[2litre]

Hi All,

Just wanted to put my latest OB's up for all to see.

This one was built for my son-in law in Montana. I was cleaning house of old drivers (I guess I mean aged) and built these for him but mainly to lighten my driver load by 8. Sound gets a bit bright as you crank the volume but they sound nice at a normal level. All drivers are old console pulls, the four 12's are all from the same year and manufacturer (Magnavox). Estimated cost involved, $100.



These are what I'm listening to now. Quick and dirty but give suprising results. They use the 6.5" drivers from an old pair of Realistic Solo 1's (8ohm, 50-14Khz) mated with an old pair of Magnavox (CTS) 8ohm 15 inchers. 1st order XO at 128Hz and 180Hz on a baffle that's 18"x34". Easy to listen to for extended periods. I like these alot but I'll admit they do need some tweeters. Estimated cost involved so far, $30.



I'm going to measure the driver SPL's and try out a new 2nd order (180Hz and 360Hz) crossover on them before building some cleaner baffles.

R/ Jim
 

[Bob in St. Louis]

Very nice Jim, but I think your son-in-law got the better end of the bargin.
He got the nicer baffles and better "cool factor".

How's the bass on your rig? Decent?... Nice?... VERY nice?
Nothing better in life than inexpensive Open Baffle, is there.  aa

Bob

[2litre]

Bob,

Yeah, he got the nicer baffles but he got drivers that didn't integrate as well. But hey, free is free right? He's not complaining.

As for the ones I'm listening to now, I'm truly surprised. They were last minute throw togethers all around but in the end these drivers seem to be very compatible.
 
Last night I played with the XO slope and points. We (my wife and I) like the simple 1st order better than the 2nd order. I switched the XO point on the 6.5's up a bit from 180hz to 256hz and that really helped the full rangers open up. It made the top end sound a bit more extended. So I think it will be just tweeking inductors and capacitors between 127hz and 256hz to get the right 'gel'. I'm bringing them over to a Frugal Horn buddy of mine this Sunday so we'll have yet another set of ears for input.
 
As for bass, I think it's in the very nice category, but not into the Very nice category. I have a pair of SI's and a pair of Augie's so I have a point of reference to go by. I think the bass is equal to the SI's, maybe even slightly more pronounced. I bet the Qts of these Maggie 15's is higher than the SI's, probably better than 1.0. They go deep but with a touch of rumble or bloat. Not as tight as an SI's and not as deep as an Augie.

No, I can't beat the price at all. All the drivers were free and the baffles are rough stuff 5-ply scrap. I only have money in the inductors and caps. That's what makes these speakers so nice, so much for so little. Pure luck!

Unfortunately I can't measure driver T/S parameters but I intend to measure SPL this Sunday so I can add input into the discussion as to what SPL difference is needed between an FR and a bass driver.

R/

Jim

[markC]

Cover those baffles with cork and they'd probably benefit sonically and be   more purdy

[DanTheMan]

2litre, I used to have a set of those magnavox woofers.  Their Qts was around 1.1 or 1.2 and their Fs was around 55Hz.  I wish I could remember their efficiency.  I want to say it was around 95db at 1 watt.  They have a nice sound that can be run considerably higher than what you are running them at.  They came from a console with just a horn above them.  I want to say that crossover point was about 1k or maybe even higher.  My memory isn't serving me too well, except for the fondness of their sound.  They were from my dad's console that he should have never thrown out.  But that's a whole other story.  Be careful if you run those through a high watt amp.  I was playing them rather loud one day, and one of them blew.  My SI is better in every way, but for the $$$, those things are a very nice sound as well.

[2litre]

I'm running everything through an old silver face Pioneer SX-450 15WPC receiver. I check for cone excursion regularly ever since my first wattage mistake with old drivers. 1/4 volume is nice and they're about at thier limit at 1/3 volume but they're fairly loud at that point.

I hope Fs is a bit lower. Sure seems like it but regardless I like the way they sound. I agree that the 15's can go up a lot farther while still giving good sound. I've also forgotten what the original capacitor was on them but IINM it was a 10uf crossing over to the 12ohm (16ohm nom.) horn.

