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Grant Slack

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  1. Hello, Linkwitz described the problem as somewhat intransigent, requiring either impracticably small or impracticably large enclosures to mitigate the effect. He mentioned some chemical-engineering-grade filter materials that have promise, but did not develop the idea much, and was thinking of it as more suited for an open-back woofer than an enclosure. IMO the back-energy does not so much present as non-linear distortion, but as an effect on the frequency response. Which it is best to equalise for subwoofers in any case, since the net FR is room-dominated. I think that will serve only to increase the problem in the chamber closest to the back of the cone. In the same way as a car muffler increases the pressure between the cylinder and the muffler. Such a device really makes things worse at the start of the pipe in order to make them better at the end -- which is not where you are most concerned. Regards Grant
  2. Hello again. Just last month I heard a presentation by scientist and engineer Jack Davis, who was R&D Manager at Duntech some decades ago. Basically they set out to make speakers that could reproduce a square wave as closely as possible. Naturally, full time alignment was at the core of their approach. It was very interesting, and there was evidently very little attempt to cut corners to meet a budget in those speaker designs. Look after them and they should serve you well -- if your room can live with them.
  3. It's a pity when a nice piece of furniture like that 1880’s red pine cupboard turns out to be a glorified drum and has to go. 😢 We audiophiles pay such a high price sometimes....
  4. Hello, that is quite a sexy look IMHO. But what is it? And what can you tell me about it? Thanks Grant
  5. Welcome Kent. Adding to the Adelaide contingent can only be a good thing. :) Regards Grant Slack
  6. A very highly complimentary review of the Exact cartridge (as a part of a P6 deck review), including excellent measured performance, is available here, link. Regards Grant
  7. Hello, I believe that you are going to have problems with sound quality with an 'open plan' room such as yours. Especially with your listening position only having one side wall. Asymmetry brings its own problems. Am I correct to assume that the same system did not have deficient bass in a different room, and you have recently moved to this room and noticed the lack of bass? If so, in your previous room, were the speakers also away from the walls, and your listening position also? In other words, what else did you change besides the room itself? It has been correctly noted that the bass is always higher in the corners (and also along the walls, but most in a corner). It is not a 'problem' that there is less bass where your seat is (D) than at A, B, and C. It is natural. In fact, if your speakers were perfectly flat from 20-20,000 Hz, you would experience excessive and very lumpy bass response as you walked into the room corners. So, forget about what C sounds like, and focus on getting good sound at the listening position. I also support other comments, that bass traps and similar will not solve your issue. I would be curious to know what the sound is like if you sit at '5.4' (as written on your plan). I would expect less problems from the open side wall. Also, if you move your seat right against the back wall, to get more bass from the natural boost that occurs at walls. You would want some decent absorption behind your head though, maybe between the curtain and the glass. It's not ideal, but it might help with the issue. I am also thinking that your room is rather bright (reflective surfaces), including the floor. This tends to 'boost' the treble and midrange output, which can make the bass sound relatively weak by comparison. It also makes the room too 'echo-ey' for best sound. Some wall-to-wall carpeting with felt underlay will help, along with well-placed heavy drapes, especially on the central sections of the front and rear walls. You mentioned "getting some acoustic work done". If you mean hifi-type acoustic panels, this tends to be very expensive and no better than heavy curtains. In fact it can be worse, mainly because the price, combined with a desire to be attractive in a decorative sense, tends to lead to not enough treatment being installed. All the best with finding a solution. Regards Grant
  8. Hello, I feel for your frustration! Let us go through a few checks methodically, and see if things turn around. I don't own Audyssey, but I have a Yamaha AVR with auto calibration, and I know the generic process. Before starting, I want to mention that, although the REW room simulation is plotting a frequency response, and allows some modelling of room 'seal' and surface absorbtions, don't expect a measured result to look much like it, other than a few of the room mode frequencies being visible. In other words, it is useful for positioning listener and subs, but not great as a prediction of frequency response. FWIW, as a matter of fine tuning, I would un-tick Room is Sealed, and set gyprock ceiling absorption to at least 0.5, and add 1ms of delay to subs 3 and 4. Now. To reality. The first thing to check is what your receiver has done with loudspeaker sizes after the calibration process is completed. Make sure that every main speaker and centre speaker and surround speaker are all set to small size. You might have set them to small size in the setup, but the receiver often changes this, by mistake, during calibration. If it has reset any of your speakers to large, that speaker is playing the bass frequencies for that channel and bass is not being sent to the subwoofers. Also check that the calibration process has not flipped the phase, or altered the distance, to any of your speakers and subs. It happens. One