Finally, lower cross-over point for my Eminence Alph15A OB woofers with B200's ~

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-Richard-

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Change is good... usually it comes from another direction... an experience that makes one rethink things again.

I recently heard a "commericial" closed baffle design (using thin plywood) with rave reviews from owners, (actually it was described as a semi-open baffle design which caught my interest) using one full range driver and a ribbon tweeter. The designer was on hand and we played a number of my familiar CD's with his own CD's as well. Highly focused instrumental positioning, the voice floating deep in the space between the speakers.... very articulate... but the room I heard them in was much too over-damped... the electronics were astronomical... the preamp alone was $20,000, the CD player $9000 (combined that's a down payment on a house). I would have to hear them again in a "live" room to know what they really sound like. The designer may visit me at my home with his speakers in tow.

I came home and played my OB's... the crossover point for the one Eminence Alpha 15A's per baffle, with the B200's playing full-range, was very high... well over 1000 Hz. The sound was very rich harmonically and sumptuous in the mid-range. But after listening to the closed baffle design with its tight focus I was immediately struck by the lack of upper frequency nimbleness, articulation and "air".

I undid the Alpha's intending to listen to the B200's alone... yet once again... to become familiar with it without the Alpha's in the mix. It became clear that there was something wrong with my integrated amplifier. That started me trying to chase down the source of the distortion... I sanded all of the tube prongs... and endlessly switched them back and forth. Finally the sound stabilized. I began to listen to the B200's full-range and alone. The sound was fantastic... highly articulate, nimble, fast and detailed on top, with space around voices and instruments... the mid-range was rich while the bass was more of a "suggestion"... almost enough to be able to live with them if one had to (psycho-acoustically the brain does "fill-in").

I listened for hours going through many different types of music from my CD collection. Then finally I switched back the Alphas again... this time bringing the cross-over point to 275 Hz (the lowest simple coiled inductor I presently have on hand). That filled-in the lower bass very effectively... once again I heard what made me fall in love with this combination in the first place. I can throw quite an array of gushing adjectives at this current set-up... but I think a lower cross-over point might work even better... I will be ordering a couple of simple inductors very soon.

So why did I have the cross-over point so high for so long. Habit of course plays a role in this... but by carefully going over everything in my mind I have become convinced that the amp must have gone into distortion some time ago... and I compensated by raising the cross-over point until I no longer heard it... and the exaggerated mid-range really did allow a great many of my CD's to sound much better then they really do (poor engineering).

I am just sharing my insights here. With Warmest Regards ~ Richard

scorpion

Hi Richard,

Nice to here from you again. But I read this post with a little smile on my lips.  :)

Now to the problem. The Alpha15 is not so easy to master passively with 6 dB/oct slopes as I was learning the hard way with my MJAO.
The Alpha respons with the pronounced 2 kHz hump is the problem. I had to put both a Zobel-filter and a Notch-filter in the MJAO 6 dB-filter to be reasonbly satisfied.

I think you should rather follow MJK's original passive design putting a 12 dB-filter on the Alphas, 9 mH coil and 68 uF cap like he says: http://www.quarter-wave.com/OBs/OB_Design.pdf here. This filter is calculated for 200 Hz.
It has been built by so many to satisfaction evidently so it should be a safe bet. It will work.

Good Listening !

/Erling
« Last Edit: 29 Oct 2010, 12:34 pm by scorpion »

ttan98

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The Ear is very sensitive around 200Hz up to about 3-5KHz, I suggest you experiment with x-over around 200-250Hz, preferably closer to 200Hz. Try 1st or 2nd order filter, in most cases 1st order would suffice.

Cheers happy listening.

scorpion

In this case you are outright wrong ttan98. I know ! How do I know, because for the MJAO I had to go through almost all possibilities.
If you want to stay with 6 dB/oct you can't igonre how much is sneaking around in the upper Alpha register and this is also what you hear if you listen separately to this kind of crossover.
This is why I recommend 12 dB/Oct in the first place.


/Erling

-Richard-

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Hi Erling ~

Once again Erling, you have provided important information (not only for me but for everyone considering using the Alpha, B200 OB combination) that should work its magic with the integration of the Alpha's with the B200.

I am still a "beginner" when it comes to many of the fundamental technical procedures, so I have question for you, Erling: how is it best to hook up the "9 mH coil and 68 uF cap"... do they hook up (together) on the same positive lead wire of the speaker cable (which is broken "open" for them) while the negative leads tie-in to themselves (are "continuous" and do not touch the prongs of the coil or cap).

