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New Large Advent - Reverse Engineering - Some Measurements


Pete B

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I finally got around to measuring a pair of New Advents and the woofer inductor is .3 mH (measured about .298 mH @ 1 kHz), .36 ohm. This makes sense because it looks much like the original Large Advent Woofer inductor without the iron. It is air core.

Interesting that the flush mount orange donut tweeter, while looking like the original orange tweeter is very different. Rvc = 2.3 ohm, much lower, and Fc = about 2 kHz, Qtc = about .5. Compared to the orignal with an Fc of about 700 Hz, and much higher Q.

They've moved up the crossover frequency, and the acoustical response of the tweeter plays a much stronger roll. The tweeter response is going to be about - 6dB at 2 kHz simply due to the higher Fc and lower Qtc. This reduces the tweeter's excursion, and they did it to reduce failures.

It should have a very high voltage sensitivity with a 2.3 ohm DCR and in the "extended" position it is driven without any series resistance.

They were in the forward sounding, in your face detail race of those times. The electro-acoustical response of the tweeter high pass is going to be about 3rd order, 1st from the XO, 2nd from the tweeter. They should sound better in the decrease position where there is 2.5 ohms in series with the tweeter.

I have A/B'd 16/16 Rev1 Large Advents with these New Advents and don't like the New.

The New tweeter might work very well with some series R to raise the Q and lower the output, combined with a second order electrical network to get an approximate LR 4th order electro-acoustical response. This would require a full redesign of the XO of course. I do like the New Tweeter better, except for the high Fc.

Pete B.

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Thanks for your comments Doug.

I'll comment about your question from the other thread here:

The original larger value probably provided a small amount of baffle step compensation, and a lower XO point. I believe they lowered the inductor value to raise the XO point and provide higher system voltage sensitivity by removing any compensation that the larger inductor provided. I've not fully measured the XO responses so this is just a theory for now. They were going for loud which sells in show room demonstrations.

I know a top notch engineer who worked at Advent at the time, and he told me this story years ago, when I mentioned that something did not sound quite right with the Large Advent. Their goal was a decent sounding system that would sell - be loud and detailed in showroom demos.

Do people really believe marketing literature?

My brother and I spent a good amount of time listening to the early Large Advents, 16/16uF Rev1, around the mid 70s. He was I think 20 and I was mid teens, and he said flat out, something isn't right in the midrange. I noted that they were a bit boxy sounding, and the high end extension was not quite there. I also noticed that there was something right about them, that the driver integration was very good, never sounding like part coming from a woofer and part from a tweeter, not coming in and out of phase as you moved around the room or stood up/sat down. He agreed about the integration but said they had too much midrange, not real or natural sounding. The Advent marketing literature said they were the best sounding speakers in the world, or something like that. We both laughed about it and said what a load of BS. They certainly had their strengths and were a lot of speaker for the money.

We had both built our own speakers by this time.

Pete B.

>I stand corrected.

>

>Do you guys think that the inductor value was lowered this

>much to let the woofer roll off more on its own rather than

>being "forced" by the higher value of the original

>Advent?

>

>Doug

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I mentioned in the previous post that the driver integration was very good with the early Large Advent. This was something that was lost in the New Large Advent, they are less focused and the sound does change much more going off axis. The driver integration is not as good.

I measured the woofer XO transfer function and it is as if the inductor does almost nothing. The woofer response is about 2.7 dB down at 10 kHz, it's only -1.5 dB at 2 kHz. They might as well have left it out if this was the type of response they were looking for. This does pass a sanity check since the woofer inductance usually limits the attenuation rate with simple first order networks.

This design is so bad, that I'm tempted to do a quick redesign because I think it has a lot of potential.

Pete B.

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Guest kaiser_soze

Pete,

Once every couple of months or so, I take a look at this forum to see if there is anything interesting going on. The last few times that I have done this, after reading one or two of your posts, I decided to leave. The same thing has happened just now, but this time I'm going to say something before I leave. The thing that I don't understand, is why you think it appropriate for you to portray your subjective assessments of the way a certain speaker sounds, as equivalent to objective fact. That is not something that I would do. I remember that in the first post of yours that I read, you talked about how one speaker "blew away" another speaker. That sort of language just turns me off. I don't object to you or anyone else having subjective opinions about the quality of the sound of any particular speaker. What turns me off is when you portray those subjective opinions as being one and the same as objective fact. The reason that turns me off is that it absolutely implies that if my subjective opinions are not in agreement with yours, then as far as you are concerned, you are right and I am wrong. I am going to go away now for another couple of months, and if and when I ever do return, I will be pleased if perchance you have ceased the habit of portraying your subjective assessments of speakers in a manner that implies that they are the equivalent of objective fact.

