Big Audio Dynamite

[Patrick Bateman]

How many of you have listened to a set of dipoles and realized they do some things better "conventional" speakers?

How many of you have been curious about the buzz around waveguides, and wondered if it was time to try one out in your next project?

Has anyone considered using BOTH in the same speaker?

If so, read on...

I've been experimenting with horns then waveguides for close to twenty years. Though my experience with dipoles is not as deep, I've been curious to learn more, especially after reading linkwitzlab.com.

Before we get into the details of this project, I think it's important to state a few of my biases up front. I am not someone who does DIY projects to save money or to clone an existing design. So if you want to learn how to make a Linkwitz Orion or a Geddes Summa for $500, this isn't the thread for you. Both of those speakers are spectacular, and I'd wholeheartedly recommend BUYING a set if they suit your needs.

The idea of this project is take the influences of a handful of great speaker designers, and distill them into ONE speaker.

I wanted to name this speaker after a band that's been influenced by half a dozen genres. A lot of names popped into my head, but naming the speaker "Beck" or "Prince" didn't have a good ring to it. So I'm sticking with "Big Audio Dynamite."

Here's the wikipedia entry; watch this thread for the next few months, and we'll find out if the speaker can effectively mix as many influences as the band did.

Big Audio Dynamite

Big Audio Dynamite was a British musical group formed in 1984 by the ex-guitarist and singer of The Clash, Mick Jones. The group was noted for its effective mixture of varied musical styles, incorporating elements of punk rock, dance music, hip-hop, reggae, and funk into a unique sound.

[Patrick Bateman]

This speaker is going to be a 2-way, which can be augmented by a sub. For the high end, I will probably use a BMS neo compression driver, since it worked so well for my last project.

For the woofer our priorities are high-excursion, good power handling, and smooth response to the crossover point. The crossover point will depend on the woofer; the bigger the woofer, the lower the crossover point.

What do you guys think of these choices:

GR-Research M165X
Dan Wiggins has convinced me that XBL^2 is the way to go. I've listened to his speakers with the Extremis, and the bass response is incredible. Unfortunately, it's no longer available. The M165X looks like the next best option. According to zaphaudio.com the M165X does not have a copper shorting ring. I believe Wiggins has argued that it's not necessary. Nonetheless, the 165X is compelling, but the Extremis would be an attractive option if it was still for sale.

Peerless Exclusive 8in Woofer
The Peerless has the shorting ring that the GR lacks, but it doesn't have as much xmax. However, the increase in surface area might make up for that. The GR costs less.

Seas CA22RNX
I stumbled across this after seeing a positive review of the ER18RNX. It's not clear if the CA22 has copper in the sleeve; if it does, it may be competitive with the Peerless, for less money.

Eminence Basslite CH2010
This one may look like an odd choice - it's a guitar speaker. It's xmax is among the lowest, and it's response isn't flat. But the excursion problem is offset by the high SD, and the rising response is out of our passband. I'm also a big fan of high efficiency drivers. It has a hemp cone, which is unusual.

P-Audio SN-12MB
One of the most underrated midranges I've come across. After hearing the Geddes Summa, I bought and measured one of these in the interest of making a high efficiency two-way. My measurements show that this speaker has flat response, high efficiency, and is reasonably priced. For our application, it's low xmax and low QTS may be a deal breaker. In a conventional enclosure, it's great.

I haven't settled on a midrange (yet.) The P-Audio is probably my favorite. It's low XMAX looks like a deal breaker, until we consider it's MUCH higher SD.


Lets do the math.

P-Audio SN12MB has an SD of 530cm^2 and an xmax of .35cm. That gives us a swept volume of 186cm^3, or .1855 liters.

Peerless Exclusive 8in has an SD of 221cm^2 and an xmax of .55cm. That gives us a swept volume of 122cm^3, or .122 liters.

What does this mean to us? It means that even though the pro sound midrange looks like a lousy candidate for a dipole mid, it's surface area trumps the XMAX of a more-modern motor design.

[Patrick Bateman]

One thing someone is bound to ask, is why not use dual midranges? For me, this is a question of cost, design complexity, and directivity.

Two Peerless eights will cost more than a single P-Audio 12; a D'Appolito midrange is trickier to cross over; and a BIG woofer offers superior directivity (this is why the Summa uses a VERY expensive 15in woofer.)

I ignored one of the most popular DIY eights because metal cones are a challenge to crossover, and it has low excursion. But what if we use TWO?

