I'm Fixing a Hole/Heil...

[toddalin]

In the immortal words of The Firesign Theater, "And to think, all I had to do was to put the balls on the other side!"

The following shows the typical nearfield response for the Great Heil. Actually, the differences in the various Heil plots are, at least in part, as to how far the microphone was when taking the reading. The further that the mic is to the diaphragm, the more attenuated the high frequencies relative to the lower frequencies. This is because the higher the frequency, the faster it rolls off due to "atmospheric attenuation." This is not the same as "spreading losses" (i.e., 6 dB per doubling of the distance). Sound energy is lost as it vibrates the air molecules imparting some of this energy to the air, and the higher the frequency, the greater the loss. A "very nearfield" plot (i.e., at the diaphragm) will show more rise between 1 kHz and 10 kHz than shown here.

In the past, I had gone to great lengths to make a "lens" to take out the 10kHz peak, but that portion of the band is still elevated by close to 5 dB ("sound clear as light?").

Then I cross them over at 3kHz to the woofer. But the natural dip at 2kHz really brings down the curve between about 2 and 4.5 kHz creating a "hole" (dip), and the peak just above 1kHz still adds some to the woofer creating a bit of a peak in the band.

I had been putting a piece of sound insulation along the back side of the Heil to remove the rear wave and it's reflection. Using the RTA, I noticed that this "insulation" was creating a reflection that was cancelling the ~6kHz in the near field making the natural dip even worse, but with a very high "Q" factor. Removing the insulation restored the dip.

So, if that's all it takes to change the nature of the sound, what else could be done to the "rear" of the Heil with profound effects on the near field?

Any time you put something along the back of the Heil that interferes with the rear wave that creates any sort of reflection back toward the diaphragm will have profound effects on the nearfield!

I've found that I can "tune" the Heil and push that 2.8 - 5.6kHz up by over 3.5 dB to near flat removing the hole and increasing the order of the crossover below 2kHz by influencing the rear wave. The size, shape, and placement of the "obstruction" will have a profound effect on the frequency response and you really need an RTA to set it up properly.

And what obstruction works? Cut it to size and the material is springy so that you can move it back and forth. I cuts with a kitchen knife. You will get a whole difference response pattern depending on whether you place the flat side or curved side toward the tweeter. The curve will actually nestle right into the tweeter's vee and the flats will fill the space making a perfect fit. And, you cannot get this into a position where it would contact the bridal veil.

https://www.michaels.com/product/24-eva-foam-half-round-dowel-by-artminds-10624918

 

[toddalin]

Of course as we all know, "Without pictures, it didn't happen!"

Without:

With:

 

[toddalin]

Wow! Just Wow!

 

[toddalin]

This picture shows the results of pushing the half round all the way into the rear recess. I think I may just stay with this, or just a hair less, for a while. Note that this also makes the tweeter louder because it brings in more of the frequency band, at least from the front side. Again, this is using a second order Butterworth crossover tuned at 3kHz.

 

[toddalin]

Actually, the microphone is a bit low for the tweeters. I sit with my head just above the pillows.

 

[brianjrealto]

very interesting!
your first image has the Dowel in place with the black acoustic foam across the backside of the Heil. are you removing the acoustic foam piece while the Dowel is in place for your RTA readings?

 

[toddalin]

No, but the foam is very thin and does very little to block the rear wave. On the other hand, when I put a piece of sonic barrier just inside the foam, it definately impacts what happens in front and was actually creating a "suck-out."

I don't want the rear wave as I feel that it is counter to a great soundstage and especially imaging, which as good as it was (best I've heard), got better.

Here you can see how the foam held the sonicbarrier. BTW, the triangular extensions have now been replaced with 3D printed "flairs" and the front baffle, that removed the 10 kHz peak, has been removed.

 

[toddalin]

Interesting... When the RTA's mic was placed in the seating area, the rear-round was creating a dip and new peak where it combined with the woofer. I had to reverse the Heil's phase and move it back ~1/2" to get rid of the peak and get a flat curve through that area. Sounds even better now! It is now out of phase with the woofer (as would be expected) whereas before it was in phase.

 

[jcidave]

Interesting... When the RTA's mic was placed in the seating area, the rear-round was creating a dip and new peak where it combined with the woofer. I had to reverse the Heil's phase and move it back ~1/2" to get rid of the peak and get a flat curve through that area. Sounds even better now! It is now out of phase with the woofer (as would be expected) whereas before it was in phase.

It is interesting to see your comment about putting the Heil in reverse phase from the woofer. I have never tried this but might experiment with it. I know that when Ricky was with ESS, he was recommending moving the Heil back 1 inch from the factory mounting on all the original series speakers. I have also not tried this.
I know on the AMT3 Rock Monitor with the 6.5 inch and 2 - 10 inch woofers that the 6.5 inch is intentionally wired out of phase from the factory. Perhaps an out of phase driver just stands out from the rest of the system.

