Choice of Speaker Drivers
Some comments about the drivers I chose to use
Tweter : RAAL 140-15D with Amorphous core
Mid: C-Quenze 18 H 52 17 06 SD
Woofer: C-Quenze 23 I 52 20 08 SD
These mid and woofer has now been replaced – see below
From Diyaudio http://www.diyaudio.com/forums/multi-way/93218-lgt-construction-diary-124.html#post1291397
i haven’t read the complete thread but i really have to say that i very much appreciate your work – wonderful design and building!
And also the finsish is more than impressive.
But here some feedback from my experience on your midrange issue:
Knowing both, the C-Quenze, the ATC midrange and also others my conclusions today are:
– the C-Quenze driver is the perfect driver in an extremely broadbanded application. It doesn’t like to be cut off, neither at the upper nor at the lower end. The more it is cut off the worse it will sound. It is best used with the fastest tweeters crossed over to it above 3.5 kHz. It will even handle a x-over point around 5 kHz easily! It doesn’t really like filters steeper than 6 or a very soft 9 dB (needed for Kapton voice coil former).
Being used that way there’s nothing compareable out there!
We have measured it’s dynamics and we have found that it is even faster than most tweeters are! There are very few (tweeters!) that can compete with it’s speed. It’s resolution abilities are, used properly, far beyond any other midrange i know, which does not pay for it’s resolution abilities, due to the hard membran material, with heavy brakeup modes.
– the ATC is the perfect and in my eyes the best real midrange. It has a perfect “midrange behaviour” and the question is how to protect it from the lowest frequencies and to avoid getting into that extremly long decay point at around 5 kHz without disturbing to much it’s nearly perfect natural midrange abilities. It is less demanding than the C-Quenze regarding definition of x-over point to tweeter. Can be crossed over lower to tweeter than C-Quenze.
So the summary for me is:
Ultimative 2-way and 2-1/2 way systems with high x-over points
ATC SM75 for:
Ultimative 3- and 4-way systems
But as you already have decided to use the C-Quenze in your system as midrange i think, that even if the initial idea was to have the RAAL working down to 1.5 kHz to get closer to a “point source” it would be worth trying to put the x-over point significantly higher and taking the risk to cause other problems which i expect to be less disturbing than having a midrange that seems to lack dynamics (which it surely doesn’t!).
I can tell all that because we have made pretty much the same experience with the C-Quenze midrange as you decribe when we worked with it in the beginning but we have solved the issues in the meantime going to higher x-over points … and using nearly no damping material in its box.
Concerning x-over design:
I could imaging that at least to find the best concept for the x-over design of your TMT, an active programmable x-over would help a lot. And they are less expensive than one would expect …
Finally, another point which should not be underestimated is that the Audiotechnology drivers really take their time to brake in…
I wish you all the best and good luck for your ambitous project!
Even if i am very rarely looking in the diyaudio, please leave me a message if you are interested in a more detailed feedback concerning the experience with the the C-Quenze mid.
More info here
Thanks for the suggestions.
Where to begin…
I’ve re-worked the mid driver cutouts with a 45 degree bevel. I’ve also been playing with something called noisestop(or was it noisekill?) which was given to me by my father and is used in ceiling and floor voids to soundproof multistorey apartments. Its a foam of some kind and is about an inch n’ half thick and very dense, its open cell as you can breath through it.
To start with I wrapped a load of this around the rear of the driver and packed all area’s of basket window openings taking care not to impede cone movement. Foolish move. This stuff really does soak up a lot of rear wave and it sounded dead. Took it all out and just placed some toward the top and bottom of the basket windows as these are in close proximity to cabinet walls. Sounds much better like that and not one bit of that shouty and forward quality I was talking about before.
I also put back in the large foam section that sits at the very rear of the mid enclosure as this definitely helps the upper bass clarity. You can really tell the difference with and without.
I did try other combinations but these either made no difference or none that I could definitely pick up on or they had a negative effect. I consider what I’ve settled on to be optimum.
I’ve also been playing with a 3.5way crossover using the upper midrange upto 820hz where baffle step kicks in and the lower midrange I’ve been using with alsorts of crossover points because I’m no longer tied up with MTM issues. Tuesday spoke some excellent advice on the last page. The AT really does sound a lot better up higher but I think the real problem is that the RAAL really doesn’t have the mass and weight in sound to convince at 1.2Khz, I’m pretty sure its that which was sucking some of the dynamics away. I’ve got a great sounding setup going where I’m using the the AT upto 2.5Khz. The sound is lot more full and dynamic. Not quite as clean as when I was running the RAAL at 1.2Khz but it has weight, soul and body in the upper mids and lower treble.
