[markC]

Hi Richard,
Interesting experiment with the phase plugs. I've never tried them and have moved to a 2 way set-up with tweeters, so I don't see a need for them in my current creation.
About the zobel; if you look at the frequency and impedance graph for the B200, you will notice that the impedance starts a steady rise at about 1000 hz. As the impedance rises the amplitude also rises- it gets louder after 1k, (in a nut shell). The lr circuit attenuates the response by about 4 db, (depending on what value components you use). But the graph shows an amplitude  about 8-10db greater from about 1500 hz to 8k hz.
The zobel in effect will equalize the impedance so that it does not rise and the 4 db attenuation will be more in line with the overall output. Clear as mud?

[-Richard-]

Hi MarkC ~

Your explanation was clarity itself... I am deeply grateful to you for taking the time to explain things so cogently... it all makes perfect sense... not only that... but you have helped me to see the all-important points where the B200 rises out of a flat response... this makes it quite clear why the passive "filters" you are suggesting are so important in helping to establish a flat response.

Of course filtering does impact on the efficiency of my 2.5 watt 45 SET amp... so far it is fairing quite well with the use of the LF circuit... the zobel may challenge things a bit too much.

The Korneff 45 SET does amazing things with the B200's... people with deep pockets pay huge amounts of money in the hope of creating music in their homes like this... and never do! So I would like to keep using it as long as I can.

No wonder so many designers are turning their attention to OB's. If they are clever and pay attention to the issue of speaker efficiency we low watt SET enthusiasts would be eternally grateful.

Warmest Regards ~ Richard

[markC]

Yea, I feel a bit foolish forgetting to include the efficiency trade off. That, of course, is of a great concern when set's are involved.
I keep forgetting about that 'cause my amps to speaks are like Godzilla vs. Bambi.
Even though I have tubes as "the amplifier", in my hybrids' I'll bet set and B200's are sweet.

[dweekie]

Saves the efficiency with this circuit.  Check it out.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=99662&perpage=25&pagenumber=1

[scorpion]

Hi Richard,

Sorry for the s in Alpha15s, only meant as plural. I don't think it is confirmed that Emerald Physics CS2 uses them. One guy in diyAudio was very determined.
And he by the way had a really beautiful OB with 2 Alpha 15 and a Supravox 215 Bicone.

The Alphas are specified down to 41 Hz now for fs, for music that will certainly be okey. The dipole drop is compensated quite a bit by a raised bass caused by the
high Qts value. I have to check out the Alpha speakers myself. I have come half-way with a small dipole with German speakers, it will be a passive design and I have not yet done the crossover, however the OB is built and measured. The Bass is a 15" A&D 1524 with fs 44.4 and Qts .74. My indoor measurement shows bass down about 3 dB at 40 Hz and the quality is very good. It is paired with a Monacor fullranger SP130/X which is a true gem at 24 $.

Dust caps could be a great nuisance especially if they create air trap resonances behind them. The B200 voice coil is vented though.

MarkC and dweekie has dealt with the LR-circuit. The proposed 'in-between-filter' is of course not loss-less either, but the loss could be easily compensated by
preamp volume. I made a Spice simulation of the proposed circuit into a 100K load which it was calculted for with this result:

 

Not so impressive compared to the passive circuit or what you can do with analogue or digital EQ, but cheap !

/Erling

[-Richard-]

Hi Scorpion ~ Thanks for your insights and clarification regarding the Eminence Alpha-15A's.

I purchased a pair from US Speakers... $120 per pair... they don't go down nearly as low as Hawthorne Audio's 15" Silver Iris Augies... which sell for $300 a pair... they are supposed to go down to 30Hz.

My budget is rather strained at the moment... the SIA's are originally based on the Eminence 15" drivers... but according to Darrel they are made with more structural integrity. However their sensitivity is rated at 88db which along with the higher price I wanted to avoid for the moment.

After ordering the Alpha 15A's I read on the Hawthorne site that he suggests that they are really not that sensitive throughout their entire frequency range... hummmmm... isn't it always like that!

My other thinking is that I may not need the visceral, prodigious bass that is accorded the Augies performance.

Perhaps merely filling-in what the B200's are already producing... at admittedly a severe loss of SPL's... may do the trick of creating a convincing bass... however after experimenting with the Eminence, I may find that I need to go the route of the Silver Iris Augies... or something comparable.

I need a passive cross-over for the Eminence Alpha 15A's... that would begin to cut off its frequencies above perhaps 150Hz, or200Hz, or 250Hz according to how well it integrates with the B200's and what it sounds like.

