Paramour II - MagneQuest upgrade

[paulw]

In re-reading this thread, I thought of another thing. The BH-5 Magnequest transformer has some teflon in it, in places that are sonically significant. It may take longer to break in fully than a more old-fashioned design. I'd expect the difference if any to be more in the very high frequencies, but of course how these subtle things manifest subjectively is sometimes surprising!

Yes, I got that point from trawling through the archives - just sitting tight playing music and movies for now & waiting for some extra MagneQuest magic to arrive - as I'm sure it will ;

[paulw]

Well the MagneQuest magic has indeed arrived - the upgrade is worth every penny.  However (there always is a 'however' isn't there) bass output is considerably more articulate and seemingly deeper and this is giving me a bit of a problem as I'm perhaps 'overspeakered' for my rather small room with three way corner horns rated at 102db/w with 15 inch bass units.  The better bass is coupling with the room a bit to well!  Would there be any mileage in altering the value of the Parafeed capacitor (higher/lower?) to reduce low frequency output?

Paul

[Paul Joppa]

Could be. The speaker impedance fluctuates quite a bit in the deepest bass for most speaker designs, and this can interact with the parafeed capacitor. It's different for every speaker, so there's no reliable way to predict the effect.  I'd try something smaller - start with the old 3.3uF, then maybe 5-6uF (you could parallel the two 3.3uF and listen in mono perhaps) to compare with the 10uF; that should give you an idea of what the effects will be. It's possible but (IMHO) unlikely that a larger capacitor will have much audible effect.

You may of course just be hearing the effect of the corner location, combined with the SET's moderate damping factor - room acoustics are always difficult!

[Paul Birkeland]

You can indeed lower the parafeed cap to induce a bit of rolloff.

It's easier to lower the value of the coupling cap (cheaper cap with less voltage across it).

The formula is C=1/(2*R*Pi*F) where R is the grid leak resistor in ohms (249000) and F is the -3db rolloff point. This will give you a C value in farads.

PJ would have good ideas on values to try, but I would suggest trying coupling caps that move the frequency up 10hz at a time until you find what you like.

[Doc B.]

Bear in mind that you can create a bit of a hump in the bass response just above the roll off point if you shrink the cap size too much. If that hits right where your bass boom is it could get worse instead of better. I'd consider reducing the cap size as a last resort and try getting the speaker to work with the room as well as possible first.

[paulw]

Bear in mind that you can create a bit of a hump in the bass response just above the roll off point if you shrink the cap size too much. If that hits right where your bass boom is it could get worse instead of better. I'd consider reducing the cap size as a last resort and try getting the speaker to work with the room as well as possible first.

Yes, basically reading the above posts it would seem that further passive bass traps will be the order of the day as I feel (given my room dimensions) that a cap value change may be toying with the response below my problem area - I'll try and plot it this evening.  The impedance curve of the speakers seems reasonably benign with a minimum of 5ohms and a max of 9ohms from 10 to 500Hz (impedance curve supplied by the speaker designer) and nothing over 13.5ohms at all.

Paul

[paulw]

Doing some 'quick and dirty' measurements from the listening position with a basic SPL meter I would appear to have a significant 'hump' in output from 85-105Hz with the peak at 96Hz.

Paul

[Doc B.]

To know if any of that hump is due to the amp's frequency response you really need to measure the response of the amp into the same load that your speakers show it. It is most likely that the hump you are seeing is a composite of several room modes with the one at 96Hz being the worst. The place to start is to move your speakers a foot or two and see if the hump changes

[Grainger49]

Are the Pi Corner Horns like Klipsch Jubilees, with a side built into them?  That is, the Jubilees do not need the corner to function.

[paulw]

Are the Pi Corner Horns like Klipsch Jubilees, with a side built into them?  That is, the Jubilees do not need the corner to function.

The room corner is integral to the design, this actually forming part of the bass horn.  The main reason I went for these was that fitting tight into the corners they take up less virtual floor space than my mini-monitors which like to be 3 foot into the room.  No I've come to the conclusion it's going to have to be more passive trapping but targeted at the mid 90's specifically.

Paul