Finally finished - Long post.

[5th element]

This whole process started when I spied a pair of Audax HM130Z0s on ebay, they were 'damaged' goods, so to speak and went for peanuts.



I say damaged, but nothing was wrong with them, the only issue was that the previous owner had used them in a world audio design. They recommended sticking some draft excluder to the cone - to dampen some of the breakup inherent within the cone. The result of this was some slight damage to the sticky coating applied to the cone, it was basically pulled off when the strips of draft excluder were removed. You can see this in the picture, but the damage isn't particularly bad.

In the auction, the picture supplied wasn't very good, it made the drivers look a lot worse then they actually were. I had always wanted to try some of the prestige aerogel units and jumped at the chance, no matter what state they were in. They went for £5 each a steal I'd say, of course this ended up at £10 each with P&P on top of it.

At the time my loudspeakers comprised of a scanspeak D2905/97 tweeter, a SEAS W15CY001 used as a midrange, with a pair of XLS 10" 830452 on the bass, all open baffled. This had its compromises in that the H baffle was crossed a little to high and the W15 was working a bit to low for it to be comfortable, either way it worked surprisingly well. The Aerogels arrived and I quickly made up a baffle for them and the SS97, altered the Xover and sat back.

Wow was all I could say. The sound just exploded from the speakers and was very lively; it was if the training wheels had been removed. Dynamics seemed more real with far less sense of overhang, when something stopped or started it happened far more quickly.

Increased sensitivity? Light damped cone? Quite possibly. The Audax is 6.5dB more sensitive and the cone some 40% lighter then the W15. What I experienced ties in well with most information you read, within this website regarding sensitive loudspeakers. What’s more the Aerogels did all this without losing anything over what the W15 is good at.

A few months later and a pair of HM100Z0s showed up on ebay, I looked at the spec sheet, 93dB sensitivity and 2.5g mms, I thought, now that’s probably got some potential, but would most definitely need a lower mid driver - and to that a completely new active crossover and two more channels of power amplification.

I looked around DIYaudio for any info on the HM100s and read nothing but glowing reports, where I was also reminded of IPL acoustics. Ivan still had some of these in stock and along with the age of the drivers on ebay, 10 years, and knowing the drivers had been through various versions, if the price on ebay went too high, I'd just buy new. This is what I ended up doing. Surprising that a tiny amount of damage on the HM130s reduced them to £10ea whereas the HM100s went for significantly more, around £70 for the pair Inc P&P. A new pair only cost £79 Inc P&P.

I got the pair and listened to them, they sounded great, but now I needed a lower mid. What had attracted me to the drivers in the first place, was most likely related to the aerogel cone, so naturally I wanted the best chance at preserving this - back to ebay. A few patient months later and I had a pair of HM210Z12s shipped from France. - The now discontinued prestige Aerogel drivers DO show up on ebay, just infrequently, so if you see any and are interested, snap them up. They are very easy to work with and sound fantastic.

The active xover I had previously built was limited in what it could achieve, originally being built for a sealed three way By good fortune more then anything, the sections I had used, worked with an open baffle, mainly because the shelving networks used to compensate for baffle step also work for the roll off intrinsic to open baffles. It was very 'rough' considering there were no notch filters to smooth out the peaks before an open baffle rolls off, but it was far better then nothing at all. Boiled down, I used the HM210Z12 as the bass driver, crossed over at 400hz to the HM100 which passed over to the SS97 at 5000hz. It sounded great, apart from the fact one 8" per channel can’t go very loud equalised flat to 50hz on a 12" baffle.

Also at this time I had lost my copy of LspCAD and was flying blind. Unable to measure I just did the 'best' you can without a huge amount of experimentation. Let this be a lesson to the benefit of software developers. I contacted Ingemar and managed to get my copy of 5.25pro back. Immediately I measured and redesigned the xover. Instant gratification. The sound just jumped up by a few miles. Yes you really do 'need' to measure to get great results.

