Ultimax UM15-22 and 2 Passive Radiators

[Fochops]

Hi all,
I have been gaining some valuable insight in the home theater realm. I have started building a quasi-home theater in my living room that so far has impressed me. My subwoofer game is lacking though as I have one powered acoustech 12. I plan to step up my game, I have been tossing around a design for a sub enclosure that will be both cool and functional. I wanted your thoughts. It will be around 6.6ft3 before driver and radiator displacement. I have modeled it in Winisd and it looks very promising. I have one concern though, passive radiators tend to roll off steep and the ultimax subs aren't best known for excursion. If you look at the results you can see a steep roll off around the 20.8 Hz mark (which is ok by me) but when we look at the cone excursion it gets nasty around the 17 Hz mark. Will a 20 Hz HPF save the driver from over excursion? Woofer and radiators have been purchased, these are what I will be working with, and I plan on purchasing a Crown XLS 2 2002 to drive it. What suggestions are there for the 20 Hz HPF? I have read that it is already native in the crown amps but that's hearsay and I'd rather not drive a woofer on hearsay.

 

[everettT]

That driver is best used in a sealed cabinet. Model the Dayton RS series if you want to use PRs or ported. Also any ported or PR would need some filter to protect the drive below tuning.

 

[Fochops]

That driver is best used in a sealed cabinet. Model the Dayton RS series if you want to use PRs or ported. Also any ported or PR would need some filter to protect the drive below tuning.

I was hoping to get it to dig a little deeper. With all the parameters input the graphs are impressive. I modeled it in a sealed enclosure and was not enthused at all. What would you suggest for a HPF?

 

[everettT]

I wouldn't use it in your design, I'd use the RS. The UM in a moderate sealed enclosure and lots of power yields good results down low.
In a PR, a simple HPF should be all you need, but again not with that driver. Here is Josh's thoughts on the driver

Data-Bass: Subwoofer Measurements

data-bass.com

 

[lovinthehd]

The Crown XLS 2002 doesn't have the appropriate dsp (it's dsp for hpf/lpf is for a crossover, the lowest HPF that can be set is 30hz I believe). I think it would be the XTi 2002 that would have that capability....or use the XLS with a miniDSP unit.

 

[lovinthehd]

I wouldn't use it in your design, I'd use the RS. The UM in a moderate sealed enclosure and lots of power yields good results down low.
In a PR, a simple HPF should be all you need, but again not with that driver. Here is Josh's thoughts on the driver

Data-Bass: Subwoofer Measurements

data-bass.com

Different driver, tho, he's asking about the 15"

 

[everettT]

Different driver, tho, he's asking about the 15"

IIRC it is the same instance. I seem to recall @TLS Guy modeled it once and was not good.

 

[Fochops]

I wouldn't use it in your design, I'd use the RS. The UM in a moderate sealed enclosure and lots of power yields good results down low.
In a PR, a simple HPF should be all you need, but again not with that driver. Here is Josh's thoughts on the driver

Data-Bass: Subwoofer Measurements

data-bass.com

That is a detailed review, thank you for that. It is on the 18" and I am doing the 15". I'd imagine the sub would act close to the same as the 18" within reason mechanically. At 800 watts in a sealed enclosure I'd still be hitting around 108db at 20 Hz which isn't terrible. If I did 7ft3 I would have an F3 of 30hz. That seems like a large sealed enclosure though. It peaks better at 4-5ft3 but looses db at the lower end.

 

[lovinthehd]

IIRC it is the same instance. I seem to recall @TLS Guy modeled it once and was not good.

Just saying it wasn't the same driver. Don't know how similar or if it's just TLS' preference too.

 

[everettT]

That is a detailed review, thank you for that. It is on the 18" and I am doing the 15". I'd imagine the sub would act close to the same as the 18" within reason mechanically. At 800 watts in a sealed enclosure I'd still be hitting around 108db at 20 Hz which isn't terrible. If I did 7ft3 I would have an F3 of 30hz. That seems like a large sealed enclosure though. It peaks better at 4-5ft3 but looses db at the lower end.

It takes eq and power to get there, but is easily obtainable. Mark Seaton uses the 18 in his F18s that get 10hz in room with very good output. He is using up 2400 watts for a single unit.

F18+ & F18-Slave Subwoofer – Seaton Sound, Inc

seatonsound.net

Also this filter/eq will get you there

Linkwitz Transform

miniDSP is a leading manufacturer of Digital Audio Signal Processors for the HomeTheater, Hifi, headphone and Automotive market. Join our large community of Audiophiles, Engineers and DIYers using our innovative products.

www.minidsp.com

 

[Fochops]

It takes eq and power to get there, but is easily obtainable. Mark Seaton uses the 18 in his F18s that get 10hz in room with very good output. He is using up 2400 watts for a single unit.

F18+ & F18-Slave Subwoofer – Seaton Sound, Inc

seatonsound.net

Also this filter/eq will get you there

Linkwitz Transform

miniDSP is a leading manufacturer of Digital Audio Signal Processors for the HomeTheater, Hifi, headphone and Automotive market. Join our large community of Audiophiles, Engineers and DIYers using our innovative products.

www.minidsp.com

I stumbled across the minidsp 2x4 as well, would that be a viable option? I like the thought of dialing in the HPF.

 

[lovinthehd]

Many of us use minidsp units....and that would be one thing they could do....

