Dual woofer OB configurations, which and why?

[oktyabr]

Hello all,

I've spent the last three days reading related threads here and abroad on various combinations of large woofers on an open baffle but the threads that seem to show the most promise initially all dried up two or three years ago without any solid answers!

So, I'm posting here. Feedback and suggestions welcome.

What I want to do:

Open baffle! Why? I like the sound of open baffle/dipoles, at least the DIY's I've heard, and commercial products like ML SL3s and more than one pair of Maggies I've personally owned too. Secondly, I just moved into a house that while not ideal for OB presentation has a considerably larger listening area (the living room) than our last house and I'm itching to get busy! And my wood working skills are far from great.

Full range, a complete 10 octaves, my personal "holy grail"! The closest I've come to this is a pair of vintage Teledyne AR9 (18Hz...30Khz, 87dB SPL at 1W/1M, -3dB at 28Hz) that I miss dearly and the Snell Type B (a true 20Hz... 20Khz) that I never got to own long enough to miss!

For the time being I plan to build something relatively modular. I want to make use of a pair of Audio Nirvana Super 8's because I have these already on hand. Later I might like to try some Fostex and Mark Audio, probably the Alpair 7. A speaker I don't have to entirely rebuild just to switch out the upper frequency driver(s) is ideal.

Background: Like many others I think MJK's work on OB was inspiring, and initially I've given a great deal of thought to just constructing an Eminence Alpha 15a (or GW 18") H-frame and tossing a separate baffle on top of it for the upper range driver(s). But will this get me down to a usable 20 Hz? Hard to say with my room until they are placed.

Ok, so I've also taken a keen interest to some double woofer OB alignments like the Beer Budget Version of $10,000+ Jamo Open Baffles and I know footwork has been done using not only Eminence drivers but even the ridiculously inexpensive GRS 15" woofers. Ok, so that's an option. But that probably won't get me into a true 20Hz territory on the bottom end either, at least not with ease...

So what about dual H-Frames, using either the Alpha 15's, the GW 15 or 18" or the GRS 15"? The H-Frames *seems* to be the way to go to squeeze those last few dbs out of the lower 20's and a dual woofer alignment should(?) help compensate for the loss of individual SPLs, right? Even if I start with one H-Frame, keeping "modular" in mind, how hard would it be to reconfigure the low pass for a pair of H-frames, something like the Linkwitz Orion?

Of course there are other exotics... Nelson Pass seems to prefer a slot loaded design (is there a proven build using GRS 15" woofers?), "W" frames, and so on, but the threads on these, the ones containing detailed and useful build information anyway, are even more rare.

I don't have the budget to include an active crossover and serious EQ, at least not to start. I'd like to stay passive if possible, as simple and as cheap as possible. I DO have multiple SS amplifiers at hand (and one or two chip amps), most with variable gain controls, so I'm hoping that with a simple low pass on the woofers and allowing the full range to run (mostly?) full range I should be able to compensate for any severe SPL differences by simply attenuating an amplifier.

So bargain wise I guess I'd like to know if anyone has built stacked dual GRS 15" H-Frames and if so how did they work out? Can you share a lowpass design and maybe some in room measurements? If no one has done this yet, why not? Are there advantages to simply putting the woofers on an open baffle, ala Jamo r909, that I'm missing somewhere?

With as low a budget as possible, taking crossover components as well as drivers into the equation, what is the easiest way to get a usable 20Hz out of a dipole design? Are duals not worth the extra trouble and expense? Is the tried and tested Alpha 15 (or GW 18") H-frame the best bang for the buck?

Again, many thanks in advance.

Cheers!

[AllenB]

I'm not the expert here, but I did run Eminence 15" drivers dipole for a year or two. I had them equalised into the twenties. I found a single driver per side gave reasonably good levels. They would have been enough if I hadn't equalised them but if I had to do it again I would use more cone.

Also if I remember rightly it took about 50W to drive them.

[oLjud]

Alpha 15 in H-frame plays down to ~40Hz.
The limited xmax is the main problem for Alpha 15, at least according to me, I like to play loud. But without EQ is Alpha 15 price worthy!

[StigErik]

Considering the fact that cone excursion goes up by 8 times when you go one octave lower with an OB, you will find that reaching 20 Hz requires A LOT of cone area.

I have managed to get good clean response with enough SPL at 20 Hz, but it required sixteen 21" woofers in large H-frames....


