[Danny Richie]

Just so you guys know, the flat baffle will not give you the low end extension that the driver is capable of. You just aren't separating the front wave from the back wave enough.

You can get much more low end extension using it in a H frame.

If you want it to still look the same as if it is on the same baffle as an upper driver then you can make a U shaped frame around it. That will extend it quite a bit, but be sure to brace it really well and/or use some thick side panels.

[Bob in St. Louis]

Thanks Danny.
What are your recommended measurements, if I may ask?
An "H" with eight or ten inches on either side of the driver?

[Danny Richie]

Thanks Danny.
What are your recommended measurements, if I may ask?
An "H" with eight or ten inches on either side of the driver?

The real key is, how high does it have to play? That limits how deep an H frame can be. If it has to play higher up then it can't be deep. The same goes for adding side panels.

[Bob in St. Louis]

Roger that, thank you.
I've been using them in OB, and have not ventured into the other letters of the alphabet ('H', 'U', 'Z'....)
The clarity and punch they deliver "as is" works well enough for me....if I need more, I fire up the IB. 

Bob

[Danny Richie]

By separating the front wave from the back wave more you don't give up anything. You just gain low end extension.

[bdp24]

By separating the front wave from the back wave more you don't give up anything. You just gain low end extension.

Except that the deeper the H- or W-frame, the cavity resonance of the frame becomes a concern at an ever-lower frequency, right Danny?

[Danny Richie]

Except that the deeper the H- or W-frame, the cavity resonance of the frame becomes a concern at an ever-lower frequency, right Danny?

It will only create a cavity resonance if the wavelength that the woofer is producing is a short enough wavelength to propagate within the cavity. And rule of thumb is you want to be over an octave away from it.

In most of these applications the depth is not deep enough and the woofer is not playing up high enough for there to be a concern using a woofer this big. The bigger concern is a stiff enough cabinet that will not flex under the pressure that the driver creates.

[lowtech]

The bigger concern is a stiff enough cabinet that will not flex under the pressure that the driver creates.

Interesting;  I learned something new.  I thought a woofer mounted in free air (or in an open cabinet like an H-frame) creates zero pressure because the front and back waves are out of phase.  Maybe I'm reading too much into what JohnK has to say about it?  http://musicanddesign.com/roomgain.html


Edit: What I learned was not to believe everything I read in this forum. 

Those woofers still put a lot of pressure within the walls of the H frame.

"A monopole, such as a closed box woofer, is a pure pressure source. A dipole, like a H-frame woofer, is a pure velocity source."

S. Linkwitz

Maybe Danny just got his terminology mixed up?  Understandable given all the drama in his personal life at the moment.

Also, I think if one were to measure the panel resonance of a 20" H-frame constructed out of 3/4" plywood, they would find that the primary resonant frequency would be well above the cavity resonance (i.e. > 400Hz; that's roughly two octaves above the acoustic cutoff).  This might affect poorly designed speakers that attach their midrange baffle directly to the "bass box", but most of the better full-range dipole designs have had decoupled woofers for the past 8 years or so, making this pretty much a non-issue for me.

Maybe I'll try some of this miracle damping material for kicks - if I can find someone selling it locally.

[MarvinTheMartian]

Lowtech:
Both are correct only because these are very different scenarios.
John's article explains why an OB woofer does not pressurize the listening room.
Danny was discussing OB woofer cabinet construction requirements.
If you built a sealed sub with 2 or 3 12" woofers, you would naturally build a very solid and well braced cabinet.

Danny's comment could be paraphrased ...
"H" frame open baffle woofer construction also requires a very solid and well braced cabinet.   
The front (+) wave racing around to cancel the back (-) wave puts more stress on the side panels than you would imagine.
Especially toward the very front and back where there is no natural bracing because of the large open areas.

Danny Am I close?
Shawn

[stevenkelby]

Shawn, Lowtech understands that perfectly, he's just a trouble making troll. Don't waste you time feeding him.

[Danny Richie]

Interesting;  I learned something new.  I thought a woofer mounted in free air (or in an open cabinet like an H-frame) creates zero pressure because the front and back waves are out of phase.  Maybe I'm reading too much into what JohnK has to say about it?  http://musicanddesign.com/roomgain.html

Those woofers still put a lot of pressure within the walls of the H frame. Here is a story that you can relate to. One of the first things I noticed when I listened to a set of Orions that were owned by a friend of mine was the coloration in the bass region. Laying my hands on the thin 3/4" solid hardwood that the sides were from confirmed considerable flexing that was muddying up the bass. He later lined them with No Rez and it made a considerable difference.

[lowtech]

Laying my hands on the thin 3/4" solid hardwood that the sides were from confirmed considerable flexing that was muddying up the bass. He later lined them with No Rez and it made a considerable difference.

Stick-on damping material that reduces cabinet flexing?  It must be very heavy to prevent wood from flexing at the bottom octave operating range of the woofers.  Maybe it also reduces pressure in the cavity?  Do you sell this No Rez material?  I'll have to try it out.

[Danny Richie]

Stick-on damping material that reduces cabinet flexing?  It must be very heavy to prevent wood from flexing at the bottom octave operating range of the woofers.  Maybe it also reduces pressure in the cavity?  Do you sell this No Rez material?  I'll have to try it out.