Having regained my copy of LspCAD I got measuring and designed the new xover for the 5 driver 4 way. 2*XLS on the bottom, HM210Z12 lower mid, HM100Z0 upper mid and SS D2905/97 covering the top. This xover included all the bells and whistles required to do everything properly, its complicated, and made use of all pass delay networks, something I had never used before.

One thing I asked in another thread was about the use of these. You can usually satisfy the phase response of a loudspeaker using just one network, but it’s not time coherent, the wave front from the tweeter is still reaching your ears earlier then the midrange. I was slightly sceptical about the inclusion of two more of these to make the design time coherent too, but having built the final design I am not anymore.

The previous design had been an acoustic 2nd order LW at 5000hz that was phase coherent (read, NOT linear phase), but not time coherent. The new version is a 4th order LW at the same frequency, but is now phase and time coherent. The difference isn't subtle, the phantom centre image is now ROCK solid, in a way I've never heard before from any loudspeakers, either of my own design or silly high price things at hifi shows, apart from a TacT demonstration that was far too loud. The stability and tangibility of this central image is one of the things I rate no.1 in a system, if it cant do a respectable job at this then its not worth listening to. There is always some bleed through, at least to my ears, from sibilants that irritate me. You have the central image, yet when a singer annunciates, the spiky parts are heard directly at the tweeter, blurring the image slightly. With the delay networks this effect is significantly reduced. Linkwitz himself says ‘Active crossover circuits that do not include phase correction circuitry are only marginally useable’. I used to take this with a grain of salt, passive speakers don’t have the luxury of really using delay networks and yet the world gets by fine without them. However I am now sold on these things. While it is true they offer fantastic flexibility, allowing you to practically choose any slope and xover frequency - the additional benefit of time alignment is just as important imo.

Which leads onto a picture of them heh Just plain boring MDF at the moment (I usually change things far too often to make it worth making them look pretty.) which makes them look fairly boring. Open baffle active loudspeakers always look unimpressive to me because there is simply not a lot to look at, however if you like driver pornography I guess they are great!. Take a listen and you’re blown away mind you, and that’s where it counts. Not to mention the relative compactness, I can’t say I miss the 100L bass boxes I used to have in this ‘small’ UK room.



The active xover itself will make purists run screaming. Not only is it an opamp fest (32 per channel counting duals as two), but its also plugged full of trim pots I need this to be adjustable after all.



You do not know how long it took to solder, cramming that many components into such a small space tests your dexterity with a soldering iron, especially when you need to get to the copper top (ground) with fragile polystyrene caps and plastic trimmers all around. It’s like those games to test your stability, where you navigate a wire hoop along a wiggly journey made by another wire, if the hoop touches the wire BEEEEP! You lose. Only this time if the iron touches anything it melts and then doesn’t work. I had two cap fatalities. Let this be a lesson, you may only scrape the surface of a polystyrene cap and think ‘oh it will work just fine, only its value may have changed a little’, WRONG its broke. If you can oversize the PCB do it, at least within reason, we don’t want 10cm of copper connecting two things together, but the more space you give yourself the easier it will be in the end to assemble.

Which conveniently leads on to the case, which you can just about see, its not big enough to accommodate the new PCBs so whilst I sort out a new one, its all wired together a little bit Heath Robinson. Due to this there is a little bit of hum due to all the exposed wires, turning off the computer monitor that sits closely to the right cuts out a buzz, so once inside a new case it’ll be fine. The noise level is practically inaudible at the listening position; it’s just nice to get it ‘silent’.

[5th element]

Bah posts are limited to 10000 characters

The only trouble at the moment is I am a pair of amps short! So the old Kenwood KA3020SE, I used back when I was 12 or so has been brought out to power the bass units. The amplifiers I use at the moment are a design by Randy Slone, design 11.4 from his High-Power Audio Amplifier Construction Manual. I really like the sound of this amp and was completely amazed at how good it was when I first built the 4 channels I have now. I am building 6 more channels, 2 for myself and 4 for my parents, along with a redesign of their current loudspeakers. My father built them many years ago, a design by Dave Berryman(sp?) the DBS6, I’ve designed an active xover for them to go along with the power amps, so that should be a nice upgrade for them.



