Have you built the Markwart crossover for 604 8G/8H ??

[LowOhms]

Hello,

If you have built up the Markwart crossover for 8G/8H, could you please tell me the value (ohms) of P1 (the L-Pad or potentiometer) that you arrived at ? I am curious to see if there is much variability in the resistor value when all is said and done based on room and listener preference. I am laying things out, and with simplification always in mind, am curious if there is a 'standard' value of P1 +R4 that I could replace with a single resistor. I already have all of the parts (including potentiometer), so building the original design will be easy if I need to do that.

I would also be interested in how much back and forth it required to arrive at the optimal L-Pad / pot setting - dead obvious the first time, or much tweaking to get there. I anticipate putting the crossover at the inside bottom of the cabinet due to external space constraints (plus my wife is OK with a big tube amp on the floor, not sure about a couple of big PIO crossovers as well). So pulling the backs off the cabinets for multiple adjustments can be done, but will be a bit of a pain. Just trying to think ahead - my Klipsch crossovers are not variable, so maybe I don't know what I am missing......

thanks and regards -- Roger

Hi Roger,

I simply would tell your wife, on a temporary basis ( two weeks, not months) you will leave the crossovers OUTSIDE of the speaker so you can GET to the pots easily to adjust them. You will be worn-out having to put them in and out, and you will never get it as good, as if you could, if you can get to the adjustment control easily. Its human nature.

The idea of then replacing the pot with a fixed resistor is GOLDEN, I love that !!! Its acceptable, if you have-to, to parallel two resistor values, to get a desired end-value, an "odd" one. However, avoid series-connecting two resistors, because it is a audio no-no. Series-connecting Rs is the worst way to get an "odd"-ohmic-value, sonically speaking.

Think of a plate or cathode resistor in a tube amp, one would NEVER series-connect there. However, I have seen some of the best builders in the world use paralleled resistors on plate and cathodes, as a sonic enhancement. FYI : Its a far better practice, if multiple paralleled Rs are of equal value BTW.

Also Roger, it would be IDEAL to have equal room-loading of both enclosures, ( eg: both in corners ) and it would be IDEAL to have the same exact Ohmic value of pad-down Rs, your own carefully - selected " single compromise value " in each crossover. So be sure, ( before replacing the pots with fixed Rs ) to set both pots to equal Ohms, a value YOU like, and re-position the speakers minutely, incrementally, to your taste, as a fine-balance. Its a very good idea to measure and record it all on paper, take notes to preserve your tedious work in set-up. Take your time, do it incrementally.

When I eliminate my ALTEC crossover pots, the entire top end got quieter, with less distortion, and on well recorded material, you will hear a better sense of front-to-back depth, and hall reverberation information. The soldered pad-down resistor connection goes a long way towards being nicer to hear.

I am responding to your post, because I am soon to be in a similar boat as you are. Just last week, I swapped speaker-walls, and when my DIY SET tube amp rebuild is done in February, I need to do the exact procedure I have detailed above, and then eliminate my pots.

Have fun, hope you get to feel much better.


Jeff Medwin.....Low Ohms

[zelgall]

One problem I had with several (five, six?) different pairs of 604s is that they rarely measure close enough to each other to use one value of padding for both left and right, particularly if you have furniture that isn't mirror imaged in the room:-) I'm sure that someone here (and I'm not pointing any fingers at anyone with a ridiculous handle) will claim that their pair was anointed by a historical figure or an industry expert that can prove this pair is virtually identical. I say BS to that based on my and dozens of others experience over decades of use. If you get a matched pair it's like winning Powerball. Just saying.

I found it easier to get one speaker/crossover at a time set up and then play both and compare, then physically switch just the crossovers left to right, to hear if there was a change that my limited measuring equipment didn't pick up in room. It took a bit of time but the end result was quite good.

At one point I bought Jeff Markwart's own 604-16X pair (through this site) that he wrote about and tried to recreate his crossover results but rooms are different and I didn't want something that was a copy but didn't sound right in my room.

Baffle width seems important as well and can change the results compared to other users I know or read about that use this style of crossover.

I think that there is some experimenting to do rather than relying on others results.

[rogerh113]

Sounds like the best approach is to leave them out of the cabs while I am tuning them - that should be pretty simple. I will have to tune the bass port as well, so will probably need to be in that mode anyway for a short while.

regards -- Roger

[SD-50]

Just finished a working model and still tweaking it. Once it sounds the way I like will install fixed resistors, good quality ones. I like carbon-film ones. A recent pic showing the massive Russian Teflon caps soldered in last weekend.
The XOs are on the floor behind the speaker to allow for quick changes.

[BillWojo]

Those teflon caps look like 0.22uF? they are massive for that size. I just ordered some Russian K42Y-2 0.1uF for bypass caps. I'll try them with the Solens and later with my oil caps.
Your build looks good, how is it sounding?

BillWojo

[Elitopus1]

I am very interested to know how those bypass caps sound on these xovers. I have been thinking about adding some to mine.

Bill
I just checked out those K42Y-2 on ebay. Those are cheaper than the other Russian caps I have been looking at. Let me know your impressions when you get them hooked up. I might have to order me some of those

[SD-50]

Those teflon caps look like 0.22uF? they are massive for that size. I just ordered some Russian K42Y-2 0.1uF for bypass caps. I'll try them with the Solens and later with my oil caps.
Your build looks good, how is it sounding?

BillWojo

Yes, they are .22uf. Partsconnexion has them for about $10, a bit more costly than e-bay but less of a pain. The XOs are sounding very good, music is layered, transparent, musical.

[LowOhms]

Sounds like the best approach is to leave them out of the cabs while I am tuning them - that should be pretty simple. I will have to tune the bass port as well, so will probably need to be in that mode anyway for a short while.

regards -- Roger

Roger,

Consider this : Why do everything, all at once???. Yes, anyone reading this Forum, knows about bass port tuning.

The mids and highs could be gotten right first, and then, live with the system for a few months, learn what it does, ...... THEN fool with port size.

I personally intend to do my own A7-800 port tuning LAST, and only when all else is attended to in the mids and highs, as best as I can.

Those are just my own thoughts however, YMMV, have fun.

Jeff Medwin

[GM]

If one were to build a house, etc., would the roof be first?

With that in mind, consider how a horn 'constructs'/reproduces a wide BW signal.

GM

[rogerh113]

Hi,

I think all of the input is useful, particularly as I like to methodically plan my work so there are no (or reduced) surprises. I actually expect the tuning of the speakers to be an iterative process. I probably will start to address the most annoying aspect of the sound first (boomy bass or missing/overly aggressive highs). The extra wild card, aside from the high end tuning and port length, is the impact of the wooden Magnificent grills (assuming I can repair them, which I think I can). I have to assume that there will at least be a high end impact, and possibly some bass impact, from the grills. I should be able to determine that by leaning the grills against the face of the speakers. I have a feeling I am in for a lot of back and forth testing, and trying to figure out what sounds best relative to what I can realistically get away with (wife probably fine with grill cloth and maybe wooden grills, but possible not big naked speakers in the living room). I'm guessing the big naked speakers will sound best..... One good thing is that it generally does not take me a long time to figure out what I like sound wise (generally just minutes). I do understand that there is some break in time for the PIO caps, so patience will probably be required. I have done none of this before, so it will be a grand adventure.

Laying out the crossovers now, but probably at least a month before I a well enough to start working on the speaker cabinets again. I almost have the second cabinet deconstructed, and after that I get to actually start building the cabs up. Really looking forward to it.

regards -- Roger