The AM Forum

Today was the first day of moving out of the Fort Worth storage on short notice. This is a 30x50 space if which I have 1/3. I was planning on moving my stuff, which is a set of full shelves 45FT long, 2FT deep, and 14FT tall, 1260 cubes. Got most of that onto a couple of trailers today and into a barn in Gainesville TX. Whew.. But one of the other guys, who had manuals and vacuum tubes, wants to be rid of the vacuum tubes. That volume is maybe 400 cu. ft of new tubes, and about 220 cu. ft of tested good used ones. In total maybe 5000-7000 tubes.

Thing is, many of the tubes are going to be the ones people have 'shunned', not 6V or 12V, and only a very few 50-200W TX tubes. So, what to do? I will never use the "TV set tubes of strange voltages". They will just be stored, only to have value after the apocalypse.

I got to determine how many 'good' types are there, and whether it is worth the sum being asked. Among the tubes are many 4-digit military or industrial types, but probably only a few of the kinds sought by audiophools. I'm going to keep what I need for spares.



Of the odd voltage tubes, there are some obvious ones that would be good for projects as long as the builder could lay hands on a few spares each. Today we do not have to use filament transformers unless we want to. A dc-dc switching supply cost less and is always regulated, and other things like wall warts and computer brick supplies are of use to beginners.

What about the idea of offering simple 1-2 tube 'beginner' kits made up with these tubes, including sockets, of which there are hundreds available, and basic instructions? I was thinking about reaching first time builders, with extremely simple things like a 1-tube audio amp or similar almost foolproof little things. Each kit would be bare-bones but include a couple spare tubes, socket, and a list of where to get the other parts, and all the parts would be common types from the breadboard/chassis to the power transf. The idea is the builder could work according to his skills, budget, and choices, whether he wants a JS arrangement on a 2x4 or a nice chassis with a real aluminum knob.

The idea is 100% -not- to offer a complete or state of the art hi-fi amp or super low noise RF preamp, but just to offer something very cheap to get someone started in case they want to try a tube project but not plop down $200 or more on something they are not sure they could even do.

I was thinking about $20-25 including lower 48 shipping as a price. No two would necessarily be alike (unless requested), depending on what tubes were on hand. Topics would be very limited, just an audio amp that could drive a small speaker or headphones (depending on the user's option at build time) and a broadband RF preamp with a few dB gain to use with a beginner's typical shortwave radio. The documentation is easy, one size fits all pretty much. Instructional stuff.

Venue might be ebay or a website. Is this a crazy idea?

Neat idea, Patrick. I like it. There are some young hams at the university I work at who I believe would enjoy something like that.

ldb

Check out those 4-digit types, particularly receiving tubes.  Often, they are military or industrial versions of standard tubes, allegedly built to more rugged or exacting specs.

The idea has merit.  There are a few websites that offer tube type kits now.  The obstacles would be the manual kitting & any 'customer support' activities. I think your intended price range is very competitive, based on the other websites. 

As Don said grab all the good stuff. Then unload the weird stuff ASAP not worth the time and trouble.

If you have a bunch of chassis and a punch, why not offer an "experimenters kit" with a cheapo chassis and maybe 4 holes pre-punched?   Judging from the hammy hambone homebrew stuff I've seen, chassis work seems to be a problem for many.

The thought was to provide a tube, a spare, a socket, and as much instructions as can be put on a CDROM.

Documentation on a CD is simple, once it is done, and does not have to be different for each project or tube.
Tube manual
generic schematic
generic 'pictorial' diagram

and basic instructions showing:
what each part is on the pictorial and schematic and what it is for,
how to find the tube pinout in the manual and apply it to the schematic,
where to order the other parts
where to find 'free' parts, like salvaging a radio chassis or other junk.
what the voltages in the tube manual mean and how to make them or get them
-also the need for isolated power from the AC line
where to find free tech support - I won't be able to provide any, no time.

I am not going to supply any parts that connect to the AC line. I can't accept that kind of liability.
At $20-25 shipped, I do not have time to punch chassis or round up and package other items. I don't have the chassis anyway.

I'd rather involve the beginner in hunting their parts, and hopefully more experience and satisfaction would be gained.
If I were to supply certain things, like an output transformer, etc. the cost could not be $25.
--Triode USA gets $20 for a cheap OPT -5K Ohm, 6AQ5 type, 5W; and worse yet, a 3W Hammomd, 100Hz-15KHz, 25mA output transformer is going for $40!! this is absolutely insane because it is a $3 part at best.

