[BenjaminWebber]

I want to build a pair of OB's that my 45 tube based SET amps will like.  I have been doing a lot of reading about OB's lately, but there are too many choices!  Perhaps not with a SET 45 amp and a meager budget.  Maybe I can sell some stuff and get to $1K.

My actual listening room is 16 x 14 x 8 feet.  The end I listen from opens up into the dining room, so it's an L shape.

I built a pair of Voigt Pipes a number of years ago with Fostex 166's.  They turned out good, but by the time I got them sounding good (with more than a little help from friends I made on the internet) I felt like I had been really ignorant when I built them.  So, with the encouragement of the mentioned friends, I built a BIB with the Fostex 208 sigma and TA90A.  At that point, I did nothing but listen to music whenever I had spare time.  I quit lurking on the forums.  I did things to my room and speakers that got rid of the shoutiness that bothered me at first.  I did things to reduce the boominess in the bass, but never got it perfect.

Most of the past few years I have driven my speakers with a Cary Rocket 88.  Then I got my SET 45 monoblocks.  I consider myself a very lucky soul.  Paul Weitzel of Tube Research Labs and I became friends.  I did some polishing plates for him, and he worked on designing a pair of 45 monoblocks for me.  He sent them home with me, though he intended to do some more tweaking on them.  But, on 1/30/2016 he passed away.   I can't say how many watts they produce.  Each monoblock has a three tube line up (6SN7, 6BL7 and 45).  I was pleasantly surprised that the SETs have better defined bass than the Rocket 88, in addition to the golden midrange.  Ironically, the improved bass was what set me on a quest to try to get it even better.

I became intrigued by the OB idea and began to silently lurk on the forums again.  One day when I had a couple spare hours I took a box knife to some drywall and made an experimental JE labs style baffle with some medium sized oval drivers from an old Grundig console that I had.  WOW!!!  I have no idea what sensitivity they were or anything.  I had enough gain for CDs but not enough to do my phono well.  Next I used a Saturday to make another JE Labs style baffle with a large oval shaped driver from an old RCA console.  These play plenty loud for any source, have even more impressive bottom end, but are not as well balanced.

I have looked at various designs on the net.  Troels Gravesen's OBs, but they are out of my price range right now.  I have been very intrigued by the OBs of Musical Affairs.  But again, those field coil drivers are out of my budget.  I don't get away with spending money on audio.  But unlike most, I seem to manage to get away with murder as far as turning the living room into what looks like a recording studio, having large speakers in the room etc..

 I have considered selling my Rocket 88 and some other stuff to get Audionivana's 15" alnico driver and running it full range in an OB.

As I write this, I am also leaning very heavily towards an Eminence A15 with some small full range driver. This may sound strange, but I have some concern about having too much (or probably just boomy) bass.  I have read good things about the Visaton B200, but have concern about a raising FR.  I have concerns about efficiency with my SETs.  Whatever I do will be built around them.  Should I use a plate amp on an A15?  I have not done any active crossovers before.  I like the way my SET's do bass, and I think I would prefer to do it all with them if advisable?  I don't want to melt my SETs either!  I don't require a lot of volume.  I do like to listen to all kinds of music, including large scale symphonic.

Sorry my wife is not here looking over my shoulder.  She would tell me that I am too wordy! I would just like someone to point me towards a tried and proven OB design that my SET 45 amps and room will be happy with, that I will be able to afford by selling my Rocket 88 and maybe some other things.

 I have a table saw and chop saw etc.  My brother lives an hour and a half away, but has more tools and better tools.  From what I have seen on Youtube, my hat is off to Spectral and others, but I seem to have the bug to build something again.

