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I give you.... FrankenStereo...

207.167.13.69
Posted on April 5, 2016 at 08:35:02
Presto
Audiophile

Posts: 5957
Location: Canada
Joined: November 10, 2004
 I call it my "FrankenStereo" - For all you vintage gear heads out there: it's a 3-way active system with sub, Marantz SR6200 7 channel receiver for 100Wx4 for (4)mids and (2) Tweets, front pre-out to Fostex LAB 600 for 300Wx2 for (4)woofs. Behringer CX3400 sums L & R LF channels into mono signal for sub, ran back through receiver 0.1 I/O for level control. Crossover is vintage UREI 525 Stereo 3-Way 18db/octave (3rd order Butterworth) with home-brew unbalanced RCA patch-bay in the back.

This was done so my high-performance DSP audio computer (aka, fancy shmancy DSP based crossover) can be re-purposed so my kids can have a computer at their moms house. Had fun and saved $1000 bucks that I didn't have anyways. Ah, the things we do for love, hey?

Sound is immediate, tuneful, high PRAT (if you're into PRAT), nice sound-stage, background is adequately black, bass is strong and tight, and the highs are silky rather than hyperdetailed, yet the detail is still there. It's just not as clinical as my DSP setup.

The Marantz is quite transparent amplification, really, and the differences between the DSP crossover and the outboard UREI are, to put it mildly, easy to discern.

The "older/slower" PC I am using for playback now can't do DSP, but it can still manage to implement a phase correction plugin in the audio player - meaning I can still get transient accurate performance even with an outboard crossover that doesn't have this functionality.



Top to bottom:

Marantz SR6200 (10+years old)
Fostex Lab 600 (30+ years old)
Behringer CX3400 (<10 years old)
UREI 525 (35+ years old)
Computer Circa 2006 Cicero Pentium IV / Windows XP box
Soundcard is Auzentech Xmeridian 7.1 2G with LME49720 Op Amps.

Speakers:

Home Brew WMTMW design with 7" Seas ER18RNX reed-cone woofs, Vifa 10MD09-08 4" Fiberglass mids and a Vifa D26NC55 tweet. Cabinets have 2" radius front vertical edges, are rear-ported and and stuffed with all kinds of wacky bracing and insulation. Crossover points are 60Hz 4th order (to sub), 330Hz 3rd order woof-mids and 2200Hz 3rd order mids-tweet.

Can't wait to get home to my monstrous creation!! :P


Cheers,
Presto

 

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RE: I give you.... FrankenStereo..., posted on April 5, 2016 at 08:40:16
airtime
Audiophile

Posts: 11287
Location: Arizona
Joined: February 4, 2003
 Wow, that really is an interesting collection of audio gear.

I don't believe I've actually even seen some of those pieces!!!! But they do look like fun to play with.

I'm using that Seas woofer in my SR-71. I think they will be the next "classic" Seas driver. Right up there with the legendary 25FE-W in the yea old A-25.

Enjoy
charles

 

RE: I give you.... FrankenStereo..., posted on April 5, 2016 at 14:27:30
briggs
Audiophile

Posts: 1674
Location: Connecticut
Joined: April 16, 2002
 I am a Seas enthusiast and expect much of this driver, although I have not heard it. I find it curious that he crossed to the midrange at 33O Hz, 3rd order, when I expect the Seas unit to be an excellent midrange driver.

 

RE: I give you.... FrankenStereo..., posted on April 5, 2016 at 16:15:52
airtime
Audiophile

Posts: 11287
Location: Arizona
Joined: February 4, 2003
 I think you're mistaken. The SR-71 is a LR4 xover at 1750hz.

 

Not mistaken, posted on April 5, 2016 at 16:40:15
briggs
Audiophile

Posts: 1674
Location: Connecticut
Joined: April 16, 2002
 The 330 Hz crossover is Presto's, not Krutke's.

