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Author Topic: you move sixteen tons and what do you get? tube kits?  (Read 28414 times)
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WBear2GCR
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« Reply #25 on: September 12, 2011, 09:53:34 AM »

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! Cheesy

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...

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« Reply #26 on: September 12, 2011, 12:06:44 PM »

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....
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« Reply #27 on: September 12, 2011, 02:41:27 PM »

run 17 volt tubes at 12 volts so they last forever
softer glow makes them sound more mellow
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flintstone mop
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« Reply #28 on: September 13, 2011, 08:48:51 PM »

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.
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« Reply #29 on: September 13, 2011, 10:38:36 PM »

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! Cheesy

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...



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.
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« Reply #30 on: September 13, 2011, 10:49:51 PM »

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

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.
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« Reply #31 on: September 14, 2011, 01:33:53 PM »


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
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« Reply #32 on: September 14, 2011, 07:30:36 PM »

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.
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« Reply #33 on: September 15, 2011, 02:03:01 AM »

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.
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« Reply #34 on: September 15, 2011, 09:19:54 PM »


Patrick,

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

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
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« Reply #35 on: September 15, 2011, 10:24:22 PM »

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.
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« Reply #36 on: September 16, 2011, 04:28:47 PM »

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.

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.

Quote
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.

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."

Quote
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.

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

Quote
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?

Quite so. Cheesy

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

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...
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« Reply #37 on: September 16, 2011, 04:43:49 PM »

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.

* spkr.pdf (674.39 KB - downloaded 357 times.)
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« Reply #38 on: September 16, 2011, 05:51:41 PM »


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...

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« Reply #39 on: September 16, 2011, 06:18:59 PM »

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...
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« Reply #40 on: September 16, 2011, 10:45:34 PM »

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.


* LTV_Ling TPA-850.jpg (137 KB, 1221x1027 - viewed 714 times.)
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« Reply #41 on: September 19, 2011, 12:32:21 AM »

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 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.

Quote
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?

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.

Quote

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.

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!

Quote
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 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.

Quote
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.


Sure, no problem here...

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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.

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! Cheesy

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... Cheesy

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

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...

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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.

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...

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« Reply #42 on: September 19, 2011, 06:34:24 PM »

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.
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« Reply #43 on: September 19, 2011, 06:37:43 PM »

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.
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« Reply #44 on: September 20, 2011, 11:24:26 AM »

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 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,
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« Reply #45 on: September 22, 2011, 09:13:53 PM »


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! Cheesy

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. Cheesy

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