New 604 Cabs

[Alien_Shore]

wow - mad skills!!
That's impressive. It's a shame though that your stain didn't work out. The tops look great.

I gotta get a router (or find a friend with one)...that's great how you did the inset baffle cutout. Maybe I can get some plans from you or some help with construction for the newbie...

So what frequency are you tuning them?

[voice of the theater]

Those turned out great Cradeldorf! I like how you not only offset the speaker hole (which, from what I understand, helps to prevent reflections inside the cabs cancelling each other out), but you offset them the opposite of each other so you have a "right cabinet" and a "left cabinet". I really like that approach--when purchasing a pair of factory Altec cabinets (with offset holes), they were always identical so there was no "right" or "left" cab. I'm sure that made it a lot easier to sell them (in pairs and as singles)--you didn't have to order a "right" and a "left". Anyone know if Cradeldorf's approach will enhance stereo imaging compared to the "traditional" Altec approach?

EDIT: It's a shame you had to paint those beauties. I really like the look of the grain just as it is in the photos. If they were mine, I would have been tempted to just put a clear coat on them. But then again, I've always been a sucker for blondes!

[GM]

I like how you not only offset the speaker hole (which, from what I understand, helps to prevent reflections inside the cabs cancelling each other out)

Anyone know if Cradeldorf's approach will enhance stereo imaging compared to the "traditional" Altec approach?

EDIT: It's a shame you had to paint those beauties. I really like the look of the grain just as it is in the photos. If they were mine, I would have been tempted to just put a clear coat on them. But then again, I've always been a sucker for blondes!

The insulation inside the cab is for damping down its reflections, so at best, the offset will allow less internal damping, which is a good thing normally.

What the offset [or heavily rounding over the cab corners] is for is to average out the eigenmodes [standing waves] between the driver output and edges of the cab, so that the peaks/nulls are much lower in amplitude.

It enhances stereo only to the extent that there's less 'dilution' of the signal arriving at the listening position [LP] due to comb filtering of direct to reflected sound across the driver.

With an effective acoustical baffle width around 34", it will have a ~200 Hz eigenmode with both even and odd harmonics, so offsetting the driver in a golden or acoustic ratio is a good plan on wide baffles when it will have output down to the baffle?s fundamental.

Then there?s the speaker/room boundary eigenmodes to contend with. The horizontal ones can be dealt with adequately by toeing the speakers in as long as the angle is > 6 deg/channel.

Vertically, it gets more complex unless you slope the baffles a like amount to deal with the floor, ceiling eigenmodes and ?floor bounce?, which is the angular reflection between the speaker and LP, with the latter best dealt with by placing the driver at floor level.

A compromise to deal with all this is to locate the speakers up off the floor at some golden or acoustic ratio and angle them up/down and left/right at least 6 deg.

Since imaging/sound-staging is perceived principally in our acute hearing BW, just outputting the phone BW [~250-3500 Hz] in these locations is usually sufficient, so a suspended/angled studio monitor with a separate sub system consisting of at least one sub/room mode is about as good as it gets without building an acoustically ?neutral? room.


GM

edit: Me too, though when used in an HT app, they need to be a very dark color and preferably a matte finish.

[Panomaniac]

What are you using for a crossover?

[GM]

After seeing your impedance plot, which showed a ~ 4x larger vent tuning, I realized I forgot to double the port radius for the calculator I used, so have deleted this post and edited my original one.

Sorry about that, guess it was another 'senior moment' and why at least basic measurements should always be done.

The revised calculation is 48.08 Hz based on 8.5 ft^3, so with a 47.1 Hz measurement, the cab's net Vb is closer to 8.8 ft^3. As such, what, if any, change in vent tuning would be up to you since it's close enough to the driver's Fs unless driven with a high output impedance.

If you want to tune it to Fs, then make the vent large enough to make the two peaks the same amplitude, which should be around 122.72"^2 or the driver's effective piston area in this case, which is considered the reflex ideal.

If you think it will perform better tuned lower, then I don't recommend tuning it < 0.707x Fs = ~38 Hz = ~39.6"^2.

GM

[GM]

You're welcome!

'Senior moments' at 50?! That's awfully young based strictly on my observations.

Hmm, you posted that this is a three layer 3/4" construction, so the vent length will be 2.25".

I don't see how you came up with a 168.3"^2 vent, but it's way too big plus in a simple reflex as your cabs are, Av = Sd or ~122.72" is the largest/optimum that should be used.

This, and all other on-line calculators I've tried calculate too long a vent [~70%! for this one], so as a general rule I prefer folks not use them if other than a closed vehicle or small room app where there's going to be some decent amount of room gain.

Some math that calculates an almost identical value to mine is in one of WP's PiAlign docs: http://www.google.com/url?sa=t&rct=j...MUbS-b8YN7Mt5w

Load them into Excel or similar, input this alignment and you're good to go if it calcs a Fre [Hz] = 53.681:

Vb [ft^3] = 8.8
Lp [in] = 2.25
Dp [in] = 12.5

GM

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[GM]

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

[Alien_Shore]

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

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

[GM]

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

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

GM