Speaker Based on SEAS' L12 RE Recommended Enclosure - diyAudio
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Old 2nd July 2011, 11:16 PM   #1
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Default Speaker Based on SEAS' L12 RE Recommended Enclosure

I'm designing a speaker employing the SEAS 5" coaxial L12 RE and using a version of SEAS' recommended enclosure. The twist is that SEAS' enclosure is boxed-shaped and what I'm working with is biomorphic/spherical enclosure that should match exactly the internal enclosure volume of SEAS' recommended box. Essentially, the goal is to duplicate the performance and sonic characteristics of what SEAS has recommended with their box in every way, but with an entirely different form.

I'm looking here for feedback and confirmation on whether I'm properly matching the original design in my interpretation, in terms of volume and tuning.

Attached is SEAS' recommended box enclosure. Following post: SEAS Driver data sheet and non-box enclosure.
Attached Files
File Type: pdf seasA.pdf (154.0 KB, 139 views)
File Type: pdf seasB.pdf (109.0 KB, 83 views)
File Type: pdf seasC.pdf (132.9 KB, 76 views)
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Old 2nd July 2011, 11:59 PM   #2
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Noticing that the total Vb (2.84 litres) is the same, however the Vb subtracting for internal objects is different (due to wall thickness), 2.385 for the box and 2.515 litres for the spherical shape. Which volume should be observed and stay consistent in order to replicate the performance, the one subtracting for internal objects or the total Vb?
Attached Files
File Type: pdf L12 specs.pdf (149.4 KB, 43 views)
File Type: pdf seas box.pdf (36.9 KB, 42 views)
File Type: pdf seas sphere.pdf (34.3 KB, 63 views)
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Old 3rd July 2011, 12:35 AM   #3
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Changing the design like that invites errors. This is mainly due to diffraction related issues.

The biggest of these could be the baffle step compensation. Where baffle step occurs, varies in precise accordance with the cabinets shortest frontal dimension, usually the width. Creating a circular enclosure like that will most certainly alter the baffle step point, you can minimise how much this will affect things by keeping the circles diameter the same as the width of the SEAS enclosure.

Other diffraction related problems could show up, but due to the coaxial arrangement and the loading the mid/bass cone provides to the tweeter, the usual diffraction bump/issues could very well be minimised to insignificant levels. Due to the small size of SEAS' enclosure the ripple/bump would occur at around 2000hz, this also coincides roughly with the xover point so some of this could be handled in the xover.

I don't want to sound like I am simply repeating what I said in the other thread, but that's effectively what I am doing. At the very least I would say match the width of SEAS cabinet in the one that you create and then go from there.

By the way, did contacting Europe Audio help in any way?
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Old 3rd July 2011, 01:23 AM   #4
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I've been in touch with Europe Audio and most certainly will be again - it's an excellent source, thanks. Regarding obtaining the SEAS driver, they're due to get back to me on this, as they don't yet carry it.

Looking at baffle step issues, the enclosure is indeed spherical so the driver is not mounted onto a circular flat baffle, rather it's mounted flush into the sphere. I'm not sure what effect this may have in terms of the baffle step (please try to clarify if game), but I'm aware that Olsen did some of the early research in this area and into edge diffraction and the spherical enclosure might have offered some advantages.

The SEAS recommended enclosure is narrower than the sphere's diameter - is this at all what you're referring to with keeping the circle's diameter the same width (if it was assumed that the circle's diameter was less than the box baffle)?

I'm using the SEAS crossover suggestions, followed to a T, but if the difference in respective baffles is affecting the sound, perhaps the x-over needs tweeking as well.
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Old 3rd July 2011, 02:05 AM   #5
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Ah a sphere, yes that would be a better shape. Indeed as far as I am aware I think the diameter of the sphere now governs the baffle step point. Or rather if you were to use a tear-drop shape the widest point of the drop would govern it.

Of course, if you're using a sphere the diameter directly = the internal volume so you don't have any room for playing around. I remember seeing a series of graphs that showed diffraction in different shaped cabinets. I don't think a perfect sphere was the best either, but I might not be remembering that correctly.

