing agreement existed between the firms. I have been told that postwar England had very strict limitations on imported goods to promote their domestic industries. We could sure use some of that these days in the good ol' U S of A! Actually plenty of Lansing/Altec Lansing technology was evident in many European products both pre and postwar. Lansing Mfg. Co. sold speaker components to AGA Baltic in the Netherlands in the late 1930s. I have seen both Philips and Osso (Spain) compression drivers which used the Lansing 285 design of radial slit phasing plug and were obvious permanent magnet knockoffs of the Lansing 285.
The UK Westrex 2090 series of compression drivers were based on Altec technology, the 288C I believe.
The 2390A drivers in my speakers are obviously reversed and an ex Westrex employee I have been in dialogue with has indicated a lot of development was put into them.It wasn't just a case of taking the back cover off a 2090 to create a 2390A. The 2326A's are a continuation of the 2080/2090 Acoustilens domestic speakers developed in the 1950's. Apparently the aim was to produce a system that was more domestically acceptable with regards to physical size (although they are by no means small) and capitalise on GEC development of small compression drivers used as dome transducers.
The efficiency is obviously less than the horn loaded Acoustilens but is still respectable at around 96db. They were by no means cheap and were listed as POA. Apparently they were over ?200 each and were probably the most expensive domestic speaker in the UK at the time. They have an extended frequency range over the Acoustilens at both ends of the spectrum and produce a much better stereo image.
There were a number of UK manufactures that used Western Electric , Altec and Lancing technology.
BAF, with their 513 compression drivers and 519 bass units are almost carbon copies of Lancing 284/5 & bass units that they may have just been rebadged although the field coil plug was different
BAF later produced the Gaumont Kalle / Rank 379 which seems to be a copy of an Altec 288 series but with a diaphragm that uses a half roll surround a la JBL
BTH / AEI produced 18" field coil and PM bass drivers and PM dual concentric s that used a copy of the Jensen V2/ Western Electric 4181a / IPC basket and cone. The field coils required a different voltage so I assume they were not rebadged.
STC seem to have manufactured WE 555 and later PM drivers
Vitavox probably used altec technology but produced product that were not direct clones
RCA obviously used the parent company technology
In Europe there was:
AGA Baltic which I always thought were from Sweden
Standard Electric in Hungary that produced WE 555 drivers. There may be a connection with Tungsram here.
MET in France produced PM versions of the WE 555
Philips in the Netherlands certainly have Altec characteristics
Korting in Germany produced a copy of the Jensen / western Electric 13.5" field coil driver
I'm sure that there were many more but it really indicates how good those original designers really were as some of the companies I've listed above were huge companies with large R&D facilities and yet chose to manufacture (and I'm sure it must have been under licence) another companies design.
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