Part of the fun and learning is to scrounge parts.
On the other hand, a Hammond plate trans. for 150V can be had for $17. A 6.3V 1A or 2A filament transformer looks like a 2250-to-6 Ohm transformer. This works pretty well for experimentation uses. I have a pair of PC speakers that use the 6.3V transformers for output. They make about 1W or so.

Do these factors (supplying only the tubes, socket, and CDROM) make it a bad idea?

A cheap 300 ma 6.3 fil xformer makes a FB output tranny for a single ended 6V6 or 6AQ5.

As GFZ and KYV said, "grab all the good stuff. Then unload the weird stuff ASAP not worth the time and trouble." Makes good sense.

And, you said, "The thought was to provide a tube, a spare, a socket, and as much instructions as can be put on a CDROM" "for $20-$25 shipped". The buyer then has to go out on the their own to find the rest of the parts  ??? And further, you said, "Part of the fun and learning is to scrounge parts"  ??? Maybe for you, but, I'm willing to bet, not for a lot of people.

Why don't you just take a medium or large USPS Flat Rate box, fill it with several pounds of stuff, and just sell it as a "Radio Experimenter's Mystery Box". Seems like a simple way to relieve yourself of parts/tubes/stuff/etc., and buyers can do whatever they want with it.

OK I am convinced I suppose.
How do I unload these? -how to 'get rid of the weird stuff asap' being unable to make a real 'kit'.

1.) Tubes - It's been tried.. No one in the business of tubes wants odd-filament receiving tubes. Its the whole series filament string issue, they won't pay anything for them.

2.) I have hundreds of panel meters. - same issue, all different kinds..

3.) boxes and boxes of misc. coils, resistors, and capacitors.

4.) thousands of pilot lamps of odd voltages.

and many other parts too many to think of, boxes and boxes of them that I want rid of.



The experimenters' box seems like one way. maybe the post office flat rate box provided I can get an acct and never stand in a line to get supplies or to drop off packages in that awful place. (why I use fedex but it is too expensive to ship 'junk' with)

Pat a gentleman I knew went SK a couple of years back.  He had scads of parts, transformers, resistors, caps, coils, coil stock, and many tubes.  The transformers ranged from those that could be used for receivers or small transmitters up to Gates BC 1 iron.

The people who bought the estate took only the equipment and left all the parts completely.  The problem is you will spend more time than the value if you try to sell the stuff.  Here all of it went to the dump ground that I did not save.  I didn't have enough room for a lot so I cried.  I tried every tube merchant I could find and none wanted the odd types even for shipping.

Do as suggested, keep the good stuff and throw away the rest.  You will spend less time and save more money.

The USPS medium flat rate priority mail box postage is 10.95 at the counter; 10.50 if you pay online and print your shipping label.

The USPS large flat rate priority mail box postage is 14.95 at the counter; 14.20 if you pay online and print your shipping label.

Drop the boxes at the counter and go, or just give them to your postal carrier.

Patrick,

   Maybe come up with an audiophile amp made from vintage parts. Go for single ended, all triode, low power, and don't use any negative feedback. Make sure at least something says Western Electric too. Then put on the auction site for $10K "Buy it Now". ;D

Jim
JKO

http://www.ebay.com/itm/Western-Electric-VT52-45-245-Altec-Tube-Power-Amplifier-/260846663778?pt=Vintage_Electronics_R2&hash=item3cbbac3862#ht_4286wt_1185

I seriously doubt something saying Western Electronic will perk anyone's interest. 

  Well maybe not most hams, but to some audiophiles, the WE name is nirvana. Just look at the mystery of the VT-52 used on that homemade amplifier using WE VT-52's:

http://www.vt52.com/

  Price of admission is $9999!! I bet it sells too, "as-is"  ???

Jim
JKO

I'll look at the tubes closer and see if the price is ok for what I need and what may have to be pitched. All the other stuff did not have to be paid for, so no worry on that.

Western Electric - Western Electronic  -  Different Companies

Patrick,

IF you have reasonable quantities of the SAME TYPE, then you may be able to do something... otherwise, NG.

The only way to do a kit today, one like you suggest, is to do a web page with a write up, full instructions, a youtoobe video, then be active on one or more DIY type audio or electronics sites talking about the project. Then you can sell the requisite tubes... that's a fair amount of effort, since you have to be prepared to field the newbie questions... so IF you can make $25/per kit profit, and you can sell 100 kits without much effort on your end (meaning that you have slaves to pack and label the boxes) and you can sell the kits in a reasonable period of time then you may have something worth trying - especially if you can follow it up with more and better... once you have the "captive audience".