I would deeply appreciate it if anyone has an idea what the simplest passive filter would work in this arrangement(?)

Hi MarcC~ I deeply appreciate all your suggestions and insights... I was merely sharing what may be my 2.5 watt SET 45 amps "power" limitations... it may be that the addition of the zobel circuit you recommended could be overcome easily by raising the volume of my preamp as Scorpion suggests. It is certainly a worthwhile experiment... thanks for your help!

Just a quick thought about passive filters generally... using the LR circuit (inductor and resistor in parallel) to tame the upper frequency rise in the B200's works well on one level... but I hear a loss of transparency and air and "speed" that makes the B200's so startlingly "real" sounding. It has me asking a few questions: do I respond to dynamics that are exaggerated in order to "feel" the music more acutely? do I need (or prefer) a "hot" top-end presentation to bring about more excitement at the expense of smoothness of presentation, does a hot top end (that rise we are all trying to tame) favor the music I most listen to?

No answers yet.... I am still listening... still trying to make sense of it all.

Meanwhile thanks to everyone for your incredible help and kindness.

Warm Regards ~ Richard

[MJK]

After ordering the Alpha 15A's I read on the Hawthorne site that he suggests that they are really not that sensitive throughout their entire frequency range... hummmmm... isn't it always like that!

My four Alpha 15A drivers measured efficiency is 92.5 dB/W/m, with floor reinforcement this value rises significantly, with an fs of 40 Hz and a Qts of ~1.2. In my big baffle they go low enough. For a driver with a lower Qts the roll off will start well above fs so a stated efficiency is an over estimate for low frequencies.

Perhaps merely filling-in what the B200's are already producing... at admittedly a severe loss of SPL's... may do the trick of creating a convincing bass... however after experimenting with the Eminence, I may find that I need to go the route of the Silver Iris Augies... or something comparable.

Using one Alpha 15 on a reasonably sized baffle with a passive crossover at 100 to 200 Hz the target efficiency for the full range driver will be about 90 dB if you want a balanced response. So you will may need to pad down the B200 to get it to mate well with the Alpha 15A

[JohninCR]

Hi Richard,

Here's something you may find interesting.  I've been using B200's with no filter and only 3db of boost at the very bottom.  I typically don't turn on my woofers unless I plan to listen loud, so about 90% of the time it's B200's only with no filter.  In addition, beaming is so minimal that it's a non-issue, and on top of it all, I pick up a bit of sensitivity, to go with better balance in directivity than normal OB's.  That's why I've stopped building speakers.

I'm using my mostly finished dipole waveguides that I was working on back in Feb.  The reason it works so well with the B200 is it's gradually rising response up the frequency where beaming starts.  Essentially what the WGs do is contain the wavefront within the 90° angle of the waveguides, so as frequency decreases and the natural dispersion of the driver widens past 90°, the waveguide keeps the wave focused, which really flattens the response by preventing that natural roll-off to a large extent.  Instead of padding the higher frequency down with a filter, I bring the lower frequencies up. 

I also find the overall sound more realistic than my other OB efforts, because past 45° off axis the frequency response is more balanced as is all at a much lower level.  With more typical OB's well off axis, the bass rolls off quickly leaving an exaggerated midrange (not highs because they beam), so the reflections of that off axis response don't have good frequency balance.  That's probably a big part of the reason I simply couldn't live with the uptilted response in my narrow room, since the off axis reflections with exaggerated mids were likely a bigger portion of my overall response than in a wider room.

Something to think about if a more complex build becomes a possibility.

John

[-Richard-]

Hi JohninCR ~

Always the explorer and experimenter into the possibilities of solving otherwise complex driver performance problems with the use of innovative and ingenious sound shaping baffles, I am not at all surprised that you have come up with an incredible design solution that takes full advantage of the B200's excellent performance areas while working out whatever performance issues the B200's needs help with. Bravo, John!!!!!

I have seen your ingenious front-facing and back-facing wave guides and I instantly found a broad smile creeping across my face... beautifully designed and conceived!!!!! Besides being beautifully designed, that it actually works is a tribute to your creative and indefatigable spirit!!!! Nice work!

You are one of those writers John, whose sense of certainty is infectious... what person working with the B200's would not want to build a pair of your wave-guide "baffles"?

Have you published a schematic on AC that gives the measurements of your sci-fi looking space age wave-guide baffle yet? If so I would love to study them to see how I can get around my crude woodworking skills to accomplish making a pair... I think your own skills are developed since you published your last set of pictures of your "barrel-like" baffle design on the original OB threads.