Part of my tinkering with inductors and caps will be to see whether I'll be better off bringing the 6.5 down a bit or letting the 15 run up a bit more. I think letting the 15 run up a bit more will give the better result. I have only round number inductors to play with, a 9 (141hz), an 8mh (159hz) and a pair of 3's and 4's to combine for a 7 (182hz). I don't think I'll go below a 7mh.

I've thought about cork.
Now here's a question-
I'm going to build new baffles for them, similar in look and construction to the ones that went to my son-in-law. I was thinking of using cork, glued to 1/2" ply and covered with some reproduction speaker cloth normally seen on old Grundig radio consoles. This panel would bolt to another 1/2" speaker baffle with the drivers mounted from the rear. Once torqued together the two baffles would make a dampened 1" baffle. I'd radius the driver cutout on the outer baffle only.

Besides the effort and cost involved moving these rough cut speakers into the 'keeper' category, does anyone see any down side to this idea?

R/

Jim

[markC]

If you like the sound and are going to throw a few dollars at the project, I would recommend going to the "depot" or similar and getting some Russian birch plywood. Not expensive and if you give it the old knock test against regular ply, I think you'll know why I suggest it.

[2litre]

I whipped these together using what I had around the garage.

In the past I've used 11-ply, 3/4" birch and was intending on using a similar grade but only in 1/2". In fact the speakers in the first picture were made with remnants of my last sheet of 3/4" 11-ply.

It has a nice fine finish on both sides and in all the sheets I've gone through I've yet to find a void.
I'm pretty sure my local supplier doesn't list it as Russian or Baltic though.

Is this similar or equal to the grade / quality you're speaking of?

R/

Jim

[Bob in St. Louis]

Jim, thanks for the info.
I think you might just be on to something regarding the constrained layers and cork. Although it tends to make it more challenging when you rear mount on a one inch plus baffle and radius the front.
How about using a router to carve a "nest" the driver can sit down into from the front?

Bob

[hurdy_gurdyman]

Bob,

Yeah, he got the nicer baffles but he got drivers that didn't integrate as well. But hey, free is free right? He's not complaining.

As for the ones I'm listening to now, I'm truly surprised. They were last minute throw togethers all around but in the end these drivers seem to be very compatible.
 
Last night I played with the XO slope and points. We (my wife and I) like the simple 1st order better than the 2nd order. I switched the XO point on the 6.5's up a bit from 180hz to 256hz and that really helped the full rangers open up. It made the top end sound a bit more extended. So I think it will be just tweeking inductors and capacitors between 127hz and 256hz to get the right 'gel'. I'm bringing them over to a Frugal Horn buddy of mine this Sunday so we'll have yet another set of ears for input.

In my many experiments with XO's for the Silver Iris drivers, I keep coming back to a first order low-pass as just sounding "right". I couldn't get a second or third order to do it for me. Even the notch-filter used on the Reference SI 15 is just a modified first order. However, the high pass is another matter. No matter how much I tried, I couldn't get a first order to work right on any of the SI's, including the 10" Coaxial and the new Sterling 15 Coaxial. The more complex slopes just integrate better. The new Sterling will have a third order slope on the high pass, which makes an incredibly invisible XO point.
 

As for bass, I think it's in the very nice category, but not into the Very nice category. I have a pair of SI's and a pair of Augie's so I have a point of reference to go by. I think the bass is equal to the SI's, maybe even slightly more pronounced. I bet the Qts of these Maggie 15's is higher than the SI's, probably better than 1.0. They go deep but with a touch of rumble or bloat. Not as tight as an SI's and not as deep as an Augie.

I haven't stumbled unto any old Maggie 15 woofers, but I had some 12" ones. They are nice sounding bass drivers and may be the best bargain out there for OB on the cheap if you can find them for next to nothing. One does have to be careful of how much power to feed them, as they just aren't as rugged as the newer breed of woofers.

