Need advice converting B&W 602 s2 into 3-way - diyAudio
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Old 2nd March 2009, 03:37 AM   #1
doobie is offline doobie  Australia
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Default Need advice converting B&W 602 s2 into 3-way

Hey all holy audio folk!

Looking to build HQ 3-way speakers out of my B&W 602 s2 speakers and need advice or ideas from anyone that's tried doing this before.

Here are list of current plans;

Cabinet construction;
-Marine ply front rear baffles or mdf
-Granite black galaxy side panels
-Pine frame with internal matrix bracing
-Bitumen sound deadening material throughout
-All drivers time aligned

Separate cabinets for tweeter,mid,woofer;
-1" B&W tweeter in free space above mid with plastic taper tube removed and TL sealed enclosure as close to mid as possible.
-7" B&W mid in sealed 11 litre enclosure with matrix bracing,bitumen damping,pyramid acoustic foam
-10" dual woofer push pull sealed 75-90 litres enclosure with one driver facing front close to mid other driver directly behind on rear baffle magnet on outside,matrix bracing,bitumen damping,pyramid acoustic foam.

Crossover details:
-aiming for 1rst order (if can get away with it)
-350hz and 3khz
-HQ components,low dcr inductors self wound with 3mm thick copper air core
-will test with cheap components first before settling on exact crossover points!

Woofer driver specs;
-10" Kevlar/Paper -
-150wrms
-8ohms
-88db (1w @ 1m)
-Qms:2.41
-Qes:0.54
-Qts:0.44
-Vas:138.3 Litres
-Fs:25hz
-Tuning frequency:30hz
-Recommended box:75 litres ported

I've used Bassboxpro for simulations which indicate bass response at -3db@49hz and -6db@36hz.
I've provide a link on B&W 602 s2 review with specs on response which seems to show sensitivity @87.9db approx.

http://www.audioxpress.com/reviews/media/AX201DA.pdf

Questions;
-What do you guys think of this design will it work,what problems do you see?
-Using push pull design should bring sensitivity back to 88db counting 6db baffle loss to keep even with mid/tweeter response,is this right?
-The B&W tweeter has 4ohms and woofer has 8ohms on back of driver but I'm thinking woofer is actually 4ohms judging specs in link,trying to get away from using any zobel in crossover?
-Will I lose sensitivity with mid in sealed enclosure crossed @350hz?

Sorry if post is all over the place,don't really do much posting anywhere and this is my first post here!
Welcome and appreciate any thoughts,suggestions,constructive critasisim,or help from anyone who has done project similar.

Thanks.
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Old 2nd March 2009, 04:44 AM   #2
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I think you should start by giving us the specs including crossover points, driver type and dimensions, port dimensions, and cabinet dimensions of the standard B&W 602 S2 first, then from there explain the modifications you are going to make. Explain what you are adding to the stock units.

Now I could search the internet and find all this out for myself, but it would be so much easier if you just gave us the information.

Start with what you have, then tell us where you want to go.

Steve/bluewizard
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Old 2nd March 2009, 12:04 PM   #3
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If it is Hq reproduction you are looking for, just go for active crossover at 80Hz,18/24db/octave.

And put your effort in making 2 or 4 good bassmodules instead?

Thats how i did it, and i'm very pleased with the result.
not B&W 602 though.

Good luck
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Old 2nd March 2009, 02:04 PM   #4
doobie is offline doobie  Australia
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Hi Steve,

What I'm trying to do is get rid of 602 box completely,use tweeter and mid driver in new 3-way cabinet time aligned array.

When I originally purchased them,I wanted B&W 603/604 s2 but had no room at the time so chose 602 instead and now there hard to find so I've decided to try convert these to something better.

-Basically tweeter will be in seperate sealed enclosure maybe TL type.
-Mid range woofer in sealed enclosure of approx 11 litres to 22 litres.
-Bass woofer will be in sealed enclosure dual 10"push pull of 65 or 90 litres.
Dimensions :H727.5 x W277.9 x D449.6 for 90litre bass enclosure.
or H650.8 x W248.6 x D402.2 for 65litre bass enclosure. 30mm baffles and 30mm side panels.Further adjustments is size will be made for bracing.
Crossover points will be approx 350hz and 3khz approx.

