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Old 12th July 2013, 07:48 PM   #21
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This is basically the Dynaco A35 enclosure.
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Old 13th July 2013, 12:22 PM   #22
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Yes, it seems to be a slightly similar design, except that in the A35 the chambers are separated by a kind of cloth-damped slot.

http://p10hifi.net/TLS/classics/imag...-A35-plans.gif

Maybe this damped tube approach might be more useful for those mid-woofers with higher Qts value to reduce the pronounced mid-bass response. This Peerless woofer has Qts value of 0,44. It seems like there might not be much advantage in using this kind of double-chamber enclosure with this particular Peerless unit.
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Old 13th July 2013, 04:01 PM   #23
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Quote:
Originally Posted by dumptruck View Post
This is basically the Dynaco A35 enclosure.
yup a simple resistive port
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Old 13th July 2013, 04:04 PM   #24
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what's that... a 35-38 year ago design?
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Old 13th July 2013, 06:40 PM   #25
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Quote:
Originally Posted by d1030180 View Post
Yes, it seems to be a slightly similar design, except that in the A35 the chambers are separated by a kind of cloth-damped slot.
It's not slightly similar - it's the same. Aside from the specific volumes and tunings, etc., the resistive slot is equivalent to your "20x4 cm cardboard tube stuffed lightly with poly wadding from both ends". A port with some stuff in it is a port with some stuff in it . As for when this type of cabinet would be best, I don't know. I suppose you could look for measurements of impedance, bass response, and driver parameters from an A35 and see what it looks like the benefit was there.
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Old 14th July 2013, 12:36 AM   #26
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dumptruck,

Thanks for your clarification.
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Old 14th July 2013, 02:44 AM   #27
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Quote:
Originally Posted by dumptruck View Post
It's not slightly similar - it's the same. Aside from the specific volumes and tunings, etc., the resistive slot is equivalent to your "20x4 cm cardboard tube stuffed lightly with poly wadding from both ends". A port with some stuff in it is a port with some stuff in it . As for when this type of cabinet would be best, I don't know. I suppose you could look for measurements of impedance, bass response, and driver parameters from an A35 and see what it looks like the benefit was there.
Wouldn't you say that a resistive slot is a type of controlling device very different from the damped resonance of a vented system? Of course what the OP is working with is a different type of vented system as the exit of the port is to a second chamber. I don't understand the meaning of "A port with some stuff in it is a port with some stuff in it".
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Old 14th July 2013, 03:30 PM   #28
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Quote:
Originally Posted by d1030180 View Post
Thanks for your advice. This time I placed the microphone exactly 3 mm away from the dust cup and set the sine wave volume in such a way that the dB meter reading was exactly 100 dB at 200 Hz frequency.

The first chart shows the frequency response in a cabinet with a 40x4 cm cardboard tube that was lightly stuffed from one end.
The second chart shows the frequency response in a 34L sealed cabinet.

The data shows decreased sound pressure level around 44-88 Hz area in the "vented" cabinet, while there seems to be a very slight level increase in the 14-34 Hz area. 100-120 Hz output is also higher in the vented cabinet.
Dynaco, shmynaco, back to the experiment...

Which impedance curve corresponds to which response curve?
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Old 14th July 2013, 05:02 PM   #29
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Here is a composite chart with measurements from 34-litre sealed cabinet (blue, red) and a cabinet vented with 4x40 tube (yellow, green).
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File Type: png Leq+Z.png (160.0 KB, 86 views)
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Old 14th July 2013, 06:43 PM   #30
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Wow - the green line looks like a classic bass reflex Z curve and the yellow line spl dip corresponds with the maximum driver damping from the tuned box. If the port were vented to the outside air, the dip would be a gain in overall spl. Instead the energy is dissipated inside the cabinet.

Nice experiment !

Last edited by 4Torr; 14th July 2013 at 06:49 PM.
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