[JohninCR]

Thanks Malcolm,

Take a look at the pic again.  That 15 woofer will snug up to the 13.5" diameter hole I'll cut in the
baffle from behind.  It's vibrations will be isolated from the baffle that way.  Plus it's not married to
that speaker.  I can do the same with any 15 I choose.

You can't tell very well, but the rings around the driver cutout are recessed, so the 8" B200 will mount
flush with the baffle for a cleaner look.  Probably not necessary with an 8" driver, but it looks better.

My music and XO are all in my computer, so the clean digital signal is copied to as many outs as I want
to use and each is filtered in the digital domain and sent to the offboard sound card.  Those DACs
convert to analog to go to the amps and then directly to the drivers.  Only the DACs, amps and cables
are between the digital signal and my drivers.  No excess circuitry or other performance degrading links
in my audio chain.

In the long run, I guarantee you want OB bass.  You take the room mostly out of the equation, no modal
problems, plus the free air operation of the drivers make it sound more natural and clean to begin with.
You also have the added benefit that you can listen louder without disturbing others because OB bass
stays in your room far greater than boxed bass.  Once you hear rich full OB bass, then you'll understand.

[hurdy_gurdyman]

Hey John,

I think your latest baffles have to take the prize as the best looking speaker you've come up with yet. Good job. I'd be proud to have a pair that looks like that in my living room.

Dave

[Rudolf]

I was just curious how much bass the Fertin would produce on it´s own - without bass augmentation. I simulated the driver on a quite small baffle, since Malcolms room is rather small too. Simulation program was MJKs OB worksheet.

The baffle is 50 cm wide and 90 cm high with the driver center 50 cm from the floor. I did not want to go lower, fearing the soundstage would drop too low. The listening position was supposed to be 3 m from the baffle with ears at 90 cm height.
The resulting SPL:



Red line is the frequency response without a reflecting front wall. You can see the floor bounce attenuation at ~700 Hz.

Blue is the response with the baffle 1 m from the front wall. Frightening, isn´t it? But compared to the red line we get a nice bass boost up to 100 Hz.

The pink line shows the response if the frontwall distance is 0.7 m. We loose some bass below 60 Hz but gain more between 100 and 200 Hz.

I would like to lead your attention to the relative positions of the pink and blue dips and peaks. They are almost completely out of phase between 150 and 400 Hz. If you could imagine the pink line as a side wall reflection (and blue as front wall reflection) or vice versa, both together would result in a much smoother response. Lower limit (-6dB) should be somewhere at 60-70 Hz. At 1 W input the cone would travel 1 mm @50 Hz.

Driver specs were as posted by Bob Jackson, Qts=0.416. Since you can almost double that value with the Fertin 20X, there is much potential to raise bass output. Remember that this result is without any EQ or filtering. I don´t expect this to be a final result, but just some smallest OB dimensions from which to start the discussion again and to step up.

Rudolf

[JohninCR]

Rudolph,

Do you have a link for a tutorial for doing accurate measurements?  I have a measurement
mic and connection to my computer.  Plus I have quite a few different drivers and baffles
along with the willingness to put the work in to obtain something useful for everyone. 

To me it just has to be done, because those kind of graphs don't represent reality.  I've yet
to hear any OB driver/baffle combination that sounds anything remotely close to those graphs.
I'm talking literally hundreds of combinations over the past 3 years, both inside and outside,
and using tone sweeps often clicking 1 herts at a time or 1/2 musical note at a time.  The
closest I've come to anything similar is with folded bass units with the resulting sharp null
one octave above Fpeak as predicted by Linkwitz.  This is understandable because whatever
we do has little effect due to the long wavelengths.  Once I did hit upon a combo that sounded
really dead, which I attributed the small harmonic ripples in response being hit (sharp notes landing
on the bottom of ripples or something similar.  I just trimmed and inch off the baffle and then it
sounded fine).  There has to be some basic flaw in the assumptions used to create the graph
above, even if it's just the fact that no one places their baffles exactly parallel with the wall
behind the speakers.  I'm sorry but other than the bass frequencies, where wavelengths are so
long, trying to reduce the behavior of OB's to the math involved is a hopeless task because too
many variables make it too complex.

The bottom end of the graph makes sense and coincides with my gut feel that the Fertin isn't
going to make much bass on it's own.

Here's how you use the Fertin and get bass.  I can't wait to measure them to see if those edge
diffraction wings worked.  It's really amazing what having drivers and a quick rubdown of linseed
oil can do for looks.  As usual the work is really going to slow down now that I can listen to them,
kinda hard to do with boxes (ie use them before construction isn't complete).

