My 3-way OB new project

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Moondog55

Moondog55

diyAudio Member
Joined 2007
#1
OK i'm asking for help to start off.

I have bought some cheap MDF and that is going to set my baffle size, I've played with some programs and apart from the poor power handling the responses I get look reasonably good.

I am looking now for some advice on possible modifications/tweaks to the cheap bass drivers I'll be using.
Aussies will know Jaycar, and some may be familiar with their CW-2125, it is a stamped steel frame with the book T/S parameters Fs 32; Re 7.2; Qms 4.00; Qes2.32, which makes Qts 1
.46.
Vas is 166 litres
Thermal power handling is stated as 50watts but X-max is only 3.5mm/7mm P-.P.

If I modify the baskets where should I start??
Is there a best order in which to work?
I have considered filling in the gap between magnet and basket first using epoxy filled with Aluminium powder ( because I have lots of that ) and then lining the spokes with some stick-on felt, followed by some damping on the frames, using cost effective means ( funny but epoxy may work out cheaper than blue-tac ) and then some cautious PVA on the cones.
I have had sucess with PVA coating these drivers in another project.

Baffle size is 1810 X 455mm and can be as thick as I want using multiple layers, depth of side walls now open to discussion.
 
#2
Hi Ted,

Is the PVA to reduce Fs or to help control breakup? Those specs look wonderful for OB use already, and 3.5mm xmax is not too shabby IMO. With 2 x 12" per side they should give plenty of volume displacement.

I've never done a lot of driver modification but bitumen/tar on the basket spokes should effectively damp any ringing. I don't know how relevant this is on a woofer that will be used low down, but I intend to do my cheap OB woofers like that.

What are you baffle dimensions likely to be?

Will you be considering transformer-bass?

Simon
 
#4
Hi Simon
PVA to reduce cone break-up by making cones just a little stiffer is the intention, but adding a couple of grams will also reduce resonance a tad.
Hi Stuey
Jaycar specs are 92dB 1W/1M, X-baffle shows 90db at 45Hz which is more important, slight rise to 100 and a steep fall-off and big dip at 300, but 300 or close too is where I intend to put the Xover so I'm going to need some help there.
I don't hink I'll be using T-base with these WAF on the added expense and all.
How-ever if they don'r perform all that well I can add it at a later stage.
The cheap off cuts are 455 X 1810mm and I have 24 of them so I can make this baffle as thick a I like, I ca even use the Frankenstien trick" to curve them id I use the 8mm stuff and not the 12mm.
It is the depth of the side wings that is going to keep me awake at nights, to deep and the mids may have trouble too shallow and I loose bass, and I'm still thinking about that big sealed 15inch sub from 40Hz down, which effectively makes this a 4-way systemwhich means I have to go active at leaast for the bottom 2 crosses 40--.. 200/300 or thereabouts
 
#5
Simon please note thats 4 per side, I'll be using the standard layout WW MTM WW, but offsetting mids to one side and trying my hardest to get MTM spacing as tight as possible, I have thought about insetting the tweeter and laying the frame of the Vifas over the top but that may be too hard
 
#6
4 per side! Why on earth are you fretting about xmax? You'll have loads of bass with these monsters.

WWMTMWW sounds like a real challenge to build. You don't want any wings behind the mid drivers so you'll need some that start deep and go in, then flare out again at the top.... or something like that. Another option is sealed mids, as the OB loading is most useful for the bass (an odd option but not without merits IMO).

T-bass is very helpful for SQ and deep bass but you're quite right, it can easily be retro-fitted. Just keep your eye out for cheap ~500VA transformers in the meantime, I don't think you'll regret it.

Simon
 
#7
Well I did some sim-work on the mids and getting to 110dB seemed to be possible but the bass can only go to 105 before the voice coil pops out, and my assumption was that IF i needed to do any BSC I'b prefer to do that in the bass, I hate the thought of padding down the mids.
If I do have to pad down the mids I'll maybe do it by running them in series rather than in parallel, but in parallel I get that extra 6db and I loose that in the bass by running series/parallel.
Those p-13's are only 88dB/1W/1M factory spec.
This is why I asked for help, 3-ways are HARD when you want to get them almost right first time and at $95- each I wanted to do the Vifa midrange justice.

It's enough to make you start tearing your hair out, and I don't have that much left.
 
#9
ROFLMAO

indeed

At least i can concentrate on making them sound Ggooooodd rather than maximise WAF by making them "pretty"
It was SWMBO who bought me the P-13's after all.
One of thes days I'll have the money to do a really efficient system so that we can listen to symphony's at "live" level but by then we'll both be living in a sardine can and won't have the room.
There used to be a 15inch version of these woofers ( 15 years ago they had a Qts of 1.56 ) 4 of those a side would have been good too
 
#10
lol @ SWMBO - new one to me but I could guess what it meant instantly 😀

I'm sure you'll get great SPLs close to the "live" sound, and because it's OB the bass won't be lagging behind.

