Dayton RSS390HF sub project question....

[jjkozlow]

I'm building a pair of 150 liter (5.3 cu.ft.) sealed enclosure for this driver. Based on what others have done with this driver, that seems to be a good size. It ends up in my modeling to be a .709 Qtc with an F3 of 32Hz without any boost.

Want to check in with a pro here to see if this is going to work. This is for 50/50 music and movies.

I am using the BASH 500 Watt amps which do have a mild 2dB boost at 30Hz.

Someone is telling me that, "With 5.3 liters sealed you will run out of excursion below 30Hz. Have you looked at the excursion curve for the alignment you propose, your asking for nearly a 1/2" peak to peak beyond the drivers rated X-max."

I'm no excursion curve expert; so is this true? If so, I do have a Behringer FDP. Would "reversing" the boost with that device help?

Thanks for any thoughts!!

[richie00boy]

The box size is irrelevant to when you will run out of excursion, all it means is how much power you need to feed it to reach the SPL you want at a specific frequency.

Given that your sub is for all intents and purposes flat to 32Hz, 2dB boost at 30Hz is unwanted so should be removed from the amp if possible.

You need to set SPL targets and how low you want it to go, then from there work out if these are do-able or if you need a new driver or adjustment of expectations.

[jjkozlow]

Thanks. I don't ever listen too loud, so my SPL goals are not great. At 65Hz I'm modeling 113dB's and 100dB at 30Hz which is plenty.

I do like pipe organ music though, so my low-end goal is to get to 20Hz, even a modeled F10 of 20Hz is fine by me.

Based on the Bagby subwoofer calculator, with an input of 500 watts (which is exactly what the driver can handle RMS) I'm getting an F10 of 18.56Hz without the bass boost and 16Hz with it. The BASH amp has a 19Hz low pass filter so I know those numbers are unreachable in theory, but I should be fine at about 10dB down at 20 Hz right? Maybe much better with room gain and the fact I'm building a "pair" of them?

[jjkozlow]

Also, forgot to add but the filter at 30Hz is changeable. Do you guys think it would be safe to add like a 2dB boost at 23-25Hz to improve the low end with my suggested alignment? Or am I going to "run out of excursion" with 500 watts pumping into the driver?

[pjpoes]

the lower the boos is added the more excursion problems you will have actually. Also, I think saying that enclosure size and excursion aren't related is misleading. THe increased pressure in a smaller box alone has an impact on the amount of excursion a woofer does at a given frequency. There are other issues at play here though. Looking at a speaker design and saying that it exceeds excursion at max power is a worthless statement. Most subwoofers can exceed their linear capability at power limits. You won't be reaching those limits very often, or at least you shouldn't be. If you are, then enclosure and amp aren't the issue, you are simply asking too much from your poor little sub. Though I have my issues with LT cuircits or boost at all to extend response, when used in moderation, it does work in real life, without having an intolerable impact on excursion limits, at reasonable listening volumes. Keep in mind that the reason excursion increases so much at the boosted frequency is because the amp is being forced to produce more power at that frequency as well, to exceed xmax by that much, more than likely the power curve would show it asking for in excess of 500 watts. Since the amp can't produce that, more than likely the amp will clip before the speaker does. Neither is wanted of course, but I think it shows the misunderstanding this person has of how this all interacts. Essentialy, this is a play between the mechanical limits of the woofer and the power output ability of the amp, and both are affected by the boost.

