[firef4ly]

Good afternoon all,


A few months ago I bought a BIC F-12 for my 600 sq. ft. open living room which, while was better than my home theater in a box sub, left the lady friend and I wanting more "rumble" in our chests. In order to fill this craving I am looking into building a subwoofer using an old Eclipse SW8122DVC subwoofer I have had sitting around since 2006. Using BassBox 6 Pro I have made some boxes, but to tell you guys the the truth I'm just lost on how powerful this thing will be based on what I am seeing.


Also, I don't know what kind of amp I need to buy to power this thing to it's potential. The Dayton audio 500/1000w amps I see on Parts-Express are within my budget but I have a few issues. BassBox shows the speaker bottoming out at around 10hz with 500w of power, but if I move the power loads to 273w (8 ohm load on this speaker) I no longer have to worry about bottoming the driver out. Can I run the speaker at 500w and the 24db/octive cutoff save the speaker from bottoming out? How does that cutoff work?


Now for the limitations. I plan on building this box as a table that will be behind the couch so I can throw all those darn pillows she has to buy on something else besides the floor. I am looking for dimensions around 22in H x 45in W x 15in D so that I can put 4in legs on it and a top that is 6in off the ported enclosure. I would like to keep my price for an amp under $350. Lastly, I would like to keep the design of the box as simple as possible because I don't have the knowledge to make a multi angled design.


Thanks for your help

 

[LTD02]

sounds like a good project to keep those pillows off the floor.


your designs look fine so far. make sure to use a large port (1/3 or so of driver area or larger) so you don't get 'chuffing'. slot ports are pretty easy.


when you hit a driver in a ported cabinet with some power it is possible to damage the driver, so high pass filters are generally recommended. could you clarify your question on "how they work"? do you in general how does a high pass filter work or do you mean on a specific amplifier? if it is the latter, it depends on the amplifier, so link to the one that you think might work.


all the general advice applies. build it heavy. brace it well. make sure there are no air leaks and so on...


btw, i'd choose the lower tune. what is that about 18hz or so?

 

[firef4ly]

Thanks for the response LTD02


The box was originally setup with a 16hz tune, so here's one with a 10hz tune. I also made a graph showing a single 4" port (red line) and 2 3" ports (yellow line).


If my understanding is correct a high pass filter cuts of low frequencies after a certain point, and a low pass filter cuts off high frequencies after a certain point. What I don't understand is how the 24db/octave cutoff plays into the graphs. Does the 24db/octave cause the graph to go vertical at the points of cutoff (orange line), or is it cause a steep drop (green line). If it causes a steep drop then I can push the driver to 500w and not cause the driver to hit its xmax but still get some low frequencies. Otherwise I guess I need to wire the driver up for 8ohms and drive it with 273w of power so it does not go over its xmax.


These are the dayton audio amps I was looking at.
http://www.parts-express.com/pe/show...number=300-807
http://www.parts-express.com/pe/show...number=300-809

 

[firef4ly]

I know it is a holiday weekend and most on here are probably trying to get ideas for their own build but could someone explain to me how the high pass/low pass filters on dayton audio amps work, and how the decibel per octave ratings work. For example the 500w Dayton plate amp from parts-express offers says it has a 28db per octave drop off.

 

[Rob Flanery]



Quote:
Originally Posted by firef4ly /forum/post/20900161


I know it is a holiday weekend and most on here are probably trying to get ideas for their own build but could someone explain to me how the high pass/low pass filters on dayton audio amps work, and how the decibel per octave ratings work. For example the 500w Dayton plate amp from parts-express offers says it has a 28db per octave drop off.

Someone with more knowledge (and measurements) than I will be able to set me straight if I am wrong, but I am of the understanding that the performance and accuracy of the filters is sub par when compared to aftermarket offerings like the Behringer DSP1124 or other units.


Having said that, I use a 70W plate amp to power one of my subs and rely on the filter in concert with an FMOD 30hz low pass and have no bad things to say about it's performance. I think that the quality of the filters will rely partially on how hard you plan to push the sub. If you don't intend to run it out on the ragged edge I would think the built in filters would do OK.

 

[flyng_fool]

The high pass filter prevents any freq below the ability of the driver from continuing through the signal chain. If the driver attempts to play a freq lower than it' design, it unloads and does all kinds of nasty things so you want to prevent it. The low pass filter is for the upper end so it transfers those freqs to your mains. Above 80 Hz or so sounds go from omnidirectional to directional so you don't want to be able to localize your sub. A 28 dB/octave filter is basically a butterworth crossover. It acts as a "brick wall" type filter where the output drops off dramatically at the designed frequency. At least I'm pretty sure that's correct, i'm certainly no guru. But, in an extremely long winded answer to your question, I believe the green line represents the drop-off. I'm not aware that there is a true "brick wall" style crossover where it would drop straight off.

 

[Mpray1983]

Is 273 watts puts you in excursion why not just use a 240 or 300?