No, I can't beat the price at all. All the drivers were free and the baffles are rough stuff 5-ply scrap. I only have money in the inductors and caps. That's what makes these speakers so nice, so much for so little. Pure luck!

Unfortunately I can't measure driver T/S parameters but I intend to measure SPL this Sunday so I can add input into the discussion as to what SPL difference is needed between an FR and a bass driver.

R/

Jim

[hurdy_gurdyman]

About old console speakers, many of you know I have recommended these before for ultra-low cost OB's. They can sound surprisingly good. Besides the impressive bass drivers on old Magnavox consoles, there are many 8" and 10" drivers out there that do very well down to around 100 Hz or so and have a very musical mid-range. I have a pair of 10" Jensens and a pair of 10" Zenith's that are very pleasing to listen to. I also have a pair of 8" RCA's that sound quite nice. All of them are power limited, but should do great with most tube amps and smaller SS amps that aren't run into clipping. For the typical garage sale/thrift shop price, they can't be beat. Maybe they aren't as accurate as what can be had now, but they are way, way cheaper to buy. A good way to try out OB sound for those doubters out there.

Dave aa

[DanTheMan]

hope Fs is a bit lower. Sure seems like it but regardless I like the way they sound.

Those figures were given to me a long time ago.  I'msure they weren't below 50Hz, but they always sounded like they were to me.  I bet because the Qts is so high the looseness of the driver probably gives it a wide resonance peak.  So it probably does play a bit deeper.  I've also noticed that big drivers just sound deeper than small drivers with the same Fs.  I always attributed this to lower power compression d/t the cone not having to move as far on peaks to gain the same volume.

BTW, I feel like those speaker are deserving of nice baffles.  If I still had mine, they'd be in my second system doing just what you are doing--only crossed over to an 8" JBL FR driver of a more modern vintage.  For the $$$, they can't be beat.

[2litre]

Bob,
I had though of mounting the drivers from the back of the panel because of all the different sound enhancing driver mounting techniques you read about, that is the one I can do easily.
But I see your point. They'll be hanging off the back of 1" worth of material. Now if the difference between front mounting and rear mounting is more of a tweak than a proper design absolute, then I'll just front mount them to the back baffle. The tightly oversized holes in the front baffle will basically make the drivers flush mounted anyway, right?

Dave,
I agree with you whole heartedly on the merits of old console drivers. I've been an advocate of them since I tried my first OB 3-way set up with some 12's, 5's and 2.5 tweeters culled from an old Packer Bell console. They're perfect 'introductory' OB drivers.
Find a console (SS or tube, it doesn't matter but it's easier if all drivers come out of the same stereo console) with intact drivers, add a simple XO and a sheet of ply and Wham, OB OG style!
Almost always pleasent sounding and usually very efficient.

Thanks Dan, the main reason for building new baffles for these is to get practice on building 'keepers'. All my speakers up until the ones I gave to my son-in-law looked just like the ones I'm listening to now, rough and unfinished. I need to get better.
8" JBL of a more modern vintage? Currently available?

Thanks all.

R/

Jim

[DanTheMan]

8" JBL of a more modern vintage? Currently available?

Unfortunately they are not.  And I'm not getting rid of mine.  I found them on ebay--8 of them for $16 NOS.  Unfortunately upon arrival, three of the drivers had mold growing on the cones and one of them I blew up playing my guitar through it.  Now I'm down to four and they are at my dad's not even being used!  Theya re sweet drivers though that they stopped making in the 80s I believe.  Definitely bass lite, but just using four of them seemed to cure that to some extent.

[2litre]

Well it was a good Sunday over at my buddy Doug's house. Very informative and at the same time a bit embarrassing.
Although we didn't dismount my drivers to do SPL testing we did do system frequency SPL testing using his audiophile test CD running through his DVD player and Sonic Super T-amp. We set the amps volume level for 70db using a sine wave and an RS meter on a tripod at our listening distance of 80" from the speakers.

The good:
My OB's were generally flat within 3db from 50Hz out through the 6.3K tone.
They were +10db on the 100 and 120hz tones.
They were only down -7 on the 40hz tone but down -13 on the 31hz tone.
Doug thought the midrange sounded very nice and that they wern't necessarily bass heavy, which had been my concern.