I think this has got to be a 3.5way design as it sounds so much better. I was A/Bing the 3-way vs. 3.5way and thanks to the PC XO setup you get to instantly compare the two. A massive difference where not only is everything more focused but the integration is improved and finally I have dynamics in the mids! You can also now sit closer without having that annoying two drivers working together sensation.
The overall integration between all the driver units is really spot on. Its amazing really considering the size of them and the number of driver units but I think its one of the most coherent speaker I’ve heard. Right from HF to where the 8’s roll off to nothing its all seemless. I’ve been running sines from top to bottom and its almost pitch perfect.
So what a fantastic weekend! Its starting to sound like a great speaker rather than just a good one Nowhere near done yet though and I think I’m only just scratching the surface here with more to come.
Shin’s implementation can be found here
Here’s the filter transfer functions for the LGT, crossover types are Transient perfect Neville/Thiele 1st order. Also in the overlay is an actual un-smoothed mid driver measurement after correction. The black line shows the perfect summing of the filters.
The design is 3.5way:
W = 8″ upto 200hz
M = 5″ 200hz – 800hz
T = Ribbon 2500hz+
M = 5″ 200hz – 2500hz
W = 8″ upto 200hz
Hi again Arthur,
It sounds like your system is basically the LGT but in slimmed down TMW form. At least from a driver perspective anyway.
The thin midrange problem I was having and which you seem to be relating to was due to some over excessive stop band correction which Uli fixed and showed me how to avoid. Before making any changes are you sure you haven’t fell into this trap also?
During this project I made a few discoveries about the RAAL ribbon which will very likely apply to any ribbon. I’m not sure about dome tweeters but their dead and lifeless nature means it probably doesn’t matter how they’re used, they’ll still sound unnatural. Dome tweeter jokes aside, if I crossed the RAAL low at 1.5Khz it simply sounds wrong in comparison to what I have now. You lose the presence and body of the upper midrange/lower treble and this is true despite very similar measured performance. Perhaps it is odd high order harmonic distortion from the ribbon being crossed low? Perhaps it is a mass/radiating area issue? I’m not 100% sure about either but I can say it doesn’t sound as good. Try the Raven at 3Khz, since your crossing to the 5″ the narrowing directivity of the mid driver will improve overall power response and better mate the directivity patterns of the two drivers at the crossover points. I assume you mid and tweeter spacing is close here.
I would try to abandon the steep filters for use with AT drivers, it harms the sound more than it helps. They’re wideband and smooth at both ends so why create a problematic solution to an issue that doesn’t exist. Its best to evaluate on the basis of each case and go for the lesser of evils approach. For example I found steep filters worked well with the ATC midrange but this was actually beneficial because I was running it right upto its upper and lower limits where resonanaces and distortion, respectively, became an issue overiding negatives surrounding steep filtering.
In this instance I chose 24dB LR slopes and it really does suit the AT’s offering a good blend of stop band rejection, lessening driver to driver crossover stopband interaction along with promoting a more cohesive sound from drivers more effectively blending creating less of a sense of shifting directivity lobes and tonality. By this I mean with steep filtering the drivers can become more subjectively isolated and I find I can tell a shift of sound direction and tonality when different frequencies, covered by different drivers, are playing. A bit more crossover overlap from shallower filtering can create a more cohesive speaker and we are lucky that we can make the drivers behave optimally to virtually eliminate the phase problems from doing so.
You’ve also got a lot going on down low: A sub crossed in at 150hz to an 8″ driver that then works to 350hz. I haven’t heard your system so can’t say whether it works and maybe you have preference for this setup but looking at it on paper its less than optimal IMO. Personally I’d shift the mid down to 200hz which allows it to cover yet more of the frequency range, it works excellently in my setup where I tried it at 500hz, 300hz, 200hz and 150hz. 200hz had the best blend of mid/upper bass weight and seamless integration out to the midrange.
For the 8″ I’d use this with just a low pass and no high pass then bring the sub in at non directional frequencies to blend with the overall sound and fill out the low end. Reason being the sub will be some distance from the main driver array and at 150hz sound is directional. Crossing in at say 50 or 60hz is much better.
These are just my thoughts on how I’d do it and not everyone agree’s on how things should be implemented but since your not 100% happy with the sound and we also have similar drive units then I think some of the ideas might be worth looking at.
Blow up image of my Mid – Audio Technology
Mid cabinet Vb=10 Liters, F3=120 , Qtc=0.45 , QL=7.
Bass cabinet 32Liters. Reflex hole Fb=33,F3=62,Q=7
Some more photos for my speaker
Recently, I get to know a speaker design whose product are selling at US$66,000 using the same drivers as I am. While we were discussing our speaker design, I was offered to use his C-Quenze which can crossover at 6000Hz at an irresistible price. So, here is it, the old (right) and the new (left) side by side.
