'LGT' Construction Diary

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diyAudio Member
Joined 2004
'Tarantism' Construction Diary

Hey folks.

Why is it such a PITA when trying to decide what to build next? You generally want to build something better than your last or at least significantly different, which isn't always that simple. Then you've got to sit down and play around with driver choices which could lead you around in an almost never ending circle and finally you have to balance all this within in a set of constraints, goals and a budget. Talk about banging your head against a wall. But we all do this for love so I'll quit my moaning right there.

The first steps are probably the most important so its wise to spend as much time as possible here until everything feels 'right'. In this vein I've been quietly messing around with a few designs over the last couple of months including a brief play with a Manger which whilst stunning in some respects also proved difficult to live with so decided to stick with traditional drivers and what I feel comfortable and familiar with.

Here's a quick run through of the main idea's I looked at along the way before arriving at the final design at the bottom of this post.

It all started off with a good idea of what I wanted. The original goals were a 2-way MTM using a wideband driver to cover as much of the freqency range as possible. Something along the lines of a Raven 3.2MMX and a pair of TAD 10" mid/bass crossing at maybe 800hz but the costs were astronomical for the drivers alone and wasn't confident that the sound would match the cost.

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Still looking at the idea of a wideband+woofer but without the costs of Raven+TAD setup I then chanced upon the Manger which has always interested me. I'd now got a little more greedy and decided I'd like to have generous bass handling capability so as to do away with the need for subs. So stuck four Peerless XLS10 in each cabinet, the plan was to cross these at around 200hz with the Manger. Only problem was that the cabinet was simply huge in relation to my room. Deep bass needs volume but I couldn't spare this much.

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At this point things got a bit confused, which is never good, and I'd really thrown out any real semblance of goals and just wanted something suitably impressive. This was generally a mis-mash of huge 3-way WMTMW designs of which I had no hope of successfully integrating into any average size British living room short of one in a small mansion, which sadly I don't live in. They all looked impressive though and the design specifics worked at least on paper. But none had any feel good factor about them and the last of these concepts were simply an aesthetic extension of the last speakers I built.


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I lost interest for a short while, sold my Perceives, which were the last speakers I built, and bought a pair of commercials - KEF Reference 201. I also got back into home theater and decided I'd like to tailor my next design in that direction.

So now that I'd got some direction again I got thinking about a compact design that would fit the ideals of home theater speaker. I ended up settling on the Manger for each of the front channels with these all being housed in a single wall mounted enclosure. The Manger is really ideal for this application because you've got no horizontal arrangement associated problems, had I not used the Manger the design as a whole would have been far more cumbersome but instead it turned out simple looking but effective all the same.
To cut a long story short though, I ordered a Manger to try out and after some time experimenting decided that I'd have a tough time living with them. That's not a put down on the Manger, simply that it had a couple of traits that happened to be polar opposites to what my preferences were, so despite sounded pretty fantastic in some area's it was never going to be a winner for me.

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At this point I'd got fed up and simply bought a full 5.1 line up of the KEF Reference loudspeakers. These speakers are awesome for home theater, I love em to bits for that but then again a lot of speakers do HT really well. The fronts are also no slouch for music but there's nothing much that stands out, sure they do nothing badly but on the otherhand because they don't do anything standout it all makes for a rather pedestrian listen. They're still better than a good proportion than the overpriced stuff you normally find in commercial land though.

So with that said I thought at least I've got a nice listen to be carrying on with whilst I make more serious plans for the next project.

I've been working away on this design for the last few weeks now progressing it naturally, juggling compromises and driver choices. The first couple of designs were really a strong nod towards compact and much of the design was built around this. In the end I felt I'd compromised a little too much although it was a definite step in the right direction.

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After playing around with small details of the above design I ended feeling something different was needed without so much emphasis on compromises in order to obtain compactness.
Its here where I arrived at what will be my next project: The Tarantism. Strange word but I found and read the meaning of the word over on Answers.com:

A disorder characterized by an uncontrollable urge to dance

It instantly seemed to sum up what I want from a speaker and so Tarantism it was.

