[Graham Maynard]

I know that many members here have used the Visaton B200 during the last couple of years, and I am a recent new owner, but I'm not sure whether those who ran these drivers still have them, or felt that they needed to be replaced within owners systems for reasons I now know only too well about.

My first reaction upon hearing my 'new' B200s was one of horror at what I had just bought, them being so 'shouty' and phasey in the upper treble reaches. 
Then my horror became anger at having to modify these brand new drivers in order to get them sounding 'right';  ie.  remove a dust cap which was merely glued to the cone !!! and apply light foam to the pole face in order damp the resonant chamber within the voice coil.

After this I knew I would be using these drivers as the basis of an open baffle project, and so I tried several different dust cap arrangements to see what could best be done to further improve reproduction. 

I tried phase plugs and was not happy with any shape, so tried concave and convex dust caps, with and without a centre hole, also with and without foam damping of the dust-cap, but I really could not have imagined that I would end up with what I have now.

I have a whole line of different centre cap trials here which *empirically* led me to this solution, and which leaves any new B200 or one fitted with a phase plug seeming so poor and incoherent at high frequencies where roll-off and phase change otherwise unavoidably occurs due to their cone shape.

I should at this stage like to inform other B200 owners how to try this mod for themselves on a one-to-one basis, so that they might independently comment here as to whether they think the mod is worth trying.

If anyone else agrees that it is worthwhile then the mod will be revealed here.  I have no ulterior motives, but I wish to be careful that I don't pit my own opinion as being authoritative.

This dust-cap modification mod will be for B200 alone, but if it proves worthwhile there is no reason why it cannot be applied to other manufacturer's wide-range drivers, whereupon owners of those will need to make their own empiric determination on a per-driver-type basis.

My move to wide-range was because I had completely given up on having crossovers in the main frequency range.  Good bass, plus good mid, plus good treble does not make for good reproduction. Period.  However, up to now I have been plagued by the air side resonances, response peaks and also a lack of high frequency coherence due to the conicular shapes of wide-range drivers.

I had prefered elliptical drivers which are less shouty due to their diametric variation, but this mod overcomes that aspect and leaves me wondering why I have not read about this type of mod before !

Anyone got a B200 without its dustcap and without a phase plug ?
They would need to fashion a new dust cap to try this mod.

Needless to say I am not angry with Visaton any more, for I would not otherwise have gone on to try this very simple mod. 
I have read comments about the B200 being good on voices and transient attack - but wait until their owners hear this !

Cheers ....... Graham.

[Greg Erskine]

Hi Graham,

Great to see you posting again.....I was getting very concerned by your silence.

Sorry for being OT.

regards

[Graham Maynard]

Hi Greg,

My amp situation sorted but not LS.
Much B200 related thinking, checking and listening here.
This has been most worthwhile for me so far, so I'm hoping the results can be repeatable for others too.

This to be the main driver on a narrow baffle, with other 8"ers compensating for baffle step diffraction and providing 'fast' bass
(so that there will not be any need for series BSC on the B200).

My aim is to achieve the same additional LF cone area as a 15"er, but of course a series/parallel with extra magnets and low mass small cones can also increase LF efficiency.

Cheers ......... Graham.

[mcgsxr]

I have removed the dust caps, and have installed Planet10 phase plugs, but they are just magnetic, not permanently installed.

I am, as I believe my history would showcase, up for experimentation.

Share on!

[markC]

Yes, Graham. Please, do tell!

[ttan98]

Graham,

If it applies to B200 do you think it will apply to most drivers? If so how, ie a general "formula or shaping technique" which applicable to phase plug that can be made by individuals?

cheers.

[Graham Maynard]

Hi mcgsxr,

Magnetic phase plugs - neat.
I am of course aware of you 'hands-on' past, and thus I should be very pleased if you could check out and report on this mod.
At least you could always clip the plug back in again if your are not completely happy.
Please make contact via my messages e-mail so that I can forward details.
Might be rough notes at the moment;  I need to put some thought into more detailed instructions with photos.

