A few Open Baffle Subwoofer questions...

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theater_lover

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A few Open Baffle Subwoofer questions...
« on: 14 Aug 2020, 02:43 pm »
If what I have read is correct, a 100Hz wavelength is around 11 feet long, and 20Hz is around 56 feet long.

1) Doesn't that mean that the baffle size of most H/W frame designs really isn't doing much to stop the front and back waves from interacting?  The real problem is the back waves bouncing off the front wall and coming back around the front, no?

2) As such, would a "baffle-less" design work nearly as well (although I understand the cabinet design is offering structural rigidity that helps performance)?

3) In both cases, would DSP be able to (be required to) smooth out the interactions?

Thanks.

Captainhemo

Re: A few Open Baffle Subwoofer questions...
« Reply #1 on: 14 Aug 2020, 04:00 pm »
You  end up   with a figure 8 like  readiation with nulls to the side.  You  can therefore place  them up close to side walls  but you'll want  a minimum of  3' off the front   wall Most  are not using  any dsp other than the  A370's  built in PEQ.  A 12db/oct slope and  2  24db/oct slopes  are built into the   A370.

You'll   get fast, clean bass flat down to  20 hz


jay

mijostyn

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Re: A few Open Baffle Subwoofer questions...
« Reply #2 on: 14 Aug 2020, 04:52 pm »
theater lover you are absolutely right. It is a bad way to go about producing bass. Linear array dipoles such as planar magnetics and ESLs do interact with the room better than baffled speakers at frequencies above 100 Hz or so but below it is very problematic. Getting deep bass out of an enclosed driver is not easy either but today we are blessed. With DSP and a lot of power you can make big drivers in small enclosures make deep bass. If you put the enclosures up against walls and in corners you limit bad room interaction particularly if you use multiple units. The Enclosures have to be very heavy and another trick is to use two opposing drivers in each enclosure so that they force cancel. This decreases distortion to very low levels. People have this impression that you have to use like drivers at all frequencies for them to "match' correctly. This is faulty thinking. You use the best drivers and topography to do the job. Mounting a subwoofer driver in even the heaviest baffle board and expecting it to make flat bass down to 18 Hz in a room is a physical impossibility. You want to limit room interaction as much as you can not increase it!
If you want to have fun take two identical speakers and put them side by side right next to each other but facing in opposite directions. Now reverse the polarity on one of them and see what happens to the bass. The speakers have to make it down to at least 30 Hz. 

mijostyn

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Re: A few Open Baffle Subwoofer questions...
« Reply #3 on: 14 Aug 2020, 05:44 pm »
Jay, You need to get yourself one of these https://www.parts-express.com/omnimic-v2-and-dats-v3-dayton-audio-speaker-measurement-bundle--390-809
Once you use one of these I think you will reject the word "flat" from your audio vocabulary.
In free air your dipole woofers radiate in a dumbbell pattern but in a room? All bets are off. Bass is omni directional and the wavelengths are frequently longer than the room. The interaction with room  boundaries is complex. With a sealed woofer you are lucky to be +- 3 dB at the listening position. With a dipole woofer you are lucky to be +- 6 dD. Move around the room and the bass will go +- 10 dB in places. Just measure at the listening position then 6 feet in front and 6 feet behind then compare the graphs. 

SoCalWJS

Re: A few Open Baffle Subwoofer questions...
« Reply #4 on: 14 Aug 2020, 08:36 pm »
This could get interesting....

 :popcorn:

Speaking from my experience, there is a difference in how an OB Woofer LOADS & interacts with the room that is the biggest factor (or one of the biggest - exact reason is beyond me.)

Example. I have several subwoofers and a problematic room. I have a “Hollow void” in a built-in alcove designed for shelving. It is about 1’x2’x 10’ tall. The thing vibrates like mad at certain frequencies (It’s been awhile since I measured - a little below 20 Hz to 30 some-odd Hz.)

Vibrates with:
JL Audio f113
AV123 MFW-15 Turbo
Velodyne f1500r

Does NOT vibrate with:

GR Research Super V’s
GR Research Super 7’s

I do not understand it, but it is obviously evident. The result is “better” or “Cleaner” Bass. It is very obvious when the frequencies are those at which it is in full “Dance” mode, but I know it is just less obvious at slightly higher frequencies. I would imagine that the other walls in the room are doing the same thing , just not as loudly or obviously.

I have used multiple room treatments to reduce this issue (GIK Tri Traps sand OC 703 stacked triangles. While it has helped greatly, the problem is still there.

My 2 cents....

Also. I have the OmniMic as well as REW & a calibrated USB MiniDSP Mic. I get more useful info from REW. OmniMic is just easier to setup and use.

