[MJK]

I found the discussion on these two drivers so interesting I decided to do a quick study to see what possible performance differences existed in an OB system.  I modeled a smaller baffle with a Visaton B200 and one 15" woofer and then modeled my larger baffle using a Lowther PM2A and two of the 15" woofers.  The results were very similar.  I think I have included enough details so that you can get an idea of what was simulated in each model.  A summary of the results can be found at :

http://www.quarter-wave.com/Augie_vs_Alpha.pdf

Hope you find this interesting and useful. Comments and discussion are always welcome.

[scorpion]

Both interesting and useful. It is surprising that the Alfa doesn't need more augmentation to extend as deep as the Augie. As JohninCR has pointed out Eminence published IB response curve is wrong, it should be much more extended into low-bass before slowly falling off. The difference between the drivers come from the basic difference in sensitivity and may be the Eminence is a little helped too by its lower Qts-value. I read it that you have no specific 6 dB OB roll-off compensation but only stated boost from 200 Hz downwards. The Augie even though not as effecient seem to extend level to about 30 Hz when the Alfa start falling at 40 Hz.

I have not heard either the Eminence or the Augie so I could not say which to prefer. But I have been given opportunity to compare cheap
 (20$) high Qts chinese made 12" woofers and Peerless SLS (125$) low Qts but longthrow 12" woofers for OB-subs and the difference is not very pronounced once the cheap unit has a decent build quality.

I find your matching between the basspeaker and the fullranger very telling and noteworthy, something that always should come into consideration. I also assume that the fullrangers position on the baffle also is fully intentional. I would like to hear your comment about
crossover and phase in the B200 case as I didn't understand if both drivers were crossed at 200 Hz or if the B200 is run fullrange.

I always thought that speaker manufacturers should publish full TSP parameters and IB(IEC)-response curve plus impedance curve,
you shouldn't have to guess parameters.

/Erling

[Brad]

It looks like the Alpha is a pretty good match for the B200's.

The sensitivity match must help in smoothing at the xover point.

[MJK]

Erling,

The difference between the drivers come from the basic difference in sensitivity and may be the Eminence is a little helped too by its lower Qts-value. I read it that you have no specific 6 dB OB roll-off compensation but only stated boost from 200 Hz downwards. The Augie even though not as effecient seem to extend level to about 30 Hz when the Alfa start falling at 40 Hz.

I think the big difference between the two is the weight of the cone.  The Augie has a heavier cone which drops the fs 13 Hz and also the sensitivity.  Then a bigger magnet is used, but still the result is only 89 dB/w/m.  So major differences are fs, SPL/w/m, and cost.  I think they are both very good drivers and a buyer should review the differences and see which one better fits their application. 

As Brad observed, the Alpha is a very good match for the B200. I have found it also goes very well with many of the Fostex drivers.  The Alpha is a versatile driver for a smaller OB design.

The simulations include the roll off and diffraction due to the baffle size and shape so the 6 dB OB roll-off is included.  Also included is the floor boundary condition and if desired a rear wall reflection. 

I have not heard either the Eminence or the Augie so I could not say which to prefer. But I have been given opportunity to compare cheap
 (20$) high Qts chinese made 12" woofers and Peerless SLS (125$) low Qts but longthrow 12" woofers for OB-subs and the difference is not very pronounced once the cheap unit has a decent build quality.

That has been my experience also, all of the Eminence drivers I have are very well made and high quality.  I think the performance differences will be minor.

I find your matching between the basspeaker and the fullranger very telling and noteworthy, something that always should come into consideration. I also assume that the fullrangers position on the baffle also is fully intentional. I would like to hear your comment about
crossover and phase in the B200 case as I didn't understand if both drivers were crossed at 200 Hz or if the B200 is run fullrange.

The positioning on the baffle does influence the response and I just did a quick survey of different positions to tame the major peaks and nulls, a better job of optimizing is probably possible.  Both drivers have a 200 Hz crossover, I do this to cut down on the displacement requirements of the full range driver.   I connected the drivers out of phase in the smaller baffle simulation to fill the deep null that occurs at the crossover frequency when the in phase option is selected.  In the big baffle simulation the drivers are connected in phase.

I always thought that speaker manufacturers should publish full TSP parameters and IB(IEC)-response curve plus impedance curve,
you shouldn't have to guess parameters.

