Sloped baffle

Good questions.

I do agree with what Bombaywalla just posted- knowledge and experience in many different areas is required. I know of no way out of that, to simplify a home-designer's life.

Driver selection is by far the most important factor. If all we care about is making the best sound, instead of spending money on the newest technology (usually inferior, I find), then here are the important questions to ask before selecting any drivers:

- How far away will I be from the speakers?
- What kinds of music will I play most?
- How loud will I play, even if only on occasion?
- How large is my room?
- How low in the bass do I want the speakers to go? Here, it is best to use 'body feel' as your guide. If you want to shake the house and your lower pants legs on electric bass, then the speakers need to have good output to 40Hz, but not any lower.

Listening at ten feet away in a room that is not entirely open into the rest of the home, this amount of low-bass output requires a low-distortion eight-inch woofer with a large-diameter bass port tuned to ~40 Hz, or a sealed-box ten-inch woofer, flat to 40Hz (good luck finding that in today's marketplace), at the minimum. There is no reason to use multiple 8 or 10-inch woofers per cabinet.

Which means this will be a three-way design to be able to use a first-order crossover, since no 8 or 10-inch woofer can meet a tweeter.

On the top end, choose ~1" dome tweeter, not one made of metal nor of 'ring radiator' design. That means ~3kHz crossover point. The eight or ten inch woofer means ~300Hz crossover point, or slightly higher. And that means using a 4 to 5-inch mid driver showing no cone breakup nor the HF resonance of metal-cone drivers.

All these drivers need very flat frequency responses. Avoid drivers with impedance-curve wiggles, as those indicate resonances and cone breakups. Avoid molded plastic cones and metal cones.

Sorry- got carried away. I cannot put out my version of the Loudspeaker Design Cookbook here.

Do know that, by careful manipulation of the Zobel parts in my passive crossovers, I can fine-tune the time-coherence between drivers (their individual phase responses), for a better blend. This cannot be achieved digitally without custom programming and the consequent extra signal processing (assuming the right measurements can be made, which is not likely).

But you can always listen to your adjustments, and for that process, I recommend you listen to only your left speaker, but not in mono. Start with getting that speaker's voice range right, such as on a older Diana Krall recording. And get rid of cabinet reflections with wool felt for at least the tweeter, or you are screwed from the beginning.

For a home designer, the results with a simple passive crossover with Zobels or with a digital first-order crossover/EQ/time delay setup will be satisfying on most music. However, the sound would still 'not be quite right' on enough other music to make you think there's something wrong with your source or room or cables or amplifiers.

That turns out to be the residual phase shift of the speakers, which is what I finally fixed .

I will continue to think about questions Bfwynne and Lewinskih01 posed and get back to you.

Best,
Roy

My goodness, I just glanced through the XO paper by Dr. Brüggemann. With all due respect, he is not right in many ways about how crossovers work!

The technical details are far too lengthy for here, but I will point out that, in Fig. 8 on his page seven, he described 'lining up the peaks' from a woofer, mid and tweeter. Instead, what must be done is to line up WHEN each driver's pulse JUST BEGINS to turn upwards from Zero. That's a point easily judged for the beginning of a tweeter's spike, but not on a woofer's slow rise (hence a measurement problem). Thus I advise not bothering with his paper, sorry.

The diagrams from Bombaywalla on his Picasa page DO get that starting alignment correct, although I see some problems:
- The scale used shows a definite starting point to the woofer's pulse. That point is not well-defined when the horizontal scale is expanded.
- The loudness of the mid driver seems low, but I could be wrong.
- The summation pulse is not close enough to the ideal.

But it is late now, and no one is paying me to analyze what may be wrong there- just wanted to point out some suspicious items.

Best,
Roy

Hey Roy.

Thanks for the thoughts again.

Thanks for pointing out that mistake in the paper, about aligning start times vs peaks. Seems something easily fixable by setting different delays in the software. So the software approach still is limited by all the previously mentioned aspects, but not an additional one :-)

I spent good time reading your website, particularly the development of the Calypso HD. Very interesting too.

In reality my system would be 4-way, as I have a pair of subwoofers I intend to continue to use. They are 12" Rythmiks in a sealed, DIY and very heavy enclosure. So below 80Hz I wouldn't need the woofers to get there, hopefully making their selection easier. Maybe an 8" woofer in a sealed enclosure does it?

