Another speaker thread

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simon
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#211 Re: Another speaker thread

Post by simon »

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. :mrgreen:
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.
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#212 Re: Another speaker thread

Post by simon »

ed wrote: Thu Apr 08, 2021 9:25 am I love the bench Simon.
which cramps do you use?
Just the Festool guide rail clamps.

https://www.screwfix.com/p/festool-fsz- ... lsrc=aw.ds

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.
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#213 Re: Another speaker thread

Post by JamesD »

I really like these speakers :-)

Came across these yesterday when looking for some new clamps - price looks good...

https://www.powertoolworld.co.uk/makita ... lunge-saws

ciao

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#214 Re: Another speaker thread

Post by ed »

Ahh...we might be at cross purposes...I have very many of the type you linked to...

I was referring to the holes in the top of your bench and thought you would be using them for hold-downs, which are a different type of clamp.
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#215 Re: Another speaker thread

Post by simon »

JamesD wrote: Thu Apr 08, 2021 11:36 am I really like these speakers :-)
:-D
Came across these yesterday when looking for some new clamps - price looks good...

https://www.powertoolworld.co.uk/makita ... lunge-saws
That's a really good price for rail clamps. Makita and Festool are compatible profiles (and Triton and no doubt others too).
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#216 Re: Another speaker thread

Post by simon »

ed wrote: Thu Apr 08, 2021 1:42 pm Ahh...we might be at cross purposes...I have very many of the type you linked to...

I was referring to the holes in the top of your bench and thought you would be using them for hold-downs, which are a different type of clamp.
Yep, I think we're talking the same thing ed - they slot in to the holes and can be tightened down. Awesome for some stuff. But I'd like some ratchet jobs for speed, but not, yet, for £42 each.
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#217 Re: Another speaker thread

Post by simon »

Here's the measurement of the SB29 sub. The plan is to use them up to 65Hz, and they look pretty good from 18/19Hz up to crossover frequency to the 285s.
SB29 @ 2m.jpg
SB29 @ 2m.jpg (77.66 KiB) Viewed 11465 times
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#218 Re: Another speaker thread

Post by simon »

It get's a bit more interesting then, this is the combined plot for all four drivers run full range (protective cap for the supertweeters.
miniQuasar full range amp 2m listening position.jpg
miniQuasar full range amp 2m listening position.jpg (105.84 KiB) Viewed 11464 times
I'm not fully convinced by all the measurements - some aren't quite what I've had before. Will need to review this when the active crossovers are in place.
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#219 Re: Another speaker thread

Post by simon »

The green plot of the 285GMF is a bit curious with a sizeable peak and trough. This could well be a room effect. Putting the room dims in to this calculator gave a number of frequencies

http://www.mcsquared.com/modecalc.htm

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
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#220 Re: Another speaker thread

Post by ed »

Hi Simon...
apologies for belabouring the topic, but this is what I understand as a hold down:
sjoberg hold down.jpg
sjoberg hold down.jpg (28.84 KiB) Viewed 11430 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.
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#221 Re: Another speaker thread

Post by simon »

Ed, exactly right - insert the short 90° leg in to the hole, when it reaches the bend turn it so the remaining part sticking out is vertical, and clamp it down. I'll try to get a photo later.
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#222 Re: Another speaker thread

Post by ed »

got it!, many thanks..
that's a bit cunning cos they end up being dual purpose.
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#223 Re: Another speaker thread

Post by IslandPink »

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.
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#224 Re: Another speaker thread

Post by JamesD »

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)

James
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#225 Re: Another speaker thread

Post by simon »

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.
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