No CD, no instructions, nothing printed except sales blurbs... everything on the web.

It's 2011 - Heathkit days are long gone.

              _-_-bear

PS. otherwise it's gonna be an ebay job, assuming you have quantity >10 per tube type, and better more like 100pcs per... then if you get $50 for a lot you might end up with enough to buy a nice used FLEX Radio! :D

A bit OT, but Jim, where is this $9999 number? That's a home built system, looks pretty nice with Oris (tractrix) horns on a Lowther type speaker... I don't think he sells his system...??

Many of the audiophool sites or products tend to whip up a fervor over the worship of one or two kinds of tubes, 'backed up' not by scientific information but by a long monologue.

The tubes or equipment in focus unsuprisingly seem to be the ones being sold at exhorbitant prices and often solely by the 'whippers' of the fervor. Those things are good for people who like to buy boutique art.

Best amp I ever listened to had a pair of 6CD6's with cathode feedback and global feedback. It sounded better than the no-feedback $15,000 SE 211 amp. It also made 40W, not 10W.

The best speakers have 2-4% THD at a few watts input and the single ended amplifier with no feedback is frequently no better. I have never seen a speaker system that stated THD at 110dB SPL, which is a reasonable requirement. They don't dare to do that because they don't like double digit facts. It does not matter how clean the amp is at that point.

There is a guy I know on ebay that was selling $5 tubes like a 6J6 for $35. They are NIB and all, but he claims that his high priced ones sell for more because people think they are getting something better. If I buy the lot, the unwanted tubes will end up in someone else's possession, and moved with their labor. There are collectors even for those. I just have to figure out if the tubes I want are worth the $ asked. I saw a couple of NIB 100TH's. Those would help defray costs of sold on ebay. I can see the ad copy now, "rare and unearthed from a private hoard, never touched.." Because of the volume, I don't want to pay more than $1 each for a NIB spare unless it is a power tube.

I would suggest running an ad in a national electronics magazine and sell grab bags filled with old hard to find parts. Just put all the small stuff in a barrel and mix it up, then sell it by the pound plus postage.

IF this was true at one time, it is no longer true.

More than a decade ago, I owned a pair of Stage Accompany printed ribbon tweeters. They ran from ~1.5kHz up past 20kHz... rated at 100db/1w/1m they also were spec'd at a level of 128dB SPL/1m and at that level they were <1% THD!! Work backwards to an average listening level of about 90-93dB SPL and you can see just how LOW the distortion of these units are/were... these were pro units intended for PA/SR use and studio monitor use.

However, almost all of the better pro drivers, especially compression drivers are spec'd for THD and IM at high or full power levels. JBL pro woofers are also spec'd similarly... many other manufacturers also do this.

FYI...

                _-_-bear

PS. I do not want to listen at 110dB average... thanks...

110 is for peaks. Good news on the tweeters. I am glad you know about this and spoke up.

What brands of mids and other low frequency drivers have low distortion with high input power?

I would like to review the facts on them because soon I will replace those types in some enclosures here because I am increasing the power level. 15" and two 6" in each.

I was just on the JBL site  and didn't find any specs for high power. Only glossy marketing material. I guess I can call them with my needs and ask for assistance.

The pro site has specs and downloads... JBL. Somewhere in there.

Look into pro drivers, lots of them out there now.
Also into modern ribbon tweeters (pro) and compression drivers and waveguides...

There is a 6" midrange from 18 Sound (I think) that has very high output - it's being used by bass players on top of a rear hornloaded 15" driver...

The Eminence line handles oodles of power in their woofers... up to 2kw iirc... amazing.

                        _-_-bear

PS. ya see, when you get the reference sensitivity UP to >100db you can drop the required POWER in the amps DOWN, so suddenly a PP or SE triode of modest size becomes both rational and great sounding! :D

PPS. I did not suggest that you BUY from JBL, only that they have for a long time provided reasonable specs that are published...

PPPS.. another way to drop the distortion is to drop the power per driver down for a given SPL... that equals "line array"... often a very very good solution in a large space...

If you want to sell to audiophools why not make up some new special B.S.?

Your old N.O.S. tubes undobutedly have aged naturally unlike most other newer production tubes which have a hard sound.