 

RE: I give you.... FrankenStereo..., posted on April 6, 2016 at 09:29:28
Presto
Audiophile

Posts: 5957
Location: Canada
Joined: November 10, 2004
 Briggs:

You're absolutely right. That 7" driver is a very good candidate for a 2-way. But, my design philosophy was that I wanted a 3-way with flat low distortion response beyond the crossover points. Really, I could have ditched the mids and gone with a full-sized good quality Scanspeak tweet and made a nice MTM... but I wanted to try a WMTMW. I was limited by the size of woof I could use because of the limit on baffle dimensions as I started with an existing enclosure that I modded. I could have easily gone with 8" or even 10" woofs for that type of design and would have if I was building the boxes completely from scratch.

What I like about this system is the lightweight rigid fiberglass cones of the mids that result in a 2 gram (!) moving mass. They're not the most powerful drivers around, but two of them per side does the trick. They have a very flat full-range response but likely start distorting like crazy in the lower end, and I have no desire to cross them any lower than 300Hz (aka, use them as mids). They WOULD excel when a 3/4" tweeter with a higher Fs is use - you could cross at 2750 or even 3K with these units - they reach out to 10k!

Another design mantra was the center spacing of drivers for the mid-high transition. With a 4" truncated mid and 1" truncated neo-tweet, you're not going to get tighter mid-to-tweet spacing unless you get into mid-domes.

There is something very homogeneous about the sound coming from these speakers. Driver blending seems to occur almost naturally when using common-sense crossover points - even with 3rd or even 4th order slopes. I've been listening to these for 5+ years and have had no desire for change, other than for the sake of the interest in hearing a different design for comparison.

What I like is that I can use different active crossovers (DSP, external) and get really good results, but indeed tonally it turns into a different speaker each time I do.

The Seas driver *does* have a shelf in the response between 1 and 2k (it's more of a well controlled breakup) that needs to be addressed, but the way I've chosen crossover points and level matching of the mids this is largely taken care of.

Cheers,
Presto

 

RE: I give you.... FrankenStereo..., posted on April 6, 2016 at 09:36:00
Presto
Audiophile

Posts: 5957
Location: Canada
Joined: November 10, 2004
 Airtime:

I really want to get the Zaph ZR 71 kit for no other reason to "hear" how Zaph voices his speakers (plus it's allegedly just a damned good 7" base solid 2-way). I build a Kreskovsky-designed 2-way for this reason as well, to listen to one of his designs and have a reference around the house. Having a Zaph reference would be of great value to me as a DIYer.

The Urei sounds better than I thought it would - I would have never imagined it would be suitable for hi-fi and some would say it doesn't. But, the soundcard I am using has amazing detail and clarity and it's quite clinical for an audio interface of it's cost and format. The LME49720 op amps made a big difference to. The Urei has sort of a "ahead of it's time 80's hi-fi sound" to it, with a prosound edge. It's very smooth with a silky high end but what is impressive is the *slam* and impact you can get from this thing. It's just so engaging and lively.

Two more things I would like to try is a pro-sumer higher end 8-channel interface (firewire or USB 3.0) and a more modern outboard crossover like a DBX driverack. I just don't have the scratch for any new audio toys right now, so I assemble different systems from the gear I have sitting around...

Cheers,
Presto

 

Yep, posted on April 7, 2016 at 13:29:54
Presto
Audiophile

Posts: 5957
Location: Canada
Joined: November 10, 2004
 Zaph's ZR71 is an asymmetrical 4th order at 1750 Hz.

With my active crossover, I am using 3rd order *electric* filters. It is a considerable design restraint to have fixed-order/fixed-Q filters, but thanks to driver selection and good extended flat response this ended up working okay for this "spur of the moment" design. A fixed crossover would not be my first choice for a new design, aka if I was out purchasing an outboard crossover. Selecting crossover type/order/Q is just too powerful and versatile to pass up when working with (most) real-world drivers... I would not have even bothered to try this, but I using my DSP crossover application I was able to simulate what 3rd order BW (fixed Q) filters would do for the response, and it seemed to work pretty well. Had it been an abomination I would not have chosen that path, because of all of the equalization required. I like to get filters right to get the desired acoustic response rather than use textbook filters and eq the living hell out of it.