From your design point of view, it might be better to adopt a tear-drop type shape. Something akin to the shape that lots of sonus faber speakers adopt. This way you can keep the baffle narrow and have the widest point of the drop match the width of the SEAS enclosure. This would help with the baffle step issue. If you then keep the top of the enclosure flat and mount the driver the same distance away from the top as SEAS do this should also help to minimise diffraction differences between your cabinet and the SEAS one. As you're not using a sphere you can extend the drop backwards as is necessary to fulfil the cabinet volume requirements, you could also extend the height of the cabinet too to help with volume requirements. Having a flat bottom would also help with supporting the speaker.

Of course any cabinet for the L12 is rather midget and therefore not too hard to construct. Perhaps you could experiment with different shapes and see which one you prefer? Certainly a bog standard rectangular shaped box is a doddle to make, especially if you use a normal drain pipe style port. Maybe making a square sided cabinet as per SEAS design would be a good idea anyway, this way you'll know how the thing should sound as per SEAS design. Then you could make a sphere/tear-drop and compare the two.
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Old 4th July 2011, 03:51 AM   #6
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At this stage and for the purposes of this design, the shape is set, though it would be interesting to experiment with shapes as Harry Olson did wit Bell Labs many years ago (here's the AES paper on diffraction effects from Olson various enclosure shapes

The Sonus Faber site was of particular interest to me, so thanks again there.

I wish to be more certain that I'm getting some of the basics right in this attempt at matching the SEAS enclosure with the spherical one. The Fb, as I'm showing it in bassbox, is at 72Hz. SEAS describes their recommended enclosure as a 2.5 litre box. My spherical enclosure is 2.4 litres when calculated subtracting internal objects, and 2.8 without. When manufacturers describe box volume, are they typically doing so compensated for internal displacement of objects, or totally empty? SEAS doesn't say what their specific tuning frequency is, but according to my bassbox recreation of their enclosure, it's 72Hz. Is this high? Perhaps not for a satellite speaker. When I tune it down by altering the port, the response in the midbass region tapers down earlier - it looks less flat in that range.
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Old 23rd July 2011, 09:51 PM   #7
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That's the paper I was talking about before. Indeed it seems that the sphere is the best shape with regards to diffraction and gives you the smoothest transition between 2 to 4pi, of course this will be anechoic so the room will come into play and distort this somewhat.

A sphere should be okay providing that the diameter of the sphere is the same as the width of the SEAS enclosure. This as described before is because those dimensions govern the baffle-step frequency and any deviations from the SEAS enclosure will bring about errors. Of course you can see how much a square shaped box differs from the sphere with regards to the irregularities of the response. As I mentioned before an enclosure as wide as the SEAS will create a bump around 2000hz which will probably have been factored into the SEAS crossover. Obviously this bump would not be present in a spherical enclosure so you do run the risk of running into some response anomalies. At the end of the day the only thing you can do is build it and find out.
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Old 28th July 2011, 11:20 PM   #8
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The sphere is accepted as an optimal shape with regard to edge-diffraction and the lack of parallel surfaces reduce standing waves, but the latter point, is not something I would describe as readily audible with what I have here.

At present, I'm now listening to the SEAS recommended box-shaped MDF enclosure alongside the equivalent volume spherical enclosure, and they do seem to sound almost identical, in my judgement. Perhaps I will later learn what I should likely be heard and in fact discover it to be so in practice.

Watching the long excursion cones move, however, I do notice that they seem to do so somewhat differently. It appears that the cone in the sphere is moving...it's difficult to explain...as if the vibrations of the membrane do not match the music as closely, visually at least, as that of the box, though the sound is quite the same The sphere's cone appears more violent. I may try to experiment with equalisation just to determine if these perceived variations are more in the subsonic range. Perhaps the narrow diameter/long vent withing the sphere is playing a role in this, though theoretically, the tuning fb is the same. Any thoughts?

Last edited by lucadelcarlo; 28th July 2011 at 11:46 PM.
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Old 29th July 2011, 01:26 AM   #9
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A sphere may be best for external diffraction, but worst for an internal standing wave:
Exclamations
perhaps an internal baffle is required to break up the wave?
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Old 14th September 2011, 08:23 AM   #10
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I was wondering how your design is going... Iam considering using the seas in a small nearfield monitor design: designing a accurate satelite - subwoofer monitor set... where to begin?
But quite a lot of people think it is not such a great idea. What do you think?
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