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>Pete,

>

>Once every couple of months or so, I take a look at this forum

>to see if there is anything interesting going on. The last

>few times that I have done this, after reading one or two of

>your posts, I decided to leave. The same thing has happened

>just now, but this time I'm going to say something before I

>leave. The thing that I don't understand, is why you think it

>appropriate for you to portray your subjective assessments of

>the way a certain speaker sounds, as equivalent to objective

>fact. That is not something that I would do. I remember that

>in the first post of yours that I read, you talked about how

>one speaker "blew away" another speaker. That sort

>of language just turns me off. I don't object to you or

>anyone else having subjective opinions about the quality of

>the sound of any particular speaker. What turns me off is

>when you portray those subjective opinions as being one and

>the same as objective fact. The reason that turns me off is

>that it absolutely implies that if my subjective opinions are

>not in agreement with yours, then as far as you are concerned,

>you are right and I am wrong. I am going to go away now for

>another couple of months, and if and when I ever do return, I

>will be pleased if perchance you have ceased the habit of

>portraying your subjective assessments of speakers in a manner

>that implies that they are the equivalent of objective fact.

Hi Tom;

When I fist looked at your write-up, I thought, what can I do to try to make a difference here.

I then went away, to leave it for someone else to comment.

This really bothered me, enough, that I came back to try to do something at least.

First off, thank you very much for writing your concerns, instead of just disappearing again.

This site with it's numerous forums, is kept alive and well, by it's members that do write.

I am not a technical person, and I am ok with that.

There is a variety of members here, men and women, from all walks of life, and from all over the world.

The range here is from, English as a second language, novices and very technically oriented members.

I do get lost in some of the more technical articles.

If I see something that I can add to or shed a different light on, I do try, at times.

I am sometimes proven wrong, on issues that I feel strongly about.

Another persons perspective sometimes opens my eyes.

I am still learning.

If you just go, then we can not gain by your interest in this very nice and very interesting hobby.

When you see something that you feel is incorrect, just say so, we won't bite your head off.

Likewise if you feel you can add to a topic, please do so.

Everything here can be discussed in a friendly and adult manner.

By you just going away, we all lose.

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>Pete,

>

>Once every couple of months or so, I take a look at this forum

>to see if there is anything interesting going on. The last

>few times that I have done this, after reading one or two of

>your posts, I decided to leave. The same thing has happened

>just now, but this time I'm going to say something before I

>leave. The thing that I don't understand, is why you think it

>appropriate for you to portray your subjective assessments of

>the way a certain speaker sounds, as equivalent to objective

>fact. That is not something that I would do. I remember that

>in the first post of yours that I read, you talked about how

>one speaker "blew away" another speaker. That sort

>of language just turns me off. I don't object to you or

>anyone else having subjective opinions about the quality of

>the sound of any particular speaker. What turns me off is

>when you portray those subjective opinions as being one and

>the same as objective fact. The reason that turns me off is

>that it absolutely implies that if my subjective opinions are

>not in agreement with yours, then as far as you are concerned,

>you are right and I am wrong. I am going to go away now for

>another couple of months, and if and when I ever do return, I

>will be pleased if perchance you have ceased the habit of

>portraying your subjective assessments of speakers in a manner

>that implies that they are the equivalent of objective fact.

Sorry that my style irritates you, however there are many things

that irritate me such as not duplicating my experiment using the

same speaker design, or even building the circuit at all. Then

you object when we do not agree, we're not even doing the same

experiment and it is you who needs to do the work. Let's just

agree to disagree, and let's take this discussion to another

thread:

http://www.classicspeakerpages.net/dc/dcbo...g_id=1281&page=

Pete B.

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  • 2 weeks later...

