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Hi Roberts, Romy and others,
Before this thread vanishes in undeserved obscurity, I have a question or two for you. I understand that the issue is a complex one and should be addressed with more care and paying attention to detail than I am doing here, but I would like to know your thoughts as the situation bears some similarities to the one discussed here and it might be worth picking your minds when the issues have been freshly discussed. It will be some months before I have the time to set up my system in this room, so this is not remotely a hypothetical question, but given that the house is in France and I am presently in the UK, I cannot attempt several different solutions before actually having to move in with what I hope is the solution with the best chance of success.
So what is the definition of success for me as far as the lowest bass is concerned? Well, it works on two levels at least, not surprisingly. It must pressure the whole room uniformly, be capable of integrating with what'shappening in the music without either attracting attention to itself unduly or indeed by its absence. This is the common feeling I have with 90% of all systems out there, that the lowest octave is simply missing.
In an ideal world, I would like my bass to be happy with a dedicated 50w of tube amplification if at all possible. I am a great believer in a homogeneous tone throughout the entire frequency range and the tube I will be using to start with (6C33C) can produce a maximum of 40-50W in a good design. Therefore my second level definition of success, although I am comfortable with the idea that it may not be achievable, would be a ULF solution that would not need more than 40-50W at full power to give peak listening volumes of 90-95 db although I never play that loud in practice, the courtesies of social living being what they are, and I am mindful of the dangers of hearing damage to young children, who get habituated to listening to high volume levels. Achieving this is my definition of success at level 2.
We are dealing with a rectangular room of about 6.5m by 7.5m but with a ceiling height of 2.4-2.5m in a very old townhouse where the walls are made of stone and probably no less than a metre thick everywhere. I have considered (theoretically) several solutions and the one that I favoured for a while was an infinite baffle for ULF (15-40Hz) but that would require the temporary loss of a 5 centuries old wine cellar which I am, understandably reluctant to do.
My second solution was a 'line array' of 2x6 Scanspeak drivers (the elegant unobtrusive solution), or possibly 6x18" McCauley 6174 (equivalent to 20 Scanspeaks) or even 6x21" Maelstroms (equivalent to 27 scanspeaks) unless McCauley somehow can be convinced to sell their 21" woofer separately). Obviously the position and implementation of this type of solution is so dependent on the mid-bass channel that I may well mention it. If this is the solution, I would not have a midbass channel, much as I would love to, as I could not accomodate such a channel and devote only part of the room to my playback which I would like to be part of the main family room, and not overwhelm it entirely. In my much smaller current room, I am able to achieve this by keeping all my equipment restricted to three racks in a different room. In my new bigger room, unfortunately all the equipment racks will have to be inside the room itself.
I am not prejudiced to any form of solution, provided it works, and the last possibility I was looking at was two dual tapped horns that would fit in the room corners and then maybe have two 3.5m midbass horns along the side walls. On paper, this solution is appealing, and I CAN SEE A NUMBER OF ADVANTAGES TO THIS. I have read that Eric of Volvotreter in Germany and maybe John Hasquin are proponents of tapped horns, but I am worried they may suffer from the same problems that I have so far associated with all ported enclosure and transmission line designs that I have heard (in fact I own dipole subwoofers(Mirage BPS400), ported speakers (Spendor BC1), IMF TL80 (transmission line) and must say that I now harbour serious doubts regarding these solutions on the basis of their specific topology.
Roberts, I read carefully your pertinent, clear and helpful observations in your above post and wonder whether you might clarify or expand on a couple of points you made that, idiot that I am, could not follow as well as I would have liked. Here goes:
 RF at Ona wrote: | |
When two loudspeaker drivers are placed close together they become acoustically coupled and so more efficient than when spaced well apart. On in-phase signals, two closely placed drivers would play louder in the bandwidth where they are acoustically coupled but have significant destructive interference for out-of-phase signals. I think this might well apply to the mid-bass horns. |
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Robert, I would think this would not be a problem if the ULF signals were summed and the identical 'mono' signal sent to both channels. We can thus enjoy the benefit of increased efficiency whilst staying away from the problem of cancellation of out-of-phase signals.
| RF at Ona wrote: | |
In addition to these effects, on in-phase signals the pair of midbass horns might also function something like a two-sector horn where the combined mouth area determines the low frequency cut-off. The low frequency cutoff would be lower for the two horns running in-phase signals than for a single horn. |
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Robert, bluntly, this is maybe a good thing, yet another benefit of close placement of mid-bass horns, as you get two for the price of one, that is lower frequency cut-off. Does that suggest and in your experience, would this mean that two 50Hz horns would actually act as a single 40Hz horn? Like anyone in this hobby, I like getting something for free, but is this lower frequency cut-off really free and without downside (other than catching one unawares in planning mid-bass+ULF integration).
| RF at Ona wrote: | |
Now the same issues and analysis applies to your woofer towers and with the new placement of the towers some of these effects may have become exposed. If these effects are significant than your new wider spaced ULF towers might actually be functioning more effectively in their upper range than the midbass horns in their lower range on stereo recordings with phase differences between the channels in this frequency range. |
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I am not too clear about 'their upper range.' Do you mean that the lower range of the ULF towers are in principle compromised because this is an area where they overlap the upper range of the mid-bass channel and therefore the area where we have in-phase summation and out-of-phase cancellation (across the whole 42-500Hz of the mid-bass channels I would say)?
| RF at Ona wrote: | |
Because of the low-pass roll-off on the ULF you may have found that a significantly elevated gain for the ULF is improving the music reproduction where the mid-bass horns have unwanted cancellation effects.
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If the above is happening to a significant degree, then the comment here probably follows and does not need clarification. However I would still be grateful if you would expand on the reasons why this is so. It might help others who missed out on their physics classes when they were looking at the properties of soundwaves in secondary school.
| RF at Ona wrote: | | But this elevated gain does not hurt the reproduction of the ambient/environmental sounds intended to be reproduced by the ULF towers because these sounds are much less sensitive to output level than the musical signal. |
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Oops. You are going too fast! This is the reason where I disagreed most with Romy earlier, although maybe it came out as a disagreement in approach to music reproduction generally. Intuitively, I think Romy is right but intellectually, I do not follow why we (that is Romy above and I think you, and prabably Bill, seem to do so as well) make a distinction between ambience informations and other musical signals which inhabit the same frequency range. I would like to undertand this better. Further, why separate ambience information in such an arbitrary fashion? Applause that Romy mentions above does not live in either ULF or midbass, see link below:
http://obiwannabe.co.uk/tutorials/html/tutorial_applause.html
In brief we are looking at 700Hz, 1300Hz-3KHZ, when we look at the complex frequencies inhabited by applause (male, females, groups, different clapping rythms all have implications for the produced frequencies but non in the mid-lower bass regions). I would say that ambience information inhabits generally everywhere where you can potentially have the musical signal per se.
| RF at Ona wrote: |
How significant these effects are in practice are less clear. Stereo phono records usually become quite monaural in the low frequency range to facilitate both cutting the master and playback tracking. CDs and other modern digital sources may have enough out-of-phase bass for the coupling/cancellation effects to be noticeable. |
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Roberts, I like the way you reason. This is the final touch to a line of reasoning that was not too difficult to follow but in concluding with this point, shows such an excellent insight in the whole process that I understand again why I amongst others like to read here.
Best regards
Rakesh
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