Bass output through the hole in the wall.

[Ultrasonic]

I will not do that! I want hidden subwoofers.

Fair enough . Hope it works out well.

 

[voodooless]

4th order bandpass would give 3dB extra headroom. I know this is theoretical, but am I right in my assumptions?

If you're fine with only <50 Hz, sure.

 

[Launagis]

If you're fine with only <50 Hz, sure.

But if I pull down everything above 20hz (I can use op to 10 bands of PEQ for each sub), I can get past 50hz? For example, in your graph the output at 20hz and 90hz is the same - 95dB. I don't say, that the output quality would be the same for sealed vs the bandpass at 90hz, but if I EQ things, I could get maybe to 70 or 80hz in bandpass? I get that the roll off would be very steep that way and the integration could be difficult, but I'm not sure I can know that without trying.

 

[RHO]

@voodooless For the 4 woofers I used 200L for the sealed part and 100L tuned to 30Hz in the vented part, for my sim in WinISD. What would the result be if you simulate that in BoxSim?
2 woofers with both enclosures half the size, tuned to the same frequency could work out nicely if WinISD gives somewhat accurate results.
You do lose 3dB efficiency.

 

[voodooless]

@voodooless For the 4 woofers I used 200L for the sealed part and 100L tuned to 30Hz in the vented part, for my sim in WinISD. What would the result be if you simulate that in BoxSim?
2 woofers with both enclosures half the size, tuned to the same frequency could work out nicely if WinISD gives somewhat accurate results.

That will give you just more output if the volumes scale with the amount of woofers. Given the same diameter, it just means more air must go through it, leading to possible scuffing sounds and more distortion.

 

[RHO]

That will give you just more output if the volumes scale with the amount of woofers. Given the same diameter, it just means more air must go through it, leading to possible scuffing sounds and more distortion.

I mean when using the 2 instead of all 4 woofers, but halving the enclosure volume (compared to the 4 woofers) would result in the same transfer function only reduced in amplitude. Right? It looks quite nice in WinISD. And the 2 woofers would reduce the air velocity in the vent drastically.
How does that TF look in BoxSim? (2 woofers 100L/50L-30Hz) That would give an idea of how well WinISD simulates a 4th order BP. (I suspect BoxSim is much more accurate.)

 

[voodooless]

And the 2 woofers would reduce the air velocity in the vent drastically.

Why would they? Same airflow for same SPL I would assume.

How does that TF look in BoxSim?

It doesn’t model port airflow, so can’t tell you.

 

[RHO]

Same airflow for same SPL I would assume.

Right, I forgot to adjust for equal SPL after removing the 2 subs from the simulation.

 

[Cbdb2]

This reminds me of TRW-17 rotary subwoofer, learned of it few days ago thanks of ASR :

Eminent Technology TRW-17 Rotary Subwoofer

And now for something completely differenta subwoofer that looks like a fan and can reproduce frequencies down to 1Hz and below. Yep, you read that right1Hz and below. Developed by Bruce Thigpen and available from Eminent Technology, the Thigpen Rotary Woofer Model 17 (TRW-17) breaks entirely...

www.soundandvision.com

1Hz-20Hz

Great you pay $40k so you can hear aircon rumble and semis going by outside the studio in bad recordings that should have filtered those out. Theres no music below 20hz, with one exception, 32' pipes. And even with a pipe organ those low freqs. are usually reduced or eliminated because they need high levels and that makes mixing/mastering difficult. Imagine how quickly a tone arm with a 10hz resonance will feedback while your room shakes from the turntable rumble from one of these. Even movie LFE tracks have very little below 20hz because they dont need it.
Look at any THX speced subwoofer, they cut off at 20hz.

 

[Launagis]

Practical question - I already have 26.5ltr box for SW26 and I can make "add on" box with 125mm hole and play with some pipes. So the question:
What volume should the ported box be? Does it matter greatly? WinIsd suggests 23ltr ported section. Should I stick with that number?
26.5ltr sealed section, 23ltr ported section, 125mm pipe diameter and 1.3m pipe length.

