Large Advent - Best of the Best - IMO - Pete B.

[Pete B]

I'd been thinking for some time that I should do a how to build

the best Large Advent thread, what parts to use and so on. I had

hoped that the New Large Advent tweeter would be close enough to

the old that it could be used with the old crossover, however this

is not the case due to it having a much higher Fs. My conclusion

is that I don't like either tweeter. Some have used the Jensen

standard dome replacement tweeter to replace the older red donut

tweeters, however, having seen a 5012 crossover I notice that a 3rd

order network is used that protects the dome tweeter from low frequency

energy. I don't believe that it's a good idea to just drop the

newer tweeters into the old systems which have first order, and

second order networks.

Pondering what to do lead me to the EPI tweeter, which according to

the Human web site has an Fs of 1380 Hz and a Qt of about .9:

http://www.humanspeakers.com/diy/parts/002.htm

I like this tweeter, the original at least, and the parameters are good for

an electro-acoustic fourth order Linkwitz-Rily crossover at about

1500 Hz. I happen to have a pair of Genesis 2 speakers here which

I've read have the same tweeter, however, I measure an Fs around 2 kHz

and a Qt of about .5. This is not good, and I'm not sure if Genesis

altered the design or if the parameters have changed over the years.

The EPI tweeter is of robust construction and has the highest Xmax

of any tweeter that I know of, and I always thought it sounded good.

The EPI 100 used just a simple 10 uF capacitor to the tweeter for a

first order crossover.

The Advent woofer and EPI tweeters were exemplary low cost driver

designs, both outstanding in their day.

The Genesis speakers are leaving in a few days, so I'm going to take

a quick shot at a crossover for this hybrid. I do have my eye on a

pair of EPI tweeters and will measure them to determine the parameters.

I do believe that I'll end up with a modern tweeter due to limited

availability of the older EPI tweeter. Here's a picture of the hybrid

that I'm working on:

The masonite Genesis tweeter requires no cutting but it

does require new screw holes, each tweeter covers the holes of the

other, nice. Note that this woofer has the wrong dust cap, and

stiffer foam, it will be replaced soon. I always wished that the EPI

100s had the bass of the Large Advents.

I prefer the New Advent box because it moves the drivers closer together.

I have a minor preference for the masonite woofer, which

has a longer VC former and an inverted edge, but it requires cutting

to fit in the new box, the grill might also not fit. The New Large

Advent woofer is close enough for now:

http://members.aol.com/basconsultants/PLB-ADV1C.jpg

[Pete B]

I quickly worked out a new crossover for this hybrid.

It sounds good at moderate levels but there is

something seriously wrong with these woofers.

I've noted that their surrounds are too stiff and they

have the wrong dust cap. They bottom

when driven hard without really producing much bass.

I tried both woofers with the same results. I finally

brought out an early Large Advent with a masonite woofer

that I refoamed. It at least gives a hint of that hit

you in the chest type of bass, none of that from the poorly

repaired woofers.

My guess at this point is that the

New Advent Woofers were refoamed in a way that set the

rest position further back and allowing them to bottom

more easily. I've got a pair of New Advent Woofers that I

have to refoam and will use them in these speakers.

I'll try to get a better idea of what's wrong with the other

woofers when I have some time and/or the interest.

[dynaco_dan]

Hi Pete;

This ii a very interesting project that you have started, thank you.

I will be following it along, until it's completion.

Good work and good luck, Pete.

[Doug G.]

Pete,

The repairer didn't glue the surround on top of the cone did they? That would push the rest point further back I believe.

Does the spider look like it's pushed in at rest?

Doug

[Pete B]

>Pete,

>

>The repairer didn't glue the surround on top of the cone did

>they? That would push the rest point further back I believe.

>

>Does the spider look like it's pushed in at rest?

>

>Doug

Hi Doug,

No it's not on the top - glued to the back of the cone.

Just checked the spider with a straight edge, by eye it looks to

be at least 1/16" back. The edge looks like a standard .5" wide

10" type, very different from what I see in the original foam.

1/16" is significant considering that the full linear throw is

.25" as far as I remember.

I remember the VC wind height as being .75" has anyone looked at one

recently to confirm this?

[Doug G.]

I don't know about the wind height as I've never had a VC out of these but I know a couple of mine have the spiders recessed at the inside a bit like you describe. These are masonites, however.

It doesn't seem to affect the operation although I imagine if I really pushed them it might.

As Vern said, keep us posted on your progress.

