OB Woofer Assist - does it make a different SP wave than a sealed box?

Been Playing today with an 18" on an OB as a Woofer Assistant to a wideband driver. Basically playing with the speaker level crossover values and driven by its own amp whos level I can set independently.

It makes bass, oh, definite bass. Drums and Bass guitar sounding very fast and I can make a nice integration with the wideband driver.

However, it's not tactile bass. It doesnt shake my guts, nor punch me in the stomach. I cant feel it. It's very different than the bass the reflex port sub made, when I was using that for extension assistance previously. When I go to an adjacent room, the bass is gone. This wasnt the case with the "normal" sub - that transmitted bass through the whole house.

Although pleasant to listen to and certainly far better than just the wideband driver alone, it feels like a compromise to not have the "tactile" component.

How can this be? Is it making some kind of different pressure wave? That only my ears hear, but none of the other senses / organs pick up?

Depending on your situation, this could be a tolerable compromise. Especially if you like to listen to music and there's other people about. Like above / below in an apartment building. Or my wife who cant tolerate the tactile bass, but with this setup I can listen in one room with her in another and no problemo! No more asking me to turn it down / lower the bass!

I'm sure there's many who would dislike OB bass because of this missing part. What fun is that? You want it to knock you off your feet, right? Just wondering what's going on. Thanks!
 
Hi Freddi, yeah, in the listening position it sounds great, but as I said no punch in the guts.

No bass propagation throughout the house either. The antithesis of those cars with the killowatt subs driving past 150 yards away - and you can hear the bass inside the house clear as day.

I want GW1858s, but am going to make do with the single 4 ohm, 40 Hz Fs 18" woofers I got. Yeah, wish I just bought the GWs, but I believe I can make these work just fine for my personal listening situation.

Mainly wondering why there's no "Visceral" with an OB, while with any box, walls of concrete wont stop it. Yet my ears hear the bass just fine, just dont feel it.
 
It is an intresting question and something I have been pondering as well but in my case it is the difference between my previous BR expirience and a higher order series tuned qw horn (ROAR) you feel it more, and at lower levels, I had a similar expirience with the THAM15's.

It is as you say a tactile difference, you really do feel it, juat speculating here but maybe it can be explained by looking at the impulse response, or it may simply be that there is a level difference, have you meassured the spl and and made a comparrison? (I have).

In my case i ran a previous system at the same maximum spl level due to my neighbours, when switching from (in that case) a 15tbx100 in a sealed box to using the same drivers in the THAM15's running at the same max spl the sensation was much more physical.
 
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There is no momentary room pressurization with OB woofer

If no pressurization, how does it work as well as it does - apparently? I thought sound was an alternating pressure / rarefaction wave in air -

Listening last night [Pink Floyd's Dark SOTM "Time"] that bass note right after the clocks decay away is $%^ there - solid - as nice as I've ever heard it. But without the visceral impact.

This is as fundamental as it gets in understanding how speakers work - and I dont get it. Just asking, cause I think it's important. Will continue to enjoy whether I (we) ever work it out into a satisfactory explanation.
 
Been Playing today with an 18" on an OB as a Woofer Assistant to a wideband driver. Basically playing with the speaker level crossover values and driven by its own amp whos level I can set independently.

It makes bass, oh, definite bass. Drums and Bass guitar sounding very fast and I can make a nice integration with the wideband driver.

However, it's not tactile bass. It doesnt shake my guts, nor punch me in the stomach. I cant feel it. It's very different than the bass the reflex port sub made, when I was using that for extension assistance previously. When I go to an adjacent room, the bass is gone. This wasnt the case with the "normal" sub - that transmitted bass through the whole house.

Although pleasant to listen to and certainly far better than just the wideband driver alone, it feels like a compromise to not have the "tactile" component.

How can this be? Is it making some kind of different pressure wave? That only my ears hear, but none of the other senses / organs pick up?

Depending on your situation, this could be a tolerable compromise. Especially if you like to listen to music and there's other people about. Like above / below in an apartment building. Or my wife who cant tolerate the tactile bass, but with this setup I can listen in one room with her in another and no problemo! No more asking me to turn it down / lower the bass!

I'm sure there's many who would dislike OB bass because of this missing part. What fun is that? You want it to knock you off your feet, right? Just wondering what's going on. Thanks!