B&W 602 s2 specs:

The 602 box has 22 litre flared ported box.
Port size is 50mm diameter 95mm length.
2-way 4th order crossover(1rst order on woofer 3rd on order tweeter)
7" woven kevlar mid driver
1" metal dome tweeter
Frequency response 52hz - 20khz +/-3db
Sensitivity 90db
Impedance 8ohm (minimum 4.3)
Power handling : 25-120wrms
Dimensions : H490mm x W236 x D306

I provided link of detailed measurements take on B&W 602s2 in post.

My aim is for sound quality so choosing for sealed or push pull cabinet designs no ports,overall similar look to early B&W 801/802 series 1.

Thanks,
Steven.
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Old 2nd March 2009, 02:04 PM   #5
doobie is offline doobie  Australia
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Sorry forgot to add,
I have B&W 602s2 speakers and all building materials needed(granite,marine ply,pine timber boards,bitumen sheets,pyramid foam,copper wire for inductors).
I do not have bass drivers as yet but the 10" ones mentioned are ones looking at but open to other driver recommendations and designs.

Thanks,
Steven.
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Old 2nd March 2009, 07:31 PM   #6
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When you say 'mid driver', I assume you mean 'mid-bass' driver. The original speakers were 7" bass (midbass) and 1" dome tweeters(?).

The height dimension of 460 mm or 19.3 inches, indicates that these are some reasonably large bookshelf speakers.

To this original speaker, you want to add some combination of 10" low bass drivers?

Any chance you know the current crossover of the B&W's?

I confess, I'm not an expert on speaker building. Being dirt poor, I'm more of a cut and hack designer.

I personally think your plan for the low bass end, being 2x 10" push/pull woofers, is a bit of overkill. But, on the other hand, if well balanced, it could certainly work.

One approach is to treat this like a half-way system, as in a 2.5-way system. Use the current crossover for the 7" and 1", get them in the new cabinets, run a low end frequency sweep, and find the baffle step. This could also be determined with simulations using various software packages. Others here know far more about this than I do.

At some point in the frequency sweep, the response should drop by 6db and level off again, usually in the 100hz to 300hz range. That 6 db drop represents the baffle step. The center of the falling slope of that drop off should be your midbass to low-bass crossover.

Below the step, both mid and low are playing, above the step, the low-bass fades out.

Another approach is to simply treat it like a standard low-bass, mid-bass, high 3-way speaker. But you can't ignore baffle step. It would be nice if the low-bass were still coordinated with the baffle step to assure flat smooth response.

The difference between this and the 'half-way' system and this full 3-way is, of course, that the is a full crossover between low-bass and mid-bass.

Another alternative, is to treat the push/pull 10" as a separate system, similar to a subwoofer. Leave the existing system as is, in the new cabinets or in separate cabinets, and add the low-bass to it. In this case, I would explore using a separate amp to power the low-bass end.

The difference between this and a subwoofer would be a passive crossover and likely a higher crossover frequency. Plus it is only likely to function down into the low 30's, rather that sub 20hz as some subwoofer claim to do.

My central point is, I would keep the mid-bas, tweeter section as close to what it currently is as possible to eliminate complication in the design. Though, you seem to have design tools to aid you, I think the easier you can make it, the better the end results will be.

Further, do you really know the T/S parameters on the B&W speakers. You will probably need that to make your design and simulation software to work.

If is possible to buy a Dayton woofer tester for something like 100, and while not the most sophisticated software, it will give you all the design parameters you need to accurately design proper cabinets for the mid-bass section.

Again, I'm admittedly in over my head in the details of this design, but conceptually, I hope I have helped, or at least opened the door to more discussion.

Steve/bluewizard
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Old 3rd March 2009, 09:35 AM   #7
SimontY is offline SimontY  United Kingdom
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I don't mean to sound negative, but I personally wouldn't bother with granite side cheeks and push-pull woofers. It's going to make it a hard and expensive project. The granite would also negate the plywood's good properties to some extent. It'd be so much easier to just make a nice plywood box and put a good quality 12" woofer in there. Sealed might also not sound bassy enough if you like the B&W sound. How about a de-tuned port? This could go very low and without the typical boomy sound associated with ports. Just thoughts.

I used to own the DM602 S2 and it was a very good speaker at this price point. The 7" kevlar mid/bass sounded wonderful. The crossover point, like on most B&Ws, is 4Khz.

I'd, again - personally, not touch the upper crossover at all, other than to upgrade the caps and white coffin resistors. My recommendation would be Mundorf Supreme caps and Kiwame resistors. Then just add an active crossover between the "602" part and the woofer part. As suggested this could be at baffle step frequency, or just below like B&W would - ~200hz.

This could be a wonderful speaker. Good luck!

