ultimax 18 box modeling help needed.

[Jwhite]

Re: ultimax 18 box modeling help needed.



This is the footprint I would like to use I have never liked this stand since we brought it home. I would like to replace this with my subwoofer I would not be loosing anymore space than I already dont have. I am open to suggestions at this point. My wood working skills are up to the task but my designing skills are lacking. What can I do?

[Beau]

Re: ultimax 18 box modeling help needed.

I have an alternative for you - since it seems you might be a tad overwhelmed right now.

Rather than design something, there are a lot of merits of using an existing design for a somewhat similar driver.

Google "Martysub" or "Marty subwoofer".

It is based on the Dayton RSS460HO, but will also work for the SI HT 18, and several others. It is fairly well documented.

Given the size of the stand you are looking to replace, you may be able to build two - and place them end-to-end.

There are dimensioned drawings available. Build complexity appears to be fairly low.

[Chris Roemer]

Re: ultimax 18 box modeling help needed.

J, did you perhaps miss reading post #2?

[Jwhite]

Re: ultimax 18 box modeling help needed.

No chris I read post number 2. I guess I will just build that enclosure and live with it.

[JRT]

Re: ultimax 18 box modeling help needed.

No chris I read post number 2. I guess I will just build that enclosure and live with it.

I would suggest slowing it down a little bit. Some who might give you some help may not be able to afford immediate time to do so.

[Jwhite]

Re: ultimax 18 box modeling help needed.

JRT I am in no hurry. I am still reading and trying to learn.

[RoboCam]

If I use 3/4" MDF, what should the dimensions of the enclosure be if I want a 14 cubic foot cube (plus additional volume for driver displacement and the port)? I would like to use a rectangular port along the full width of the bottom (unless you think I should use a round flared port - how many watts would a single 6" flared port handle at 15Hz?), so I need some help calculating the port's dimensions. I'd like it tuned to 15Hz and not chuff at up to 2000 watts if possible (to handle brief peaks).

I'm still playing around with the design, so nothing's set in stone. All I know is that I want it to be able to reproduce the low C of a pipe organ clearly (16 Hz). I believe this song reaches that note at the 0:56 and 1:06 timestamps.

https://www.youtube.com/watch?v=SZ4AAL7vx-4

I'm listening to it on my earphones, and it sounds lower than the 20Hz tone on my test CD. Can someone confirm? I'd also like to know if this driver is better suited for this than the Dayton Reference Series 18. In other words, which one will produce the highest output at 16Hz if given 1000 watts? I will be powering it with one of the Crown XLS amps. My plan is to have 2 of these in my basement music system. If necessary, I will add two more. I'll have sealed subwoofers handling the bass above around 30Hz.

And to play with another idea, how many 4 cubic foot sealed UM18s would I need to produce the equivalent 16Hz output of a single UM18 at 1000 watts in the above ported enclosure?

Re: ultimax 18 box modeling help needed.

Here are my thoughts on some good enclosure sizes for the Ultimax 18.

Possible enclosure alignments:

Car Audio - 3-4 Cubic Feet Sealed, anechoic F3 30/27 Hz

HT/Music - 4-6 Cubic Feet Sealed, anechoic F3 27/26 Hz, Qtc 0.9/0.8

Home Theater - 8 Cubic Feet Vented, 20 Hz tune, anechoic F3 = 18 Hz

Infrasonics - 14 cubic feet vented, 15 Hz tune, anechoic F3 = 14 Hz

Infinite baffle use - OK

The parameters of the UM18-22 make it usable in a variety of enclosure configurations - it's not restricted, for instance, to sealed enclosures. If necessary, you can squeeze one into a 6-cubic-foot vented box tuned around 20 Hz. Variety is the spice of life.

[Chris Roemer]

A cube with a 30-1/2" OD should get you close enough to 14cf.
A 6"id PVC port that's 15" long should give you a 17Hz tune (use a generous flare on the exit, and "aim" it away from your listening position (to the rear would be best)). Models show that at 1000w RMS (the thermal limit), the Xmax isn't exceeded until below 15Hz. It should deliver 16Hz @ 115dB.

A 25" OD cube gives you 7cf (sealed), but no number of closed boxes will give you output @ 16Hz equivalent to the vented box unless EQ'd about +9dB @ 18Hz. That boost needs 8x the amp power of course, if any amps can even be set that low?

[RoboCam]

Actually, I want to port it at 15 Hz, and it looks like a 6" port is too small. The air velocity would be 40 m/s at 16 Hz with 1000 watts. I modeled it in WinISD with a rectangular port of 30.5" x 1.75" and 39.5" long, and the port velocity drops down to an acceptable 21 m/s under those same conditions.

I think I'll put the port on the same side as the UM18 because I don't want the room to load the port and UM18 differently because of how far apart they are from each other.