I'm very curious how you are "EQ-ing" the open baffle woofer. The response of a driver like this will be anything but "flat" and you must compensate for that using boost and/or cut. You will need more than just a "crossover" if you want to do it right.

Also, I have found that the room size has a significant effect on the bass below 50-60Hz for an open baffle system. If your room is not large, you will not get the deep impactful bass from an OB woofer pretty much no matter what you do. In a large room the bass will be better. It has to do with the size of the room and size of the wavelength of sound (without going into details).
 
Okay, here's the "xover" part.

Had to start somewhere, so I bought a pair of the original xovers. Throwing everythin' I could find from my junkbox, they ended up like this - added inductance (parasitic resistance not included) and added capacitance...

Yes, that is 5000+ uf, from 4 X 10,000uf power supply caps I removed from a Sherwood amp. connected back to back. Only value I have 4 of...

I'm driving these with a Dayton class D amp, 75 WPC. Was using a 50 WPC class D, which didnt even get warm at my listening levels.

So I'm getting a reverse rising response if I shelve what's shown up by the volume level on the Dayton amp. I eventually want to design such a "reverse rising response" into the amp itself, by modifying the rear panel bass/treble adjustment circuitry. It appears to be op-amp based. (No schematic, of course! That's never stopped me)

However it is I came to crafting the xovers and adjusting the amp volume to taste, the bass sounds fantastic; all notes even and plenty deep. It just doesnt sound like an acoustic bass is standing there between the speakers, as the visceral that instrument is capable of doesnt come through. I'm elated with the sound, also that I can listen at a comfortable level - with bass - w/o bothering anyone else in adjacent rooms of the house. Compromising on the visceral oommpph in order to be able to do so.

I've owned bass capable 15" speakers in the past and I know what certain tunes from the 70's and 80's are supposed to sound like. I can measure, as I did with the sub, but just havent got around to setting that up since putting the 18's into the OBs. The Dayton 12" sub was extending the bass similarly, but that would propagate further through the house structure than what I'm hearing and not feeling now.
 

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Okay, here's the "xover" part.

Had to start somewhere, so I bought a pair of the original xovers. Throwing everythin' I could find from my junkbox, they ended up like this - added inductance (parasitic resistance not included) and added capacitance...

Yes, that is 5000+ uf, from 4 X 10,000uf power supply caps I removed from a Sherwood amp. connected back to back. Only value I have 4 of...

I'm driving these with a Dayton class D amp, 75 WPC. Was using a 50 WPC class D, which didnt even get warm at my listening levels.

So I'm getting a reverse rising response if I shelve what's shown up by the volume level on the Dayton amp. I eventually want to design such a "reverse rising response" into the amp itself, by modifying the rear panel bass/treble adjustment circuitry. It appears to be op-amp based. (No schematic, of course! That's never stopped me)

However it is I came to crafting the xovers and adjusting the amp volume to taste, the bass sounds fantastic; all notes even and plenty deep. It just doesnt sound like an acoustic bass is standing there between the speakers, as the visceral that instrument is capable of doesnt come through. I'm elated with the sound, also that I can listen at a comfortable level - with bass - w/o bothering anyone else in adjacent rooms of the house. Compromising on the visceral oommpph in order to be able to do so.

I've owned bass capable 15" speakers in the past and I know what certain tunes from the 70's and 80's are supposed to sound like. I can measure, as I did with the sub, but just havent got around to setting that up since putting the 18's into the OBs. The Dayton 12" sub was extending the bass similarly, but that would propagate further through the house structure than what I'm hearing and not feeling now.

It looks like the response of your filter is more or less a first order lowpass. That will compensate for the dipole cancellation, however, the effect of the driver's response must also be included into the equation.

On an open baffle a driver will have a response that is very much like its free-air response, that is a second order highpass with F~Fs and Q~Qts. Unless your driver happens to be one of those "high Qts" open baffle specific ones, the driver's own response will be "drooping". If you want those lower notes that give you more visceral bass then you must also flatten (via boost of LF or cut of HF) the portion of the response due to the driver itself. This would be like (in your terms) an additional "inverse" second order high pass filter. You might be surprised how much additional power is needed to make up for all of these losses when the driver Qts is e.g. around 0.35, which is the typical Qts for a driver designed to be used in a vented or sealed box.