Simon
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Old 3rd March 2009, 11:36 AM   #8
sreten is offline sreten  United Kingdom
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Hmmm.......

A commercial 2-way into a 3-way .....

One obstacle could be the tweeter is set to the sensitivity of a
baffle stepped bass/mid, (common in commercial designs, the
tweeter magnet is only as big as it needs to be) and this means
that you must keep all the baffle step in the bass/mid unit.

In other words a sub / satellite system. (IMO a genuine 3-way
involves both bass and mid drivers in the BSC arrangement).

I would suggest the subwoofer route is more sensible / flexible.

Make new (sealed) beefed up cabinets if you like keeping the
top section of the front baffle. Do not discard the tweeter tube.

A small standmounted cabinet is far easier to make sound good
than a large floorstander. Subwoofers are relatively easy to make
that operate below all panel resonances. A 4 ohm plate amplifier
with 2 8ohm drivers in seperate cabinets gives position flexibility.

Regarding a 3-way with 6.5" and 1" see :
http://www.deadwaxcafe.com/vzone/david/david.htm

/sreten.

Granite side cheeks might work if attached by an intermediate
damping layer that is selected for restrained damping mode.
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Old 3rd March 2009, 01:49 PM   #9
doobie is offline doobie  Australia
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Cheers on replies,

Basic aim is a TMW full 3-way speaker with 1"dome high,7"mid range,2x10"bass push pull.

B&W 602 s2 is large bookshelf speaker with 4th order crossover @4khz.

My new proposed crossover 350hz & 3khz approx complete 1st order.

Reason behind using dual 10" push pull is sound quality,smaller overall speaker foot print size,better depth than smaller drivers,plus no need for speaker stands.

Haven't done any major tests yet but had planned too just wanted advice or council first before embarking,been contemplating these mods for while now.

I do not have t/s parameters on B&W 1"tweeter or 7"mid bass driver yet but if anyone has would be grateful for any help!

Although I know already I found your explanation on baffle step excellent Steve/Bluewizard,do appreciate any advice!

Baffle step seems to be between 350-550hz according to review which is why I chose 350hz approx but may end up different with driver tests in sealed enclosure.

I'll try to knock up some dummy boxes do tests and driver measurements soon to know for sure before buying 10" bass drivers.

Also,was considering using 60-80hz roll off for rear 10" pulling bass driver,read that it can improve bass response in bottom end and help with crossover mid range blend?

I'm only looking for clean extension to mid 30hz upwards hopefully without equalization needed and will be using 300watt@4ohm mono block amplifiers on each,but may even opt for active/passive option for bass depending on tweeter/mid range test results.

I already have subwoofer that I'm currently about to build to compliment bottom end,15" type r Alpine with 600watt class d amp module,though need to construct cabinet yet which will be 100litres approx.

I will post pictures and info as I begin construction.

Thanks,
Steven
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Old 3rd March 2009, 02:15 PM   #10
SimontY is offline SimontY  United Kingdom
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Interesting... with a sub to sit below I'd aim for 40hz extension on your 3-ways. And again I'd like to urge you to leave B&W's excellent crossover alone. I can't see how it's possible to improve on it. These are multi-award winning speakers from the biggest speaker maker in the world. This is not an area you can improve, other than by upping passive component quality.

Areas you can improve on greatly are in cabinet quality and bass extension and dynamics, by going 3-way.

Although baffle step will kick in at about 400hz on paper, B&W haven't had a problem making a full-sounding 2-way there, so the woofer element in your design doesn't need to be more efficient than the upper sections . You could end up with bass that is too efficient, which is another good reason for going active on the bass. If you need more reasons, here you go - the power handling and max ouput level of the speakers will be much higher by going active between bass and mid, and distortion reduced. It also means you have no passive parts to ruin damping of the woofer(s) so they'll sound tight and clean - and no large inductors to buy, as you'd need in a good 3-way.

Push-pull isobaric is a fairly pointless technology, it potentially doubles woofer cost, adds complexity and does what? Slightly reduces distortion. The main benefit is allowing you to use drivers that were designed for a larger box than you can accommodate. This is a moot point if you buy the correct woofer in the first place. Please at least consider this before buying the woofers.

Also, if you decide to go passive, consider quite a small closed box, enhanced by Graham Maynard's T-bass circuit. This will give you closed-box quality (or better) and ported extension in a small size. Drawback is needing a strong amp that can drive low ohm loads and the need to buy two large toroids and two large inductors for the circuit.

Simon
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