Double Bass impulse compensation and the smallest 4*10 ever for DB

[Matthijs]

a thread on the slab side made me think about the uses of "impulse compensation" for bass cabs. Impulse compensation is placing two speakers on opposite sides of a cab. The idea is the cab itself won't vibrate in reaction to the speakers moving. The result is very accurate overall response. And, depending on how you use this, extra bass response from the omnidirectional bass frequencies from the backside speaker.

Now this made me think about another design goal I've been thinking about: If you want to reproduce the sound of an acoustical instrument with a traditional speaker cab, you miss the omnidirectional resonances and sound coming from the instrument that 'place' that instrument in its environment. You're aware the instrument is actually making sound in front of you because of the sound from all around the instrument is bouncing from the walls and objects in the room. One part (and only a part) of the gap between a EUB and a DB is in that sensation.

Now what if:...

I'm pretty sure I've got 4 old celestion 10" speakers stacked away somewhere. If I'd put them in all 4 sides of a small cube shaped cab, what I hope this would do is:
-The cab would be omnidirectional and heard all over the stage.
-It would render a more "acoustic presence" of the intrument.
-It would get a lot out of the speakers in terms of accuracy, transparancy and transientresponse.
.You get the combined lower bass response and power handling of all 4 speakers in a box almost as big as a 1*10".
-The direct combing and beaming effects would be minimal, because the speakers are all the way on different sides.

I think this might work very well for amplifying a EUB or DB in a lot of situations. It might not be very usefull in loud situations or in a acousticly difficult room. The interaction with the room would be maximal, something we often like to avoid playing DB, but for EUB it might be a plus.

Should I start tinkering this weekend? Or can you write off the whole idea in a single post?

 

[drurb]

Phase cancellation, varying frequencies, constructive vs. destructive interference, uncontrolled influence of reflections on all of the above. The situation would be quite different if the design were optimized for, say, a home environment, where the distances to the reflective surfaces could be adjusted and fixed with driver responses adjusted accordingly. I don't see that happening for equipment used to gig. Sorry.

 

[DoubleMIDI]

Hi Matthijs,

Just putting the four speakers on different sides of a box, giving them the same signal might be a bit simple, but you can try that. Some years ago I read in a computer music research context about a cube with at least six speakers, probably even more, I cannot remember exactly, each driven by a separate power amp getting the signals from a sound diffusion system distributing different frequency band in different amounts of the original signal to the speakers. The box was rather small and used 6" speakers or even smaller ones. I think it was made for higher pitched instruments than for double bass, but since we now have cabs that work with 6" drivers, why not trying it.
Unfortunately I cannot remember the name of the device, but I think I heard it in a concert and can remember that it sounded good. I think it was at the ICMC (International Computer Music Conference) 1997 in Thessaloniki, Greece. But it existed before and was only used at a concert there, I think.

 

[Matthijs]

Phase cancellation, varying frequencies, constructive vs. destructive interference, uncontrolled influence of reflections on all of the above. The situation would be quite different if the design were optimized for, say, a home environment, where the distances to the reflective surfaces could be adjusted and fixed with driver responses adjusted accordingly. I don't see that happening for equipment used to gig. Sorry.

Let me put it this way: when you're hearing a unamplified drum kit or say a violin, do you ever think "too bad about al that phase cancelation, varying frequencies and constructive and destructive interference?"

My idea is that al this could be serving a function.

 

[Matthijs]

Thanks DoubleMiDI, over time there have been more experiments with audiosources that are built to emulate a omnidirectional point source. The ones I know about are were aimed at the higher frequencies, but I think it can also have a use for bass.

I'll try to make some time this weekend and put something together. I'm not to serious about this, als because Drurb offcourse has some valid points. This thing is not going to revolutionise bass amplification overnight. But it might actually do well for some purposes.

 

[Matthijs]

Now I did have some spare time today so I went searching for those speakers. Turns out there are only three of them left. I did consider turning this into a trangular cab, but that would be too far out in the left field.

I did find an old 10" cab with a eminence b102 and a second b102. So I decided to turn it down one notch and turned the small closed 1*10 into a impuls compensated 2*10 .

I tried the result with a slab, a eub and my db. With the slab it actually sounded pretty good. More bass, and more importantly a pretty nice transparent bass response. The whole spatial effect worked pretty good. It gave a very natural vibe without any prominent weird response effects and it did so with the cab in different places and from different angles.

Now with the EUB, ... The result was strangely very different and in no way usable. It sounded distant, like the cab was placed much farther away. The overall response was okay and also pretty evenly spread through the room but lacked bloom.

Surprisingly the result with db is somewhere in the middle. The bass end of things is pretty good. You get the strange sensation of hearing you bass only louder, but prominently from a few feet away. Like there are two bassplayers in the room. I'm not sure I like that, but it might sound very natural for an audience. The main down side is the clanginess of these b102 speakers, they are not suited for DB. That's probably why I buried them far away.

Overall conclusion: fun project but in this form not a real use for db. I might keep the cab for the slab.

 

[brianrost]

Lots of unusual speaker designs that have been developed over the years. Various ways of using twin speakers face face to face as well as back to back have been done. I once owned an Ampeg "dual drive" cab with two 15s back to back. The thing was small but super heavy because of the second speaker. It didn't sound different than more traditional cabinets. Today AI and Schroeder are making unusual dual speaker cabs.

 

[drurb]

Let me put it this way: when you're hearing a unamplified drum kit or say a violin, do you ever think "too bad about al that phase cancelation, varying frequencies and constructive and destructive interference?"

My idea is that al this could be serving a function.

No, because they do not occur in the artificial sense that such arrangements of speakers would create. There is a decades-long treatment of these issues. It's not new.

That's not to say that you shouldn't try and have great fun doing it!

 

[Povl Carstensen]

I had the same idea, but never got it built: A column speaker with two say 10 inch speakers back to back at the top. My one other design idea was to have no bottom in the speaker enclosure. So the bottom of the column would work as a bass reflex opening, its size regulated by variable height feet in each corner. I would experiment myself to find the best setting/height.
Never got around to building it though. I used the two speakers in an cabinet I allready had, and moved on to other things.
I could imagine phase cancellation (or what you call it) effects in this design, but it could be fun to try.

 

[Matthijs]

I once owned an Ampeg "dual drive" cab with two 15s back to back. The thing was small but super heavy because of the second speaker. It didn't sound different than more traditional cabinets. Today AI and Schroeder are making unusual dual speaker cabs.

This thing is super heavy too. Those eminence b102 have a pretty big magnet, so two of them in a tiny enclosure makes for a pretty efficient doorstop.

I gues if I'd lowpass the back speaker at say 160 hz you'd never hear it had a speaker at the back.