Doug

[Pete B]

Original masonite large advent woofer cone and VC, and to

answer my own question the wind height is 5/8". I have a spread

sheet for calculating the motor characteristics based on the

physical parameters. The Large Advent woofer has an Xmax of only

.13" or 3.3 mm, and Xmax50 of .313" or 7.9mm and a mechanical limit

of .62" or 15.8 mm. A headroom figure that I like to calculate is the ratio

of mechanical Xmech .62"/ linear Xmax .13" = 4.8 or expressed in dB: 13.6 dB.

Also interesting is that the theoretical

motor strength reaches zero at an Xmax of .5" before reaching the

mechanical Xmax figure, nice work. This is a very well thought out

motor. However, the linear Xmax is much lower than I thought.

For years I thought it was linear Xmax that made this such an outstanding

woofer, when in reality it is the large mechanical limit and headroom.

Also interesting

about 4 turns were left off the top layer on the cone end only

which is a way to provide better symmetry in the motor, it was

not done in the AR-11 woofer that I examined:

http://members.aol.com/basconsultants/ADV_VC1.jpg

[Craig25]

That backside of the speaker cone looks like some of the original "mash" of slurry that Henry concocted.

[Pete B]

The cone looks to be of similar construction as the AR-11 woofer, and I believe that it is a modern manufacturing technique, perhaps vacuum formed. It looks like normal paper from the front, but has the irregular pattern on the back.

Forgot to mention that the original Advent woofer has longer than typical voice coil former. This offers more voice coil heat sink area.

[Pete B]

The Genesis tweeters are gone as they left with the speakers.

A memeber here has helped me out and I now have a pair of EPI tweeters.

I wondered years ago if Genesis had licensed the EPI design or simply stolen it. I do remember hearing the story that while they obviously taylored their speakers after EPI, they did their own design work at Genesis. It is clear that the Genesis and EPI tweeters are different. The EPIs have a paper dome, and a soft cloth suspension whereas the Genesis have what seems to be a heavier, phenolic impregnated cloth and the suspension seems to be stiffer. I'm going to measure the EPI tweeters some time soon.

There is a fellow (Brian Levy) on the Audio Asylum board who worked at Genesis as the companies controller and he confirms this story:

Posted by Brian Levy on January 07, 2005 at 10:16:25

In Reply to: Re: Huw worked at Genesis, not EPI posted by DavidLD on January 7, 2005 at 09:46:14:

Actually, the companies did not share componnts as they were separate and distinct with seperate development departments. The inverted dome tweeter was developed by EPI and later Genesis sort of borrowed the design and made their own version. In the beginning some of the EPI investors backed Genesis but by the early 70s George Samuels was in control and there was no love between the companies. Genesis went out of business in the 80s and the name was bought by another company and sold Genesis speakers but these had no technology relationship with the originals.

I would connect them only in the fact that they used the inverted dome technology and both were in NH. Other than that not really connected.

Here's the post where Brian Levy states that he was controller for Genesis Physics:

Re: Brian, a little off topic... - Brian Levy 18:30:19 04/13/04 (3)

In Reply to: Brian, a little off topic... posted by rodney on April 13, 2004 at 10:22:18:

Started in electtonics in my father's store in 3rd grade- 1953. Touched the HV on a picture tube standing in a puddle of water in his repair shop. From there learned the trade, weekly member of the local ham radio club, held several tickets before a teenager. Rebuilt from scratch a Motorola console tv/radio/phono. Weekly trips to Boston where I met some of the "founders" who knew my uncle, a sales rep for electronic tubes and parts. Started hussling, running with the crowd, a couple of years in NYC at RCA tech and learning interesting things about direct drive 8 track motors produced by Lear Jet. Moved on to sales and management at Cramer Electronics in the Boston area that eventualy was bought out by Olson Electroncis, then a short stint in Boston as a manager for Tech Hi-Fi, bought 4 Tech franchises, sold them went on to finish A.Sc. in Business Management, B.Sc. in Accounting. Controller for a couple of companies including Genesis Physics in Newington; them to Florida and law school and an interesting case involving a Japanese patent suit against British companies related to the bi-amp internal crossover which sort of brought my interests back into audio as a hobby. Teen years were great since I kicked around between Boston through NY corridor with some great older friends who are now the legends so often spoken of here. Sadly, as I found out during the Japanese law suit, all were dead or just shy of it.

That's it in a nutshell.

