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Hello All,

First post, I’ll do my best to be coherent (so go easy...).   I really could use some guidance and reality checking.  I’m trained as an engineer, so not a complete idiot, but electrical engineering was always confusing and acoustics, somewhat baffling (hah.)

I’m trying to reconstruct the Double Advent system of my high school days, back when my older brother would come home from college and we’d pair up our respective pairs of The Advent Loudspeaker.  Not being made of money, I concluded that rebuilding four speakers was going to be cheaper (well...we’ll see) than buying four refurbished.  Plus, it would be fun.  At this point I plan to drive them with my old but soon to be professionally refurbished, Nakamichi SR-3A receiver.  In high school I had a Dynaco PAT4 preamp and Stereo 80 power amp.  Based on my reading, I’ll probably install Pete B’s BSC circuit into the tape monitor, stuff the cabinets with fiberglass, perhaps add additional braces inside the cabinets.  (Though I haven’t been able to find a thread that indicates exactly why this is helpful, can anybody help?)

I managed to procure four New Advent Utility cabinets and separately, four steel frame, square magnet woofers.  One set of woofers needs refoaming, I’ve purchased the surrounds for these from Rick Cobb (looneytoon2001).  The second set has been refoamed...improperly, to the front of the cone face rather than the rear.

QUESTION 1:  Frankly, I’m inclined to let a sleeping dog lie, but:  Does anyone have experience on the impact on sound quality when the refoam is to the cone front rather than the cone back (on the steel frame Advent woofers)?  If I chose to re-replace the surrounds on the incorrect refoam, does anyone have tips on how to best remove the existing foam from the front face of the cone without damaging the cone?  Being a chemical engineer by trade, I’m not necessarily shy about using solvents (properly), but that would not be my preference.  I know that some of you could probably refoam these woofers blindfolded by now, so I could use your guidance.

So, obviously, I’m on the track of rebuilding four The New Advent Loudspeakers (NLA)and not four The Advent Loudspeakers, (OLA) and this is where it has gotten tricky.  There seems to be a large quantity of original, offset mount fried egg tweeters available, but very few flush mount fried eggs.  Of the flush mount fried eggs that I’ve seen (including the one that I’ve purchased 😒), a fair percentage seem to have decent sized (~3-4mm) holes poked into the diaphragm by the protective mesh or other trauma.  I’m skeptical that such damage can really be repaired.  I’m finding (and maybe to be expected) that there are also a large number of OLA crossover boards available and not too many NLA crossover boards.  Realistically, I plan to completely rebuild the crossovers, even down to the Masonite boards if needed, so that’s really not a showstopper, but finding enough good flush mount tweeters seems to be a problem.

I'm starting to leans towards using the OLA fried eggs instead of the NLA flush mount fried eggs, knowing that I’d need to use the OLA crossover design also.  It seems to me that the only real difference, given my understanding that the steel frame woofers can serve as a drop in replacement for the Masonite woofers, is that the cabinet volume is slightly larger on the NLA due to the baffle being placed a little more forward since the flush mount tweeters don’t need the grill standoffs.  

QUESTION 2:  Is reverting back to the OLA tweeters and the OLA crossovers in the NLA cabinet a stupid idea?  If stupid, why?  

If not stupid, then I have a choice of either mounting the OLA tweeters directly to the baffle, where the tweeter will now stand proud of the cabinet face, requiring standoffs if I want to use the grills and looking a little wonky since the grills will now also stand proud of the cabinet face, or I could perhaps countersink the tweeter assembly by routing 1/4” to 3/8” of depth out of the front face of the baffle where the tweeter mounting flange is located.  

QUESTION 3:  Does countersinking the tweeter assembly make sense?  If I reinforce the tweeter mounting area by solidly gluing a square of MDF to the interior side of the baffle, right behind the tweeter assembly, is that likely to degrade acoustic performance?

QUESTION 4:  My Nakamichi receiver, is rated at 45 W/ch into 8 ohms (minimum), 16 ohms minimum with A+B outputs driven.  I believe that it’s STASIS design may make it somewhat more vulnerable to low impedance loads, but that’s so far out of my wheelhouse that I’ve no idea what to think.  I’ve seen measurements for this receiver down to 2 ohms.  However, I’d prefer not to burn it up and I know the Double Advents, driven in parallel can go to pretty low impedance.  I believe the OLA tweeters and crossovers are better in this sense than the NLAs.  What things can I do to minimize the strain on the amplifier?

