[Bob in St. Louis]

(Wait, "next time"? This is the build that was supposed to bring me eternal audio contentment)

You're new to this hobby, aren't you?   

Thank you for the complement Jon. I'm watching your build with interest as I've always thought those 909's were pretty sexy. On top of that, you're doing a fantastic job.

Just a heads up though, it's easier to have a damp rag handy during clamp time to wipe up the glue as it squeezes out than it is trying to sand it off once it dries. Less change of damaging the MDF trying to sand off the glue and wood glue is harder than MDF.

Bob

[jonirvine]

You're new to this hobby, aren't you?

Oh yes, very new in a lot of ways.  I have a lot of experience with car, stage and video editing related audio but this is the first time getting in "deep" with it all, esp from a diy perspective.

Just a heads up though, it's easier to have a damp rag handy during clamp time

Actually, I used zero clamps.  My friend who has the CNC also has what's called a vac bag.  He threw it in there.  It gives about 120lbs of pressure evenly throughout the whole thing... it's like those storage bags that you vacuum seal but 10x more powerful.

[Bob in St. Louis]

Just for the record, I was teasing about the 'new' comment, based on your idea that any part of this hobby is "eternal"....there's always something shinier to draw our attention. 

I'm familiar with the vacuum press. It's a fantastic system, but does make it hard to wipe the glue off before it dries.

Bob

[jonirvine]

oh no worries Bob... I totally know what you mean.... I was joking too when I said "eternal" knowing that this hobby will probably never provide ultimate contentment. hahahaha.

[MJK]

But Alpha15 bass superiority is a bit of a myth. Simulation of the units on a 40 x 20 " baffle, two of them placed about the same as on your Jamo baffles looks like this:

Alphas first, crossed at 200 Hz 2nd order L-R:





Betas, crossed at 160 Hz, to give the same SPL level as the Alphas, 2nd order L-R:



So what is the main difference. The Betas may be about 3 dB down compared to the Alpha at 40-50 Hz in all other frequencis they will be more or less equal.
This is the trade-off then, some dBs in the very low bass instead of overall clarity and articulation.

Erling,

I know you don't like the Alpha 15A woofers, that is OK. But looking at the two plots you have produced, what in particular causes the Alpha in your opinon to be at a disadvantage in clarity and articulation compared to the Beta? High frequency roll off is almost the same.  At these low frequencies I do not see cone break up being an issue. All I see is a bit more low end extension, I cannot believe that is the issue. The AE Dipole 15 and IB 15 both go even lower into the bass frequencies and that has not produced a similar observation. Your words and your plots seem to tell opposite stories.

Martin

[scorpion]

Hi Martin,

You are right the difference is not in the simulations, that was my point really. 
I think we should agree that we disagree in this matter.
In reality I think loudspeakers, as other things also, perhaps not perform as ideal as theoretical assumptions proclaim.

/Erling

[MJK]

Erling,

OK, the simulations tell one story.

Where do you think the problems you hear in the Alpha 15A come from and what is the key difference in the more expensive AE 15" OB woofers? There are now quite a few other OB and cost friendly woofers (high Qts and low fs) from Goldwood, GRS, and Eminence. Is one brand better than the others and if so what is the reason? I have both low cost and high cost OB woofers and have swapped them in and out of my system and with the exception of bass extension do not hear that large a difference at sane listening levels.

Martin

[jonirvine]

MJK, (btw thank you for sharing your research with the world, it's been very helpful for me) if I'm planning on bi-amping the subs and the FR's separately, where do you think I should start with my lowpass c/o, assuming I'm running the TB's wide open?  I have one friend who does 80hz and another who does 125hz.  Is it really just taste/preference at that point?  Or is there a way to quantify via a simulation or some other means beyond my abilities?

[MJK]

Jon,

You do not want to run the full range driver without a crossover, you need to design a crossover for the woofers and the full range driver to ensure a smooth and controlled transition. Without the crossover you will have uncontrolled reinforcement and cancellation of the SPL responses from the different drivers.

I am not sure how you are designing your OB speaker system, I do have MathCad worksheets available that will handle your exact configuration with either passive or active crossovers. I am sure there are also other programs for doing the simulations required to engineer an OB system.

If you are using a trial and error approach that can also produce a decent design if you are patient, purchase a variety of parts to try in the crossover, and have an intuitive feel for how the crossover works.

Martin

[jonirvine]

I do have MathCad worksheets available

Thanks Martin. Where can I find such worksheets?  Are they for purchase?

Honestly, I'm pulling most of my design from other projects I've seen on the forums and a friend of mine who has a similar setup with Fostex/Alpha's.  I'm more of a left-brained guy so I have a difficult time understanding the electrical engineering stuff.  But I do know how to plugin values into a worksheet!  The main thing I'm looking to find now is how the TangBands would look simulated on an open baffle.  I don't have a PC so I can't use Edge or that other "B!" one.  So if you have a worksheet that is mac-compatible, that'd be much appreciated!

thanks!

[MJK]

Using a Mac pretty much leaves you out in the cold when it comes to speaker design hardware and software.

I probably do not have all the baffle dimensions exactly correct, but here are two recommendations for crossovers that you can use as starting points. These both assume the Alpha 15A drivers are wired in parallel.


