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DIY Ultimax Sealed vs SVS

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Dimitris_dsgg

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Joined
Oct 14, 2025
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Hi everyone, merry Xmax!!


I’ll try to keep this as short and clear as possible so I can explain the situation, my needs, and ask for advice.


Room: 13 × 12.5 ft with 9.8 ft ceilings (does not open into a larger space when the door is closed)


Usage: Music and movies. We listen to a lot of bass-heavy music since this room also functions as our home gym, but we also watch movies and TV series.


AVR: Denon X-2700H


LCR: Monolith 365C + 365T


Surrounds: Kenwood Series 21 satellites


Subwoofer: (don’t laugh) Logitech Z-5500
I converted it to passive and connected it to a NEC A-230E amp. I believe the NEC has a preamp stage inside, because when I tried to power the Logitech sub with another amp, it didn’t produce any signal at all (not sure why).


I previously owned dual Monolith 13s, but I sold them because they were huge and we needed the space for other equipment in this multi-use room. Now I’m stuck with the Logitech sub, which heavily distorts during movies or when I turn it up (obviously there’s no proper limiter).



What I want to upgrade​


I want more bass. I’m not necessarily chasing infrasonics, but above 27 Hz (or even 31.5 Hz) I’d like to reach SPL levels of 120 dB+.


Limitations​


Maximum subwoofer depth: 19 inches



Prices for dual subwoofer options (Europe)​


  • Dual SVS SB-1000: €1,500
  • Dual SVS SB-2000: €2,100
  • Dual SVS SB-3000: €2,800
  • Dual SVS SB-5000: €5,600
  • Dual SVS SB-17 Ultra: €7,400
  • Dual Arendal 196 1S: €2,000
  • Dual Arendal 1723 1S: €3,000
  • Dual KRK S12 G4: €1,300


DIY option​


I could also go the DIY route with these sealed kits, powered by a pro amp:



Amp: Behringer NX6000D – €460



Questions​


How do these Ultimax sealed kits (15 or 18) compare to the other subs on my list?
For example, could dual UM18s provide more SPL from ~30 Hz to 80 Hz compared to the SVS SB-17?


If the CEA-2010 data I found for the Ultimax 18 is accurate, it seems this driver can easily outperform the SVS SB-4000. However, I can’t find CEA-2010 measurements for the newer SVS models (SB-5000 and SB-17).


Any advice or real-world experience would be greatly appreciated.
 

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The flat packs are good options. I'd get the 15in kit for your needs. Your space is small for 120fb sub output, even 15in at be overkill, but that's for you to decide!
 
PGansz said:
The flat packs are good options. I'd get the 15in kit for your needs. Your space is small for 120fb sub output, even 15in at be overkill, but that's for you to decide!
Click to expand...

Thank you! I had dual Monolith 13's until a few weeks ago and I never found them to be overkill (only space-wise, unfortunately). I run my subs hot and I want that power (I know I don't need it).

So, should I get dual Ultimax 15's? Are those going to give me +120db above 28 or 31.5hz?
 
Dimitris_dsgg said:
...
  • Dayton Audio UM18...
  • Dayton Audio UM15 ...
Click to expand...
Just note that the original Ultimax subwoofer drivers have been replaced with the Ultimax II.
The new ones should be an improvement, although I'm not sure how much the price or T/S parameters have changed.
 
a4eaudio said:
Just note that the original Ultimax subwoofer drivers have been replaced with the Ultimax II.
The new ones should be an improvement, although I'm not sure how much the price or T/S parameters have changed.
Click to expand...
Th new Ultimax II has a higher fs, bigger motor, more power handling, has more Xmax, and lighter mms resulting in about the same frequency performance but higher SPL.
 
