Push Pull Subwoofer Build?

[davewantsmoore]

18 hours ago, Primare Knob said:

As I understand you can control xMax curve or "efficiency" by changing the box volume, is this what the size of the box is all about?

Yes....   If you hold the power constant... and change the box .... then that will change how much the driver moves.

18 hours ago, Primare Knob said:

Is it save to assume that they have a 3dB or peak reserve?

No.  The datasheets indicate how much distortion to expect at close to full power.

18 hours ago, Primare Knob said:

The other thing I haven't read into yet is, do I need to protect the amp or woofer from very low frequencies?

You need to prevent the amp from clipping, and the woofer from moving too much.....   Low frequencies could cause either of those things, but on their own are no concern.

[almikel]

On 25/11/2018 at 3:21 PM, davewantsmoore said:

 

I linked the wrong one.

 

There's a 1x500w plate amp and a 2x250w plate amp.

 

Hope that makes sense.

 

and a 2 x 500W version (into 4 ohms) FA502

they look like the go.

In PK's case the 2 x 500W (into 4ohms) "should" give some headroom

https://www.hypex.nl/product/fusionamp-fa502/159

 

@Primare Knob are you still looking at multiple Dual Opposed sealed enclosures?

My internet is on "go-slow" - I'm trying to see if the amps are 2ohm safe??

If not you would need 1x 2ch plate amp (FA502) for each dual opposed sub (if using the 4ohm RSS460HO) with each driver powered by a 500W channel.

That would be 1 hell of a sub and 2 units the same would have ample headroom for your requirements.

 

21 hours ago, Primare Knob said:

As I understand you can control xMax curve or "efficiency" by changing the box volume, is this what the size of the box is all about?

as the box size increases you'll need less EQ (and amp power) to push the driver lower in a sealed box.

I'll have to defer to @davewantsmoore on driver excursion at a particular frequency with varying box size - does a larger box have lower driver excursion compared to a smaller box at the same SPL or the same excursion? ie ignoring power requirements, does a larger box allow higher SPL based on driver Xmax?

 

21 hours ago, Primare Knob said:

The hypex amps are rated in RMS but it doesn't state anything about the peak power output. Is it save to assume that they have a 3dB or peak reserve?

Not if you want to play it safe - work on the RMS power as the maximum.

 

21 hours ago, Primare Knob said:

The other thing I haven't read into yet is, do I need to protect the amp or woofer from very low frequencies?

when applying EQ to boost lower frequencies in a sealed sub - during the design phase it's highly recommended to model excursion and stay within Xmax, and within amp power.

Too much EQ can easily chew through excursion and amp power.

 

Sealed subs are different to ported or tapped horn subs - ported and tapped horn subs have massive excursion increases below tuning - driver busting excursion.

Sealed boxes don't have this - excursion still increases as frequency drops but not dramatically. Still be careful with lots of EQ.

If you've designed for the excursion and amp power required in a sealed box, IMHO a high pass filter isn't required to protect the driver.

 

I initially had a 20Hz high pass filter on my T20 tapped horn sub, but removed it after some simple tests (finger on the drivers with sine sweeps at elevated volumes) showed that with my room gain, 15Hz "in room" is achievable without excursion going nuts - not very quantitative - but I'm comfortable cranking the stereo knowing my sub stays within its limits.

 

I think with your SPL targets and design process, you will remain well within the "envelope" of achievable SPL/Xmax/amp power - especially if you build 2 subs - more so with 2 x dual opposed subs.

 

cheers

Mike

[davewantsmoore]

4 minutes ago, almikel said:

I'm trying to see if the amps are 2ohm safe??

Yes, Hypex nCore amps are.

 

5 minutes ago, almikel said:

does a larger box have lower driver excursion compared to a smaller box at the same SPL

No.   If the excursion is the same.... then the SPL is the same.

 

The box size, will affect the power required to achieve the SPL (excursion).

 

 

5 minutes ago, almikel said:

ie ignoring power requirements, does a larger box allow higher SPL based on driver Xmax?

No.   How much the driver moves (ie. how close it goes to xmax) ..... is exactly the same thing as "how much SPL"?

 

If you have woofer, moving a certain amount .... they produce the same SPL!       (The power required, and box size, are just circumstantial).

 

5 minutes ago, almikel said:

Sealed boxes don't have this - excursion still increases as frequency drops but not dramatically

In theory .... a sealed box SPL decreases by 12dB/octave below the system resonance.... and the excursion stays constant.

 

5 minutes ago, almikel said:

not very quantitative

... but quantitative enough.    "finger says that's not nuts" ... is a measurement technique.   

