Pete B Posted February 2, 2020 Report Share Posted February 2, 2020 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. Quote Link to comment Share on other sites More sharing options...
Pete B Posted February 2, 2020 Author Report Share Posted February 2, 2020 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) | Quote Link to comment Share on other sites More sharing options...
Aadams Posted February 2, 2020 Report Share Posted February 2, 2020 @Pete BThanks for doing this. Quote Link to comment Share on other sites More sharing options...
Pete B Posted February 3, 2020 Author Report Share Posted February 3, 2020 I wrote if for our local audio club then thought why not here also. Quote Link to comment Share on other sites More sharing options...
Martin Posted February 5, 2020 Report Share Posted February 5, 2020 Pete, I have also seen "reports" of an A40, but those reports are not correct in that no A40 model was ever sold in the US. There was no A35XL, but there was an A40XL which was, more or less, an A25XL in a larger enclosure that was very similar to the A35 enclosure. Quote Link to comment Share on other sites More sharing options...
Pete B Posted February 5, 2020 Author Report Share Posted February 5, 2020 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: Quote Link to comment Share on other sites More sharing options...
Martin Posted February 9, 2020 Report Share Posted February 9, 2020 This "A45" was not sold in the US and was likely a European Scan product, of which there were several. Quote Link to comment Share on other sites More sharing options...
ChrisM Posted February 10, 2020 Report Share Posted February 10, 2020 A robust discussion of the Aperiodic topic if one cares about the nuts and bolts: https://www.diyaudio.com/forums/multi-way/115810-model-aperiodic-boxes.html A interesting application of it by a respected designer: http://www.troelsgravesen.dk/JBL_L100_08.htm Quote Link to comment Share on other sites More sharing options...
TheFrugalAudiophile Posted February 20, 2020 Report Share Posted February 20, 2020 Quote A robust discussion of the Aperiodic topic if one cares about the nuts and bolts: https://www.diyaudio.com/forums/multi-way/115810-model-aperiodic-boxes.html For those of us with no engineering expertise, it's tough to follow. The question is, how does it sound? Natural, musical, etc. Well, at least that's my two cents. Quote Link to comment Share on other sites More sharing options...
Glue Posted February 26, 2020 Report Share Posted February 26, 2020 Living close to Denmark I was naturally torn into this sheet ! Great info ! Quote Link to comment Share on other sites More sharing options...
Glue Posted February 26, 2020 Report Share Posted February 26, 2020 Has anyone heard of a 30X - should be a A25 without the vent ? Quote Link to comment Share on other sites More sharing options...
Glue Posted March 13, 2020 Report Share Posted March 13, 2020 On 2/26/2020 at 9:52 PM, Glue said: https://www.flickr.com/photos/187315959@N06/49644344698/ https://www.flickr.com/photos/187315959@N06/49644871921/ https://www.flickr.com/photos/187315959@N06/49644869201/ Quote Link to comment Share on other sites More sharing options...
Glue Posted March 23, 2020 Report Share Posted March 23, 2020 So here we go ! The Dynaco 30XL as they were sold to me seem very much being A 35 after all ? The chamber interestingly is parted in a dampened 30x27x20 part and a similar sized empty upper cabinet housing nothing but the tweeter . The port to the upper is covered with a cloth. The gunk old stone wool had been reused when rewired - not sure if the caps are still original ... I wonder if any one has altered these in specs? Most of all I require the Inductance of the coil please! Any information would be greatly accepted - ? https://www.flickr.com/photos/187315959@N06/49690960332/in/dateposted-public/ Quote Link to comment Share on other sites More sharing options...
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