Problem with Audax Pro 13 Kit

[phibes]

Last year I built the Pro 13 Kit using Audax's TWO25A16 tweeter and HM130CO bass/mid. The design when finished sounded good and was slightly coloured in the bass, which at low SPLs gave good detail and character for a small speaker - 8 litre enclosure.
The problem I encountered was that when I introduced even moderate volume in bass passages (not necessarily very low, but energetic) the bass driver would clap out violently. After trying a reduced internal volume and extending the port vent, I resorted to using a 250uf bipolar capacitor in series with the inductor. This fixed the clapping out behaviour but to the detrement of the low end character that the speaker originally exhibited. I didn't mind as most of my subsequent listenning has been in a second system with the assistance of a 300mm Audax sub and they performed admirably in that set up.
I have loaned them to a friend to use and he actually had borrowed them prior in their original configuration. He has no sub and is dissappointed this time around as he really enjoyed them in their original form.
I can rewire them back to their original configuration, however, my question is if I reduce the value of the capacitor in series, will that take me back toward what I had originally? Any suggestions would be much appreciated.
Cheers

[Bill Fitzpatrick]

You would have to increase, not reduce, the capacitor value to increase the bass. The greater the capacity the closer you would get to the original.

[phibes]

Thanks Bill,
Obviously I got the advise to use the 250uf cap and it did work in filtering the bass. Any suggestion as to the value of the cap in series that would get me some way back to what I had?
Cheers,
Keith

[Bill Fitzpatrick]

Depends upon the impedance of the woofer. 1000mfd might get you close.

But, face it, you probably were just exceeding the speakers limitations. Maybe your friend wouldn't be so heavy handed with the volume control and you could leave out the cap altogether.

[sreten]

1000uF sounds the right ballpark.

Suggest you use 4 x 250uF in parallel with one speaker
and experiment till you get the right value, then you''ll
know how many 250uF's you need.

For this sort of alignment its normal to tune the reflex port
higher than usual so it booms a little, the series capacitor
will then bring the bass back to flat - retuning the port
should allow the use of the smallest series capacitor without
losing too much bass, whilst maximising low bass rejection.

The technique is not used often due to the cost of decent
capacitors (a parallel film type bypass will improve midrange)
but was exploited in the original Wharfedale Diamond.

sreten.

[phibes]

Thanks for the info Sreten and Bill. I'll experiment with the port and the additonal capacitors and see what results I get. I could return to the original configuration easily, however, the volume levels at which the bass driver clapped out were not high at all. In their original form, about 98% of the music content was fine accept for the odd deep or energetic bass passage that would cause the bass driver to go into maximum excursion.
Cheers

[Bill Fitzpatrick]

Turning down the bass control on the pre would accomplish pretty much the same thing and no need to fool around with caps.

[sreten]

Originally posted by Bill Fitzpatrick
Turning down the bass control on the pre would accomplish pretty much the same thing and no need to fool around with caps.

Good point. With your average Baxendall bass controls should
approximately work as it has a variable turn over frequency.
(Unlike Baxendall treble controls)

It will be less effective, but will help.

As with the capacitors, higher tuning of the port will allow
a little more bass cut to be applied (some bass cut will be
needed unlike the flat case) without losing too much bass.

If you go this way I suggest shorten the standard port length
by half - this will give a 3dB peak at 100Hz - which corrected
by the tone controls should give higher power handling.

sreten.

[Svante]

Originally posted by sreten



Good point. With your average Baxendall bass controls should
approximately work as it has a variable turn over frequency.
(Unlike Baxendall treble controls)

As with the capacitors, higher tuning of the port will allow
a little more bass cut to be applied (some bass cut will be
needed unlike the flat case) without losing too much bass.

sreten.

The opposite would also be true, if you apply a bass cut, the risk is that your friend just turns the bass up, and the effect will be pretty much nothing.

[sreten]

Originally posted by Svante


The opposite would also be true, if you apply a bass cut, the risk is that your friend just turns the bass up, and the effect will be pretty much nothing.

Quick off the mark and quite true, however I've since edited my post

Turning up the bass on my suggested misalignment is not a good idea.

sreten.