 

5 minutes ago, almikel said:

I think with your SPL targets and design process, you will remain well within the "envelope" of achievable SPL/Xmax/amp power - especially if you build 2 subs - more so with 2 x dual opposed subs.

Yep.    Being realistic, 105dB type levels are only ever reached in a domestic situation for very short term peaks on dynamic content.     Content which is not-dynamic, is going to need the dial tuned down - as 100dB average levels aren't what typical people consider comfortable.

 

... so if we're talking about putting in close to full amp power, and running a few mm past xmax.... for just those really big short peaks.    Then everything is going to be fine.

[Primare Knob]

I have been working with the following drivers and I think the Dayton UM18-22 is the winner. The dual opposing RSS390HO is a good candidate as well, but the price makes this a harder choice.

I find it interesting that at 20Hz it doesn’t really matter which driver or amp you use as you always seem to end up within the same range. I now understand why some setups use more than 2 subwoofers as this seems to be the only way to increase LF output at the low range without pushing into possible distortion levels.

 

RSS390HO X2, 90 litre cabinet ($2825 - $3050)
101dB at 20HZ single sub at listen position xMax maximum, amp 500W RMS
104dB at 20Hz dual sub at listen position xMax maximum amp 500W RMS
+1dB needed for peak output which should be fine for driver cone excursion (xMax +1mm) or amplifier (650W peak).

HypexFA502 x2 $1650
Dayton SPA1000 x2 $1175
Dayton RSS390HO x4 $1400

 

RSS460HO x1, 85 litre cabinet ($2100 - $2700)
98.5dB at 20HZ single sub at listen position xMax maximum amp 500W RMS
101.5dB at 20Hz dual sub at listen position xMax maximum amp 500W RMS
+3.5dB needed for peak output which could potential not be fine for driver cone excursion (xMax +6.5mm +50%) or amplifier (1300W peak, unless a 1000W amp).

HypexFA502 x2 $1650
Dayton SPA1000 x2 $1175
Dayton RSS460HO x2 $1026

 

UM18-22 x 1, 170 litre cabinet ($2100 - $2700)
100.5dB at 20Hz single sub at listen position, xMax well within limits, amp 500W RMS
103.5dB at 20Hz dual subs at listen position, xMax well within limits, amp 500W RMS
+1.5 dB needed for peak output, cone excursion well within limits, could be fine for the amp (700W, or using a 1000W amp)

HypexFA501 x2 $1134
HypexFA502 x2 $1650
Dayton SPA1000 x2 $1175
Dayton UM18-22 x2 $912AUD

 

The UM18-22 has the biggest potential to stay clear of distortion limits but requires the biggest cabinet. I could potential go for a 100L cabinet and 1000W RMS amp and still stay within xMax and outside peak amp output. Does a smaller cabinet have any other negative effect besides xMax efficiency?

 

From all drivers, the UM18-22 has the biggest potential and headroom for when I am searching for more or if my room changes.

 

I have taken into account a -3dB drop of in room SPL vs the theoretical -6dB drop
I don’t yet know if the cabinet includes driver volume or not
I have not taken any room gain into account.

 

I can save roughly $500 using the Dayton SPA1000 instead of the Hypex FA502. Are the Hypex plate amps worth the extra cash, beside the DSP functionality?

Edited November 28, 2018 by Primare Knob

[davewantsmoore]

Quick google of the RSS460HO shows a couple of people mention it is underrated in xmax.    Might pay to confirm that data...  Although I've seen some varying claims for xmech (one as low as 19) ... so not really sure what to say there.

 

The UM18-22 has a larger xmech, which people reliably, quote so I assume it's mentioned in the datasheet.

 

4 hours ago, Primare Knob said:

Are the Hypex plate amps worth the extra cash

It's hard to say - as I don't know a lot about the Dayton amplifiers.   I would guess yes.   They are both lots for the money, ie. the Hypex amps are good value.... and very very well performing amps based on the data.    Is there data for the Dayton amps?  (If no, you might think that is telling).

[davewantsmoore]

4 hours ago, Primare Knob said:

Does a smaller cabinet have any other negative effect?

It may mean the driver needs more power to achieve a certain amount of motion.

 

4 hours ago, Primare Knob said:

I have not taken any room gain into account.

What I typically do is.    Do all my sims and calculation based on a flat response.... ignoring room gain.

 

Then when I put the driver in the room, I get a "free" bass..... which usually works out to about the amount I wanted to tilt up the bass response anyways.

 

Crude... but.

 

[Primare Knob]

Dayton Audio 18" Reference Series HO
"Running the driver in free air with sine waves indicates that it is capable of nearly twice as much stroke as the Xmax would indicate with a value of about 20 mm seeming like a good value for "useful" excursion after which the output distorts heavily."
 

