[scorpion]

As far from sane as I am I have come up with a scheme to produce something of a universal OB-Bass/Sub in I-pol (courtesy Timo, Germany) this is the flat OB, next will be an U-dipol, next a symmetrical H-dipol and last an unsymmetrical H-dipol. So for myself I wonder is the assymmetrical H-dipol something interesting ? Something needed, I think I have solved problems of continous adjustment. Saying this much I will also say that the scheme will allow very good isolation of Bassinfluence to reach Mid- and Treble units.
/Erling

[MJK]

Erling,

What do you mean by symmetric and asymmetric H dipoles? Are you offsetting the baffle in the H frame so that the lengths are different for the front and back paths? Or is this something else?

I have some interesting H frame measurements from my new dipole speaker system that I am putting together into a project document for my site. Hopefully, I will post them and more details in the next couple of weeks.

Martin

[fergs1]

hopefully another for the alpha 15

[scorpion]

MJK,

That's right Martin, different lenghts in front and back.
Yes, I thought you would come up with H-dipoles, I suppose very much like my own decisions of 2 Alpha15s per side ?

/Erling

[MJK]

Erling,

Actually I used different drivers, one Goldwood 18" woofer (sorry fergs1) and a Jordan JX92S full range, since I did not want to disassemble my big Lowther OB system until I had something new for listening to music. I wanted to design and build something that was more affordable for the full range driver. The Alpha 15A would also work in the design and I will recycle them in my next build since they are great OB drivers.

I will be very interested in your H frame measurements, I am not convinced about the U frame option yet. The H frame is a very interesting concept and I think we are just starting to tap into the potential applications.

Martin

[scorpion]

I say, the Goldwood is nearly perfect. 

But would and could you respond back with dampening applied to the Goldwood chassies either in form of Bitumen or as many others have endorsed, clay,
besides being undamped, I think these measures would interest quite a few outside.

For the H- and U-frame what I have come to design is a baffle with rubber outings to close against the sides nothing special, but if you stumbles at it. Rubber is in fact Caravan Camper fittings. Hi-Fi ?

/Erling

[MJK]

I say, the Goldwood is nearly perfect. 

But would and could you respond back with dampening applied to the Goldwood chassies either in form of Bitumen or as many others have endorsed, clay,
besides being undamped, I think these measures would interest quite a few outside.

The Goldwood is another inexpensive woofer that is a good candidate for non-EQed dipole. In an H frame it gets a little deeper then the Alpha 15A but is not quite as efficient. At the moment I do not have any damping applied to the basket of the Goldwood, it is only operating at the very low frequencies so I do not believe that ringing of the basket is a real issue. I do need to add some additional weight on top of the H frame to kill the rigid body motion at low frequencies.

Martin

[scorpion]

As I haven't built the prototype yet I will build that and then come back for more measurement feedback.

I'll wait for your publishing of this new OB design, which I suppose you actually built ?

/Erling

[Rudolf]

So for myself I wonder is the assymmetrical H-dipol something interesting ?
/Erling

I had thought about that myself, but could not find a convincing reason to have something between a full dipole H-frame and a not really dipole U-frame.
What I still wonder about is the best position of the midrange baffle WRT the H-frame. Positioning the midrange baffle on the center of the H-frame leads to early reflections from the H-frame top. Positioning at the front of the H-frame means a delay between midrange and woofer. I don´t hear a definite "better or worse" between both positions, in fact I hardly hear any difference. Linkwitz clearly opts for the baffle in front option. What do you think/hear?

Rudolf

[scorpion]

Rudolf,

Glad to arise some interest. In fact I have had the same questions myself.
However as settled now I am to come back with definitive measurements. Please let me know what you think those should be and how. Indoor or free air etc. I think there may be an opening for something like 2/3rd H-dipole, just because that might attract an optimal air mass loading. But that is also as much speculations as the Golden Mean. And above all, I have in my thinking, gone out from MJKs rather narrow U- and H-dipole definitions. I don't think going any much further will result in different results.

/Erling

[MJK]

As I haven't built the prototype yet I will build that and then come back for more measurement feedback.

I'll wait for your publishing of this new OB design, which I suppose you actually built ?

Yes I have built the system and have been listening, measuring, and adjusting for the past week. The Goldwood woofer is in the H frame while the Jordan JX92S is in an OB that sits on top of the H frame enclosure. That was probably not clear in my original response. This allows me to try a variety of full range drivers in different OBs on top of the same H frame, or I guess even beside the H frame if required, which supplies the bass for the systems. The active crossover lets me set the relative levels of the H frame and OB to produce a balanced SPL response.

