Pete B

Fixed it in the original post, seems to me the A40 _should_ have been called A35XL for the naming to be consistant. There were also versions with dual woofers with pictures posted on here. The file name is A45 but I'm not sure if that is correct:

Interesting, first I've heard of these.

I wrote if for our local audio club then thought why not here also.

@TheFrugalAudiophile I've been building and designing speakers since I was a kid and I like to study the classics to see if there are any "tricks" or design methods that are not mentioned in the literature. That is my main reason for studying many of the vintage designs. My brother and I as teens read the stereo mags and we debated with my dad about Dyna A-25 s, Large Advents, and we also heard KLH 6 s at the store. We ended up with Advents because the store didn't have A-25 s and they seemed like the best deal. I was given a pair of A-25 s in college in need of repair so I know them fairly well but I bought this pair in order to measure an "Aperiodic" design which I have not yet done other than to read the literature on it. My current view is that they wanted to "cram" that 10" woofer into the smallest box possible which if sealed would have led to a high Fc and High Qtc. The lossy leak lowers the Q but does not really help bass response. It is a non-optimal design IMO. What the A-25 really wants is a much larger box 2 -3 cu ft tuned to 35 Hz with a moderate amount of internal damping. It also needs a modern tweeter. The DeVore Orangutan supports this theory - note that they are tuned to 43 Hz for strong bass for Low E on a bass guitar in the still too small box: https://www.stereophile.com/content/devore-fidelity-orangutan-o96-loudspeaker The A-25 is a very old design and it shows, as are many vintage speakers, both the woofer and tweeter have paper voice coil formers providing very limited thermal capacity. The OLA in contrast has a strong bronze former that will take massive power. Tweeters usually have paper thin aluminum VC formers. The A-25XL has a newer version of the woofer with an aluminum former and a stronger ceramic magnet, many say that they do not sound as good probably because the stronger magnet removes some of the built in baffle step and some contouring of the woofer's response is needed to compensate. The A-25 has a 1.5" tweeter that has very limited output above 12 KHz. A-25s sound reasonably well balanced even though there is no crossover on the woofer probably as a result of the high VC inducance acting to shape the response. I've never bothered to measure the A-25 frequency response or seen one published, but they sound so good that I've always been suspicious of a depression, perhaps large, around 2 KHz. Sure enough, I found a magazine published response and it was there. It also showed the steep roll-off in the bass around 75 Hz. I started a thread here with some history and links to the articles on the A-25, one with frequency response curves: http://www.classicspeakerpages.net/IP.Board/index.php?/topic/11431-some-history-on-dynaco-founded-by-david-hafler-and-ed-laurent-in-1955/ There are 10 dB dips in the frequency response on axis but they go away slightly off axis, so if you position your speakers right it is possible to get a much smoother response. Even with all the negatives about Dyna A-25 s you can get a really nice balanced sound due to them having a tweeter level control and in the right position a smooth midrange. Leaving a bit of the midrange notch can make them "magical" because it seems to match well with what is needed from 2 speakers producing stereo in a home listening room. Just do not expect to Rock out at party levels for hours on end. Use them with a 50 to 100W max amp being very careful on the level and use the power just for peaks. I once started a thread on the Stereophile Forum "When Bad is Good" to discuss how sometimes theoretically correct is not "best" in a home listening space.

The leaky bass vent is described as aperiodic by Dynaco and here is an old article on the concept: https://www.updatemydynaco.com/documents/AperiodLoudspeakerCabinetDesignWW1956.pdf Here is a post on aperiodic venting by Richard Pierce from 1994 on rec.audio.highend the action and reality of a variovent can be accurately modeled using a standard vented model (4th order) with the following adjustments: 1. Since the vent diameter is relatively large and the vent length essentially the thickness of the panel it's mounted in, the actual vent mass is quite low, that results in a box resonance which is much higher than would be considered reasonable for a vented system, which means that a system aligned with such a port would indeed have a very strange response, if it were not for the fact that: 2. With the damping in the vent, the port losses are extremely high, the resulting Qp is VERY low (around 1-2 max), and thus the action of the port at box resonance (at the high frequency it has) is significantly attenuated to the point where the contribution to the system's total volume velocity is essentially attenuated to insignificance. The result is a vented system with a high Fb that has a very low Qb. Such systems, while still technically 4th order, approach 2nd order behaviour at and below resonance for a significant range. What advantage does this have? Well, with normal woofers, it's not clear. It has no efficiency advantage over properly designed closed boxes, it does not have the bandwidth or efficiency advantages of lower-loss vented systems. It might have an advantage when you are forced to use a high-resonance, high Qts woofer (just like some of the woofers Dynaudio makes, for example). But, magic it is not. -- | Dick Pierce | | Loudspeaker and Software Consulting | | 17 Sartelle Street Pepperell, MA 01463 | | (508) 433-9183 (Voice and FAX) |