Now, if you look at the proposed design, with the proposed amount of boost, what you find is that it is well within its limits as reasonable listening levels. For music, I would be quite suprised if you listened much above 100 decibles. In fact if you do, turn it down, thats not so safe. What you find is that the setup is fine at those frequencies and output. Actually, I just ran the sumulation, with 30hz and 2.5 decibles of boost, at 100 watts, you end up with output at around 105 decibles to 30hz, and then it drops off from there. The speaker actually asks for less power at that frequency, only around 35 watts compared with the 100 watts throughout the rest of the band. This is caused by impedance swings and the fs of that box. It's maximum impedance is focused at 30hz, and you can run around 150 watts to the sub, which will give you 108 db's output flat to 30hz. From around 38hz up the speaker is capable of over 112 decibles, so you really are only limited below around 35hz or so. Again, thats only at those brief moment peaks, and at levels far exceeding what is typical. The only arguement I can see here is that your are limited durring dynamic peaks, but when you consider that music rarely has more than 10-15 decibles of dynamic range, which is just sad, but a truth of modern digital recordings, and consider that Movies aren't that much greater, I don't see it being a major issue. None the less, if you do listen to music at 100 decibles or more average, and the music is very dynamic, exceeding swings of 15 decibles, then you might hit those limits, and it might be bothersom. This could be more true with movies, but will be depending on room size and interaction as well. Noticing that you are building a pair, to get a better sence of what this is doing, simply build it as if its two in one box. That will give you what would happen if they were stacked ontop or next to each other. This will massivly increase your "headroom" and output, over 6 decibles based on the rules of thumb. On the other hand, if you use them in seperate corners, or in opposite sides of the room, you won't see much appreciable gain, but will have a smoother response. That is something for a different discussion, but I hope this is helpful.

[richie00boy]

Originally posted by jjkozlow
Based on the Bagby subwoofer calculator, with an input of 500 watts (which is exactly what the driver can handle RMS) I'm getting an F10 of 18.56Hz without the bass boost and 16Hz with it.

I've never heard of the Bagby thing. Don't get misled by the 500 watts power handling - that's just the voicecoil thermal capacity. It bears no relation to if you are exceeding Xmax or not.

You need to model what excursion limited SPL you can achieve.

[bjorno]

QUOTE].Do you guys think it would be safe to add like a 2dB boost at 23-25Hz to improve the low end with my suggested alignment?.[/QUOTE]

Of course you can, but the improvement in bandwidth would be just JND and paid by loss of dynamic range.

QUOTE].I do like pipe organ music though, so my low-end goal is to get to 20Hz, even a modeled F10 of 20Hz is fine by m.[/QUOTE]


F10 is already below 20 Hz. See the picture that tells another story.

QUOTE].Or am I going to "run out of excursion" with 500 watts pumping into the driver?.[/QUOTE]


Not if you lower the box volume too, at least less than 20L but then the cut-off will be close to 60 Hz.

b

1(1)

[jjkozlow]

Thanks for the replies. The actual box may turn out slightly smaller then 5.3 cubic feet because of bracing, the driver and then the plate amp itself. Of course, stuffing it will increase its size right back, more or less.

I'm actually using the program written by Jeff Bagby, its real name is "The Subwoofer Box and Circuit Designer" 2.0 spreadsheet and it's VBA modules. It seems to do an OK job, but it is getting diffeerent numbers then, say Unibox. I like the layout better which is why I use it.

For output, I get a max output of 113 decibles and at 30Hz I get 110dB so I'm pretty close to what pjpoes states. That's more then enough for me as my mains also have built in subwoofers using the matching RSS265 and RSS315HF drivers. I probably have yet to 100 decible PEAK in my room, I'm no loudness freak.

My computer is having a tough time opening what bjorno posted, with what I think is Martin King modeling. Anything worrisome there? He states "see the picture that tells another story".....

If you guys think I should reduce volume some, I can always add extra bracing. You think knocking out some volume would be beneficial? PE calls for optimum volume of 4.1 cubic feet but I was going after a bit more low end hence why I was making it bigger. Or do you think this sucker (a pair anyhow) will be OK "as-is".

Again I appreciate the sage advice!!!

[jjkozlow]

Also, thanks pjpoes I just did what you said and modeled 2 in a 300 liter enclosure w/1000 watts and the 2dB boost at 30Hz to give me a better idea what a pair will do. Yes, I use them in seperate corners to get a more uniform response. Regardless, it lifted max output to 119dB about the 6 you predicted! It also lowered F3 and F10 by about 2Hz. Bonus.

[richie00boy]

Changing box size will not affect output unless you start to hit the thermal limit of the voicecoil by making the box very small. A big box just needs less power to drive, that is all. I think people are confusing the issue.

Your chosen software vs Unibox give different results probably because they are based on different mathematical principles. For instance I follow Bob Bullock's calculations, which may well be different again. But at least Bob Bullock is a respected and peer-reviewed author, with the academic background to match.