6.3 and 12.6 filament volts draw extra AC current. 17 volt tubes must have better sound due to lower parallel tube lead EMF.

I'm sure others here can come up with more....

run 17 volt tubes at 12 volts so they last forever
softer glow makes them sound more mellow

JBL are strange folk.....Won't sell direct to a regular schmoe.......Better to try ePay.
I did pretty good with a 12 inch JBL. woofer from eBay.

Hello Bear,
The space is about 10x20.. The speakers now are a pair of 3/4" high density sealed cabinets about 4x2x1.5 FT (10 cu ft), with a sealed 0.7 cu. ft midrange enclosure built in.

The woofers are 15" Eminence 150W units,
and there are two 6" mids from Pioneer HPM-150's
- (the HPM-150 had one mid, I put two in parallel),
and on the high side in parallel are a harmon kardon 2" dome tweeter and a HPM-150 1.5" cone tweeter.

I am using the HPM-150 crossovers. Somewhere might be the round 360 degree ribbon? tweeters, but I can't lay hands on them at the moment and have never needed them, the system is very clear and crisp up there.

Amazing this stuff is that old and still works fine. The original HPM-150 woofers are gone as the foam surrounds rotted away and stupidly I sold them off to a hobbyist for a few bucks.

I have been using the 175W Altec 1570B amps we have discussed earlier. BTW how is that output transformer working?
Short on bass power, but they will move the Eminences till they bottom out. I can do this at 30Hz where that amp barely makes 80W.
Even with them pushing that much air, I can't get the bass volume I am looking for. I do not feel it, the house does not rattle.. The original Pioneers didn't do any better. That is why I'd like to go back to the 800W shaker table amps.

I'm probably confused over what is going to improve this. The cabinet size was suggested by a guy that supposedly knew sound systems. I have a feeling it is too big for one 15" speaker, or that I could be using two or more such speakers.

All other things equal, does the cone travel of a given size woofer result in a given acoustic output?

Am I fully extending the Eminence speakers because the cabinet is so big it is like an infinite baffle and they have little resistance?

I'd like to get to 16Hz provided I can throw enough power into it. I have always liked to listen to classical recordings having low frequency content like the 1812 overture cannon and some sacred music played on the organ, as well as many other classical pieces. I've heard those selections with a very expensive pair of speakers and it was much better in the bass response per watt than what I have now, but the amplifiers were lacking, or more truthfully the speakers were smaller and not designed for high volume levels.

This is why I want the speakers to provide bass all the way down to subwoofer range, and I guess they do but the bottoming out is annoying and that is why I have not put the Ling shaker amps back up; they'd also destroy the single Eminence because they make >100W at 8 ohms and they gobble power.

The room is well broken up from an acoustic standpoint but the dimensions worry me as being small for the desired wavelengths.

Would there be any sense to putting a 15" woofer on the back of the box? How about one on each side? The shaker amps are designed for 1 Ohm. They got lots of amps, not so many volts and they will go to DC, but there is a 5Hz filter switched in internally. If I add more woofers, then will I need to add a tuned port? I'd rather not because it messes with the evenness of the frequency roll off unless sized perfectly and I don't have all those tools at my disposal.

There is no room for horn woofers, these are about as big as can be dealt with in this room. I am willing to trade efficiency for very low frequencies and can budget 800W per channel for bass to do it if I can use these cabinets. They are super strong, have been great. I can reinforce them a little more if necessary but they already have screwed and glued reinforcements at the seams and one 2x4 front to back. These cabinets are as large as small no-horn theater speakers, so why shouldn't I be able to get those SPLs?

I've looked at a lot of car stereo type woofers 15" and some 21" or 22" because some have 4 Ohm coils. Many seem to be very stiff in the suspension and that makes me think they are not efficient.

And I can't seem to make heads or tails of the parameters given for many woofers. I don't recall so many of them even being stated when I built these cabinets. They sound just fine and 100W/ch is loud, but I'd like to bump it up to the KW/ch level with a tri-amp setup for the headroom and see if I can make a watt or two at 20Hz.

Sorry for the big long story but that's what's up.

Makes me think of rebranding the tubes.. new #'s, data printed on old papers.. They'd be so sweet as preamp valves. I'd probably get the same treatment as QST gave that phony antenna matcher guy. There is some truth to operating tubes at low filament voltage and low current in very high impedance circuits. -and they never burn out. Uncovered from the dust of the ages.. makes me remember I have a few old issues of that "Osborne I" magazine from ancient days. On the cover is the mujah hadeen gathered around an Osborne (at the time the Soviets were there?). Only my decency prevented me from ebaying that and claiming it was Osama in his twenties. I ought to get those out of the garage.