This page provides some background about how Dynaco was started in 1955: https://dynaco.com/history.php I've not found much written about how Dynaco got started producing speakers and I'm going to emphasize the A-25 here. Greg Dunn had a page on Dynaco but it is now only available in a .pdf. https://us.v-cdn.net/5021930/uploads/attachments/2/7/7/0/8/54784.pdf The vast majority of Dynaco speakers used high quality drivers from SEAS, however there was an early production run of the A-25 that employed Scan Speak drivers. The Scan version is easy to spot having the vent on the top rather than the bottom. Dyna produced 4 main models, all 2-way, that were imported into the US: A-10 very small mini monitor sized speaker A-25 $79 each, medium sized bookshelf, vented aperiodic design A-35 large sized bookshelf, sealed aperiodic design A-50 very large "bookshelf", sealed aperiodic design There are reports of an A-40 and perhaps a few others but they are very rare. All of the above systems employed drivers with ALNICO magnets and paper voice coil formers resulting in limited power handling. The XL series employed drivers with aluminum VC formers and stronger ceramic magnets. I'm only aware of the A-25XL and A-40 versions. The stronger magnets made them about 3 dB more efficient and the aluminum former more resistant to thermal failure. I had never seen a test report with frequency response measurements until recently. Here is a .pdf with reviews of many Dynaco products and 3 of the Dynaco A-25: https://www.updatemydynaco.com/documents/DynacoReviews.pdf from this page toward the bottom: https://www.updatemydynaco.com/#DynacoCatalog1975 Note that one of the reviews has frequency response curves and the on axis curve is not very good having two glaring 10 dB dips in the midrange, however the 30 degree to the left or down correct the problem. The speakers should sound much better upside down placed low or facing forward but to the left of on axis. It is also interesting to note from the frequency response curve that the bass response drops like a rock below 75 Hz. The rolloff is 4th order 24 dB/oct because they are a vented system. Some incorrectly claim a gentler roll-off for open Aperiodic systems but they would be wrong. Some reviewers claimed that the A-25 will produce 30 Hz bass but that would be wishful thinking or mostly distortion. The normal production runs of A-25 s were not "mirrored" with most having the tweeter a few inches right of center. Oddly, my pair of A-25 s ARE mirrored so left toward center of the right speaker, and right of the left speaker should have much better frequency response. It seems that the tweeter needs to be further away and therefore tilting them back should also work for pairs that are not mirrored. I restored my A-25s by refinishing the boxes, recapping with Clarity 5 uF caps that are within 2% of the design value, adding gold binding posts and machine screws to mount the drivers. Tested the resistors for spec value and cleaned the selector switch contacts with Deoxit. Note that they are mirrored by probably coming from different production runs.

My interest in the EPI 100 s started with my brother mentioning that they were recommended by Stereophile, back when they first came out, I also read very positive reviews in the magazines. I think it was a C or D ranking but at least they got a recommendation. I went out to listen to them and they did indeed sound very good. Their strengths are deep bass roughly to the mid 40s, smooth midrange, and a clean extended high end to at least 15 KHz if not 18. On top of it all they sound VERY good and real, like music in the room. Note that there is a version with a tweeter level control and others without, I would always add the level control because they sound best with about 3 ohms in series with the tweeter. Yes, they are bright without the control but there is a simple solution get the correct version or add the level control.

Hi, Yes sure if I have room I'll bring them.

I remember looking at Ken's mod but I have very little memory of it, I think it was simple perhaps film caps but that is just a guess. @kavalski Do you have OLA or NLA s and how many watts?

