yes i meant that. also for what i get an infinite baffle would still have all the bad things going on with baffles (perhaps) and with room pressurization... so it seems you have some real advantages over them: i've been asking my self what to consider for a definitive system, infinite or open...
just more curiosity: to what frequency do you think the back wave is absorbed? does it hold true for the lower octaves?
just more curiosity: to what frequency do you think the back wave is absorbed? does it hold true for the lower octaves?
WRT to the width and height modes you seem to be a bit luckier than I am, but my proposal was mainly addressing the remaining length modes. If they are no issue in your arrangement, please forget about my rantings immediately.
That's what dipole theory would predict ...
Fully agreed.
Erik,
it could be that recently I have come off a bit more destructive than intended. In fact I really admire your state of dipole art. I just can't refrain from thinking about where you may be doing overkill.
Rudolf
Sure a good look - and - now you clearly beat me on 4 x 15" each side !
Clever idea to minimize height too.
As I already know a little about your room treatment, I quite often was thinking that this "dead front wall" might be somehow beneficial for OB (not for the sub of course). How do your guests comment on that?
Michael
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Hi,
Would it be possible, even a tiny bit of possibility, that you might want some more forceful impacts? (I'd like to emphazise that I'm not questioning your taste of music/sound, it's just a discussion and I'd to find a way to understand each other some more.... )
As you know I'm also using dipole bass and love it a lot. However I love the sound quality of a 'true' horn bass, too. I've also heard excellent 'boxed' speakers with some very good characters I'd like to have. They are all different, I can not say which is the best (or which is the 'correct' one).
Back then I built the 'big' OB bass with 3x18" per side (with baffle of 1.2m wide x 1.1m high), I was actually quite disappointed. There's sheer SPL capability alright but lack of something (I thought) very important. Compared to those ordinary 'boxed' bass, OB has an obviously cleaner decay (its interactions with room help a lot, too, I guess), thus better presentations in textures and tones, better definition of pitches... etc. But a well-built boxed bass has its strong point in the powerful leading edge of slamming (bested by horn, which is explosion-like), and doing it with a sense of effortless.
I'd like to have the strong points of both sides. (I confess, I'm greedy.) When I hear a bassdrum (live, right in front of me), the seamless combinations of slamming impact, the weighty boom, and the clear decay are so beautiful and overwhelming. The closest playback I've heard is by horn (by the intense energy and control). OB does some parts very well, box does some other very well, and both are lacking something, pity.
I'm not able to explain it clearly, I'm sure someone else can. I'm just always thinking that the cures should be as close to the problems as possible.
I think the major 'problems' of dipole bass are the last 2 things along the stream -- acoustics, and the electro-acoustic interface. What we can do in the acoustics is very few, given the intrinsic character of dipole - there're also benefits in this "problem", well, so be it.
While in the electro-acoustic interface, it's a pity that only so less have been explored. Adding boost by EQ of line-level signal (or in the digital domain) is the most common practice of a dipole system. But, teens to 20dB of boost in the signal, that's almost equal to 2 power amps in series !! Doesn't that scare you? (I am scared!)
Right, a woofer would need very high voltage (gain) to overcome the huge impedance peak around the fs (to get the 'power'). But that 'cure' is somewhat too far from the 'problem', isn't it?
Big pro-style woofers have fs impedance peak of more than 100 Ohm commonly (mine is over 200 Ohm in my own measurement). Together with low-Q roll-off and dipole loss, how much voltage (gain) is needed to 'catch up' ? The scale is scary. Why not just feed it with more current it needs? OB bass needs current, especially those with mid to low Q woofers.
At the first glimpes (and by Ohm's law), it looks pretty much the same by feeding the woofers with high voltage by low-Z, or high current by high-Z. But there must be differences in the operations of gain stages, feedback mechanism, and the amp-spk interactions.
I'm sorry if it sounds like preaching, but I feel even more sorry to see the T-bass circuit or the high output impedance amp (which can deliver the needed current) keeps being ignored by the growing OB fans. Maybe because it's a topic between amps and speakers, so ignored (or at least overlooked) by both sides. I also found it's awkward to put such a topic in either this speaker forum or in the amps forum. (Maybe we need a forum of 'system integration'). I wish more people can share this concept and make good use of it. Or better yet, someone please correct me if I'm wrong here. (Prove I'm wrong to have a better sound by these.)
StigErik, your system is very very admirable. I'd say it's already one of the best systems in the world without hesitation (without hearing it). And you're even improving it contiually in an amazingly quick pace! Before you add another 4 woofers, please give the above concept a try. I'd love to hear what you get.
Interesting you should single out orchestral bass drum.
