WMTMW, the final overkill?

[Jussi]

Hi again !

It's been couple of years since I got my WWMTM Beethoven style open baffles running. Didn't actually finish them at any point and now it's time to move on.

First maybe I should mension few points why change a working concept. First WWMTM dipole was and still is a compromisse. Compromisse between WAF (where it still didn't exactly shine), difficult acoustic conditions and overall performance. While WAF is now gone (literally) I can do much more dramatical solutions as long as I'm pleased with it myself. Second mather is the overall sound. I like the dipoles open presentation but I don't think it's quite the thing for me. Then there is the kick and slam where open baffles just can't give the beating I'm looking for.

Basically this planned concept makes compromisse between room acoustics and raw performance. Therefore (and also while roomdecor is now only in my hands) I can and will unleash some acoustic treatment for my livingroom. Basically turning it more like a music / movies space while compromising it's "livingroom" properties. But since it's also a livingroom I'm not planning to paint it all black or anything as dramatical.

So here we are.

Personally I'd need some opinions and suggestions on two things. First the overall structure and design of the speaker and secondly how I acoustically connect it to my room (basically acoustic treatment questions).

First few things about my room. It's 5,2 deep, 2,6m high and 3,7m wide (approx 17' x 8' x 12'). Front wall is almost completely covered by window and the door to balcony. About 40cm wide pieces of wall a on each side before corners. Sidewalls a plain and made of concrete. Propably the biggest problem and acoustical challenge. Rear wall is thin to bathroom and 1/3rd of it is a open doorway to rest of the apartment. Present dipoles are positioned approx 0,5-0,6m (2ft) from sidewalls and 1,5m (5ft) from the front. Listening position is also about 1,5 (5ft) of the rear wall.

Originally I run few different approaches through my mind. One was or actually still is (as a backup) a standard closed cabinet MTM using my dipole midrange drivers Seas W18E (older model) in a Dynaudio Confidence C2 style slim cabinet. Naturally this doesn't give the slam I ask and they need a subwoofer system to work with. For that duty I thought of multisubwoofer setup. A bit like described years ago in Harman multisub paper. Naturally 80-200Hz area is weaker that with full WMTMW setup along with vertical directivity and of cource less manly looks.

I know most people would just listen their music though some high quality 2-ways but those just aren't for me.

I also got few encouraging experiences from Dunlavy owners in similar acoustic environment (SC IV and SC IV/a which is very similar to this). So. Full scale (compared to room size) 3-way WMTMW it is. I already have two woofer cabinets under construction and I'll measure them in the room so I can deside is it "go" or not. How WMTMW W-W section behaves, how can I position them and so on.

Driver selection is pretty similar to my dipoles. They have Scan Speak 25W/8565-01 woofers, two on each side, with twin W18E Seas units and I presently use Genelec 8050A tweeter above 1800Hz (4th order crossover). Also thought to experiment Dynaudio T330D in this setup.

Personally I like Dynaudio Evidence Master looks and I've heard the speaker couple of times. Modular construction is a must in this one. Simply too large and too heavy to move around in one peace. Two woofercabinets sandwiching mid-tweeter section.

Single 25W needs +65 litres sealed space to have <0,7 Qtc. So I started out of 70 litres for each driver. This makes top and bottom cabinets rather large and using similar size midrange cabinet it makes midrange cabinet way too large for my midranges. Almost 60 litres for two W18E that makes Qtc around 0,5. I don't think there is that much harm from it but should I really go for it or perhaps cut it to 35-40 litres and use the extra space for even heavier bracing and damping? What kind of construction do you recommend? I've seen different diffusor type cabinet internals, bracing solutions etc but which one is most recommendable? Range is about 200-2000Hz.

As for the room I thought to place some bass damping to front corners (40x40 triangle shape fit), catch 1st sidewall reflections to Ecophon Master Alpha or perhaps use QRD or even skyline diffusor there. Then have some Master Alpha on the ceiling (propably with some air between Alpha and actual ceiling).

Well. First impressions? Questions? Suggestions? Complaints?

[j.michael droke]

Hi there: Suggest reading GM's post (in subwoffers) concerning the Danley DTS10-KIT and especially the reply #5 from DaveCan for information as a starting point in a blank room bass reproduction. ...regards Michael.

[Brett]

Two must reads for the type of system you're looking at.
Jack Bouska's system and
Stig Erik's system though he is now travelling in the opposite direction to you.

Not so long ago I was planning 4 speakers similar with HE drivers and a bunch of subs. Since I got the Unity's the mains have stayed symmetrical, but I've gone to WMT for the surrounds.

[Jussi]

Michael,

Which thread do you refer?

Brett,

Those indeed are intresting designs. I've familiar with Stig Eriks previous models but this seems to be at least bigger and probably better as well. Acoustic solutions look very similar to my thoughts as well but I can't use as heavy treatment to front sector that Stig Erik has done. I have windows in that direction and don't care to block them.

Stig Eriks sand filled midrange cabinet is very intresting. I think I'll have to mail him and ask more details how cabinet is build, what shape interwalls and bracings it's using and so on. I think basically a tapering pyramid could be pretty ideal if it has enough sealed litres in it. That way there can't be any standing waves between walls at any frequency and the whole space can be filled with damping material. But like with Stig Eriks design filling rest of the space with sand make them extremely heavy.