Thinking more about a XO redesign, and it is clear that the New Advent crossover is at least as high as 2 kHz given the acoustical response of the tweeter. I'd like to move this to 1.5 - 1.8 kHz and a LR 4th order could probably be tricked out of the existing tweeter by using an electrical network with slight peaking around 2 kHz to help recover some response. It would still be non-ideal, with some droop around 2k but this is close to the BBC dip area and can sound quite good.

I like the Advent 10", I think it is the best acoustic suspension woofer that works cleanly up into the midrange. The original Advent tweeter has some serious limitation, primarily top end extension, the New Advent tweeter does not reach low enough. I've been pondering what might be the best tweeter. The best from the same time frame that I might look into is the EPI inverted dome tweeter. A modern version of this tweeter is currently being hand made at Human speakers, but it has been modified with an aluminum dome:

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

It was tested and was very good in many ways, but does not have a very flat amplitude response:

http://206.13.113.199/ncdiyaudio/mark/Test...002_tweeter.htm

I wonder if the original EPI tweeter was flatter?

This tweeter has an Xmax of .76 mm one way and can handle a low crossover point being of rugged design.

A tweeter that is about 3 dB down at 1.5 kHz, with low distortion and flat response is what's required. I would choose the Vifa D26NC55 as a modern pick however it is being discontinued. The North D2506-S would work well with the chamber plugged to raise Fs, however it also will not be available to the public in the near future. The SEAS 27TDF would probably be the one, would have to look closer.

The best of the best might be the later Jensen, Large Advent woofer:

http://www.classicspeakerpages.net/dc/dcbo...1283&page=#1325

combined with the original EPI tweeter.

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Guest One-Shot Scot

>I have A/B'd 16/16 Rev1 Large Advents with these New Advents

>and don't like the New.

>

>The New tweeter might work very well with some series R to

>raise the Q and lower the output, combined with a second order

>electrical network to get an approximate LR 4th order

>electro-acoustical response. This would require a full

>redesign of the XO of course. I do like the New Tweeter

>better, except for the high Fc.

>

>Pete B.

I A/B'd New Advents with their original crossovers with New Advents which had original crossovers containing new poly caps and new resistors. I didn't like the speakers with the original crossovers.

I then A/B'd New Advents featuring the partially-rebuilt crossovers with a pair of New Advents featuring new crossovers that I built from Jantzen 0.33mH a16 GA copper foil inductors, poly capacitors and Mills resistors. I didn't like the New Advents with the partially-rebuilt crossovers.

All speakers had very good quality original drivers and all of the woofers had been re-foamed with factory-style surrounds.

Now I am experimenting with sound dampening materials for the inside of the cabinets. So far, every upgrade that I have made has resulted in a better sounding New Advent loudspeaker system. I thought the original New Advents sounded great and now I think they sound even better.

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  • 1 month later...

Some members have asked for the New Large Advent crossover schematic:

Please note that one woofer measured well below 4.5 ohms and while it is not far off, I've measured several Large Advent woofers and all the others were very close to 4.5 ohms:

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

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  • 2 months later...

These turned out to have stained grille cloth and I decided to remove it and, well tossed it in the washing machine. Big mistake, came out half the size of the original. Dry clean only, should have known.

It seems that Advent was fairly consistent I have early, 1973 LAs, later, New LAs, and Advent/1s. They're all about 16-17 threads per inch, of material that looks like a light and very open burlap. I'd say higher quality than burlap, but does not seem to be linen.

The LAs are a light tan color, the Advent/1s are a bit more brown making them look about right for a barn.

Anyone know of a source that best duplicates the thread count, texture, and color of the original Advent material?

I've looked locally, at several stores that did not have very good selection. It seems difficult to find that very open weave.

I don't need perfection, would not mind going more on the light color side.

Going to look on e-bay next.

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Thanks, I have been looking on ebay and will check that out.

Thinking now, after looking, that the original cloth might have been a natural linen.

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  • 3 months later...

>These turned out to have stained grille cloth and I decided

>to remove it and, well tossed it in the washing machine. Big

>mistake, came out half the size of the original. Dry clean

>only, should have known.

>

>It seems that Advent was fairly consistent I have early, 1973

>LAs, later, New LAs, and Advent/1s. They're all about 16-17

>threads per inch, of material that looks like a light and very

>open burlap. I'd say higher quality than burlap, but does not

>seem to be linen.

>The LAs are a light tan color, the Advent/1s are a bit more

>brown making them look about right for a barn.