Are there other things that I should watch out for?

Sorry for the length of this post.  Thank you for your consideration!

AustinJoeC

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Welcome Joe!

I have some limited experience with the Advents so I'll try to help and hope others will chime in. Pete has a lot of Advent experience I think. Be sure to read this page: http://baselaudiolab.com/ADVENT_LA_XO.html

  1.  It makes no difference, sonically, whether the foam surround is glued front or back so yes--let sleeping dogs lie.
  2. I see no problem with building "new" OLAs (but let's see what others say). On my OLAs I built new crossovers from scratch, using air core coils.
  3. Countersinking the tweeter may cause diffraction problems. Let's see what others say. That very small amount probably won't matter and your grilles will fit.
  4. dunno

The pics below show new inductors compared to the old and a shot of the new xo installed. You can also see the simple front-to-back bracing I added. The more rigid the cabinet the better.Good luck. Watch for other comments and keep us posted (pictures please)

-Kent

 

inductors.jpg

new OLA xo.jpg

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Hi Kent,  regarding the additional bracing you installed; did use any screws, or was it a simply a tight fit with glue applied? If so, which glue did you use?

I still have some very old 'Franklin's Horse Hide' glue left over from my father's collection of tools and related items. I recall building my own speakers cabinets around 1966 and I had used 'Franklin's' glue wherever I was able to, in all the joint corners and along the baffle wherever it met up with the sides and it was as strong as, well, a horse.

I had checked on that same brand a while ago and as I recall it was bought out and is under a different company name with some ingredients removed also so, I'm not certain if it has the same strength. As I recall when you tore apart a section where it was used, it would take a layer of the plywood with it.

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Hi Frank

I used countersunk flat head screws and carpenter's wood glue. I have used hide glue (the new stuff omits the horse) but I think any glue will do.

I do like hide glue. Franklin's is still sold as Titebond: https://www.popularwoodworking.com/article/hide-glue-in-liquid-form/

Kent

braces.jpg

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Nice pics, JKent, and very well constructed project. The adhesive strength of the glue is only of marginal importance here (I've got no horse in this race.... sorry 'bout 'dat....:P), and in this case, two struts may be overkill. The stiffeners look like solid oak, and they act as simple compression struts to minimize any flexure of front and/or rear cabinet panels.

To the OP: welcome aboard, and I assume you are talking about the famous double "stacking Advent" configuration? I am much less familiar with "Large" Advents than I am with the Smaller model, but I believe there may have been several configurations of crossover circuits throughout the history of the OLA and NLA production runs , so this may end up being your stiffest challenge. You may be on a smart track seeking the more available earlier 'offset' tweeters, but before proceeding down this path, you may want to check/confirm the shape and cut-out dimensions for tweeters in your cabinets before purchasing some used drivers that just might not fit the factory prep of your four NAU cabinets. 

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As someone running stacked OLAs....

Question 1:  Rubbing alcohol (90%+ works faster, of course) to clean them up, safely.  I would refoam them all at the same time with the same foams.

Question 2/3:  Not stupid.  Allegedly the woofers between the OLA and NLA perform the same as you noted, and if not the same, darn close.  If you want Large Advent tweeters of some form, the NLA tweeters apparently had issues with their ferrofluid, with some of them leaking or solidifying, and you're struggling to find working ones.  If you can find four that work fine, you're probably golden.  OLA tweeters are easier to find.

Countersinking the tweeters would make me...nervous.  There's speculation (based on tests) that the OLA was built with the grill intended to be the baffle for the tweeter; the tweeter touches it.  Adding grill standoffs would then make the NLA cabs look goofy, so...man, you can countersink the tweeters, I suppose.  It might be okay?  I'm honestly not sure.  It could also cause some deleterious effects from the hard edge around the tweeter.

Question 4:  If BOTH your A and B channels can drive 8 Ohms, you should be okay.  I drive one set on my A's, another set on the B's, and then run them together.  I haven't had any issues yet, but I also haven't tried to really force the issue into painful loudness territory.

