Nice! Always appreciate your posts, Patrick.

 

Even before Clark purchased the Grand National, it was well known for it's impressive image. The key to this image are the waveguides that are located underneath the dash.

Here's a pic of the waveguides in the Speaker Works Grand National. According to their website, these were the first set. If you look at the compression driver, you'll notice that it uses a "two bolt" pattern. Only one compression driver uses that pattern these days, a company named Radian. (It's possibly an Emilar, but Emilar is no longer around.)

If you've seen some of my other projects, you may be familiar with the horns and waveguides that I've fabricated. I know that horn fabrication is anything but easy. USD Audio sells an excellent set of waveguides, and for this project, I am going to use them. Here is a pic of my set. If you'd like to build the Grand National in a Box, you can get a set of USD Waveguides here:

USD Audio WaveGuide BC-300

Here's a pic of the waveguides in the Grand National. In my car I've found that waveguides under the dash are a lot less obtrusive than kick panels. And there isn't a kick panel in the world that will keep up with the GN (or the GNIB.)

Clark retired from competition undefeated. Some might argue that his success is due to a combination of solid engineering by Speaker Works, along with a series of upgrades. The most noticeable upgrade was the replacement of original compression drivers with more expensive units. Radian compression drivers retail for about $150 new, about $50 used. The compression drivers in the picture above, likely Altec 288C, are worth about $2500. IF you can find a good used pair. In addition to that, it was reported in CA&E that the Altec compression drivers were modified.

While the Altec is a fine driver, it is also very old, and sought out by many audiophiles. Due to the relative scarcity of clean used units, expect to pay top dollar for one. I wasn't interested in spending $2500 on a set of compression drivers, so I personally chose a competing model from JBL. (fun fact - JBL stands for "James B Lansing", as in "Altec Lansing.")

The model that I chose was the JBL 2470. It's readily available - on any given day there are at least two or three sets on Ebay.

It's affordable - about $300 to $400 for a working pair. Better yet, get one with a blown diaphragm, because we're going to replace it anyways.

As I see it, the main advantage of the JBL is that it has a smaller voice coil than the Altec used by Clark, but it's bigger than the Radian used by SpeakerWorks. A small voice coil increases high frequency response at the cost of power handling, and the use of a large compression driver allows us to play lower than the Radian.

Of course this is all just theory...

Let's find out how this will work in the real world.

 

...If you look at the compression driver, you'll notice that it uses a "two bolt" pattern. Only one compression driver uses that pattern these days, a company named Radian...

So do B&C, Pyle, Selenium, and Eminence.
Buuuut, you can get adapters either direction to use regular threaded drivers with 2 or 3 bolt horns, or 2 or 3 bolt drivers with threaded horns.

I had the same USD waveguides you've got, but I used some (relatively) large piezo drivers with a standard 1.375"-18 thread and made ABS adapters to the waveguides. I'll see if I can find pics.

[edit] Can't find pics, and my eBay auction where I sold them is too old to access. I think I used Motorola KSN1188A piezo drivers, they supposedly had a frequency range of 800hz-20khz.

 

According to Car Audio and Electronics, Richard Clark made a number of improvements to the waveguides in the Grand National.

Even with a set of $2500 compression drivers, the Grand National still required a narrow band EQ. The reason is that the horns have a series of peaks and dips. The EQ is used to fix that.

The reason that I named this thread "Grand National in a Box" is that I want to demonstrate a solution that's within reach of people who don't have years of experience tuning horns.

Before I demonstrate how to do this, I'd like to discuss why the GN needed a narrow band EQ.

Even though the horns in the GN are hyoooge, they're not as big as they need to be. Ideally, the horns should be about four times as big. Because the horns are too small, peaks and dips will appear in the frequency response. I will demonstrate this shortly.