[hum4god]

that looks gorgeous John . the wood is just beautiful.

what bass driver do you use and what x over freq. and slope?

how does it sound?  do you get satisfying bass?

Rudolf , thanks for the simulation , i wouldn't know how to do that .
60 Hz down is not too bad .
i am playing with the idea of making the baffle taller and play around with some wings in prototypes to see if that makes a considerable difference .

still don't know if i should build two subs or try to add a bass driver in the baffle?
are there bass drivers that are able to give me , lets say at least around 30 Hz ?
or do i have to go really HUGE to achieve that in an ob?
i am afraid box bass is too slow and closed in , but perhaps its just fine below 60hz?

thanksfor all the great help
malcolm

[JohninCR]

Thanks Malcolm,

I went to a couple of lumber mills today looking for more of the same.
I've had those planks for over 2 years waiting for the right project.
That species of tree isn't being cut any more, so it may be 50 years
before these can be duplicated.

The woofers are the Hawthorne Augie.  I need to measure before I can
dial it in perfectly, but they're sounding really good right now with 6db
of low Q shelving boost at 35hz, a rumble filter at 27hz to avoid overexcursion,
and a 1st order low pass at 125hz.  On the B200 I'm using -5db .5Q notch
at 2400hz to tame its hot range, +4db at the very top, and a 1st order high
pass at 100hz to reduce its excursion and sweaten the midrange.  My active
system make it all a snap with a few mouse clicks.

Regarding output, all I can say is that OB fans have been sold a bill of goods
with commonly held beliefs.  Using only enough baffle to act as window dressing,
I'm getting rich full bass better sounding than I've ever had in my in my 12'x21'
room.  I'm not talking about chamber music.  Although I listen to a variety of
music, to meet my needs I have to be able play stuff like Pink Floyd and reggae
at levels that most would find silly.  My subs are totally unnecessary for music,
so I need to build a true HT duty sub to cover only from 27hz (my room's dipole
bass threshold) on down.

[Rudolf]

Do you have a link for a tutorial for doing accurate measurements? I have a measurement
mic and connection to my computer.  Plus I have quite a few different drivers and baffles
along with the willingness to put the work in to obtain something useful for everyone.

 
I´m afraid I don´t have such a link. You should be best prepared after reading "Testing Loudspeakers" by Joseph D'Appolito. But this recommendation is not from personal experience - it only mirrors what I hear in the net. The instructions that came with the software I use are too specific to be used as general advise.

... those kind of graphs don't represent reality. I've yet to hear any OB driver/baffle combination that sounds anything remotely close to those graphs.

They don´t represent what you hear, but what you will measure - in a way. One has to remember that those graphs only show reflections from 2 walls (although the most important) while a room has 6. And they do not know about first and second (and all following) wavefronts - something the ear can quite well distinguish. But as I believe those simulations are efficient tools to direct you in the right direction. In the end the ear has to decide what it likes best.

There has to be some basic flaw in the assumptions used to create the graph above, even if it's just the fact that no one places their baffles exactly parallel with the wall behind the speakers.

I don´t see more "basic flaws" in those simulations than in the software that launched men to the moon.
But certainly one has to know what conclusions can be drawn from simulations and what can´t. You might compare it to a technical drawing of a car, which doesn´t look at all like the finished car, but holds all informations needed to build that car.

The bottom end of the graph makes sense and coincides with my gut feel that the Fertin isn't
going to make much bass on it's own.

You ain´t seen nothin yet. Didn´t I tell in my post that "there is much potential to raise bass output"?

Rudolf

[JohninCR]

I don´t see more "basic flaws" in those simulations than in the software that launched men to the moon.
But certainly one has to know what conclusions can be drawn from simulations and what can´t. You might compare it to a technical drawing of a car, which doesn´t look at all like the finished car, but holds all informations needed to build that car.

I probably worded that wrong, but at least the moon travellers got there and back, most of them anyway.
Taking too much liberty with the assumptions in this case, doesn't make it to the front wall and back to my
listening position, much less to the moon and back. 

Joking aside, I understand your point.  No doubt it's quite complex software, and all the math may very well
be exactly correct.  The problem is that it predicts an exact spot in space, and when you move off axis from that
single point it all changes, yet we have 2 ears.  Also, doesn't it assume that the baffle is parallel with the wall
and the listening position is directly on axis, a physical impossibility except in a strangely shaped room?  When
modelling corresponds better to real world results like it does for the bass region, I'll be more than happy to use them.
In the meantime, I question their value as tools for building OB's.  The bass region is easy enough to predict without
tools.