About crossovers:  I would go with the Rev.2 crossovers Pete B. spells out on his page, linked to above.  If you're building the crossover from scratch, maybe others have some feedback.

You going to add the decrease/normal/increase functionality?

Another cabinet thought:  make sure you're willing to buy enough fiberglass insulation to properly stuff them.  Someone correct me if I'm wrong, but I believe the current general recommendation is 2 lbs of insulation per cubic foot?

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I've been meaning to do this for quite some time now as I have the same amps, the Phase Linear 400's to use and I have one set of the exact same Advent speakers, a second set would be easy to acquire as they were very popular in the late 1970's when I bought my first pair for $200.

At one point I vaguely recall reading even some 'high-end' purists gave credit to this set-up's quality of sound.

https://www.stereophile.com/content/vintage-stereo

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As noted before, Pete B has a wealth of information on the Large Advent both new and old.  Some seems to be easier to find in this forum, some in AudioKarma.

Now my two cents worth:  From what I've seen the original concept of stacking the Advents was originally for the OLA's with speculation that the distance between the woofers was significant.  Anyone else read or heard this?  The woofer placement on the NLA and OLA are different, with woofers on the OLA being closer to the bottom of the cabinet.  I believe Pete's opinion is the NLA and OLA tweeters are not interchangeable( unlike the woofers), you need to match the crossovers for the tweeters.  The inductors for the woofers are also different.  My experience with stacked Advents and a 5dB BSC proved to overaccentuate the bass.  If you do a BSC you might want to consider either making a few different values or going with a variable one as was done by one AKer.  There is also the question of whether the Advent is a true 8 ohm speaker, running two on one channel can cause problems if the amp isn't up to it.  As I said, my two cents worth.  A bit from experience, most from reading these forums for the last two years and some other searches into the Advents.  Frank, your picture above is awesome.

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The photo is swiped from the internet, all I did was correct the color a bit*.  I do suggest looking for a follow-up thread about that same system pictured.

Although and generally speaking, the Advent is an easy load to drive, I do believe running double speakers on any single amplifier is an eventual recipe for disaster.

Whether 8 ohm and especially 4 ohm will no doubt cause a degree of stress for most any amplifier and is generally not recommended.

I originally purchased my set of Advents in 1978 for a girlfriend at the time, she's gone but the speakers remained, luckily. My summation of their sound was somewhat of a small-scale version of the AR sound though with a touch more high-end frequency offered and also with a punchier bass, though lower bass extension was mostly absent. There in was the problem for me as they could at times sound artificial because of the extra dose of punchy upper mid-bass in my opinion. And the fact that it is still a two-way system and I prefer a three-way made it easier to understand.

Regardless of the speakers used in 'stacking', amble wattage is needed and under powering them is actually futile in terms of 'head-room' and ultimate transient-response with the handling of peaks of any given program material.  Though some here will forcibly insist that almost any amp will do the job, that assumption is not the path to be taken when one is seeking the best in sound reproduction.

Just the other nite, I was as listening to some Oscar Peterson and Eddie 'Cleanhead' Vinson and although the piece was demanding about 75 to 125 watts @ 4ohm RMS for the body of the music at moderate levels of 65 to 78db at 15 feet distance from the speakers, when  'Cleanhead's' alto-sax suddenly came storming in, the meters jumped to around 175 to 250+ watts around 82-87db. Had my amplifiers not been capable of such needed power, the clean and realistic sound would not have been realized. Consequently, the alto-sax came through effortlessly and realistically loud and clear as it would've in real life. If one doesn't have that luxury when powering a true hi-fi system, the peaks and transients meld into a congestion of sound that is anything but realistic and the transients, details, and harmonics, get lost and are not realized or heard as they should be.

Go tell that to some of the low-power using thick-head folks that insist their listening is correct and that all is as it should be.  It's not unless substantial high power is used. And although the Advents in discussion here are relatively much easier to drive, there is no substitution for high wattage. Those who insist otherwise, are missing the point.