The original thread for this is here at AudioKarma with impressive pictures of the new place: https://audiokarma.org/forums/index.php?threads/♫-saturday-march-21-2020♫-new-england-winter-frankenfest-in-west-boylston-ma-at-the-masonic-church.898711/ It’s time to get psyched up for will promise to be our must epic event yet! Thanks to Bill aka SpikeDart who found us the site and is our local liaison. We are renting the Masonic Lodge - which is a converted church - This location will only be a few minutes further for folks driving from the masspike. Address: 12 Church Street West Boylston, MA 01583 We have the facility all day so the doors will be open at 10 AM for setup and we’ll wrap it all up by 5PM. Obviously, we’ll be asking people to stay and clean up any mess - we want to be invited back! This is a much larger an nicer space than what we’ve been using most recently in Sutton and it has a variety of areas that can be used for selling and auditioning systems. Admission will be once again be a paltry $5 each - if you’re bringing along disinterested people they’ll be free - but anything you can contribute will certainly be appreciated. You should enter through the front door and pay your admission fee after which you can use the side doors to bring in treasures for sale in the lower level function room. T shirts and sweatshirt orders will be available for pick up just inside the front door as well. There is parking in the side lot, on the street and in the field behind the building. The upper level auditorium area will be used for auditioning systems. There is also a medium sized and smaller side room that can be used for auditioning systems. The lower level will be used for selling and there’s a kitchen area. There are a limited number of tables - if you partake of them only take one - if you can you should bring your own as well. There are a limited number of power outlets - if you need power for a system bring extra extension cords and power strips. Everyone should bring some appropriate snacks/drinks. Alcohol should be OK in moderation - but this hasn’t been an issue in the past and most of us are driving a fair distance so it’s best to watch your consumption. Of course no smoking inside the facility. I will post a Barter Town thread in about a week and link it here.

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Holiday Season price drop over

The early versions of the Paradigm Studio 100 had a pair of 8.5" woofers port tuned to a very low 20 Hz. They have tremendous power handling around 20 Hz but could probably use a little boost there to get the most out of them. There was an excellent review many years ago in Audio magazine. Here is another review: https://www.stereophile.com/content/paradigm-reference-studio100-v2-loudspeaker-measurements

I remember seeing that Peerless but it might have been very early production.

The MGC-2 has a 12" woofer and 6" lower mid! Do you know if the 4" mid was the same Peerless (KO40MRF) driver used in the MGC-1? https://reconingspeakers.com/2011/11/07/peerless-k040-mrf-midrange-repair/

@Jim Pearce I have a working pair for sale, do you still need them?

I have a vague memory of seeing it could have been in the library here or perhaps there was a patent?

That makes sense to add the level controls. It is interesting how different these are from the AR-11 for example that has 10 uF in the tweeter circuit and a bigger inductor on the woofer. The midrange differences are expected since a different mid driver is used.

I'm not sure if I've ever seen the XO schematic. You might ask Ken Kantor, or some of the experts on here. Please post it if you find it.

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Thanks very much!ACOUSTIC SUSPENSION_Audio-1955-Jul.pdf I used pdfSam (free program) to chop out the specific article.

It would be interesting to compare the 58s and 91 crossover schematics in this thread if you have them handy to post. I'm sure that they're around CSP somewhere. Nice job on the rebuild and XO swap by the way!

Anyone have the Magic Speaker .pdf that they could post here? The link to Ken's download is dead.

I always have trouble finding this historic article covering the design behind the AR-1 woofer that started it all. I thought that there was a .pdf but have been unable to find it, here's a link to it in the library here on CSP: http://www.classicspeakerpages.net/library/acoustic_research/special_sections/additional_ar_documents/commercial_acoustic_suspens/commercial_acoustic_suspens.html A few more links with background: Some history at the AES: http://www.aes.org/aeshc/docs/record.../villchur.html Ed Villchur's patent covering his new invention, filed March 15, 1954: http://www.google.com/patents/US2775309 And another link here at CSP on a very fine AR-1 sample: http://www.classicspeakerpages.net/IP.Board/index.php?/topic/8511-historic-ar-1/page/2/

Forgot to mention that I have an unrestored spare 3rd speaker that I will include for parts.