I am very much in favor of leaving the B200's alone in terms of using filters or active EQ... I know that this has always been your philosophy and guiding design principles from the beginning.

If you decide to publish a schematic that I (or other AC members) can build from we would be deeply appreciative of it. If it is propietary than I certainly understand.

Thanks for sharing your explorations with me/us John... very interesting development indeed!!!!

Hi MJK ~ thanks for the warnings and heads-up on the integration issues with the Alpha 15A. I will be listening very attentively while I work with them. I suppose having 4 Alpha's helps to compensate nicely for the cancellation issues of the OB back-wave paradigm. I am guessing that if you use them in parallel pairs they must achieve a bit more sensitivity (?)

Warm Regards ~ Richard

[JohninCR]

Thanks Richard,

I really owe the approach some more work before releasing dimensions.  Once I got the waveguides doing what they were supposed to, I got complacent and started spending my time figuring out how to turn sunlight into electricity in the most cost effective way possible.  As far as the speakers go, I'd like to try adding the Helmholtz slot loaded RLH into the mix to flesh out the bass to see if I can get rid of the EQ too.  I knew how much you'd like to avoid filters, so I thought I pop in as a reminder that there are ways to physically manipulate sound waves to achieve results similar to electronic manipulation.  The ease of manipulation before the drivers has made us all lazy, leaving the physical structures for OB's a wide open area of exploration.

Take care,

John

[MJK]

I suppose having 4 Alpha's helps to compensate nicely for the cancellation issues of the OB back-wave paradigm. I am guessing that if you use them in parallel pairs they must achieve a bit more sensitivity (?)

The combined calculated efficiency for a pair of Alpha 15A woofers in my baffle with floor reinforcement is 105 dB/W/m down to 50 Hz with a -3 dB point in the mid 30 Hz range. The advantage for the Alphas is that you can use a passive crossover, meaning only one amp, with a variety of smaller full range drivers to achieve a flat 90 dB/W/m sspeaker system. You can read about my Lowther OB system and a design article about passive two way OB speakers on my site.

[JohninCR]

The combined calculated efficiency for a pair of Alpha 15A woofers in my baffle with floor reinforcement is 105 dB/W/m down to 50 Hz with a -3 dB point in the mid 30 Hz range.

Martin, can you really say "calculated"?  Is there some formula that computes the excursion at 50hz?  I contacted Eminence directly and was told quite directly that their response curves and sensitivity ratings were not applicable below 200hz, since bass response is driven by the alignment.  Calculations are great, but they require a valid starting point. 

I'm not saying that you don't have great bass or that your 1 amp solution isn't valid, however, those numbers will only lead people to unrealistic expectations.  eg 102db at 35hz from 1 watt of input is only possible with a giant bass horn, and even then I'd want to hear it before signing off.  Numbers are great, but being a numbers guy you should really be a bit more responsible with the numbers you put on the table.  Do you really believe that just 1 watt is going to push a pair of your woofers to full excursion at 35hz?  Isn't that about what is required, even considering a full 6db of floor gain? My guess is that 1 watt will create only barely perceptible cone movement.

The bottom line is that driver sensitivity ratings aren't meaningful for low bass, especially with open alignments.

John

[MJK]

John,

I have provided my results based on my calculations and measurements. People can decide on their own if they believe or not believe what I have presented. I believe. Obviously, I do not agree with many of the statements in your post. So be it, no big deal. I'll go back to lurking.

Martin

[-Richard-]

Hi Martin ~

I for one find your insights and suggestions extremely important... your website, Quarter Wavelength Loudspeaker Design, is a source of inspiration and solid well-thought-out and documented information for many DIY designers... and I suspect commercial speaker designers as well.

So I would like to encourage you to continue to post anywhere and everywhere on AC that your experience and insights would help us to shape our ideas more intelligently and directly impact on the design decisions we make.

You have already helped me to think through the use and efficacy of using the Alpha's 15A's as a bass driver in my OB system... and I find it extremely encouraging that such a well-respected, sincere and generous soul that you are, is willing to share your ideas with me... Thanks so much, Martin... I deeply appreciate it... and I have no doubt that your findings are the result of careful observation and clear thinking. I am particularly encouraged with your insight about floor reinforcement... since I intend to place the Alpha's very low to the floor on my tilted flat OB baffles.

JohninCR's posting style is wildly confrontational... and should not be taken too seriously.

