[lord_glum]

Honestly I never considered OB speakers until I hopped on this forum and started playing around here a bit yesterday (added Hawthorne to the next possible speaker project for this fall).  Now the hawthornes interest me very much.  But I have a question in general...what parameters do you look for when selecting OB speakers and 'subs?  If you talk horns I know what to look for, but I don't know much about OB's.  I see allot of peeps run them through active crossovers....thats not my style (well not yet anyway).  I run TT/MM Preamp or Transport/dac straight to the amp.

Thanks,
Jvo

[Bob in St. Louis]

Hello Jvo, 
I see you live in IL.
How close are you to STL?  aa

Bob

[lord_glum]

I live around 2 and change hours away.  I am around the Decatur Il area...at least for now.

Jvo

[opnly bafld]

Bob, I think you are confused, you live in the
show me state,
not in the,
show us state.

Lin

[Bob in St. Louis]

I see no harm in fulfilling the mans curiosity, Lin.  aa   

Besides, the system has improved since my fellow brethren has visited. 

bOB

[Magnetar]

For bass - If you want to build a good speaker you should use a mid .7 to .85 QTS group of several bass drivers per side on a flat baffle with no wings. Wire them to get the highest voltage sensitivity your amp will drive without compromise. The drivers should start out at decent sensitivity of 90 db or more each. The idea is to move a lot of air with low distortion and still have the ability to play loud enough to sound realistic with out the resonance nasties you get with wings, folds, boxes, or (insert your letter) frames.

Biamping/triamping is pretty much mandatory and so is a good subwoofer. The sub should be of the front loaded horn type if you want the best blend and impact

[opnly bafld]

For bass - If you want to build a good speaker you should use a mid .7 to .85 QTS group of several bass drivers per side on a flat baffle with no wings. Wire them to get the highest voltage sensitivity your amp will drive without compromise. The drivers should start out at decent sensitivity of 90 db or more each. The idea is to move a lot of air with low distortion and still have the ability to play loud enough to sound realistic with out the resonance nasties you get with wings, folds, boxes, or (insert your letter) frames.

Biamping/triamping is pretty much mandatory and so is a good subwoofer. The sub should be of the front loaded horn type if you want the best blend and impact

That's one persons opinion, there will be others, be patient.

Lin

[Magnetar]

That's one persons opinion, there will be others, be patient.

Lin

Actually I was stating facts.

With a moniker like yours I'd think you might have some too.

[Rudolf]

Ivo,
since magnetar already stated the facts, this is strictly opinion:
As said, moving air is the first, second and third requirement. Power capacity is of much less relevance, since any decent driver will reach its Xmax in a OB long before its power limit.
Look for an open but sturdy construction, that lets the driver breathe: open basket and as many vents behind the spider as you can get. This will help to avoid air noise.
Large cone is better than small cone. Explanation: OBs need to be wide to allow for low frequencies. But if the baffle gets much wider than 2-3 times the cone diameter baffle edge diffraction becomes a recognizable problem. So you better have large diameter with less Xmax than small diameter with much Xmax.

While I subscribe to every statement Magnetar made about drivers above, I have different opinions (or even facts?) about baffle/frame geometries. But that wasn´t what you were asking for. 

Rudolf

[KS]

You can glean some info from these kits, drivers, and speakers designed by Danny Richie
GR-Research OB kits
Free Air Subwoofer
AV123 X-Statik

[lord_glum]

GR Research/Danny/AV123 ais not really what I am looking for....my entire HT room is GR research.


So I am still left with the age old debate....a couple of 10's vs 1 15.  I assume 1 15 or in this case 1 per channel.  If that is the case i can do some more looking for the 15" OB discussions on this board.

Thanks,
Jvo

[Magnetar]

While I subscribe to every statement Magnetar made about drivers above, I have different opinions (or even facts?) about baffle/frame geometries. But that wasn´t what you were asking for. 

Rudolf

Rudolf, I'm wanted to relieve my line array dipoles posted earlier here of their response below 80 cycles. Taking them down to 50 cycles brings the IM distortion up -

My plan is to use three of the Madison Warrior 15's (.85 qts and 35 cycle resonance) along with the spare  Pyle 21" beasts  per channel. My idea is to put them in a line array with the 21 on the bottom and drive them with a separate amp for dipole bass down to the 30's where the Horn takes over.

How would you configure these drivers? I don't think I'll need much eq which I have - and I have no experience building a TRUE 'bass' dipole or 'sub' dipole - all my other attempts or finished systems have been for midbass dipoles where the wings/folds/frame always caused problems. This may not be the case here seeing they will be crossed lower with a steep lowpass (and highpass)

[Rudolf]

Magnetar,
I certainly don´t need to tell you, but just for the records/others:
OB below the lowest room mode does not make sense at all - and you already have that covered by your horn. So hopefully we are only talking about a solution above the lowest room mode.

Let me first talk about radiation pattern:
I love real dipoles because of their dipole nulls perpendicular to the dipole axis. I don´t believe much in U frames and back folded wings because they fold back those dipole nulls too. But dipole nulls behind the speaker don´t help much WRT avoiding first side wall reflections. (In fact I even would like a dipole with the nulls folded somewhat forward)
Dipoles with that real figure-8 pattern are plain baffles and H frames. Now you see where I am going?

There is a big difference between dipoles, whose dimensions are the same or bigger magnitude than the wavelength they have to carry, and dipoles which are small compared to those wavelength. Intelligent baffle geometry and driver positioning can help in the first case to overcome/smear/equalise the dipole peaks and nulls. You don´t have that chance in the latter case.

