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Discussion Starter #1
I'm planning for a computer sub. Dayton 25W plate amp, Tang Band W6-1139SI driver, 14L ported box at 33 Hz.

So, I have all the hardware, but have not started on the box. I got the bright idea to make a "test" box out cardboard. Stop smiling. Anyway, I used the finest domestic cardboard and lots of duct tape.

It actually sounds pretty good. It would be a big improvement if I just left it as is. I checked the frequency response at what was supposed to be a 33Hz tune and things dropped off at 45Hz.

Undaunted, I added port length and tested with a 30 and 28Hz tune. All the charts look the same with the drop off at 45Hz (see attached).

So now I'm wondering if this lack of extension is due to the box or the driver. The driver models well in the low 30's. What do you think? Try not to talk ugly about the box. I am starting to like it.

response.jpg
 

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Joorge,

I've done some fairly ghetto stuff myself. We need pics.:R

What are you using for the port? Can you post the graphs without smoothing applied? It's uglier but much more informative.

I'm just guessing here but perhaps that little Dayton amp has a 45hz HPF built into it, or some EQ? I'm not familiar with it but it wouldn't be surprising. :scratchhead:
 

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Discussion Starter #3
Thanks Ricci. No smoothing - I just manually entered the data. I did a near field frequency chart and it's real flat from 45 to 100, but it has the same drop at 45.

The amp amp has no manual or specs other than what is posted on the PA site. I called PA and they said it has a 19Hz rumble filter. I guess there is a chance of a filter in the receiver. I'm using the sub out from an Onkyo CR-325. I'll check the specs.

The port is 1-3/4" I.D. tubing 10" long. I have 2 extensions around 2" each (I forget the actual length) I can add to change the tuning.



Is it possible that air leaks and flex in the box will cause the problem?
 

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What brand of duct tape are you using? And what frequency is it rated for (there should be a label somewhere saying "frequency deliniation threshold" or something like that).

Sometimes when difficult problems like this are upon us, we have to dig deep!

One time my friend's system was soundling horrible, turns out he was using speaker wire that was not rated for digital music!
 

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Could the 25watt amp just be running out of steam? Maybe it just doesnt have enough juice to push the speaker any harder any lower?
 

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Discussion Starter #7
That Moose Lodge comment may be worth a few pictures. Maybe I can put some kits together for sale to the boys.

The tape is 140 MPH high speed tape. Can't find any frequency information. Maybe it's not audio quality.

The power was worth a look. It models OK, but may not meet advertised specs. I unhooked the mains and took some readings. All my other test were with the gain set at 3 o'clock. At max gain in the 45Hz area it only had 1 or 2 dB more, so it's about done.

When I set the gain at 12 o'clock, SPL reduced 12-15 DB across the board. Should have been plenty of power available there. The same 45dB dip happened at all gain settings.

I guess it's not the power, but I'll try using the high level terminals tomorrow. I'm still looking for an opinion as to weather the cardboard can cause this dip.
 

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Yeah, maybe the whole coardboard box is flexing enough that it is acting like a passive radiator of sorts, and isn't there usually a dip in output at the resonant frequency of a passive radiator. Maybe you just saved us all a lot of time in figuring out the resonant frequency of a cardboard box?
 

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Discussion Starter #10
Hi Mike. I used UniBox and the parameters provided by PE. Here they are if ya wouldn't mind checking my work. I don't have the file necessary to include the 19Hz rumble filter in my model.

Power Handling: 50 watts RMS/100 watts max *VCdia: 1-1/2" *Impedance: 4 ohms *Re: 3.6 ohms *Frequency range: 38-800 Hz *Fs: 38 Hz *SPL: 83 dB 1W/1m *Vas: .416 cu.ft. *Qms: 2.65 *Qes: .47 *Qts: .40 *Xmax 13 mm.

Here's a link: http://www.parts-express.com/pdf/264-832s.pdf

On another front, I hooked up using a high level connection. Getting a stronger signal. Had to turn the gain down from 3 o'clock to 12 to maintain the same SPL. The sub channel is not adjustable and must be set for a much more efficient woofer.

A quick scan indicates that things got a little better. The drop off is not as steep and about 5 more Hz was gained.

hl response.jpg
 

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Discussion Starter #12
A weekend of tinkering has not helped reconcile the predicted vs actual Fb. I'm still about 10 dB down at The predicted F3 of 33Hz. Staying flat to 42Hz with F3 at 38 is the best I have been able to do.

Due to near field placement, there is apparently no help from room gain. I didn't consider that when I started.

I think I've wrung out any set up and placement errors. That leads me to speculate that:
I didn't calculate the parameters correctly.
Tang Band is fudging on their specs.
Hi tech box material doesn't support low frequencies very well.

I guess this high-tech box with space age adhesives will not be a good way to confirm performance. The little woofer is a kick to watch. It pumps hard and sounds great. I think I'm going to really like it when I get it finished.

Here's a picture of the box. Feel free to copy or modify the design.

Test Box.JPG
 

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Discussion Starter #14
Thanks Mike. Is a 1.75" port 10" long correct?

I guess I could skip the plate amp entirely and power the woofer directly from one of the output channels of the receiver. Would that work? The specs are 19 W + 19 W (4Ω, 1 kHz, FTC) 0.4% (1 kHz, 1 W).
 

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Discussion Starter #17
The FR is virtually identical with all of the combinations I have tried.

Onkyo Sub Out to plate amp LL in.
Onkyo HL out to plate amp HL in.
Onkyo HL out direct to woofer connections.
Computer sound card to plate amp LL in.
 

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Discussion Starter #19
Real box? Is this some kind of slur regarding my engineered wood product enclosure? I will continue with this fine box until I give up on using it to test response (the time is close at hand).

Great link. I agree with everything he said about that little woofer. It's a gem.

I would say the charts are very similar. The difference is he is in a 12L box with F3 of 35 and I am getting about the same values in 14L with F3 of 33. His chart closely follows the UniBox model.

The difference may be in the measurement techniques and accuracy of the equipment used. He seems to have good stuff and I am using a RS meter with the Shack cal file.

I'm thinking that the effect of my port is not in the measurements because it is in the rear. When I actually build, it will be in the front, like his. Do you think this is some of the difference?

Another puzzle is that I don't get any lower response when I add port length to what should be an F3 of 30 and 28Hz. The the model indicates this is feasible. Sorta like the box stalls out in the 38-40Hz area.
 

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Real box? Is this some kind of slur regarding my engineered wood product enclosure?
I wasn't sure if it was still cardboard or not. Wall flex and the fact the port is in the rear would explain the drop in measured output.

Another puzzle is that I don't get any lower response when I add port length to what should be an F3 of 30 and 28Hz. The the model indicates this is feasible. Sorta like the box stalls out in the 38-40Hz area.
That problem should be eliminated once a (how should I put this) "real" box is built. :bigsmile:
 
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