Dual Opposed Subwoofer project (2x RSS210HO8)

[ppataki]

This is yet another project that we will start relatively soon. It is linked to another in-process project: https://www.audiosciencereview.com/...theater-project-using-markaudio-chn110.26019/ that we are doing for my neighbor (who is the carpenter )

The above project is aiming to replace his current home theater system but it lacks the subwoofer (5.0)
The project is still not fully finished but have purchased the drivers and the amp for the missing subwoofer already.

We will use dual Dayton RSS210-HO8 drivers in parallel connection:

and a short video as usual:

New video by Peter Pataki

photos.app.goo.gl

The cabinet will be sealed and we will use the dual opposed subwoofer (DOS) concept
It will look something like this:

We are planning to use 24mm thick panels - now my neighbor has some genuine oak wood plates available; I would appreciate if anybody can comment on that please. Usually we use birch plywood but we are thinking about the oak since it is just there lying around.....

The amp driving the speakers will be a Monacor SAM-300D module at the bottom of the cabinet (since the front and the back will be occupied by the drivers and the sides are not an option due to the placement of the cabinet in the room)

Simulations look really promising:

Looking forward to sharing more details as we progress!

 

[Wolf]

You'll like it. I love my RSS210HF-4 woofers.

 

[alex-z]

A -3dB point of 60Hz is pretty disappointing by subwoofer standards, you will get nice kick drum response but not much deep bass. Would highly recommend some DSP to flatten the response at the cost of headroom.

Also, dual opposing woofers are great at reducing cabinet vibrations, but from a practical stand point, having 2 subwoofers spread throughout the room will perform much better for the same cost.

 

[ppataki]

We will indeed use DSP, forgot to mention that in my post
Based on my experience, all sealed box designs shall be corrected with DSP anyway - I use Dirac Live for all my projects
My neighbor does not have Dirac, he will use Audyssey - I will post some measurements accordingly

 

[bigjacko]

I think maybe your box volume is too small, so the fs will be too high. Do you want to try aperiodic enclosure? It should bring the fs down.

 

[ppataki]

Qtc value = 0.561 with the current box size so I think that shall be sufficient
I have designed sealed subs before and one of the learnings was that actual in-room response is way better vs the simulation, since the simulation does not take into account room gain which in my case is +15dB at 24Hz (and the same goes for my neighbor since they have exactly the same living room)
So the -15dB point in the simulation becomes the 0dB point in reality + you add the DSP to smooth the peaks and the end result is flat response down to 21Hz approx. (you can see that in the post I linked above)

FYI this is my actual measured room gain curve:

 

[abdo123]

Qtc value = 0.561 with the current box size so I think that shall be sufficient
I have designed sealed subs before and one of the learnings was that actual in-room response is way better vs the simulation, since the simulation does not take into account room gain which in my case is +15dB at 24Hz (and the same goes for my neighbor since they have exactly the same living room)
So the -15dB point in the simulation becomes the 0dB point in reality + you add the DSP to smooth the peaks and the end result is flat response down to 21Hz approx. (you can see that in the post I linked above)

FYI this is my actual room gain curve:
View attachment 171695

This is seems a bit on the low size to be honest, what is your first room mode? What are your walls made of? is the room sealed?

 

[ppataki]

Some small update, the cabinet construction has started!

Cabinet is made of 22mm birch plywood
There will be some bracing between the drivers, drivers and the amp will be flush mounted, internal damping will be applied, etc....(those are yet to be done, I will show them in the next update)
Final outer dimensions are: 40(H) * 23(W) * 38(D) cm resulting in a Vb = 19.9 liters

 

[bigjacko]

With all those drivers and electronics inside, what will be the temperature inside when playing hard? If I guessed right it looks like a sealed design, this will make air traped inside. I am not sure if it is an issue since everyone is doing like this. Do you have some knowledge around this?

 

[ppataki]

With all those drivers and electronics inside, what will be the temperature inside when playing hard? If I guessed right it looks like a sealed design, this will make air traped inside. I am not sure if it is an issue since everyone is doing like this. Do you have some knowledge around this?

Yes, temperature can be an issue. I am not an engineer but as far as I understand increasing temperature increases the resistance of the voice coil (the Re parameter) and that has an impact on the transient response of the driver (see the BL^2/Re formula)

But the truth is that these subs will actually never be driven really hard and definitely not continuously so I am not too worried about the temperature issue.

 

[bigjacko]

Yes, temperature can be an issue. I am not an engineer but as far as I understand increasing temperature increases the resistance of the voice coil (the Re parameter) and that has an impact on the transient response of the driver (see the BL^2/Re formula)

But the truth is that these subs will actually never be driven really hard and definitely not continuously so I am not too worried about the temperature issue.

The electronics don't like high temperature too. Heat is the worst enemy of electronics and make their life short. A lot of people have been talking shit about bad heat management design in amps, but there are still a lot of companies putting electronics inside speakers just like you do. If possible ask some electronic people's opinion on this.

 

[RHO]

The electronics don't like high temperature too. Heat is the worst enemy of electronics and make their life short. A lot of people have been talking shit about bad heat management design in amps, but there are still a lot of companies putting electronics inside speakers just like you do. If possible ask some electronic people's opinion on this.

Lifetime tests on ICs are done by putting them in an oven. So yes, heat makes electronics age faster.

 

[bigjacko]

Lifetime tests on ICs are done by putting them in an oven. So yes, heat makes electronics age faster.

I am not sure about IC, I assume they should be pretty robust. I am talking about capacitor mainly, those are probably the most likely thing to fail in an amp. Just to be clear I am not expert in electronics, not even amateur.... but I see a lot of electronic people complain about the thermal design, so got me interested and asked.

 

[ppataki]

The sub is now fully complete!

Some pictures:

Since only the front baffle will be visible that is the only part that has a proper finish (leather), the other sides just got one layer of black paint

We added some bracing between the drivers + the sides and I have applied polyester wool layers for damping

This is how the knuckle test sounds like (before the wool, with just the bracing)

New video by Peter Pataki

photos.app.goo.gl

I will post measurements in a few weeks' time once it is built into this system

 

[abdo123]

Try to do some Ground plane measurements to iron out any cabinet resonances that may be there.

 

[ppataki]

A small update: we just tested the sub and I need to say that this concept really works!
The cabinet remains totally steady no matter how high I push the volume. I placed my hand on it and I could literally feel no vibration at all!
Absolutely amazing! I have never ever experienced anything like that with any speakers before.
Also as I predicted, the room gain helps with the lowest frequencies, I did not have the feeling that it does not go low enough
As promised, I will post measurements later on (not so straighforward to do since it is not my system but my neighbour's)

 

[bigjacko]

Are those drivers pushed all the way back and rest on the bracing? There are some gaps between bracing and drivers, do those drivers tap the bracing and make sounds? I assume there is gasket on the drivers, but do you intend to put some gasket or wedges in the gaps? If you don't find any problem with driver hitting the bracing, maybe don't bother, it is just my thinking.

 

[ppataki]

Good point but we could not really hear that. Agree that a gasket would be desireable!
The construction is detachable so if it will become necessary we can do that.

 

[fluid]

Try to do some Ground plane measurements to iron out any cabinet resonances that may be there.

@ppataki run an impedance measurement if you can, that will show you if there are any cabinet or resonance issues and can be done in situ.
A soundcard or duplex laptop, a known resistor value and a few cables is all you need.

https://www.roomeqwizard.com/help/help_en-GB/html/impedancemeasurement.html

 

[ppataki]

Thank you @fluid, but I think that will not fly for this project, I will be happy if I can take some basic sweep measurements at the listening position