Patrick,

   Besides running the 17v tubes at brownout temperature for that mellow sound, consider that box of 500 or so 6BQ6's you got. Maybe run 20 of them off the line (6 X 20 = 120v) as an OTL amplifier:

see figure 6,
http://www.audiodesignguide.com/otl/aria.html

  Some paper napkin doodle says that will get you under 10 ohms output impedance. Triode connect these tubes, off line or through a 120/240 distribution transformer, and then add all those audiophile adjectives about the mellow rich melodious unsurpassed vacuum tube sound...

  Might not be too complicated, with an Epay price of $5K / channel + preamp.

Jim
JKO

One runs into a 100V heater-cathode voltage rating with that many 6BQ6's or 12BQ6's heaters in series. Most true series tubes are +/-200V.

Not yet sure what to do with the 12BQ6's, but I also have a case of Sperry Gyroscope selected 6J6's and a case of RCA 6GH8's, and maybe 50 or 60 70L7's. They are all mellowing like fine wine.

looking back at my speaker post.. I guess the situation is hopeless because I know so little about what makes a good speaker, except how complicated it seems to predict results. I suppose I got lucky with what I already have and they just happened to sound good.

I like the JBL 'screen' speaker systems but the cost is probably prohibitve. Beat up used ones are $1200 on ebay- there is one pair.

High efficiency seems like it comes with a really big price tag. I thought I could do it myself, haha a load of crappy tubes and speaker trouble.. sort of depressing.

Patrick,

Thanks for the iron we swapped for... it sits here mocking me... I need time, have none. :(

The trick with the parameters is to download a freeware " box simulation" or "speaker simulation" software. You input the speaker params, and the box volume, set the port or lack thereof and out pops a pretty good curve of what the response will look like.

The parameters you are looking for are:

Fs (resonant freq)
Qt (speaker total Q)
VAS (equivalent speaker volume)
Vb (box volume - you decide that)

The others are important, but not to the response curve.

You will NEVER get 16Hz. out of any direct radiator system EXCEPT in the case where you find a direct radiator (woofer) with a 16Hz. Fs AND a Qt of about .45 and you also use an infinite baffle... a real infinite baffle, like your wall or a window...

The F3 point always rises when the speaker is installed in a box.

You can get near 20Hz. with some of the newer woofers, like the Dayton Titanic, TC sounds products and others... high Xmax (excursion) and high power handling, low Fs... maybe with a little EQ... maybe

32Hz. is damn low, btw... most home speakers don't really get near that, and most don't make 40Hz flat.

The other thing one needs to produce lows with any authority is surface area... the high Xmax woofers try hard to make up for surface area with excursion, but bigger (more surface area) is better...

Horns will NOT go low enough unless the mouth is on par with the size of the 10ft wide wall... (been done, btw...). They will go loud.

The new Eminence drivers are very good and will handle a boatload of power... so EQ is your friend there... but that means a sealed box...

AND a highpass just below the lowest frequency of interest (part of the EQ curve). Look up "EBS alignment". Bob Cordell spells it out on his site.

If you really want to know more and get ideas go over to http://diyaudio.com and look at the speaker section, there are a lot of ideas (some good, some bad) and many subwoofer designs... ur shaker table amps would do well as sub amps.

You can see my subwoofers on my website: http://bearlabsusa.com/NEXT/QUADRIPOLE.html

Keep in mind this design is not simple to execute and uses a few "tricks" to make it work as it should. Also a few parts that are not commercially available that are needed to realize the level of performance that it reaches... but again you have there 4 x 12" very high Xmax/high power drivers... so surface area is needed to get SPL... fwiw the original design was ~1980...

                   _-_-bear

I always thought passive radiators would 'let the pressure out', sort of like a short circuit. How is it they reinforce the sound? Do they somehow resonate out of phase with the speaker and make the system act as a low-Q tuned circuit? The measurements you have there are very impressive. -4dB at 20Hz is better than I would expect. I have EQs, can get parametric crossovers.

I could imagine a 15" woofer of that kind might make it easier in some ways having 2x the cone area. (that is the hole size.. can go bigger but not smaller) The Xmax also is impressive. I keep seeing 11mm but 15mm is great.