I'm thoroughly pleased with the overall look and specifics of this final design. Its got that feel good factor which will allow to maintain momentum through to the end which is important with fairly ambitious projects.

Drivers:

HF, I went back to the RAAL 140-15D that I'd looked at previously.

140-15d-a.jpg


Mids will be covered by a pair of the 4" Scanspeak 12M/4831G00 in an MTM configuration.

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And bass will be taken care of by a pair of 8" Seas W22-EX001

Crossover:

I'd really prefer to wait until the drivers are here with me before making more firm decisions but 300hz and 1.5Khz don't sound entirely unreasonable. One of the reasons I went with the larger RAAL was to try and keep the XO point well down - directivity between the Scan 12M mid and the RAAL is well matched at this point and the the low 1.5Khz cross also means that the MTM configuration can be used to control the vertical dispertion of the mids which would give a better match to the RAAL's own vertical characteristics and all the while avoiding combing and lobing nasties almost entirely. The added bonus is that parallel wiring of the mids will net me a sensitivity which would put them on par with the RAAL's 95dB/1w/1m.

I'll be going passive this time as I'd like to unchain myself from using the PC or entirely digital routes. However I think the best approach would be to play around with a PCXO first off using traditional IIR filters, this would let me quickly gauge the best points and where things need addressing. Then afterwards do the usual measure drivers->import in LEAP, model passive XO based on experience with PCXO then produce said passive XO.

Cabinet:

Standard stuff here: All MDF, chunky 75mm baffles, heavy bracing and the usual high gloss silver/black finish.

Mids will be in a sealed enclosure. Each of the Seas W22 will be ported and tuned to around 32hz in a 40ltr enclosure making for good response down to 30hz.

And finally the design itself:

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Its deceptive really because it looks rather large but actually is quite compact considering. I've stuck a wireframe of the Perceives in one of those pics just to give a rough idea of size. These are pretty svelte and I'm well pleased with the overall look.

I've got drivers inbound and plan to start construction towards the end of January when its slightly warmer and more hospitable outdoors. So will update when I have more to show.

Thanks for looking and hope you enjoy,
Ant
 
ShinOBIWAN

"Up-against-the-wall" speakers might be a good marriage to your projection HT setup. A more rounded shape, like an egg timer sliced vertically to go flat against the wall, could have useful baffle step reduction and more consistent in-room bass modes. An hourglass half elipse shape might be more attractive than a simple trapazoid.
 

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Awesome plan. Interesting driver choice. Two questions:

1) Do you have a plan to deal with the very poor vertical off-axis response of the tweeter or do you not view this as a problem?

2) Why passive xover? You seemed to be one of the largest proponents of digital active crossovers. Does this mean you will also not be implementing room correction with these speakers? I was under the impression you were also a big proponent of room correction.

3) Since the choice of 8" woofers limits the lower frequency response of these speakers do you plan to use them with a subwoofer? Any ideas for that design and what you would use as a xover?
 
diyAudio Member
Joined 2004
HBarske said:
Great design.
Build it. Put a 50000$ price tag on it. I bet you'll be successful.


speaker said:


That's not marketing, it is great industrial design.

Love the first set of images.

Wow!

:att'n:


edjosh23 said:
Very nice!

I really like Tarantism, great word. I'm sure it will fit well with those speakers.

Josh

Thanks all, appreciate the sentiments :)
 
diyAudio Member
Joined 2004
m0tion said:
Awesome plan. Interesting driver choice. Two questions:

1) Do you have a plan to deal with the very poor vertical off-axis response of the tweeter or do you not view this as a problem?


Ta and hi Motion.

I do still view it as problem but the RAAL despite being a fairly long line source still offers OK vertical dispertion in comparison to ribbons of a similar sizes thanks to it concentrating the higher frequencies into a narrowing radiating area. I don't have the drivers yet but looking at the manufacturers data appears to show a smooth off axis response in both the horizontal and vertical which is definitely important. The RAAL does have good horizontal performance too.