Here’s a pic of one of the channels sans output coil, they are all ready to go they are just in need of a case.

The only thing left for the speakers, really, is to replace the tweeter with RAAL’s little 70-10. If anyone is wondering, the Linkwitz transform alone, can compensate for open baffle roll off. I am not sure of its effectiveness when used with a high Q driver however(when a simple shelving network may be more suitable), but with the very low Q (~0.18) peerlees XLS it works great. Note - when using the LT, if you are optimising it to work around different cap values you cannot just get the target gain correct and leave it at that. You also have to make sure the group delay of the network is the same too, this can take some fiddling to get right.

So to sum up, the final xover points are 100hz, 400hz, and 5000hz, all 4th order LWR, and it sounds great! The overall sound is incredibly revealing, they are not forward or fatiguing speakers, but they are not forgiving in the least. Give them a recording that’s prone to sounding forward, you all know what I am talking about, those moments when a singer sings a certain note or with a certain type of resonance and it sounds shrill and piercing. Some loudspeakers seem adept at making anyone sound like that and are considered fatiguing to listen to, people don’t like them. These speakers are not at all like this, but if its in a recoding you will hear it, I suppose this is their only flaw, some recordings make you cringe, this isn’t a flaw in the loudspeakers, but with the recording. Yes I could change the loudspeakers to smother this, but I’d lose some of the directness, I’d prefer to have more accurate loudspeakers. This isn’t necessarily a flaw in recording quality; on the contrary, you can have a very good sounding, well-mastered song, yet due to the way an instrument or singer is mixed there are moments that are unpleasant.

Phew all over I hope some of you enjoyed the read. Building this answered some questions I could find no real answer to, so if it helps plug a gap of something you were wondering about then it's served multiple purposes.

Matt.

[v-bro]

Hi, interesting stuff.

I fried a tweeter in the past by melting an Audyncap MKP capacitor just slightly on the surface with my iron. It was shorted by this and kapow the dome blew out of its socket A pretty expensive mistake...

I recently built two OB speakers myself, they're at page 114 in the 'system pictures & description' thread. They use JBL 2220A woofer that also have very low Qts. I mated them with Quad ESl-57 panels.



System Pictures & Description

[Vikash]

Great post Matt, and congrats on your build. Perhaps you can bring them to the UK Fest in a couple of months and pitch them next to my Orions

V

[5th element]

Originally posted by v-bro
Hi, interesting stuff.

I fried a tweeter in the past by melting an Audyncap MKP capacitor just slightly on the surface with my iron. It was shorted by this and kapow the dome blew out of its socket A pretty expensive mistake...

I recently built two OB speakers myself, they're at page 114 in the 'system pictures & description' thread. They use JBL 2220A woofer that also have very low Qts. I mated them with Quad ESl-57 panels.



System Pictures & Description

Those look nice, I've only ever heard raves about the JBL drivers and of course the ESLs I bet they sound great.

Originally posted by Vikash
Great post Matt, and congrats on your build. Perhaps you can bring them to the UK Fest in a couple of months and pitch them next to my Orions

V

I've always wondered what the Orions sound like and both being similar in their design approach, it would be interesting to compare them. Unfortunately I don't think I'll be able to come, bringing all the stuff along wouldn't be easy for a start, its A LOT of stuff to get them going, plus the main point, its probably when we will be in the middle of moving house -.-

[v-bro]

Originally posted by 5th element
[B]

Those look nice, I've only ever heard raves about the JBL drivers and of course the ESLs I bet they sound great.

Thanx, they have all the ingredients to create my favorite dish, offcourse never finished with tweaking

Never had better though...OB was (is!) an awakening...