3015 lf box that plays down to 30hz??

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littlemike

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Joined 2008
Small? 30 Hz? 3015 LF? Not gonna get all three. The 3015 likes a BIG enclosure, no doubt about that. I'm looking at 30" deep, 36" tall, and 23.5" wide, external. if that is too big, I can see if it is possible to squish the width any further.

This is a tapped horn, and is 100 dB 1W, 1M 2pi, -3 dB @ 33 Hz. 100 W gets you 120 dB @ 7 mm excursion, 250 watts is essentially xmax, at around 125 dB, 600 watts gets you north of 125 dB, within xmech.

30 Hz highpass is not an option.
 
jwmbro

jwmbro

Member
Joined 2007
small footprint but tall? How about a single fold tapped horn.

20" x 20", but 5 and a half foot tall:

3015LF_Tapped_Horn_20in_by_20in_by_66in.png


121dB with -3dB point at 30Hz. Highpass mandatory.

EDIT: oops, posted this before I saw that you don't have a highpass. Could get about 115dB within xmech, but exceeding xmax below 21Hz if you didn't use the highpass with it.
 
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jbell

Member
Joined 2003
justint said:
ok so any other suggestions besides the tapped horn? or I guess i could buy a amplifier with a high pass?
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Passive radiators don't have the unloading issue below system resonance that ported or tapped horns have.

A Jurassic Park T-Rex stomp turned up in a TH without a high pass = one very cooked driver.

I'm kinda intrigued by a 3015lf / PR design, and may spend some cycles investigating it.
The rule of thumb is that you need 3x the Vd of your driver, in your PR's. 3 of the dayton 12's @10mm xmax each doesn't quiet get you there, but it's close. (and they are cheap)

A PR design would allow you a small enough box to be allowed in the living room as well.
 
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jbell

Member
Joined 2003
when you click on any image in this forum -- if the image is larger than the 'expanded size window' you'll see a little white X in the lower left corner. Clicking on that will fully expand the image to it's native size and make things readable. (You can use any dimensions you like, as long as you come up with 180liters volume)

Dayton SD315-PR 12" Passive Radiator | Parts-Express.com

Is where you can buy these PR's... however I have to admit, this is a very low tech solution, and I'm sure others can come up with something a little more eloquent, so to speak....

so... anyone got a better idea for a 'no high pass' cabinet for a 3015lf?
 
Brian Steele

Brian Steele

Member
Joined 2007
diysubwoofers.org
jbell said:
Passive radiators don't have the unloading issue below system resonance that ported or tapped horns have.
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Not quite true. It depends on your selection of PRs. THEORETICALLY you can limit the excursion below Fb by selecting PRs that are a bit on the small side (=low Vd), but I would not suggest doing that, because of the possible adverse effect on output above Fb. And if you select PRs that are large enough (=high Vd), you'll likely be subject to the same excursion issues below Fb that you'd see with vented alignments.

Having said that, and as I've mentioned before here, you can basically ignore HornResp's predictions for excursions over Xmax. T/S params no longer apply. BL and Cms have likely changed significantly. And when HornResp predicts the poor driver is going to try moving 40 mm when fed a 10Hz signal at 200W, the reality is that it's likely not going to move anywhere near that amount, because the parameter values used by HornResp to calculate that excursion are no longer applicable.

Case in point - For my test TH POC#2, as part of my testing I fed the damned thing 3Hz (yes, that's THREE HZ) signals (waayyy below its ~42 Hz Fb) at ~75-100W. HornResp predicted silly excursion at that low frequency and power level. The reality - the driver didn't move anywhere near that amount, but it did make some ugly noises (distortion). It wasn't happy, but it didn't explode.

The only way to find out what the 3015LF would actually do with signals below Fb at high levels is to actually try it out.
 
jwmbro

jwmbro

Member
Joined 2007
justint said:
so on these passive radiators do I just add them to my box with the 3015lf and put one on each side or how do I set this up??
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Yeah, basically you can place them anywhere around the box, there are probably some vibration advantages two having two of them exactly opposite each other, but doubt it's a huge deal.

By the way, if you do still want to consider something with a highpass, I've got a simulation for a very small tapped tapered quarterwave tube here, which does about 116dB with a -3dB point at 30Hz, and it's only 100liters big. (In imperial units, that translates to 14" x 17" x 43" external dimensions)

It still needs some tweaking (I can get a fairly solid design at 150l, the 100l design is still a bit sketchy), but it's amazing how small you can go with these T-TQWT boxes.
 
jwmbro

jwmbro

Member
Joined 2007
Brian Steele said:
Details :)
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ARGGGHH!!! I was trying to make hornresp let me export records as .txt, so I ran the program as admin, and it deleted ALL my records!! (about 50 of them saved in the program)

In any case, I tried to recreate my design from memory, and I think I got pretty close. Take this design with a huge grain of salt, and to any of the more inexperienced users here - do not build the following design! As I said, it still needs some tweaking - my current worry is the 1/3.5ish compression ratio, which is probably a bit too high for a large paper cone driver. You could easily increase the opening size, however this either means going about 20l bigger, or losing about 3Hz extension. But nonetheless, for playing around, my highly unfinished design, if anyone is interested, please do try to improve it.
 
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