Sealed and THD

[Hifisound]

Hi all,

 

I was going through details on SVS SB12 and saw this statement - "Distortion results are good with the usual increase at deep bass frequencies seen with a sealed enclosure"

 

I am thinking of attempting a DIY project of a sealed sub with moderate SPL. Some parts shortlisted :

1) Dayton Ultimax/Titanic 15"/18" or Stereo Integrity 15"/18" HT driver

2) Crown XLS1500 amp

 

Already have a Minidsp 2x4 for EQ

 

My question is are there any specific choices in sealed design by which THD can be lowered below 10% even upto 20 Hz ? like choosing 18" over 15" or a larger enclosure ? Or is this expecting too much from sealed....

Though the measurements of stereo integrity/Dayton subs show the THD to be less than 10% upto 30Hz which should be fine for me, but thought of asking...

 

On related note , are the parts selected a fine choice ?

 

Thanks,

Hifisound

 

 

[maxmercy]

Compared to the very large increase in distortion seen in ported enclosures below tuning, sealed is better in that regard. But there is no replacement for displacement. The more air you can move, the lower, louder and cleaner you can play. There are several options:

 

1. Multiple sealed - requires more power than the other options, but best flexibility in placement.

 

2. Large sealed/IB - must be built-in, or be enormous boxes limiting placement, but requires less power than smaller sealed, and highpass capability to prevent over-excursion.

 

3. Large vented/resonant tuning - HUGE boxes, less power requirement for same dB, but a definitive low frequency cutoff requiring a highpass.

 

4. Horns - HUGE boxes, least amount of power requirement, very low distortion. But as with vented, low frequency cutoff that must be high passed (tapped horn), or measured and more gently highpassed to personal distortion threshold (front loaded horn). Also more complex to build. If you have big space, time and capacity to build, and little $, hard to beat a set of horn subwoofers if you have placement flexibility

 

All are compromises that require varying budget and space considerations.

 

What you need to determine is what does your room look like (room is almost the most important piece of the puzzle) how low you need to go, and how loud. Then what amount of space you can give up, and budget.

 

Notice that I use the plural of subwoofer. If you are looking for a single sub, you are looking at only a single seat with good sound.

 

 

JSS

[Hifisound]

Some points :

 

1) I am actually planning for dual subs and would prefer small sealed enclosures and setup using Dr. Geddes method.

2) Listening position is single seat 3 ft nearfield setup (Behringer 2031 or JBL LSR308) . Basically desktop PC setup

3) Budget $400 per sub (without amp)

4) Though will be happy if I can get 20 Hz at low THD, 30 Hz should be quite fine for the music I listen

5) Current room is 16' x 11'

6) Will be using Dayton EMM-6, Focusrite 2i2 and Rew for measurements and unbalanced minidsp 2x4 for EQ

7) Not aiming for high SPL, but for low THD.

[Ricci]

For low distortion with sealed subs the main contributors are the driver quality, the airspace that the driver is operating in and how much output you are asking for from the driver. Sealed drivers depend entirely on the driver excursion for output. The deeper the frequencies the more excursion the driver is asked for. A larger driver or multiple drivers require less excursion for the same output so distortion goes down generally. a smaller box requires more power to be applied to the driver to produce the same deep bass output so this can also cause an increase in distortion. Then there is an effect called air spring distortion which is generally more of an issue with very small sealed boxes.

 

Pick a driver with lots of xmax and linear inductance (Look for mention of shorting rings or sleeves in the motor)

Use as large of diameter drivers as you can or multiple smaller drivers. (Try for as much cone area as possible to keep excursion low. Multiple motors will spread power over multiple voice coils.) This is generally more important than the airspace each driver sees for distortion as the lions share comes from the driver selected and the amount of excursion required from it. Lets say that you can fit a 4 cu ft sealed enclosure design...Instead of using a single 15" try to use an 18" or perhaps even cramming 2 15" in each enclosure instead.

 

The Ultimax or Stereo Integrity lines should both be pretty good.

[Hifisound]

Thanks all..

I will then stick with Dayton 18" or SI 18" and a 4 cuft enclosure and see how it goes...

 

One minor question about ultimax series, there freq response is quoted upto 1000Hz.

What it would benefit would it bring to a sub which may max be used upto 120-150Hz (to overlap with mains)

[Hifisound]

One more thought :

Since I am planning to have 2 subs : I can go with one 18" and one maybe 12" ?

[maxmercy]

Thanks all..

I will then stick with Dayton 18" or SI 18" and a 4 cuft enclosure and see how it goes...

 

One minor question about ultimax series, there freq response is quoted upto 1000Hz.

What it would benefit would it bring to a sub which may max be used upto 120-150Hz (to overlap with mains)

 

If you plan on using it in a multi-way tower, but the Ultimax is not the right tool for that job.