[Pete B]

I've mentioned in this thread that the woofer shown in the picture seems to have a problem. I purchased new used woofers and refoamed them with RSSOUND foam and paying close attention to correct placement of the foam. The new woofers are the ones pictured in this thread where I discuss how I positioned the foam:

http://www.classicspeakerpages.net/dc/dcbo..._id=1386&page=2

They have a very low Fs of about 16 Hz (the woofer pictured above with the incorrect foam has an Fs that is over 20 Hz) and I decided to measure them in this system through the woofer crossover which should only introduce a small error. While this is a New Advent box, I used fiberglass from an original Advent since I believe that fiberglass is a better damping material. Here are the in system measurements with the fiberglass as stuffed for this thread:

Fc 40.6

Qe 1.0

Qm 3.3

Qtc .78

Rmin 5.5

Qts is rather low at .78, it should be closed to .9 and I decided to take a look at the stuffing material. These New Advent boxes have the vertical side braces and what I found was that the fiberglass hit the brace and little if any made it past the divider, thus keeping it pushed up against the back of the driver. I pushed it past the divider, and evened it out as it should be, then retested:

Fc 42.4

Qe 1.1

Qm 4.7

Qtc .88

Rmin 5.9

I have stated for a long time that pushing the damping material up against the back of the driver lowers the system Q, and this is a clear demonstration.

This probably contributed to the poor performance of the previous woofer, the lower Qtc causes less bass output at Fc, and more excursion below resonance. This was not a large difference but certainly measurable, and we should keep in mind that a Qtc of .707 is - 3dB at Fc, whereas a Qtc of 1.0 is 0 dB down, 3 dB is a large difference.

Also note that Fc is correct as designed being in the low 40s, the woofers pictured had an Fc of over 50 Hz that was clearly incorrect.

[dynaco_dan]

Hi Pete;

Nicely done report, thank you very much.

It is amazing to see what just placement of the fiberglass does to those numbers.

The amount of insulation and the internal dimensions of the enclosure haven't changed, just it's location, but a really interesting project.

[Pete B]

Hi Vern,

Thanks for commenting.

I'm about ready to but these back together as close to original

as possible. I'm going to put this hybrid on hold, given the issues

I found here with the Genesis and EPI tweeters:

http://www.classicspeakerpages.net/dc/dcbo...g_id=1782&page=

It would be interesting to try the Human speakers reissue of the

tweeter but I don't expect to do it anytime soon.

Probably makes more sense to use a readily available tweeter from

Seas or Vifa.

These are going to go back to original with a good set of drivers, poly

cap in the crossover, and foam back in the box.

I do enjoy finding the box resonance and Q to be correct and to

bring the system back as close to original performance as possible,

just to have an accurate demo unit.

All the best!

[Pete B]

I just weighed the above cone/voice coil assembly on a scale and it is 34.9 grams. The RSSOUND edge is 5.8 grams and a reasonable approximation would be that half contributes to the moving mass since part of it does not move.

[Pete B]

I'm using some of my Advent left over parts to build a pair of speakers with my youngest son. Nice rainy day summer project with him. So, I've got another shot at the best of the best here. I don't have an extra Advent box, but we have one that is close enough and will do. I have masonite woofers, and New Advent tweeters which I prefer, for now until I test them more, for their ferro fluid, extended high end, and ease of mounting. As complete stock systems I prefer the original not New Advent.

I quickly did a crossover the way it ought to be done, in my opinion anyway. 2nd order electrical XO forming roughly 4th order electro-acoustical crossover at about 1.5 kHz.

It sounds very good, excellent, and I'm A/Bing them to Vandersteen 2Ci's as a reference. It sounds so good, better than the Vandersteens, and I'm tempted to turn up the volume during testing, however, it seems that there is significant thermal compression in the tweeter. I adjust the tweeter pad to match the two systems at the beginning of a listening session, then find part way through that a different setting is required.

Come back the next day giving them time to cool and the Advent is much brighter. Play a few cuts turned up and they seem to be matched again, probably about a 2 dB difference estimated here. 1.5 kHz is very low for a 3/4" tweeter, so this is not surprising.

I've noticed this before in A/B testing where one system might have a woofer with much higher thermal capacity. Match levels, then after a few cuts it's no longer matched due to one heating up much more than the other.

I'm probably going to end up with the North D25 as the best inexpensive tweeter for a best of the best design.

Anyone else notice this with the New Advents?

[Pete B]

>It sounds very good, excellent, and I'm A/Bing them to

>Vandersteen 2Ci's as a reference. It sounds so good, better

>than the Vandersteens, and I'm tempted to turn up the volume

>during testing, however, it seems that there is significant

>thermal compression in the tweeter. I adjust the tweeter pad

>to match the two systems at the beginning of a listening

>session, then find part way through that a different setting

>is required.

>

>Come back the next day giving them time to cool and the Advent

>is much brighter. Play a few cuts turned up and they seem to

>be matched again, probably about a 2 dB difference estimated

>here. 1.5 kHz is very low for a 3/4" tweeter, so this is

>not surprising.

This thermal compression issue in the tweeter was operator error, so far I've not been able to reproduce it, sorry don't want to start any rumors.