I'll be very interested to see what you come up for OB bass with a full ranger.  I tried my hand at trickery with my
OB-RLH's and it worked quite well, just too big.  Then when I tried to make it smaller using the B200, it didn't work
as hoped.  Since I don't really understand how it functions, I don't have a clue how to optimize it.  I'm having too
much fun now to move it back to the front burner.  I need to convince some of you more technical types to move
to Costa Rica.

[MJK]

A couple of rules I have learned over almost 30 years of being an engineer, who spends his day running math models and comparing them to reality, with respect to math models.

1. No math model is perfect and the user needs to know the limits of its believeability.

2. A math model can be used to guide decisions and avoid obvious mistakes.  A math model is a great tool or a great danger.

3. The quality of the results coming from a math model are directly related to the skill of the user entering the inputs.  A math model makes a good engineer really good and a bad engineer really bad.

4. A math model can always be improved to yield more accurate results.

5. It is easy to find faults in math models and to use these to discredit all the results of the calculations, but then you are left with no tools and no answers.  It is better to find strengths and use the tools keeping in mind the limitations.

I believe the results coming from the OB worksheets up to a certain point knowing the math algorithms used to calculate the results.  I believe they are an excellent tool that will continue to evolve and produce even more accurate simulations.  I believe that a speaker designed and studied with the math tools will have a better chance of success then a speaker designed by gut feel.  A math model yields a deeper understanding of a speakers behavior and performance.

These are my experiences and opinions.  Others may not agree and that is perfectly acceptable to me.  If you don't believe in a tool by all means don't use it.

Martin

[JohninCR]

Martin,

I'm glad you stopped in.  Am I under the wrong impression that if you turn the angle
of the baffle in relation to the wall, those big peaks and sharp nulls in the muds just
turn into small ripples whose audible effect with music is minimal at best?  Tools are
great, but if your screwdriver only works during an eclipse in the month of December
and only in odd years then how useful is it?

Don't get me wrong, I think it's great to have you tech types involved in OB.  Maybe
now we can really advance design in this area, but we should beware of using tools
as crutches.  A lot of good people shy away from OB because it hasn't been reduced to
the numbers.  Let's take you for example, did you really need a program to tell you that
2 high Q 15's and a 5ft wide baffle would produce bass?  To me that's like putting enough
rockets on a Mack truck to get it to the moon so you have something to ride in when
you get there, instead of engineering a lunar rover. 

I'm not being critical, just trying to make a point.  I mean you ended up using some EQ
anyway, so why the big form?  A lot of people look to you for inspiration in this hobby,
and those big baffles scare people away because "if MJK uses big baffles then they must
be necessary".  That's simply not the case.

BTW, do you have permanent sides on your bass section, and the folding wings are in
addition to give you even more rear wave travel distance and deeper half space launch
off of the front?  It's hard to tell from the pics.

[MJK]

John,

Am I under the wrong impression that if you turn the angle
of the baffle in relation to the wall, those big peaks and sharp nulls in the muds just
turn into small ripples whose audible effect with music is minimal at best?

That sounds logical.  Toe in of the speaker so it is not parallel with the wall is on my list of future upgrades.

Tools are
great, but if your screwdriver only works during an eclipse in the month of December
and only in odd years then how useful is it?

If that is the level of confidence you have in the tool then I agree, don't use it.

Let's take you for example, did you really need a program to tell you that
2 high Q 15's and a 5ft wide baffle would produce bass?

When I started the project all I had were four 15" woofers with a Qts of less than 0.4 so it was not clear in my mind that I would get adequate bass.  So in my models I juggled number of low Qts drivers, baffle size, crossover properties, and placement on the baffle to get a decent response.  I only made one set of baffles.  That is what the tool did for me.

A lot of people look to you for inspiration in this hobby,
and those big baffles scare people away because "if MJK uses big baffles then they must
be necessary".  That's simply not the case.

People can draw their on conclusions, I am not really concerned with what other people will think when I am designing a new speaker project.  In this case I think the big baffles made sense.  I do have other designs with smaller baffles.

do you have permanent sides on your bass section, and the folding wings are in
addition to give you even more rear wave travel distance and deeper half space launch
off of the front?

Yes, there are 12 inch deep sides in addition to wings.  These are shown in the drawings of the enclosure.

So let me ask you a couple of questions.  I have seen your nice looking baffles above and my understanding is they are made from a special wood that is hard to come by these days.  I also noticed that your drivers appear to be mounted on the centerline of the baffle. 

If you had mounted them off center would it have reduced any undesirable ripple?  The holes are cut so you have selected your path. 

What crossover frequencies and slopes are you planning to use and how will the drivers and baffle interact in this region? 

Do you need boost on the crossover?  If yes, how much and how does it effect the crossover region? 

How is the floor going to interact with the drivers, should the woofer have been placed on top and the other driver below?