Also, you will not have an easy time measuring the response from this driver at the listening position. A nearfield will not include the dipole cancellation, and a far-field measurement needs to be done in a large space or outdoors to eliminate reflections from the room boundaries.

There is a way to model the response starting from a nearfield measurement or the response predicted by the TS parameters plus the dipole losses. You might want to give that a look.
 
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Thanks, CharlieL

I made a mistake purchasing the drivers I'm using, as I have no idea what the Qts is. I only know Fs is 40 Hz and that I'm capable of doing an impedance sweep, which I could then analyze to see if the Q is even anywhere near what it's supposed to be for an OB. I'll probably end up finding out it's <0.5, as you speculate.

"You might be surprised how much additional power is needed to make up for all of these losses when the driver Qts is e.g. around 0.35..." Perhaps I'm lucky to just be reaching 40 with these drivers - and that has something to do with the lack of "shake the whole house" effect.

I could just buy GW18s and try to recoup whatever I can from these Wharfdale labeled Chinese OEM $30+shipping 18" drivers (with no_available_T/S_paramaters_from_anywhere) on ebay -

I'm considering adding the tunnel portions of an "H" frame; rear tunnel first, as I've seen such designs for a WAW OB. As I'm not an experienced speaker craftsman, I have no idea what this "tunnel" does to the xover / filter requirements going into the driver, i.e. still needs reverse rising vs flat after the corner freq.

(I assume most doing a WAW have DSP / active filter (for the "W" part) which they can set to anything they want in no time. I have an assortment of resistor and capacitor values, for implementing anything line level.)
 
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Placing my Apex 220 measurement microphone 1' above the carpet about 1M in front of the right woofer (only woofer amp running, right speaker), using the RTA in REW with my Ivie pink noise source I get (pic 1). Did I just get lucky?

Removing any toe-in and measuring at my listening position, with both speakers running, I get (pic 2). Maybe I just snapped the image at a good moment? If I toe in at all, I get a big peak @ 70-80 Hz.

I turned the amp up quite a bit when I first turned it on and noticed "Wow, look at those cones move" at which point one of the channels shut down. Fortunately it recovered with a power cycle... So FAIK the amp could be outputting crazy high power to make it do this, using the speaker level Xovers. Not to imply line level filters would make the amp work any less, just not into such a crazy load.

Let's say what I measured is real. When I go into the room next door, I hear nothing. I'm pretty sure if I used the sub to get the same SPL over the same frequency range, it'd be just as loud in there as my listening position.

Why? (and it could be a good thing if predictable and manageable)
 

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@freddi - you're teasing. What kind of musical instrument is that in the background, upper left corner?

I tried to do a FR plot of the whole OB speaker today and it seems I like the bass just a little bit up from the rest of the spectrum. To match the SPL of the rest of my pink noise induced FR analysis using REW's RT spectrum analyzer, I had to turn the woofer amp down really far, which surprised me. Almost into "why'd I even bother" land...

To get rid of a crossover notch at ~70 Hz, I had to reverse the phase of the 18" woofer.

Then after EQing the rest of it for as flat a response as I could get, I didnt like the sound. At all. Turns out I'd rather live with the notch, than the woofer out of phase, which sounds worse... I cant even listen to the system that way, so I had to put it back in phase.

I need to find a way to run the 18 and the Lii 15 in-phase at some Xover point between the Liis natural roll off ~70 and say, a few 100. I guess the in-phase part requires Linkwitz-Riley 24 db crossovers - but the low pass output needs the reverse rising response also.

The amp I'm using to drive the Lii has a circuit opportunity for two additional high pass filter stages, which I could put over the top of the Liis 60-70 Hz rolloff, maybe that could get me 24 db / oct all told. Then what to do for the woofer XO?

Or buy someone's stereo LR 24db crossover and modify the low pass output to give the reverse rising response. Another $100 to get this OB in the ballpark of working - and sounding - right.

Maybe look into the Dayton Audio DSPB-K DSP Kernel Board. With the programmer, perhaps I could turn that into 2 low pass outputs with the 24 db slopes and reverse rising response. I'm not sure what's the best tack at this point.