reason I don't trust, or much like, auto calibration. If any of the above has happened, you probably need to lock the values, if the system allows it, and recalibrate. Do you have an SPL meter at home? If not, download an SPL app onto a phone or iPad -- one with RTA mode. We are going to use it for comparison, so absolute accuracy is not needed. You said that the bass frequencies are weaker with four subs than with just one. Let us use the sound meter to test this. Play pink noise, or a bass-frequency subset of pink noise, with all four subs running, and measure the SPL or look at the RTA graph. Now, while leaving the signal running, go to each sub in turn, and switch it off and return to the meter and see whether the bass frequencies have decreased, as they should. Eventually you will get down to only one sub running, and the bass frequencies should be weaker, not stronger. If they are stronger, you have a problem with not all of the subs being connected in phase. You should be able to adjust this with the adjustments on each subwoofer plate. Once you have done all of this, and you're satisfied that there is not a fundamental settings problem, you should be getting more bass output with four subs than one, and it should be reasonably satisfying, if not exactly perfect. This is because there is a personal preference factor in bass volume levels. You need to manually turn up the subwoofer volume a little bit at a time, all four subs by the same amount each time, until you are fully satisfied. It is worth noting, with four subs you should be getting a smoother bass response. This might mean the absence of some bass resonance and punch that might be present (and enjoyed?) with one sub because it is not as smooth, or technically correct. Instead of mistaking this for better bass, I'm suggesting in the above paragraphs that you compensate on your 'pleasure dial' by adjusting overall volume with the four subs until it is highly satisfying. I hope I haven't wasted my time and yours with these suggestions, and I hope you get the fabulous sound that you deserve, with those four subs. Regards Grant
  9. Hello, I do agree that it is a very important, non-discretionary upgrade to a serious audiophile room installation. In my opinion, money spent on expensive playback equipment is largely wasted without appropriate room treatment. May I comment, however, that the illustration at the head of the article, to wit, ...is the right idea but on a manifestly inadequate scale. The absorption panels are too thin, and the diffusors too small and shallow. Especially the panels. They could actually be worse than nothing, because they will not evenly absorb sound above the transition frequency of 200-300 Hz. Room treatments have the peculiar quality of not improving the sound a little bit, with every little bit of extra treatment. Results can actually dip, until the treatment level reaches a kind of threshold, where they become more than merely worthwhile, but essential. As an aside, may I also say that the lack of a primary listening seat, on the centreline of the speakers, is an obvious mistake, unless the speakers are placed asymmetrically in the room..... Regards Grant
  10. Hello Ken, are you using equalization based on in-room measurements?
  11. Hello Winno, I use AngelStep 48P, link. It has a very low profile of 8mm, and is an industrial material, so less prone to high markup at the cash register. I have tried component-sized pads, and I have tried foot-sized mini-pads under each foot, with equal result. (By 'result', I mean comparing by feel, with one hand on the shelf, and one hand on the component's top. I don't think I could discriminate between using and not using isolation, if I had to determine by listening to music. ) I hope this is helpful, although probably not in line with your initial question. Regards Grant
  12. Does a feed-forward amp also have to have NFB in addition?
  13. Hello everyone. Again, I find such interesting discussions going on here! However I must say, having read through the thread, that the commentary is on a curve towards the conclusion, "done well, NFB sounds good; done badly, it sounds bad". I suppose that is better than nothing: it does tell the reader that NFB is not bound to do harm. I am not aware of any objective a priori argument against the use of NFB in a global or local configuration. The big argument in favour of its use is that it would take a very large design effort, and be very costly to make, an amplifier that does what NFB does, without using it. cheers Grant
  14. Hello everyone. I support Mr Full Range here. It depends entirely on the specific driver model. It was limited to all pre-1990 models and some later models in their pro driver range. It relates to an old JBL system of labeling. JBL did not decide to be contrary: they were in the game right at the start of loudspeaker manufacture, before there were any conventions, and they chose a convention that turned out later to be in the minority. In 1990 they decided to change over to the majority convention. It does not apply to any current driver models. IIRC, the terminology used by JBL was not like "red = negative", but more along the lines of "for forward driver motion under a positive-going signal, connect earth to red". It is easy to determine on their cone drivers by applying a 1.5V cell battery, but much more difficult to do on their compression drivers. JBL have a very handy application note that lists all models affected. Link. However, be warned, if you buy a used driver, it might have been refurbished and its convention changed. Regards Grant (I see some related information was posted while I was typing this. Apologies for some duplication.)
  15. Hello Grumpy, perhaps this is not going to clear up until you change your username! Karma's a b**ch! Regards Grant
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