I also modeled a UM18 in a 4 cu ft sealed enclosure, and at 16 Hz, the difference is 11.7 dB vs the ported, so I would need 4 sealed UM18s to produce the equivalent output at 16 Hz (not as bad as I imagined). This is tempting because I could just buy the enclosures from Parts Express, greatly simplifying the build, and it would look so good, and they would also be much easier to move around.. I can flatten the response using a Linkwitz Transform and/or an EQ.

What to do. What to do. I wonder if the sealed design would sound better in a system used primarily for music. This would also simplify integration because then I could do away with the subs that handle the bass above 30Hz. But then I would have 8 to 16 subs to deal with along with their amplifiers. The ported enclosure is becoming more attractive again. I also don't think I'll be able to appreciate the benefits of sealed enclosures in the range of 15-30Hz. A ported design would also produce less distortion. Looks like ported it will be.

A cube with a 30-1/2" OD should get you close enough to 14cf.
A 6"id PVC port that's 15" long should give you a 17Hz tune (use a generous flare on the exit, and "aim" it away from your listening position (to the rear would be best)). Models show that at 1000w RMS (the thermal limit), the Xmax isn't exceeded until below 15Hz. It should deliver 16Hz @ 115dB.

A 25" OD cube gives you 7cf (sealed), but no number of closed boxes will give you output @ 16Hz equivalent to the vented box unless EQ'd about +9dB @ 18Hz. That boost needs 8x the amp power of course, if any amps can even be set that low?

[Adam_M]

I'm working a similar large sub project, Tumult 15" in 6CF ported, and I'm not sweating a lot of the things you've noted - I just don't think they are going to matter - at least to me and in my room. I'm tuning a little higher, but still have extension well into the teens. Port velocity at 1KW is controlled until about 22-23Hz - then I got to thinking.

If this thing is putting out 115+dB (and probably higher because of room gain minus whatever I lose from port compression), am I REALLY going to hear port chuffing using a 6" precision port (the flare on that thing is ridiculous)? And if I've got 115dB of boom coming out of the sub, is a little chuffing really going to bother me? Probably not.

And then I got to thinking - how often am I going to really be dumping 1KW into it? Could it really even take 1KW continuous? Probably not.

If I drop the power to 500W, the port velocity is controlled entirely*. So I made a compromise - I accepted there will be increased port chuffing between 112dB and 115dB. I think that's a perfectly fine compromise to not have a much larger box and pipe resonances (something you need to watch out for too). My ears will still bleed plenty at 112dB.

I'm not sure why you are concerned about the port and the UM18 being on the same side. The wavelength of a 20Hz wave, assuming I did the math right, is 56 feet - so I don't think moving the port to the bottom or back (a couple feet at most) will be an issue. I'm putting my sub on relatively tall feet and firing the port straight down into thick, plush carpet. That'll cut down on the audibility of the chuffing a bit, and keep critters and human critters from putting stuff in the sub.

Good luck - it'll be a fun project.

*I've got an external amp with a DSP and I'm EQ'ing the heck out of this thing, including a subsonic cut at something like 13 or 14Hz to help with excursion (but also to a lesser extent port velocity).

[RoboCam]

I've made some of those compromises in past builds too, but this is going in my basement music hifi system, where I won't be as constrained by size. Actually, I've already dropped the power in my calculations. I decided to model for 1000W instead of 2000W for short-term bursts, so it may not be ideal at times, but that's the only way to make the port size more manageable, though I might decide to make it even bigger. I'll route the port edges with a roundover bit. I'm sure I'll hear chuffing if there is any, despite how loudly it can play. Chuffing contains higher frequencies, which can be very noticeable. I can definitely hear the chuffing of my SVS 12" subs that have 4" flared ports.

The first port resonance occurs at 171 Hz, so I'm assuming it will be ok. If I tune it higher to 20 Hz, the output at 16 Hz will drop by 3 dB, wasting half of my amplifier power. Also, I want to reduce port compression. If I make the port too big, it's not a problem, but if I make it too small, it would be a huge hassle to correct.

I'd have to do some testing to know how the port position would affect the response in my listening area but what I do know is that when I move my head just a few feet away from the subs in my home theater, the low bass is gone, and the room is over 7000 cubic feet with two open walls. Even in an environment as small as a car, sub positioning is critical. If the port ends up in a location that results in a null at my listening position, that would not be good. I could move the sub, but then the front of it might not be in an ideal position, or who knows. Maybe it would be in an excellent position. This is something I'll have to think about experimenting with if it doesn't sound the way I'm hoping it will. Maybe I could use a flexible vent, haha.

Yeah, downfiring is a good idea for the reasons you mentioned. I found Easter eggs in one of mine once, lol. But for this system, I can't hide such a good looking driver, and I enjoy watching the sub in action. I'll have to come up with some way to protect them though.