Last edited:
Take a look at GSG subs, their flat packs are well designed and good quality and they specialize in "overkill" :) They have good prices on drivers and amps as well. https://shop.gsgad.com/

120dB+ at 27 Hz with low distortion is a tall order even in a small room, you are going to need a lot of power and you may want to look at "Pro Drivers" like LaVoce or Eminence especially if high SPL's are more important than ultimate LF extension. Remember CEA-2010 allows ~35% distortion @ 20 Hz to pass which even though humans are less sensitive to LF distortion is kind of a joke, my experience is <10% distortion sounds much better. Take a look at the FAQ section of the GKG site, they don't like to quote exact SPL levels but they have some graphs that help show what you are up against and you will get an idea of what is involved with building your own sub. Have fun!
 
120dbs? I can hit that in the mid-bass with a couple of my subs, but have little desire to. There have been a couple of movies scenes that make many uncomfortable at 115db.

Your bigger issue is a square room, almost. You'd be better off with two subs, treatment and more quality bass. Just my humble opinion.

Edit: looking at the max data test is like eye candy and not a real world scenario for almost everyone.
 
Last edited:
a4eaudio said:
Just note that the original Ultimax subwoofer drivers have been replaced with the Ultimax II.
The new ones should be an improvement, although I'm not sure how much the price or T/S parameters have changed.
Click to expand...

The prices, at least for the 18inch drivers, didn't increase significantly. It's like a 30euros (35usd) increase for the version II.
 
PGansz said:
Th new Ultimax II has a higher fs, bigger motor, more power handling, has more Xmax, and lighter mms resulting in about the same frequency performance but higher SPL.
Click to expand...
That's great news for me then! And I guess that goes for all the different sizes, right?
 
levimax said:
Take a look at GSG subs, their flat packs are well designed and good quality and they specialize in "overkill" :) They have good prices on drivers and amps as well. https://shop.gsgad.com/

120dB+ at 27 Hz with low distortion is a tall order even in a small room, you are going to need a lot of power and you may want to look at "Pro Drivers" like LaVoce or Eminence especially if high SPL's are more important than ultimate LF extension. Remember CEA-2010 allows ~35% distortion @ 20 Hz to pass which even though humans are less sensitive to LF distortion is kind of a joke, my experience is <10% distortion sounds much better. Take a look at the FAQ section of the GKG site, they don't like to quote exact SPL levels but they have some graphs that help show what you are up against and you will get an idea of what is involved with building your own sub. Have fun!
Click to expand...

Thanks for the help! Unfortunately, GSG doesn't have a warehouse in Europe. I contacted them a few weeks ago and the shipping costs plus the custom fees are crazy high. It's a shame that we don't have a company like GSG in Europe. We have access to great drivers like Eminence, Faital Pro, SB, Dayton etc but as for the kits we have close to nothing..

I understand now, I'm asking too much and unfortunately I don't have the room to place huge boxes.

If I asked for something like:

  • 20hz: 0dB (I don't care about those frequencies)
  • 25hz: 105-110dB
  • 31.5hz: 115dB
  • 40hz: 120dB
  • 50hz: 120dB
  • 63hz: 120dB
  • 80hz: 120dB
  • 100hz: 120dB

The above numbers are really close to the CEA-2010 2m peak SPL (from Sweetchaos) for the SVS SB-16 Ultra. And just a reminder, I'll go for dual Dayton Ultimax 15 or 18 in a sealed configuration. Last but not least, I'll feed them as many watts as they'll need.

Is that scenario more realistic?
 
Everett T said:
120dbs? I can hit that in the mid-bass with a couple of my subs, but have little desire to. There have been a couple of movies scenes that make many uncomfortable at 115db.

Your bigger issue is a square room, almost. You'd be better off with two subs, treatment and more quality bass. Just my humble opinion.

Edit: looking at the max data test is like eye candy and not a real world scenario for almost everyone.
Click to expand...

I'm definitely going for dual subwoofer configuration. Maybe place them opposite corners or something.