>

>Anyone know of a source that best duplicates the thread count,

>texture, and color of the original Advent material?

>I've looked locally, at several stores that did not have very

>good selection. It seems difficult to find that very open

>weave.

>I don't need perfection, would not mind going more on the

>light color side.

>

>Going to look on e-bay next.

I did not have much luck on e-bay. And it seems that cross stitch materials have the most open weave, however most that I've found still are not as open as the Advent material. I notice that the Advent material has a low thread count as I noted above as about 16-17 and a thread material that is thinner than most that I've found.

Two possiblities that look good but are far from exact are Charlescraft Fiddler's Lite, 14 ct., 100% Cotton which comes in a few light colors such as oatmeal.

Another is Regency AIDA 18 ct., 100% Cotton Cross Stitch Fabric, again far from exact.

It seems that a lower count such as 14 makes up somewhat for the larger thread that is typically used.

I would not use these for a perfectionist restoration, however many craft stores carry these and people can look and decide for themselves.

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  • 3 weeks later...
  • 3 weeks later...

This pair of New Large Advents were given to me by a friend who said he had them in college. He said that the woofers were refoamed by one of the top pro names. And as you'd expect they were probably driven hard in those days.

I have mentioned the woofers here in other threads, the dust caps are wrong, the foam is too stiff and not as wide as it should be. The drivers have an Fs well over 20 Hz and needed to be replaced. The in system Fc is far out of spec being over 50 Hz.

I purchased original looking woofers on ebay, and refoamed them myself obtaining a free air resonance of 15 to 16 Hz:

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

I expect these to work well and they measure well in system with a correct Fc of about 41-42 Hz.

The original tweeters had high Fc values well above 2000 Hz, one as high as 2900 Hz, this is too high:

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

I purchased more tweeters on ebay and the next pair had Fc's of 1826 and 1987 Hz, both had a DC resistance of 2.13 ohms, very low but these seem to be a good pair.

All these new drivers are going into this pair of speakers.

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I finally have a system finished with the "new" drivers that I mentioned above.

All the cabinet joints were reglued, with a bead also run around

the crossover board.

The original 13 uF caps were replaced with 13 uF polys in series with .47 ohm 5W resistors to approximate the ESR of the original electrolytics:

http://www.classicspeakerpages.net/dc/dcbo..._id=1000&page=5

All connections were resoldered, and all crimp connections were soldered. I cleaned and soldered the riveted switch lugs, and the riveted lugs on the tweeter:

http://www.classicspeakerpages.net/dc/dcbo...689&mesg_id=707

The thin hook up wire was replaced with 16 gauge Carol wire and soldered directly to the driver terminals.

The original foam was put back in the enclosure.

The grills were recovered with new material as mentioned earlier

in this thread.

I consider this to be a stock rebuild, with no intention to alter the original voicing.

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The DC resistance is quite low being around 2.1 to 2.3 ohms in most samples of the New Large Advent tweeters. I have been meaning to measure the system input impedance for some time now as I expect it to dip very low in the tweeter range. The original Large Advent tweeters have a DC resistance of about 3.9 to 4.2 ohms which further supports the theory that the New is too low.

New Large Advent Serial #U396308:

System Input Impedance grill on (recovered with new material) :

Switch DECREASE 29.5 at 41.9 Hz, 12.9 at 807.7 Hz, 5.5 at 6226 Hz

Switch EXTENDED 29.2 at 41.9 Hz, 12.7 at 842.1 Hz, 3.16 at 6491 Hz

Switch NORMAL 29.5 at 41.9 Hz, 13.8 at 807.7 Hz, 4.13 at 6226 Hz

The fundamental resonance can be seen by the large peak at 41.9 Hz, the change in the impedance peak in the extended position is due to the fact that the woofer inductor is shorted out in this position.

It can be seen that the impedance dips to 4.13 ohms at about 6.2 KHz in the Normal position and therefore the system should be rated as 4 ohms.

It dips to a dangerously low 3.16 ohms at 6.4 KHz in the extended position where all of the Advent resistors are shorted by the switch. Note that this dip would have been 2.69 ohms if I had not included a .47 ohm resistor to match the electrolytic ESR. This is dangerously low, many amps will have a hard time even with the 3.16 ohm load and I suggest not using the "extended" position. The system is far too bright in the extended position anyway.