I could not agree more.  I am surprised that Hawthorne Audio does not provide this data, it makes doing any scoping design before buying difficult.

[scorpion]

Martin,

You have perhaps observed that we are discussing the EDGE- simulation program by Svante Granqvist of Sweden in the NSB-thread. I have already given the url on several occasions: http://www.tolvan.com/edge/. Together with your new software and some other Internet sites , notably Linkwitz and Kreskovsky, MusicandDesign, we have now powerful instruments for different aspects of OB design and evaluation.

When explained I see clearly your intentions. Yes the Alfa should go very well with B200. 

/Erling

[MJK]

Erling,

My worksheets use the same methods as the EDGE, I correlated the results for just the baffle diffraction part using the EDGE, but also includes the driver's SPL response and the floor/rear wall reflections.  I am working on improving the baffle edge modeling using a recently publish JAES paper.

[scorpion]

Martin,

This proves both softwares to the point. Just what you started to use and is familar with.
But challenging would be to move on to winged baffles and for instance the shape of your own Lowther baffle and simulating
those.

I do would like some elaboration on your baffle with regard to a little different sizes for other drives, for instance
do you think you could thrink baffle widht or also thrink backward sides without running into difficulties regarding resonances
and response. Perhaps with an Alfa and a B200 in mind ? I did find your possibility to fold back wings and put away the baffle when not listening ingenious 

/Erling

[MJK]

Erling

do would like some elaboration on your baffle with regard to a little different sizes for other drives, for instance
do you think you could thrink baffle widht or also thrink backward sides without running into difficulties regarding resonances
and response. Perhaps with an Alfa and a B200 in mind ?

I don't know, I have not looked at either option.  The MathCad worksheets could be used to look at different baffle sizes and to see if something even smaller could be made to work.  Right now I have not put much thought into how to model the sides and how much the depth influences the response.

I did find your possibility to fold back wings and put away the baffle when not listening ingenious 

I can't take any credit for that idea, I have seen a number of hinged wing designs on the Internet over the years.

[JLM]

Martin,

Being an owner of MLTL's that were designed based on your work and the fascination that I have for OB's, I read with interest your ventures into OB design.  From your link above:

"These speakers produce a very large sound with incredible dynamics and power. The characteristics of the presentation are very similar to my Lowther DX3 ML TL speakers but the effortless dynamics are much better."

Realizing that the OB is much larger, complicated, and expensive; and that it requires multiple amps,  additional dual 15 inch woofers, and active crossovers; one shouldn't be too suprised that dynamics are improved and that the typical large sound of OB is provided.  Your experimentation demonstrates what is required to properly design and build a full range OB.  I find this most useful as another benchmark (Linkwitz's Orion being another).

It proves again that full range OB can be done, but IMO at a rather extreme example of brute force.  It's the simplicity of concept that attracts me to OB.  This excercise takes us a long way from simplicity and practicality such that I lose interest.  After owning MLTL's for over 25 years it seems to me that the little extra cabinetry in a well designed MLTL wins over a "super-charged" OB.

What I would be more interested in would be more of a head to head comparison between MLTL and OB, where the same (comparable) drivers/amps/etc. are used.  Perhaps the Fostex FE-167E full range driver and Eminence Alpha A15 woofer in a smaller baffle, that you mentioned.  The FE-167E could be mounted in the same OB in both cases with the MLTL 15 inch woofer installed in a separate cabinet(s).  I eagerly await any findings or opinions you come up with.

[MJK]

JLM,

Realizing that the OB is much larger, complicated, and expensive; and that it requires multiple amps,  additional dual 15 inch woofers, and active crossovers; one shouldn't be too suprised that dynamics are improved and that the typical large sound of OB is provided.  Your experimentation demonstrates what is required to properly design and build a full range OB.  I find this most useful as another benchmark (Linkwitz's Orion being another).

larger? Not necessarily.

complicated? The OB was the easiest "enclosure" that I have designed to date, much easier then a resonant full range driver enclosure and accompanying BSC filter.

expensive? If you have more drivers you have more cost, but expensive is a relative term. Typically when I see a DIYer posting looking for cheap as a prime design consideration I stop reading. Compared to the time commitment, the performance to cost ratio, and the other costs associated with equipment in the system spending some money on drivers is a small expense.  You don't need to spend a lot of money to get good quality drivers, in my opinion people looking for the next 99 cent special at PE or a $5 full range driver that does everything are wasting their time.

multiple amps and a crossover? Probably, but I have seen some people using passive crossovers with an OB 2 way system.  If I build another OB system I will try for a more compact, moderately priced, and possibly passive system.