"a little smile on my lips"... yes... I was quite happy before with a very high cross-over point, which you pointed out at that time was not desirable sonically... in absolute terms, you were quite right of course. I can't account for why exactly I thought I needed the mid-range to be so rich at the expense of upper frequency information. I am still learning... and that is the beauty of building ones own OB speakers and continuing to experiment.

What you are suggesting Erling, is obviously more than just a cross-over point, that ttan98, is suggesting and that I was (originally, before reading your post) thinking of as well (thanks ttan98, for sharing with us)... can you just share with us what your combination of an inductor and cap is doing sonically, that is different from a "simple" inductor used alone to generate the cross-over point.

In other words, how it affected the sound... that would help many of us less sophisticated OB builders to "see"/grasp what your very important suggestions are doing to help the integration of the Alpha's with the B200's... it would help me (and everyone interested in this) to understand what makes your suggestion work as well as it does in this case.

Thank you for your kind feedback and help, Erling (as always!)... extremely appreciated here.

With Warmest Regards ~ Richard

opnly bafld

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Hello Richard,

The coil and cap causes the response to be down 12dBs at @400 hz vs. being down only 6dBs @400hz with just a coil. The Alpha has a huge peak at 2k which the 12dB/oct x-o helps tame.

http://www.parts-express.com/pdf/290-407s.pdf

Here is a helpful link for wiring:

http://www.apicsllc.com/apics/Misc/filter2.html

Lin

-Richard-

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Hi Lin ~

Thanks so much for the links. I am still not certain how to hook up the 9 mH coil and 68 uF cap that Erling is recommending. Do they both hook up to the positive lead of the speaker cable (like a single-coil inductor would be)?

Warmest Regards ~ Richard

opnly bafld

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Coil goes inline with +
Cap goes across + and -

See second diagram (second order - two way crossover) low pass section.

Lin

canzld

Hi Richard - scroll down to the first diagram. cap goes across the terminals of the alpha15

http://www.colomar.com/Shavano/crossover12db.html

canzld

whoops - sorry Lin - you popped in there while i wasn't looking - my post is clearly redundant.

Richard
'I can't account for why exactly I thought I needed the mid-range to be so rich at the expense of upper frequency information. '

if you like it -keep it , there's no need to account for it. If you like a rich mid-range - enjoy it for what it is -your personal taste. Most buy speakers that are voiced the way they like, some more 'accurate' than others. Sound wise - the lower you take the alpha, the more you will hear the character of the B200, faster and clearer -more 'air'. If you are worried about implementing the 2nd order xover for now, just do first order as low as the coils you have allow -the alpha peak at 2K will still be there, but your B200 should dominate in this frequency range.

all the best

-Richard-

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Thanks Lin and Canzid... I deeply appreciate your help (thanks for the link Canzid).

"if you like it -keep it , there's no need to account for it. If you like a rich mid-range - enjoy it for what it is -your personal taste. Most buy speakers that are voiced the way they like, some more 'accurate' than others."

I guess I was thinking out-loud... in the sense that perhaps other DIY OB designers may be asking themselves similar questions about where they want their music to play... what kind of presentation they would like to concentrate on.

You are quite right Canzid, in all of your insights. People who purchase commercial hi-end speakers are actually choosing a "sound"... they may be under the illusion that what they are hearing is more "real" than what other choices in speakers are giving them... but in reality it is just the "presentation" that they find desirable (or not).

I think having the cross-over so high on the Alpha's (over 1000Hz) gave a smoother performance all-over combined with the B200's... voices, violins, cellos, piano and so on, sounded rich, full-bodied, fully realized as "presences"... captivating really. Perhaps the 50's sound that I grew-up with (I had an audio system when I was a young teenager... I was crazy about music).

But recently I found myself thinking about using another driver besides the B200's... with a more delicate top end and more transparent over-all. I began searching for an 8" driver and found myself looking once again at the field-coil types (apparently at 12 volts they get nicely jazzed-up... with terrific low-level resolution)... also Alnico... David Dicks has Alnico drivers that are not insanely expensive (although expensive enough to be out of reach for me now)... but his 8" is inefficient compared to most full-range Alnico drivers (around 91db... which could compromise the performance on my 7-watt integrated tube amplifier... let alone any consideration for a possible future SET 45 tube amp).