Warmest Regards ~ Richard

[Michael V]

Richard,

I have very little experience with OB speakers (and even less understanding), but I thought I would share my setup because it seems to be in line with your goals.   Driving the entire speaker system with a low-powered SET is important to me.

After some experimenting with the bi-amped Hawthorne SI/Augie combo - which does sound very good in its own right - I currently use a B200 fullrange, in parallel with the Silver Iris woofer from 250hz down.  The 'crossover' consists of one 5mh inductor per speaker, which is just across the woofer.  This sounds very good to me, although it doesn't get you much below say 45hz.  Until that point it is very full and coherent throughout the frequency range.

Smaller baffle is also important to me, so I have 20x36, with both drivers centered and a couple inches from their respective top/bottom boundary.  Still experimenting will small wings on the lower half of the baffle.

The SI woofer is similar to the Alpha 15, but as I understand it, it will be more powerful in the bass until it runs out of steam as it approaches Fs.

If I didn't already have my SI woofers lying around, I would look into the Hawthorne Sterling woofer (assuming you can purchase that separately from the full Sterling coaxial unit).  It has a lower Fs, among other differences.

Anyway, thought I'd throw that out there!

All the best,
Mike

[-Richard-]

Hi Mike ~

Wonderful to hear from you... it sounds like you have been doing quite a lot of listening in the OB paradigm... and that suggests you know more about OB's than you suggest... what I find about the OB experience is that over time it informs the "ear" what is really going on with "conventional" box speakers and even horn variations.

Martin said it quite rightly on his incredible Quarter Wavelength Loudspeaker Design web site, referring to his own design experiments with an OB "These speakers produce a very large sound with incredible dynamics and power." And that creates a certain "reverse-engineering" conceptual thinking... one realizes why one has not been satisfied before with the commercial speaker offerings.

Thanks for the inductor value and advice... I will certainly try it.

Yes... I have been following the introduction of Darrel's new Sterling driver offerings... a bit pricey for me... unless of course the sound is state-of-the-art... comparable to the field-coil or Ainico "wonders" that are also pricey as hell... perhaps worth it in absolute terms. Time and feedback will tell.

Thanks again, Mike.

Warm Regards ~ Richard

[JohninCR]

Richard,

If I come across as confrontational, it's not my intention, though I have no problem voicing my strong opinions, especially if I think people are being lead astray.  Martin stated that with the dual 15's his speakers have a sensitivity of 105db at 50hz and are -3db in the mid thirties.  Now he's insinuated that he has measurements to back that up.  Great, let's see them, along with the underlying test conditions.  I'd love to be proven wrong about this, because it sure would make building OB's a lot easier, and I have an abundance of 15" pro-type woofers with specs similar to the Alphas.  I may not agree with the claimed efficiency, but I do agree with the approach.

John

[-Richard-]

Hi John ~

Martin is a highly respected speaker designer... he is particularly careful in researching everything that really matters in the speaker design process as his highly informed web site proves quite nicely:

http://www.quarter-wave.com/Projects.html

a very satisfying info-walk through his speaker projects with insights, graphs, technical information galore and it is all free... there for anyone to read and glean valuable information and insights from. Martin's generosity in sharing his valuable experiences in speaker design is quite extraordinary. A model for all of us who would undertake that level of thoroughness in sharing our speaker building explorations with the DIY web-community at large.

If you will allow me to suggest John... and this is for our entire community... that there is a profound difference between a "dialogue"... where 2 (or more) friends take a friendly walk together and discuss something that each may have a certain opinion on... but in the spirit of sharing ideas with each other... with affection... they agree to be open-minded about... and an argument.

In the argument... each person takes a hardened stance... a position... and from that "hardness" launches their opinions at the other "friend" like hurtling a lance... in a dialogue each person shares his ideas with the other giving space and respect for the others ideas.

If someone of Martin's highly tuned experience suggests a technical approach and claims to have measured things along the way it is up to us to try things out if we wish to see for ourselves if their conclusions really hold up in our experience.

Asking someone to "prove it" is necessarily the opening broad-side shot in a fight of sorts.

I respect everyone on AC... I approach my relationships with others in the deepest respect for their willingness to share their thoughts and experience with me... with all of us. From there great friendships can develop. After all... we are all in this together... it is up to us to learn what we can from each other in the spirit of affection, community and friendship... in order to save money and have some fun.

Of course I have my moments when I am brittle. But it is not my nature.

Warmest Regards ~ Richard

[markC]

I was going to respond, but after reading your last input a couple of times Richard, I just can't follow that!
If only I could present my thoughts as clearly, (although a little less flowery).