Tyson

Re: A few Open Baffle Subwoofer questions...
« Reply #5 on: 14 Aug 2020, 09:11 pm »
Jay, You need to get yourself one of these https://www.parts-express.com/omnimic-v2-and-dats-v3-dayton-audio-speaker-measurement-bundle--390-809
Once you use one of these I think you will reject the word "flat" from your audio vocabulary.
In free air your dipole woofers radiate in a dumbbell pattern but in a room? All bets are off. Bass is omni directional and the wavelengths are frequently longer than the room. The interaction with room  boundaries is complex. With a sealed woofer you are lucky to be +- 3 dB at the listening position. With a dipole woofer you are lucky to be +- 6 dD. Move around the room and the bass will go +- 10 dB in places. Just measure at the listening position then 6 feet in front and 6 feet behind then compare the graphs. 

I use 2 measurement systems, one is an earthworks m23 which is phase perfect out to 23kh along with HOLM Impulse.  It's nice because it's very precise and back when I was designing crossovers for my 3 different iterations of active 3 way speakers it was really useful.  Now it's mostly used for bass measuring and EQ.  But my other tool is a real time FFT set to 2 second delay and no smoothing from Digital Studio Six.  I like this one because even though it's less precise than the Earthworks setup, it lets me be mobile.  So I can walk around my entire listening room and see immediately, in real time, exactly how my speakers and room are interacting. 

I've used sealed speakers and sealed subs in the past.  Even when using multiple locations for bass generation, the room is always problematic.  I have heard rooms that sound great with sealed subs, in fact a good friend of mine has a dedicated room that uses 5 Rhythmik servo subs and it sounds phenomenal.  So you are right that sealed subs in a swarm can sound great.  When we visited Duke's room at RMAF (Audiokinesis), they always sounded great with their swarm setup.  So you are right, a swarm is a good approach.

However it's not the only approach.  Self-powered OB Servo Subs will get you similar (or better) results in a real-world room.  Because they are OB, you get les room ringing (bloat).  Because they are servo controlled, you keep the "punch you in the chest" dynamics and power that normally only sealed systems get you. 

And, if the only OB bass you've ever heard is a 15 inch pro driver mounted on a flat baffle, well I agree, that setup is quite underwhelming.  But servo controlled OB bass like we are talking about here is on a WHOLE NOTHER level.  If you haven't heard it yourself, then frankly you don't know what the hell you are talking about.

Danny Richie

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Re: A few Open Baffle Subwoofer questions...
« Reply #6 on: 15 Aug 2020, 02:14 am »
First of all, what Tyson said.


1) Doesn't that mean that the baffle size of most H/W frame designs really isn't doing much to stop the front and back waves from interacting?  The real problem is the back waves bouncing off the front wall and coming back around the front, no?

The front to back wave separation actually does a lot. A H frame for instance can load the drivers, increase output, and increase low end extension.

Quote
2) As such, would a "baffle-less" design work nearly as well (although I understand the cabinet design is offering structural rigidity that helps performance)?

Not even close.

Quote
3) In both cases, would DSP be able to (be required to) smooth out the interactions?

DSP is not required. We get flat response to below 20Hz and -3db in the teens with a very uniform and even in room response in even average rooms with our open baffle servo subs.

theater_lover

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Re: A few Open Baffle Subwoofer questions...
« Reply #7 on: 14 Sep 2020, 01:33 pm »
An additional question...

The driver baffle in a H frame design is in the middle of the side baffles.
Is this equal weighting important?  I see the benefit if the drivers are facing opposite directions, but if they were all facing forwards, could the driver baffle be moved more towards the front?

This would mean more side baffle for the rear output, but less for the front.
This would be if the drivers were all facing forwards.

Thanks.

Early B.

Re: A few Open Baffle Subwoofer questions...
« Reply #8 on: 14 Sep 2020, 03:03 pm »
An additional question...

The driver baffle in a H frame design is in the middle of the side baffles.
Is this equal weighting important?  I see the benefit if the drivers are facing opposite directions, but if they were all facing forwards, could the driver baffle be moved more towards the front?

This would mean more side baffle for the rear output, but less for the front.
This would be if the drivers were all facing forwards.

Thanks.

The equal weight issue isn't important enough for a cabinet re-design. Consider driver orientation as a personal preference. 

Hobbsmeerkat

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Re: A few Open Baffle Subwoofer questions...
« Reply #9 on: 14 Sep 2020, 03:10 pm »
I've only seen it be minor issues on situations like thick, plush carpeting, where the towers may lean back a bit, but it can be fixed by putting them on dampeners with a few more in the back than the front.
If you're using hardwood floors or spikes thru carpet onto concrete, then its not an issue. There's no risk of them toppling over either way

theater_lover

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Re: A few Open Baffle Subwoofer questions...
« Reply #10 on: 14 Sep 2020, 04:07 pm »
I should clarify.  By "weight" I meant the influence of the baffle on the sound waves.

With the driver mount baffle centered to the sides, you in theory have as much blocking the front waves as rear.  The rear outputs less (driver magnet and frame in the way), so they aren't really equal, but that is the idea.

What I am asking is say you put the driver baffle much closer to the front, so little was blocked on the front, but far more was blocked from the rear.