For example consider the following system I scoped out a few months back. Consider this combination in a 40"tall by 24" wide OB as a starting point.

Full range driver = Fostex FE-167E or 166E, each is 94 dB efficient (~$63 each)

15" Woofer = Eminence Alpha series 15A, each is 96dB efficient at 50 Hz and Qts ~ 1.2 (~$55 each)

Crossover = Behringer CX2310 (~$90)

XLR Cables = six required (~$50)

Total Cost = 2 x $63 + 2 x $55 + $90 + $50 = $376 plus misc. parts, wood, and finishing.

I can say that a 15" woofer with a full range driver is extremely efficient and produces great dynamics. I am still looking at this system with a passive crossover.  This seems to provide good performance at a very reasonable price (<$500).
 

It proves again that full range OB can be done, but IMO at a rather extreme example of brute force.  It's the simplicity of concept that attracts me to OB.  This excercise takes us a long way from simplicity and practicality such that I lose interest.  After owning MLTL's for over 25 years it seems to me that the little extra cabinetry in a well designed MLTL wins over a "super-charged" OB.

Again. extreme is somewhat relative.  Depending on your perspective, my big OB might look like an extreme example of DIY speaker design.  But if I look around the Internet there are many examples of systems that I would consider more extreme and bizarre.  Some might classify TL's as a fringe design that is kind of an extreme compared to the cute little two way ported boxes on stands, but you and I know better.  Fortunately I have the space and a place in my home where I can assemble something that makes my wife shudder and close the door so she can pretend it is not there and household harmony is restored.  When I designed and built this OB system I wanted to see how far I could go into deep bass and limited myself to something I felt I could build and haul up two flights of stairs.  It could have been even bigger .......

What I would be more interested in would be more of a head to head comparison between MLTL and OB, where the same (comparable) drivers/amps/etc. are used.  Perhaps the Fostex FE-167E full range driver and Eminence Alpha A15 woofer in a smaller baffle, that you mentioned.  The FE-167E could be mounted in the same OB in both cases with the MLTL 15 inch woofer installed in a separate cabinet(s).  I eagerly await any findings or opinions you come up with.

Before I tried OB, I tried to design a resonant enclosure around my first pair of Dayton 15" drivers.  My original plan was to use an Isobaric alignment to try and shrink the size of the box and that is why I ended up with four of the drivers.  No matter what I did the box was big and going to be a pain to build and move.  It was just impractical in my mind to build a box for a 15" woofer.  While you can build a TL enclosure for any driver, my self imposed limit is an 8" driver. Anything bigger than an 8" driver and the cabinet becomes too large for me to build with my skills and resources.  This is my limitation.

Comparing my Lowther OB system to my Lowther ML TL was an interesting exercise.  The tonal balance of both systems is essentially the same.  But the added efficiency and impact of the bigger OB system with two 15" woofers is very pleasing.  The size and performance of the smaller ML TL is also good and I could easily live with it, and have for a couple of years, in my room.  I am using a pair of ML TLs in my family room and they work very well, an OB is not an option in my wife's family room.  You end up trading size for low end impact performance.  I guess I have concluded that in most cases you cannot expect an 8" driver to move the same amount of air as two 15" woofers unless you have some form of exotic horn enclosure, a BLH will be another interesting experiment.

Martin 

[JLM]

Martin,

For some unexplained reason I seem to get more of a more argumentative tone from you than others get.  I don't know how you can argue that your OB isn't bigger, more complex, and more expensive than the TL you were comparing it to.   

I'm just eager to compare bass reproduction of TL to OB in a more meaningful way.  My question to you is: "What would a performance comparable TL look like?" 