 

JSS

[maxmercy]

One more thought :

Since I am planning to have 2 subs : I can go with one 18" and one maybe 12" ?

You could.

 

But you have only a single listening position.  One sub is all that is needed, and EQ properly, and treat the room for modal ringing, and first reflections.  If you don't get enough output with one, adding another with the same amount of power to it will get you 6 more dB.

 

JSS

[Hifisound]

If you plan on using it in a multi-way tower, but the Ultimax is not the right tool for that job.

 

JSS

 

I am planning one driver per enclosure

 

You could.

 

But you have only a single listening position.  One sub is all that is needed, and EQ properly, and treat the room for modal ringing, and first reflections.  If you don't get enough output with one, adding another with the same amount of power to it will get you 6 more dB.

 

JSS

 

I can start with 18" one and then check if I get flat response and add one more if required (I doubt I will be short of SPL in my setup......)

[Ricci]

Hifi...I don't know how the UM-18 will stack up compared to the other go to low cost 18's. It isn't available yet so it is all just speculation at this point. On paper it looks good.

[lilmike]

As Ricci said - the Ultimax is still a paper tiger, we've not seen one in the wild yet. I've got no doubt that it will be in stock some day, but for now, the other choices are available, tested, and proven.

 

One thing that has been touched on, but can't be stressed enough. THD is DIRECTLY related to SPL, because THD happens when the cone moves. More cone motion, more distortion. Less SPL, less cone motion.

 

The easiest way I know of to get lower distortion reproduction at the same SPL is to add drivers. When using reasonably-priced drivers (as being discussed), this is paramount. It matters even with elite drivers, it's just that the elite stuff can be pushed a bit harder before reaching the limits. 

 

All drivers will distort, because all drivers have to move to reproduce sound. You really do get what you pay for. Bargain drivers are cheap for a reason. The driver options being discussed are definitely good values, but are not the caliber of the UXL or LMS-Ultra. At 1/4 the price, something has to give. 

[Hifisound]

As I mentioned, in my case I wouldn't be needing high SPLs, maybe 100dB (or even lower)

So I hope the low cost drivers should offer the necessary extension at low THD

Instead of starting with 18" I may even start with 12" as this is my first attempt and see what results I get....

 

Does anybody have experience with 12" ultimax ? or shall I stick to 12" RS HF/HO ?

 

How good are the parts-express knock down cabinets ?

[lilmike]

If you're gonna go through the work to build a sub, build a proper one.

 

To make the same SPL, the 12 will have to move at least twice as far. 

 

The 12 has a cone area of about 500 sq cm. The 18 has a cone area that is double that. 

 

Double the area means half the excursion for the same volume displacement.

 

100 dB at the seats means a lot more at one meter. When the driver starts below 90 dB at a watt, you're already asking it to take peaks of several hundred watts.

 

No experience with any of the knock-down cabinets.

 

 

edit: typos and clarification

[maxmercy]

Hfs,

 

Can you draw us a quick layout or pic of the room?  I think you may be able to get away with a small(er) sub(s) if you use them in the nearfield.  

 

JSS

[Hifisound]

Attaching the layout of room (almost to scale)

I was thinking of position 1 and 2 for subs.

 

 

[maxmercy]

http://www.diysoundgroup.com/subwoofer-flatpacks-2.html  for CNC cut cabinets.

 

You should be just fine with one or two subs if you only have one listening position.  Your mains can dish out around 105dB clean, and you will only be 1m away, so 15s or 18s for the subs for very low distortion.  If you will not listen too loudly, 12s could easily work.  Definitely treat the front wall and ceiling, and the back wall.

 

JSS

[Hifisound]

Thanks!

[Hifisound]

On this site, I see there is one car audio driver based subwoofer too (MTX 9515-44) with very good measurements

How good are/will be the T8000 series drivers ? Anybody has experience ?

 

T815-22/44

 

http://www.mtxaudio.eu/products/caraudio/subs/item/t815-22?category_id=3

http://www.mtxaudio.eu/products/caraudio/subs/item/t815-44?category_id=3

 

I can go with more bigger box than one used for 9515...

[Hifisound]

And can't resist asking about this

 

http://www.seismicaudiospeakers.com/18-Raw-Subwoofer-Driver-Speaker-18-p/new%20madrid%2018.htm

[lilmike]

And can't resist asking about this

 

http://www.seismicaudiospeakers.com/18-Raw-Subwoofer-Driver-Speaker-18-p/new%20madrid%2018.htm

 

Nothing to see there. There are far better options out there for nearly the same money.