Martin

[-Richard-]

Hi MJK/Martin ~

Sorry for sounding like I am trapped in a bubble of time and rather late to the proceedings here... but how would you characterize the sound of the Goldwood woofer you have in the H frame before and after the H frame? Also... does the H frame simply deepen the LF response... or does it give the LF response more weight... a more noticeable presence?

Any description you can provide will help me to understand better the functional nature of what the H frame is doing.

I must try a temporary H frame as soon as I can to hear what it can do for my simple arrangement.

Meanwhile the higher crossover point of the simple coiled inductor I am using on the Alpha 15A is having a remarkable effect on bringing everything to life in a thoroughly "analogue" sort of way... the depth of the midrange in particular is uncanny... and yet top to bottom it sounds entirely balanced... it distinctly reminds me of playing LP's when I had my large coaxial Wharfdales.

Warmest Regards ~ Richard

[MJK]

Richard,

I have only spent a few hours listening to the new speakers so I cannot really assess all of the pro's and con's of the design. I did not try the Goldwood on an OB, I looked at an OB design using my MathCad models but the Goldwood did not offer any advantage over the Alpha 15A on a reasonably sized baffle. In fact, for an OB the Alpha 15A performed a bit better due to the higher Qts, both drivers rolled off at about 40 Hz. I picked the Goldwood because it had a lower fs compared to the Alpha 15A, a Qts of about 1.0, and was very reasonably priced at Parts Express. I am not convinced that a decent bass driver producing frequencies below 200 Hz has much of a sonic signature, it should be well below any driver cone/frame anomalies and act as a rigid piston. The Goldwood drivers were a closely matched pair and well made for the price, good quality/process control.

In the H frame the Goldwood gets down to about 20 Hz, this is a clearly audible change from other speakers I have in the room that are tuned to 40 Hz. I used a crossover between 100 and 200 Hz to the Jordan JX92S drivers on an OB, still playing with the settings, so the Goldwood only provides bass reinforcement. With an H frame you really don't want to crossover much higher if you want to avoid the first quarter wavelength resonance of the enclosure. Eventually my goal is to try a number of other 3" to 5" full range drivers in OBs paired with the Goldwood H frame, I can adjust the crossover and match levels easily with my active bi-amped set-up.

I have tested the speakers and am correlating the MathCad predictions to see what I can learn for the next design. This is always an interesting process and I am already finding a few questions that I need to spend some time studying. Hopefully, I will be listening some more over the next coupl eof weeks as I do this correlation work.

Martin

[-Richard-]

Hi Martin ~

Very clear description of your current explorations... thanks for taking the time to share that with us. Your insights and careful attention to every aspect of your explorations is always revelatory... and deeply appreciated.

It sounds like an easy, simple combination to work with... the Goldwood as a stable "constant" below... providing "bass reinforcement" that ends between 100 to 200 Hz... and a smaller fullrange driver above. That can certainly give you an excellent idea of how each of the fullrange drivers you use perform within the parmeters of the OB you have designed.

I suspect that a smaller fullrange driver might contribute to a sense of intimacy... a "drawing-in" to the musical presentation.

As you have explained, placing an H to the sides of my Alpha 15A's would work against the current high cut-off I am experimenting with... around 1200Hz... I assume it would "bloat" that higher range adding a good deal of distortion... not the least of which is the 1/4 wave resonances you pointed out to us.

Thanks for your help, Martin, in sharing your astute observations and thinking with us.

Warmest Regards ~ Richard

[MJK]

Richard,

It sounds like an easy, simple combination to work with... the Goldwood as a stable "constant" below... providing "bass reinforcement" that ends between 100 to 200 Hz... and a smaller fullrange driver above. That can certainly give you an excellent idea of how each of the fullrange drivers you use perform within the parmeters of the OB you have designed.

Exactly! A constant bottom end in a smaller package that can be paired with different full range drivers or even mid/tweeter combinations. I have three identical amps and a three way active crossover so any combination should be achievable from Lowther to Fostex and even to SEAS or Skanspeak drivers. Should keep me entertained for a while.

Thanks for your help, Martin, in sharing your astute observations and thinking with us.

My pleasure, this stuff is so interesting and discussion is always appreciated on my end.

Martin

[-Richard-]

Hi Martin ~

No doubt you must have mentioned this in earlier posts... but what are the "three identical amps" you are currently using for your investigations, and what does the "three way active crossover" consist of? I wonder if you could spend a bit of time describing how the three-way-active-cross-over works?

You also mention that you are working with a "smaller package"... which I assume means a smaller baffle size... the result of using a large well-designed-for-the-purpose woofer in an H configuration... which you indicted gives a very substantial bass response: "In the H frame the Goldwood gets down to about 20 Hz"... thereby avoiding the need for a large flat baffle surface, or one with wings, which is one reason why so many would-be Open Baffle enthusiasts are not tempted to experiment with it (the Wife Acceptance Factor or WAF).

