[jeffreybehr]

Anyone build an OB system in MTM format?  I seem to be obsessed with building an OB system using these...



...6-1/2" bass/MR drivers removed from a mid-‘80s Kindel PLS-A*.  I understand one quality an extended-range driver must have is clean, nonedgy upper-MR and trebles, and these sound rather good simply in hand and driven full range with music.

I’m thinking I’d run the two 6-1/2s in parallel and of course full range; together they’ll be around 4 Ohms and (I think) around 93dB sensitive which puts them in flea-powered SET range for my listening levels**.  I’ll add a tweeter with a high-enough crossover to fill in the top.  Initially I’ll use one of the 1" domes from the PLS-As, but if it all works, I expect I’ll need a better tweeter.  I prefer a soft rather than etched treble (and less treble energy than flat, too).  I know nothing about tweeters; can someone recommend one not over, say, $200/pair?

I’m thinking of a pretty narrow front baffle, just wide enough on the bottom to accommodate a 10" hi-sensitivity woofer and another one above it if I need it.  I have lots of the Kindel drivers and might initially add a couple-more Kindel drivers wired in series and driven thru a choke set at, say, 40Hz to fill in the bass.  Just haven’t gotten nearly that far yet. 

I’ll baffle this to the rears, both sides, with maybe the baffles less deep towards the top than the bottom.

What do you think?  Worth $100 of MDF and some hours?

My current system can be seen here http://forum.audiogon.com/cgi-bin/fr.pl?vdone&1126390461&read&keyw&zzjeffrey%20s .


* One reason might be that I own 28 of these drivers!
** about 95dB peaks at the listening position in a largish (3200CF) room with plenty of depth to work with.  Currently I’m running 84dB-sensitive speakers with 120 Watts of PP-paralleled triodes.  Nine dB gets me in 845-based-SET range.

[JohninCR]

Here's a simple one that Davey did.  Also, plywood is much easier to
work with for test baffles.

[jeffreybehr]

Uhh...pic doesn't work.

[gitarretyp]

My speakers are an OB MTM that rick craig designed (see my gallery for pics). I'm very happy with the end result.

[Davey]

http://home.comcast.net/~dreite/Davey/Davey.htm

Davey.

[JoshK]

Among those already mentioned, the NaO (and mini-NaO) is an MTM dipole baffle, so is the Arvo Part, the Linkwitz Pheonix and the Orion variation known as Bob. 

[jeffreybehr]

Anyone care to recommend tweeters?

"...but if it all works, I expect I’ll need a better tweeter.  I prefer a soft rather than etched treble...  I know nothing about tweeters" [except some of them sound QUITE 'hard' and unattractive to me]..."; can someone recommend one not over, say, $200/pair?"

[gitarretyp]

It's not a dome, but i'd recommend the BG Neo3 PDR. It's a very smooth and great sounding tweeter, and it's cheap (see Zaphaudio for some tweeter tests). You CAN use it in dipole configuration, but it's not the best way to go (dipole tweeters aren't really recommended anyway). Also, it's safe to cross rather low (~1.5-1.7k), which is a good thing for an MTM.

[jeffreybehr]

gitarretyp, TYVM for the recommendation.  When I get this going, I'll try them.

[andyr]

(dipole tweeters aren't really recommended anyway).

Given the Orion & the NaO - 2 very respected designs - use cone tweeters and are dipoles, I wonder why you say that?     To say nothing of the famous Maggie ribbon?   

Also, it's safe to cross rather low (~1.5-1.7k), which is a good thing for an MTM.

Can you explain why crossing low is good for an MTM configuration?  What's the problem with crossing over at, say, 2.5/2.6Khz?   

Regards,

Andy

[gitarretyp]

(dipole tweeters aren't really recommended anyway).

Given the Orion & the NaO - 2 very respected designs - use cone tweeters and are dipoles, I wonder why you say that?     To say nothing of the famous Maggie ribbon?   

Also, it's safe to cross rather low (~1.5-1.7k), which is a good thing for an MTM.

Can you explain why crossing low is good for an MTM configuration?  What's the problem with crossing over at, say, 2.5/2.6Khz?   

Regards,

Andy

The orion does not use a dipole tweeter. It has to do with having an even power response (this is written up on the linkwitz site). The lower crossover on an MTM reduces lobing problems caused by phase cancellations from the driver spacing.

[andyr]

Thanks, gitarretyp,

Your definition of a "dipole tweeter" seems to be one where sound comes out the back as well as the front ... am I correct?  (whereas I was thinking that a "conventional" tweeter mounted on an OB qualified!   )

If so ... then, yes, the Orion & the NaO are using conventional tweeters.  But the Maggie ribbon is a true dipole ... so why do you regard this as "not really recommended"?     Maggie HF is regarded as some of the best, period!   

And thanks for the explanation about the lower crossover point reducing lobing problems caused by phase cancellations from the MTM driver spacing.

It seems to me a speaker designer is caught between Scylla & Charybdis here, since a crossover up around 2.5/2.6Khz is not as much in the critical ear-sensitivity region as a crossover of 1.5/1.6Khz is!   

Regards,

Andy

[gitarretyp]

Thanks, gitarretyp,

Your definition of a "dipole tweeter" seems to be one where sound comes out the back as well as the front ... am I correct?  (whereas I was thinking that a "conventional" tweeter mounted on an OB qualified!   )

If so ... then, yes, the Orion & the NaO are using conventional tweeters.  But the Maggie ribbon is a true dipole ... so why do you regard this as "not really recommended"?     Maggie HF is regarded as some of the best, period!   

Yes, by dipole i mean a driver that radiates roughly equally and in opposite phase on opposite sides of the driver. A dipole tweeter decreases the smoothness of the power response, and a rear firing tweeter makes room placement harder. I am not a speaker designer, so if you're really interested in all of this, i'd highly recommend reading over the articles on linkwitz's site.

[jeffreybehr]

I tried and abandoned it.  Just too thin sounding the the lower-MR/upper-bass, even with 48 X 42" wings.  'Tis now obvious this is NOT the right driver for OB use.  Oh well.





The lower 3 and the top one were wired in a net-6-Ohm series/parallel arrangement and driven thru the largest inductor I had lying around.  They added virtually no bass.  Since the MTM pair were in parallel, maybe I should have tried just 2 'woofers' in parallel, but I didn't.  Didn't measure sensitivity either, since the tonal balance was sort of hopeless.