New 604 Cabs

Hmm, we're still having a 'failure to communicate'.

[2] 3/4" layers of MDF = 1.5" + a 3/4" layer of Oak on top = 2.25" thick, ergo the vent is 2.25" long.

Or are you saying that only the top plate has the Oak layer?

If so, then based on your measured tuning, the existing rounded off vent effectively 'shrinks' it for a given length down to ~79.1"^2.

Cutting it out to a 12.5" effective diameter [122.72"^2] will require adding a 3/4" vent extension to tune it to ~Fs.

For a 1.5" long vent, 11.9"/111.22"^2

I just noticed you either used or DATS calculated a 12.75" Sd, so to use Av = Sd, then 127.676"^2 x 2.5" long.

GM

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Originally Posted by cradeldorf

Okay, I hooked up my DATS to the speaker and did an impedance sweep.Okay, according to my altec literature my port is too small...I wish there was a way to determine how much larger to go? BTW the tuning frequency at the bottom of the dip where the phase crosses zero is 47.1hz

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Yep in a BR cabinet, first hump bigger = port too large, second hump bigger = port too small.

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Originally Posted by Alien_Shore

Yep in a BR cabinet, first hump bigger = port too large, second hump bigger = port too small.

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This assumes a Fs tuning is the goal, which normally isn't desirable with modern electronics.

GM

Quote:

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Originally Posted by cradeldorf

Okay now, would I be correct in assuming that your saying for a 1.5 depth port for my cabs to tune to 47.1 hz that I need a port that is 111.22 square inches? and that's without rounding the port edge with the router, correct?

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No, this is to tune it to Fs.

?? You already have a 1.5" long vent tuned to 47.1 Hz. If you wanted it in a straight cut vent it would need to be smaller.

GM

You're welcome!

Correct, though unless you're using a high output impedance amp [what are you using?], tuning them much higher [~flattening the upper impedance peak], then 'critically' damping the vent to quell its 'ringing' will probably be better overall as it will bring up the mid-bass, lower mids and I'm guessing this is what you're missing based on your previous cab experiments.

That said, if I were there, I'd take advantage of the way oversize cabs by tuning them to Fs and use some cheap 25 ohm pots in series to dial in the amount of output impedance required for flattest woofer in room response, then adjust the HF level and maybe wire a by-pass cap around the L-pad to let the extreme highs through, then replace the cheap pots with a fixed resistor bank using commercial grade non inductive power resistors. High output impedance EQ on the cheap.

This assumes of course that the amp has enough power to handle the load without going into clipping when you 'crank' it.

GM

Cradeldorf glad to see you are making progress. I have been looking for a new design for my 604's there are almost to many options..... I see you have tried a few and more than most. Have you tried a MLTL yet?

What EQ?

GM

Sorry, meant what are its settings for each channel.

GM

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Originally Posted by juniper

I have been looking for a new design for my 604's there are almost to many options..... Have you tried a MLTL yet?

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Short of horn loading, the MLTL yields the best overall performance WRT LF extension Vs acoustical damping plus allows more tuning flexibility and driver location, so has been my 'no brainer' default vent alignment since the '60s after auditioning one offered by RCA, though it was marketed as being simply a reflex. Seems Harry Olson missed a good patent opportunity with this one.

GM

Bummer, hope it's just a 24 hr bug. Lots of it going around down here in the S.E.

GM