Quick google of the RSS460HO shows a couple of people mention it is underrated in xmax.    Might pay to confirm that data...  Although I've seen some varying claims for xmech (one as low as 19) ... so not really sure what to say there.
 
The UM18-22 has a larger xmech, which people reliably, quote so I assume it's mentioned in the datasheet.
 
It's hard to say - as I don't know a lot about the Dayton amplifiers.   I would guess yes.   They are both lots for the money, ie. the Hypex amps are good value.... and very very well performing amps based on the data.    Is there data for the Dayton amps?  (If no, you might think that is telling).

That is what Nada has mentioned before. Reviews on Data Bass suggest the bigger xMax range for both drivers.

At the moment the UM18-22 is a bit cheaper than the RSS460HO, where the UM18-22 has more room for future changes but doesn't get fully utilised as the RSS460HO.

On AVS forum people suggest the RSS460HO has more quality while the UM18-22 has more quantity, as that is also how they are marketed. Is there any merit in these claims?

I like to go for quality, and both drivers perform similar in a similar sized box. The RSS460HO having a bit more output in the upper bass range. Performance in size and price are roughly the same and doesn't give a real preference picking one or the other.

[Primare Knob]

The other thing that probably is out of league is perhaps use passive radiators to downsize the box.

[almikel]

The other thing that probably is out of league is perhaps use passive radiators to downsize the box.

Ported or passive radiator would typically require a larger box than sealed

[Primare Knob]

Ported or passive radiator would typically require a larger box than sealed

I am playing with that at the moment, but doesn't give me the results I was hoping for.

[davewantsmoore]

3 hours ago, Primare Knob said:

Is there any merit in these claims?

Probably less than comments on forums would make you think.

 

The important thing for quality is keeping the non-linear distortion low.... ie. keeping excursion low, and power input low....  and after this, flat frequency response.

 

UM18-22 seems like a fine plan.

[almikel]

9 hours ago, almikel said:

Ported or passive radiator would typically require a larger box than sealed

 

8 hours ago, Primare Knob said:

I am playing with that at the moment, but doesn't give me the results I was hoping for

I've never modeled passive radiator boxes, but they behave the same as ported boxes, so for the same driver, both ported and passive radiator will require a larger box than sealed...but will produce lower bass than sealed with no EQ on the sealed box...

...as Dave has said previously, the ported/passive radiator enclosure/design is applying EQ via the enclosure.

 

In a high end sub (or subs), such as you're designing, so long as sealed designs can meet your LF and SPL targets (amp power and excursion), IMHO I would stay with sealed.

 

If you're still planning a "dual opposed" design to minimise cabinet vibrations, and more than 1 sub of the same design, then that will produce prodigious clean bass most bass pigs would be proud of 

 

Based on what @davewantsmoore said, the Hypex FA502 is safe at 2ohms, so you could run 1 x dual opposed sub (2 drivers in parallel) on 1 side of the amp, and another dual opposed sub on the other side of the amp.  

 

I'm envious !

 

cheers

Mike

  

[davewantsmoore]

11 hours ago, Primare Knob said:

use passive radiators to downsize the box

How loud?

How low?

How big?

 

Pick two .... then we can design subwoofer for your needs.

 

You seemed to be set on 105dB in the listening position, which is about right .....  So do you have an enclosure size goal? .... or?

[almikel]

4 minutes ago, davewantsmoore said:

How loud?

How low?

How big?

 

Pick two .... then we can design subwoofer for your needs.

Hoffman's Iron Law

[Primare Knob]

How loud?
How low?
How big?
 
Pick two .... then we can design subwoofer for your needs.
 
You seemed to be set on 105dB in the listening position, which is about right .....  So do you have an enclosure size goal? .... or?

Just tinkering with all the possibilities, learning along the way. Trying to see how much I can push it.

105dB @20Hz at 2.2 meter with 2 subs of undistorted bass. Anything below 20Hz is a welcome bonus. Just trying to fit that into the smallest box, or a visual small box.

Can some fluffy stuffing help to make the box accousticly bigger, or does this not work for subwoofers.

[davewantsmoore]

6 minutes ago, Primare Knob said:

Anything below 20Hz is a welcome bonus

I think that's a good idea.    So, 105dB@20Hz ....  What size box would you like to have?

[Primare Knob]

I've never modeled passive radiator boxes, but they behave the same as ported boxes, so for the same driver, both ported and passive radiator will require a larger box than sealed...but will produce lower bass than sealed with no EQ on the sealed box...
...as Dave has said previously, the ported/passive radiator enclosure/design is applying EQ via the enclosure.
 
