604-8G's in large boxes

[cbb]

I have a line on a pair of, I am told to be the duplex 8's. I have just seen them but the lighting was not the best and I could not see the backs. I have not had the chance to listen to them yet as they are behind may other speakers and the owner is in the middle of a home project. The horns are metal and have 6 cells each. The 15" woofer have the wet looking accordion type surrounds. They seem to be in great condition and are in an enclosure with a small rectangular port almost at the bottom of the box, the driver is pretty high up in the box though. I thought they may be in the 620 enclosure but seem to be a bit deeper and possibly wider. I thought they were 12" drivers at first as the enclosure is so large. I would guess about 40"h x 28"w x 25"d. No controls on the front and the whole front is not covered with a grill only a smaller square to cover the 15" driver attached with velcro.

The owner claims they weighting in the 200 pound range. The seem to be covered with a commercial grade oak look laminate. Was anything like this actually made like a model 17 or am I looking at some type of well made home brew?

Thanks!

[Old Guy]

Sounds much bigger than anything factory I have ever seen. Looking forward to pics if you get them.

[GM]

Yeah, sounds like one of the many MLTL designs I've done for others, so wondering who/where..........

GM

[cbb]

Yes, they are in the Atlanta area. Can you tell me a little more about your design for the Duplexes, GM? Mass Loaded Transmission Line I believe. Suppose they would be heavier at the bottom due to some type of weights? Could this be the ultimate box for the drivers?

If I can get them at a reasonable amount I would be glad to post some pictures. Maybe I would be allowed to get a snap anyway.

Hope they have a similar sound to my jr. VOTT's, Heathkit AS-101's.
Any comments on their sound or approximate value would be wonderful!

[Todd W. White]

Those dimensions are pretty close to the ones for the Altec Model 620 Enclosure/Model 17/18: 26" wide x 18" Deep x 40" High.

Are you sure the horn is metal and that it is a true multicell?

[Panomaniac]

I thought the -8G had the Mantaray horn. No? Or is that the K?

I have a pair in very big boxes. About 14 ft net. Works real well. Plays low, very dynamic.

[GM]

Those dimensions are pretty close to the ones for the Altec Model 620 Enclosure

I keyed in on the horizontal slot vent at the extreme bottom and no visible XO description, but in retrospect it could very well be a custom 620.

GM

[GM]

Greets!

Not much to tell. They all are designed to meet the needs of the app as best I can within its limitations. Given free rein, I prefer to make the cab at least = to the driver's Vas and tuned to Fs since it yields the most in-room tuning flexibility, but most of the vintage Altecs have very compliant suspensions to get both high efficiency and good micro dynamics to minimize the tonal/clarity differences between a point source driver and compression horn, so few folks are willing and/or able to 'afford' a pair of 20-30 ft^3 cabs.


The MLTL alignment is a way to get the driver up to around/at seated ear height and reduce its footprint somewhat, but primarily to mass load the vent enough to increase its acoustic efficiency via 1/4 WL pipe resonances to better damp the speaker system.

I imagine they're technically top heavy when loaded with 604s, but properly constructed, a large MLTL will have a sufficient footprint for good stability and weigh enough that it will take as much effort to knock it over as an equivalent weight lineman at the line of scrimmage. For the typically small ones I design for ~full-range (FR) drivers, I recommend an outrigger style base same as NHT used on their late/great 'flagship' tower designs and to get good vent pipe loading efficiency, a massive top plate such as marble, slate and/or heavy potted plant or similar perched on top.

For point source drivers there's two 'ultimate' cab alignments, open baffle (OB) at one extreme since it wants to 'feel' a matching acoustic impedance on both sides of its diaphragm with the trade-off being no usable LF gain BW without significant frequency response shaping that severely limits its dynamic headroom, or a reactance annulled back loaded horn (BLH) being its acoustically opposite extreme where it has no usable HF BW.

From this we see that the best compromise appears to be a relatively high tuned BLH to keep its inherent delay low with the second best being an OB, both alignments XO'd to an efficient (massive) LF/sub system. After these, 'best' seems to be more a personal sonic preference + needs of the app such as space limitations, WAF, etc..

WRT comparing a 604 to a VOTT, the closest sonic match to my ears would probably be a 515 variant of the M19 with motor type being dependent on which one the 604 has, so potentially it will be quite a bit different to Heathkit's Valencia variant, but women generally prefer a much 'smoother', slightly 'recessed' sound, so it's been my limited experience that once dialed in combined with its superior wide BW coherence, it wouldn't surprise me if she preferred the 604 overall. You too, for that matter.

GM