Far too lean 604-8Gs in 620 kabs

[Todd W. White]

Be careful not to remove too much damping material - if you do, you'll set up some nasty standing waves inside, not to mention making the loss of perceived LF response due to wasting the energy wiggling the box.

[KBergsson]

Hi Todd, I only removed damping from one side and bottom so that top, back and one side is still covered.
Sounds fine, but no change in bass output.
Regards
Kjartan

[bowtie427ss]

That said, for deep bass, a very large cab tuned to Fs is required, especially when driven by a high output impedance tube amp.

Quoted for emphasis.

A graphic analysis of the frequency response characteristics of the amplifier/s would probably help shed some light on "where's the bass?".

[KBergsson]

Hi BBC454SS, i dont know the output impedance of my Quicksilver KT88 monoblocks. But I dont think it is high compared to most pentode tube amps. Quicksilvers have e.g. been regarde a great match for Quad electrostats.
Regards
Kjartan

[KBergsson]

Hi I exchanged the 25uf Mundorf caps in the J. Markwart crossover with some inexpensive oval GE 25uf caps. Got more bass and much better resolution in the low end. Im going to exchange all the caps in my Markwart crossover, what do you recommend?
I'm not into expensive caps in general, use russian PIOs in my quicksilvers.
Regards
Kjartan

[GM]

Thanks for all the good suggestions.

I have however been playing with the shelving pot in the JM filters and it does not have a huge effect, everything is a little more up front on the one extreme setting and a little slower/darker on the other extreme. I use the middle position for most of my listening.

You're welcome!

Hmm, something is not right, a 25 ohm pot will convert an 'in your face' sounding speaker down to a muffled sounding wide BW woofer, so with a 30 ohm pot it should have an even more extreme range. Again though, the relatively large by-pass cap will tend to just tone down the lower HF, hence the suggestion to try smaller values to increase the pot's ability to deal with baffle step loss.

Still, the cab is large enough to generate plenty of bass down to around 40 Hz IIRC, so I still think there's a leak somewhere. That, or your speakers are out-of-phase with each other, canceling out much of their bass output.

GM

[KBergsson]

I agree GM, something is fundamentally wrong, but I cant put my finger on it.

The speakers are not out of phase now because if i reverse the speaker leads on one side, the bass disappears altogether and the instruments appear to be are all over the place on the outside of the speakers.
I have fixed potential leaks around the 604s. I have used some putty to stop potential leaks around the terminals and original crossover.
I have the speakers right up to the walls in corners (solid outer walls).

Bass is there ....but as said before it is severely attenuated compared to higher frequencies, so it never really comes into play, I'm also missing the richness of e.g. contrabass string and box resonance, the inexpensive 25uf cap brought a tiny bit of that into the picture compared to the 25uf mundorf I got with the Altecs.


I'm going to connect the original Altec filter this evening (21uf and 1.8mHy in the bass network and 6uf, 12uf and 0.6mHy in the tweeter network), see what that changes. It should at least uncover if there are errors in my implemetation of the J. Markvart mid EQ.

I'm also going to check if the units (if for example a recone has been performed) are internally out of phase (802 vs woofer). Measure the woofer and compression driver se if there is a mismatch (8 contra 16 ohm or whatever).


Best regards
Kjartan

[GM]

Let's not forget the amp's potentially huge impact on all this also: http://www.hostboard.com/forums/f700...ml#post1823199

Then there's the signal going to it.............

Corner loaded into massive/rigid outside walls typically requires running the horns pretty 'hot' to balance out the strong mid-bass that defines virtually all the vintage Altec large speaker alignments. Historically, I've often tuned such cabs lower to allow enough CD horn EQ be used to minimize the mids/HF horn's 'honk'/'screeching' highs.

GM

[KBergsson]

Hi before I connected the std crossover I decided to try a smaller bypass cap. Used a 2 uf no real improvement but the mid eq showed a lot more difference between min and max. Then I tried bypassing the eq altogether, wow!! Top a little hot but there wa a lot better overall balance. Now I have been playing for a couple of hours, bypassing the mid eq but keeping 3ohms in series with the top (even using the winged c kt88 in the quicksilvers). Something is definitely wrong in my implementation of the mid eq. Bass is back and sound is glorious. Hope this lasts
Kjartan

[cradeldorf]

Hi before I connected the std crossover I decided to try a smaller bypass cap. Used a 2 uf no real improvement but the mid eq showed a lot more difference between min and max. Then I tried bypassing the eq altogether, wow!! Top a little hot but there wa a lot better overall balance. Now I have been playing for a couple of hours, bypassing the mid eq but keeping 3ohms in series with the top (even using the winged c kt88 in the quicksilvers). Something is definitely wrong in my implementation of the mid eq. Bass is back and sound is glorious. Hope this lasts
Kjartan

Yaayyy!!!!!!!!!!!!!!!!!