By lowering the Alpha's cross-over I instantly gained an entirely different musical perspective... the (somewhat) missing transparency is now there... but the rich textural harmonic resolution is also there... not as smooth all-over as with the higher crossover of the Alphas... but the sound I was looking for.

Until one builds their own Open Baffle speakers, and continues instead to purchase commercial speakers (especially the boxed variations) they will not have the opportunity of so easily shifting the sonic presentation around... unless they explore variations of cross-over points and different driver combinations in their expensive commercial speakers (which could void the warranty and make resale more difficult).

I have a question: I was originally using a cable that went from my B200's to the Alphas (with the inductor spliced in)... now I have a separate cable for each driver (one for the B200 and one for the Alpha) and both are attached to the same binding post... in other words I have 2 speaker cables attached to each post (and each going to separate drivers, the B200s and Alpha's)... could that hurt my amplifier... am I stressing my 7 watt EL 84 tube amplifier by doing this?

Is it better for the amp if I attach the cable from the B200's to the Alphas (instead of originating from the same binding post at the back of the amplifier)?

With Warmest Regards ~ Richard

opnly bafld

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Richard, wired either way the amp "sees" the same load.

Lin

scorpion

Hi Richard,

I have been away during the weekend, but you have had good advice in the meantime. However if you should want to supress the Alpha's but for the bass,
I think MJK's crossover is good. It looks like this (from Martins' paper refered to above):



The coil in the positive lead and the cap over the positve and negative terminals as in the picture.

/Erling

-Richard-

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Hi Lin ~

Great!!! Thanks Lin for the feedback.

That is what I wanted to hear... I cannot explain it... but both speaker cables wired at the amplifier binding post seems to be creating far more of a dynamic presentation... I suspect that I did not have the B200 to Alpha cable attached effectively (I prefer not to solder... tomorrow I am buying solid copper alligator clips... I like the idea of moving things around as I continue to learn).

Thanks Erling ~ You are always such a positive source of inspiration and help! Our DIY OB community is an incredible group of friends... stretching around the world. I couldn't (nor continue to) do it without your help.

Honestly, if people looking for expensive speakers could hear what my simple (and cheap) system (integrated amp, OB speakers, cheap CD player, even cheaper cables) using a simple DIY OB sounds like, they would be truly astonished. They will not get this level of performance with those expensive behemoths.

Recently I had a student over (I facilitate a college level program here in Ojai, on the teachings of J.Krishnamurti) who is a composer and incredible performer on the piano, and he was curious about my OB baffles... I played him an assortment of music... he was utterly astonished and got it immediately... the palpable presence, the rich harmonic complexity, the saturated color palette (musically speaking) and clearly defined instrumental textural surfaces... he really loved it... sharing the sound of my OB's with such a highly sophisticated musician as Kevin, and having him hear the magic, was really fun!!!

With Warmest Regards ~ Richard

Vix

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Hi Richard!

I was reading you experiences with Alphas and Visatons and couldn't understand how could you cross so high! :)

 I have open baffle 120x50 cm, no side wings, Eminence Beta 15 at the bottom, Visaton B200 on top. Biamped, with an active crossover. I was considering your situation, and, while first order crossover is best in terms of phase coherency, it's just too shallow for my taste, at least with the OB dimensions I have (the biggest-still-domestically-accepted).
So, maybe you could consider buying another solid-state amp for Alphas and go biamp route. It will give you much more flexibility in adjusting the relative gain, crossover frequencies and slopes. The only additional cost would be another SS amp and an active crossover. Nelson Pass of Pass Labs (actually Firstwatt) has designed a crossover specifically for this purpose:

http://www.firstwatt.com/b5.html

Don't take this as advertisement, as I am in no way affiliated with Firstwatt,  I am just a happy DIY-er.

Regards

Vix

-Richard-

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Hi Vix ~

It sounds like you and I have a very similar OB.

"I was reading your experiences with Alphas and Visatons and couldn't understand how could you cross so high!"

I want back to that high cross-over point again, a few days ago, and listened carefully. Sam Kim's re-vamped Heathkit 151A EL84 tube integrated amplifier is so incredibly dynamic... like fireworks or laser beams sparkling with intense energy... that the high crossover point of the Eminence Alpha 15A actually works. What I hear (again) is a very smooth harmonically ultra-rich mid-range... extremely coherent all-over presentation. Honestly, it is a sound people would probably gladly pay thousands to have... people who value an ultra-rich midrange for voice, jazz, classical... violins, for example have a super-saturated resin texture that is entirely seductive. Voices have a depth of warm moist resonance that is fleshy and liquid.

