[omegatt]

Greetings ,
Thanks for having me in your fantastic circle.  I am very excited by the prospect of building an OB,  getting away from the HIFI magazine driven merry go round of upgrades , dissatisfaction, more upgrades less satisfaction etc, etc, etc.
 
As a complete novice regarding this speaker building buisness I wounder if you would indulge a couple of probably obvious questions.  I get the bit about driving a single high efficiency speaker from a low powered amp,  but many threads have 2 drivers in an OB driven by serperate amplifiers.  Is this because the low powered amp could not drive the bass unit ? I am considering using an 18-20 watt amp so could I drive bothspeakers from the same speaker terminals on the amp ?

Second Q.  If you have to have to have 2 amps how does the signal from pre-amp get split to go to 2 amplifiers ?  Links to some simple wiring diagrams / photos would help

Thanks for your patience / sufferance

Tony

[ebag4]

Hello and welcome Tony!

To answer your first question, two amps are often used because the full or wide range driver and the bass driver's sensitivities do not match.  Using a separate amp for the bass helps to alleviate driver sensitivity mismatches by allowing you to increase the volume on each amp separately.  To do this with one amp you would have to closely match the drivers sensitivity ratings and then use passive components between them to get them to match.  Also, I feel that more power is typically needed for the bass driver so in this case a separate more powerful amps can be used for the bass and a smaller amp for the full range driver.

As for your second question, there a a couple of ways to feed the signal to both amps.  One is to use the high level(speaker output) signals from the full range driver amp to the bass driver amp and then on to the FR drivers, this is my preferred method because I feel it imparts the "Flavor" of the full range amp into the bass section.  Note* Use caution if your FR amp is a "T-amp" as these amps cannot have their negative outputs tied together, many bass or sub amps have a common negative.

Another method is to split your preamp signal (either with a "Y" cable or if your preamp or source has a second preamp out you can use that) and send one set to you FR amp and the other set to you bass amp.

I hope this helps.  I am sure others will chime in with other/better info.

Best,
Ed

[panomaniac]

Wow Ed!

That's about the most perfect answer to the question I've ever seen. Well done. 

Tony.  Just read what Ed said.  It's all there.

[omegatt]

Wow Ed!

That's about the most perfect answer to the question I've ever seen. Well done. 

Tony.  Just read what Ed said.  It's all there.

Agreed,  Ed you are too modest,  a fine explanation to my lack of knowledge, Thank You. Now just need to decide which driver(s) etc etc.   More reading of the Circle required 

[Dmason]

I agree that is about the most succinct and well thought-out answer to the entire OB Question there is. That post should be a sticky.

One thing I would like to add is regarding the use of speaker level outputs. The advantages of using a wideband driver are that usually they allow you to use very low powered amplifiers, which sadly, tend to be the best sounding ones, with the greatest limitations. Second, when using the speaker level outputs to connect to a bass amp, like a sub plate amp, these amplifier topologies seem to have high damping rates and good slewing capabilities, which allow them, it would seem, from my observations, to track the output of the flea powered amplifier, and you get a muscle amp being told what to do by a single ended triode amp, or similar. This is a good thing. The only downside seems to be that it requires the flea amp to be run full range, which means it is dissipating ~40-60% of its available juice for a lower register signal that isnt being heard. A 2 watt amp relieved of bass duty is alot of amp, witha wideband paper cone driver, it seems. Plenty of dynamics. I find that boxless sound combined with the well known dimensional aspects of SET portrayal, it is a good fit.  Many people find it to be a sort of "destination audio" combination. I guess my point is that if chosing OB speakers, single ended tube amps, especially triodes, do amazing things with the sound. You can get set up with both SET and a bass amp with controls, for under $500. It does NOT have to be prohibitive. I have a friend using the Tone Tubby Ceramic 8 inch cone with a Neo ribbon tweeter, and a Bottlehead SEX amp, and some Eminence bass speakers of 15 inch diameter, with a 300 watt switching amp, and this set up sounds fantastic. Unbelievably good. Total investment was around $800. I find older 6X9 paper cone car speakers sound great on OB. Any driver sounds its best, when unloaded.

Bottom line, OB is a great way to go if you are inclined. Many are it would seem, and it doesnt have to be expensive.