Even with an ideal horn, diffraction occurs at the throat and at the mouth. I won't bore you with a technical discussion of diffraction. If you are interested in learning about it, this interview is a good start:
http://www.audioxpress.com/magsdirx/voxcoil/addenda/media/mowry1008.pdf

Have you ever listened to a horn loaded loudspeaker at the club, and noticed that the midrange has a "screechy" and "raspy" coloration in the midrange? Ever noticed that it's particularly offensive at high volume? That's diffraction you're hearing.

Anyways, diffraction is A Bad Thing.

In a moment I will show you how the GN's EQ is used to deal with the symptoms of diffraction. The EQ is used to cut the peaks and fill in the dips.

I have another solution - let's fix the cause, not the symptoms. The cause of the peaks and dips is diffraction and reflections, so let's treat that. You can't eliminate it completely, but you can treat it with about five bucks worth of PVC pipe and open cell foam. Sure beats using a thousand dollars worth of studio EQs

Here's a full writeup on the diffraction treatment:
The HOMster! (or How I Learned How to Fix a Horn) - diyAudio

Kudos to Dr Earl Geddes - these treatments were inspired by his extensive studies on diffraction and psychoacoustics.

Here's a close up of the diffraction treatment on the USD horn. There are additional pictures in the diyaudio thread.

 

Let's get to the measurements.

Here's a distortion measurements of the "stock" USD waveguide, along with the modified waveguide.

Most manufacturers don't publish distortion measurements; even high profile manufacturers like Morel, Scanspeak and Dynaudio don't offer them.

John Krutke and Brandon (aka Augerpro) have generously published distortion specs of popular tweeters.* In their measurements, you'll see that a good dome tweeter has distortion that's 20-30db below the fundamental. Now look at the graph above. Even the unmodified horn has distortion that's about 30db below the fundamental, at least above 2khz.

The performance of the Radian is good, but the performance of the USD waveguide with the JBL driver is even better. Above 3khz the distortion is virtually unmeasurable.

The Radian is still very good though. Though the JBL can play lower, it's over twice the size, and the Radian can play higher. It also has an efficiency advantage.

Personally, I prefer the JBL. It has more efficiency than we'll ever need, the response of the modified horn is smoother, and the JBL plays lower with finesse, thanks to it's very low distortion. Note that the 2nd harmonic distortion is very low - this is due to the silver shorting ring in the motor. Even the Altec doesn't offer this feature.

* Zaph|Audio
* Home (drivervault)

 

OMG! I never realized how big those horns were.

Now I get why my ID Mini's don't have the bonecrushing dynamics I have heard about in the GN.

I do like them though and small format tweeters don't do it for me much anymore.

Great thread, PB. You are the man!

 

The horn in the Grand National was half of the puzzle. The treatment of the car played an important part in the car's imaging and dynamics. But we can do even better

(If anyone wants me to clarify anything in the next paragraph, please let me know. What I am about to say is a big part of the reason that "conventional" horns sound so bad.)

Imagine that you have a speaker, mounted underneath your dash. When sound is emitted from the diaphragm, it's moving at 13.5 inches in a millisecond. Reflections and diffraction are bad, but they're exceptionally obnoxious in the first five milliseconds.

OK, hold onto that though for a second.

In the CA&E article*, Clark said the following:

"Absorption material was added to almost all the upholstered interior surfaces. Unlike mass damping, which only prevents resonance, the absorbtion material that I chose also reduces unwanted reflections inside the car. These reflections can cause unwanted secondary imaging cues.

Now if we agree that reflections in the car are unwanted, why treat the car alone? Why not go waaaaaaay back to the driver itself, all the way to the actual diaphragm? Which is exactly what I've done.

In this pic, you can see that there's sound absorbing foam in the waveguide. But why stop there? There's polyfill inside of the compression driver throat, in fact there's sound absorbing foam INSIDE the compression driver's chamber.

Clark had the right idea, he's just going about it a different way than I am. In the Grand National, Clark is absorbing reflections in the cabin. What I'm suggesting is to absorb the reflections AS SOON AS POSSIBLE. As in, right at the diaphragm.