Oh, I'm definitely not putting a subsonic filter on mine. I like to see the subs move. Though I don't think any music is going to significantly unload a sub ported at 15 Hz, and I'm sure the UM18 will handle extreme excursions with no problem. Curtain Shaker should give it a challenge.

https://www.youtube.com/watch?v=UWnMYdbTtfg

Back in the 90s when I had Cerwin Vega VS150s, I used to play this song and watch the woofer unload. I had no idea what the frequency of the low note was but we just assumed for fun that it was 18 Hz because it was track 18 on the CD.

https://www.youtube.com/watch?v=lb-rzvG7ETc

Maybe I should just build it like this.

https://www.youtube.com/watch?v=Xgv2eE4Isuw

Ears bleed at 112 dB? Have you played with subwoofers in cars?

Thanks, I'm sure it will be fun project.

I'm working a similar large sub project, Tumult 15" in 6CF ported, and I'm not sweating a lot of the things you've noted - I just don't think they are going to matter - at least to me and in my room. I'm tuning a little higher, but still have extension well into the teens. Port velocity at 1KW is controlled until about 22-23Hz - then I got to thinking.

If this thing is putting out 115+dB (and probably higher because of room gain minus whatever I lose from port compression), am I REALLY going to hear port chuffing using a 6" precision port (the flare on that thing is ridiculous)? And if I've got 115dB of boom coming out of the sub, is a little chuffing really going to bother me? Probably not.

And then I got to thinking - how often am I going to really be dumping 1KW into it? Could it really even take 1KW continuous? Probably not.

If I drop the power to 500W, the port velocity is controlled entirely*. So I made a compromise - I accepted there will be increased port chuffing between 112dB and 115dB. I think that's a perfectly fine compromise to not have a much larger box and pipe resonances (something you need to watch out for too). My ears will still bleed plenty at 112dB.

I'm not sure why you are concerned about the port and the UM18 being on the same side. The wavelength of a 20Hz wave, assuming I did the math right, is 56 feet - so I don't think moving the port to the bottom or back (a couple feet at most) will be an issue. I'm putting my sub on relatively tall feet and firing the port straight down into thick, plush carpet. That'll cut down on the audibility of the chuffing a bit, and keep critters and human critters from putting stuff in the sub.

Good luck - it'll be a fun project.

*I've got an external amp with a DSP and I'm EQ'ing the heck out of this thing, including a subsonic cut at something like 13 or 14Hz to help with excursion (but also to a lesser extent port velocity).

[Chris Roemer]

You lose -1dB @ 16Hz by lowering the Fb those 2 Hz.

[Adam_M]

I'd strongly consider using the precision port specifically- that roundover on both the inside and outside helps, and is far bigger than any router bit I'm comfortable using. I wouldn't be so confident you'll hear the chuffing in that case except perhaps in the most extreme edge case. I spent much of my early builds chasing academic perfection and designing for those edge case until I actually tried the compromises and found which ones are ok and which ones aren't -again to me. Those isn't one I cases but it won't cause issues if you do.

171 for the resonance is borderline to me, I'd rather it be 2 octaves away, but I'm also making a similar compromise.

Yes, I acknowledge that moving your head or the sub can activate/engage different room modes. Below a few hundred hz, response is dominated by the room. That's why I've got 6 (4 open baffle) drivers in 4 locations covering that range. To me, that works far better and is more important than sweating port location details.

I can tell you from experience that having the port a few feet from the driver isn't an issue. As far as the wavefronts are considered, those distances remain acoustically small. I've got a speaker that's tuned a little higher with the port almost 4 feet from one of the drivers and I promise you its not an issue.

I'd down fire the port only, not the driver. Give it a try. You might like it. Plywood is cheap.

I can't think of a good reason to go without a subsonic filter. At worst it's neutral ( if you don't have material playing to unload the sub, it filters nothing) and if you do, it protects the sub, but to each their own. You'll no doubt see the sub move. I'd personally rather sacrifice deep subsonics instead of shelling out for a new driver damaged by mechanical overexcursion.

[billfitzmaurice]

I want it to be able to reproduce the low C of a pipe organ clearly (16 Hz). I believe this song reaches that note at the 0:56 and 1:06 timestamps.

A pipe organ doesn't produce much at 16Hz. What's heard are the second, third and fourth harmonics at 32, 48 and 64 Hz.
http://www.pykett.org.uk/reedpipetones.htm

This isn't unique to pipe organs, it applies to all low frequency instruments.

[RoboCam]

Ah, yes, this is why you have to boost the fundamental. However, the song in the link I provided has a strong fundamental with little harmonics. When I listen to it on my headphones with the low bass boosted, it sounds so good. I want to reproduce that experience on my speaker system. When I play that song on my system with 6 SVS 12" ported subwoofers, it sounds like garbage, which is understandable because it's out of their designed range. This is why DIY is the only affordable solution.

I've hesitated building something like this for years because I kept telling myself that I can just enjoy this rare occurrence on my headphones, but I think I'm changing my mind.

A pipe organ doesn't produce much at 16Hz. What's heard are the second, third and fourth harmonics...