[omegatt]

DMASON

Thanks for the imput,  the aspect of using a low powered SET amp was what I was usure about in my initial thoughts.  I have a 300b SET amp which puts out 8-9 watts.  but had an option of getting a 20watt tube amp which I thought would be able to drive both drivers.  When you say a bass amp with controls do you mean that you an dispense with the crossover and filter at the amp ?  If so could you name an example similar to what your friend uses as this sound just what I would be aiming for

Thanks

[Dmason]

First, I wouldnt bother with a 20 watt tube amp if you already have 8 watts 300B. I know of no 20 watt tube amps that would sound as good as 300B, except maybe for 845, 805 or some other jumbo transmitting tube. My point was that OB allows and encourages the use of wideband paper drivers of reasonable sensitivity, and an 8 watt SET amp will, trust me, drive the daylights out of the whole thing, but you wouldnt want to waste the amp on powering some big, dumb bass drivers, when its entire output can be dedicated to the meat of the message, the main driver, and any little tweeter you care to add, if deemed necessary. Were it me and I had a 300B I might just be tempted to indulge myself alittle more and sport for the Tone Tubby Alnico 10, now you have SET, hemp cones and Alnico motors. You cannot fail to have jawdropping sonics at home. I really, really liked Jon Ver Halen's idea of using a motor-Run can cap to high pass the signal going into the expensive Lowther PM6A, so as to completely avoid any IM distortion introduced from bass frequencies, in the cone.

Completing the bass picture is easy with one order from Parts Express as far as I am concerned. Seems the Eminence Alpha 15 is the budget champion, with specs that are ideal for OB and come with Martin King's seal of approval. There are more elaborate offerings, from DIYCable, AESpeakers, GR Research. For plate amps, I think the BASH amps are about as good as it gets. These are true switching amps with a good record, super high damping factor which comes in handy for moving big, heavy, cones, and come stock with an impressive array of control, including I believe a one band parametric EQ on one of them. From my own experience, the use of iTunes one octave EQ has been a godsend for cheap, easy and effective contouring. I find every album, if not every song benefits from some tailoring.

For the bass, it seems many people are getting away using the active level XO on sub plate amps, and letting the mains driver roll off acoustically, which begins ~400Hz anyway. In truth, in my experience and that of others, it is pretty hard to fail. I am of the opinion that it is a waste of tube juice, powering big cones with nice flea amps.

Soon Richard Waxberg will have some observations on using different value choke coils at varying low pass frequencies, and running the whole thing with I believe a Heathkit of maybe 8 watts, because it is tweaked into triode.

[Saurav]

I'm using a pro-audio line-level crossover (Behringer CX3410). Most people will cringe at that But the preamp is connected to that, and its outputs go to a 2A3 SET for the midrange and tweeter on my OB, and an SS amp for the woofer. Passive crossover between midrange and tweeter. For my next speakers I may stick with the same setup, or I might try an active 3-way, since I have a 3rd amp I could use.

There are different opinions on the use of line level crossovers. I like the idea of of relieving my 4W amp from having to process bass signals that the driver won't even produce, I think the advantages outweigh the disadvantages. YMMV, of course.

[Dmason]

I agree completely. Using SETs completely relieving the tubes, output transformers, and midrange drivers of any bass information is THE way to go. Using SET's and OBeez this way is amazing. Use ALnico motors, like Lowther, or Tone Tubby, or some other, with SET and OBeez, and it all starts to make perfect sense.

8-12 inch diameter mains cones seems best.

If it sounds good, it is good. There are no rules.

[mcgsxr]

I use an active Xover to remove the 100Hz and down from my SEP Magnavox, and coupled with the b200 Visaton's on OB, with phase plugs, in my room is great.  I use a BASH sub amp to drive 2 subs, also OB, and I am quite happy.  Have been for more than 3 years now too.

Lots of ways to skin the audio cat, I look forward to learning more about how you go about it!

[panomaniac]

Yes, active bass is the way to go for OB.  Unless you have big baffles and multiple drivers.

But here's the funny thing;  Even tho I'm currently running plate amps on my OB 15s, the bass is different with different main amps.  Yes, the signal is running speaker level to the plate amps, but the plate amps "should" be doing the grunt work, not the main amp.

Despite that, the difference in bass response and feel is noticeable between different amps.  Guess it's time to try line level into the plate amps.

FWIW, all of the biggest, best systems I heard in Europe used SS amps for the low end. SET was reserved for mid and treble duty - only.

[omegatt]

Yes, active bass is the way to go for OB.  Unless you have big baffles and multiple drivers.