I know it seems absurd to put a bunch of sound absorbing foam in front of your speaker, but it works. The graph above compares how the USD horn performs with and without treatment. The difference between this one, and the one I posted yesterday is that it uses the same compression driver. This helps illustrate that it's not the compression driver that's creating all those nasty reflections - it's the horn. In particular, it's the horn's mouth

• The graph at the top is untreated. The graph at the bottom is the treated horn. I shifted the bottom graph by 10db, to make it easy to compare.
• See that big peak at 2800hz in the untreated horn? But see how it's NINE db lower in the treated horn? What that means is that over FIFTY percent of the sound we are hearing in the untreated horn is due to reflections! How awful is that? With reflections like that, it's guaranteed to audibly color the sound, and create "false imaging cues" as Clark alluded to.
• Sometimes it's hard to determine what's causing a peak. But the dip at 1400hz confirms that the two are related.
• In the treated horn, we see the peak is reduced by half. The dip is virtually gone.
• Notice that the treated horn doesn't have a lot of the weird "squiggles" in the response.
• Most important of all, note that the response of the treated horn doesn't jump around as much... In other words, the soundstage isn't going to change if you move your head two inches. Accomplishing that goes a long way towards creating an authentic acoustic environment.
• This diffraction treatment has been discussed extensively at diyaudio, and is inspired by the Gedlee Summa speakers. Good stuff, and highly recommended for the home, theater, or studio.

At this point, you're probably wondering, what does all of this have to do with the dynamics of the Grand National?

Here's how this works. According to the research from Geddes**, the sound of diffraction is exceptionally obnoxious. Clark freely admitted that the foam in his car played a big part in it's sound. I'm suggesting an alternative which is even more effective (and very cheap to implement.)

If you're still on the fence as to whether this is audible, try this experiment:

Get a small efficient speaker, and listen to it outside, where there are no reflections. Literally hold it up in the air, at least a few feet away from anything. Now take the same speaker, and play it near a very hard reflective surface. For instance, a kitchen countertop. And don't just set it on the counter, press it right into a corner, where there are a ton of reflections.

What you'll notice is that the sound on the kitchen counter is raspy and congested, and intelligibility is very poor. And the same might be said about an untreated horn.

* the CA&E article has been posted here: http://www.diymobileaudio.com/forum/diy-mobile-audio-sq-forum/69060-natural-bass-6.html#post883102
** http://www.audioxpress.com/magsdirx/voxcoil/addenda/media/mowry1008.pdf(check out the AES papers too, if this piques your curiosity.)

 

How is that big horn motor mounted to the horn body? I can't tell by looking at the picture.

In that same pic it looks like Clark is wearing a fishing shirt, must be an avid fisherman. Wonder what the biggest he ever hooked was.....

 

I am very intrigued by this project, Patrick. Can't wait to see what you lay out before us.

 

Does this mean that the unity based WG to be placed on top of the dash is now defunct?

Fine by me as it was going to be quite an eyesore. I am quite tall so under the dash is not going to be easy but much more of an achievable task.

Keep it coming as the other solutions involve the midbass which can keep up with the top end and the low side which should be the easiest of all solutions.

 

No, the Unity horn is the ultimate solution. The whole reason that I named this thread "Grand National in a Box" is a riff on "home theater in a box."

This is an accessible solution, that's relatively affordable. Most importantly, the midbass and the tweeter are so well behaved, you won't need an equalizer and a microphone to get this to sound good.

When I finish mapping this one out, it's going to be the kind of system where you can literally put the pieces together, hook them up to an active crossover, adjust the levels, and *boom*, you're done.

The Unity is waaaaaaaaaaaaaaaaaaaay more complex. But if you have the time and the patience, it's the ultimate.

 

I have a feeling the original driver in the picture was a large format driver. Most use a 4 bolt pattern mounting attachment...they probably just used 2 of the 4 holes.