The MTM will allow me to control the dispertion of the mids around the 1.5Khz XO point and provide a better match than could be afforded just from a simply mid-tweeter arrangement.

Both the 4" Scan mid and the RAAL both have an extended and flat response so crossing will be made that bit tidier and produce good acoustic slopes without the need to start shoring things up with the digital route.

2) Why passive xover? You seemed to be one of the largest proponents of digital active crossovers. Does this mean you will also not be implementing room correction with these speakers? I was under the impression you were also a big proponent of room correction.

I brushed on it above but the Perceive 2 really forced the need for an active solution because I was running the mid right to the limit of its operating range and also had one of the nastiest FR you'd ever likely to see. So to get the best from that you needed 4 notch filters and 48db+ slopes. After messing around with both passive and active it was clear things benefitted from the digital trickery.

From all accounts this next project looks to imminently suitable for a passive network and a fairly simple one at that. I'd also like to have a bit of change this time. Passive filters don't crash, suffer from latency issues or require any maintanence once setup :D Things might change if it turns out the active route once again is very definitely superior.

I wouldn't be without the room correction though and this can still be implemented when the PC is acting as the source regardless of passive speakers.

3) Since the choice of 8" woofers limits the lower frequency response of these speakers do you plan to use them with a subwoofer? Any ideas for that design and what you would use as a xover?

Yes these will be good to 30-35hz so a sub will still be essential for HT, but not for music. I simply couldn't get away with a design that included hefty and capable subs yet still remain fairly compact. I did look at that idea though.
 
diyAudio Member
Joined 2004
m0tion said:
Also, just thought about this. How is this thing not going to tip over?

Not sure what you mean... well I do but I don't think it will be problem - remember the concern about the leg that held up the Perceive's?

In the end it turned out that the only danger of cabinets falling over came from them being placed on flimsy tables ;)

I think sheer mass just makes things tough to move unless you really do something daft. It worked last time so fingers crossed anyway.
 
RAAL despite being a fairly long line source still offers OK vertical dispertion in comparison to ribbons of a similar sizes

This might be true, I did a little math though just to get an idea for what the response might look like. At 10 degrees off vertical axis the response is down ~8dB@20KHz. Now, maybe it's cause my mommy didn't breast feed me long enough, but I'm 24 years old and I can't hear 20KHz tones. So lets look at a frequency I can definitely hear, 10KHz. At 10KHz the response is down ~4dB 10 degrees off vertical axis. Thats definitely noticeable, but maybe your listening position isn't a full 10 degrees off axis so you won't get all of that effect.

I sit about 11 feet away from my stereo speakers, so for me 10 degrees off vertical axis is +/- ~2ft assuming my ear height and the height of the tweeter are equal. So, at 11 feet away 5 degrees off axis, probably a very "safe" bet as far as frequency response goes is +/- ~1ft. Not too bad at all, although I think most people listen a little closer to their speakers than I do. So, lets look at an 8 foot listening distance. At 8 feet you'd get +/- 1.4ft for 10 degrees and +/- 0.7ft for 5 degrees off axis.

It appears that these probably won't be speakers you'll be able to walk around the room and still enjoy similar quality to your listening position, but maybe that isn't a goal for you. Also, one other thing I noticed is that the tweeter height on these speakers is significantly lower than the tweeter height on the Perceive V2's, any reason for that?
 
diyAudio Member
Joined 2004
m0tion said:


This might be true, I did a little math though just to get an idea for what the response might look like. At 10 degrees off vertical axis the response is down ~8dB@20KHz. Now, maybe it's cause my mommy didn't breast feed me long enough, but I'm 24 years old and I can't hear 20KHz tones. So lets look at a frequency I can definitely hear, 10KHz. At 10KHz the response is down ~4dB 10 degrees off vertical axis. Thats definitely noticeable, but maybe your listening position isn't a full 10 degrees off axis so you won't get all of that effect.