But here's the funny thing;  Even tho I'm currently running plate amps on my OB 15s, the bass is different with different main amps.  Yes, the signal is running speaker level to the plate amps, but the plate amps "should" be doing the grunt work, not the main amp.

Despite that, the difference in bass response and feel is noticeable between different amps.  Guess it's time to try line level into the plate amps.

FWIW, all of the biggest, best systems I heard in Europe used SS amps for the low end. SET was reserved for mid and treble duty - only.

Right just about to prove my ignorance here but,  if I were to follow the general consensus here and have say my 300b driving the full range driver, and a plate amp such as the BASH one suggested by Dmason.  The plate amp has volume and a filter built in so do I still need a crossover for the bass driver or is this adjusted using the volume / frequency filters built into the plate amp ?

[mcgsxr]

Assuming you are talking about using speaker level inputs for the plate amp, the plate amp will have a variable Xover, and volume, and phase so you can adjust it one time to suit a balance between main driver and helper woofer, and as you raise and lower the volume on the main amp, so too with the bass driver follow.

[omegatt]

Assuming you are talking about using speaker level inputs for the plate amp, the plate amp will have a variable Xover, and volume, and phase so you can adjust it one time to suit a balance between main driver and helper woofer, and as you raise and lower the volume on the main amp, so too with the bass driver follow.

Perfect

Thanks

[lowrider]

I use an AV processor to split the signal, sub out to subwoofer, line to tube amplifier, like it has been said before, the tubes and the full range will sound much cleaner without the extra effort to play bass... 

You can get pretty good processors used, if you dont care about the latest video gadgets, and you get a good DAC included...

[panomaniac]

I use an AV processor to split the signal, sub out to subwoofer, line to tube amplifier,

Interesting approach.  On the processor do you set the main speakers to "small" to limit the bass going to them?

A PLLXO (Passive line level x-over) could work well here, too.  Between a preamp and the tube amp.

[lowrider]

I use an AV processor to split the signal, sub out to subwoofer, line to tube amplifier,

Interesting approach.  On the processor do you set the main speakers to "small" to limit the bass going to them?

Of course, you also have choice of frequency most times, it sounds very very good...

[omegatt]

Completing the bass picture is easy with one order from Parts Express as far as I am concerned. Seems the Eminence Alpha 15 is the budget champion, with specs that are ideal for OB and come with Martin King's seal of approval.
For the bass, it seems many people are getting away using the active level XO on sub plate amps, and letting the mains driver roll off acoustically, which begins ~400Hz anyway. In truth, in my experience and that of others, it is pretty hard to fail. I am of the opinion that it is a waste of tube juice, powering big cones with nice flea amps.

DMason

I am taken by your argument to indulge myself with the TT 10"  alnico+ SET .  However in my limited listening room 15' x !0'  with speakers firing down the length of the room I am a bit concerned that a 15" bass driver may overwhelm the room.  Do you think that a smaller driver may be more siutable, secondly is a tweeter needed to fill in the gaps above the top end of the TT 10".

[Dmason]

I say indulge in the TT10's, slap them onto a baffle, get used to them, Erling shows they model fantastically well, and decide about a bass driver later. Michael's idea about the Dayton is gold, Erling's idea about a "topless" U baffle is a proven variation on a theme, and personally, with some contouring, to jack up the treble reach, I found I got very used to just the Tubby 10, as it was.

These drivers with SET amps are just stunning. They sound sooo good on their own with prerecorded music that you will be more than happy to enjoy them on their own, while figuring out how to optimize the whole thing to your room and taste. www.svvintageamps.com  Scott is your man.

[omegatt]

I say indulge in the TT10's, slap them onto a baffle, get used to them, Erling shows they model fantastically well, and decide about a bass driver later. Michael's idea about the Dayton is gold, Erling's idea about a "topless" U baffle is a proven variation on a theme, and personally, with some contouring, to jack up the treble reach, I found I got very used to just the Tubby 10, as it was.

These drivers with SET amps are just stunning. They sound sooo good on their own with prerecorded music that you will be more than happy to enjoy them on their own, while figuring out how to optimize the whole thing to your room and taste. www.svvintageamps.com  Scott is your man.

Thanks

Already decided that Scott was going to get my buisiness,  $230 verses around $ 500  !!!!! here in England,  just have to hope they are packed well and survive the journey