 

TS Parameters

• Resonant Frequency (fs):   48Hz
• DC Resistance (Re):  9.5 Ohm
• Mechanical Q (Qms):  2.3
• Electromagnetic Q (Qes):  1.1
• Total Q (Qts):  0.75
• Compliance Equivalent Volume (Vas):  157.7 Ltr
• Mechanical Compliance of Suspension (Cms):   63mm/N
• BL Product (BL):  21.2 Tm
• Diaphragm Mass Airload (Mms):  173.5g
• Surface Area of Cone (Sd):  1.3k cm²

 

The specs that are there don't impress me at all. The list is incomplete though. The Qes is too high, the woofer will be boomy in even a fairly large sealed box. An Re of 9.5 ohms is higher than I'd expect (8 ohm), or lower than I'd expect (16 ohm). 

[lilmike]

On this site, I see there is one car audio driver based subwoofer too (MTX 9515-44) with very good measurements

How good are/will be the T8000 series drivers ? Anybody has experience ?

 

T815-22/44

 

http://www.mtxaudio.eu/products/caraudio/subs/item/t815-22?category_id=3

http://www.mtxaudio.eu/products/caraudio/subs/item/t815-44?category_id=3

 

I can go with more bigger box than one used for 9515...

Looks suitable for a sealed box, that's about it. Qes is a bit high still.

 

Better than the seismic, by far, but not likely going to be a "low" distortion motor. 

[Hifisound]

These alternatives just came up came up on my search on Amazon.com ( and seller also being Amazon)

The reason for such a search was that Amazon sometimes gives free global shipping for products sold by Amazon, so such an alternative will quite cheap for me as compared to Dayton/SI where shipping price to India will be same or more than driver price

Even was looking at some drivers from Eminence/Earthquake (sold by Amazon)

But I don't think any matches the params of Dayton/SI, so not much option I think.

[Ricci]

Looks suitable for a sealed box, that's about it. Qes is a bit high still.

 

Better than the seismic, by far, but not likely going to be a "low" distortion motor. 

 

 

I disagree about the MTX 9515...Look at the distortion results, the lack of an inductance hump, the  amount of power dumped into the driver and the size of the test box (Tiny!). Low distortion requires at least a few things...A BL curve that is symmetric and linear with stroke and inductance and suspension components that behave in the same manner. Additionally for subwoofers this behavior needs to be maintained over substantial voice coil displacements and high power handling is also needed to prevent compression effects and allow the driver to use those excursions in reasonable sized enclosures.  The 9515 is one of the few long excursion, high power drivers that actually puts it all together well. Lots of aluminum in that motor which actually seems to be utilized where effective at linearizing inductance, 4" voice coil with substantial power handling, and legitimate xmax specs of over 1". Unfortunately it is super expensive now after being brought out back from discontinued status.

 

I've never used the 8500 series and it seems to be a substantial step down from the 9500 but MTX drivers do seem to have competent engineering put into them.

[Hifisound]

Though I know its parameters have commented upon, I will just post the data I got from the company for seismic

 

• Manufacturer: Seismic Audio
• Model: NEW MADRID 18
• Piston Diameter = 400.1 mm
• f(s)= 38.36 Hz
• R(e)= 9.67 Ohms
• Z(max)= 48.27 Ohms
• Q(ms)= 3.462
• Q(es)= 0.867
• Q(ts)= 0.693
• V(as)= 196.800 liters (6.951 cubic feet)
• L(e)= 1.69 mH
• n(0)= 1.22 %
• SPL= 92.97 1W/1m
• M(ms)= 194.10 grams
• C(ms)= 0.09 mm/N
• BL= 22.84 
• Xmax=13mm

And also a huge list of Freq Impedance Phase data

[lilmike]

I disagree about the MTX 9515...Look at the distortion results, the lack of an inductance hump, the  amount of power dumped into the driver and the size of the test box (Tiny!). Low distortion requires at least a few things...A BL curve that is symmetric and linear with stroke and inductance and suspension components that behave in the same manner. Additionally for subwoofers this behavior needs to be maintained over substantial voice coil displacements and high power handling is also needed to prevent compression effects and allow the driver to use those excursions in reasonable sized enclosures.  The 9515 is one of the few long excursion, high power drivers that actually puts it all together well. Lots of aluminum in that motor which actually seems to be utilized where effective at linearizing inductance, 4" voice coil with substantial power handling, and legitimate xmax specs of over 1". Unfortunately it is super expensive now after being brought out back from discontinued status.

 

I've never used the 8500 series and it seems to be a substantial step down from the 9500 but MTX drivers do seem to have competent engineering put into them.

 

For clarification, I was referring to the 8500 series. I've not seen any Klippel data for the 8500s. 

There is certainly competent engineering there, but when the cost comes down, parts must get left out. 

 

Judging by my experience with the lower tiers of MTX drivers, the steps are significant. Like everything else you do get what you pay for (once you know what value is).