Electrostatic speakers and other large close tolerance types like planar ones are out for me, too much dust, cat hair, and some cigarrette and cigar smoke in this old house, so they'd die after a while.. But I am happy with the highs here, just bass response is lacking. I am envious of the ones on your site but I'd ruin them here.

Infinite baffle.. like cutting a hole in the 1.25" thick wooden floor of a pier and beam house? The advantage of pier and beam and an old house that can be hacked up a bit without losing much value. The floor problem would be fear of bugs under the house eating the speaker after a while.

I'll find some of that software and see what it says.

So, you show two of the subwoofer cabinets there. Am I right that each one has the 12" speaker and a passive radiator?

Have you found foam surrounds to deteriorate faster than rubber or impregnated cloth? Foam surround deterioration is what killed the original woofers.

No it is a phase inverter. It is in phase at the most resonant point. The main cone actually stops moving for the most part...

The response with TWO is far better than with one.
I only put one of those drivers into the cabs. Ever.
Never got to it.
It is on the list for this year.
Before I go deaf.
Ha.

The things kind of make the building feel like someone set off something BIG when there is a percussive LF sound recorded. The walls seems to pulse out...

<patting myself on the back> I have rarely if ever heard low bass like this in a home system, or even a pro system (they do go far louder), it brings a new dimension to many recordings... you can also hear things like "room rumble" on classical recordings, like one harpsicord recording... it helps one to 'appreciate' the spatial aspect of the recording space.


Those are commercial ESLs... not my manufacture.
There a quite a lot of high Xmax woofers today. Impressive.
Today my main system is largish format horns from ~200Hz up... they have what we call "jump factor."


Yes.
Or a wall.
Fiberglass screening keeps the bugs and mice out... mold is a problem.


Quite so. :D


Yes foam dies before rubber (usually) and much faster than cloth... but these lasted >20years before a rebuild was needed.

Today's foam is a different foam, lasts longer.
I am considering marketing a coating to add some protection from oxygen and UV... we'll see.

You can buy surrounds and "re-foam" most woofers if ur careful...

ok, taking Bears advice on the woofers. I am going to have to use a ported enclosure. having these 'small' enclosures with no port or passive radiator or anything else, makes them suck at 30Hz and below, like 10dB worse. That is what I have now, and why all the writing about mo' power.

Believe it or not a 4x2x1.5 FT box, while a big thing to have in a living room, is too small for a low frequency sealed enclosure.  dang. I thought they were pretty big speakers actually. A port or passive radiator is necessary. I did not understand that before but after playing with this one program, it became clear.

Found a $172 woofer at Parts Express with an Fs of 18Hz and has a "Vas" of 9.9 cu ft, near the 9.28 cu ft I have available. Dayton RSS390HF.

Using a port of PVC pipe to tune the box to just below the woofer's frequency, the last chart in the attachment, it looks much better. Just compare the first chart to the last one. A port is only a hole saw away, and the boxes are large enough for the ports to fit! I used the "BoxPlot 2.0" program. There are many programs, some are confusing, and some won't let you enter the box you already have but instead they want to tell you what to build. That's no good if you have to do it bass-ackwards for retro-fitting. "BoxPlot 2.0" made this pretty easy.

In case that is not enough, Yes I can put two of those speakers in each box (two 15" are like one 21"), but the program says the air velocity in the port will reach more than mach 0.5, unless the port is made a larger diameter at which point it becomes so long that it would have to be folded. More insights there. but I am not going there. besides what bear said, the rest of this was learned from that one program.  Also, I no longer think that the ports on those crappy little PC speakers are just for looks.

Patrick, 10db of boost in a sealed box is not too much if you reach 25Hz for example. but that depends on the power available in the amp vs. average listening levels + peak + 10dB WRT the max power handling by the woofer.

As far as porting, or any other box, no you can NOT add another woofer into the same box. That is essentially the same as doubling the VAS spec for the one woofer. Of course you get higher output, but the Fb goes up probably by double - so if you were at say 28Hz. for F3 with one driver, then with two in the same volume box you'd likely end up with a lumpy response and at 56Hz. or so...

                _-_-bear

The woofer you show is not bad at all... but don't use a hole in the box for a port, use PVC pipe or carpet roll tube (cut to length). Make sure ur using enough
ports to exceed the required volume of the port...

Check out the Parts Express Titanic driver as well...

The driver you are looking at has a "magic" Qts of 0.42, which means it will work close to optimally in almost any reasonable volume you put it into... fyi.