Are you getting the best bass output that is possible? 

All of these trade-offs could have been done in an hour or two with a math model.  You have cut the holes and done some finishing work on the baffles, did you make all of the optimum decisions?  How do you know?  It would be a shame not to get the most out of that exotic wood.  But, maybe you are smarter then me.

Martin

[JohninCR]

Hi Martin,

Don't get me wrong, I think it will be great to have tools to model what goes
on with an OB in room, which correlate to a reasonable extent with reality.  I
feel like I have a good enough handle on the bass region using simple formula's
as tools.

Regarding your questions, keep in mind that I have multiamping capability, and
my active crossover, EQ, time and phase correction are computer based, so
I have full flexibility.

Since the NoBaffle test provided sufficient bass, I wanted to try a minimal
baffle with the B200 on top.  First, I tried flat plywood using the same dimensions
as the pieces of wood I've been saving.  They sounded fine with music and my
ears didn't pick on any big problems using a tone sweep, so I built the baffles with
the addition of the angled wings (for looks and to create a more gradual pressure
drop to hopefully help reduce edge diffraction).

I'm still in construction and finishing up magnet mounting of the drivers to totally
decouple them from the relatively lightweight baffle.  Once finished, I'll do measurements
to fine tune the XO and EQ.  If I identify a baffle related problem, I'll address it on the
backside.  eg You asked about the central placement of drivers.  Yes, that's purely for
asthetics and I can easily add more wood in back to one side than the other to change
the current symmetry.

I'm coming from a fullrange minimalist approach, so for now I'm running +6db of boost at the
bottom with a 1st order LP at 125hz on the woofer.  On the B200 I have -5db of low Q EQ at
2400hz, +4db boost at the very top, and a 1st order HP at 100hz.  I really need to do
measurements before I can get more complex with the XO.  I did play around with some
steeper slopes by ear and quickly became lost, even with the ability to correct the resulting
phase shift.  I understand much better now when people say that XO design is an art.

Once I get it all dialed in, I do want to try a higher efficiency 15 and see if I can make a
one amp, 1st order passive solution work well.  With the small baffle, I may have to pad the
B200 down too much, so I may have to go with the FE108, and/or add some baffle toward the
rear, which I've made work before.  There are lots of ways to skin a cat.

No, I'm not smarter, I just take a different approach.  I start with the form I want and make
it work for me.  It hasn't gotten me in too much trouble yet.  Shoot, even the NoBaffle test
worked better than I thought it would, but I got ridiculed for even trying it.

[Bob in St. Louis]

but I got ridiculed for even trying it.

You've "moved on" quite nicely since. Carry on the good work.

Bob

[JohninCR]

but I got ridiculed for even trying it.

You've "moved on" quite nicely since. Carry on the good work.

Bob

I haven't moved on, just a little side trip for now.  I think I can make the NoBaffle
look work with some type of rings to address diffraction, but I need to do some
experimenting first, unless Martin comes up with a model factoring in edge geometry
and side depth.  I don't want to even attempt to think about that math.  I leave
that to the experts.

[Bob in St. Louis]

I ment you had moved on from being ridiculed. Sorry. 

Bob

[hum4god]

i just tried to find a matching bass module to match the fertins on an ob and came across linkwitz' dipole and the ripole idea from Axel Ridthaler.
anybodu have experience with either one of those and wants to share bilding plans and driver ideas for them?
here is a link to different kinds of basses . on the bottom are the dipole / ripole configurations.
thanks
malcolm

 

[JohninCR]

I've built W-baffles ala Linkwitz's dipole woofer along with hybrid versions using the ripole approach (narrow pathways).
Manifolds work well for a compact form and deep bass.  You can also achieve the benefits of push/pull and mechanical
vibration cancellation.  Where manifolds are lacking is in the area of top end extension due to resonances resulting from
the cavities formed. 

Another reason that I'd restrict manifolds to deep bass is impulse response.  Think about it, you have a driver moving 90
degrees to the listening axis, and it compresses a column of air to be forced out of the pathways.  Where the wavelengths
involved are extremely long, this works fine, but as you go up the frequency spectrum there is definitely a noteable sonic
difference compared to sound radiated directly from the driver cone when you use a manifold alignment.  Deep bass, no
problem, but trying to integrate with your efficient Fertins, especially used in their low Q range, seems problematic to me.

I do have interest in testing a manifold approach using small drivers, so the pathways are quite shallow, resulting in better
impluse response and raising the point of resonances.  Based on the SQ of a free breathing large driver that I'm now using,
I don't know if I'll ever get around to trying a bunch of small drivers in a manifold.  Scorpion was planning to try something
along the same lines, so you may want to ping him regarding results.