Damping of sealed SEAS L26 and W15CY001

[novec]

I'm throwing together a 3-way with a single SEAS L26 10", two W15CY001 5" Excel mids and a Vifa XT25. As per the picture, they bass will be in a separate ~50 litre enclosure, while the mids share one 11 litre volume. Both enclosures are sealed. I'm using sandwiched 22mm MDF, with the addition of a single 22mm panel for the baffle. This results in a 40mm baffle and 25mm walls for the bass, 22mm wall all round for the mids. The bass box is amply braced, as the next picture shows, whereas the mids are (so far) kept unbraced.

So, to the question - how to dampen these things? I have a lot of 40mm sealed glass wool sheets from earlier designs, but I don't know if they'll be of much use here. I also have some 6mm bitumen sheets. I'll use a Behringer DCX2496 for all crossovers, with the possible addition of some more advanced filtering in some digital amps later.

Datasheets:
SEAS W15CY001 5" Excel mid
SEAS L26RFX/P 10" bass

[novec]

Here's a sketch of the bracing and sandwich buildup of the bass box. The omitted layers are simple D-shaped layers with no bracing.

[Dave Bullet]

Not related to your damping question... more of a concern about frequency response...

What xo points are you using? One L26 is not going to be efficient enough for 2 W15's. You won't get adequate BSC unless you equalize (and then L26 is excursion limited), unless you don't listen to bass heavy music.

David.

[Norcad]

Like Dave Bullet says, that closed enclosure for the L26 will give you three "problems";
1. The sensistivity is to low (you need an extra 4-5dB for baffle step compensation reg to mid/tweet.

When simulated in Bassbox Pro6:
2. -3dB@50Hz, -6dB@35Hz could be better
3. Maximum electric input power 10w@35Hz!

I have tried the L26 in 50L closed, an with som bassheavy music they actually reached the mechanical Xmax!
I also tried the same enclosure with a vent Ø76 L360 and that gave me -3dB@35Hz and max 30w@35Hz.
So if you already have buildt the enclosures, I would go BR. If not; build it bigger and go for BR

See my thread here for som information:

DIY Seas 3way

[demogorgon]

Hey there Novec, long time no see.

I do agree with Dave and Norcad here, x-max will be an issue if your pushing the volume.

as for dampening: i allways thought it as a tool to increase cabinet Q factor (the cabinet volume the speaker "sees"), and if cabinets were sized right to begin with, not an issue?

-Marius

[ShinOBIWAN]

Like the design Novec.

I agree with others regarding the single L26. Couldn't you double up and increases the volume of the woofer cabinet?

EDIT: What about going with a pair of L22's instead? These only need a small enclosure to get fairly good extension. You could keep your existing cabinet volume. I've used the L22's myself in this config and they really can rock when needed.

[5th element]

Originally posted by Dave Bullet
Not related to your damping question... more of a concern about frequency response...

What xo points are you using? One L26 is not going to be efficient enough for 2 W15's. You won't get adequate BSC unless you equalize (and then L26 is excursion limited), unless you don't listen to bass heavy music.

David.

Novec mentions that the DCX2496 will be used for the xover, therefore this will be active and any sensitivity differences will be a non issue.

My question would be, why are you using two W15s when one would be perfectly adequate? If you're playing rock/pop/dance etc, you're certainly not going to be SPL limited by the midrange, so having two just adds to the cost and difficulty of design.

Do you have any specific reasons for wanting the XT25? The W15s really don't want a high xover point, nor does the XT25 want a particularly low xover point. I understand the attraction to the XT, but there are other tweeters with better performance, where a low xover point is concerned.

Also the issue with one L26 per channel, this depends very much on how much space you are trying to fill and if you have any special demands for the loudspeakers. If you're just a normal guy, listening at normal levels in a normal sized room then one L26 per channel would be fine, imo.

[Norcad]

I tried to fill my 50L closed totally, and compared it to an emty enclosure. Unfortantly the changes was very little.
The sound wasnt the biggest issue, the cone displacement was.

I do think that its very difficult to find a damping material who will help with this low frequencies.
IMO the damping materials job is to stop resonance from the enclosure walls, to stop standing waves, and to stop midtone leaks through the drivers cone. With a alu cone the last one is hardly an issue. When testing CA 26 in a box with little depth it was a difference in sound when I put damping material right behind the driver.
If a bass enclosure is build rock solid, and there are no paralell walls and the dimension is from a "golden ratio", much of this problems are already taken care of.
In a smaller midtone enclosure, with higher frequencies to deal with, the difference is bigger, and audible.

[novec]

The component choice and design are actually a long story. It all started with a dynaBel S33 kit I bought, with the XT25, two cheaper 5" SEAS and one CA26RFX 10". Suddenly there was a sale on the W15s, so I traded in the four mids I had for the W15s, and the CA26RFX for the L26. I wanted the Excel 10", but that was just too far off my price range. That's why I stayed with the XT25 tweeters too; I already had them, and didn't have the cash to trade them in for anything considerably better. So now I'm stuck with how to make the best of what I've got...

To be honest, I don't think x-max will be that much of a problem, at least not in the apartment I've got now. I very rarely need to go louder than the dynaBel C22 I've got now, and they've only got the two 5" woofers each.

Like 5th element pointed out, I'll have the DCX2496 to take care of all the crossovers and level adjustment, and probably some minor equalizing as well, so that makes my component mess a whole lot more manageable.

If you think a single W15 would be a better match for the L26 and XT25, that might be an option, although I'd rather not do the full redesign. The upside of it is that I can use the two remaining W15s for the center channel, which is a stock C22 now. The dynaBel designer made some pretty nice crossovers for me, which I won't need once I go active between mid and high on these main speakers.

Hyggelig å se deg igjen, demogorgon!
Norcad: Du får snart mail

[5th element]

Ah so there is a story behind everything.

Originally posted by novec
If you think a single W15 would be a better match for the L26 and XT25, that might be an option, although I'd rather not do the full redesign. The upside of it is that I can use the two remaining W15s for the center channel, which is a stock C22 now. The dynaBel designer made some pretty nice crossovers for me, which I won't need once I go active between mid and high on these main speakers.

Its not so much that a single would be a better match, its more, what do you actually gain by having two? All the issues associated with MTMs and a harder load for the amplifier. Yes you 'gain' 6dB more output for a given place on the volume control, but in this case it's not necessary. The W15 shouldn't exceed its xmax, even if crossed at 150hz with 2nd order acoustic slopes, the coil would probably fry before you reached the end of its linear excursion. Having the second driver would reduce distortion and lower compression, but do you really need it? Or would you notice it?

If you are spending this amount of effort in the box design, it would probably be a good idea to knock up a simple test box and try a few things out. Build what your ears tell you to. If you prefer the WMTM, go for it, if you can't tell the difference go WMT, and if you prefer the WMT, you've got the mid/bass units sorted for the centre channel.

Additionally if you've already built the MTM sections, if you choose to use MT instead, you can always use one of the MTM sections for the centre channel, so it wouldn't all be to waste.

The XT25 should work fine with the W15, it just doesn't offer the same flexibility of other tweeters in this particular area.