I am using 330 and 2200 as Fc points because they are reasonable points considering each driver's range and they sum more favorably with less equalization required. Sometimes these points choose themselves, really, and you just have to pick your poison - aka which design tenet you're most hung up on. I could have gone 2500 or even a bit higher with such a small tweet-to-mid center spacing... but, I didn't need to. (I originally did because the Vifa D26NC55 is much cleaner above 2500 but 2200 was not a big sacrifice by any means.) I don't have distortion data for the 4" mids, but given their 3/4" voice coil diameter and relatively small magnetic structure I am certain it's going to be much sweeter as a dedicated midrange. What's impressive is how much power I can get out of these rather small looking little mids (at two per side) when they're only handling "3 and change" octaves. I really really like them as mids.

The goofiest thing about this design is indeed crossing over at 330 to a 7" driver, but as I said, an 8 or 10" would have been a better choice if designing the baffle from scratch. I *really* like the bass from those Seas woofs though! Tight, tuneful with decent sensitivity for a 7". Much more sensitive than the 7" Dayton metal cone drivers I had in there... they are very flat and low distortion but they need a bit more power. That's the nice thing about active... you can compensate for different driver sensitivities with the turn of a knob.

Cheers,
Presto

 

RE: Yep, posted on April 7, 2016 at 17:00:33
briggs
Audiophile

Posts: 1674
Location: Connecticut
Joined: April 16, 2002
 After some sixty years in audio, I'm a minimalist, two-way, two driver, first order series passive crossover guy. This stuff is way beyond me.

Enjoy!

 

RE: Yep, posted on April 11, 2016 at 18:39:59
Presto
Audiophile

Posts: 5957
Location: Canada
Joined: November 10, 2004
 Hey Briggs:

When you cap off a tweet (1st order electric) to blend it with a fullrange that is rolling off naturally, you can get a reasonably flat response... but what you can't normally get is the kind of impulse response that a 1st order ACOUSTIC design will get. Ironically, a 1st order acoustic design takes a bucket full of components for the requisite level and impedance equalization, and since only cuts can be made in the passive domain, they're not normally that sensitive either. (85-86db 1w/1m or therabouts).

Interestingly... if you get the Thuneau Arbitrator plugin and use a PC for playback, you can make any speaker system (passive OR active) transient accurate.

My take on "time/phase coherent speakers" is that they can measure well and even produce square waves, but there are other aspects to a speakers design that are probably even more vital...

I've done a/b comparisons with 4th order LR and 4th order LR corrected (aka transient accurate, confirmed with measurement) and to be honest... it's a very subtle difference at best.

Tonal balance and drive integration is far more important, IMO, than TA performance, but some TA aficionados would scream HERESY!!

Anyways, enjoy your capped off speakers.

I think I want to try a system with a full-range and capped off tweet now.

Sounds like a lot of fun!

Cheers,
Presto

 

RE: Yep, posted on April 12, 2016 at 10:15:42
briggs
Audiophile

Posts: 1674
Location: Connecticut
Joined: April 16, 2002
 I would avoid any speaker system design requiring "a bucketful of components", and I did not say I advocated simply capping off the tweeter and letting the woofer roll off acoustically. I have experimented with that and was not satisfied with the results I got. I will not claim that it is a bad approach, though. There may be cases where it works. I failed to make it work for me.

What I did say is that I prefer (this is different from advocating) two way first order series. I will add that my primary listening interest is chamber music. I may be playing on a very different field from you.

I believe I define sophistication differently from you. In my case, a speaker system consists of six components: woofer, tweeter, capacitor, inductor, padding resistor on the tweeter and an enclosure. I think that is enough for the home builder to cope with, regardless of his level of technical "sophistication". I made a living designing computer systems and business processes, and worked long and hard to make them simple. That, to me, is sophistication.

And, thanks anyway, but I did not need the tutorial on crossover theory. I appreciated your telling of your listening experiences, but you did not specify what kinds of sources and program material you listened to. You should not expect to hear something that was not in the source material in the first place.

 

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