I'm surprised by your decision to cross over so high, I've not seen many OB 3-ways done like that, but it should keep the mids clean. I just worry about having too strong an upper bass. It will possibly need to be EQ'd somewhat.

Simon
 
#11
300/ 400 is the equal power frequency. half the music power below half above OB the Vifas will handle 35 watts crossed over that high, I can cross-over lower it will depend on the smooth integration of bass and mid of course, and the D-27 will handle 20 watts easily if crossed around 2500/2700 i have seen a multitude of designs based around thes 2 drivers and everyone uses a different XO but few people use the P-13 above 3K.

I will probably wind up using the Behringer CX **** 3-way and a passive at the top end, lots of flexibility with amps but I am hoping the vintage Trio will get warmed up for this one

http://www.thevintageknob.org/KENWOOD/L07M/L07M.html

My midrange amp and I'll probably use the Rotel 1070 for the bass even if it is a little overkill
 
#12
If anyone has experience with other ways of doing this please let me know, I have been advised to use "H" frames for the woofers, WAF on those may be lower, but I have had a thought, lay a 2woofer H-frame on its side and then mount the plain baffle sitting on top, I could even use 3 woofers in the base "H-frame" yes it would be wide but perhaps I can fold it internally somehow, I have a dozen of these woofers to play with althoughi was going to use 4 of them or at least 2 in another project for friends,

So how would WWW MTM W look aesthetically, baffle sitting on a box thats 2 woofers closest to the floor for the extra boost
 
#13
Moondog55 said:
If anyone has experience with other ways of doing this please let me know, I have been advised to use "H" frames for the woofers, WAF on those may be lower, but I have had a thought, lay a 2woofer H-frame on its side and then mount the plain baffle sitting on top, I could even use 3 woofers in the base "H-frame" yes it would be wide but perhaps I can fold it internally somehow, I have a dozen of these woofers to play with althoughi was going to use 4 of them or at least 2 in another project for friends,

So how would WWW MTM W look aesthetically, baffle sitting on a box thats 2 woofers closest to the floor for the extra boost
Click to expand...

I've decided on stacked W enclosures...not the most elegant, but the most efficient way of packaging 4 12" drivers.
 

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#16
Moondog55 said:
I have been advised to use "H" frames for the woofers, WAF on those may be lower, but I have had a thought, lay a 2woofer H-frame on its side and then mount the plain baffle sitting on top,
Click to expand...


I dont understand, and it may be what you describe, but you could turn a tall H-frame 90 degree so that woofers are side-mounted , which means you could have any number of woofers making a line-array...it may give a different and problematic polar pattern, but who knows...it may work

Ofcourse it means that the woofers will have to be crossed low...dress it with speaker cloth, and your wife will be happy 😉
 
#17
pictures of the woofers?

PVA will increase mass by a small amount, lower Fs, raise Qt. If you really want to stiffen them do front & back... for bass use i tend toward 3-5 coats on the front, 1/2-2/3 of that on the back.

Sor OB use damping extraneous noises from air moveing past the frame & spide noise is sometimes necessary. Epoxy is a good (but fiddly) way of stiffening the motor/basket junction ... one Canadian manufacturer did this by putting a tube over the back and then filling the tube with epoxy -- turned out to be too much work for production.

dave
 
#18
Dave i'm the world worst sketch artist or i would have done that already, i'm still working on it, damn I should have been in bed hours ago; it's 4AM here and the damn birds are starting to twitter OK more coffee and keep going.
Verbal description, "H" frame box 600 X 445 with 2 woofers, lay it on its long side, then in the centre line put flat baffle 445 wide and as tall as needed.
So in "H" frame 2 x 12inch thats WW then in the flat baffle above it the rest of the drivers laid from bottom to top
W MTM WW
looking sort of like an upside down "T", this allows the use of an extra woofer for power handling, but still places the tweeter about 900mm off the floor, and depending on how I wire it a 6Ohm load not 8
 
#19
The Qt on your drivers is, i understand, 2 high for a ripole....

I'd want to get all 4 woofers as close togrther & as close to the floor as possible... you could consider a U (just on the lower part, with the bass drivers mounted on the sides)

Given the (purported) high quality of these, mounting them push-push-push-pull is something to try to scheive (complicates construction, but can be made very waf friendly -- the W-frame shown can achieve this -- tie the drives together with ready-rod instead of using screws, or t-nuts top mount the drivers,

dave
 
#20
 
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