single or twin midbass, what are the options?

[Puggie]

My project keeps changing with alarming regularity, first the drivers changed and now I'm looking at going with single midbass not twin.

HELP!!

This is the first thread:

TL and the derivatives using two midbass drivers in a D'Appolito style configuration

The basic idea was to make a set of tall thin speakers for music and home theatre WAF/SAF approval is very high on the agenda as they are to go in the living room and the Volt transmission line design was not popular at all (it was bigger than the TV which didn't help).

I've got a set of 4 Audax AP100Z0 midbass drivers and 3 Morel USA MDT-20 tweets to play with. Now the boxes will be 5.5" wide 38" high and either 6.25 or 7" deep. This gives me 11 to 13 litres to play with and I planned on tuning to 50-55ish Hz. Now originally I was planning to use Morel mids which work in next to no volume but my bank balance said the Audaxs would be better the Audaxs do drop lower which I like but they requre significantly more volume.

So the wood is cut, the drivers are sat there, do I go with my original plan of D'Appolito (MTM) in each cabinet, this gives me more SPL and a nice looking group delay, OR do I go with a single mid and tweet which should in theory drop a little lower but the group delay gets a bit high and I'm worried about it getting boomy. The other thing is if I only use one mid per cabinet I have two left over which I can use to make a centre channel speaker with the odd tweet I have left.

What are my other options, two mids with one on the back of the cabint etc, what are the pro's of this layout? anything else I should look at?

[pinkmouse]

The MDT-20s should go nicely with the APs. Which measurements are you using for the simulations? The factory ones are a little "generous", you might be better off using the similar results that Vikash and I got through different methods in the other thread. My ongoing active project is using 5L sealed boxes, and they get down to about 85Hz...

Have you thought about Isobaric? Not that you have particular box size problems, but they might be a fun project!

[Puggie]

These are Vikash's drivers

I'll have a look for your thread, yes I've been using the factory driver specs in Bass Box Pro 6.

looking at your results, then dual drivers in 11l sealed would work quite well too (another option) I also have some 5.25" passive radiators from another project I can throw into the melting pot!

Not really thought about isobaric as I don't need a smaller box.

[Puggie]

Would it be possible/successful to do a 2.5 way setup from a MTM setup? I'd like to try a D'Appolito arrangement using the Audax's overlapping the face plate of the Morel tweet, would it be feasable to then lower the Xover of the lower mid to get a 2.5 way setup for the baffle step compensation?

[pinkmouse]

I don't see why not, but it will increase the complexity of your crossover. Depending on your crossover frequency you may need to cram the drivers quite close together to avoid comb filtering. Had you had any thoughts on that frequency yet?

[Vikash]

Originally posted by Puggie
These are Vikash's drivers

I'll have a look for your thread, yes I've been using the factory driver specs in Bass Box Pro 6.

I've got the original Speaker Workshop file with all the measurements etc. for those drivers. I should have offered it ages ago but it slipped my mind. Let me know if you want it (although I think the important stuff is already on my website).

Also, there were lots of ideas floating though the original thread that PM started about these drivers. If you fancy wading though it, it may spark some more ideas.

[pinkmouse]

After thinking a little more, I would go with your idea of using one Audax per box, and save the other two for a centre with your remaining tweet. If you stick with sealed boxes, you will get a nice gentle rolloff at the bottom end that will aid the addition of a sub when you get round to it, and matching between fronts and centre is fairly important for a realistic HT soundstage.

[Puggie]

I did have a read through the original epic thread and it did give me plenty of ideas (that is part of the problem), its just knowing where to start with them. I have the wood cut (nice Latvian Birch ply) so my cabinet size is pretty much decided but thats all that is set in stone. Thanks for the offer of the info Vikash but I think I have all the info I need off your website and speaker workshop makes my brain hurt.

My plan was to mount the 2 midbasses on the surface of the box overlapping the face plate of the Morel MDT-20 (which would be flush mounted) by about 1/2", so there would be about 3" between the edges of the two midbass drivers, pretty close. I was planning on about 2-2.5Khz for the crossover frequency because I know the Morels can play low and stay clean doing so, it also gets me away from the point where the Audax gets peaky and starts to break up (5kHz ish).

Crossover complexity does not worry me, I intend building the cabinets and mounting the drivers, then spending months on playing with different Xover designs (that is what has happened in the past anyway).

If I did go for dual mids I would hunt down another pair of Audaxs for the centre channel, I cant see that being a real problem finding any more, I'm sure a few people bought them and will not get around to using them.

[Puggie]

We need an 'edit post' button so I can keep updating this thread with my thoughts witout looking like a post *****!

My plan was to rear fire the port, mainly for asthetic reasons it would therefore be nice and easy to plug it if I prefered the sealed response, of alternatly assemble the rear of the cabinet with screws and foam draught-excluder strip to seal instead of gluing it, so it can be replaces with out a port if I decide. I could also then try a rear firing second driver for baffle step and remove it if it doesn't work as well as I'd hoped, does that make sense?