When I ran my Monolith 13's the infrasonics were amazing, the whole house was shaking and my ears could feel the air pressurized. But when I played music, they made me wanting more. Maybe all this was because of the bad placement.

I understand now, I'm asking too much and unfortunately I don't have the room to place huge boxes.

If I asked for something like:

  • 20hz: 0dB (I don't care about those frequencies)
  • 25hz: 105-110dB
  • 31.5hz: 115dB
  • 40hz: 120dB
  • 50hz: 120dB
  • 63hz: 120dB
  • 80hz: 120dB
  • 100hz: 120dB

The above numbers are really close to the CEA-2010 2m peak SPL (from Sweetchaos) for the SVS SB-16 Ultra. And just a reminder, I'll go for dual Dayton Ultimax 15 or 18 in a sealed configuration. Last but not least, I'll feed them as many watts as they'll need.

Is that scenario more realistic?
 
Dimitris_dsgg said:
I'm definitely going for dual subwoofer configuration. Maybe place them opposite corners or something.

When I ran my Monolith 13's the infrasonics were amazing, the whole house was shaking and my ears could feel the air pressurized. But when I played music, they made me wanting more. Maybe all this was because of the bad placement.

I understand now, I'm asking too much and unfortunately I don't have the room to place huge boxes.

If I asked for something like:

  • 20hz: 0dB (I don't care about those frequencies)
  • 25hz: 105-110dB
  • 31.5hz: 115dB
  • 40hz: 120dB
  • 50hz: 120dB
  • 63hz: 120dB
  • 80hz: 120dB
  • 100hz: 120dB

The above numbers are really close to the CEA-2010 2m peak SPL (from Sweetchaos) for the SVS SB-16 Ultra. And just a reminder, I'll go for dual Dayton Ultimax 15 or 18 in a sealed configuration. Last but not least, I'll feed them as many watts as they'll need.

Is that scenario more realistic?
Click to expand...
If you're good with EQing the low end and have a measurement microphone, the 18 can put out the numbers you're looking for.
 
Dimitris_dsgg said:
I'm definitely going for dual subwoofer configuration. Maybe place them opposite corners or something.

When I ran my Monolith 13's the infrasonics were amazing, the whole house was shaking and my ears could feel the air pressurized. But when I played music, they made me wanting more. Maybe all this was because of the bad placement.

I understand now, I'm asking too much and unfortunately I don't have the room to place huge boxes.

If I asked for something like:

  • 20hz: 0dB (I don't care about those frequencies)
  • 25hz: 105-110dB
  • 31.5hz: 115dB
  • 40hz: 120dB
  • 50hz: 120dB
  • 63hz: 120dB
  • 80hz: 120dB
  • 100hz: 120dB

The above numbers are really close to the CEA-2010 2m peak SPL (from Sweetchaos) for the SVS SB-16 Ultra. And just a reminder, I'll go for dual Dayton Ultimax 15 or 18 in a sealed configuration. Last but not least, I'll feed them as many watts as they'll need.

Is that scenario more realistic?
Click to expand...
Have you looked at the other options in the Dayton Audio lineup? There are variations in the Reference Series from High Output to High Fidelity as well. The HF subwoofers have lower extension but less ultimate SPL. Everything is a compromise!
 
PGansz said:
Have you looked at the other options in the Dayton Audio lineup? There are variations in the Reference Series from High Output to High Fidelity as well. The HF subwoofers have lower extension but less ultimate SPL. Everything is a compromise!
Click to expand...

I have looked at the Reference Series but I don't think I'd want to go lower than 28hz and have lower SPL overall. Also, the Ultimax Series is said to be a great lineup from Dayton.
 
Dimitris_dsgg said:
I have looked at the Reference Series but I don't think I'd want to go lower than 28hz and have lower SPL overall. Also, the Ultimax Series is said to be a great lineup from Dayton.
Click to expand...
They go lower, but really need to be ported which means bigger.
 
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