The New Advent Loudspeaker Review (Vintage Speaker)

[SDX-LV]

Probably meant to be used near or even on a wall, that adds bass support.

Probably meant to be used with a tube amplifier that has significant roll-off on highs as well?

 

[mhardy6647]

I'll be getting a pair of Dynaco A25's in for testing this weekend. The owner wants me to replace the crossover components (a cap and some resistors). I won't be able to send one to Amir, but I will take lots of measurements. As I recall, the woofer had a big rubber surround and usually doesn't need repair.

Yeah, although (FWIW) in my experience with the Dynaco loudspeakers (i.e., SEAS woofers, in most cases, and if memory serves*): 1) the surrounds more than occasionally will suffer partial detachment from cone and/or frame (reparable, of course, but careful alignment is required) and 2) VC dragging is fairly common, too.


DSC_9644 by Mark Hardy, on Flickr
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* maybe ScanSpeak -- or maybe ScanSpeak, too? I forget & I am too lazy to check today.

 

[Dennis Murphy]

Yeah, although (FWIW) in my experience with the Dynaco loudspeakers (i.e., SEAS woofers, in most cases, and if memory serves*): 1) the surrounds more than occasionally will suffer partial detachment from cone and/or frame (reparable, of course, but careful alignment is required) and 2) VC dragging is fairly common, too.


DSC_9644 by Mark Hardy, on Flickr
_____________
* maybe ScanSpeak -- or maybe ScanSpeak, too? I forget & I am too lazy to check today.

That's the larger varient of the A25--the A50? It looks like the same drivers in a bigger box. The woofers on the two I just got in are in great shape. I've listened and compared, and have taken a lot of measurements--I'll post later today.

 

[jkasch]

IIRC, the A50 had two 10”. I’m thinking A35.

 

[Dennis Murphy]

IIRC, the A50 had two 10”. I’m thinking A35.
View attachment 143388

Right you are.

 

[Dennis Murphy]

Well, I ran into a little snag in measuring the A25 woofer parameters--the woofer was sealed with glop rather than a gasket, and I haven't been able to get it out yet. So I'll just post my impressions of and measurements for the whole speaker system.

I'll preface this my saying both speakers are in excellent condition. The owner is a prominent recording engineer (he does the broadcast recordings of the chamber music series from the Phillips collection in Washington, D.C.) and used these as on-site monitors back in the day.

Overall sound: I think most of you would be pleasantly surprised. Heard on their own, they are quite balanced with no glaring colorations. They are certainly a step up from the Advent I sent Amir, although no match in the deep bass. The bass isn't very extended, but reasonably tight with a bit of a "whump" in the midbass. The upper highs are quite smooth, and the midrange is full with no nasal quality. However, there is a lower treble, upper midrange peak that smears the detail in that range, which becomes quite evident when you switch to a modern design with a fully optimized crossover and smaller woofer. In comparison, the midrange on the newer design is much more open and detailed, and more relaxed at the same time. The more complex the musical material, the more obvious this is. But still, if you just walked into the room I don't think anyone would hold their nose and ask to switch speakers. I think the best description of the sound would be "pleasant and quite enjoyable, but lacking in midrange detail."

Here are some measurements of the on and off-axis response, all with the 5-position treble switch to the "Normal" position and no grill (the grill doesn't make that much difference because there are already sharp diffraction-inducing raised edges on the cabinet). I'll give bass measurements and comments in a second post.

 

[Dennis Murphy]

And here's the system impedance and a nearfield measurement of the woofer. The last plot is a nearfield of the New Advent loudspeaker that I took, followed by a copy of the impedance measurement Amir made of the Advent. Two findings stand out. First, the Advent has way deeper bass response. That's due in part or mostly to the Advent's larger cabinet and to the aperiodic loading slot in the Dynaco, which introduces leakage in what would otherwise be a completely sealed cabinet. Although the aperiodic loading is intended to lower the box tuning impedance peak, it's interesting that there isn't much difference between the Advent and the Dynaco in that regard. The Dynaco peaks at about 17 Ohms, the Advent at 18 Ohms. Both peaks are lower than what I measured in a sealed design I just finished using the Scan Revelator 7" woofer, but I'm not sure what the practical difference would be even for a tube amp. I think the main point of the aperiodic tuning was to allow use of the large 10" Seas woofer in the small Dynaco cabinet.

