Monacor SP-310CX Coaxial Driver MLTL's

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dario_does_stuff
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#106 Re: Monacor SP-310CX Coaxial Driver MLTL's

Post by dario_does_stuff »

Hi, I have the same drivers since few years, and at the time I built the cabinets following the K&T article ("studio 10") with very few modifications to the original drawings, but now I'm moving to another house and I want to make new cabinets in my own style, so I found this thread and the speakers look very similar to what I had in mind at least from an aesthetic standpoint, but they are near 50 liters of volume! with a very short port, so my question is: did you calculate the measures using software or was it just for looks? (nothing wrong about that!) or something in between?
I designed mine in CAD (solidworks) and from my calculations it needs around just 20 liters of volume: I wanted to have a floor standing speaker too, so I would need to make like a stand or some fake bottom (I don't know how to call it, english is not my first language).
I'm also very torn about where to put the port, because the whole point of the coaxial, at least in my case is to have a perfect phase response, and anywhere I put the port, I would end up with some phase issues, one way or the other, but I think I will put them at the very bottom of the box, facing forward.

By the way, I'm driving them using a DSP (minidsp nano AVR HDA) with active crossover and room correction, that's how I'm able to keep the phase along the frequencies.
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#107 Re: Monacor SP-310CX Coaxial Driver MLTL's

Post by Scottmoose »

It's a mass-loaded quarter-wave, not a pure Helmholtz, so conventional vented box calculations are inaccurate.

You'll have phase rotation with any vented alignment irrespective of where the vent is located; the only way to avoid that is to run them sealed. Assuming it's a conventional Small-derived vented box and you don't have one dimension significantly stretched relative to any others, you can locate the vent more or less where you want. They'll all have subtly different room interactions, but if they're not in close proximity to boundaries (floor, walls etc.) the differences are small. Technically in close proximity to the driver provides maximum gain; whether you want maximum gain is another question entirely: in most cases you don't so in most cases I'd avoid that kind of placement.
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dario_does_stuff
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#108 Re: Monacor SP-310CX Coaxial Driver MLTL's

Post by dario_does_stuff »

I know you said it's a MLTL, and for sure I'm not really an expert on MLTL designs, but but with a hole like that shouldn't that behave more like a ported box?
How's that so different, apart from the placement of the driver? I guess the quarter wave placement of port and driver should amplify the resonance along the height of the box but the physics of the box itself shouldn't change.. I'm sorry if I'm saying stupid things, I'm used to do similar calculations when designing the intake and exhaust of racing engines and I'm trying to apply the same math. :mrgreen:

anyway about my ports, my idea was that outside the resonance frequency the port could interfere with the driver itself if they are next to each other, canceling the wave similarly to an open baffle. that's why I was planning to put them as far as possible, but then I would end with more and more delay to my ears if I put them apart (the whole premise of the coaxial was to avoid that).. Probably the trick is to put the port near the driver but also trying to damp anything above the 100hz and call it a day!
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#109 Re: Monacor SP-310CX Coaxial Driver MLTL's

Post by Scottmoose »

Everyone a Maserati! ;) Short answer: no. If you are familiar with induction and exhaust design you will be familiar with the fundamental difference. A Small type vented box assumes Helmholtz resonance, i.e. the baseline assumption is derived from a uniform internal air particle density and no standing waves. An MLTL / MLQW actively generates and uses standing waves as part of the alignment.

Since most vented boxes are likely to be rolling off reasonably briskly (notwithstanding any 1/2 wave modes of the duct) most output above 100Hz is already likely to be quickly attenuated so when people see a vent near the base of an enclosure and claim they can hear delay caused by the distance, they're listening with their eyes rather than their ears in this narrow sense. That doesn't mean there are no issues though: it depends on the box. 9 times out of 10 in such cases, any audible issues that may exist are due to excess group delay which is a matter of overall acoustic design rather than the vent position per se.
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#110 Re: Monacor SP-310CX Coaxial Driver MLTL's

Post by Scottmoose »

...addendum to the above: vent resonant modes can also be an issue, hence care is sometimes needed in balancing the CSA / length ratio. Setting other considerations aside temporarily, if for reasons of space or similar you end up needing to compromise and have to make a choice between a reduced vent CSA (higher air velocity in the duct) or greater duct length (greater potential for self-resonant modes) I tend to view the former as the lesser of the two evils, since you can usually locate the vent in such a way as to prevent the excess air velocity being audible -typically a rear-baffle location is sufficient.
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#111 Re: Monacor SP-310CX Coaxial Driver MLTL's

Post by chris661 »

... and even then, the port velocity shown in the graphs only occurs when you play a full-power sine tone at that frequency.

