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Pete B

Some History On Dynaco Founded by David Hafler and Ed Laurent in 1955

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This page provides some background about how Dynaco was started in 1955:
 

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.
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:
   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.

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The leaky bass vent is described as aperiodic by Dynaco and here is an old

article on the concept:
 
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) | 

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

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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.

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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:

DYNA-A45.JPG

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This "A45" was not sold in the US and was likely a European Scan product, of which there were several. 

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