Think OB makes the room irrelevant? Think again.

jimdgoulding · « **Reply #40 on:** 1 Jul 2011, 09:33 pm »

I personally like the sensation of pressure if I understand you right but don't yet understand why a OB is less able to do this. How much of this is contributed by the enclosure or speaker placement within the room? Thanks.

megasat16 · « **Reply #41 on:** 1 Jul 2011, 10:59 pm »

OB Line Array makes the room less irrelevant than the OB Point Source.

Line Arrays and OB Line Arrays have less SPL drop out as you move further from the speakers. An OB Line Array has less Floor and Ceiling coloration than most OB speakers.

JohnR · « **Reply #42 on:** 1 Jul 2011, 11:43 pm »

Quote from: jimdgoulding on 1 Jul 2011, 09:33 pm

I personally like the sensation of pressure if I understand you right but don't yet understand why a OB is less able to do this.

Because the driver is open to the room on both sides, the total static pressure (i.e. at 0 Hz) that it can generate is zero. I'm not sure though that at (low) audio frequencies this isn't simply a matter of SPL capability - affected by placement, nr of drivers etc.

jimdgoulding · « **Reply #43 on:** 2 Jul 2011, 01:03 am »

Thanks.

JohnR · « **Reply #44 on:** 2 Jul 2011, 01:15 am »

I should rephrase the second sentence - barely makes sense even to me

I meant that the idea that boxes subs "pressurise" a room at audible frequencies - I'm not sure that is really correct. If an OB bass system were able to generate the same SPLs down to 20 Hz, and in-room frequency response is flat in both cases, then I am not sure that there would be any difference. The "if" is that most can't do that e.g. how many OB subs would you need to get the same SPL as 4x15" boxed subs?

Consider that in theory, a ported sub can't pressurize a room at 0 Hz either, as the port will equalize the pressure.

I guess I'm really arguing with myself here...

jimdgoulding · « **Reply #45 on:** 2 Jul 2011, 01:34 am »

Well, I appreciate that you are. On some music, classical mostly, I sometimes get this sensation of feeling the weight/impact of a full orchestra at climatic sequences. I've attributed this to my room (smallish and enclosed on all sides in the front end) but wondered if the port could be contrbuting

. Any ideas?

Pez · « **Reply #46 on:** 2 Jul 2011, 01:45 am »

Quote from: nickd on 1 Jul 2011, 07:11 pm

Pez,
put 4ea 15" woofers in couple of big boxs or 24 ea 6" woofers in a couple of big boxes run a low sweep using a couple of hundred watts and you will understand. Your ears feel like you are changing altitude. It is "sound pressure", I understand that much, but in bigger systems I therorize the pressure affects your ears differently in a sealed or ported design than OB. I have heard all three. To my ears the OB sound seems just as loud but I don't feel quite the same "pressure" that a sealed or ported system makes exciting the same air

just my expierence. Thats why I like the Circle always somthing new to debate among like minded friends.

Ah, now I get what you're saying and thank you JohnR for further clarifying. So if I am understanding correctly this is more a function of bass. Where a boxed speaker can affect the sound pressure in a room to a greater degree for longer and a OB speaker pretty much equalizes itself when creating bass virtually instantaneously. I would think in absolute terms this is an area that Sealed and HUGE cabinets would really outshine anything when absolute SPL is concerned and OB would not really pressurize a room because of self-cancelation???

Now I'm sure I've really confused the issue.

jimdgoulding · « **Reply #47 on:** 2 Jul 2011, 02:15 am »

Dunno, Pez, maybe you're on to something. As a footnote to what I am trying to describe above, may I throw this word into the mix . . propulsion. That present in OB designs? I don't remember it so much with my Acoustat Three's but could be they didn't have the driver excursion(?).

Tyson · « **Reply #48 on:** 2 Jul 2011, 03:09 am »

You need about 4x the woofers in an OB setup to equal a single sealed or ported woofer system down low. OB's roll off faster with frequency, and will need more EQ to bring up the low end (also eats up amp power). From a pure output standpoint, it's no contest, a sealed or ported box is much more potent in the lowest frequencies.

jimdgoulding · « **Reply #49 on:** 2 Jul 2011, 03:51 am »

Thanks, T.

PDR · « **Reply #50 on:** 2 Jul 2011, 03:59 am »

I know what your saying....potent.
I have two dual 12" subs, I use with my arrays....they can make your chest pound....at my age I dont like it.
I find the OB bass pleasant and it doesnt seem lacking.......it can be loud and low, but it doesnt hurt.