I have by no means studied this at all so what follows has the goal of providing real-world examples rather than representing what I think might be best. I spent some time at Madisound.com to skim over the drivers they carry. These 3 woofers, non-metallic, from known brands. Sure, price was a simplistic way of focusing...I know it's wrong, but for this purpose...

Scanspeak Classic
Scanspeak Revelator
Accuton Ceramic

None of them is really flat down to 80Hz, let alone well below that. But they are quite flat to 100Hz, so the "problem area" seems to be rather narrow in the 80-100 Hz...hopefully not a huge deal.
Both Scanspeaks seem to be able to work well for a crossover around 500Hz. The Accuton maybe at 1kHz?
None showing wiggles on the impedance curve within these ranges.

The midrange was more difficult than I expected. VERY few drivers are flat within their expected range. Here are two looking good:

Accuton. This one looks as it could be used higher up, up to 5kHz per their recommendation.

SEAS. This one is a lot cheaper, but good on paper.

What's your take on ribbon tweeters? Clearly, you prefer non-metal dome tweeters, and non-ring-radiators. But why not ribbons? Or AMTs, such as Mundorf's? Their frequency responses look very good, and they extend well beyond 20kHz pretty flat...

I realize A LOT more thought needs to go into proper driver selection. But I am taking away that such selection is critical. Since I won't have the skills to design a proper passive XO, it could make sense embarking in all of this if the Acourate approach was good enough.

I won't get tired of saying it: thanks for the fantastic food for thought, and taking the time!!

Here's a simple un-tweak that may have helped just a little tweak (pun)... dunno.

For the longest time, I lifted the back of my speakers so they tilted forward. Here the old thought process:

My listening position is below the level of the tweeters. The speakers are about 44 inches high and my listening position is about 10 feet back. But my couch sits very low. I thought that by tilting the speakers forward, the tweeters would beam directly at me and treble would be improved.

Here's my current thinking, courtesy of this thread:

Lifting the back of the speakers as described may have augmented treble response, but the tweeter voice coils are even more forward of the mid and woofer driver voice coils than before the tilt forward. So ... to the extent there was time incoherence before, I'm just augmenting it.

So, at the expense of maybe losing a little treble, I attenuated an already non-optimal time incoherent situation just a tad.

Bottom line: it's probably in my head, but I think the speakers sound a little better. Little less bassey, a tad more coherent and invisible.

Btw, a couple of weeks ago, I switched back to the 4 ohm taps on my amp. There's definitely a noticeable change in coloration because the output impedance off the 4 ohm taps is lower -- and output voltage regulation is tighter. Bass is tighter and more extended. Upper mids/low treble are less bright.

But I also think the amp is "happier" with the load presentation because a good part of the speaker's power delivery demands are in the bass/low midrange region which specs at 4 ohms (70 Hz to 700 Hz). IOW, better impedance matching with the amp where it counts the most.

Still want to check out the DEQX.

Cheers,

BIF

You are quite welcome.
I know what I write doesn't pose questions to you all. Instead, I've mostly laid out the facts and some science. It's up to you to use those to develop your own questions. This is how I proceeded back in the early 1970's, by reading all of the AES papers and many others on speaker design in old and current magazines, on acoustics, studied basic physics, calculus, and psychoacoustics. Later, I returned to university to master all the math, and to learn more about how materials behave when vibrations exist and when electromagnetic fields pass by/pass through.

Sometimes I would find an error in the logic or math of someone's research paper. Usually, I used a paper as a springboard, expanding upon the author's thoughts and test methods, to better look at 'something' in detail.

To choose that 'something' to examine, to fix, or even to ignore, I first had to understand the very basics of WHY and HOW that 'something' would be important to what we hear, and then learn WHY and HOW 'it' occurs. This included how and why cabinets vibrate, cones break up, critical damping is achieved, a tweeter can fail to move on very tiny sounds, the air itself distorts... countless questions.

