Two dome mids in an MTM arrangement……anyone tried it?

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mayhem13

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Joined 2008
#1
So 2” dome mids…….fabric……sound amazing but limited in their lower end response as it relates to power handling……..MAYBE 700hz on a good day with transient peaks. How would I get around it?…….well two of course! Now the problem becomes the C2C spacing……BUT is it really a problem up around 5khz with such wide dispersion driver?………..could a 19mm dome pull off the transition?……the SB Acoustics SB19 certainly has the power handling on paper

https://www.parts-express.com/Dayto...Fabric-Dome-Midrange-8-Ohm-285-022?quantity=1
the smooth response on these is uncanny

https://www.madisoundspeakerstore.c...oustics-sb19st-c000-4-3/4-dome-tweeter-4-ohm/
and just as smooth. I’ve used this tweet before and it’s a hidden gem……just as good as an OM1 IMO

The faceplates of the mids would need to be truncated to get them close as would the face of the tweeter……or mount the tweeter flange over the faceplates of the mids…..closer time alignment sacrificing some diffraction.
 
#2
Removed the front plates to mount them as close as possible.

20231226_084559.jpg
 
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#7
John Krutke reported a severe problem in the surround around 2kHz (afair) for later produced charges .... maybe a wrong coating that hardens over time .

The metal dome version has a double surround! (someone presented a cut through model)

We are still waiting for measurements of the 3 inch HiVi DM7500/7600 model 🙂

praying to the gods above (lol)
 
#8
The Hivi DMB-A is better than the Dayton RS52-FN and costs under $30. The problem with the RS52 is the excess hash in the CSD and high odd order HD across the board.

The Hivi DM7500 has an unworkable FR curve and consequently phase issues across the upper register. Definitely not worth the $100 price tag.

The only 3" dome I'd consider is the ScanSpeak D7608-9200, despite a few strong opinions that it doesn't have enough lower mid capability due to excursion limits. The main issue with this mid is the high Qts and open back venting which needs the appropriate sized aperiodic dampened back chamber to work well. The Qts can be lowered to .75 and it can be crossed at 700 3rd order with a very clean CSD and low odd order HD. Do not think of using it without a chamber, even as a dipole.

The Morel MDM55 (CAM558) is another great dome mid. It can be crossed around 800 3rd order or around 900 2nd order. The top end is very smooth and rather detailed. Upper useful limit is 4k with a 2nd order LP and works well with a 19mm HF dome. It happens to work best with the CAT378, which lines up acoustic centers perfectly. Expect roughly 88 dB/W after xover or 92 dB/W for 2 of them. You'll have to cross around 3k if using an MTM configuration and slightly overlap driver flanges to reduce CTC spacing.

The Morel EM1308 is very similar to the MDM55 and you'd be hard pressed to hear the difference. The faceplate helps with dispersion, but it also adds some diffraction artifacts due to this. It sounds just a tick cleaner in the lower mids, but the slightly better performance isn't worth the extra cost. The large flange also makes tighter CTC spacing harder based on the typical LP used with these smaller mids. I'd prefer the smaller MDM55 due to this reason.

A ribbon or AMT tweeter would work better in MTM with two mid domes due to narrow HF vertical dispersion, reducing combing effects compared to wider radiation of HF domes. This can be a problem for people who prefer a taller HF sweet spot, but it really works well with highly reflective ceilings and floors.
 
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#9
@Marveloudio The main reason I wouldn't use the RS52FN is the extra hash in the upper mids. The consistency is another issue on its own, common with Dayton dome drivers. Specifically the metal dome RS52AN has had at least two revisions over time, but hasn't fixed the consistency. This one sounds better than the fabric version, but still has significant issues making it too rough on the ears for longer periods of time. The 10k ish breakup resonance it has needs to be suppressed even with steep LP filtering. It can sound nice if very specific crossover design considerations are made, but it won't be as smooth as the cheaper Hivi DMB-A.
 
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#17
mayhem13 said:
Now the problem becomes the C2C spacing…
Click to expand...

Ideal is a quarter wavelength at the XO point.

At 5kHz that is about 1.7cm.

What you get is combing (It looks worse than it sounds) which will limit the sweet spot.

comb-filter-diagramX.gif


Note that quarter wavelength at 700 Hz is just over 12 cm, you likely can’t get the mids close enuff to the woofers to meet the quarter wavelength criteria.

Most multiways fail the C-C ideal criteria and it becomes one of the compromises one makes when designing a loudspeaker.

dave
 
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#18
profiguy said:
@motokok. Those Vance D reviews never state anything negative in them, which makes me think he doesn't want to upset the manufacturer. Thats hard to look at as an unbiased review and doesn't give much practical guidance to go by.
Click to expand...
Yes, his data speaks for itself, but the writing is just mindnumbing description of his measurement tasks with absolutely nothing at all on interpreting the data, even with wonky frequency responses and corresponding impedance plot blips, just to end with something bland and meaningless about the fact that the driver...exists 😆. Look at the new OEM Ellipticor review as an example.
 
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