That sound is the biggest difference between the best home stereo and the real thing in my experience - even the best reproduction I have heard does not come close to getting this right.
The real thing sounds absolutely huge but at the same time subtle and articulate.
Unless the SPL drops around fs there isn't a problem to cure. All the woofers I've measured and seen datasheets for are more or less flat to fs and rolloff below that. So the impedance peak is just a reflection of the suspension's mechanical resonance making the woofer more efficient; what matters is the output SPL. So there's no need to run high voltage to force a constant input power across the spectrum.
I'm not saying it sounds like the real thing at home, but its closer than ever.....
Its difficult to get both the very powerful deep fundamental tone and the overtones right, AND make it sound like its coming from the rear part of the orchestra. Usually the deep fundamental is some kind of rumble that doesnt sound like its a part of the overtones.
My guests rarely comment the dead front end. They are more occupied with why on earth I listen on 2 meter distance when I have a 7 meter room..... The never heard the word "near-field" you see..... and they are often a bit confused by that "head-phone like" clarity the room and speakers present.Sure a good look - and - now you clearly beat me on 4 x 15" each side !
Clever idea to minimize height too.
As I already know a little about your room treatment, I quite often was thinking that this "dead front wall" might be somehow beneficial for OB (not for the sub of course). How do your guests comment on that?
Michael
No, it doesnt.
Its all a matter of how much overall gain is actually needed. For my subwoofer section, no gain is needed, rather the opposite. Even at 20 Hz I have to attenuate the signal 3 dB to make it level with the other drivers. To turn the problem all the way around: I have -29 dB EQ @ 100 Hz, it THAT a problem?
I know the T-bass circuit has been a topic here before. I dont understand what its supposed to improve. Maybe I'm stupid, but I dont. I'd like to see measurements and good theoretical explanations, not just comments like "its great, you have to try it".
I agree with you CLS that dipole woofers may sound clean but lack "attack" and "slam". With my giant H-baffles, the "slam" is back, and I expect more with four 21" per side.
well that's certainly a crazy experience I haven't come across before OB
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I sometimes think about applying some room treatment too, but actually I like the room to be "life".
In my case - not having a whoppy 7m and the corresponding room volume – covering the complete front wall would possibly bring down reverberation too much.
So I practice in philosophy now and then, if I should apply just "some" treatment at strategic places.
Looking at the sketches below – the most beneficial places IMO to apply either absorption or diffusion would be at the front wall precisely where the first phantom source occurs – somewhere in the middle between the speakers
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What you think ?
Michael
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No, it doesnt.
Its all a matter of how much overall gain is actually needed. For my subwoofer section, no gain is needed, rather the opposite. Even at 20 Hz I have to attenuate the signal 3 dB to make it level with the other drivers. To turn the problem all the way around: I have -29 dB EQ @ 100 Hz, it THAT a problem?
I know the T-bass circuit has been a topic here before. I dont understand what its supposed to improve. Maybe I'm stupid, but I dont. I'd like to see measurements and good theoretical explanations, not just comments like "its great, you have to try it".
I agree with you CLS that dipole woofers may sound clean but lack "attack" and "slam". With my giant H-baffles, the "slam" is back, and I expect more with four 21" per side.
I'm a bit confused. In an earlier post you stated "I have +26 dB of EQ @ 20 Hz, meaning that the sensitivity @ 20 Hz is 93 dB. Not bad! "
Are you still boosting with +26db @ 20hz or -3db?
What is your measured reverberation time in your room? According to the "Master handbook of Acoustics" 300-600ms is the ideal for listening rooms.
In my experience strategic "broad-band (150hz and up)" absorption in a small room is the way to go, as this actually helps with diffusion in the room, especially the flutter echo of parallel surfaces. It's well known that 1st reflection points should be treated at the floor, ceiling, and sides. However, the sides can be experimented with to adjust the width of your sound stage by applying different absorption/diffusion properties. Diffusion works best when the point of reflection is farther than 2m I think.
Thanks for your thoughts !
Haven't measured RT but like it pretty much the way it is now.
Have you done some treatment and could you possibly describe before / after experience on OB ?
I've done a lot of acoustic and room simus and even worked as a consultant in that field for larger rooms (cinema) - but have no first hand experience with the combination of "relatively small home audio rooms" plus OB - concerning treatment...
Michael
Haven't measured RT but like it pretty much the way it is now.
Have you done some treatment and could you possibly describe before / after experience on OB ?
I've done a lot of acoustic and room simus and even worked as a consultant in that field for larger rooms (cinema) - but have no first hand experience with the combination of "relatively small home audio rooms" plus OB - concerning treatment...
Michael
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