Some results for aperiodic build QA-25

[lasse]

Hi all,

(Continuing from build thread:

http://techtalk.parts-express.com/sh...d.php?t=228431)

Today, I got some measuring results for you to see and to comment on.

Obviously, I have managed to reduce the impedance-peak to plactically none at all. If this is good or bad, we´ll se. The overall SPL is about as could be expected, I gusess, but with one exception and that is the "trouble" in the nearfield-measurement abot 600 Hz. Any thought what that can be???

I even replaced the driver to check if there was something wrong with it, but in that case, both my chosen drives suffer from the same decease.

XO-point to tweeter 2-2.2 kHz???

I have one problem and that is related to method: Nu method for pulling the T/S-values isn´t operative on this system ( I get to measure impedances at so low freq. that my system isn´t reliable) so I can´t figure out Q for the system. Is there another method for measuring or simulating the Q?

Please chime in and comment, I´m on unchartered ground here (at least for me) which is great fun.

Regards//lasse

[lasse]

On the other hand, I got some "normal" results when aiming the mic between the driver and the vent (I know, there isn´t supposed to come sound from the vent but still...)

Best regards and I really need advice by tomorrow (Swedish time). Should I continue with tweeter mounting or do something radically about the vent or....

//lasse

[Pete Schumacher ®]

What Feyz said.

Also, the anomaly is showing up in the impedance plot as well. So, if it's stuffed well and it's not standing wave reflections, then it's most likely a cone flex or suspension resonance.

[lasse]

Hi and tanks for the feedback.

Yes, I guess that you have to consider that this woofer is more than 40 years old and the design is even older so......

The main thing at this point is to establish that the ap-vent arrangement seems to work as thought and the best sign of this is probably the impedance-plot.

I will carry on with the tweeter installation today, will go for the Dynaudio D260´s (not 40 but abt 15 years...)

Will be back

Best regards//lasse

[lasse]

Hi all,

The project of cloning the Dynaco A-25 to my system, the QA-25 is moving along (but I have to ask anyone of you skilled in the use of Speaker Workshop, how to interpret some of the results)

I have assembled one unit and made complete Imp and SPL measurements on both drivers in box and also on the two drivers connected in parralell for AC-measurements.

In the attached picture, the right hand side is a condensation of the AC-simulation. I focus on the area of XO, abt 500-3000 Hz and have pulled the drivers in depth compared to the "connected" one. One strange thing can be seen. The situation in the pic is as close to eachother as I can get and this happens when I assign +0.75" to the woofer. As I understand the sign-convention, this means that the woofer is pushed backwards, but this isn´t logical. The tweeter should be pushed. (See the pic of the speaker)

The upper left side shows the SPL for the two drivers in-box with the same gating and with 1/12 octave smoothing (all measurements has been made using the same gating) I think that a 2000Hz XO is a good startingpoint.

Can anyone explain the sign-convention used in SW?

Regards//lasse