Sincerely,

Benjamin     
     

[Abby356]

Hey Ben,

I'm no expert by any means, but I have experimented with a couple of nice drivers (Fostex F200A and Tangband 1808) on the JE Labs OB.
If i were starting fresh I would take a long look at this most recent design shared by the ever generous Nelson Pass over on DIY Audio. It incorporates some clever tricks (slot loading and floor coupling the bass) and could work with a variety of drivers for both the wide range and the bass driver. With your 45 amps you would obviously be using those on the wide ranger and using a separate amp w/crossover to drive the big woofer. You could easily use a plate amp to run the woofer and a simple passive crossover on the wide range driver to roll off the bass frequencies. Nelson used the Eminence Definimax 15" and commented that he preferred the sound from a lower Qts driver which is somewhat contrary to accepted OB practice. He also has a trick First Watt B5 active crossover that he uses that is specifically designed for this type of 2 way OB set-up.

Regards,

Daniel

[mcgsxr]

I ran the Visaton b200 for 10 years on OB.  Run stock on their own I would agree they lacked enough bass for me.

I found them excellent after Planet_10 phase plug mod, and biamped with subs.  I uncovered them during the long, long Gravity well of a darkstar thread here.

I would consider either a plate amp for 2 of them, or find a used Crown XLS 1500/2000/2500.  They have built in 24db/octave Xover, TONS of power, and you can daisy chain amps through them.

There are a number of well conceived and documented Martin King "kits" out there that I would strongly consider, and some really nice designs floating around this circle.

I would not discount either Danny's GR insights, or the Hawthorne options either.  Excellent stuff.

[bear-hifi]

I would recommend the Hestia OB project.  Great sounding OB with a low cost and a good project to start with.

http://www.audiocircle.com/index.php?topic=108003.0

[matevana]

If you want to try something a little more challenging (rewarding), the Hestia V Dome's can be had with a high efficiency woofer that will work well with SETs. It's also available as a flat pack, so you would only need to assemble the parts.

[BenjaminWebber]

Thank you very much Abby356, mcgsxr, bear-hifi and matevana!!!  This will give me much to chew on for awhile.  BTW Abby356, How did the Fostex F200A and the Tangbang 1808 compare in the JE Labs Baffle?

Sincerely,

Benjamin

[gab]

Benjamin - there are several GR Research Super-V speakers available used in the Trading post area and in the GR Research circle.

The Super-V top section is 97dB/w/m and should do OK with the 45 amp. The bottom woofers are actively powered. Here is more info: http://gr-research.com/super-v.aspx

I believe the silver ones shown in the link above are avail from Danny as well (unless he has already sold them).

Sorry - I just saw your budget is $1K

I had a pair of the GPA 604 series 2 duplexes and the GPA crossover mounted on a JE Labs open baffle. Don't know how well it would fair with the 45 amp though. Here is a used set on Ebay but who knows what they will end up selling for:

http://www.ebay.com/itm/401117970471?rmvSB=true

[-Richard-]

Hi Benjamin ~ I am using a 45 SET Yamamoto A08S amplifier to run my Lowther PM5A Alnico drivers on my 2-way (2 drivers for each baffle) Open Baffle design. I use a small 7-watt 'digital' amp to drive the Eminence Alpha 15A bass drivers which 'crosses over' at around 250Hz using a simple coil inductor. Inductors have different ratings that cut (or fade) the higher frequencies at different Hz frequencies.

Here are some suggestions: I had Shigeko Yamamoto install a 16ohm Power Transformer on my 45 SET amplifier to match the 15 Ohms of my wide-range Lowther PM5A's. So it is helpful if you know both the Ohm rating of whatever driver you are planning on using for your wide-range driver, and the Ohm rating of your 45 SET amplifier's power transformer. Some amplifiers have multiple taps, such as 4 Ohm, 8 Ohm and 16 Ohm taps. If you do not know the Ohm rating of your power transformer you can probably safely assume it is 8 Ohms, which is a kind of universal rating.

The most important consideration is perhaps the efficiency of the driver you have in mind to use for the wide-range driver; the driver that will handle the frequency range from, say, 100Hz or 250Hz to the top of its frequency range, which can be 10,000Hz to perhaps 16,000Hz.