Now imagine stacked New Large Advents wired in parallel, the impedance would dip to about 1.6 ohms with the original electrolytic or a poly with series resistance added. This is far too low and might explain why so many amps in the 1970s often went up in smoke.

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New Large Advent Serial #U396308:

System Z grill on (recovered with new material) :

Switch DECREASE 29.5 at 41.9 Hz, 12.9 at 807.7 Hz, 5.5 at 6226 Hz

Switch EXTENDED 29.2 at 41.9 Hz, 12.7 at 842.1 Hz, 3.16 at 6491 Hz

Switch NORMAL 29.5 at 41.9 Hz, 13.8 at 807.7 Hz, 4.13 at 6226 Hz

Removed grill (this grill was recovered with new material, switch=normal)

woofer peak now = 31.9 Z max at 41.9 Hz

With original 1972 Advent grill woofer back to 29.9 at 41.9 Hz

Note that the change in impedance peak with the grill on or off indicates that

it makes a slight change in the system Qtc. The new

grill material is very similar to the early Advent material. The

change in system Qtc can be seen in the following System T&S measurements:

=========== Switch Normal ===========

--- No Grill | New Grill | Advent Grill

Fc = 41.62, 41.36, 41.36

Qtc = .883, .864, .878

Qec = 1.07, 1.06, 1.07

Qmc = 5.13, 4.69, 4.81

Re = 5.45, 5.46, 5.46

=========== Switch Extended ===========

--- No Grill | New Grill

Fc = 41.63, 41.41

Qtc = .833, .826

Qec = .995, 1.00

Qmc = 5.12, 4.74

Re = 5.11, 5.11

Note that the system electrical Q (Qec) is lowered with the switch

in the extended position where the woofer inductance (DC resistance) is shorted out.

The system mechanical Q is lowered by the acoustical resistance of the grill material as

can be seen in the reduction of Qmc. Qec and Qmc are the two system parameters

that determine the total system Q (Qtc). Note that there is also a very slight mass

loading by the grill as can be seen in the slight reduction in Fc with the grill on.

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In case anyone is curious about the accuracy and calibration of the LAUD test system that I use, let me offer this:

I have a 3 ohm 1% test load that measures 3.00 ohms on a Fluke

Multimeter.

It measures ruler flat across the audio band when measured with LAUD.

There is slight gradual phase error just visible at 20 kHz probably due to filter mismatch in the sound card.

Moving the cursor from about 5 Hz on up reports 2.99 to 3.00 ohms up to 10 kHz, worst case error is 3.03 or .03 ohms at 20 kHz. This is obviously 1%.

For reference a medium gauge clip lead adds .06 ohms to the measurement.

The phase error is typically .1 degrees, should be zero, and gradually reaches -3.1 deg at 20 kHz, also an excellent result

for a low cost measurement system.

The frequency is derived from the crystal controlled clock on the sound card and should be highly accurate and repeatable.

The sound card is an improved version specifically for use with LAUD.

I believe that it has upsized coupling caps to provide flat amplitude and phase response below the audio band.

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Guest speaker freak

I to had to replace my cloth for my large advents i found some burlap type material and my local fabric store it was the closet that i could find and it is a pretty good match.

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I measured the other system with the "new" drivers mentioned above, but all the original caps and wiring as a comparision to the recapped unit:

New Large Advent Serial #U396378 WITH ORIGINAL ELECTROLYTIC CAPACITOR:

System Z grill on (recovered with new material) :

Switch DECREASE 5.5 at 6226 Hz

Switch EXTENDED 3.17 at 6491 Hz

Switch NORMAL 4.17 at 6491 Hz

Here is the other data repeated from above for comparision:

New Large Advent Serial #U396308:

System Z grill on (recovered with new material) :

Switch DECREASE 29.5 at 41.9 Hz, 12.9 at 807.7 Hz, 5.5 at 6226 Hz

Switch EXTENDED 29.2 at 41.9 Hz, 12.7 at 842.1 Hz, 3.16 at 6491 Hz

Switch NORMAL 29.5 at 41.9 Hz, 13.8 at 807.7 Hz, 4.13 at 6226 Hz

I don't think I could ask for better agreement and this demonstrates how important it is to use a resistor to duplicate the electrolytic ESR.

Pete B.

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