1. Active Crossover

Low Pass 2nd order LR at 200 Hz

High Pass 2nd order LR at 300 Hz

No bass boost needed, woofer and full range driver wired in phase


2. Passive Crossover

Low Pass 2nd order

1.0 ohm resistor in series with a 4.7 mH inductor (ERSE Super Q) in series with the driver, a 135 uF Capacitor in parallel with the driver.

High Pass 2nd order

39 uF in series with the driver, a 7.2 mH inductor (ERSE Super Q) in parallel with the driver

Note the drivers are wired out of phase. The SPL of the woofer can be raised or lowered by changing the value of the 1.0 ohm series resistor. Do not use a tube amp, stick with a higher powered SS amp. Minimum electrical impedance is just under 5 ohms.


In both cases the system produces about 93.5 dB/W/m output.

[jonirvine]

Wow, thanks Martin for all of your help

My only question is:

Note the drivers are wired out of phase.

I always thought it was "bad" to have speakers out of phase.  What is the rationale behind this?

Also, I'm assuming you mean to wire them this way:
Figure A


not this:
Figure B

[MJK]

The woofers are wired together in phase, but the Tangband is connected out of phase with the woofers in the passive crossover (not in the active crossover where everything is connected in phase).

[scorpion]

Martin,

I will try to give you an as correct answer as possible by revisiting the Alpha15s and compare with th IB15s. However I will be away for almost two weeks now, so it will take some time. But I will come back to your question.

/Erling

[MJK]

Erling,

That would be great. I am curious to know your opinion concerning the differences you are hearing between the Alpha 15A and the IB15 woofers. Is there a design defect or limitation inherent in the Alpha 15A, maybe at higher power levels versus lower levels where I tend to listen, compared to the AE driver. The AE drivers are definitely better made units. No comparison in build quality of the two, it is not even close. Or is what you are hearing more related to the extended low frequency range of the IB15, more deeper bass providing a more satisfying result, which is what I hear. I am not too concerned about frequencies above 200 Hz, knowing the AE driver will excel compared to the Alpha 15A, since this frequency range is not being required in my style of OB speaker systems with low crossovers.

While the frequency range from 20 or 40 Hz up to 200 Hz seems like a limited narrow spectrum, compared to everything else up from 200 Hz to 20 kHz, it does contain a lot of the signal/information that makes music sound so good. To prove this to yourself all you need to do is listen only to the woofer in this type of OB system to realize that what you are hearing is most of the music but dulled slightly by the lack of the top end from the fullrange driver.

When you have time I am still interested in your observations,

Martin

[Rudolf]

I believe that in such a comparison we need distortion and waterfall (CSD) measurements - done at different volume levels. Nobody will doubt that the AE driver can play a lot louder with less distortion. But maybe we can see, up to what levels the Alpha will play "safe" too. Pano's poll on http://www.diyaudio.com/forums/multi-way/204857-test-how-much-voltage-power-do-your-speakers-need.html does suggest that listening levels might be quite different from one individuum to the other.

Lately I covered the stamped steel basket of a midrange driver with anti drumming compound. The before/after difference was only vaguely visible in the response and THD diagrams, but had a huge impact (much reduced ringing time at 1 kHz) in the CSD.

Possibly such effects make the real difference between both divers.

Rudolf

[Lazz]

Rudolf, have you compared the sound quality difference on the midrange driver.

[Poultrygeist]

MJK,

I drive my Tang Band W8-1808 with a 2a3 amp sans crossovers atop your H-frame Alpha design. The Alphas are driven by two Dayton APA-150 which have built in crossovers set at 80hz. This system totally humbled the expensive Zu's I could no longer justify and finally sold. How could a passive crossover benefit this system? 

[MJK]

Poultrygeist,

In the past month or so another DIYer has been e-mailing me recommending I try the no crossover approach to my H-frame and OB speaker systems. His arguement was interesting enough to convince me to give it a try. My dBX active crossover allows me to run without the crossover so I have basically two amps powering the two drivers in parallel. I have run the simulations and spent some time listening and comparing this configuration to my baseline set-up.

The simulations made it look like a total mess with either a broad peak (no crossover) or a deep null (one sided crossover) in the regions where the drivers overlapped. The sound was not as bad as the simulaton showed, but it was not as good as with the baseline crossover. The crossover on both drivers helps smooth the transition and to my ears produces a more balanced sound without the emphasis (peak) or de emphasis (null) on a narrow band for frequencies around 200 Hz. With the correct crossover on both drivers the sound from the speakers was just cleaner.

Martin

[jonirvine]

So here's where things are at with my project.  I'm still sanding away and routing the baffles but all the components are in (FR's Alphas, caps, inductors, etc).  I've also come across some good deals on craigslist so now I have a Msuci angel Tube amp and even traded my old Wharfedale's for a 300watt poweramp.  I've spent more money that expected on building materials so I've had to adjust my initial plan a bit.  Thank you for everyone that has helped my fine tune this project (esp Poultrygeist who has entertained my many emails.)

So here's my dilema.  This system is going in my humble home theater in my basement. Instead of having 2 systems in there, I was hoping to combine the 2 into one somehow while being able to switch between 2 channel and some sort of Dolby SS.  The only way I can figure out how to do this is to have a preamp/integrated amp that can switch between the sources and also process the dolby when needed.  I have a Harman Kardon AVR25II but I'd rather replace that with something more audiophile worthy that won't disrupt the nice audio signal i have coming from my dac.  Any ideas on this? See below: