Idea for tall slim B3s design- MMTMM

Hi all,

I noticed that on Zaphaudio.com, Zaph's poll suggested that a tall slim floorstanding unit with an optional side-firing sub was something in great demand. A little thought about my living situation (apartment complex, not much space) made me realize that this might be best for me as well. Rather than wait for a design, I thought I'd get the ball rolling.

First, I suggest using the Hi Vi B3s driver as an extended mid running from 200-300hz up to the tweeter crossover. http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=297-427

Next, the Dayton ND20TA tweeter running as high in frequency as possible. This tweeter is selected to minimize center to center spacing for the high crossover. http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=275-030

Finally, for the bass I propose the RS180S, chosen for its size and versatility.http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=295-364

The main problem with this driver (so i hear) is the high frequency breakup. Because I propose to use this driver in a side-firing application from 30-40hz up to 200-300hz, it should be passable with a second order crossover. Any breakup modes will be at a higher frequency(more directional) and 90 degrees off axis to the listener. I took inspiration for this from the Linkwitz Pluto (linkwitzlab.com), where he uses a 5" driver at 90 degreees off axis all the way up to 1khz. I think that the RS180 will be reasonably omnidirectional and able to be placed within 1/8 wavelength at 250ish hz.

Some things to note about this project: The entire package will be 5-6 inches wide in MMTMM arrangement. Max SPL should be safely over 100 db at 1 meter, maybe 105 db optimistically. Crossovers can be 2nd order; this is definitely a three-way design. Depending on how I align the RS180, I think this can be made to function from below 40hz up to 25k.

Total cost of drivers is around $160 per pair. Second order crossovers should keep parts count low, and reduce crossover cost. Obviously, the low crossover could be improved if it is active.

I will be looking at the possibility of loading the mids into a tapered terminated tube, and having a transmission line for the RS180. I might be able to cram all of this in a 5" by 11" by 32" package.

So, what do you think?

Joe
 
Hi Joe,

Thanks for reading my poll and the interest in a project like that.

I've been a little busy on business lately, but that hasn't stopped me from at least thinking about what I wanted in an MTM. I may just post another poll to see what you guys think. Mainly, I wanted to find the right balance of cheap, slim, good looks and good sound. (not neccessarily in that order)

Within and hour or so, I should have another poll up. Of course, the B3S is a nice super-slim option which would be pretty cheap for all the drivers required. For the side firing sub however, I wanted a plate amp powered option, probably of 12 or 10", 8" at the minimum.

John
 
Zaph, the M4N could be good for a slim MTM. I plan on getting a pair of these to play with. They are cheap but they look very nice from their specs. From their impedance and frequency plots the first breakup looks to be at 6k.

The B4N might be good too if you cross over steep and low. It's first breakup is at 3k.
 
Good morning, all.

Zaph said:
... Mainly, I wanted to find the right balance of cheap, slim, good looks and good sound. (not neccessarily in that order)
I think I'll steal that as a motto for the project :cool:

Zaph said:
Within and hour or so, I should have another poll up. Of course, the B3S is a nice super-slim option which would be pretty cheap for all the drivers required. For the side firing sub however, I wanted a plate amp powered option, probably of 12 or 10", 8" at the minimum.

John [/B]

I agree with you on the woofer size, if you're in a "normal" house. The plate amp is a great idea, though- I hadn't thought of that. If I see one that plays well to over 1khz, it would help a lot.

Ap said:
Joe - sounds like a great idea/design.
I had been thinking about something similar.
I feel you could increase height to 40", possibly reduce depth a little & still keep it domestically acceptable.
Going for a TL on the bass might be overdoing it.

Thanks Ap- I agree that it could be taller and acceptable... but the TL might be necessary for this design to work to its potential. The reason why hinges on the B3s midrange. If I can push these much below 200 hz, then there are more options. The problem is that for a midbass running up to 300 hz in a cabinet less than 5 inches across internally, the depth and height start adding up to a good portion of a wavelength inside the passband for a box with any sort of volume.
 
jdybnis- I think you're on the right track with a driver larger than the B3s. Going MTM with 5" drivers could probably get enough midbass to cross to a 10" side-firing woofer without problems in directivity. Furthermore, a 10" could have enough displacement to withstand a linkwitz transform, and the whole cabinet could be smaller for it.

The main problem that remains is cost. I have a very limited budget and already own a nice 250 watt amp. Low-order high-frequency crossovers are a big win on cost, so that's why I want to do it like that. If I can find a 5" midbass that does 100hz-3ish khz, and crosses easily to a cheap tweeter... then I'm happy.
 
I'd wouldn't discount the 4" midbass. It seems that there are more cheap tweeters that sound good above 3k than below. And going from the m4n to the m5n the price goes up 50%. Also the higher crossover means the crossover parts are cheaper.

With the right ported/TL alignment you could probably get strong performance with a 4" down to about 150Hz. I'm not really knowledgeable enough to really figure that out off the top of my head. I'm guesstimating here based on comparing the Vd with a ported 8" two-way that's flat down to 40Hz. Add in a $50 sub driver and I think your good down to the 20's in a small room. Maybe the 8" quatro or one of the TB subs like the one onsale today at PE.
 

Pallas

Member
2004-08-23 5:59 am
This project sounds interesting, if not necessarily for hard-core audiophiles at least to build as presents. I'd consider building a pair to replace the crap speakers in my sister's HTIB. (It's Koss thingy from Best Buy, and the electronics box with its TI PurePath amps is surprisingly good but the speakers unsurprisingly suck rocks through straws.)

I like the Aura NS3 for the midrange, for a variety of reasons that have been well-discussed. (To summarize, cheap, underhung low-distortion motor, massive excursion for a 3" driver, smooth FR.) For the tweeter, does anyone know if there's a US supplier for the ATD spiral planars? E-Speakers.com used to carry them, but they don't list ATD any more. That's a really, really sweet tweeter that basically nobody has used because it requires a three-way design. (Genesis used it commercially.) Then again, a German planar/ribbon vendor Expolinear (who generally do a good job of editing their collection, and as BerlinerInnen are ipso facto cool) lists a HiVi model as their replacement for the ATD spiral. It appears to be available in the USA, too. Even if it's more expensive than the alternatives, its resistive impedance should allow fewer crossover parts.

For an optional sidefiring woofer, given the emphasis on a slim baffle John Janowitz's new 10" sub seems to recommend itself. It is a bit pricey, though a "slimline NHT 3.3" (i.e. speaker designed to be against the wall, creating its own virtual room corner for the woofer while sticking the mid and tweet out far enough into the room to sound good) is a very cool idea.
 
I got a pair of those Hi-Vi R1TL tweeters around a month ago. Very good stuff, but there are so many tweeters available in that price range and I haven't heard most of them so there may be even better deals out there. Excellent off axis response, if that interests you. Hi-Vi recommends them to be crossed at 3.5k, I've got 'em at 4.5k. I'm quite pleased with them so far.
 

Tazz

Member
2003-04-05 4:58 am
Alberta
Hi All,

I am watching this thread (and the Zaph audio webpage) with great intrest as this is similiar to my next project. I am currently working on a MMTMM centre channel design based around the HIVI B3S and the HIVi TN25 tweeter. I just got all the parts in as well as required tools and will be slowly building the .29 cuft box which will be mounted in my fireplace mantel. Solen audio has helped with a box and cross over design and I hope everything works out. I would like to build a similiar MMTMM also with the HIVI B3S and a side firing subwoofer.

TAzz
 
Good Thread.

I have been pondering this type of set-up also. I have comment on my thought and let people bat them around a little.

I was thinking of building a MTM with 5" Dayton reference and 1 1/8" Dayton Tweeter. Using a sealed enclosure. Similar to this project:

http://www.partsexpress.com/projectshowcase/triune/index.htm

Then raising the tweeter to my ear position while seated and boxed a vented box underneath for a side firing woofer. I was going to use a 10" Dayton Reference (assuming the depth of the cabinet can handle 10" & the volume worked out OK). I would use a rear firing port.

My thought would be to use a 2-way crossover between the 5" and the tweeter. Let the sealed enclosure (top half of cabinet) handle the low-pass on the 5".

Since the 10" is removed from the MTM, I was thinking of using only a high-pass on it. Maybe around 200 Hz or lower range.

Technically you would have overlap between the 5" and 10" but since the 10" is side firing, I think it work out OK.

I personally wouldn't add an amp to the woofer, I am afraid it would be too bass heavy for my tastes. I would consider selecting a 10" with a higher sensitivity then the MTM to maybe boost the bass output a little. Maybe a woofer with a sensitivity in the 90-95 dB range and MTM in the 85-90 dB range.

Just my thoughts. All academic, not real data to speak to.

FYI-
NHT had a model with this exact config. It was an older model though.
 
The crossover between the M in the MTM and the "sub" woofer is something I've been thinking about too. I want to build something relatively low cost. So a standard passive crossover at 100Hz seems out of the question unless I'm willing to go with electrolytic caps and steel core inductors.

