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I hate speakers... |
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ServerBaboon
Senior Member Joined: 16 Jan 2008 Location: NW England Status: Offline Points: 968 |
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Are we talking about the Leaks now or the Ushers or the whole ensemble? Edited by ServerBaboon - 18 Jul 2011 at 5:12pm |
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Steve
------------- Various bits of GSP Kit ..well two so far, unless you count the cables that is. |
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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Leaks.
Removed tweeters and blanked off holes, they are now within 1dB. Mounted tweeters separately, with pink noise they were up 6dB above LF units - in need of attenuation - next job... |
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That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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As I may or may not have mentioned, speakers are something I used to enjoy, DIY build, install and actually use myself.
It's only really been the last 10 years since moving to this semi-attached single storey house with cinder-block party-walls having many unfilled joints lurking under the plaster, that headphones have ruled. Ideally the structure of our homes should attenuate all frequencies by around 60dB to ensure peace and quiet both ways, but the vast majority don't, and believing "love thy neighbour as thy loves thyself" should act both ways... Now, unfortunately, low frequencies are very difficult to tame. And there's a reason for that: it's to allow elephants to communicate over vast distances (it's a good job the elephants that live in the UK are kept in zoo's or we'd have a lot of very dead occupants of squashed cars... and this is probably why Hi-Fi isn't as popular in South Africa...) The point I'm trying to make is that bass is the hardest sound to attenuate in building structures and beyond. When low powered amps were the norm many years ago it may have been OK to stand speakers on the floor and push them back to the wall to gain more acoustical output at low frequencies, but today, with high powered amps, we really need more than ever to consider others (although often it would seem the opposite is taking place). Speakers on properly designed stands can decouple the bass from the structure so that we only have to deal with airborne noise (and repairing the floor when the other half discovers the mess the spikes have made...). So when we get a pair of 1960's speakers like the Leak "Sandwich" and support them appropriately, away from the wall the intended bass output drops. What also happens is the tweeter output stays the same, so the sound balance is terrible! Therefore, I decided to measure the comparative outputs of bass and treble drivers using a test record having a pink noise track and an installers sound level meter. I found the tweeter's output to be +6dB SPL at 1 metre (sound pressure level) compared to the bass driver. What to do? Obviously the tweeter requires attenuating. This has to be done without upsetting the crossover turnover frequencies so the attenuation needs to result in the same impedance load on the crossover. This is done with an "L-pad" attenuator which is a posh way of describing a potential divider. As we are dealing with power here, we could think +6dB is four times the output (3dB being times 2 in power terms) but in sound pressure terms we find +6dB is the same as with signal voltages: twice in other words. I made up a rudimentary "L-pad" to do -6dB to correct for the tweeter's output, measured it with the meter and found it to be flat. Now, all this is with the cabinet in disarray as the tweeter's were out and stood atop the cabinets. One good thing is that tweeters don't rely on a sealed box or ports and things to work near to proper. But when mounted onto the "baffle" (front panel), the pressure wave they generate will be reinforced so you expect the acoustic output to go up. Auditioning therefore has to have the final say. And with a sub-baffle attached there was a bit more "life force" to the music - vocals were fuller rather than being recessed as they were with the tweeters stood by themselves. So, that's where I'm up to as I type. I have provided a gaping cutout in the existing baffle board above the bass driver to take the rear of the tweeter, which will be mounted on a sub-baffle with its "hat" sealing it off from the rest of the cabinet, which, in turn, will be screwed to the existing baffle. The tweeter-offset to the same side - both cabinets - has been remedied so they are central above the bass driver - this should ensure better imaging. There will, I'm sure, be all sorts of reflections because of the 5/8" step between sub and existing baffle, but then again, the improvements should be better output matching and a centralized image, so I'm willing to listen through such imperfections which may well turn out to be minor. The whole lot will look ugly but the original product looked almost as bad with grille removed. If I can unpick the grille material I will make a hole in the grille board to align with the tweeter's new position and use them with grilles on. The grilles should disperse any less-than-forgiving reflections as mentioned above. Here's the picture of where I'm up to (below), and the proper L-pad resistors have just arrived so I'm going to get busy and get these modified Leak "Sandwich" two ways finished ASAP. (the speaker on the right is shown with tweeter "hat" positioned where it should eventually reside) |
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I really must apologise for all the work I have created for you Graham
Adrian.
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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If it were not for Leak using tar board for cabinet damping it would have been more of a "pleasure". The moment you drill or saw into tar board, it smears and clogs the drill flutes and saw teeth. The only remedy is by soaking the cutting tools in white spirit. However, think of the cost of decent monitors! Something this size like the Harbeth monitor 40 costs over £6K per pair. The smaller monitor 30 is around £2K. If we take an average of these prices we're talking about £4K and we don't come across that sort of money easily. Having said that, as a check measure, I have ordered the shoebox size Harbeth monitor 20's at just over £1K. So what's all the fuss about speakers at HQ? The Proprius power amp of course - we need to ensure it truly delivers before we dare think about manufacturing them. |
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tg [RIP]
Moderator Group Joined: 19 Jan 2008 Location: Sydney Status: Offline Points: 1866 |
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Are you going to send a pair to Geoff Husband to review? |
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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@ tg, at least I hope Geoff will want to listen to the amps.
And now the results of the last couple of days of frantic work... The Sandwich Leak should have made! |
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