woofer tuning

[quindecima]

When I built my speakers I installed two adjustable round 41/2 in. vents but haven't the faintest idea of what to listen for as far as tuning goes. They adjust from 6in. to 11in. I had them all the way extended when I put them togeather and now have closed them up all the way, the sound seems crisper. What do I do, listen to what sounds best????? As a side note I was going to try a pair of 077's but I was just listning to Beethoven's 'Romance for violin and orchestra #2 in F major' and am wondering what I could be missing just as they are. I don't think I could hear anything the 077 would put out. BTW 416-8b's and 802-8g's and 811B horns.

[Zilch]

Shorter tube = higher tuning frequency, "punchier" bass, typically, but not as extended at the low end.

Longer tube = lower tuning frequency, more extended, less prominent bass.

Depending upon the box size and driver parameters, too short a tube = boomy bass, too long a tube = tubby bass.

You can measure the different tunings to find out your range of adjustability.

Download WinISD to see how varying port length alters the tuning of your own box/driver combination.

[quindecima]

Thanks for the info!!!!!!!

[Zilch]

Details via PM, here's the results:

Driver = Altec 416-8B
Two 4.625" ports each cabinet
@6" Vb = 6.451 cuft, Fb = 34.96 Hz, F3 = 42.65 (Blue)
@11" Vb = 6.343 cuft, Fb = 29.44 Hz, F3 = 44.46 Hz (Orchid)

[quindecima]

Thanks Zilch! You did something for me that would have taken me days to figure out, to say the least. I appreciate your effort in this matter.

The graph looks pretty flat from 60hz all the way up and it looks like the short vent is the way to go (?). What does what I am looking at actually translate to in the real world (I hate it when I am ignorant of specs)

[Zilch]

What does what I am looking at actually translate to in the real world (I hate it when I am ignorant of specs)

Changing the port length alters the box tuning. At 11" it's 29.5 Hz. At 6" it's 35 Hz.

I know zilch about Altec drivers or their optimum application. I put in 50 watts 'cause I don't know what the power rating of that driver is. See post #2. It'll play lower with the longer port, but then can't take as much power down there.

Running flat and rolling off rapidly creates an augmented bass in typical rooms, which some consider unnatural. It's a matter of perference, and how your room, tuning, and box location "play" together.

[BB6P didn't like the T/S parameters, but I didn't recalc them. I just click buttons here.... ]

[quindecima]

I think 50 watts is a good choice. I know that driver will be O.K. at 100 watts maybe more but I am using tube mono amps at 70 watts max per side and it doesn't take much knob turning before I am pretty loud.

[Gary L]

Good luck with this one Quin!
The info from Zilch is great and I am sure it means something in the "real world" sound.
I went thru the same process with my very similar cabinets and found it frustrating at the very least.
For me it is less a matter of the charts and graphs and more a matter of "Lend me your ears".
I settled on 5" tubes and can't really tell much difference at all but they do sound quite nice to me.
YMMV but this is one of the tuffest things I found whit getting it right.

Gary

[WTPRO]

Hi Quin

If you ever feel the urge to measure drivers and predict their response in a particular cabinet, I invite you to have a look at what the Woofer Tester can do. This tool as evolved recently to include a vented and sealed box simulator, but it also sports a feature you wont find anywhere else. An algorithm was developed that finds the match between measured and simulated electrical response, that as others like to put it, 'auto-magically' reveals the effective box size, tuning and losses.

If you follow the link below it will take you through the steps you would go through to test a driver, design and then align a box. At the bottom you can see how well the results line up. Incidentally, testing and modeling of the non-linear Rem/Xem reactance has also proven to be quite an advantage. The driver for this particular example was chosen because of its large Rem/Xem value. That is, it would presumably be more difficult to exactly model.

http://www.woofertester.com/wt2boxbuild.htm

Best regards
Keith Larson, WT-Pro
DSP and Analog Consultant
Lincoln, Ma

[WTPRO]

I would also like to invite anyone interested to our home page with a whole new look and feel... and products.

http://www.woofertester.com

Best regards WT-Pro