So the operating range of any bass dipole is restricted to the dipol-loss-range below the lowest dipole peak. JohnK explains this in some of his Tech Studies: http://www.musicanddesign.com/tech.html

If you build a 21" wide H frame with a depth of 21" (front to back), the first dipole peak will be at ~320 Hz. This peak will in no way be "peaky" - just the upper end of the 6 dB/oct dipole roll off turning down to the first dipole null. This H frame will give you ~6 dB more efficiency than a 21" wide OB. Crossing over to your line array at 80-100 Hz you will be well away from that peak too, even with a low order x-over.

That´s what I would recommend for your 'bass' dipole array.

[Bob in St. Louis]

What frequency range are we talking about reproducing here Jeremy?

Bob

[MJK]

I see allot of peeps run them through active crossovers....thats not my style (well not yet anyway).

For a passive flat OB system, I assume that is your interest based on the statement above, you really need a woofer with a Qts > 1 and an fs of about 40 Hz. In a moderately sized flat OB you will not get below about 40 Hz no matter what driver fs is used. You also need the bass driver to be 6 to 10 dB more efficient then the mid/full range driver and any tweeter so that it mates well. It is an advantage to cross over the bass driver at about 200 Hz with 12 dB/octave filters to account for the OB hump produced in the SPL response.

Things change a little with an H frame. You can get much lower in frequency with a lower driver fs but the requirement is still a Qts > 1 and a crossover at or below 200 Hz. An H frame will slightly reduce the driver efficiency so you need to be careful selecting the mid/full range driver and any tweeter.

These are my general rules of thumb for scoping drivers for passive OB/dipole geometries. There is no substitute for running simulations to design your system before you buy any drivers. Design cannot be done by lots of talking, you need to make numbers and take measurements. In my opinion simulations followed by measurements are keys to getting a good result. I guess some would argue that trial and error building would work for designing an OB system, anybody who can do that is much smarter than me.

Martin

[Graham Maynard]

>> just for the records/others:  OB below the lowest room mode does not make sense at all

>> Let me first talk about radiation pattern:
I love real dipoles because of their dipole nulls perpendicular to the dipole axis.

Hi Rudolph.

Please count me as 'others'; why does OB below the lowest room mode not make sense ?
Anyone reading this could be put off before they start, and maybe miss out on clean LF reproduction to the excursion limit of the LS/drive. 
The lower the driver Fs the cleaner the low bass reproduction.

Also, we don't get nulls perpendicular to the driver axis in a real room, that happens in free space only !

Cheers ..... Graham.

[Graham Maynard]

>> In a moderately sized flat OB you will not get below about 40 Hz no matter what driver fs is used.

Again this could put folk off before they start.

How low a baffle will output is related to cone displacement and drive.

My baffle is flat and just 18" wide, but 30Hz is a doddle. 

Cheers ........ Graham.

[Rudolf]

Please count me as 'others'; why does OB below the lowest room mode not make sense?

First because the power demand becomes excessive since you will have almost immediate and complete shortcut of front and rear radiation.
Second because in the pressurised-room-situation below the lowest room mode any decent closed box sub will work perfectly well.

Anyone reading this could be put off before they start, and maybe miss out on clean LF reproduction to the excursion limit of the LS/drive.

Below the lowest room mode no dipole will sound as clean as any decent closed sub can. So I don´t say: forget lowest bass, but: do it with a monopole.

The lower the driver Fs the cleaner the low bass reproduction.

That may be well right if you look at the driver without the room. But there is a paradigm change in the room below the lowest room mode.

Also, we don't get nulls perpendicular to the driver axis in a real room, that happens in free space only !

OK, if you insist.   Would 12 dB less than on-axis be sufficient?

Rudolf

[MJK]

>> In a moderately sized flat OB you will not get below about 40 Hz no matter what driver fs is used.

Again this could put folk off before they start.

How low a baffle will output is related to cone displacement and drive.

My baffle is flat and just 18" wide, but 30Hz is a doddle. 

The original post indicated a passive preference, in other words no EQ for the low end. Your 18" wide baffle is flat down to 30 Hz without any EQ or added circuitry? You have SPL measurements that show this type of performance?

The only way I can see to get bass below 40 Hz with this assumptions is to use many drivers (more than two) for the bass so the net result is so much more efficient then the mid/full range driver that the loss due to the OB roll-off is no longer important. You can afford to throw away a lot of bass efficiency. But I seriously doubt that an arrangement with three or four 15" woofers can be done on what I would classify as a moderately sized open baffle.

A low end down to 40 Hz is really quite good, people will be surprised at the bass performance. If you look in Stereophile at the measurements of the speakers being reviewed, that don't cost >$10k, not many get to 40 Hz.

Martin

[lord_glum]

Wow...lotsa typing going on.

My original plan was to use 1 sub setup in my ht room for experiment and then move this to the listening room.  This originally started as an OB sub question but has moved on to more OB discussion in general since I may build a set. 

My issue is the 'sub' output w/o having a preamp.  My system does not have a sub output thus the experimenting in the HT room with this...  I have seen circuits to get around this, but have not done research.

I don't need the sub to go low...i just want a bit of speed w/some pep.  I have run horns in the past, i will run horns in the future...this is just another area i have not yet explored that i am working towards....

Thanks for all the dicussion...I think i am starting to get it.  A bit.

Jvo