The bad:
They were off the meters scale on the 8K tone. So much for 14K as the upper end of the full range drivers.

So we added a pair of old 1" cone tweeters using an on hand 4.7uf cap (4.2Khz). They integrate well with the full rangers and now extend the FR to +/- 3db out past the 12.5K tone. I've since replaced the 4.7uf with a 3.3uf (6Khz). Obviously still the same high end but with a bit less coloration of the midrange.

There were a few suprises.
His P10 / Fostex 108 Frugal Horns had very similar numbers to my 15" OB on the 40 and 31hz tones, down by just a db IIRC. Room placement was important for this.
Just how razor sharp his Frugal Horns present sound. Listening to them is like having on a pair of room sized headphones. My OB's were much..... wider, fatter, tubbier, rounder? Definately not razor sharp 
Just how much those little 1" cone tweeters helped my OB's. I didn't think they would add as much as they did to the sound.

In the end I learned a lot about my inability to correctly determine frequency and Doug admitted that he wouldn't kick my poor OB's out of his house, as long as I kept the added tweeter.

I bet his 108's and my Maggies would be a fantastic pairing.

R/

Jim   

[hurdy_gurdyman]

Jim,

If you're 15 inch driver is doing even close to 6 kHz, that's pretty good! Few modern 15 inchers can get anywhere near that high. Yes, old console drivers aren't usually the last word in speed/detail. Most of them have just to small of magnet/cone mass ratios. However, they do tend to sound very musical, and for the price, who could complain?

Try some 8 or 10 inch console drivers with a helper driver below 100 Hz. These should get you up closer to 10 kHz and sound faster.

Dave aa

[DanTheMan]

I bet his 108's and my Maggies would be a fantastic pairing.

I bet you are right.

I had some 10" AlNiCo driver I pulled from an old Fisher console that had clearer MR than the Maggies.  They had huge AlNiCo magnets though.  Unfortunately they made no bass except for in a sealed box.  They might have been able to do some other sort of enclosure, but they were originally placed in a sealed box.  The Fisher was also filled with German made tubes that sound awesome even after how ever many years old they were.  The TT in the console was the most sturdily built I had ever seen before.  I should have pulled that too. Why did I get rid of those things

I agree w/Dave,(maybe the only time I'll ever admit that ) console speakers are great for experimenting.  You can even find things that you can live with for a long while.

[Taperwood]

Greetings everyone.  Doug here, Jim's friend.  Jim pretty much summarized our findings on Sunday.  What I would like to add is that against my Frugel horns, his OB's sounded very, very nice; a slightly warmer sound and, of course, much better on the low end.  What was surprising was their openness, and despite what Jim said they were not that far off my Frugel horns in terms of resolution.  Certainly nothing that you would notice without direct A/B testing.  What I learned from this is that nobody should turn their nose up at old drivers they might find or have laying around.

Doug

[JohninCR]

Doug,

A really nice combo is 108 Frugel's + OB bass reinforcement.  It max placement more flexible and relieving the little 108's of some of their bass duties sweetens them up a bit more, not to mention that it permits greater dynamic range.  I tried this almost my accident when I was evaluating some 6x9's as OB bass augmenters.  I just propped them up with only a small piece of foam between the magnets and my Frugelhorn baffle with no baffle at all on the 6x9's.  The amount they fleshed out the bottom end of the Frugels was impressive.  The only explanation I could come up with is that somehow the dipole output rearward combined just right with the rear output of the Frugels, so they enhanced each other in the front wall reflection that was about 1m away.

[Taperwood]

Thanks John.  I have been sorely tempted to try something along the lines of Martin King's article with my 108s.  I love my horns as they are, however, and after a full year of tweaking them I just can't bring myself to pull the drivers, so I would have to buy another pair and start from scratch.  I do have one old 15" console woofer like Jim used, so I might try a single OB just to see how it sounds once I can scrounge up some crossover parts.

Doug