In a high end sub (or subs), such as you're designing, so long as sealed designs can meet your LF and SPL targets (amp power and excursion), IMHO I would stay with sealed.
 
If you're still planning a "dual opposed" design to minimise cabinet vibrations, and more than 1 sub of the same design, then that will produce prodigious clean bass most bass pigs would be proud of [emoji41]
 
Based on what [mention=108814]davewantsmoore[/mention] said, the Hypex FA502 is safe at 2ohms, so you could run 1 x dual opposed sub (2 drivers in parallel) on 1 side of the amp, and another dual opposed sub on the other side of the amp. :thumb: 
 
I'm envious !
 
cheers
Mike
  

I can't find a good way to calculate box size based upon dual opposite drivers. My guess on other designs is that the box doesn't need to be 2x as big as with a 2 driver box.

Spec wise, the dual RSS390HO doesn't outperform a single RSS460HO in the low bass region. Money wise it's more expensive.

I am not sure which model Hypex you have in mind, but the FA502 is a plate amp with two power amps that can be bridged.
2x500W into 4ohm (dual opposed) or 1x1000W (single) into 4ohm or 1x1200W into 8ohm. It seems that there isn't much headroom beyond peak RMS.

On a different note, it also has a fan. I can't find any info on how loud it is.

[Primare Knob]

I think that's a good idea.    So, 105dB@20Hz ....  What size box would you like to have?

The smallest. In my thinkering it seems to hover around 90 litre netto.

[davewantsmoore]

1 minute ago, Primare Knob said:

I can't find a good way to calculate box size based upon dual opposite drivers.

If you've got WinISD... Just select 2 drivers in the wizard, and go at it.

1 minute ago, Primare Knob said:

I am not sure which model Hypex you have in mind, but the FA502

The NC500 module datasheet shows (depending slightly on the load impedance) that the distortion begins to rise dramatically at about 400w .... and reaches 1% at 500w.

1 minute ago, Primare Knob said:

I can't find any info on how loud it is.

I have not seen either of the models which have fans. .... but I read it is very(!) quiet.

[davewantsmoore]

6 minutes ago, Primare Knob said:

18 minutes ago, davewantsmoore said:

I think that's a good idea.    So, 105dB@20Hz ....  What size box would you like to have?

The smallest. In my thinkering it seems to hover around 90 litre netto.

 

2x 12" drivers

750 watts

25 litres

15mm excursion @ 105dB

 

This is with a -6dB @ 20Hz  response.... and a rolloff of 24dB/octave (not the typical 12dB/octave of a sealed box).

 

If you add the room gain that WiniSD is ignoring .... You will get back to close to flat response down to 20Hz or below ..... I'd recommend more than one of these, of course ..... but the box is nearly smaller than what you need to fit the drivers.     Just a quick fire example anyways.

[Primare Knob]

 
2x 12" drivers
750 watts
25 litres
15mm excursion @ 105dB
 
This is with a -6dB @ 20Hz  response.... and a rolloff of 24dB/octave (not the typical 12dB/octave of a sealed box).
 
If you add the room gain that WiniSD is ignoring .... You will get back to close to flat response down to 20Hz or below ..... I'd recommend more than one of these, of course ..... but the box is nearly smaller than what you need to fit the drivers.     Just a quick fire example anyways.

Is there a specific driver, or is this a general specification for a 12" sub? And is the power required per driver or total?

[davewantsmoore]

10 hours ago, Primare Knob said:

Is there a specific driver, or is this a general specification for a 12" sub? And is the power required per driver or total?

That's a driver which is designed for a small box.   It's total power.    In a really small box (say 15L per driver), it takes ~500w to get each driver to its absolute limit of ~20mm.

 

It's just an example of "extreme small".    If you have a size preference, make it known... Like I said before think about "choose 2" ... and the other one (of size, LF, SPL) will just work itself out.

 

 

[davewantsmoore]

11 hours ago, Primare Knob said:

Is there a specific driver, or is this a general specification for a 12" sub?

It's "general" in so far as a 12" "piston" moving back and forwards X amount will make Y SPL.

 

Depending on the certain driver design.... it will need a certain amount of power to move, which will also depend on the box (the air in the box is part of the system).

[Primare Knob]

Size is a bit flexible. I prefer a small size as it will make them less intrusive in my small room, but I like to get more bass at 20Hz and below, than what I have now with 2 single 12" subs.

Let's say, 400x400x800mm or 500x500x500mm external as a maximum. Not sure of 18mm is thick enough. I was planning to use 2x16mm plywood.

[Wozza_Lee]

Off topic but look at Martycube's over on AVS. I have built 4 and am extremely impressed