My open baffle dipole with Beyma TPL-150

[evanc]

I use a pair of eminence 15s per side in open baffles. The bass seems adequate to me. I would definitely look into an active crossover. I have one made by peavy that cost little money. It only does the bass the other drivers are passively crossed. Being able to adjust the volume of the bass as well as the crossover point seems important to me. I find that my system sounds better when I high pass the woofers at 40 hz. I would go a bit lower, but my crossover has this frequency filter so I use it. Make sure that the baffle is heavy. I thought mine was over the top, but I can see the baffle rocking when I turn the volume way up. If your local your welcome to listen to mine....
Evan

[franzm]

Could these touch your taste?
Visaton - Lautsprecher und Zubehör, Loudspeakers and Accessories
Visaton - Lautsprecher und Zubehör, Loudspeakers and Accessories

[Pano]

John Busch has built a good number of dual woofer OBs. Let's see if he will drop in here for a comment.

[John Busch]

Hello all. As Pano posted, I have built quite a few OB designs. Some single, dual and quad woofer designs. These include both prototype and fully completed designs. In dual formats 10" up through 21". Low Q, medium Q and high Q woofers. Most passive, some active.

Some are two way, and some 3 way. Some with coaxial midrange and high frequency drivers. And so on. Most have used dual 15" or 18".

I have worked with the GRS 15 and Goldwood 18 plus many others from MCM, Eminence, PE-Dayton and so on. BTW, for low cost, low to mid output systems, the GRS for the money is a real sleeper. Working on a single woofer format (Ultra) and dual woofer format (Ultra Squared) Have posted some info over on the Audio Circle OB forum.

Anyway, like all designs, it gets down to your personal goals for the system. You can make anything reasonable work if you take the time and effort. The Original Post throws a lot of general info out, but is not specific enough to make any actionable advise.

So, need to know a general idea as to, well, your OB system goals. Overstating the obvious, cost usually drives a lot of decisions. You can build a surprisingly musical OB that can honestly play down to 30 Hz for less than $140.00 each all in. But, there are some limitations. Mainly, how loud it will play and it requires quite a bit of power. Kinda big for most folks too. On the other end, a very large three way with high quality cosmetics using 4 large woofers and an active crossover can easily cost $ 10,000 a pair. Basically with more money you can play louder and with increased baffle size you gain efficiency.

Look forward to hearing more about what you want to accomplish and how much you can spend.

[oktyabr]

Thanks for the links and suggestions!

@AllenB Thanks! That's the type of first hand (even if it's subjective) opinion I find valuable. At least I know the Alpha 15s are capable, if done right. Hitting lower is one reason I'm leaning towards augmenting them with H-frame or similar design...

@oLjud Thanks! A wide sampling of opinions is grand to have. 40Hz seems low (high?) for the Alphas in H-Frames (per MJK specifications).

@StigErik And many thanks for your reply too. I'm not after a flat 20Hz, not in my room anyway, only usable bass into the 20's. Lower would be better I suppose but I'm really interested in knowing what can be done with 2 woofers per side in OB. PS Thanks for the link!

@evanc Thanks for the tips! I've read similar posts about weighting down the H-Frames, and even using carpet spikes (I have short, tightly wound carpet). Will certainly be considering active x/o, especially if I can't buy enough passive components to make experimentation cost effective (passively).

@franzm Yes! I've considered using at least a ripole, Linkwitz inspired "W frame" and Mr. Pass's slot loaded woofer alignment. I'm still concerned about trade offs though, compared to simple OB alignments and the H-frame (best of both worlds?) Hoping someone who has built more than one of the above might chime in with first hand opinions?

@Pano Thanks! I've read a few posts by John Busch (and yours as well!) but have never found his webpage or key thread to his project(s). I'd be very interested to hear his thoughts too.

I'll clarify my "design goals" a bit: While I've read many positive reviews of a single H-Frame, both Alpha 15 and GW 18, it seems that two woofers per side might be more useful to get closer to my 20-20 holy grail. What I would like to do is buy four woofers, leaning hard towards the Alpha 15, the GW 18, and perhaps the GW-215/40/8 15" (a bit cheaper than the Alpha) and then experiment. I think the first thing I'll probably do is whip up a simple flat dual woofer OB and play with that. Then a single H-frame woofer and live with that for a while too. Ultimately perhaps ending up with dual H-frames or similar (has anyone experimented with a dual woofer alignment similar to the Orions that could comment?)

With this in mind I'm also trying to balance a budget for X/O. If I decide to go passive what is the best combination of components to let me experiment, switching between 8 Ohm single woofer and dual, paralleled at 4 Ohms? Big inductors add up to big $$$ quickly, especially in good quality ones. Can smaller ones be combined to allow me to change between 4 and 8 Ohm low pass without having to buy twice as many parts? If so are there any trade offs to consider doing it this way? If YOU wanted a passive low pass "construction kit", what would YOU buy?

Obviously if the passive bits end up close the price of an active then I might as well start active and save the passive for down the road a bit, after I've settled on some sort of alignment.

Again, thanks in advance!