 

[mhardy6647]

That's the larger varient of the A25--the A50? It looks like the same drivers in a bigger box. The woofers on the two I just got in are in great shape. I've listened and compared, and have taken a lot of measurements--I'll post later today.

The A-50 has two of the woofers in a very large (floorstanding) enclosure.
I believe the one whose image I posted (which is, in fact, half of a pair) to be an A-35.
As an aside: I found them on the swap pile at the Harvard (MA) town dump many years back. The woofers had the aforementioned issues and I ended up having to replace one of them.
The A-35 has an internal aperiodic vent between the woofer and tweeter sections -- as I believe was mentioned earlier in this thread.
They're very nice loudspeakers -- as is the A-25. Coupla pairs of the latter here, too. Everyone should have, or at least spend some quality time listening to, a pair (IMO, of course).
There is a modern "reboot" of the A-25 using current drivers -- it's not inexpensive, though.
http://www.seas.no/index.php?option...eas-a26-kit&catid=66:seas-diy-kits&Itemid=250

 

[Aperiodic]

Interesting stuff.
Yes, A-35 was a slightly larger version with a sealed two-camber cab, the divider containing the port.
A50 had two 16Ω woofers paralleled.

It occurs that a couple A25s, for the right price, might make a good low-buck system with a 'budget' modern sub. IIRC I saw the 'A26' for, what, $2500 a pair?!? Not competitive at that price. A 'cheap & cheerful' eBay or thrift shop find, OK...

Advent's literature discussed the driver size/cab size choices. The basket they used was big enough for a 12" cone but they made a 9" custom cone. Definitely went deeper than the A25, but with the right sub.

I opened my A25s back in the day and coated the baskets with plasticlay as suggested by Frank van Alstine. Opening them was intimidating but not that difficult, I can understand why Dennis might be reluctant to open speakers that aren't his, but it's the only way to access the crossover cap. Speaking of diffraction, a thin layer of plasticlay on the front panel might alleviate that a bit. I'd be careful not to let any on the grill cloth though- you'd never get it off (or run the speakers without grilles).

Thanks to Dennis for the data. One question, the phase plot for the A25 looks more uniform or does that have someting to do with the graph?

 

[eddantes]

I had a set of bullnose Advents... I never warmed up to them and eventually went through 3 pair of A25s: 2 originals and one XL. Still own a set of originals. Funny that the low end never impressed on the Advents and yet on the A25s I always felt a nice robustness. I wonder why my impression doesn't jive with measurements - unit variation? Probably, just a faulty memory.

 

[mhardy6647]

Yes. They did this on the production line for each speaker, according to Dynaco literature of the time (which I have unfortunately long since lost.)

Box tuning peaks are indeed present on every box speaker but there is a difference- to an amp- between an 8x peak and a 2x peak. Is it that farfetched to suppose that that might make a difference, especially to a load-sensitive 30WPC transformer-coupled tube amp?

Heh, tracked it down.

 

[Aperiodic]

mhardy6647 you are my hero... I have been searching for that for years. I don't see that page in the linked material though- which doc was it in?

Not an 'urban legend' after all, eh? Maybe that's why it still gives a decent account of itself > 50 years after its introduction- and why you can't reproduce the results using homebrew, 'seat-of-the-pants' methods....

Interesting that those who have expressed an opinion here seem to prefer the 25, considering that the Advent sold for quite a bit more during their parallel lifespans.

 

[mhardy6647]

mhardy6647 you are my hero... I have been searching for that for years. I don't see that page in the linked material though- which doc was it in?

Not an 'urban legend' after all, eh? Maybe that's why it still gives a decent account of itself > 50 years after its introduction- and why you can't reproduce the results using homebrew, 'seat-of-the-pants' methods....

Interesting that those who have expressed an opinion here seem to prefer the 25, considering that the Advent sold for quite a bit more during their parallel lifespans.

It's a 1971 Dynaco catalog scan. You can just download the catalog via the link at the bottom of that page. Free registration required to download hifiengine's content -- and well worth the effort (IMO). Lots of good and useful stuff there, old and new.

PS It may seem as though I have no life, but that's not the case at all. I do have a life -- just a really boring one.

 

[Dennis Murphy]

Interesting stuff.
Yes, A-35 was a slightly larger version with a sealed two-camber cab, the divider containing the port.
A50 had two 16Ω woofers paralleled.