In my experience it is hard to get good sound out out of a midrange driver when it is getting the full range electrical signal. The low frequency energy seems to degrade the midrange even if the driver doesn't run out of xmax.
 
jdybnis said:
The crossover between the M in the MTM and the "sub" woofer is something I've been thinking about too. I want to build something relatively low cost. So a standard passive crossover at 100Hz seems out of the question unless I'm willing to go with electrolytic caps and steel core inductors.

That's part of the reason I wanted to go active. The impedence compensation required with low crossovers means not only large values but more components. I just remembered this project here:

http://www.knology.net/~wesnor/sassyt.html

Dan Wesnor is a great designer and I'm sure this speaker sounds increadible. But each side has 40 pounds worth of crossover components. This would probably be good for someone who has 2 channel receiver and is not interested in a plate amp or additional crossover electronics.

So, by going active with a plate amp and a decent crossover such as a Behringer unit or any HT receiver, we avoid all those extra components.

Specifically, I'd like to use the MCM 50-6266, which was a $50 version of Parts Express' 300-792 150 watt plate amp. They are functionally the same thing. The MCM version sold out as word got out about the deal. These amps have boost, which means I'll need a low Qts woofer with an early rolloff. This is generally not a problem, as there are several choices. The first that comes to mine is the Peerless 10" XLS, which would work perfectly with the boost, handle all the power, and have a tiny enclosure size too.

The one issue with using a plate amp is that I will lose the super slim profile I was after. The PE/MCM plate amp will require a cabinet that is 8.5" wide. If I don't use the plate amp I lose the flexibility of adjusting the subwoofer level to match the MMTMM.

If for some reason I choose to go fully passive without the plate amp, I'll probably take a different design route with the side firing woofer. I'd mount it a little bit higher off the floor and closer to the front, and cross over higher and steeper to avoid all the impedence compensation components. With a higher crossover though, I have to consider the phase shift of the side firing woofer. At 250 hz, the wavelength is about 54". Assuming the center of the side mounted woofer is 5" back from the baffle and the woofer is about 3" further away from the listening point due to it being lower than the woofer, that calculates out to about 50 degrees of phase shift at 250hz. So then I'd end up going with asymmetrical slopes to compensate.

Keeping the crossover low and active removes the phase shift issues of a side mounted woofer.

I've got some cabinet design ideas to keep the top parts slim while allowing for the 8" width on the lower section. I'll have to draw something up to look at.
 
Zaph said:
Keeping the crossover low and active removes the phase shift issues of a side mounted woofer.

YES! Active woofer gets my vote.

Might I suggest you look at the WR125ST for the MM or MMMM part? I think the FR is ideal and the high impedance will make for an easier load. When I voted in your poll yesterday it seemed the higher-quality driver version was leading.

BTW, if there had only been one choice for dipole in your last poll instead of two, it probably would have won.
 
Zaph,

It's good to hear your response. I knew there were issues with pushing the crossover too high in a side-firing woofer, but the phase issue passed my notice. I guess the "within 1/2 wavelength" spacing for drivers at crossover is only a good rule of thumb within a plane normal to the listening axis. I was ready to push the RS180 as high as 400 hz, since a TL should take care of any standing waves that would form in the large volume required for the woofer. I can simulate TLs with mathcad, but I would have to do crossover and driver offset on paper- I don't have any software for it. I'm just too lazy/busy to do any sort of iterations of that stuff on paper.

One thing is certain, though- if there isn't a good way to turn this into a 3-way with moderately high woof-mid crossover, then an active crossover is the only way.

You mention that the plate amp will increase the width of your baffle to 8.5"- is that from mounting the amp on the rear of the enclosure? Sure, cosmetically that would be best, but I think there could be other solutions. The plate amps could be used outboard near the main amps. Also, it might look OK to mount them on the side of the enclosure and use some black grille cloth to cover them and the side woofer.
 
audiobomber said:


YES! Active woofer gets my vote.

Might I suggest you look at the WR125ST for the MM or MMMM part? I think the FR is ideal and the high impedance will make for an easier load. When I voted in your poll yesterday it seemed the higher-quality driver version was leading.

BTW, if there had only been one choice for dipole in your last poll instead of two, it probably would have won.

IMHO, the WR125 isn't the best performer in that size range. (although it does have the widest bandwidth) Refer to my test results of the WR125 vs RS125 vs Seas L12. The price point of the RS125 makes it look appealing when buying a set of 8. I think I'd have a hard time choosing between the RS125 and the Aura NS3-193 for a slim version.

Yup, If I had only one option in the last poll for dipole, I'm sure it would have won. Still, there's a big difference in those two options however. A full passive dipole would be a big challenge to pull off.