Lowering the crossover point.

[Alien_Shore]

Of course the best will be to measure them up.

You heard him CD, send them to me and I'll measure them for you.

[aditya]

There are a few things I wonder about, The first 604 was 20 ohm and had a 2000hz crossover point, the "B" looked identical and it had a 1000hz crossover point, the "C" which has a slightly different horn had a 1600hz crossover point and the "E" which began using the accordion surround had a 1500 crossover point.


In the earlier days, the ohms ratings (impedance) alloted to drivers were very much without any fixed rules. The spec given was purely an assesment of the manufacturer alone. For example, Philips ratings were always the same as their DCR values. But later on the computed values (impedance) at 1KHz was accepted as the standard value.

Though in most cases this impedance value turns out to be 1.25 times the DCR value, this is not the same for all drivers, especially in the case of older and unusual drivers like the 604 types. Here the imedance values can be the double of the DCR value, as their f/imp slopes rise very fast, an indication of their very high efficiencies/sensitivities.

Regarding the varying crossover 'f' choices, I think it was part of the usual R&D stuff. A standard '15 inch' speaker has its toughest task while trying to reproduce the range between around 350Hz to 550Hz, b'coz this is the zone during which its cone's physical limitations start coming into play, and restrict the HF stretch severely beyond 1KHz. Now the HF horn in the 604 is perfect for 2KHz, but limits itself below 1KHz. So this way after trying out both the limits for various reasons, they finally settled for the middle path at 1500 Hz.



I'm pretty happy with how they sound they have a real 3dish type of sound. When Avatar is playing all those weird bug noises in the jungle are going off to the side of you and above you It's kinda freaky but cool. I am considering different cabinets again, not because I don't like these but the other day when I switched back to the altec receiver from the marantz I literally made the back panels of these things distort. (they're barely 3/4 thick particle board with no bracing at all,The baffle is the same way) the bass was so much more deep than the marantz that when I fired up the altec and Nady eq the back panels of the heathkits were shaking violently enough to sound like a distorted speaker. I've since tuned them in nicely but when I think of how much power they must be producing to jump the cabinet panels by better than a 1/4 inch I started thinking Butcher block thickness cabinets are in order.

Nice to hear that you are happy finally. I am curious to know....
What is your present xover choice ?
What adjustments did you need via the Nady equalizer in order to make the sound better ? B'coz the reverse of this adjustment is your speaker+xover+amp's response ! Let us know.



That chart is a great find Aditya, I've never come across it in my hunting adventures.

Thanks.

[VolvoHeretic]

Sounds to me like you need a nice 417 12" guitar speaker in there for a midrange driver.

[aditya]

I'm running the 1.5mh iron core Erse super Q inductors on the LF and a 7uf cap with a 3 uf cap side by side with the leads twisted together to form 10uf caps for the HF. The nady settings are like this.

From your equalizer settings, it is very clear that the woofer in the 604C has gone sloppier, I mean the mass-breakpoint has moved downward, and as a result the high-end response of the woofer has suffered badly. This clearly indicates a loss of gap-flux or weak magnets. The HF portion seems to be ok.

[aditya]

One of them I sent to GPA about 2 years ago to be remagged the other one has had nothing done to it. funny how they both have the same DCR.. I borrowed a meter from the college to measure them.... I wonder if it needed to be calibrated?. I didn't really know what I was doing other than sticking it on the 200 OHM setting and checking them. there were no directions with the meter they just have them piled up in a tub for the students.

Are you referring to the left side of the equalizer? where the sliders are almost centered? Because I could move them up higher but thats when the cabinets started flexing like something from a Ren and Stimpy cartoon. I'm thinking I want to build real Onken Jensen cabinets for them.
I'm not real sure the entire cabinets were flexing but the back panel was sure making a racket maybe if I did some heavy duty bracing on them they'd shut up. They are about 24" by 30" 1972 particle board that I swear looks more like 5/8 instead of 3/4

Remagging is usually done only after the speaker is completely ready otherwise. So the DCR remained the same.

About your meter accuracy, you can always measure a known value resistor, say 10 ohms, and check it.

About the equalizer setting, it is not the left side, it is the peak at around 600 that looked unusual. A 604X rarely suffers here. But however, all these are based only on an assumption that like most people you also like a set up which is tuned to a 'flat' response, b'coz there are no other tangible proof available here. I think it is high time you get these drivers measured up systematically, thru someone more acquainted with the process. Otherwise it will be almost impossible to get predictable results, as the variables are too many, and we even do not know where the 'square-one' is, to go back if needed.

[GM]

'Sounds' like ya'll aren't factoring in the amps used, which were ~matching impedance originally, decreasing down to vanishingly low by the time of the 'E'; so originally, driver impedance was listed as a function of network impedance and the VCs would have been wound to have a DCR/impedance that yielded the desired inductance to achieve the flattest, widest BW over some average power band. As output impedance dropped, the driver's impedance would become increasingly more dominant for a given Qts, power handling.

Note too that compression horns will add enough acoustical loading to raise the nominal impedance up to 2x Rdc over their pass-band, dropping back down when the horn unloads and only functioning as a direct radiator, so with a loading cap I?m not surprised its Rdc is considerably < a woofer?s ~12 ohms for a nominal 16 ohms impedance.

With re-cones though, I?d be surprised if GPA still has period correct coils for the early series or even much choice of nominally 16 ohm coils beyond the ~12 ohm ones for the 416, 515 where inductance should be ~the same, so it seems reasonable these are the ones used in 605, 604 re-cones.

WRT the XO point ?floating? between 1500-1600 Hz with the small horn, I assume this is due to how the XO?s alignment changes with driver VC design between models, which with re-cones may actually work out to yet something different if the original VCs aren?t used.

Short of GPA listing a customer?s options to choose from, one can only measure what one receives, which in some cases we know is well shy of the mark.

This ?E? plot should be in the ?ballpark? from around 300 Hz-up for most of the small horn 604s when driven with a typical SS amp: http://www.lansingheritage.org/image...itor/page2.jpg

GM

[GM]

About the equalizer setting, it is not the left side, it is the peak at around 600 that looked unusual.

Not seeing any EQ setting........

GM

[GM]

I'm not real sure the entire cabinets were flexing but the back panel was sure making a racket maybe if I did some heavy duty bracing on them they'd shut up. They are about 24" by 30" 1972 particle board that I swear looks more like 5/8 instead of 3/4

Bracing, doubling [or tripling if 5/8"] the panels are obviously required if they flex and if the rest of the cab isn't made from at least 3/4" no void marine grade, BB or Apple ply with at least one 'X' brace, then it's probably flexing too, or if not, will be when the back has been sufficiently stiffened up to transfer the air load to the next 'weakest link'.

GM

[GM]

I posted a picture of it on the page before this one. Hostboard probably logged you out before you could get there....I hate that log out thing!!!! >: (

Hmm, I'm logged in and stay logged in even when the forum disappears/reappears unless it's a major update. Anyway, I was looking for a plot, but I now see it's a picture of the sliders. Interesting EQ, mostly the opposite of what a 604 would need.

GM

[voice of the theater]

Hmm, I'm logged in and stay logged in even when the forum disappears/reappears unless it's a major update. Anyway, I was looking for a plot, but I now see it's a picture of the sliders. Interesting EQ, mostly the opposite of what a 604 would need.

GM

Cradeldorf, are you using the tone controls on your amp in addition to the Equalizer? If so, what are you adding with the tone controls--any bass?