Was wondering if you can put your finger on the difference in sound you are getting with the out of phase wiring?

 

[toddalin]

It is interesting to see your comment about putting the Heil in reverse phase from the woofer. I have never tried this but might experiment with it. I know that when Ricky was with ESS, he was recommending moving the Heil back 1 inch from the factory mounting on all the original series speakers. I have also not tried this.
I know on the AMT3 Rock Monitor with the 6.5 inch and 2 - 10 inch woofers that the 6.5 inch is intentionally wired out of phase from the factory. Perhaps an out of phase driver just stands out from the rest of the system.

Was wondering if you can put your finger on the difference in sound you are getting with the out of phase wiring?

I will try to get you a visual when I get some time. Know that I have the Heil on a second order Butterworth at 3kHz.

 

[toddalin]

I
Was wondering if you can put your finger on the difference in sound you are getting with the out of phase wiring?

These were taken in the approximate listening spot.

Tweeter in phase with woofer. Note the peak:

Heil out of phase with the woofer. Note the dip. A dip is less obtrusive to the ear than a peak, but the answer may be to keep them in phase and increase the rolloff on the woofer for less overlap. Recognize that results in the seating location will differ from the nearfield measurements of the woofer and Heil and what works in nearfield may be less than desireable in the farfield. I've got more Audyn caps on hand to increase the rolloff and this is what makes it a hobby for me.

 

[toddalin]

Round 2, I knew they were smoother than that.

Anyone who reads speakers tests recognizes that the mic placement with respect to the drivers can be extremely sensitive to small changes in the verticle placement, especially through the crossover area. I reset the mic as shown in the picture, which is more in accordance withs where I actually sit and a bit further out from the cushions.

Here the Heil is in phase with the woofer. For this test, I left the 18" disconnected and this is the JBL 2251J 10" woofer (actually about 9-3/4"). The 18" is all done long before this point and really shouldn't affect the outcome through the crossover area to the Heil. Here you see the peek and dip that I had first alluded to before performing the first photos that smoothed out the dip some.

Again, in phase:

And out of phase. Actually looks pretty good for the location of the mic when considering room acoustics.

 

[toddalin]

This is really an interesting concept in that I am using "destructive interference" and running the crossover points a bit past each driver letting the peaks cancel each other out rather than using "additive interference" and not quite letting the crosover points meet so that peaks are additive with each other.

I know of no other speaker that uses this methodology, but I can tell you that these image better than anything I've ever heard, and I have JBL L200/300, JBL L112s, Altec Big Red Supers (triamped), and Chartwell LS3/5As.

 

[highend64]

Interesting! Where do you have the crossover point set at? Is this a Butterworth or LR network?

 

[toddalin]

Just WOW!!! Soundstage and imaging have now blown the walls and ceiling out! Much of the soundstage and imaging even hold up when you open your eyes! All "glare" (caused by peaks in the upper midrange) is gone!

You can hear the slightest touch of the pan-pot. Every little noise and source equipment hum and buzz is audible. You hear noise gates open and close. Anyone who has never heard fantastic soundstage, imaging, and microdetail is welcome to come by (Orange County, CA) and bring their media, playable on an OPPO 95. SACDs are probably best (and you can really appreciate them), but well recorded Red Book CDs do very nicely.

 

[automojo]

Interesting.
Agreed a much better application then a major alteration to the front.
A number of threads here over the years have gone over the advantages/disadvantages of blocking the rear output of the Great Heil.
(Although none I recall involve directly plugging the rear opening.)
As well as switching the phase of the mid driver.
Kind of a mixed bag as what people preferred, as I recall.
I had mine blocked from the rear for about a year-but went back to wide open.
(I didn't directly block the opening-may be a worthwhile visit-just to hear the differences.)

If your always sitting in your listening chair, the rear dispersion, or lack of isn't a huge deal
But if you tend to move around, the added air from the rear is real bonus IMHO.
While your technically not in the sweet spot, your still benefiting from added detail/air and larger soundstage.
Especially in their current placement, a huge added benefit for my setup.
(The biggest reason I moved from the excellent sounding 3-way ESS PS1220's to the AMT3's was the dipole Great Heil-when done right close to the feeling of a Magnapan , without the huge panels, kids knocking them over, and placement issues)
Porkloin and I conducted together an extensive series of experiments with placement, side, side/back blocking, noting the advantages/disadvantages. Both ended up coming to the same conclusions preferring the wide open Great Heil. And for AMT3 @ current positioning.
Him also mimicking my grill boards with the then stock top side openings.