So it seems that you have solved what has been characterized earlier as the biggest problem in the OB paradigm... substantial bass response in a neat package that does no harm to the full-range driver, while keeping to the design principles of dipole functionality.

That should translate to a baffle size that would be entirely aesthetically pleasing... personally I like the idea of creating a constant in the design of the LF that allows for experimentation with various fullrange drivers or midrange-and-tweeter combinations... it opens the door to full range drivers that we may not be presently considering... but that might bring enormous performance benefits to the Open Baffle sound.

Please keep us informed, Martin, as you move more deeply into this area of exploration. Really nice to read about it... very exciting!!!!

Warmest Regards ~ Richard

[MJK]

Richard,

I have three Rotel RB-1080 SS amps, these are 200 watts per channel each. Right now I am using two of them for the Goldwood H frame and Jordan JX92S OB that sits on top. The crossover is a dBx Driverack PA digital crossover, it can provide two or three way crossovers with EQ and a few other features. I have enough XLR cables to configure any system set-up I select.


The H frame is approximately 21" wide, 21" tall, and 16" deep. This is not small but it is significantly less intrusive when compared to my Lowther OB that was in the room until last month. The WAF does not enter into my designs since she has banished my stereo and music collection to a room above the garage.

Martin

[-Richard-]

Hi Martin ~

Your Rotel RB-1080 SS amps are known for extraordinary speaker control and a wide gamut of frequency reach. Good stable amps for your frequent driver and baffle design changes. They seem to come alive at higher volumes. Certainly having your own dedicated listening room is really quite nice... especially given that at least part of your creative life is given over to a fearless exploration into speaker design.

What preamp/s are you currently using with them... or does your source have a volume control on it... or is that another function of your dbx driver-pack?

I am beginning to read the information on the "dBx Driverack PA digital crossover"... here is one web page with information for those google-shy: http://www.bswusa.com/proditem.asp?item=DRIVERACK-PA
review: http://www.musiciansfriend.com/document?doc_id=89558&src=3SOSWXXA

I always worry about op-amps in the signal path of EQ devices... but I have not heard them recently and perhaps that is not so much of an issue as I remember it being. So many variables change when one begins to change components around. Fresh listening is mandated and in fact is the only way to keep "learning" alive... otherwise we fall into an ultimately untested "conditioned" response.

Thanks as always, Martin, for sharing information with us that could help us to understand more completely what we are all working with... we are not aiming for concensus... that is too limiting... but rather a deeper understanding... a deeper insight... into design solutions that could bring the Open Baffle magic with in reach of our DIY efforts. Your help is always exemplary, Martin.

With Warm Regards ~ Richard

[MJK]

Richard,

What preamp/s are you currently using with them... or does your source have a volume control on it... or is that another function of your dbx driver-pack?

I am using the Rotel RC-1090 preamp, I got a good deal when I bought the preamp and one of the amps together. I am sure that there are better amps and preamps then the Rotel but for the price I found them hard to beat. I really wanted a much more expensive amp and preamp combination and I auditioned them both at home, I could not justify the significant cost difference for at best a very small performance benefit that the higher end products provided. I can make a much bigger improvement by spending the money on speaker designs.

I am beginning to read the information on the "dBx Driverack PA digital crossover"... here is one web page with information for those google-shy: http://www.bswusa.com/proditem.asp?item=DRIVERACK-PA
review: http://www.musiciansfriend.com/document?doc_id=89558&src=3SOSWXXA

Again, I am not sure that the dBx is the best but at the time the Behringer was not available so the dBx won by default. It is easy to use and I have found that it works very well. I got mine factory new off of e-Bay much cheaper then the price shown in your links. I have a soft spot for dBx equipment and own a few vintage early 80's signal processors that were used when I played vinyl back in the day.

I always worry about op-amps in the signal path of EQ devices... but I have not heard them recently and perhaps that is not so much of an issue as I remember it being. So many variables change when one begins to change components around. Fresh listening is mandated and in fact is the only way to keep "learning" alive... otherwise we fall into an ultimately untested "conditioned" response.

In my opinion, speaker problems and room problems swamp electronic problems. I don't buy into the purist approach and will use any piece of equipment if I feel it improves my system's performance. I am just not that interested in tubes, interconnects, cryo, power cords, wall plugs, and speaker cables as means of claiming huge improvements. I believe they are capable of making subtle changes that may or may not be improvements to the system response. I believe in reasonable cost for good/great performance, at some cost level it seems you are paying for status/ego and minimal gains.

Hope that helps,

Martin

[dyohn]

An off-topic question for Martin King:  You mentioned an H-frame dipole "with wings."  Can you elaborate on what you mean by this?