When I switched back (again) to the 275 Hz cross-over point, that heightened velvety creamy mid-range perspective was replaced with a very fast upper frequency agility... with a slightly boomer bass... and too-much of an all-over dynamic effect... a leaping out at you and grabbing your attention bristling with energy effect... which I finally traced to my cheapy Pioneer CD (universal) player.

So that explains the mystery to me of why I preferred the higher cross-over point for the Eminence bass driver... with my Heathkit and CD player, it resulted in a creamy, liquid mid-range magic... and smoother bass integration... at the expense of a less agile upper frequency perspective and less transparency.

Because of tube issues in the Heathkit (those old NOS tubes!) I switched to the Red Wine Signature 70.2 (SS) with a tube preamp. With the 275Hz cross-over point the music is relaxed and still sounds convincing. The somewhat faded instrumental accompaniment embedded in the background of older female-voice jazz recordings does not have the same "light" as with the Heathkit. But the HF instruments, like violins have a but more transparency and the upper keys of the piano have a sharper more realistic striking tone.

I know that our forum does not usually indulge in this kind of very subjective writing... which makes sense given how much variation exists in our approaches to OB DIY design solutions. But since this thread has a somewhat "personal" slant to it... I thought I would share with everyone what I am hearing.

I like your suggestion Vix, of using Nelson's B5 "active" cross-over component... it sounds perfect (thanks for the link). It is, however, $1500!! Before I would purchase that, I would spend the money on the PHY Alnico dual-concentric 8" driver, which uses no crossover... or the Supervox 215-2000 field-coil 8" driver. Lust is alive and active in my audio imagination... it is only my budget that lags behind somewhere in the "real-world" (where those purchases languish in the shadow-world along with other "out-of-reach" desires).

OK... I will hook up the Sig 70.2+tube pre for the Alpha's and the Heath for the B200's, as soon as I get new tubes for the Heath (to see if it really is a tube issue that the Heath is suffering from). That should at least give me some control (different volume setting for each driver).

I am seriously wondering about Nelson's 5 watt (SET land) F2J SS amplifier for my OB's... anyone have experience with that? Lowther America designers, who are using the new Lowther field-coil drivers, designed specifically for OB's ($5000 now, $6000 in 2011), use the F2J to drive them in their OB design (the bass is an "active" driver). What I hear from the designer: they are very smooth, incredible detail retrieval, none of the shouty issues of the "standard" Lowther drivers.

Tantalizing stuff those field-coils... but when the music plays in my simple, cheap OB's, the magic washes away all desires for "better" or "more". That is the magic of music... it supersedes all interest in technology.

With Warmest Regards ~ Richard

nicksgem10s

Hi Richard,

Great to see you back on AC  8).

I always enjoy hearing about your experience with audio.  You are gifted at expressing what you are experiencing in your system and more importantly with the music.

I felt compelled to chime in just a little bit off topic.  I have enjoyed learning and using OB speakers the last several years. 

I have used the following open baffle designs:  Fostex F200A, Emerald Physics CS-2, Audience A3 (4 drivers per speaker, and most recently the Supravox 215-2000 EXC Field Coil drivers.

I do not have many regrets in life, but one was selling the Supravox about a year ago.  They are special and they are worth the price of admission.  In all honesty I believe they are one of the biggest bargains in audio.  They are that good.  I just had a need for funds at the time. :duh:

I will most definitely own them again in the future when the audio budget allows.

Keep posting your experience and participating on AC.  Hope you have a great weekend.

-Nick 

Vix

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Hi Richard,

I agree that the cost of the new B5 crossover may be a bit prohibitive, but since I've gone DIY route , I am not so concerned. It's surprising that you still like the sound character of Alpha (crossed) so high. I couldn't stand Beta 15 at anything more than 200Hz. It had a sort of peaky-nasal-muddy midrange. But , since you enjoy the sound as-is, just go ahead. I've noticed that the choice of amplifier has a big impact on sound, so maybe that combination of tube amp, Alpha and Visaton B200 somehow combines to give satisfying result, even if it goes against a common 'logic' of what should (not) work. Presently, I am crossing Betas at 80 Hz low-pass, and Visaton at 150 Hz hi-pass, second-order . During two years, I have tried various combinations of crossover points/ slopes and I am still playing. In the meantime, I am listening to music.. :)

Enjoy

Vix

djn

I messed with a passive crossover for my Alphas for quite some time.  I ended up buying two BASH 300 plate amps and really like the ability to change crossover points at will.  I know my horns go down to 200hz so I started the crossover point at 150hz but kept moving it down and landed on 100hz.  Great transition from OB horn to woof.  Gotta love the Alpha.