Doesn't happen often with a 2-way HiFi speaker, but more of a concern for subwoofers - particularly the ones I build.

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#112 Re: Monacor SP-310CX Coaxial Driver MLTL's

Post by Scottmoose »

Indeed. :lol:

Agreed. I've run across audible vent velocity from other speakers, but usually a/ when they were being cranked, and b/ when the duct was obviously badly undersized in cross section (poor design). Most of the time -narry a problem. Not to say vented boxes don't have issues (or any other type of load is devoid of them), just that this usually isn't a major one.
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#113 Re: Monacor SP-310CX Coaxial Driver MLTL's

Post by dario_does_stuff »

Scottmoose wrote: Tue Apr 21, 2020 10:51 pm Everyone a Maserati! ;) Short answer: no. If you are familiar with induction and exhaust design you will be familiar with the fundamental difference. A Small type vented box assumes Helmholtz resonance, i.e. the baseline assumption is derived from a uniform internal air particle density and no standing waves. An MLTL / MLQW actively generates and uses standing waves as part of the alignment.

Since most vented boxes are likely to be rolling off reasonably briskly (notwithstanding any 1/2 wave modes of the duct) most output above 100Hz is already likely to be quickly attenuated so when people see a vent near the base of an enclosure and claim they can hear delay caused by the distance, they're listening with their eyes rather than their ears in this narrow sense. That doesn't mean there are no issues though: it depends on the box. 9 times out of 10 in such cases, any audible issues that may exist are due to excess group delay which is a matter of overall acoustic design rather than the vent position per se.
Thank you for the explanation, I'll try to find some books about speaker design because there are few things I really struggle to understand but I don't want to get off topic, so maybe I'll start a proper thread about it in the future, but to my (untrained) eyes there are some speaker designs that fall in the middle between different design concepts and use more than one principle, In car engines and industrial stuff they even implement active systems to take advantage of one or the other (variable length ports, active resonators and many other tricks). I mean, normal ported boxes can still have standing waves at certain frequencies, and MLTL boxes like these ones can act as ported boxes when they are not playing at the mode frequency.
Anyway.. here in italy we have at least another week of total lockdown so I guess it's time for studying! :mrgreen:
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#114 Re: Monacor SP-310CX Coaxial Driver MLTL's

Post by Scottmoose »

You will note the phrase:

A Small type vented box assumes Helmholtz resonance, i.e. the baseline assumption is derived from a uniform internal air particle density and no standing waves. An MLTL / MLQW actively generates and uses standing waves as part of the alignment.

The second sentence tells you the fundamental difference between the two: an MLTL / MLQW actively generates and uses standing waves as part of the alignment. It may dominate the alignment, or it may be a constituent part of it. That depends on the specific design. The transition can be said to occur when an enclosure of a given volume has one dimension stretched sufficiently relative to the others that the eigenmodes alter the alignment away from what pure Helmholtz derivations assume with that drive unit, in a box of that volume and those vent dimensions. Thus, an MLTL / MLQW enclosure is one that specifically accounts for and utilises standing waves as functional part of the alignment. I hope that gives you a better idea.

Yes, I'm reasonably familiar with induction & exhaust design and its history. The 383 and 413 long-ram ('Sonoramic') induction setups are interesting examples from the early 1960s US automotive sector; likewise the 4-4-2 W30. Since the engines from the muscle car wars are typically well documented in the public sector, they're the ones most tend to look toward in terms of interesting examples of induction setups, but there are a huge variety from there and the aerospace sector which can inspire techniques in other fields.
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