[Brett]

Originally Posted by Jussi

Brett,

Those indeed are intresting designs. I've familiar with Stig Eriks previous models but this seems to be at least bigger and probably better as well. Acoustic solutions look very similar to my thoughts as well but I can't use as heavy treatment to front sector that Stig Erik has done. I have windows in that direction and don't care to block them.

Stig Eriks sand filled midrange cabinet is very intresting. I think I'll have to mail him and ask more details how cabinet is build, what shape interwalls and bracings it's using and so on. I think basically a tapering pyramid could be pretty ideal if it has enough sealed litres in it. That way there can't be any standing waves between walls at any frequency and the whole space can be filled with damping material. But like with Stig Eriks design filling rest of the space with sand make them extremely heavy.

Sand is wonderful for damping resonance. There are some drawings on one of the old pages here

[Jussi]

Originally Posted by Brett

Sand is wonderful for damping resonance.

I guess they are but they don't kill standing waves and other problems that for example parallel walls cause. I think cabinet should be well braced, cabinet parts forming non-parallel surfaces and then have proper resonance damping.

Sand is good also because you can add it after you've positioned your speakers and just finish the installation by filling up. Sand makes it very heavy and difficult to move and carry.

[Brett]

Originally Posted by Jussi

I guess they are but they don't kill standing waves and other problems that for example parallel walls cause.

I never said it did. I linked it to show you the way Stig Erik did it in a precious build. I understand there is a difference between panel resonance and the acoustic modes of an enclosed space.

Originally Posted by Jussi

I think cabinet should be well braced, cabinet parts forming non-parallel surfaces and then have proper resonance damping.

I am the poster boy for heavy bracing, mainly using a variant of the B&W matrix.

Originally Posted by Jussi

Sand is good also because you can add it after you've positioned your speakers and just finish the installation by filling up. Sand makes it very heavy and difficult to move and carry.

My current builds are way too heavy anyway so I'm not adding sand, but once built and positioned, they generally don't move, so it's not an issue unless you're an obsessive tweaker.

[Jussi]

Originally Posted by Brett

I never said it did. I linked it to show you the way Stig Erik did it in a precious build. I understand there is a difference between panel resonance and the acoustic modes of an enclosed space.

Sorry, I didn't mean to accuse you of anything.

Stig Eriks speakers seem intresting but they make me wonder couple of things. First there are pretty large areas where there is no bracing between inner cabinet and outer cabinet. Sure there is sand but sand doesn't grip cabinet parts together in any way. It actually push them apart by its weight. Second thing is the filling itself. It's known that sand compresses into smaller space in time while small grains find their place. Therefore I'd expect some space below ceiling surfaces which leave it open for resonance while 19mm MDF isn't exactly connected to sand.

Two ideas. First I think the sand containers should be something like a funnel or at least shaped enough like a funnel. This way sand will find it's place and fill containers all the way. Maybe containers could have caps at the top where you can check and even add more sand if needed. Secondly cabinets overall construction should be taken care of. In this mather I think there are few even better solutions than sand. Bitumen or even lead-bitumen can be used and these materials also attach cabinetparts together.

[Brett]

Originally Posted by Jussi

Stig Eriks speakers seem intresting but they make me wonder couple of things. First there are pretty large areas where there is no bracing between inner cabinet and outer cabinet. Sure there is sand but sand doesn't grip cabinet parts together in any way. It actually push them apart by its weight. Second thing is the filling itself. It's known that sand compresses into smaller space in time while small grains find their place. Therefore I'd expect some space below ceiling surfaces which leave it open for resonance while 19mm MDF isn't exactly connected to sand.

SET doesn't strike me as silly enough to have left out sufficient bracing to stop those issues. My guess would be the drawings are incomplete, either becasue a version of these is made commercially and because it's a personal/DIY site he might not have been bothered - the general principle shows.

Originally Posted by Jussi

Two ideas. First I think the sand containers should be something like a funnel or at least shaped enough like a funnel. This way sand will find it's place and fill containers all the way. Maybe containers could have caps at the top where you can check and even add more sand if needed. Secondly cabinets overall construction should be taken care of. In this mather I think there are few even better solutions than sand. Bitumen or even lead-bitumen can be used and these materials also attach cabinetparts together.

Agree with this. The last set of stands I made had an opening the size of the vertical shaft for this reason; simply remove the speaker and top up after sone time, and to make it easier to pour out to move house. I don't think a small air gap is going to be critical though.

My new TT bases are being filled with sand (garnet).

[Jussi]

I started thinking. Is 25W/8565-01 the best option for this sort of solution?

I know it's still a very good driver but still it puts me thinking of different options. Naturally any other choice puts my Scans on sale but that's also one option.

First thought that bounced into my mind was fitting 18" PA woofers into play. Similar setup that Stig Erik used in his speakers. But that make cabinets way too wide for W18 mids and I don't want to go for Stig Eriks solution of cutted frontplate. I know using W18 in a 3-way is a compromisse, just like Stig Erik mensioned in his report, but I don't intend to go further from full scale 3-ways.

But what about 15" PA woofers. For example L15P400 RCF:

RCF - L15P400

Rugged design, good +-8mm linear excursion, good efficiency and clean responsegraph. Large cones, much less excursion needs compared to twin 10" version. Sticks into 400mm wide cabinet and also fits into compact closed cabinet. Little over 22 litres for Qtc 0,7.

I also checked couple Dunlavy designs width to depth ratio. With ratio of 1:1,625 (650mm / 400mm) my design would still be between SC-IV/a (1:1,5) and the big SC-VI (1:1,8). I don't like square shape cabinets myself..