Far too lean 604-8Gs in 620 kabs

[KBergsson]

Do you have the HF shelved down [AKA baffle step compensation or BSC] to tonally balance it? This will make it sound too lean if not. Ditto if there's any cab leaks which will turn a reflex alignment into a lossy sealed one with a very high F3/Fb. That said, for deep bass, a very large cab tuned to Fs is required, especially when driven by a high output impedance tube amp.

GM

Hi GM, im using the J. Markwart filter unchanged (using the 8g suggested values) as published here " Simplified 604-8H EQ Crossover ". I welcome any suggestions to modify this filter.
There could be a small leak due to a small damage on the gasket (between cab and unit) around one mounting hole on one of the speakers.
Im not expecting deep bass and they seem to go reasonably deep if there is real deep bass on the record, but it is more that the bass is very dry and attenuated compared to the mids and top.
Regards
Kjartan

[Todd W. White]

This was a problem with some of the post-Electro-Voice takeover 604's, but should NOT be a problem with yours. I have personally made side-by-side comparisons of a 604E that had been freshly recharged and reconed by GPA and a brand new GPA 604-8H-II, using the same crossovers (designed by Jerry K. Hubbard), and, though the HF sounded a bit different between the two, as one would expect, the LF was identical. Something else is going on here...it's not the speaker's design fault.

[VolvoHeretic]

Are you guys sound junky purists who use no tone control? I’m a low brow stereo aficionado and use a heavy dose of bottom and top EQ and my A7’s play plenty low, although I have to adjust for every different song and volume change and they sound great whether playing classical, jazz, fussion, or rock. Or play them flat and just stand 100 feet away and then they have all the bass you could ever want.

[KBergsson]

Are you guys sound junky purists who use no tone control? I’m a low brow stereo aficionado and use a heavy does of bottom and top EQ and my A7’s play plenty low, although I have to adjust for every different song and volume change and they sound great whether playing classical, jazz, fussion, or rock. Or play them flat and just stand 100 feet away and then they have all the bass you could ever what.

My first amp bought in 1974 or 5 (a Sansui au-6500) had tone controls and i used them. I sold it in 1980 and havent had an amp with tone controls since. They fell out of grace with most manufacturers as well as the DIY crowd.
Regards
Kjartan

[VolvoHeretic]

My first amp bought in 1974 or 5 (a Sansui au-6500) had tone controls and i used them. I sold it in 1980 and havent had an amp with tone controls since. They fell out of grace with most manufacturers as well as the DIY crowd.
Regards
Kjartan

My amps don't have tone controls either, but I have a $60 Radio Shack 15 band EQ which works and sounds amazing and loss in fidelity purity is more than made up with tonality equality(are those even words?).

[GM]

Are you guys sound junky purists who use no tone control?

Not me, once I learned about such things, I've always used some form of response shaping EQ, especially CD horn EQ, and back when dbx first offered a digital RTA/EQ with the ability to save multiple response curves one could choose from its remote 'on the fly', I gladly paid a full month's salary for it, which at the time was quite a 'stretch' for me financially.

It lasted around 25 yrs of ~daily use, so got my money's worth, but its many generations newer replacement is way more than my retirement budget can recover from in these trying economic times.

GM

[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]

Hi GM, im using the J. Markwart filter unchanged.........

There could be a small leak...........

Im not expecting deep bass............ the bass is very dry and attenuated compared to the mids and top.

I don't have my notes available, so don't recall 620's exact tuning, etc., but it should do 40 Hz solidly. To go lower requires either a larger cab tuned lower or a lower vent tuning and corner loading for the 620.

Even leaks around screws can ruin a reflex's tuning, causing a much higher F3, Fb.

Regardless, once you're sure there's no leaks, Jeff's XO has an adjustable HF shelving pot same as the OEM unit, so as it is dialed up, the tonal balance shifts to an increasingly mid-bass heavy one and if you don't like what it does to the extreme HF you can experiment with higher/lower by-pass cap values [c4].

WRT weak magnet testing, I know of no way for the casual DIYer to test them, but the dead giveaway is that it increases the driver's Qts a lot, meaning you'd be here complaining about having a 'fat'/'slow'/'boom' bass due to the 620 being too small and too high tuned for them without plugging up the vent and even then it maybe too small.

GM