A lower VAS driver would be desirable... more like 3.5cu ft to 4.5cu ft. (oh wait, is that a 15" driver? if so higher VAS is to be expected - I am thinking of 12" drivers).

Usually drivers with higher VAS will have higher reference sensitivity... although few have low Fs... it's a balancing act.

You may want to check out 2 x 12" drivers in your cabs... you can likely find 3.5-4.5cuft VAS drivers, and if you get 8 ohm drivers, run them in parallel for 4 ohms you will get a 6dB boost in output compared to a single driver... that might work well for you.

It's a balancing act.



Also, most rooms have some "lift" on the bottom... the sim packages provide anechoic response...

The woofer I cited is a 4 Ohm. I am glad it passes muster.
I also looked at the Titanic "Dayton Audio TIT400C-4 15" Titanic Mk III Subwoofer 4 Ohm". The Fs is 24Hz on that one, but the Vas is only 5.46 Cu Ft, 88.7dB/1W. It beats the HF subwoofer by 1dB. I didn't choose it because the Fs was higher. I like them, but was trying for the lowest Fs, thinking that is the key to the lowest frequency.

You said I can not put two speakers in the box because I would double the Vas. The box is 9.28 cu ft.
Does this advice mean instead of this speaker:
Vas 9.9 cu ft
Fs 18Hz
I could not alternately use two of these:
Vas 5.46 cu ft
Fs 24Hz

even though I have roughly preserved the Vas?

I thought the box being tuned by a port to a given frequency had more to do with it than the Vas increase of adding another speaker.

The sealed box is out of the question now and will be ported (ducted with a tube), being identified as part of the problem. The program showed me that if a duct is added, I can tune the box down farther than it is at present (sealed). It showed me that to go without a duct it would have to be 25 cu ft (no way). The program also shows those lumps pop up (last chart, from 50-100Hz it starts) when things get too far off and I hope to keep them to 1db or so in the program (my mileage and craftsmanship precision may vary).


The entire reason I considered two or more speakers (2 Ohms/1 Ohm) is the LTV-Ling TP-850 amplifiers.
Their output voltage is 29VRMS and they will make 850W into 1 Ohm forever, and 450W into 2 Ohms, etc.

They are not too practical but I consider them "decor-appropriate" and they will keep the rack from tipping. I like them for many quality related reasons and they are paid for. I briefly considered doubling the voltage in the amps, basically replacing every semiconductor and bumping the power supply up 2x. I have done it on small-scale, made a 60W/ch Pioneer receiver do a sweltering 250W/ch peak into 4 Ohms, but am not doing it on these having 28 TO-3 output transistors each

The software didn't say anything about the volume of air in the port but only gave the air's speed.
What is the key to volume of air in the port?
The port will be a ducted port, I should have mentioned that, well I did say it was 4" ID by 9/17" long. That was one choice that came from the software. The software indicates that the larger the port (or if more are used) their length has to increase too. The software takes your box volume and tells you the new resonant frequency for whatever ducted ports you create in the box.

Two 12's would be OK but I already have a 15" hole and want to stay with that size.

About your horns, I am familiar with the effect of sound that can literally slap one upside the head. I experienced a small amount of that with a pair of 8" full range speakers that had been pressed into midrange service. The guy who was a bit of a sound reinforcement tweeker said they were guitar amp speakers. The percussion was incredible. I can only imagine the experience of horns which would be much better fidelity.

You are aiming lower than 99% of all CDs have ANY information! FYI.
There are some that do go down there... not many.
Organ stuff, and some movie sound tracks, and a few other things...

You can not go by Fs, you have to go by F3 in the specific box.


Yes, but you have to run the simulations to see what the usable F3 will turn out to be!

This will depend on the three main paramaters: Fs, VAS and importantly Qt! All three plus Vb.


Absolutely not. Especially with a ported system, the box tries to tune itself to a given freq, going lower is rarely successful, although you do get port output at the lower freq, it is way lower in level unless the other parameters "match up".

Simple test, take the sim software and double the VAS value and see what happens to the response when everything else is the same!


The response of a sealed box and ported are very different. You have to deal with it differently. Sealed will require EQ in most cases. Ported requires the proper T/S parameters WRT the box volume in order to get a reasonably flat response across the passband. SOME RIPPLE is acceptable in many cases.

For example the nominal C4 alignment (chebychev) has a bump before rolloff, but goes lower that the B3 butterworth, which exhibits lower Q and less ringing - same as an electrical filter.



Sure, no problem here...