[oktyabr]

Originally Posted by John Bsuch

Hello all. As Pano posted, I have built quite a few OB designs. Some single, dual and quad woofer designs. These include both prototype and fully completed designs. In dual formats 10" up through 21". Low Q, medium Q and high Q woofers. Most passive, some active.

Some are two way, and some 3 way. Some with coaxial midrange and high frequency drivers. And so on. Most have used dual 15" or 18".

I have worked with the GRS 15 and Goldwood 18 plus many others from MCM, Eminence, PE-Dayton and so on. BTW, for low cost, low to mid output systems, the GRS for the money is a real sleeper. Working on a single woofer format (Ultra) and dual woofer format (Ultra Squared) Have posted some info over on the Audio Circle OB forum.

Anyway, like all designs, it gets down to your personal goals for the system. You can make anything reasonable work if you take the time and effort. The Original Post throws a lot of general info out, but is not specific enough to make any actionable advise.

So, need to know a general idea as to, well, your OB system goals. Overstating the obvious, cost usually drives a lot of decisions. You can build a surprisingly musical OB that can honestly play down to 30 Hz for less than $140.00 each all in. But, there are some limitations. Mainly, how loud it will play and it requires quite a bit of power. Kinda big for most folks too. On the other end, a very large three way with high quality cosmetics using 4 large woofers and an active crossover can easily cost $ 10,000 a pair. Basically with more money you can play louder and with increased baffle size you gain efficiency.

Look forward to hearing more about what you want to accomplish and how much you can spend.

Hi!

It seems I posted the same time you did!

You will see reading my first post that I realize I was a bit vague about my design goals. This is intentional to an extent. I'm not sure which way I want to go yet, hence trying to gather as much opinion as possible and also trying to work around a "construction kit" type of parts list that will allow me to experiment. I'm glad you have experience with the GRS 15" and I will definitely dig deeper to find your posts on it... certainly a sweet price point! I'm not a registered member at AC yet but have read many, many threads and posts there on the OB topic. Perhaps you can share a specific link or two?

Anyway, I'll try to define what I listen to and my budget (hoping my wife NEVER finds this post!):

My listening room is actually an "open floor plan" that combines kitchen, dining area and living room into one open area. The dimensions are roughly 16' x 32' or just over 500 sq.ft. with my favored listening position about half way down the length, stereo equipment along one of the narrow ends, kitchen and dining area at the other. The walls are 10' ft with a 14' vaulted ceiling that runs the long dimension. Short, tight weave carpet on the living room side of the space, hard wood on the kitchen end of it. Not an ideal listening room but a vast improvement over what I've been living with for the last year. I think I can live with 20-24" wide speakers, as tall as they need to be, without sacrificing much WAF in the process (she gets to decide on how to finish the final product), with them placed closer to the rear wall for everyday low volume use and pulled out two or three feet for "serious" listening.

I listen to pretty much any kind of music from classical to electronic to modern rock. My personal leanings are towards recordings of live jazz and blues but I also share the house with my wife and our son so the music style can vary widely. Usually lossless FLAC although I've recently gotten back into vinyl and have been spinning a lot of that, mostly classic rock, as well. Yesterday I used a simple SPL meter to see what sort of sound levels I typically find enjoyable. From my favorite sitting position, which puts my ears about 4m/12ft from the front baffle of my speakers, I see an average volume level of between 75-80db SPL, with the occasional kick up to 90db SPL depending on the selection (and who might be sleeping). Probably 60-70db SPL during dinner time, etc. where conversation might arise. I never did measure 1m but I'm sure that can be accomplished.

I run a Dayton DTA-100a T-amp (50wpc) but also have a 150wpc MOFSET based SS and a vintage Yamaha M-65 (170wpc@8ohms, 2ohm stable, 20wpc pure class A mode) and a couple of SS receivers available as well.

My budget is, well, flexible to an extent. One of the reasons I got into DIY is because I like working with wood (even though I'm not really any good with it) and because I perceive an extra value in building speakers myself. As I plan to at least initially recycle some full range drivers I have on hand I am trying to keep the woofer section as reasonable as possible. $400-500 could be squeezed out of my checking account without worrying too much about how to finance a divorce lawyer at this point. BUT, I'm also in the process of selling some stuff that could double that budget, maybe even kick it up into the $2000 range, in the very near future... basically trading one project "hobby" for another one. Still, I'd like to find the most economical price point without sacrificing too much SQ in the process. I realize this can be a trade off.

I very much like the idea of an OB woofer "construction kit" that will allow me to experiment with single and dual configurations with different sorts of baffles/frames and over all alignments. The GRS woofers seem to be priced so low as to make me wonder if they even have magnets on them but if reasonable results can be had then this would certainly leave me more budget headroom for crossover components, etc.