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mattkhan

Distinguished Member
I thought I might as well kick this one off now even if it doesn't go anywhere particularly quickly given the other 2 builds on the table....

The final (he says hopefully) piece in the DIY jigsaw is the surrounds. I've considered a few options for this but an 8" coax keeps looking like the most viable option albeit not a perfect solution. Firstly though what am I looking for?

1) low profile but not necessarily "small" in total enclosure size
2) suitable for use at ~4-5' distance
3) capable enough in the LF to integrate with my existing sub
4) smooth frequency response throughout the range
5) consistent off axis performance

Unfortunately this is a rather problematic combination;

2 strongly suggests a coax as it gives you that point source behaviour almost for free
3, assuming you don't go ported, strongly suggests multiple drivers to handle the LF
2 & 3 would suggest an MTM with a coax in the middle (possible more like a 2.5 way with the 2 Ms really as Ws and the TM in the middle) as that maintains the point source like behaviour BUT the wavefront will not be fully integrated at a 4' distance so we need a coax alone
4 & 5 suggest a waveguide as coax's tend not to have great HF performance due to the way the T is mounted within the W
3 suggests a bigger coax than an 8" but the bigger drivers tend to have worse performance on point 4 (full range FR)

Therefore, short of changing the laws of physics, something looks like it has to give.

My current thinking is that point 3 has to give and hence I'll accept weaker midbass performance from a surround speaker in order to gain an improved midrange.

For this option, http://www.bcspeakers.com/products/coaxial/8-0/8cxn51 looks nice though it needs modelling to review exactly what the LF performance looks like. The provided graph shows it falling off sharply under 200Hz, low Vas and high sensitivity suggests a port is required for the extension I'd need here.

file


Another option is a larger coax and hence, potentially, compromising HF performance. This sort of graph gives an indication of the problem

http://www.bmsspeakers.com/index.php?id=12cn680_curves

both drivers look fairly ugly to put it mildly o_O
d3970a5797.jpg


something like http://www.bcspeakers.com/products/coaxial/12-0/12cxn76 looks cleaner but likely needs a *much* bigger box (not modelled it yet but Vas is much higher)

Another, more expensive option, would be to go with a radian coax. AIUI http://radianaudio.com/product/5208c/ is used in http://reaction-audio.myshopify.com/collections/speakers/products/cx-8?variant=2843909953 and is available from some french retailers for ~€300.

Perhaps their 10" option is the best of all worlds - http://www.teamaudio.fr/media/catalog/product/datasheet/radian/5210-8+8.pdf - ludicrously smoothed response curve. A 10" surround is quite possibly serious overkill but I think that ship has already sailed so .... :beer:
 

scoobysmiff

Active Member

sjackson

Well-known Member
People on AVS seem to be liking the "Volt 10" kits which is an Eminence Beta 10cx (or now a custom lx) with various CD's like the Denovo 150 or the PSD2013S.

I'm considering them but I think the boxes are just too big/deep for my sitting room. I wonder what a 6" or 8" Eminence would be like with a similar CD.
 
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sjackson

Well-known Member
The volt 8 uses the eminence beta8 IIRC

It does yes as does the 6". I guess I'm looking for something with a thin profile
 

mattkhan

Distinguished Member
I am getting somewhat close to going for the radian 5210 despite it being apparently impossible to get accurate specs for it. However it is reportedly a fine coax so perhaps a gamble is required here.

A 10" coax might be considered serious overkill an 8" needs alot of excursion to cross to a sub at 80-100Hz without a port so a bigger driver seems essential. This 10" will be massive overkill in maximum output terms but that seems very much desirable in a coax so as to minimise the effect of the woofer on the way it acts as a guide for the CD. The 10" is also not that much more expensive than the 8" so..... There is also a nice symmetry to 10s all round, pointless symmetry but still :)

For a box, I am thinking of another angled face. I measured up and a 15" square face would fit nicely, angled to aim towards the listening position at about 15 degrees down. This gives ~0.8ft3 which should be plenty.