Hi markC,

The new dust cap dimension is critical for the B200, and thus is most unlikely to suit any other driver without considerable trial and error.  So at this stage it would make sense to see if other B200  'circlers  think the effort worthwhile. 
Do you have a B200 to give it a try on ?  If yes, then do please e-mail me.

Hi ttan98,

Yes I see this mod suiting some other drivers, but the performance of twin-cone types, any with shallow cones and any which are not underhung might end up being degraded. 
_______________________________________ _____

There are those who rightly feel that cutting a driver immediately reduces its resale value.  However, many wide-range drivers exhibit dust-cap related inadequacies and can immediately be improved by fitting a phase-plug anyway, as indeed some manufacturers already do.

In one go, a phase plug fills the resonant chamber ahead of the central pole piece, and gets rid of any indirectly coupled dust cap induced incoherence.

Anyone who does not want to cut their B200 can genuinely improve reproduction by fitting a series inductance filter as described in other  'circle  threads, or on the Visaton website. 

Further improvement can also be gained by adding an inexpensive Eminence APT50 supertweeter without its plastic horn, and by placing soft 'foam fingers' in front of the cone to damp/diffuse the wave symmetry in front of the B200 cone which leads to high frequency energy beaming and on-axis frequency response ripples.

Simply wire a 22 ohm resistor across the APT terminals to damp it, and series connect 'in-phase' with the B200 via a single quality 220nF capacitor.  A 3 way selector switch to be 'off', or to parallel up either a 100nF or another 220nF with the first 220nF will usefully make for HF adjustment to suit different recordings.

However, the APT must be time aligned with the B200, which means the APT must be close to and as vertically above as possible, with the front horn opening level with the frontmost surrounding chassis edge of the B200. 
This positions the front of the magnet and APT diaphragm level with the centre cap of the B200, but ! leaves its phase plug protruding out from the front panel !

Time alignment with circa a 15kHz crossover? 
YES.
We might not be able to hear such high frequencies but the filter capacitor cut-off is not very sharp (low 'Q'), so if the alignment is not correct the 'augmentation' becomes destructive at audible frequencies. 
An APT makes the B200 more 'liquid' sounding and takes away much of the residual harshness.

Arrange the foam fingers vertically as in this test photograph.

http://server6.theimagehosting.com/image.php?img=Fingers.a9d.jpg


These *useful* soft foam fingers are off 4" paint rollers. 
Simply soak in boiling water to soften the adhesive and slide off the roller shaft.
Here they were here angled inwards towards the cone centre;  the top one reduces surfaces resonance modes, the lower one ditto plus diffracts/absorbs a portion of the axial high frequency beam.
I have used these and similar before with other wide-range drivers.
_______________________________________ ___

Whilst the above might assist those wanting to improve reproduction without cutting out a B200 dust cap, there is much more to be gained by doing so


Cheers ............... Graham.

[-Richard-]

Hi Grayham ~

I have enjoyed all of your correspondences... and I find your recent work with the B200's exemplary!!!!!!

A wonderful exploration using creativity and ingenuity to bring the B200's to a higher level of resolution and effectiveness... Bravo!!!!!!!

For the sake of clarity... the Planet 10 phase plugs... which I am also presently using... has a metal screw drilled into the bass of it... so that the flat metal wood-screw-end is flush to the phase plug's wood base... it is the actual magnet used in the B200 that "attracts" the metal wood-screw at the base of the phase-plugs that causes them to "attach" to the bottom well of the voice coil... anyone who is creative enough to have fashioned their own phase-plugs can do the same thing... just drill a wood-screw into the base and keep it flush to the bottom.

I am extremely interested in all of your wonderful and enlightening experiments... and I would also like very much to try your suggestions.

Question: do the 2 soft "finger" foam devices actually "rest" on the inner paper cone of the B200's?

Your description of taking the B200's to a higher level of performance certainly has me excited.

Do you prefer I PM you for details? or are you planning on sharing the details on this thread?