*In that photo are what appear to be corner bass-traps. I can understand the bass-traps being used with those little Advents as I've mentioned they have a mid-bass peak and using traps is one way to quell the over-emphasized woofer response. For the past two years I've used similar 'traps' but, mounted on the front-wall of the ceiling corners to slightly subdue what I felt were reflections from a slight over-abundance of 'upper-mid' information from my four stacked AR-LST's in relation of my listening room being 26 feet by 13 feet and my listening position being 15 feet from the speakers. By doing so, using the traps also slightly tightened up the bass which was beneficial in the long rectangle shape of my listening room. I have been thinking of using smaller 'traps' at the rear of the room but, the distance from the speakers to the 'rear' wall has not proved to be too much of a problem though it probably would be something I'd have to try before I'd have an opinion on it.

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Hello All,  Whoa!!  At first, after you post, you see the “views” pile up and wonder if anyone will throw you a bone and respond.  Then, it’s off to the races!

Thank you Kent for the welcome and the advice!  I’m pretty sure I’ve seen your rebuild elsewhere on the site and was very impressed!  The modern inductors seem so much better from a construction accuracy perspective.  I could imagine that one could adjust the length of the coil easily enough to match those to 0.1% (though I most definitely do NOT plan to do that.)  I see that you’ve spaced the inductors beyond the real estate of the original crossover assembly.  Does that help reduce coupling between the inductors?

When I looked at the bracing photo (nice, clean work, BTW) I was struck by the thought that the greatest insult to the integrity/rigidity of the box is to cut a great, honking hole in the baffle to accommodate the woofer.  Has anyone looked at putting a reinforcing ring around the woofer cutout?  I would think that a 3/4” thick x 1.5” wide MDF ring, where the inside radius is flush with the woofer cutout, and solidly glued, would really stiffen up the baffle and minimize any twisting of the woofer.  Though no idea what it would do to the sound.... I’m dangerous like that.

Ra.ra, thanks for the welcome and, having thrown out the phrase “simple compression struts” in casual conversation, I suspect you might have a useful opinion on the above reinforcement question/idea!  

I’ve already had to change directions multiple times on this project as I learn what’s most likely doable, so one of the first things I did was buy a cheap lot of four Advent tweeters (two OLA, one green 2.5” magnet Smaller Advent (are you still looking for that one Pete?)) and the aforementioned damaged, flush mount NLA.  Looks like the mounting holes are a perfect match between the OLA and NLA fried eggs, so at least that’s not going to be an issue.

Ajfink, thanks for the comments and the encouragement!  I believe I’ve also seen the recommendation for 2 lb of fiberglass per cu.ft of cabinet, but I’m going to have to find that thread again.

In the interest of maintaining design integrity, I definitely plan to put the 3 position high frequency switch in.  However, based on what i’ve read about the dangerously low impedance in the Extended position on two pairs running in parallel, I will be scrupulously avoiding that setting...and I will try to avoid window rattling volume levels.

Why the rev 2 and not the rev 3 crossovers?  I’ve always assumed that the rev 3 was probably where they settled because it was the best optimum.

Frank, beautiful setup!  (Though I assume you don’t have any three year olds wandering around ( I KNOW I can climb to the top of that!))

While I agree in principle with your comments about enough power, all I can say is that when we added a second pair of Advents (in 1975) and drove both in parallel with my Dynaco 40 wpc amp, the sound improvement was awesome!  Qualitatively better than the singles.  So I plan to start with the Nakamichi, 45 wpc (which I think is a qualitatively better amp than the hand assembled (by 16 YO me and my Dad) Dynaco), and see what I get!  Still, if you ever get tired of your Phase Linears....

Guido57, I’ve been reading extensively both this site as well as AK, so thanks for the confirmation that these are the best sources.  What I’ve seen is that it’s the positioning of the tweeters (top speaker placed upside down on bottom speaker) that gives the best results.  Still, as a high school kid, we placed both speakers upright and were thoroughly impressed.  

I’m going to have to again find the reference for the variable BSC using the rotary switch.  That was a beautiful rendition of a really nice design.

Thanks again, all!  I will post updates on my progress, though I may not be able to start in earnest until we begin and finish constructing a garage apartment to rebuild and lodge them.  I haven’t pick up a soldering iron in over 40 years...whew boy.

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Pete, thanks for this link.  I’ve seen this previously and it does give me concern.  How much better is the situation, impedance-wise if I’m using the OLA fried eggs and using either the Rev 2 or Rev 3 crossover?  Should I simply not hook them up in parallel?  Are the A/B outputs on a typical receiver a parallel output?  (In which case, I’m thinking, it makes no difference to hook one pair to the A output and one pair to the B output, because they are both drawing from the same source.)