It occurs that a couple A25s, for the right price, might make a good low-buck system with a 'budget' modern sub. IIRC I saw the 'A26' for, what, $2500 a pair?!? Not competitive at that price. A 'cheap & cheerful' eBay or thrift shop find, OK...

Advent's literature discussed the driver size/cab size choices. The basket they used was big enough for a 12" cone but they made a 9" custom cone. Definitely went deeper than the A25, but with the right sub.

I opened my A25s back in the day and coated the baskets with plasticlay as suggested by Frank van Alstine. Opening them was intimidating but not that difficult, I can understand why Dennis might be reluctant to open speakers that aren't his, but it's the only way to access the crossover cap. Speaking of diffraction, a thin layer of plasticlay on the front panel might alleviate that a bit. I'd be careful not to let any on the grill cloth though- you'd never get it off (or run the speakers without grilles).

Thanks to Dennis for the data. One question, the phase plot for the A25 looks more uniform or does that have someting to do with the graph?

Heh, tracked it down.

View attachment 143440

I don't have the technical background to evaluate this, but it would be great if someone with expertise in woofer design could chime in. I did manage to get the woofer out and test its free air parameters. The Fs is 31 Hz, or about 10 Hz higher than the Advent woofer. The Qts is .93, so this is definitely a true acoustic suspension woofer. They don't make them like that anymore.

 

[Keith Conroy]

I don't have the technical background to evaluate this, but it would be great if someone with expertise in woofer design could chime in. I did manage to get the woofer out and test its free air parameters. The Fs is 31 Hz, or about 10 Hz higher than the Advent woofer. The Qts is .93, so this is definitely a true acoustic suspension woofer. They don't make them like that anymore.

Is it possible to post all the TS parameters you measured. Did you do a mass added test to get VAS etc......?? Someone earlier put a nice link to a speaker kit by SEAS. As I understand it, this is supposed to be a modern copy of the A-25. The spec's of the SEAS woofer used are quite a bit different then your measurement. The QTS is ".39 " ........FS is 25hz. The EBP product on the woofer you measured is quite a bit lower then the current SEAS woofer being used in the re-make. So they both fit a sealed box profile but your woofer fits better. I wonder if the motor system on your woofer has lost some energy over time.? However High 'Q"'s were the order of the day in many woofers designed during that time period. Sealed box design was more popular back then also. I'm trying to remember when exactly TS data came on scene?? I don't know the MFG. date of the A25's from xxx date to yyy date?? So while we now routinely look at TS data, during the time period I'm not sure engineers did? As I remember in the 1970's TS data in design was very very new. The companies Koss and Electro-Voice were some of the 1st companies that advertised TS engineering in their designs. I point this all out because if you didn't have TS data available you were designing speakers in a different way. If it's helpful I will post full TS data on the current SEAS woofer used in this kit. ANYWAY THANK YOU DENNIS FOR ALL YOUR WORK!

 

[Dennis Murphy]

Is it possible to post all the TS parameters you measured. Did you do a mass added test to get VAS etc......?? Someone earlier put a nice link to a speaker kit by SEAS. As I understand it, this is supposed to be a modern copy of the A-25. The spec's of the SEAS woofer used are quite a bit different then your measurement. The QTS is ".39 " ........FS is 25hz. The EBP product on the woofer you measured is quite a bit lower then the current SEAS woofer being used in the re-make. So they both fit a sealed box profile but your woofer fits better. I wonder if the motor system on your woofer has lost some energy over time.? However High 'Q"'s were the order of the day in many woofers designed during that time period. Sealed box design was more popular back then also. I'm trying to remember when exactly TS data came on scene?? I don't know the MFG. date of the A25's from xxx date to yyy date?? So while we now routinely look at TS data, during the time period I'm not sure engineers did? As I remember in the 1970's TS data in design was very very new. The companies Koss and Electro-Voice were some of the 1st companies that advertised TS engineering in their designs. I point this all out because if you didn't have TS data available you were designing speakers in a different way. If it's helpful I will post full TS data on the current SEAS woofer used in this kit. ANYWAY THANK YOU DENNIS FOR ALL YOUR WORK!

I didn't do a mass added measurement for Vas, but I will tomorrow. I've worked with the modern Seas"replacement" woofer, and while it does work sealed, it's not an acoustic suspension design. The mechanical suspension isn't compliant enough for that. I'm not aware of any major woofer manufacturer that is marketing acoustic suspension designs today. Although the woofers in my A25's look to be in excellent operating condition, the electrolytic tweeter cap has drifted out of spec. It's supposed to be 5.0 uF, but measures 6.2 uF. I'll be replacing that with a poly cap.