I purchased the relatively expensive Lowther PM5A Alnico drivers because they are rated to be around 98db sensitive. My Yamamoto puts out about 2 watts. I suspect your 45 SET amplifier also puts out around 2 watts as well, even though they are mono blocks. The 45 tube is extremely linear and balanced with a wide frequency range but it really only puts out 2 watts or less, according to the circuit used of course. A design can be used that 'pushes' the 45 tube, but it will severely shorten the life of the tube over time. I have heard that using the monster-sized EML 45 tubes can give the 45 SET amplifier a little more 'volume' or 'presence'. I am currently using RCA type 45 tubes which were cheaper then the $400 a pair EML tubes.

So I would not consider using a driver with less than 96 db sensitivity, if you want to be able to play your music without clipping, which is a form of distortion. It is true that SET amplifiers 'clip' less sharply than most solid-state amplifier circuits. But it is better I think to try to get as an efficient driver as possible.

As it turns out, my Lowthers and Yamamoto 45 SET amplifier play music quite lovely together. I never run out of 'volume', and sometimes Deborah and I like to play our music to realistic levels. I think the match of the power transformer Ohm rating matching the Lowther Ohm rating is a critical part of their nice performance together.

So you are most probably working with 2 SET watts and you need a driver that can play those 2 watts beautifully and efficiently. Look at the db sensitivity of the driver first before making any decisions. If you have a friend with highly sensitive speakers you can take your 45 mono blocks to their house for a listen. If you live near Los Angeles, or within 2 hours above Santa Barbara, California, you can visit Deborah and I and we can hook your amplifier to our Open Baffle set-up so you can hear what it sounds like.

The SET circuit used for the 45 tube will also allow you to use high sensitivity drivers that do not necessarily use Alnico magnets. And drivers with other magnet variations are often cheaper than the Alnico types. That can possibly help to save you money. If the company or reseller of the drivers allow an in-home audition with a return-policy that can be very helpful as well.

Good luck with your search, Benjamin. Your amplifier is probably fantastic. Now you just need a highly efficient speaker to go with it. Great musical magic awaits you!!

With Friendship ~ Richard

[BenjaminWebber]

Richard, you sound like a really nice guy.  We were in San Francisco a month or so ago.  I would love to hear your system and talk about all this stuff, but I live in Yakima, Washington.

 I assume my 45 SET amps are configured for 8 ohms, but really don't know.  And, can't ask the designer now.  I do know that the output transformers came out of a dead SET (I think 300B) amp.  They had a few wires coming from the secondary side that are not being used.  Currently, I don't know how to tell what impedances they might be for.  If I did, I could maybe I could see if there is a set of (currently unused) wires that are for a 16 ohm tap.

Matevana, your Hestia V Dome speakers look REALLY cool.  I have been swamped with work and have not calculated the prices of most of the OB's presented to me by those who have responded.  But, I think it may be best at this juncture to go with the most simple and economical OB's.  Too bad a guy (without any reputation) can't build a pair of speakers, play with them for a year or so.  And then turn around and sell them for what he had into them, to then try the next thing.

Like I say, I seems to get away (more than most) with having set ups with really low WAF, but not spending real $$$ on audio.  Nobody else in the family is interested.  I can get away with trying to sell things though.  It sounds like I should perhaps start my selling my Cary Rocket 88 and buying a Yung 300 or Bash 300 plate amp, or used Crown?  This, as it appears I should biamp in most OB setups, and can adjust the level and low pass to the bass driver.  This will be new territory to me.  I also had been thinking of selling my Fostex T90A's and Fostex attenuators.  I never noticed it until I got my 45 amps, but even when I had my Fostex Sigma and T90A integrated the best I could, I noticed a loss of "integrity" when I would turn them on.  I missed them when they were out, but for the most part, preferred the sound with just the 208's in my BIB's.  I liked the T90A's with my JE labs OB's/old RCA drivers for a while, but found I could actually relax and get into the music more without the T90A's.  That is part of why I started experimenting with the JE Labs OB with just one driver in it.  But now, I do want to try at least a FR with bass assistance.  And of course, a designed pair of speakers, versus me just finding a driver and throwing it on a baffle.