You can see that the new version 18I520613SD 4 ohms has a underhung motor and a stronger magnet. It is also 4 ohms instead of 8 ohms. But should post no problem with my DSP crossover system. A closer view
– underhung motor
– Rdc: 4,0 Ohm (in box minimum: ca. 5,5 Ohm)
– FS: 37,7 Hz
– VAS: 31,2 L
– Qes: 0,27
– Qms: 2,7
– Qts: 0,25
– Eff. SPL: 89 dB
– X max: +/- 4 mm (if properly used this corresponds to 105 dB max sound pressure = party level)
Box: vented, ca. 10,5 L, vent and drivers volumes excluded
Fb: ca. 55 – 60 Hz
F3: 54 Hz
The new mid driver is a lot more dynamic and well articulate. Because it can cross now at a much higher frequency, I can avoid the sensitive frequency range <5KHz. I am now crossing it over at 4.5KHz, may go higher later.
Now, the problem comes to the woofer. With this spec: Bass cabinet 32Liters; Reflex hole Fb=33,F3=62,Q=7, you can see the F3 is quite high and looking at the simulated curve, the woofer starts to drop its SPL at about 200Hz. The bass is therefore sloopy and lack of life.
To meet with this new fast mid, I have also custom made a new woofer. This is based on 8’ flexiunit with the following characteristics:
Flexunit 8X77_20_08_SD_KA with C-Quenze 23I52 (your actual woofer)-like frame (thickness 6 mm and 6 holes equally spaced on diameter 211 mm, to fit in your cabinets)
Kapton-Alu voice coil former
Rdc: 4,0 Ohm
Fs: 24 Hz
Vas: 90 L
Fs / Qts: 100
This is the testing parameters directly from Per Skaaning
With the same box, F3 is now 36.64 Hz.
Here are the 2 drivers side by side!
You can see a much bigger magnet! In this new driver, even though the high motor strength in a theoretically a bit too large vented volume, however due to the high motor strength it still stays reasonably small. Compared to the old c-quenze, this one is a lot more dynamic, more details, bigger and has a more 3D soundstage. Everything just opens up and the ambiance also improved. The vocals and Cello sounds so much better and I think this is due to the enhanced harmonics!
There are several differences between the 23I52 and the 8 inch flexunit woofers which are important. The first one is the bigger voice coil which i beleave results in better cone mechanics. The second point is the Kapton / Alu voice coil former which reduces the losses of the motor by reducing the self induction of the motor while moving. And the third point is that the moving mass as well as the BL/Rdc is increased.
Simulation with new woofer
Now, to blend in all the drivers, the best results can be obtained by running the midrange as wide as possible with flat filters and to adapt woofer and tweeter to the mids natural behaviour (resulting in sources playing in phase as good as possible at all frequencies).
Just a small note about Fs/Qts. This ratio has been widely used to determine if a driver is for vented Vs sealed box. While that is a generalization, it is typically quite accurate. As a general rule, the higher resonance magnification(overall Q) the more suited it is for a sealed, and then infinite baffle use, likewise, a better self-damped speaker(low Q) is more suited to ported enclosure. This is because a high Q speaker has to be used in an application that allows for the high levels of energy stored in the speaker at resonance to be dissipated over a broad and relatively linear frequency range(centered at fb). Using a high Q speaker in vented box is not satisfactory because it does not offer broad and linear damping curve to counteract the effect of high Q, resulting in a non linear, and peaky amplitude response and very poor transient decay. Likewise, using a speaker with a low Q in a sealed box is not optimal because it is, in actuallity overdamped in these alignments. And while not hurting transient decay as when using a high Q driver in a vented, this will lead to a relatively high F3. However, if the F3 is suitable for your purposes their is absolutely no reason not to use it in a sealed alignment because the amplitude response does remain linear.
For sealed box, QTC isnt really related to out and out performance figures and spl. Was it is related to it the sound characteristic you can expect to get from your driver(s)/sub. A high QTC will give you a very profound upper bass characteristic. This will give lots of audible bass, the real chest thumping stuff. A low QTC will subdue this sound and lean more towards this upper bass sound being much more understated in favour of a cleaner lower sound.
If the QTC is very high in room, it can become overpowering and even boomy, if its too low then you might find the sub seems to really rumble but you cant really hear it like you probably think you should. In each case the response graph for the sub will be quite similar (changing to reflect the volume of the cabinet), but the resulting sound will be quite different.
Lastly, just a brief video on ribbon replacement. Alex is a genius, he already envisage that the ribbon can come loose over time or after a long flight. There are heat shrink at both ends of the ribbon and when heated up, help the tighten up the ribbon. Watch this video for the full account.