Glad you found a combo platter that works.
Some really prefer a direct radiator style approach.

I personally don't have a sonic issue w/ESS chosen crossover points.
Blends well with the other drivers I settled on.
Like anything else audio, YMMV.

What seems to draw people to the Heil is it's very natural sounding. Esp compared to many other ribbons. And to keep this even keeled composure at all volume levels.
I can recall more than a few commenting on they were not sure if the Heil was totally accurate, but that it sounds damn good. A ease and comfortable sound to it.

Interesting Oskar apparently was never a fan of ESS's approach using larger woofers, and preferred woofers under 10" dia.
Going sealed, if possible, helps improve the woofers transient response, and helps it blend better IMHO.
It would be interesting to hear a infinite baffle setup with the Great Heil:


One of the bigger differences I have noticed w/Great Heil over the years has to do with cap choice.
Not trying to start a rabbit hole cap argument, but the right cap, just like this experiment, gives you the ability to fine tune your speaker to your personal liking, and maximize the natural sound and ease qualities of the Heil.
Ribbons like the Heil, Emit seem to be very sensitive to changes, and caps play a huge part in the final result.
I recall reading a article on Arnie Nudell, where he mentions Mundorf Supreme's as being his personal favorites at the time.
Myself settled on a 1/3 Superior Z; 2/3 Mundorf Evo Oil mix for the transition driver and Great Heil.
Driven by 35 wpc of KT88 power, superlative IMHO.

 

[toddalin]

I feel that the soundstage, imaging, detail, and clarity are enhanced by not letting a rear wave bounce around the room, off of different substrates, in unexpected ways. My room is large with a sloped ceiling with one speaker in front of a brick fireplace with a full length mirror and the other in front of a wall with large pictures.

When I blocked the rear with the half-round, the soundstage, imaging, and detail went through the roof and I now hear all kinds of things (easter eggs) I never heard before.

But the half round acts as a "brick wall" filter at ~3kHz. The 2251J has its peak at 2,550 Hz and if I let the Heil play lower, it adds to this peak. But the half-round serves as a ??? order filter. The other day I increased the capacitance on the Heil from 4.7 to 7.4 mfd without changing the inductor and the 2,550 peak did not increase, though the area just above increased considerably really flattening out the curve and increasing the Heil's slope.

 

[automojo]

Interesting.
Will have to experiment.
I don't have any issue with detail or imaging as it is.
The dagger for me with the earlier experiment was the lack of air and space.
(The forward presentation was definitely more forceful, then when wide open.)
That Magnepan like quality.
Where you can move about in the soundstage so to speak.
A quality that is a matter of taste for sure.

Like anything else audio, changing one thing usually means a trade off in another area.
But choices are good.
And the cool thing about the Great Heil, is it's design leaves lots of possibilities.
Not too many drivers you can run with decent result dipole or monopole.

Another experiment I would like to try is running the Heil with a higher crossover point, and substituting a dome midrange, for the transition driver, and twin 8" woofers in a large sealed cabinet, so no subs needed.
I know some associate a dome mid with being better for classical or jazz, because of the wider presentation.
I found with my dome equipped Infinities, fire up a track of say, Smashing Pumpkins Rhinoceros with 35 watts of EL34 power. It has all the power and detail and space one could seriously hope for IMHO. Sealed bass and all...
Easily brings back fond memories of those Metro show's @ '89, or Trito's Uptown.......

 

[toddalin]

I had no issue with soundstage, imaging, and detail before the half round. But this adds a whole 'nother level that I've never heard before..., and once you hear it...

Give it a try and let us know your impressions. I got the half rounds at Michaels and they were on sale for 75 cents a stick (one is more than enough) back when. Could just be the best 75 cents ever spent to enhance a set of Heils.

And..., I am wondering if a crossover is even necessary. Some people have reported running their Heils FULL RANGE without failure! I've heard the plates "rattle" when accidently fed bass (luckily(?) did no damage), and am wondering if back loading the driver creates a pressure that could even prevent this. If no crossover is necessary, aren't we better off running without one and it's deleterious effects?

 

[automojo]

Sure.
I let you know.
Not sure on the crossover, but it might be akin to running them in a sealed box.
I have a spare and a few older diaphragms that one could experiment with.
The current OE high pleat (unique to the early production AMT3's) that are in there now I rather not mess with.
They are in perfect shape, never over driven it appears.
Agreed speakers in theory would be better without crossovers electronic or caps .
But I'm thinking you would still have rattling Heils....or not ideal sound. But it would be interesting to see exactly what those cats are doing...
Who knows?
The Heil diaphragms are tough, except to high power over large periods of time.
Eventually over time it either kills them, or reduces their output when the pleats stick together, and get wavy.