Does that make sense??

jimdgoulding · « **Reply #51 on:** 2 Jul 2011, 04:46 am »

Whew. Dual 12" subs in my size room would not be advantageous.

JohnR · « **Reply #52 on:** 2 Jul 2011, 04:51 am »

Quote from: Pez on 2 Jul 2011, 01:45 am

OB would not really pressurize a room because of self-cancelation???

I guess what I'm saying is that it depends on what you mean by "pressurize." In the sense of static air pressure, no. However, is that relevant at audio frequencies? I'm really not sure that it is.

Anyway

Here's a plot that illustrates that placement of dipole subs is important. I know Tyson's original post was not about sub frequencies, but it seems relevant... as the room is not irrelevant. Blue is one placement that I tried. Not good. Purple is another - mucho betterer eh? No change other than placement.

The icing on the cake: everything gets better (or can) with two dipole subs. That's the green line.

JohnR · « **Reply #53 on:** 2 Jul 2011, 05:01 am »

For comparison, here are measurements of a single sealed woofer in the same room. P is in the corner, N is the middle of the front wall:

Overall, it seems to me so far that placement of dipole subs is about as important as for sealed subs, I don't think either naturally "wins."

JohnR · « **Reply #54 on:** 2 Jul 2011, 05:10 am »

Oh, I forgot to mention: the dipole subs have a 6dB/octave shelving filter from 30 Hz to 120 Hz to compensate for the dipole rolloff in the region of interest. That is to make the measurements easier to interpret. However there's no other EQ.

JohnR · « **Reply #55 on:** 4 Jul 2011, 08:03 am »

I guess that was all too much for this thread.

studiotech · « **Reply #56 on:** 4 Jul 2011, 10:56 pm »

Thanks for those measurements. They are very educational. Placement is important no matter what type of speaker you've got.

I happen to agree about the whole pressurization thing too. AS you know from my thread, I switched out from pure open baffle to sealed servo subs. There is more of a sense of visceral impact with the sealed even when both are adjusted to have the same low frequnecy cutoff and EQ'd as close as possible. If you check out JohnK's music and design website there is an article on there describing why running pure open baffle below the lowest room mode is not the best idea. This of course depends on how low you want your system to go AND the size of your room.

Many people claim the 30-40Hz response is fine for music. That is nonsense IF you want to hear everything that's on the recording. Since I've heard response in a music system that reached to 20Hz and below in the studio and at the mastering facility, I could not go back to anything less. There is relevant musical and environmental content down there. I have several recordings that have a certain hall ambience and/or rumble that really adds to the width and depth of the soundstage with stereo bass reaching below 20Hz. Cut off the subs and your perspective shrinks.

Greg

jimdgoulding · « **Reply #57 on:** 5 Jul 2011, 12:45 am »

Hi Greg. Literally your perspective? Are you refering to the volume of space in a recording or the excitation of air in the room? I imagine it's subjectively cool in any case but I'm just wondering. And would you need a big room? I imagine you would need big drivers. Thanks.

studiotech · « **Reply #58 on:** 5 Jul 2011, 12:56 am »

Quote from: jimdgoulding on 5 Jul 2011, 12:45 am

Hi Greg. Literally your perspective? Are you refering to the volume of space in a recording or the excitation of air in the room? I imagine it's subjectively cool in any case but I'm just wondering. And would you need a big room? I imagine you would need big drivers. Thanks.

Yes, the perceived sense of space IN the recording. I'm just running a pair of 15" Rythmik servos, so nothing too huge, but they are flat to 14Hz per the specifications. I'm getting good response to just below 10Hz at the listening position. My room is not huge either, but at those frequencies, drywall is rather transparent. It's about 14ft wide, 25ft deep and 8ft ceiling. 8ft ceiling sucks out a nice area around 70Hz, but other than that I'm looking pretty good.

jimdgoulding · « **Reply #59 on:** 5 Jul 2011, 01:08 am »

I couldn't do it with my speakers (-3db at 37Hz). I had a sub for awhile and didn't experience anything like what you've described but it had only an 8" driver which I actually thought sounded better driver up instead of down. Don't think that qualifies. Well, that sounds very cool. I'd like to hear that at some point and we'll definitely check around my neck of the woods. Thanks.