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The OLA doesn't have a serious problem in the tweeter range but the woofer is nearly the

same and you can see that it also dips to 5 ohms or about 2.5 in parallel.

These dips would be fine with a high current amp that does not use any electronic output

protection that might falsely trip and is rated as safe into 2 ohms.  Adcom 5x5 series comes

to mind. 

But I don't know of any receiver that is safe with such loads.

You need a high current amp.

I tested most of my Advents with a 200W/ch Adcom and if you turn it up it is easy to see

peaks of 100W, lower power amps will clip and not sound as dynamic.

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A few thoughts I've had so far and decisions I've made as a result of this thread:

  • I've run my four OLAs - with poly caps and no padding resistors to get closer to the original ESR - with a dedicated amp, my main receiver (a Pioneer Elite), and a Sony receiver (convenience in a number of ways, long story).  With the current Sony receiver, I've run all four on the A outputs in parallel, and now have them all driven on the A and B.  I am unsure if these are parallel on a single amp or have their own dedicated amps.  Obviously, I hope each has its own amp, and I'm leaning towards thinking this is likely.  I'll check.  I've pushed them more than loud enough for my uses but obviously never to failure.
  • I do not care about this Sony receiver.
  • I initially had fuses on all four OLAs (3 amp fast blow), but currently do not.  I may return to doing this at some point.  I never blew any, but I might try 2 amp fuses next.
  • I haven't blown up anything yet, though the topic of having enough power has concerned me greatly since I started out on this journey a few months ago.
  • I just ordered some 0.51 Ohm resistors to put inline with the capacitors in my OLAs :)  Pete's got me spooked/convinced.

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The A and B speaker outputs are typically wired in parallel. There are a few exceptions. You can easily tell because if only one pair of speakers are connected and both A and B are selected, there will be an open circuit and no sound.

Since you have two receivers, I suggest powering each pair from different receivers. That is what I do. I have one receiver powering one pair and the other receiver powering the other. I connect the pre-amp out of my primary receiver to the aux input of the other receiver. This way I can control the volume for each pair to make sure that they are matched.

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7 hours ago, RTally said:

The A and B speaker outputs are typically wired in parallel. There are a few exceptions. You can easily tell because if only one pair of speakers are connected and both A and B are selected, there will be an open circuit and no sound.

Since you have two receivers, I suggest powering each pair from different receivers. That is what I do. I have one receiver powering one pair and the other receiver powering the other. I connect the pre-amp out of my primary receiver to the aux input of the other receiver. This way I can control the volume for each pair to make sure that they are matched.

 Great thought.  The manual does use the word "parallel" to describe the A/B function, but disconnecting one (or one set) doesn't disable any of the rest, so there's likely a little more going on there.

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9 hours ago, ajfink said:

 Great thought.  The manual does use the word "parallel" to describe the A/B function, but disconnecting one (or one set) doesn't disable any of the rest, so there's likely a little more going on there.

Your receiver is set up with parallel connections if you have A and B both selected and then disconnect one set of speakers and the remaining set still plays.

My OLAs are rated at 8 ohms (per the markings on the back). Two pair will result in a load of 4 ohms. Most receivers should be able to handle that at moderate volume levels.

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5 hours ago, RTally said:

Your receiver is set up with parallel connections if you have A and B both selected and then disconnect one set of speakers and the remaining set still plays.

My OLAs are rated at 8 ohms (per the markings on the back). Two pair will result in a load of 4 ohms. Most receivers should be able to handle that at moderate volume levels.

Indeed, the OLAs are rated at 8 Ohms "nominally," but they have pretty deep dips.  Per Pete B. above:  http://audiokarma.org/forums/index.php?threads/advent-nla-input-impedance-warning.830276/

That's NLA testing, but the OLA isn't too far off.

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AustinJoeC: Yes, that "protective mesh" was not very protective. I have never succeeded in adequately repairing the damage done once it's been pushed in. All tweeters I've heard in that condition distort, sometimes badly, even after attempts to repair. 