I found that with the addition of one Alpha-15 15" driver per baffle connected in parallel with the B200's... using a simple copper coil inductor to high-pass the Alpha's at 275Hz works very nicely to absorb any anomalies that the B200's may exhibit... by that I mean the combination sounds quite "organic".

But if it possible to take things to a higher level of performance that would be very exciting indeed.

Thanks again for sharing your explorations, Graham.

Warmest Regards ~ Richard

[navin]

I have removed the dust caps, and have installed Planet10 phase plugs, but they are just magnetic, not permanently installed.

Does the wood screw contact rattle?

[Graham Maynard]

Thanks to all who have contacted me.  It is great that others still have B200s.  I should be able to respond individually tomorrow, and hope that anyone trying this very simple mod will be as surprised as I was at what can be achieved.
_______________________________________ ________________

I should also like to expand upon my thoughts relating to the soft 'foam fingers'.

In the past, and especially with circular cone drivers, I have often felt it necessary to strategically position filaments or rolls of natural fibre damping materials ahead of drivers in order to reduce the low treble response peaks which can make widerange driver listening so tiring.

This damping tended to be thin and vertically in line with the edge of a dust-cap or dual-cone edge, or vertical from the bottom upwards and partly obscuring an axial 'listening' line to the lower half of the dust-cap.  They would control and disperse the beaming energy and make listening much more pleasant, but if the material was too dense you would hear it introducing diffraction interferences.

However, these same peaks were less significant when the driver was elliptical, and whilst this is obviously related to their diametric inconstancy I noted that a single foam finger up towards the centre of a dual cone eliptical could still much improve listening.

How come a circular driver 'shouts' much more than an eliptical one, and why is it that manufacturers don't make very high quality elipticals ??

The driver manufacturers leave it up to us poor sods (who keep them going) to sort out what they don't do right at outset !
_______________________________________ ________

I personally imagine into the region ahead of the dust-cap where energisation from the dustcap and from the main cone area around the dust-cap, can focus energy in a manner that becomes further magnified by a circular cone's symmetrical pressure change boundary between aperture and open space.  (Like the intense central peak which can be generated when one drop of water falls into a cup - here the volumetric shape of a cup is less relevent than the shape of its bounding edge !!! )

This is where my use of foam fingers comes in, because if these intrude into the radiating aperture then the foam bound cells of air cannot support symmetrical aperture resonance in the same manner as does free air, and the modified radial shape can no longer further peak a response due to the inconstancy of edge reacting components.

One foam finger either side renders free air movement at the aperture boundary more like that of an elliptical driver, whilst their positioning and the number of fingers used may be adjusted empirically to suit individual drivers/baffles/cabinets etc.  Even placing a couple of thin foam strips either side of a driver at the baffle edge can reduce shoutiness by disturbing waveform symmetry. 

Taking a foam finger in towards the dust-cap and within the quarter wavelength distance at the cone's natural SPL peaking frequency (often between 3 to 6kHz for 8 to 5" drivers, plus/or around 6 to 9kHz when a dual tweeter cone/whizzer is fitted ) additionally prevents the peak from developing in the centre of the radiating aperture, again by disturbing wave motion symmetry.  (An odd number of half wavelengths with respect to a cone's edge is likely to generate the greatest levels of axial peaking, and of course there is no fixed radius with an elliptical driver by which to generate any family of central odd number half wavelength peaks.  Note - this is all hypothetical - not proven, nor read about elsewhere.)

Thus, one upward pointing foam finger leaning into, but clear of Xlim cone displacement, can serve to disperse central HF and prevent central focussing whilst simultaneously disturbing radial symmetry.  Any other edge fingers coming down/inwards can further impair radial symmetry without additionally affecting forward HF projection.  (Hence those pictured in reply#6 above.)

Where a driver is fitted with a whizzer, the degree of conicular fucussing that would otherwise arise is reduced due to central distances being less coincidental within the driver's plane of radiation.  I say this in case anyone might wish to remove a whizzer, because doing so can increase the main cone focussing peak and impair reproduction.  Sure, a whizzer can introduce other peaks but these are generally less intense than those generated by a plain main cone, and they are equally amenable to foam finger taming by disturbing the symmetry of their edge induced excitation within the radiating aperture.

