Which 6.5" mid-bass for a sealed box?

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#203
andyjevans said:
You can get 150mm square section quite easily in aluminium. No woodwork!
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You can go bigger than that if you look in the right places, 200mm x 200mm x5mm ~£250 .m
https://www.metalsupermarkets.co.uk/product/aluminium-square-tube-6082t6/
They order it in.
Metalwork instead of woodwork though, I wonder.

There are more simple ways of building speaker cabs - eg quick look for a video
There is nothing wrong with joints like that. A track saw would be a better option than using a circular saw as he does. The tracks can be clamped to the work having been carefully set and the saw run's along them. A simple router circle cutter can be knocked up to suite the size that needs to be cut,

B&Q will cut 8x4 sheets up into strips etc. The sizes will be pretty accurate. Some woodyards will do the same maybe better if they are told what they are for. Routers can take various types of flush cutters, They have a ball bearing guide. Ok for removing small amounts of material. They can be run along a straight edge or trim an edge to a face depending on type. There are all sorts of options that don't need a lot of expensive kit.

There is also a surprisingly effective dust extractor available - A Henry vacuum with a boost button.

Space needed - relates to the size of sheet and parts that need to be cut.
 
#205
<< You can go bigger than that if you look in the right places, 200mm x 200mm x5mm ~£250 .m
https://www.metalsupermarkets.co.uk/product/aluminium-square-tube-6082t6/ >>

Thanks! I wasn't aware of 200mm x 200mm x 5mm. That's perfect for a Magico/Piega style cabinet. One metre cut in half gives you 18 litres per speaker. That's pretty tempting! It's expensive, but maybe worth it. You'd need to cut the speaker hole out carefully with a jig saw. A hole saw could probably cope with the tweeter hole, but not 145mm for the mid-bass cutout. Hmmmmmm....... interesting.
 
#211
markbakk said:
But an 8" starts to beam around 700Hz.
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That's another problem for Andy. A 6.5 will start to beam at a higher F and at that point may not cause typical tweeters problems. They should come in well past their resonant frequancy. Also a larger speaker is likely to suffer from cone breakup sooner. The Visaton part looks to be unusually good in that area. Penalty, ~25w part but ~12w at 40~50Hz due to cone excursion limitations. Faced with that some might choose to use 2.

Maybe one thing Andy could try is looking for a kit that provides the crossovers that uses the same volume as his bolt together cabinets. If those are a bit too large thing could be stuck in to reduce the voolume. If a little too small that may not make much difference. Vented or sealed? With vented the box tuning F is the main control of the bass behaviour at some volume, I doubt that they have to be boomy although some might set them up to be. Given a vent of some area tuning relates to it's length. Air velocity out of the vent needs to be limited - that sets a size but the bigger it is also relates to the length changes needed to tune. Something to keep an eye on. A mm change having some effect is probably a bad idea.

But this still leaves 4w. Pass on that. It's lower than anything I have used and I wonder if this relates to why Andy wants to change speakers,
 
#213
<< I use 3 watts with 6 1/2 inch drivers, and feel no need for any more power.>>

Indeed - all depends on the music, the room and the listening volume. This hasn't been an issue for me.

<< a kit that provides the crossovers that uses the same volume as his bolt together cabinets. If those are a bit too large thing could be stuck in to reduce the voolume. If a little too small that may not make much difference. >>

I've found the mh-audio site very useful for modelling this. I've been using it a lot. I've learned a lot on this thread.
 
#214
markbakk said:
But an 8" starts to beam around 700Hz. That would mean your tweeter would have to cross below that.
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What criterion are you using for 'starts to beam'?
700Hz would surely disqualify all 2-way 8" designs that don't use a full-range driver, and there are plenty of ostensibly successful RS225 designs.
The SB 8" graphs suggest 3dB down at 60 degrees at about 1300Hz.
Scanspeak 21Ws also a little over 1kHz. Purifi also.
Seas graphs are supportive but their 18cm graphs look similar - I find Seas graphs comparatively difficult to interpret.
Also RS-225 here: https://hificompass.com/en/speakers/measurements/dayton-audio/dayton-audio-rs225p-8a
 
#215
There shouldn't be difficulties for a 8" and a WG tweeter, theorical cut-off at 1500 hz that will be widthen with asymetric XO .

Beta-8A, for instance.
the difficulty is the low end imo and here we have indeed a trade off.

I say : 2 + 1 ways 😉 . You do not mind a plate amp for the sound, with DSP you damp as you like, no needs tubes here for better sound, the sub could be anything between 50 hz to 100 hz cut off according what the two sattelites will be (ideal 6" + WG tweeter) ! And here the choice becomes more evident for the quality : for instance Finalist Monitor with the NE-149W - 8 avialable at Sound imports and the tweeter and WG of your choice (so a 5 to 6" WG and a cheap but good tweeter : SB26CAC, 22 TAF/G (WG?), Morel Cat378 (already WGed), etc.

You can pay my advices by a bottle of red wine ! ahahha, plop, cork, glouglou... that's the lunch, sorry !
 
#216
1700228024937.jpeg

Here is some data from John Murphy’s book on loudspeaker design (Trueaudio) on recommended upper frequencies to avoid excessive beaming.
 
#217
jmansion said:
What criterion are you using for 'starts to beam'?
700Hz would surely disqualify all 2-way 8" designs that don't use a full-range driver, and there are plenty of ostensibly successful RS225 designs.
The SB 8" graphs suggest 3dB down at 60 degrees at about 1300Hz.
Scanspeak 21Ws also a little over 1kHz. Purifi also.
Seas graphs are supportive but their 18cm graphs look similar - I find Seas graphs comparatively difficult to interpret.
Also RS-225 here: https://hificompass.com/en/speakers/measurements/dayton-audio/dayton-audio-rs225p-8a
Click to expand...

On IEC baffles...
230607 WM resp 0-90.png

This is the response of a RS180S (at least the part under 1,5k, in 10 deg steps) in a real life box, some 8,5" wide. Now this is a 7", what do we think an 8" would do at 700Hz?
 
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