It only reduces the flexing a slight amount because of the added mass. But it does dampen out the ringing and reduces the noise considerably. Especially in this case as the 3/4" material wasn't even MDF. It was some sort of hardwood.

And yes I sell No Rez.

[bdp24]

Stick-on damping material that reduces cabinet flexing?  It must be very heavy to prevent wood from flexing at the bottom octave operating range of the woofers.  Maybe it also reduces pressure in the cavity?  Do you sell this No Rez material?  I'll have to try it out.

The owner of a pair of Orions is unlikely to add the adequate bracing that should have been incorporated into it's design and construction. The purchaser of a pair of GR Research OB sub kits, on the other hand, has been made aware of the need for such bracing in the design and construction of a W- or H-Frame, and provided with plans for building (or having built) well-braced OB frames. Adding NoRez is not a substitute for bracing (which prevents resonance), but an additional measure to eliminate any remaining resonance.

[Danny Richie]

"A monopole, such as a closed box woofer, is a pure pressure source. A dipole, like a H-frame woofer, is a pure velocity source."

S. Linkwitz

Maybe Danny just got his terminology mixed up?  Understandable given all the drama in his personal life at the moment.

I understand your confusion. Mr. Linkwitz is talking about the difference in how they act in a room.

I am talking about flexing of side panels in a H frame design. This is caused by the pressure changes within the H frame itself. Side panel flexing can often be very significant just like in my good friends Orions. The flexing of the panels also excites the upper frequency ranges with second and third harmonics that can easily be heard as a buzzing distortion.

And 400Hz is barely one octave about the crossover point of the Orion (to use it as an example). So the upper harmonics of the woofers themselves can excite the cabinet wall in those regions.

And it doesn't make any difference of the upper baffle is attached to it or not. The side panels flexing and resonance thereof is independent of rest of the speaker. It makes noise regardless.

And what I am dealing with in my personal life is not relevant in this discussion.

[lowtech]

It's okay to not always have the right answers, Danny.   

http://www.audiocircle.com/index.php?topic=35304.msg314084#msg314084

My math seems to be correct.  400Hz is nearly two octaves above the 120Hz crossover point in the Orion.

SteveL (your good friend) may have had a couple loose screws that contributed to the buzz you seem to think was due to panel flexing.  In any case, he was using inappropriate amplification with his speakers (a pioneer HT receiver), and to compound the problem was trying to drive 4 Peerless woofers in parallel with it.  The amp wasn't happy and neither was he, as I recall.

Anyway, you can believe whatever you wish and if you believe hard enough you may convince yourself of the truth.  I think there is a word for this condition.

You and Gary have a good one.  Got to go.

[Danny Richie]

It's okay to not always have the right answers, Danny.   

http://www.audiocircle.com/index.php?topic=35304.msg314084#msg314084

My math seems to be correct.  400Hz is nearly two octaves above the 120Hz crossover point in the Orion.

SteveL (your good friend) may have had a couple loose screws that contributed to the buzz you seem to think was due to panel flexing.  In any case, he was using inappropriate amplification with his speakers (a pioneer HT receiver), and to compound the problem was trying to drive 4 Peerless woofers in parallel with it.  The amp wasn't happy and neither was he, as I recall.

Anyway, you can believe whatever you wish and if you believe hard enough you may convince yourself of the truth.  I think there is a word for this condition.

You and Gary have a good one.  Got to go.

Just keep nosing around here and you'll learn.

I was thinking the Orion crossed at 160Hz though. It doesn't change the fact though that the side panels were buzzing.

Steve didn't have any loose screws and his receiver wasn't contributing to the panel flexing and resonating. And he was only driving one pair of the woofers in parallel.

The No Rez did help his sound considerably, and it was pretty obvious.

But hey, if you want to believe that 3/4" hardwood side panels is good enough for the job then feel free to build yours that way.

And I think that the misconception I have developed was convincing myself that I should continue to be nice guy and put up with your repeated comments here in my circle. I needed a wake up.    Why am I putting up with you? If you don't have something positive to contribute here then please don't.

[devinkato]

Anyway, you can believe whatever you wish and if you believe hard enough you may convince yourself of the truth.  I think there is a word for this condition.

Really dude?  I don't like getting involved in stuff like this, but I am literally shaking my head as I'm reading this.  What a pompous prick.

[stevenkelby]

I tried to warn you guys.

Danny, you have the patience of a saint. Your professionalism is something we can all aspire to. You're a better man than me, to continue behaving in the way you do, and to not let lesser men affect your own values of decency. I look up to you, and I'm not alone.

Me, I know a troll when I see one and would have banned him years ago.

I do feel some empathy though, he must be one very unhappy little man

[bdp24]

Really dude?  I don't like getting involved in stuff like this, but I am literally shaking my head as I'm reading this.  What a pompous prick.

I wish there was a "Like" icon to punch. If he is in such disagreement with Danny (I hate to put it that way, as it falsely seems to equate his and Danny's "opinions") , why read his posts? And the snarky comments like "miracle damping material", and asking the question "Do you sell this No Rez material?", obviously intended to cast suspicion upon Danny's ethics.