The most important ones are addressed in the Audio Engineering Society's Audio Anthology 3-book set.
Also, one should get The Audio Cyclopedia, even a twenty-year old copy. It is full of important info on acoustics, speaker design and recording methods, found nowhere else. Make sure you get one that's not falling apart in its binding.
Another book, out of print, is Elements of Acoustics by Temkin. You need to know calculus to get the most from it, but it's readable without that.
Finally, the Theory of Sound by Rayleigh, from Dover Press, is exactly like reading Isaac Newton's original papers. Get both volumes one and two, first published in the 1880's.

If you are interested in design but will never build your own speakers, these books are full of the very best information found nowhere else, and are written well enough to make for good, casual reading.

In these books, you get to see how others approached issues and usually find out WHY they did, along with what had been tried before then and WHY.

Knowing WHY is the most important factor in making better speakers. I can tell you most current speaker designs say to me that their designers know no more than what was mastered by 1979. If you read over the topics presented in those AES books, you'd see this for yourself, darn it.

At this point, I see nowhere on the internet any guidelines on how to select the proper woofer, etc. While I cannot help you directly with that, I can point out the principle differences in the drivers you selected, and leave you to have a good weekend!

- The Classic Scanspeak woofer has ALL of the right numbers for a sealed box. I wish it were more efficient.
- The more expensive Scanspeak woofer will not go as low in its proper sealed box. And unless you are stroking the heck out of it (not likely), it has no less bass distortion than the less expensive Scanspeak. However, it would be very slightly clearer in the lower-voice, high bass range. But then it goes nuts above 1kHz, all from its harder cone. Its first resonance at 1kHz is from its heavier rubber surround bouncing back, like a ripple in a flag, and then vibrating the cone running around its rim, like a church bell's 'first mode' of ringing `round-the-mouth vibration. The big spike above 1khz is its harder cone ringing like crazy.
- The Accuton woofer is a lot of $$, has high bass distortion, and will not go as low as the Classic Scanspeak.

- The Accuton mid driver has many wrong numbers and is not quite efficient enough.
- The Scan mid has the right numbers, its cone breakup is under control, and it has a vented suspension like the Scan woofer. Cross it over at ~300Hz. Read my Continuum 3 and Calypso speaker design papers for more info on using a mid.

- The only ribbons worth using, for sonic quality and which will not break for our purposes, are from RAAL. Excellent products, the best by far. You will need to create a Zobel to offset its inductance. Cross it over at 3kHz. Use their smallest model, for the best highs.

- I advise you fade in the subwoofer(s) below 40Hz, leaving the main three-way to run 'full range'.

So now you face a zillion other questions. Get the AES books above and the Audio Cyclopedia at the minimum for both guidance and answers, compared to the Loudspeaker Design Cookbook.

The Acourate approach is not right. I advise anyone hopefully learn what 'the numbers mean' for any driver, then use the parts I like above to fine-tune your own passive crossovers, with woofer mid and tweeter in their own boxes so you can move each one back and forth.

- You only need to build one speaker, as I posted before.
- You need a $100 voltmeter, a $200 fairly-low-distortion sinewave generator, a decent measuring mic with preamp, to run into some kind of third-octave spectrum analyzer for looking at pink noise.
- And a pocket calculator (scientific), especially to calculate real "L-Pads" for mid and tweeter using the best wire-wound resistors.
That's about it for tools, IF you go through the AES books.

When 'designers' do not understand in depth the extensive research from the past, they rely upon digital test gear. And then get many wrong answers since they do not understand 'the basics'. They have purchased an expensive tool that does not help solve the real problems. But they don't know-- they just stick a mic up in the air and tweak their crossovers to 'get the right curve' for each driver, which is soooo wrong.

And then they hear something 'not quite right', to then tweak the circuits by ear, so their favored recordings sound 'right'. And of course then brag about how carefully their gifted designer listened, how much money they (Revel/Harman) spent on a robotic speaker-comparison room or anechoic chamber (Paradigm/Canadian government). Hey, this isn't the space program where people get killed. This is an unsupervised field of endeavor, with no university program for it, requiring money more so than any real technical education. They always claim, "Well, we all just hear differently." Pooh.

And do get rid of/prevent any cabinet reflections for your mid and tweeter (get the mid's box away from the woofer's and tweeter's boxes, vertically). Put wool felt near the tweeter's dome.

Hope this gives you food for thought!

Best,
Roy