I do remember seeing a photograph of a circle or foam with triangular cutouts surrounding the edge of a driver.  I think the points of the foam were protruding over the baffle edge into its aperture, and so must have been modifying wave motion behaviour at the driver edge, but I do not know any more about this or of any explanations for the mechanisms involved;  nor even where to find it for reference.

Of course we can introduce series notch filters to reduce excitation at resonant frequencies, but any tuned 'LC' circuit in series with a driver voice coil cannot acheive the correct response in transduced 'music' time because there are additional driver impedances and time delays between waveform energisation and the dynamic cone/air excitations which subsequently become noticable as a prominent characteristic within reproduction;  like a time shifted and independent signature which peaks after one half wavelength (or longer) at the frequency of energisation, but after the rest of our music has moved on (makes for shoutiness on voices). 
I have tried LC circuits but they do seem to affect reproduction (as do crossovers) much more than say a realistically implemented 'LR' baffle step arrangement, with maybe an additional Zobel network too.

Phase plugs do reduce dust-cap + centre cone 'focus' peaking but do not alter the fundamental sound of a driver cone due to its surface and outline shape. This is a route I have tried but not one I choose to take due to the increased loss of HF output, though soft foam fingers can still help in reducing circularly symmetrical magnifying effects.

Gotta go for now.

Cheers .......... Graham.

[-Richard-]

Hi Graham ~

Thanks for the more complete meditation of what you have discovered and the effects certain "treatments" have on a circular cones radiating patterns... admittedly... I will have to read it a number of times until some of the details begin to sort themselves out in my mind.

I await your email communication with excitement... I am very interested to try your latest experiment and see what it sounds like.

Hi Navin ~

There is no rattling with the Planet 10 phase plugs... which uses a metal wood screw head flush on the bottom... however it does "move" from time to time as a result of intense frequencies being generated... so David sent along a small drop of some sort of contact goo that he suggests one places on the bottom of the phase plugs for greater stability... I haven't used it yet... it looks like "playdough".

I would pre-drill a hole in the phase plug to make certain that the head of the screw is entirely flush with the bottom of the phase plug... also... it is surprising how the magnet of the B200's snaps the phase plugs out of your fingers just before it makes contact with the bottom of the voice-coil well... a bit of a surprise the first time you attempt it... the magnet is powerful!

Warmest Regards ~ Richard

[mcgsxr]

I am with Richard - the strength of the b200 magnet is surprising - it literally pulls the plug out of my hands, once it gets close.  I have not heard any rattling either, and I don't use any such goo!

I also am interested to learn more about the dust cap mod, thanks again for sharing Graham!

[nodiak]

Has anyone tried Grahams dustcap mod? Comments?
Don

[Graham Maynard]

Hi Don,

I have not even been well enough to double check on the results myself recently.  By coincidence I started again from a fresh start yesterday afternoon.

I will report my findings this time anyway, but health/home situation means I will be slow, and physical driver mods do take time to check out.

I was also looking at augmentation with a separate LF driver, and have a desirable improvement.  This does not rely upon driver modification, but upon a circuit between the amplifier and the LF driver which partially corrects displacement loss where the drivers develop their resonance with roll-off.  I am wanting a single amp/channel set-up, so this mod suits SS amps only.  More on this soon too.

This LF mod is similar to an inductor/capacitor arrangement tried by Feddy (Karlson) on large drivers, but uses an additional transformer. 

Cheers ............... Graham.

[nodiak]

Hi Graham, sorry you're not feeling well, hope you are better soon. No need to push a report if it's difficult. I understand it can take time to determinewhat's going on with new ideas.
I am interested to hear about simple mods to drivers, and enjoyed the B200's in the past. I may check them out again sometime.
Hoping to hear from any who've tried this mod, and that it may be revealed at some point.
Don

[Graham Maynard]

Getting there. 

