Progress on the new Audiosmile loudspeaker

While we're talking about panel stiffness, what was your reasoning behind the shape and positioning of the vent? And will you be going for classic BR or for critical damping?

 

Position is because it looks good there The shape is because I've found slot ports to be better damped than traditional round ones. I think this must be due to increased friction between the close port walls. Making it quite shallow (only about 5cm long) also helps with avoiding a sharp point at which it goes off. The original Rogers also has a shallow port and the output can be seen to be nice and broad. Later models I (of the Spendor at least) had a longer port and were criticised for slightly single-note bass.

 

Coming back to this ... how about a cross panel between baffle and rear panel?

Re the bass port - the best position for a BR vent is close to the bass driver, but on a side panel, according to some experments done by Bernd Timmermanns for Hobby Hifi, a German diy speaker mag. Looks shite, of course, and I can certainly see the point of going for good looks in a commercial speaker. Happy to see it on the front baffle rather than the back panel, anyway.

The shape of the vent is probably fine if you expect the speaker to be played at domestic-friendly SPLs. Presumably this means you're going to voice the speaker for low-to-mid 80s dB SPLs, à la Harbeth, as normally, friction is what you want to avoid 'cause it leads to chuffing at loud levels. I'm sure you've read the papers by Vanderkooy et al.

Interesting project. With your chosen drive units and xo points, total radiated power should be very even over frequency, an area where I feel the original LS3/6 was lacking (this based on my experience of the SHL5). I hope to hear the result at some poiint but will probably be more inerested in the active version.

 

It's certainly worth a go but more in the traditional bracing sense.

Linking between the side walls links two identical panels with identical resonant behaviour.
There, the idea of these forces cancelling out works well.

With the back panel and baffle, the resonant behaviour is no longer identical due to the driver mountings. You therefore cannot get them to cancel out.

One interesting use of bracing can be found in the old Heybrook HB2.
Here the bass driver magnet is braced to the back panel via the tube port, which is then perforated to allow venting.
Again this is the more traditional brace effect but the HB2 uses a a heavy and quite rigid cabinet. Small 18mm high density particle board panels with damping applied.

 

Am I correct in thinking that the Epos ES14 used a tie rod between the cabinet side panels? I certainly remember the ES14 having a generally low level of midband cabinet "talk".

 

Indeed correct - well remembered

Marshall was (is) a very talented designer.
The original Epos cabinet also used damped high density chipboard in preference to MDF.
Later versions after Mordaunt Short bought Epos used MDF.

I still really admire the ES14.

 

Markus, do you have some info on why the mag thought side mounting the port was best? I'd have imagined the front baffle were best, but that does assume the higher frequency outputs from the port are decently controlled. The common reason for rear mounting ports is to help reduce the higher frequency sounds inside the cabinet coming out.

I think we should be careful not to equate port resistance with air turbulence. Turbulence is caused mostly by high air particle velocity, as opposed to high air pressure. Aperiodic loading for example, in the form of highly open cell foam increases resistance but can reduce turbulence because it slows the air velocity.

In fact if I remember correctly the centre area of a port tends to have the highest particle velocity leading to chuffing while the area near the port walls is high pressure low velocity. This is natural when you think about it, how can the air near a boundary be moving very fast? Thinking this through after your comment I guess it is not the resistance exactly that makes slot ports sound better to me, so much as simply being more of a pressure source than velocity source and thus reduce chuffing and excite the room a little differently.

 

I think that Robin Marshall had a special interest in the behaviour of speaker cabinets. I visited the Epos factory when I worked at a hifi store in the '80s. I saw several experimental cabinets, including one that had an elaborate aluminium tube framework clad with very thin (about 3mm) plywood. Another that I saw was a front baffle made from three layers of plastic material and with an integrated bass driver chassis. The experiment was machined and fabricated and I was told that the intention was that production baffles would be injection moulded. I do not know what sort of plastic was being used, but I know that the outer layers were thin and rigid and the middle was lossy. The structure was described as "constrained layer", which I guess to be the same thing as the "constrained damping" mentioned in this thread. It struck me when the ES11 was introduced that its front baffle was a cost-cut version of this experiment. It was plastic and had an integrated bass driver chassis, but it did not have the three layer construction.

 

I may have thrown it away. I'll take a look if I still have it, but don't hold your breath.

 

That's very interesting information, thank you.

In some ways I did see the ES11 as an advance on the ES14, certainly in terms of the cabinet but the 14 got superior drivers. The ES14 bass/mid is a lovely thing to see, touch and hear

Robin was a fan of the Spendor BC1 and said that the ES14 was designed as a better version of this. I want to source a minty pair and experiment with an isoplanar tweeter like that in the Kensai, especially as Robin saw the ELAC based metal dome as a weak link.
A large diaphragm isoplanar driver would suit the first order electrical crossover quite nicely, and likely better than a 1" dome.

 

Any further progress?

 

There will be over the next couple of weeks.
Simon is just back from holiday.

 

Nothing to write about yet. I've got to juggle fulfilling paid orders and developing the new product. I also went on holiday

 

Interesting looking product boys, with great crossover potential in the market.

 

Thanks Simon. What do you mean crossover potential?

 

i would be interested in an active pair..... look great.

 

Markus also said he's hoping for an active pair. What do you both mean by active - built in amps all in the back of the speaker or an active external xover with separate amps provided by the user?

I've been called to jury service recently so nothing much is going to happen for the next 3 weeks I'm afraid.

 

ideally i'd like a choice of either 1U 19" rack with line ins and out for using a choice of power amps.

or a pretty compact small box with the same connections.

something that looks like this i guess... http://www.minidsp.com/products/minidsp-in-a-box/minidsp-balanced-2x4

 

X-over and amps built into into the speaker for me, please. And I don't want a choice of power amps, I want them included in the package. If you do it by DSP, a master-slave arrangement is permissible.

 

One option is to mount the electronics in a brick and mount this on the back panel, though you have to watch the effect on the panel in a design like this. it makes it easy to swap between active and passive by simply changing bricks.
Given the high sensitivity of the design the amps can be relatively low power - certainly 30-50w should be ample in this situation, and therefore small and light.