25+ years ago I owned MLTL passive subs that used 8 inch woofers in 6 cubic foot cabinets.  They were too much for my home, but sounded marvelous in a 20,000 cubic foot chapel.  My current speakers (designed from your software and using 8 inch Fostex F200A full range drivers) are rated room flat (with BSC) to 30 Hz (good enough for music IMO).  With your modeling and modern drivers I suspect your self-imposed limit of 8 inch woofers in TL might be more than what's needed in residential settings to reproduce the maximum spls of live, unamplified music.  (Just look at TBI subs: http://www.tbisound.com/)

The FE-167E with 15 woofer and passive crossover would be a more practical OB example.  I agree that good sounding speakers, especially single driver variations, require quality drivers.  OTOH I believe that, with a proper sub, there may be a legitimate place for small, single driver OBs.  IMO this could be the most practical and satisfying application of OB. 

[MJK]

JLM,

For some unexplained reason I seem to get more of a more argumentative tone from you than others get.

I had no intention of sounding argumentative, but I definitely have different opinions of some of the conclusions you have reached with respect to the advantages/disadvantages of the OB vs TL approaches.  Lets just leave it at that.

Martin

[Bob in St. Louis]

JLM, I saw no tone, negative or otherwise, in Martins writings.
Just because Martin doesn't use the cute little smiles behind every sentence signifying he's got a grin instead of a frown doesn't mean to me he's got 'a tone'. aa
I think all is good. Everybody's happy.

Bob

[JLM]

Bob,

If you review my postings, you'll find few emoticans.

You're right, I'm happy because:

1. MJK is posting here and adding more logic than sweat to the discussions;

2. MJK's findings demonstrates what it takes to to make a full range OB and that it isn't practical;

3. So I like my MLTL's even more, regardless if the father of their design apparently isn't so thrilled with them.

But I do get fustrated that we don't see eye to eye even after continual credit is given to his modeling work and that he avoids answering my questions (here and previously elsewhere).

[Rudolf]

... and that he avoids answering my questions (here and previously elsewhere).

JLM,
just for the records I have to state that MJK has answered MY questions most accurately and most generously every time I bothered him with some. And I don´t see him avoiding answering to you in this forum (don´t know about other discussions elsewhere).
I CAN see that he avoids statements that would be too simplistic or too generalizing.

Rudolf

[MJK]

JLM,

At the risk of appearing argumentative, I would like to address some of your statements.

1. MJK is posting here and adding more logic than sweat to the discussions;

Thank you, this is the best forum on OBs that I have found so I want to participate.  I am not sure how much I will participate in some of the other forums since I am primarily interested in DIY.  I would prefer not to participate in any of the manufacturer's forums since I don't think I own any of their products.

2. MJK's findings demonstrates what it takes to to make a full range OB and that it isn't practical;

This is where you and I get into trouble.  You tend to assign your conclusions to something I have done, said, or posted as if I had declared that result.  Whatever I have done, said, or posted is only what I am working on at that time and should not be considered a final result, everything I do is evolving since I do not believe I have reached the ultimate result ...... yet.

Is the OB I have built not practical?  To some yes, to others no.  If you had phrased your comment that you felt the OB system I had built was not practical for your situation I would have no disagreement with your opinion.  But you posted a blanket statement.  I am not sure it is true for everybody looking at OBs, I have seen some that make mine look kind of wife friendly.  Who knows what I may or may not learn from this design that could make tomorrows OB design much smaller and practical for your situation.

3. So I like my MLTL's even more, regardless if the father of their design apparently isn't so thrilled with them.

Where have I indicated I am not thrilled with your ML TL speakers?  Again, you have made an interpretation of something I have done or said, applied it to your system, and then issued a conclusion and attributed it to me.

But I do get fustrated that we don't see eye to eye even after continual credit is given to his modeling work and that he avoids answering my questions (here and previously elsewhere).

I appreciate the credit you give.  We don't see eye to eye in every forum discussion.  If you have opinions and state them as such I have no problem with that even if we do not agree.  But I do have a problem when you state comments or conclusions and attribute them to me, as you have done above and a number of times in the past, and that is when a disagreement occurs. 

Now if you ask a question, I would be happy to respond with my opinion/experience and then you can decide if you like the response or not yourself.  Nothing says that we have to agree or disagree, the only opinion that should count for either of us is the one we arrive at individually after considering all of the available inputs.  Please don't get frustrated, it is only a hobby and in the grand scheme of life not all that important.

Martin

[Bob in St. Louis]

this is the best forum on OBs that I have found so I want to participate. 

I agree Martin, and hope you continue to participate.

Bob