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Thread ID: 79098	2007-05-08 03:39:00	Speaker Baffles	Hitech (9024)	PC World Chat

Post ID	Timestamp	Content	User
548177	2007-05-08 10:08:00	Graham L, a friend of mine, Brian, he wrote music reviews for the Press, built those speakers as described at that time, I built a set as well but used high density chip board, mine did not sound quite as good as his concrete ones. They are sitting in my lounge right now, my system is tri-amped c/w active crossovers and using Fairchild amplifiers, I assembled myself.	zqwerty (97)
548178	2007-05-08 19:27:00	................... They are sitting in my lounge right now, my system is tri-amped c/w active crossovers and using Fairchild amplifiers, I assembled myself.Are those similar to th ones Terry showed us where some sound is failry direct, and other components bounce sound of a wall somewhere? Do you have to have delays built into your x-over(s) to compinsate?	personthingy (1670)
548179	2007-05-09 04:51:00	Not sure who Terry is, I have the mid-range horns out of phase with the tweeter and bass horns to increase the crossover roll-offs. The folded corner bass horns use the walls as a compromise flare from the throat to the mouth. No extra delay necessary to be added to the active cross-overs as far as I knew then or now. I have never heard any pub sound system that compares to my horn system in fidelity the only thing that does is electrostatic mid range speakers, they are better than my horns in that frequency range, clearer and more subtle somehow is the best subjective impression description.	zqwerty (97)
548180	2007-05-09 05:21:00	Back to the original question: If the main problem is "resonance" of the speaker cases, a product like Jaycar AX-3688 or AX-3680 might help. Jaycar sell it to quieten car doors. These are two grades of sound deadening sheet, made of a barium loaded PVC with density 4 and 4.5 kg/square metre. Covering all the cabinet panels would probably have some effect. It might look "different", too.	Graham L (2)
548181	2007-05-09 05:57:00	Does anybody know how to fix speaker baffles to get rid of resonance in my speakers, Appreciate some help please.:help: I think we are all getting a bit hi-tech for Hitech! He simply wants some reasonable tips as to how to overcome the resonance. Now this should give all you hi-fi guru's a bit of a laugh. In the early 70's when I was just starting out with lo-fi gear I bought a pair or 3 way Philips speakers from a friend who owned a well known Wellington hi-fi outlet. (yeah I can hear you all laughing from here-Philips?!). Strangely enough these speakers were not all that bad given a price tag of $200. The main problem was cabinet resonance and a bit of a boomy bass (wooden floor). The two options that were suggested to me were the dowel bracing or using some type of wadding to fix to the inside of the boxes. Bracing was out of the question as I was on crutches with limited movement. A friend who built his own cabinets suggested trying the wadding that they use in the expensive Parkas (about 30ml thick uncompressed). Got a roll of that, glued it on all internal walls with rubber cement, made myself a pair of stands with spikes and the resonance and boomy bass disappeared. By the way the stands they were selling in those days could be made for a fraction of the price if you were a bit of a handyman. Hope that's of some help Hitech- assuming that the resonance is coming from the cabinets themselves rather than something loose internally. You don't say whether they are floor standing or on a shelf. If shelf speakers the resonance could well be form a source other than the speakers. OK all you Hi-fi buffs you can stop laughing now-I still have these speakers and they are for sale to the highest bidder (with brand new woofers to boot!). Stands are extra of course! Regards Gordon.	Gordon62 (11771)
548182	2007-05-09 06:58:00	The use of dowels for bracing the cabinet walls is an easy low tech solution as mentioned earlier. Resonance can also result from standing waves between parallel walls, as hinted at by personthingy. A very low tech means of reducing this is to glue egg boxes, or egg trays to the (inside) cabinet sides, the resulting knobbly surfaces will not reflect sound waves to the same extent as hard flat surfaces.	Terry Porritt (14)
548183	2007-05-09 07:27:00	The use of dowels for bracing the cabinet walls is an easy low tech solution as mentioned earlier. Resonance can also result from standing waves between parallel walls, as hinted at by personthingy. A very low tech means of reducing this is to glue egg boxes, or egg trays to the (inside) cabinet sides, the resulting knobbly surfaces will not reflect sound waves to the same extent as hard flat surfaces. Hi Terry -I have also heard in the good old days of sticking corrugated cardboard to the inside walls of speakers as well as the acoustic tiles-never tried it on the Philips as they were particularly hard to access from the front and no access from the back as it was glued on. We still don't know if this guy is using them as floor standing or shelf speakers which could make all the difference as regards resonance. Regards Gordon.	Gordon62 (11771)
548184	2007-05-09 08:05:00	Apologies to Terry, I did not realize you meant the Terry from this site. I too have packed "boomy" speakers with various materials including old carpet or blankets and raised them off the ground with good results. Be careful you do not use materials which shed ie glass fibre as this will get between the speaker coils and magnetic gap if you are unlucky. Concrete speaker walls do not resonate, best smooth bass I ever heard.	zqwerty (97)
548185	2007-05-09 09:23:00	..... Resonance can also result from standing waves between parallel walls, as hinted at by personthingy....Actually i wasn't hinting at that, allthough its a valid point, and is the reason that some larger speakers have a smaller back than front, thus illiminating 2 parallel side walls... Some stage monitors only have parallel ends. No i was hinting at random reinforcement making the box less perfectly symetrical, braking up the perfect shapes, making it less likely to behave badly at that perfect frequency owing to the side walls (for example) just loving a certain frequency that is mathematicly related to a dimension perfectly preserved by a perfect join of consistant materials over each of the side walls dimensions. If we are going to reinforce without absolute understanding of what we are doing, which few have, then random scraps screwed and glued into the edges, corners, or even the centre of a panel are, IMHO, a far better bet than simply adding perfect consitant reinforcement. Of course this might blow the concept of a perfectly matched pair.......	personthingy (1670)
548186	2007-05-09 10:10:00	Right, it all gets around to the same thing, breaking up the symmetry of the speaker enclosure so that it is difficult for fundamental frequencies to exist other than that due to its volume and porting ( Helmholtz resonator) if its a reflex cabinet. That's why the corner enclosure shape was so popular amongst early Hi Fi addicts, the somewhat triangular shape in plan view was not amenable for standing waves to form. Another trick that used to be used, (I'm really talking about the 40s/50s/60s era, I dont know much about whats been happening in modern times :) ), was to hang a sheet of heavy felt, about 6mm or so thick from the top of the cabinet, and full width and about half the height of the cabinet, behind the speaker. This also formed a sort of absorptive baffle to prevent internal standing waves. Another few snippets, it used to be the practice for a reflex cabinet, to match its natural Helmholtz frequency to the natural frequency of the speaker. To detect the cabinet frequency, a lighted candle could be placed in front of the port as a frequency scan at low volume was made. The candle flame would leap around or blow out at the natural frequency	Terry Porritt (14)
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