Well, looking at it closely, you can see the 2 bolts in the picture are moreorless parallel with the mouth meaning it would look like the 3 bolt triangle like the JBLs pictured.

How big is the driver? Think of a Folger's coffee can.

And also the horns in the GN were a bad design. That bend has no deflector to align the wavefront back...and the bend is pretty far down the throat. Both will cause serious nulling in the FR of the horn.

 

The 288s were 7.1" around and 5.8" deep. And weighed 28 pounds.

 

That'll make you stand out in a pack ^^^^

I have subwoofers that weigh 13 pounds

 

So you are saying if you curled the horn up more to use a larger one, one would have more reflections?

 

Hopefully this isn't an OT question, but does anyone know how Mark Eldridge tackled these issues? Surely his implementation was successful given his winning record. He must have done something different.

It seems to me that he improved the length of the horns by extending them into the engine compartment, but did they have any bends? It appears that the horns enter the interior at the base of the windshield.

Mark Eldridge: Do The Evolution (Jan/Feb 2001)

 

...Mark Eldridge: Do The Evolution (Jan/Feb 2001)

Funny that I have that February 2001 Car Sound magazine in the bathroom.

 

You know Patrick, looking at the pics again of the horn bodies, I'm more convinced than ever that RC didn't put those Altec's in the GN. In a 1000 post thread on another site there was a big discussion as to how exactly he fit those under the dash (this was a back and forth between RC and Eric Holdaway). RC said that he cut the throats of the horns, shortening them, to fit them under the dash. I call shananigans.... Take a look at the pic you posted of the original horns from the USD site and the one he is holding. The length is the same, although a little deceiving due to the angle it was photographed at. If you look on the site and the bungs in the dash, you can see the original driver. The throat ends at the top of the glove box, and is angled toward the firewall and A pillar. Even if you gutted the inside of the dash on a T body, there is no way that Altec would fit. It would be sticking through the firewall and the top of the dash.

Cool thread by the way. Can't wait to see what what you have for us next.

 

Another great thread Patrick, you should have your own audio blog!

 

X 2.

A real good Man.

 

If he shortened them, then he really f.cked things up...or made new horns. This is if the original drivers were 2" drivers. If anything to get the area progression of the flare correct, going from a 2" driver to a 1.4" driver, the horn would have to be longer.

Yes, if the horn was bent it would cause more nulls and reflections in the throat. The null points can be calculated though. Also, without the use of a deflector the wavefront is going all to hell at and past the bend. But this was probably not well understood when the horns were built.

 

I am a horn idiot. I know nothing about the subject. Would linning the horn with an absorbant material (acoustic foam) do the same thing as stuffing it with polyfill. This is a fantastic write up for those of us that are not horn inclined.

 

If you do a search on Patrick Bateman, he discusses foam to control HOM's. I once met a blind dude who suggested I line the horn's throat with those baby blankets that have a funny name.

 

Patrick, will the horn driver be supplemented with a set of tweeters considering their output is between 500Hz to 12kHz?

Or is that why the diaphragm will be replaced?

 

Read the thread he linked to at the beginning. here is the link: The HOMster! (or How I Learned How to Fix a Horn) - diyAudio

 

PB is recommending stuffing with reticulated foam and polyfill, along with poly in the compression drivers chamber.

Winslow, exactly. I would love to see a pic of the passenger side horn from the SW install book. There are lots of wrapping marks that would determine if the horns were cut. I put enough equipment in those body styles to know there is no room for what he is holding in that pic. Here is a pic from the USD site where you can see the mounting ring and bolts. Hard to see if the driver is mounted, but look at the angle the horn takes. LINK

 

Hopefully this is relevant to PB's thread. Here is a photo, in which I combined a shot of the entire dash height of the GN with a shot of the plugs. I photoshoped the perspective of the plug shot to match up to the other shot and combined them. I painted part of the closed glove box back in so you can kind of get an X-ray view behind the dash. Next will be the same shot with the Altec attached

 

According to the CA&E article, Clark improved upon the Grand National by replacing the compression drivers with a set of Altecs.