This post has been modified and reposted.

http://www.audiocircle.com/index.php?topic=53322.0

Yesterday my circuit was called 'T'-boost, from today it will be 'T'-bass.

Cheers ............ Graham.

[scorpion]

Hi Graham,

I think I'll provoke you by taking up your angle here again. There has been some debate over the B200 recently. And elsewhere you have said that a 6.5 cm long paper phase plug would really benefit the B200. Now where do we stand on this issue. I think we can take it to some decision. I will be experimenting with the B200 along your line during the coming weeks. But it would also be interesting if someone like Dave at Planet10 could be interested in applying your suggestions and perhaps also if tests are successful provide those 'Pinocchio' noses. I hope you don't think I am going to far to soon but anything that could be done to better this already good driver is worth more than a try, and it would be good to get some things going. 

/Erling

[Graham Maynard]

Hi Erling,

I just can't get doing what I would like to with audio at the moment.

I retested from scratch with a whole series of simple cones coming out from the B200 voice coil former edge after the dustcap had been removed. 
These after felt and foam layer damping had been glued to the pole face using impact adhesive.

I find that superglue will hold new dustcaps and centre cones nicely and that it can be easily broken away from the voice coil former as long as the speaker is held facing downwards and all fragments are removed. 

Yes 6.5cm was my final 'by ear' choice, but that does not mean that it is the best;  I don't trust my hearing to be good enough to satisfy others.

The new voice coil former centre (Pinocchio) cone was implemented to overcome beaming and the HF notch arising due to the original dust-cap centre co-radiating with the main cone, but with axial delay due to through-cone transmission losses and the cap being further away from the listener than are areas of cone nearer to the outer edges.

The new centre cone needs to be longer than I thought would be necessary in order to compensate for mechanical/dimension induced aberrations.

Horizontal foam fingers gapped +/-1" either side of axis and in a straight line across but clear of the front of the driver then reduce the amount of cone area 'exposed' so that we 'hear' more of the centre region only on a horizontal axis, this with reduced co-incidental interference from the outer edges.

I also found that two more foam fingers mounted vertically, close to the cone though just clear of it and each gapped 1" from the new centre cone, further broke up concentric surface wave mode inductions which lead to 'shoutiness' when reproducing loudly. 

The new centre cone with four fingers gave me a B200 which was excellent to listen to on and off axis when running flat without any component compensation, though still using a second driver to augment the B200 up to about 500Hz, and BSC which might separately need to be arranged with its own turnover and possibly via a thrird driver.

The HF response sounded as if it was much extended too, especially with regard to HF coherence. 

I had been aware of axially transduced motion causing destructive effects due to cone surface to ear distance variation with radius, and thus a reducing HF output compared to what was actually being transduced by the underhung voice coil.
When the new centre cone was extended out beyond the the edge dimension it seemed not only to correct, but to compensate for the large area induced inadequacies.
This aspect of course being something that no amount of EQ or DSP can correct !

Hope you could understand my empericism sufficiently to progress these findings where I presently cannot.

(From my own point of view I am thinking of 2x low Qes 15" drivers where others can use 1x high Qes 15".  If the Beyma SM-115N can match up into the B200 with its extended response
http://profesional.beyma.com/ENGLISH/producto.php
(look in SM - low frequency)
then I will be happy, though I am fully prepared to use additional 1x or 2x 10" if necessary to maintain upper-bass/ low-mid dynamics.)

Cheers ......... Graham.

[scorpion]

OK, Graham

I think I can follow your outline. Quite a lot to test and listen to inorder to improve the B200.
But if successful worth the job, I think. 

/Erling

[Graham Maynard]

Hi Erling,

I cannot begin to express how worthwhile the improvement is. 

The B200 does transduce the highest of AF frequencies, it is just that the HF radiation and energy profile is wrong with the normal dust-cap and cone shapes. 

I'm not saying that the additional cone and foam fingers properly correct the problem, but there is no hint of the original 'shoutiness' characteristic, and female voices, sax etc. become a pleasant instead of 'cautious off-axis' listen.

Cheers ........ Graham.