So, I shall continue my research on these designs you guys have presented to me.  Again thanks all you guys!

Sincerely,

Benjamin   

[BenjaminWebber]

[BenjaminWebber]

I decided to try posting some pictures that show my room, amps, and 2nd experiment of sticking an old driver on a baffle with my Fostex 166 Voigt Pipes and 208 sigma BIB's in the background.  And also the crazy diffusor (which really helped the sound!) that I built.  Sorry some came out upside down. 

Sincerely,

Benjamin

[BenjaminWebber]

The SET circuit used for the 45 tube will also allow you to use high sensitivity drivers that do not necessarily use Alnico magnets. And drivers with other magnet variations are often cheaper than the Alnico types. That can possibly help to save you money. If the company or reseller of the drivers allow an in-home audition with a return-policy that can be very helpful as well.

Richard, I wondered if you could elaborate a little on the "other magnet variations."  I had noticed that the 15" driver from Audio Nirvana is like twice as much of you go with the Alnico version.  What would be the advantage (if any) of going with an Alnico driver vs the same thing with the least expensive magnet?  Is it sort of like putting super premium gas in a car designed to run on regular?

Sincerely,

Benjamin

[mresseguie]

Hello, Benjamin.

I can't offer you any ideas on OB (rank beginner here). However, I really like your diffusor. Did you use 1/2" or 5/8" plywood and 2" wood screws to mount all the 2x2s (or did you use a lot of glue)?

Thanks for the pics.

Michael

[flavo]

You don't need to spend the extra money for a Yung 300. If you decide to go the inexpensive route of the Yung amps. the 100W should be all you need unless you plan on REALLY rocking out. I have the 100 hooked up to alpha 15's, live in the country and can play Black Sabbath to my hearts content with out need for more power. FWIW

Also the "Betsy" is quite inexpensive and built for OB. I found it runs out of steam too quickly for me though. Although I don't think this is the norm, and it depends on what you are listening to.  Don't think it was built for really cranking up. Before Poultrygeist got all fancy on us with his Lowther driver. He seemed to favor the eminence 12". Of which designation, I can't remember. But it is also inexpensive and a quick PM to him can get the model #.

If you don't have a ton of money, I don't think you need to spend of ton of money. But there seems to be no hard and fast go to that folks will point you to in my experience.   

[flavo]

Hello, Benjamin.

I can't offer you any ideas on OB (rank beginner here). However, I really like your diffusor. Did you use 1/2" or 5/8" plywood and 2" wood screws to mount all the 2x2s (or did you use a lot of glue)?

Thanks for the pics.

Michael

As a previous wood working professional     I can say that the thickness of  Ply doesn't really matter. The 1/2" will be lighter and therefore easier to move.  You only need about 1/2" of screw sticking into the wood. So with 1/2" ply I would use anything that was an inch or longer and a bit of glue. Not so much you need to do excess clean up, just because it's a PITB.

[gfxmla]

These are premade, and I can't speak to their sound or performance, but they are pretty inexpensive.

http://www.decware.com/newsite/Caintuck.html

Just a thought

[nicoch]

Betsy in your JE baffle for start..... then if you need more put an alpha15" under with a plate amp , small caps on input of 45 amp to cut bass 100/200hz , you will have xover, lower distortion from betsy, more power from 45 and lower distortion too!!    

[fdandrews]

To try the open baffle sound without too heavy an investment for a first project, it's hard to beat an Eminence Alpha 15 (or 2) for the bass and a small fullrange on top. I started with the Alpha 15 and BOFU on a flat board and then tried a Fostex 166en. Both sounded good. You might look at the Quarter Wavelength Loudspeaker Design website for a simple project using the Alpha and a small Fostex  that is well documented.