Right, you need "better software" although box response should show port sizes vs. velocity. Lower velocity is better.

You WANT longer ports and at least 3 x 4" ports. Actually you would like the port surface area to be equal to at minimum 50% of the Sd of your speaker, and more like >100%... so if you use 2 x 12" drivers that is more like maybe 6 x 4" ports? And you want to subtract the port volume from the Vb figure! Also the location of the ports effects how they work. For example if the port is say within 4" of a surface ( like the back wall) the surface starts to look like part of the port... that all comes into play when you go to test it and tune the port to the desired Fb frequency. So don't glue the ports in place until you have trimmed them and tested their operating center frequency! :D

One reason NOT to use short holes as ports is that they let the higher freqs radiate out without any attenuation... also they tend to sound like dog poop... :D


Don't let the hole govern your design decisions. You can just pop a board over the front and re-cut... been there done that. Pick the driver(s) that do the job properly for your application. A 15" is fine... Look carefully though, there are many speakers, and they all have different specs. Also you will not have a 2 ohm load with a single speaker per channel... but you will with two 12" drivers...

Remember you will get "room lift" on the bottom end, unless you happen to get a null due to a standing wave because of placement/listening position. So, getting super low flat may yield a bass boost down there...


Horns may or may not be of better fidelity - depends on all sorts of factors, and imo most are not very good. The good ones are incredible, the bad ones are incredibly bad and to the eye they look about the same!

Sorry I could not reply earlier, I was away for a few days...

                _-_-bear

There's some low stuff in "Sofa" by Zappa, as well as "Lucky Man" by ELP. Just in a few places but Those seem to be impossible to reproduce here. I don't know the frequencies. I've used a frequency generator to sweep the system and the bass is bumpy as it is without an EQ, part of it might be the room, but I can't get high acoustic power below about 40Hz, much lower and the cones just wag at me. I'm glad for your advice, I'll run the program some more. The #$%^& Vista PC here won't run it, but I have been running it at work on lunch time.

Too bad I can't afford those "fan blade subwoofers". Seen them, never experienced them.

BTW to the original topic, the number of tubes turned out to be 25,000 not 5,000. But I decided not to spend the $. I am getting rid of stuff. I gave away the whole pile of my stuff in that storage except for some key items. This fall I hope to do the same to the storage in Irving TX. It will be better not to have to pay rent on the storage. I know a big time hoarder so getting it moved is no problem and I can go back for things if I need them.

 I think one issue at play here is that as the speaker goes through FS, the load impedance on the amplifier rises maybe 5-10X, and a low Z output amplifier just cannot transfer appreciable power at that say 20 ohms even though the efficiency of the speaker rises at FS. Here is where a tube amplifier with minimal loop NFB might have an advantage since the amplifier output voltage will rise as the load impedance rises. Still you cannot make a transformer pass DC, but 15 to 20 HZ is doable with a big enough OPT.

  Old bass reflex speaker technology was developed at a time when tube amps did not have rs=0 like your shake table amplifier.

Jim,
JKO

Jim,

I think you are not correct.

As the solid state amp sees a higher Z load, it continues to swing the same voltage to the load. As the Z goes down it swings the same voltage to the load and increases current causing an increase in power.

The tube amp can not do the same.
Without feedback, it will have a single impedance where it transfers maximum power, above and below that Z the power will be lower, no matter what. With negative feedback the case is somewhat better, but there is a practical limitation even so due to the need of the tubes to see an optimal load on the primary side of the transformer, and they do not. The feedback tries to use extra gain to make the voltage swing constant into varying Z loads. It is not entirely successful, especially as the amp gets closer to the maximum drive/output swing.

You do not need appreciable power into a higher Z load, just voltage swing! :D

Anyhow, the "benefit" of tube amps WRT reflex (ported) speakers is in the lower Damping Factor (DF). ZFB tube amps (Zero Feedback) have an output Z more or less fixed and close to 1, whereas typical feedback type tube amps can get as good as a DF of 10. This implies a lower output Z as the DF figure rises. SO, as the DF goes up, the effective "Qts" of the woofer is raised, which makes for a sort of EQ - good in the case where some extra extension is good due to a lowish Qts of the speaker system... bad in the case of a higher Qts speaker system.

Early "reflex" speakers were built on the basis of guessing. At the time no one had a good way to characterize drivers and relate that to box volume and port tuning. A few got it right thanks (presumably) to ample empirical testing.

That about sums it up. :D

                      _-_-bear