-Richard-

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Hi Nick ~

Thank you for your very kind comments.

Ah yes the Supravox 2150-2000 EXC field-coils... around $2500 (+ shipping). Since it doesn't have a whizzer for the upper frequencies, many who use them suggest a tweeter for the ultimate sparkle and air... which I would want to avoid (a 3-way is a swerve away from the simple single wide-range coherent driver concept that hooked me into OB's in the first place). Quite right Nick, at this present time they are an incredible bargain among the field-coil drivers for OB that are available. I could fit them into my present baffle s-o-o-o-o-o easily!!!

I must admit that having to work with batteries for DC power feels like an added stress... plus the added cost of batteries and voltage regulator. Perhaps I am intrinsically lazy... or I just want to get past too much "stuff" and things to worry about. What I find curious is that none of the field-coil driver manufacturers supply the batteries and voltage regulator for their own drivers... I find that a bit of a nuisance... where is the follow-through! They could make things much easier for us... don't you agree? Still... admittedly you have me thinking about the Supravox, Nick... Someone who uses them (and has tried many different drivers in OB like you have) said that at 18 volts they come completely alive... creating that uncanny micro-detailed musical dimension field-coils excel at.

Then there are others (knowledgeable listeners) who claim they can hear no difference between the alnico versions and the field-coil versions of the same companies drivers. Also, it is interesting to note that a very talented speaker designer recently told me that alnico's never lose their magnet charge (unless they are dropped or allowed to become too cold) whereas almost all other magnets begin to lose their charge in 5 years!

The new Lowther field-coil drivers, designed specifically for OB implementation (augmented with a Visaton tweeter) received quite a glowing comment in Stereophile: "...Satchmo sounded so incredible that I was smitten. Smitten, I tell you, smitten."
http://www.lowther-america.com/
http://blog.stereophile.com/rmaf2010/lowther_and_first_watt/

OB's do things no other speaker even comes close to. Perhaps it is the fact that there is no resistance to the back wave of the drivers... all of that combined energy directly serves the music and "charges" the sound-space of the room... "igniting" it with dynamic sound. With my Sam Kim Heathkit supplying the energy, there is no way one can not be energized and stimulated by the music.

I wish the new Lowther OB's did not use such prohibitively expensive auxiliary gear in their show presentations!!! Yes... I understand they want to come on the scene with the most killer-performance that is possible. The bass drivers (Servo) are from a kit made by Rythmik: http://www.rythmikaudio.com/ that includes a dedicated amplifier. Actually not that expensive... especially considering they reportedly go down to 16Hz!! If I used them I would be unceremoniously ejected from my home (I live in a tight community of homes). I am thinking of visiting Nelson Pass to hear his version of the Lowther OB's, with his first watt J2F... if that is acceptable to him.

Hi Vix ~

True... true... when you engage in DIY everything appears so reasonable compared to the mark-up on commercial stuff. When the designer is doing something extraordinary... like in Samuel Furon's Ocellia line of semi-open baffle speakers with their instrument-tuned cabinets, the cost can be seen as part of the extensive R&D it takes to perfect their art. The incredible thing about DIY is the wiggle room one has to indulge a bit in remarkable drivers and cross-over strategies.

Still... right now everything appears so fantastically expensive. The law of diminishing returns has never seemed more unshakable to me as it does right now.

I am back to using the 275Hz cross-over... and dialing-back my bass tone control... more detail, less bass energy that tends to spill into the lower mid-range (Sam Kim designs his re-vamped Heathkit 151A with an ingenious "subtractive" tone control strategy). On most recordings the sound is quite fabulous... spatial, dimensional, ambient cues to satisfy the most demanding aficionado... saturated tonal colors that pour into my music room like precious jewels. A sound space this good should cost in the tens of thousands according to the commercial audio press. Well... we who work with DIY OB have it really good... perhaps the best kept secret in audio.

With Warmest Regards ~ Richard