You seem on the right track, but your biggest problem will not be with the speakers themselves, but will be with insufficient amplifier power, assuming that you will want to play them loud. Remember that you often can cause more damage with too little power rather than with too much and the resulting distortion can be hard on your tweeters.  You might consider using appropriate fuse protection. 

The stacked Advent idea was a response to the already-popular practice of stacking Dynaco A-series loudspeakers. Dynaco included a detailed stacking instruction sheet with every pair.  A very important difference was that the impedance of two Dynas in parallel never dipped low enough to cause trouble. Not so with Advents!  FWIW, I've been using stacked Dynas since 1970 and have never had any problems except for complaints from neighbors. 

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On ‎1‎/‎28‎/‎2019 at 12:57 PM, AustinJoeC said:

I’m going to have to again find the reference for the variable BSC using the rotary switch.  That was a beautiful rendition of a really nice design.

Here's the link if anyone is looking  http://audiokarma.org/forums/index.php?threads/large-advent-line-level-baffle-step-compensation-bsc-build-instructions.647441/page-2#post-10244574

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On 2/4/2019 at 3:40 PM, Guido57 said:

Thanks for this Guido57!  These forums are a goldmine of good information but I frequently find myself having to dig  again to find those nuggets.

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On 2/4/2019 at 1:46 AM, Martin said:

AustinJoeC: Yes, that "protective mesh" was not very protective. I have never succeeded in adequately repairing the damage done once it's been pushed in. All tweeters I've heard in that condition distort, sometimes badly, even after attempts to repair. 

You seem on the right track, but your biggest problem will not be with the speakers themselves, but will be with insufficient amplifier power, assuming that you will want to play them loud. Remember that you often can cause more damage with too little power rather than with too much and the resulting distortion can be hard on your tweeters.  You might consider using appropriate fuse protection. 

 

Martin, thanks for the comments as well as history!  I’m going to move forward under the assumption that a crushed fried egg tweeter diaphragm is just not worth the effort.

Some things don’t change in 40 years...back in my younger days there was the same “debate” about adequate amplifier power.  Seems pretty clear to me though: an underpowered amp imposes an artificial ceiling that the strong transients just scatter off of, creating a mess.  Still, to use the vernacular, “you gotta dance with them what brung yah”.  So the first version of my new vintage stereo will be with my underpowered, but otherwise very nice Nakamichi receiver at moderate levels.

To all:  recommendations on a suitable pre-amp/amp combo for double OLAs?  Pete B has recommended the Adcom 5x5 series for their low impedance stability.  I’m open to both current or vintage.  I’m not made of money, so I’m not averse to buying something that needs repairing (there’s a great repair shop within walking distance...)  That’ll be the second generation.

Joe

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On 1/28/2019 at 12:53 PM, Pete B said:

The OLA doesn't have a serious problem in the tweeter range but the woofer is nearly the

same and you can see that it also dips to 5 ohms or about 2.5 in parallel.

These dips would be fine with a high current amp that does not use any electronic output

protection that might falsely trip and is rated as safe into 2 ohms.  Adcom 5x5 series comes

to mind. 

But I don't know of any receiver that is safe with such loads.

You need a high current amp.

I tested most of my Advents with a 200W/ch Adcom and if you turn it up it is easy to see

peaks of 100W, lower power amps will clip and not sound as dynamic.

Pete, if one were to simply add some series resistance to keep the impedance above, say, 3 or even 4 ohms, does that open up the universe of acceptable power amps that could drive the Double OLAs?  (Recognizing that you’d need a more powerful (?) amp.). If this makes sense, any suggestions of a strategy to implement?

Joe

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On 2/6/2019 at 11:53 AM, AustinJoeC said:

Pete, if one were to simply add some series resistance to keep the impedance above, say, 3 or even 4 ohms, does that open up the universe of acceptable power amps that could drive the Double OLAs?  (Recognizing that you’d need a more powerful (?) amp.). If this makes sense, any suggestions of a strategy to implement?

Joe

That's the idea.  I haven't added them yet, but this is what I ordered in case I do decide to add the resistors to mine:  https://www.parts-express.com/jantzen-audio-051-ohm-10-watt-audio-grade-superes-resistor--255-941

A tiny change, but it would "take the edge off," so to speak.

I haven't added them yet, and am still on the fence.

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