I will knock up a sketchup before deciding for sure.
 

mojogoes

Remembered (1961-2016)
Wow 10" surrounds in a normal household environment! How have you managed to pass that one past her in doors matt:)
 

mattkhan

Distinguished Member
Wow 10" surrounds in a normal household environment! How have you managed to pass that one past her in doors matt:)
she's all for it!

as long as the speaker isn't too deep then there isn't really that much in, the main difference to the S150T is the width but the current surrounds are in dead space anyway.
 

mattkhan

Distinguished Member
Do you not feel much benefit to a tripole speaker in your room?
that will be an interesting comparison.

I think the S150T works well in my setup but I also think I am basically using it as a monopole so I might as well just build a better monopole. Hence the use of a coax; close seating distance so no multiple driver integration issues to contend with + a coax is all about even power response (which is traded for a somewhat less smooth axial response).
 

sims

Active Member
Why is the S150T basically being used as a monopole at the moment? Because of the close seating distance?
 

mattkhan

Distinguished Member
I spent a bit more time modelling this and came up with something v typically angled surround like

upload_2015-9-3_11-13-54.png


I then looked at the model, max spl is excursion limited below ~180Hz and is ~118dB at 1m at 100Hz. The speaker will be a bit further away but not by much (~1.5m) and it will be loaded by the on wall mounting and the side wall. This is so far beyond overkill it's not even close to being necessary. This is in the region of 20dB headroom which is just insane :eek:

upload_2015-9-3_11-15-15.png
 

mattkhan

Distinguished Member
Comparing against the 5208 in a markedly smaller box (12L vs 26L), we get the following views. The peak output here really heavily depends on the xmax and clarity on this is hard to come by. If it's 1mm then we get

upload_2015-9-3_11-26-42.png


If it's 3mm (as reported by usspeaker) then we get

upload_2015-9-3_11-27-50.png


In either case, it looks likely to be able to reproduce a 0dBFS signal at 100Hz with an MV limit of -10

Given that surrounds don't tend to have 0dBFS signals and given that I v rarely go past -10 on the MV, this suggests that the 5208 and a smaller box is really all I need.
 

MAG77

Active Member
Crickey! When shown like that with the S150T the 10" certainly does look a bit overkill!
Saying that though if you can get away with it in your room then I'd be tempted to go with overkill ! :)
 

mattkhan

Distinguished Member
had a chat with Gene at Radian earlier, v helpful guy and I now have accurate specs for the 5208 so this is definitely the way forward.
 

mattkhan

Distinguished Member
I am vaguely tempted to buy 4 and use 2 for a stereo setup, you get an extra 5% off if you buy 3+ after all :thumbsup:
 

mattkhan

Distinguished Member
Rather sooner than expected but a pair of radians are now on their way from France. A bit less than the predicted 4-6 weeks lead time :thumbsup:

Need to get a test box built sharpish, I have some spare MDF so maybe that will do
 

sjackson

Well-known Member
Looking forward to this..... I'm getting close to buying the Eminence ones myself (with the PSD2013) but struggling as the Beyma 8CX300Nd/N is not really that much more expensive and the custom XO (on AVS) is only around $40. Probably only £40 difference in total between them.
 

mattkhan

Distinguished Member
One day I will stop posting pictures of boxes in various stages of construction but that day hasn't come yet. My noobness has not quite worn off yet :D

A test box emerges.... I bought a load of big clamps for the sub but now I see I need small ones too :facepalm: I thought I would try no screw butt joints with no rabbet for this one. Bit of a bugger to get the clamps on (words may have been spoken) but seems OK so far. Only a test box anyway so will be chucked once the xo is done.

IMG_20150919_202812.jpg


Skanky slippers to indicate scale
 

sjackson

Well-known Member
For now I have an XXLS400 but it's on the list to upgrade once I complete my speaker setup
 

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