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Author Topic: B&C 18tbx100  (Read 9092 times)

Ivan Beaver

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Re: B&C 18tbx100
« Reply #10 on: July 15, 2015, 08:21:23 pm »

Is this stemming from the use of horn cabinets in older theatre speakers to make up for the lack of excursion in early drivers?  Which came from thin cones and stiff suspensions.

Interestingly in the EV 12" EVMs, the guitar model is designed to have a longer excursion than the -S model used in the PA cabinets.  Folks like Larry Carlton discovered using the much brighter -S or "short" version to counteract some of the mushiness in the early unstable Boogie cascaded preamps.

Thanks Peter, the multiple pressure peaks in the standard horn would seem to imply a pretty wild impedance response.  The tapped horn looks like it would be easier to compensate for, in spite of it's more ragged out of band FR.
As a few examples.  Ev suggested use of the 15L (lead) instead of the 15B for their W cabinets.

JBL suggested the K151 (bass guitar speaker) instead of the various "PA" speakers in their W cabinets.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Stephen Kirby

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Re: B&C 18tbx100
« Reply #11 on: July 16, 2015, 01:35:22 pm »

As a few examples.  Ev suggested use of the 15L (lead) instead of the 15B for their W cabinets.

JBL suggested the K151 (bass guitar speaker) instead of the various "PA" speakers in their W cabinets.

Thanks Ivan.  W cabs had very little volume behind the driver so a stiffer suspension, shorter excursion driver would seem more appropriate.

I hadn't known what the EV designations stood for.  Never saw a "B" driver.  Most guitar players I know think the "L" stands for "long" and the "S" in the PA boxes stands for "short" since that is a much stiffer suspension and shorter travel driver.
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Ivan Beaver

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Re: B&C 18tbx100
« Reply #12 on: July 17, 2015, 04:41:04 pm »

Thanks Ivan.  W cabs had very little volume behind the driver so a stiffer suspension, shorter excursion driver would seem more appropriate.

I hadn't known what the EV designations stood for.  Never saw a "B" driver.  Most guitar players I know think the "L" stands for "long" and the "S" in the PA boxes stands for "short" since that is a much stiffer suspension and shorter travel driver.
Most horns hav very small back volume.

In the 15" evs the b was for bass and l was for lead

The b cone is smooth and much heavier than the l

In the 12" the s is for short cone

I don't know if the l was for lead or long
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Jacob Shaw

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Re: B&C 18tbx100
« Reply #13 on: July 17, 2015, 08:28:57 pm »

Hi Jacob,

Xmax is usually just calculated from voice coil over hang plus about 25%. In practice its not that simple.

Many drivers will become unstable when they approach their rated Xmax and develop a DC offset.  The cone does not return to centre when it should.

In general soft suspensions such as the 2245 are worse than drivers like the 18tbx100.

These newer designs are able to control the diaphragm better and in doing so will make more bass in practice.  Despite what is advertised most 18 drivers will have stability beyond about 10mm.

Some designs like the 18SW115 have very good magnet design / symmetry and will make about 15mm.  9mm is good for a PA bass driver.

The loading on the driver depends on the box type and design, but FWIW the 2245 will be less stable than the 18tbx100
That hits at the point.  By worse, do you mean easier to damage?  Or just worse I. Terms of sound quality.  Is it a balancing act between durability and efficiency, or can you have both?
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Mike Smith

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Re: B&C 18tbx100
« Reply #14 on: July 17, 2015, 11:30:36 pm »

Most horns hav very small back volume.

In the 15" evs the b was for bass and l was for lead

The b cone is smooth and much heavier than the l

In the 12" the s is for short cone

I don't know if the l was for lead or long

In addition to what Ivan said:

Although most W boxes have a small, sealed back volume, the Don Keele-designed JBL 18" horn's driver chamber was about 5 cu. ft. and vented. Unusual in its day, and now.

The Electro-Voice EVM 15B cone was blacker, thicker, and more long-fibered than its sibling's cone, and had a sinewave-looking cloth edge that on early models was finished with a soft, sticky doping compound, later changed to stiff. The 15L version was grayish, ribbed, thinner, lighter, and the fibers were shorter and more compressed. That cone's cloth surround was sawtooth-shaped and always treated with a latex stiffening compound.

The 12S was created in answer to requests for a "crunchier" midrange performance. Regular-issue 12L speakers have a pronounced mid scoop along with a bit of a higher ice pick, and the 12S's shallower cone profile was found to knock off the peak and fill in the critical 2.5kHz hurt-range some guitarists prefer. Also works out a little flatter overall, but above where most users would cross for PA mids.

All EVM speakers shared the exact same magnet structure, 2-1/2" diameter voice coil and winding length, and spider (within their respective vintages). There was no difference in "throw" as it would relate to linear excursion, at least as far as the motor was concerned. That left you with very efficient midbass transducers (and bass horn drivers) but an 18" model that was, by today's standards for sure, feisty but a bit puny.

There. That is a lot of pedantic minutiae regarding EV drivers and I can't believe I remember it after all of these years.
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Mike Smith

Event Technical Systems

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Peter Morris

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Re: B&C 18tbx100
« Reply #15 on: July 18, 2015, 04:53:40 am »

That hits at the point.  By worse, do you mean easier to damage?  Or just worse I. Terms of sound quality.  Is it a balancing act between durability and efficiency, or can you have both?

By worse I mean that the VC does not return the centre position as it should.  If this happen the Xmax is compromised. Instead of having 10mm of travel for example it may only have 5mm of travel left before the VC gets too far out of the gap (in one direction)   i.e. less output and more distortion... even damage to the speaker if driven hard.

The problem is in part caused by a non symmetrical magnetic field.  The VC gets more push in one direction than the other. 

https://www.klippel.de/fileadmin/klippel/Files/Know_How/Literature/Papers/Klippel_Nonlinearity_Poster.pdf

The answer is better designed speakers, which many of the newer designs are :-) The 2245 is now quite an old design.

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Re: B&C 18tbx100
« Reply #15 on: July 18, 2015, 04:53:40 am »


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