I sit about 11 feet away from my stereo speakers, so for me 10 degrees off vertical axis is +/- ~2ft assuming my ear height and the height of the tweeter are equal. So, at 11 feet away 5 degrees off axis, probably a very "safe" bet as far as frequency response goes is +/- ~1ft. Not too bad at all, although I think most people listen a little closer to their speakers than I do. So, lets look at an 8 foot listening distance. At 8 feet you'd get +/- 1.4ft for 10 degrees and +/- 0.7ft for 5 degrees off axis.

It appears that these probably won't be speakers you'll be able to walk around the room and still enjoy similar quality to your listening position, but maybe that isn't a goal for you. Also, one other thing I noticed is that the tweeter height on these speakers is significantly lower than the tweeter height on the Perceive V2's, any reason for that?

In terms of listening position and will this be a problem, the answer is no. I always listen in virtually on axis vertically but do like to have a wide horizontal dispertion so there's not just one person enjoying the treble.

For me the issue could be power response, I'll certainly have a very nice one in the horizontal but the vertical will be compromised - how important is this? Well less important than other attributes that I've placed above and over this consideration, in other words I believe its better live with this compromise and reap the greater benefits.

Power response is important IMO though. It dictates more about the overall sound than is apparent at first. Offaxis sounds eventually reach your ear at some point, albeit reduced in amplitude and time delayed. But what this contributes is a reverberant sound field much like you'd experience in any venue. How smooth this offaxis frequency response created by the speaker dictates similarly how smooth the reverberant field is. Its fine having a speaker thats either wide or narrow dispertion but make sure that the offaxis performance is at least smooth. Personally I prefer a wide dispertion characteristic with smooth offaxis performance, the Perceives gave me that with the use of 3" mid domes. This wide dispertion tends to make the speakers seem to disappear more effectively, you can't definitely hear particular sounds coming from them but rather its from a larger soundstage. Narrow dispertion can tend to sound like its constantly reminding of you that sound is coming from the front of the room from two specific spots but they tend to image very well because the time delayed reflections are reduced.

Its really about picking a compromise because the two on one extreme you have omni and on the other you have an 18" driver used for a mid :)

So overall, the RAAL and Scan crossed at 1.5Khz will offer a smooth response on and off axis to +/- 60degrees horizontal and vertically its about +/-20 degrees. This is going on datasheets which could well hang me :) So its wide horizontal dispertion and fairly narrow vertical the important thing is that the overall power response is smooth.

BTW: The tweeter is lower on this one because that's where it needs to be when sitting.
 
It seems that RAAL provides foam triangles that limit the vertical dispersion of their tweeter so that you won't have to worry so much about getting really poor quality reflections from your ceiling and floor, but one thing that confuses me is that the foam triangles appear to cover up much of the actual ribbon! Why would that be? Maybe I'm misunderstanding the function of the foam.


Side note:

Would you mind editing your drawing to show metrics for size and perhaps a side view? Sorry for the bother, but I'm very interested in this project.
 
m0tion said:
It seems that RAAL provides foam triangles that limit the vertical dispersion of their tweeter, but one thing that confuses me is that the foam triangles appear to cover up much of the actual ribbon! Why would that be? Maybe I'm misunderstanding the function of the foam.


True Ribbon tweeters have a rigid clamp at the top and bottom of the ribbon foil which creates non-uniform vibrations plus reflections for the first few mm's or so of the ribbon. The RAAL foam may be positioned to absorb these vibrations so the more uniform center portion of the ribbon is the main contributor to the sound dispersion. I have run 3D finite element ribbon simulations that show these effects.

I have only done 2 WMTMW designs. I have not been able to get a ribbon tweeter to generate the correct dispersion in an WMTMW topology. I would use a dome tweeter, crossed to 5" ScanSpeak Revelators, crossed to 12" treated paper woofers, probably with 3rd order Xovers.
 
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