I am leaving this one up to you, but I am measuring all the options, and discussing the pros and the cons.

Here are some measurements of the distortion performance of a "stock" USD Audio waveguide, and the same waveguide where I've replaced the compression driver, filled the horn with foam, and added a roundover to reduce diffraction at the mouth.

In the distortion measurement, you can see an improvement in harmonic distortion with the large format compression driver, and a much lower F3. You may note that the diffraction treatment is having a significant effect on the driver's efficiency.

Some might think that any reduction in efficiency is A Bad Thing, but I disagree. At low frequencies I want all the efficiency I can get, which is why I use tapped horns in my own car. But at high frequencies I'm interested in low distortion and good polar response. I wouldn't care if my tweeters had an efficiency of 85db, as long as they had excellent polar response, could take a lot of power, and had low distortion. As I see it, that's what's important at high frequencies.

Note that Clark treated reflections in the car, and we're treating them inside of the horn itself.

Note that distortion in the 2nd horn is over 40db below the fundamental above 2khz. Check out the distortion figures at zaphaudio if you're curious to see how a dome tweeter behaves. Note that my distortion figures are skewed higher because they're done in a car too.

Here's the polar response of both horns. Ideally we'd like to see these lines fit in a "window" of about six db. In the untreated horn you'll notice that the polar response is particularly abysmal in the octave between 1250 and 2500hz. This is bad for a number of reasons:

• Our ear's sensitivity is extremely high between 1 and 2khz - any problem is very audible
• These horns are typically crossed over between 1 and 2khz - the crossover will exacerbate the polar response problems
• The problems with the USD horn between 1 and 2khz cannot be fixed with EQ, because they vary with angle. In other words, fix it at one spot in the car, and you make it worse at another.

This measurements shows an average of all the polar response measurements, for both horns. It's basically the "power response." In the power response it's easier to see the issues that the stock setup has between 1 and 2khz, and how the treated horn has improved things.

If any of this post doesn't make sense, let me know.

 

The JBL compression drivers that I'm suggesting as an alternative to Clark's Altecs run about $300 a pair on Ebay. I would not recommend using the "stock" diaphragm - it won't play high enough. If you can find a set with bad diaphragms, you'll save a few bucks.

Parts-Express.com:Radian 1225-16 Diaphragm Fits Most JBL 1" 16 Ohm | replacement mid hf high frequency
This is the diaphragm that I'm using with my JBLs. It's a 16ohm model. I prefer passive crossovers, and it's easier to crossover a 16ohm driver. We have efficiency to burn, so that's why I go with 16ohm.

Also, those old alnico compression drivers can't take a lot of power. IIRC, the 2470 is good for 50 watts at 8ohms. With the 16ohm diaphragms, you're basically lowering the compression drivers efficiency intentionally.

It's the same idea as using a 2ohm sub with a 4ohm midbass, but in reverse.

 

I am a fan of electrostatic speakers! Hard to beat the airy lifelike quality of voice on a ribbon!

 

I sit in front of a computer and write software all day long, and I have a pair of Summas that I listen to while I do it. After work yesterday I headed down to a local pub to have dinner. The pub has brick walls, concrete floors, and a typical PA system with horn loaded compression drivers.

Immediately I noticed that all the "texture" and "detail" was absent from the music. For instance, the bass guitar almost sounded synthetic, as if all detail had been smeared in time. And keep in mind, this wasn't a recording, there was a band playing!

Anyways, the reason that I bring this up is that ribbons are very well behaved in the time domain. Because the diaphragm barely moves, the spectral delay is very clean.

Conventional horns can't do that, and listening to that band at the pub made that obvious. All those early reflections, exacerbated by the concrete floors and brick walls, made the music sound like a muddled mess.

And getting back to the thread, we have two ways to treat that. Treat the horn, treat the room, or both.

 

Very interesting stuff. Look forward to reading more from you Patrick!