Correct Theile Parameters for 604-8k??

[DavidH]

Hello All...Probably old news for the pro's
But please enlighten me. Altec spec sheet gives Fs 24hz, Vas18 cu.ft. Qt 0.928. The
Great plains Hubbard corrections are Fs 28.5
Vas 14.58 and Qt .20 what is right?? With
the Hubbard #'s I get a 2.0 cu. ft. optimum
internal volume, yet the Altec Tech sheet
measurements were made in a 6 cu. ft. enclosure(reflex).Where am I going wrong?
What would be a good enclosure for a 604-8k
duplex. Thanks in advance for your knowledge
and advice.
Dave

[Jim Easley]

The original Altec 620 cabinet is one of the most popular. I also have a pair of 604-8K's in custom built 620's. These are large and beautiful bass reflex cabinets. Design plans are available for the 620's at several websites.
I have read the Onken cabinets are good as well. I have not as yet been able to listen to the Onkens but, they are very attractive cabinets.

[Jim D]

We have just completed construction of a set of Stonehenge III cabinets which we will be offering for sale. We also have some 620 sized cabinets which we have re-designed slightly to improve the SAF (spousal approval factor) that has a little smaller footprint than the 620. If you email me at [email protected] we can send you some pics.

[Todd W. White]

David -

I would question the results of your calculations - 2 cubic feet is just NOT right... maybe you entered a number incorrectly, or, perhaps, there is a flaw in your formula. Are you using a box design software program to design your enclosure? You DO know that not all of them are totally accurate...

The 620 (6 cu. ft.) enclosure makes the LF side of the 604-8G/H/K VERY happy, when properly tuned, of course.

Enjoy!

[DavidH]

Hello Todd
The tech sheet from the 604-8k gives Qt of .928
the Hubbard numbers from Great Plains is Qt .20,
that gives a very different number to multiply
the Hubbard Vas14.58 or Altec tech Vas18.0 cu ft.
Logic of course prevails, I know that a 5 to 6
cu. ft internal volume with the port properly
tuned should yield good results. If you take the
low Q of .20 I get a volume factor of about .136.
When you multiply .136 x Vas 18.0 cf you get2.44
cu ft.! Am I not understanding this process?
Did I skip a step? Are you familiar with the
discrepancy in the 2 sets of specs for the 604-8k?
I am ready to buy a pair, I just want to get the
most bang for the buck! Are 604-8k's ever used in a closed box/acoustic suspension application?
Thanks Dave

[RonSSS]

Hi,
I went through a similar process with my 904-8A duplex's. Very similar to the 604-8K but higher power handling.
Anyway, you can look up the specs for mine, I don't remember them right off hand. Also a low Qts value.
I used a software program called BoxPlot. It said the 904 wanted a 2.4 cuft box with a 6" duct of 4" in length.
So I built just that and the results were just fine. As you notice, the low end of these are 60 hz, not 30hz like the earlier stuff.
Putting them in a bigger box would work ok, but the LF response would not be flat.
I believe you are coming up with the correct results.
Buy them and measure the TS parameters yourself. It's not all that hard. The factory numbers are just an average for that driver type, they can vary quite a bit.
Ron

[jmarkwart]

Dave,
There is consensus that the Hubbard numbers are more accurate than the late Altec spec sheets. There is a continuum of box volumes and tuning points that you can create from this T/S data, but unassisted, i.e., flat alignments, will have net box volumes around 2 - 3 ft^3, with -3db points around 50-60Hz. Larger volumes (3 to 9 ft^3) will have somewhat lower -3db points, but will also produce magnitude dips and/or peaks and worsening phase shift/group delay responses. These anomalies cause all sorts of problems, not the least of which is degraded transient response. I agree with Ron's post on this. Altec's use of a 6 ft^3 enclosure followed their X BASS alignment process where they accept a tradeoff in passband flatness and transient response to achieve a somewhat extended bass response.
Jeff

[DavidH]

Hello and thank you to all who posted. I feel
better! I guess speakers are alot like my
vintage motorcycle engines, they may be the same
model but the dyno tells the real story!!
Thanks again.
Dave