 

[Fochops]

Comparison between sealed (yellow) and passive radiators (purple). I am still torn, I know some say not the best for passive radiators but the data looks pretty good! Room dynamics can play into both types of enclosures. Maybe I'm getting wrapped up in the data but the early roll off of sealed (from 61Hz to an F3 of 36Hz) leaves a lot to be desired. I feel like I would rather have a steeper roll off with an F3 at 21Hz. It is giving better db across the discernible frequencies. Am I missing something? I input a Butterworth n=2 HPF at 20Hz on both to control over excursion.

 

[CajunLB]

You’re don’t need that hpf on the sealed box.

 

[Fochops]

You’re don’t need that hpf on the sealed box.

The excursion without it was above the Xmax in sealed too.

 

[TLS Guy]

I was hoping to get it to dig a little deeper. With all the parameters input the graphs are impressive. I modeled it in a sealed enclosure and was not enthused at all. What would you suggest for a HPF?

We get this again and again. The Ultimax drivers are designed primarily for sealed application. They are not optimal for tuned enclosures. All sealed designs require active Eq, and you have to boost 12 db per octave below driver F3. This needs to be coupled with a high pass filter around 25 Hz to prevent driver damage. A speaker driver does not couple well to the air. The only advantage of a sealed enclosure is reduced size, after that it is all down hill as efficiency is awful. Loudspeakers require an acoustic transformer in the bottom end. That means some type of Helmholtz resonator, pipe or horn. Passive radiator enclosures roll of sixth order (36 db/octave) rather than the fourth order ported equivalent.

One thing you are forgetting in your designs is Q. Your graphs do not address bass quality. The Ultimax drivers will have too high a Q in resonant alignments. That means boomy bass.

If you want a potent 18" sub, this design of mine has been built by a number of members and they have been very pleased with it. The parameters of that driver are optimal for vented or transmission line designs. It makes for a big box though.

 

[Fochops]

We get this again and again. The Ultimax drivers are designed primarily for sealed application. They are not optimal for tuned enclosures. All sealed designs require active Eq, and you have to boost 12 db per octave below driver F3. This needs to be coupled with a high pass filter around 25 Hz to prevent driver damage. A speaker driver does not couple well to the air. The only advantage of a sealed enclosure is reduced size, after that it is all down hill as efficiency is awful. Loudspeakers require an acoustic transformer in the bottom end. That means some type of Helmholtz resonator, pipe or horn. Passive radiator enclosures roll of sixth order (36 db/octave) rather than the fourth order ported equivalent.

One thing you are forgetting in your designs is Q. Your graphs do not address bass quality. The Ultimax drivers will have too high a Q in resonant alignments. That means boomy bass.

If you want a potent 18" sub, this design of mine has been built by a number of members and they have been very pleased with it. The parameters of that driver are optimal for vented or transmission line designs. It makes for a big box though.

I certainly appreciate your input, I am in the beginnings of understanding what to shoot for. I need to read up on the Q of an enclosure. I will take a look at your design. I feel I’m on the right track of learning, I just don’t quite know yet what I don’t know if that makes sense? Again, thanks to everyone for their patience.

 

[NINaudio]

I stumbled across the minidsp 2x4 as well, would that be a viable option? I like the thought of dialing in the HPF.

With some tuning on a mini-dsp 2x4 HD I have my UM18 flat to 16 Hz in room in the sealed box that they sell for it on parts express. It is a very capable of driver, I would think you can get the 15" version flat to at least 20 Hz with a mini dsp.

 

[everettT]

I certainly appreciate your input, I am in the beginnings of understanding what to shoot for. I need to read up on the Q of an enclosure. I will take a look at your design. I feel I’m on the right track of learning, I just don’t quite know yet what I don’t know if that makes sense? Again, thanks to everyone for their patience.

The transform I linked will allow you to adjust the q for better bass and will get you the extension you desire if you are set on using that driver.

I used the math on my epik empire's when the plate amp failed on one of them and I replaced with crown amps. The results were much better than the original design as it had a simple 6db boost around 25hz followed by a simple HPF, that combo although good left a lot on the table. I can now get close to 100db at 12hz in room.

Most good sealed subs will start to roll off around 30hz at 12db per octave as stated. That means if you're at 120db at 30hz you're at 108db at 15hz (just an example). Eq and power will get the response flat to a desired extension. That eq, ie transform will provide the filters needed.

The design that Dr. Mark linked for the RS is a proven simple, but potent one, that requires no eq and less power to achieve the desired goals.

If you want to read more on theory, check out Siegfried Linkwitz here is the link to his website. He was a great pioneer in the advancement of audio science.

Linkwitz Lab - Loudspeaker Design

Design and consultation in electro-acoustics. Fundamental concepts of sound reproduction in rooms. Detailed design information for DIY construction of a subwoofer and an open-baffle speaker with exceptional fidelity. Dipole loudspeaker design for true to the original sound reproduction with...

www.linkwitzlab.com

 

[Fochops]

With some tuning on a mini-dsp 2x4 HD I have my UM18 flat to 16 Hz in room in the sealed box that they sell for it on parts express. It is a very capable of driver, I would think you can get the 15" version flat to at least 20 Hz with a mini dsp.

What cubic foot would you recommend for sealed? The Parts Express recommendation is 3.98ft3 but that seems small. Thoughts?