Cressy Snr wrote: ↑Thu Apr 08, 2021 8:20 am
Looks great as do the numbers Simon.
It’s way beyond what I would be allowed.
Thanks Steve, it looks to measure well too, I'll dig the plots out later.
TBF I wouldn't get away with them in the lounge either - we have no visible speakers in there these days, I'm lucky enough to have a room these days to contain the physical manifestations of my madness within.
I've been meaning to get some quick ratchet type clamps for ages but they're not cheap. Even the Axminster versions aren't cheap. But it's a hugely useful clamping (and cutting) system and I really should get at least a couple more.
I ordered them in Excel and then looked for possible matches. Sure enough there are some, but there are probably others too. There are two plots - one uses the multiple sweep functionality in REW, the other where I manually took a number as I wasn't wholly convinced by some of the measurements I got. Anyway, an interesting exercise.
285GMF - room effects.JPG (172.35 KiB) Viewed 5815 times
apologies for belabouring the topic, but this is what I understand as a hold down:
sjoberg hold down.jpg (28.84 KiB) Viewed 5789 times
I'm struggling to see how you could use the ones you linked as hold downs on the holes in the top of your bench
unless you thread them through the holes and turn then through 90 degrees?
you've obviously guessed this is a topic that has vexed me for years...trying to find a chaeper alternative to Sjoberg et al.
There's nowhere you can be that isn't where you're meant to be
Simon - good work - in the plot above, are both curves still measurements of the 285, or is one a room effect ?
I have got measurements of the Quasar bass/mid which I haven't posted yet, will do later.
Like you, I get a pretty messy and unimpressive measurement which doesn't bear much relation to how it sounds, but that seems to be the way things are with the lower frequencies, the characteristics of the room dominate.
"Forever fair ... and I'm touching your hair. I wish we could be dreaming .... in this dream" ( Morrison )
The link Simon posted shows nicely what room modes are present in the room and how densely they 'occupy' the space. The degree to which given modes are excited by a loudspeaker depends on its position in the room and the degree to which modes can be heard in a room depends on the position of the listener... to see the degree to which these two positions interact within a room there is a good room simulator within REW that lets you drag a speaker about within a room and see how the room modes are affected and also drag the listener position around and see how that is affected too... its quite informative and illustrates how measurements within a room will vary with certain modes increasing and decreasing as the positions change - it also lets one examine how phase and position are related at low frequencies to produce these effects...
The assumption made above is that the room isn't furnished... one can tweak the wall, ceiling and floor reflectivity but not simulate furniture...
The other big factor to take into account when looking at in-room measurements is the distance from the loudspeakers that the measurement is made from... most people overlook that for a point source radiator the direct and reflected sound pressure is equal at approximately 1m from the loudspeaker and hence measurements at 2m (normal listening position assumption) is dominated by reflected sound i.e. room sound - particularly for l.f.
In other words in-room measurements are good for showing up trends and prone to misinterpretation when looking at specific features such as individual dips and peaks... averaging the measurements around a given position helps but, as the REW simulation shows, it doesn't eliminate room effects and they can still dominate the measurement at certain positions and frequencies (modes)
I've been listening quite happily for a good few weeks now but I really do need to get the active crossovers up an running so I can bring the 285s back in. I need +-12V PS for the crossovers and I've had a rummage to see what I can throw together.
Is there any reason why I can't use a cheap 24V LED lighting SMPS with 2 no. 12k resistors between the output rails with the centre of the resistors tied to ground? I don't see why not but it's rather a while since I've played with magic smoke containing vessels so thought I'd ask before doing something I might regret.