Here's the math.

Dual Dayton Reference eights have an SD of 442cm^2 and an xmax of .6cm. That gives us a swept volume of 265cm^3, or 0.265 liters.

P-Audio SN12MB has an SD of 530cm^2 and an xmax of .35cm. That gives us a swept volume of 186cm^3, or 0.1855 liters.

Peerless Exclusive 8in has an SD of 221cm^2 and an xmax of .55cm. That gives us a swept volume of 122cm^3, or .122 liters.

What does this mean to us? A single Dayton Reference eight is trumped by the Peerless, but a pair of them may be the best bet, particularly since they cost less than a SINGLE 12. (PE has them on sale for $35 right now, versus $135 for the SN12MB from loudspeakersplus.)

[planet10]

Originally posted by Patrick Bateman
Dan Wiggins has convinced me that XBL^2 is the way to go. I've listened to his speakers with the Extremis, and the bass response is incredible. Unfortunately, it's no longer available... but the Extremis would be an attractive option if it was still for sale.

The CSS SDX7 (think offspring of Extremis) is not far away.

I'm patiently waiting for these for FonkenWoof.

dave

[Pano]

Sorry, where is the waveguide in this design? Did I miss it?

On the mids?

[Patrick Bateman]

Originally posted by panomaniac
Sorry, where is the waveguide in this design? Did I miss it?

On the mids?

On the compression driver.

IMHO, the best sounding speaker at the 2007 CES was from Emerald Physics.

While the sound is excellent, the WAF factor is nil. Based on my research into psychoacoustics and a lot of experimentation, the huuuuuge size of the Emerald Physics speakers is overkill.

Is anyone interested in the technical details? If so, let me know.

In a nutshell, here's the trick:

In order for a speaker to image well, two things are required. The frequency response of the two speakers must match, and each speaker must be time aligned. The TRICK is that we are EXTREMELY sensitive to time-alignment problems in the low frequencies, yet insensitive to frequency response problems; the opposite holds true at high frequencies, where time alignment is difficult to perceive, but a FR mismatch is noticeable.

So what does this mean?

Stay tuned for design details...

[Lynn Olson]

With the HF/LF hinge point in the 300~500 Hz range, I presume.

One of the little tricks we did at Audionics was match all speakers against the prototype. The matching technique was interesting: the L and R speakers would be facing forward, about a foot apart from each other, and connected in reverse-phase. The measuring microphone was about 1~2 meters away, and precisely in the midline. The goal was a full-spectrum null at least 25~30 dB deep.

When you think about it, this requires both precise level and phase-matching - within a few degrees - to attain a 25~30 dB null. I can tell you, it worked, and gave far more precise pair-matching than any other method, which usually doesn't take account of phase-matching across the pair.

[Russell Dawkins]

Originally posted by Lynn Olson
With the HF/LF hinge point in the 300~500 Hz range, I presume.

If you are referring to the Emerald Physics CS1, I believe it's around 1,000 Hz (with a 15" bass/mid vs the 8 inch pair on the earlier model).

Apparently Peter Walker used to do something similar for final stage QC at Quad with the ESL 57 - he'd put the speaker face-to-face and out of phase with the reference and play square waves.

[Patrick Bateman]

Originally posted by Lynn Olson
With the HF/LF hinge point in the 300~500 Hz range, I presume.

At low frequencies, timing is key;
At high frequencies, matched frequency response is key.

There IS a "hinge point", which is different for every person.

That frequency is equivalent to the distance between your ears. For instance, if the distance for you is nine inches, the frequency is about 1500hz.

This psychoacoustic phenomenon has a number of implications:
- At 1500hz, we are incredibly sensitive to frequency AND timing.
- Coincidentally, our hearing acuity is higher at this frequency, which makes point #1 even more critical.
- At two or three octaves below this "hinge point", we can get away with frequency response problems, but timing is EVERYTHING. This is one of the fundamental mistakes people make with subwoofers; they don't time align them.

Needless to say, this project is going to put a lot of attention into time alignment of the low frequencies.

[Russell Dawkins]

Originally posted by Russell Dawkins


If you are referring to the Emerald Physics CS1, I believe it's around 1,000 Hz (with a 15" bass/mid vs the 8 inch pair on the earlier model).

Sorry, disregard - I thought you were referring to the crossover point, but I see you were referring to the last part of Patrick's post.