 

[Keith Conroy]

Related to the Dynaco company test spelled out in their advertising literature quoted above. Of course David Hafler was one of the principals behind Dynaco. He was also an amplifier designer. So he clearly must have seen some value it the test as spelled out related to load??? In general a woofer with a QTS of .93 is probably not going to have a high BL product. So this does not help speaker control.

 

[anmpr1]

Related to the Dynaco company test spelled out in their advertising literature quoted above. Of course David Hafler was one of the principals behind Dynaco. He was also an amplifier designer. So he clearly must have seen some value it the test as spelled out related to load...

As an aside, from a 1999 published interview (Vacuum Tube Valley, No. 15) with David Hafler:

I always thought the speaker market was a good one. First, it is an easily produced item with a high profit margin. Also, when somebody buys one of your products chances are you could sell them a complimentary product if he was happy. I always thought we were going into the speaker business, not to manufacture speaker drivers, but to buy raw speakers, breadbox them, and handle it from there on.

I was going to Denmark regularly to handle Dynaco’s distribution of B&O products. There was a small company called SEAS who did a nice job and had good quality. We found their prices reasonable and started having them make speakers for us. I think we outgrew SEAS… we were selling 1,000 speakers a week during the 1960s.

A fellow named Skoning [designed the A25]. Another fellow came along with the idea for stuffing fiberglass in the bass reflex port to make the bottom-end more damped. The way he did it worked well and we paid him a percentage for the first 10,000 speakers… I can’t remember the exact details. So he took the credit for designing it even though he and Skoning actually worked out the parameters jointly. It came down to two final designs. The two of them looked alike, had essentially the same specs, but sounded different. We sold at least a half million of them.

 

[rdenney]

...Interesting that those who have expressed an opinion here seem to prefer the 25, considering that the Advent sold for quite a bit more during their parallel lifespans.

I think you mean that Advent sold more of them. They were certainly not more expensive in real dollars (remember the high inflation of the period--even a couple of years change prices significantly).

The expressed opinions could be related to a lot of effects that are important now but weren't in the early 70's. One is that TS designs have become the norm since that time, really not until the early 80's unless I'm misremembering, and our ears have become accustomed to less bass from speakers in the absence of subwoofers.

Here is Gordon Holt's review of the Dynaco A25, primarily compared to earlier designs:

https://www.stereophile.com/content/dynaco-25-loudspeaker

His review of the Advent from two years later, previously linked (see Page 23, Spring '71 Stereophile) in this thread, included the following paragraph:

In terms of price, of course, the Advent speaker invites comparison with the Dynaco A-25, which we reported on three issues ago. The A-25 has somewhat more transparency than the Advent, a very slightly forward sound (by comparison), a somewhat rougher and not-quite-so-extended high end, somewhat lower efficiency, and rather less capacity for producing deep bass at high listening levels.

I'm thinking Dennis's and Amir's test results are not contradicting Holt's reviews at all, but those differences may certainly reveal why some were prefer the Dynaco today. Transparency, as Holt describes it, which I think of as crispy-fried treble that I've heard from electrostatics, is more consistent with modern tastes, I think. But the more extended bass, somewhat less forward emphasis on the treble (though my Advents were generally quite flat in terms of spectral tilt in my room, measured with REW or with an RTA).

Rick "this was the OLA, not the NLA, though I'm not sure that would make a difference" Denney

 

[mhardy6647]

This Dynaco/SEAS discussion has been great! But...
Out of fairness to this thread and its subject (and to our host -- and FWIW!), I think... we should start a Dynaco loudspeakers/Dynaco A25 thread
We also should get one to @amirm to test (assuming one isn't wending its way West even now)
I do have four of them in the basement -- but all are "original condition" and one seems to have a dead tweeter

The Fs is 31 Hz, or about 10 Hz higher than the Advent woofer. The Qts is .93, so this is definitely a true acoustic suspension woofer. They don't make them like that anymore.

I don't know if that is or isn't the case, but this seems like a propitious time to mention*... umm... the "new" KLH 5, which claims to employ acoustic suspension for its woofer alignment.

https://klhaudio.com/model-five-pair/

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* or, perhaps, to "mention again"