 

[voodooless]

26.5ltr sealed section, 23ltr ported section, 125mm pipe diameter and 1.3m pipe length.

Your sealed section shows 40L in your sim.

 

[Launagis]

Your sealed section shows 40L in your sim.

I know, but I've just calculated the volume of the boxes I have right now, and they are 26.5ltr. It would make this experiment way easier, if I can just use existing boxes without big punishment for them being smaller. WinIsd simulations equalized by Xmax at 20hz, 70w for 40ltr, 90w for 26.5ltr (purple):

Steeper roll off for 26.5ltr below 20hz, some gain above that, but the difference, it seems, is very small.

 

[voodooless]

Sure, seems good enough for a simple test with whatever you already have

 

[Salt]

Interesting setting.
Some reflections: High- and Middle Tone compression drivers are all around.
What about low frequencies compression concepts?
If one driver, larger than than the whole in the wall, was used, close to the wall, what would be the result in FR in the room and what would be the optimum of enclosure in the back of the driver?

 

[Launagis]

Interesting setting.
Some reflections: High- and Middle Tone compression drivers are all around.
What about low frequencies compression concepts?
If one driver, larger than than the whole in the wall, was used, close to the wall, what would be the result in FR in the room and what would be the optimum of enclosure in the back of the driver?

I was wandering the same thing from the beginning. I just have no background or deep understanding off acoustics, hence this thread. I was even looking for some 300mm>x>125mm adapters just to try something.

 

[Holmz]

Very interesting. The way I see this:
At 10hz, the output is almost identical - around 78dB. At 20hz, bandpass pulls ahead with 95dB vs 92dB. Sealed goes to reach higher SPL with 110dB vs 105dB. So, if I cut anything below 20hz and equalize everything above to be flat to 20hz level (which means pulling down everything above 20hz), 4th order bandpass would give 3dB extra headroom. I know this is theoretical, but am I right in my assumptions?

You’re probably right, however the sealed, IB and bandpass all have different transient response and group delay behaviour.
If you are playing some steady state sounds the SPL is probably the most important.
If you are playing something that is more impulsive, then SPL may not be the sole metric to be looking at.

 

[Launagis]

You’re probably right, however the sealed, IB and bandpass all have different transient response and group delay behaviour.
If you are playing some steady state sounds the SPL is probably the most important.
If you are playing something that is more impulsive, then SPL may not be the sole metric to be looking at.

You're right, and I get it. It's just that SPL is one of the few metrics I can reasonably understand, everything beyond that I have to physically test, to see how it works. I will try to make some "mock-up" 4th order band pass box this weekend and compare it with the sealed box in similar location. I will try to do some REW measurements.

 

[Holmz]

You're right, and I get it. It's just that SPL is one of the few metrics I can reasonably understand, everything beyond that I have to physically test, to see how it works. I will try to make some "mock-up" 4th order band pass box this weekend and compare it with the sealed box in similar location. I will try to do some REW measurements.

I think that some of the box design S/W packages give the group delay.

I am gradually leaning towards a sealed box sub for 2-channel. But I also have some passive radiators so I need to figure out how to model everything as well as find the Dayton DATS somewhere to get teh actual values for the subs to put into the S/W.

As the system is also 5.x.x , as well as 2-channel, then maybe I can run a bandpass for the low LFE channels as I believe that a lot of those sounds might be rumbly things to creat tension etc… and not like jazz music etc.

It is complicated and domestic bliss also factors into what is deemed acceptable in a moderate size room that is shared.

 

[Flaesh]

I usually put high-pass at 20hz for protection

I don't use a HPF. But I very rarely listen to content that contains 10-20Hz with significant amplitude (although it's pretty funny).
And don't forget about the room transfer function. That's why I asked about measurements.

 

[Launagis]

So today I did the basics on tight schedule. Quick and dirty results - it goes full on from 20hz (unexpected), big peak around 25-26hz (listening position, brought down by EQ). Subjective evaluation - 20-30hz loads very nice, 30-80hz I have some doubts, sounds a bit "hollow", "tubby", or "dry", but no final judgement, since I spent minimum time with EQ. So the concept seems not to be a gimmick, I will proceed with evaluation.