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Vintage JBL for subwofer
Vintage JBL for subwofer
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Old 19th July 2018, 05:24 PM   #151
academia50 is offline academia50  Argentina
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Quote:
Originally Posted by bentoronto View Post
Sealed boxes have only a single parameter and the bigger the better. The ideal Q is no Q at all and the less ringing the better.

Hello Ben

I have to admit that I do not understand exactly what you want to say ... All the bibliography that I have read give as an ideal the Q 0.707 for sealed boxes ... but it is not achieved with small boxes, in fact.
That is, is the exact point of balance between the elasticity of the air contained in the box and the compliance of the mechanical system of the speaker, correct ?


Quote:
Originally Posted by bentoronto View Post

Simple so far. Too bad those three-decimal-places sims bear so little relationship to bass sound in your room. Now you are getting into the important challenging questions of room acoustics. Two boxes allow you to locate them so as to have the best possible final mixed-bass result.

Learn to use REW to tune your systems. Now the work begins.

B.
It is exactly the opposite of what I expect, that this is the final step ....

I recognize and I do not minimize the importance of the acoustics of the room at all.
But currently it behaves quite well by locating the old JBL subwofers according to the sketch attached
With these "temporary subwofers" in phase or counter phase with respect to the main ones, no difference is perceived from the listening point. If there is one when I approach the front wall, there the bass reinforcement is notorious but I attribute it to the DTQWT rear speakers (four x 10 inches)
I do not rule out in the future to incorporate a measurement system, (like the REW that you advise me), however, first I want to experiment placing the subwoofers in the same plane as the front speakers, (I think it will be two, I agree with you in that give more flexibility to do tests) could try a sub in the sector A and another in sector B, both located in two corners to further increase the gain of the room. That way I would recover some DB that I am losing due to the roll off of the sealed boxes ... it is just an assumption, we have to experiment.

But first things first, I have to build the boxes ... although I must wait for a more benign climate, today we have a lot of cold and rain in Buenos Aires, we are in the middle of winter. So I will wait for favorable weather conditions to work abroad this time, because the owner of the room (my oldest son) demands that I return it. (I borrowed it to use it as a carpentry shop when I built DTQWT)

PS: An additional advantage of good weather is when I listen to music with all the vantanas of sector B open! It is infinitely better than conditioning with acoustic materials .....
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Last edited by academia50; 19th July 2018 at 05:35 PM.
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Old 19th July 2018, 06:04 PM   #152
bentoronto is offline bentoronto  Canada
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Vintage JBL for subwofer
Quote:
Originally Posted by academia50 View Post
I have to admit that I do not understand exactly what you want to say ... All the bibliography that I have read give as an ideal the Q 0.707 for sealed boxes ...
A common mistake is listening with your eyes on a plot instead of with your ears.

It is true that when you do the math, a Q with the magic .7 (and a peculiarly small box with a disastrously high speaker resonance) you will get a nice flat visual FR. So the first error is thinking you get (or want) a flat audible FR from a flat visual FR. (How come commercial speaker makers don't seem to make small sealed boxes?)

Granted, you don't want any emphasis north of maybe 45 Hz, but you do want all the bass you can get south of there.

Nobody wants an amp with any "Q". So why settle for a speaker that rings? Speakers should be without any character at all*. That battle was settled decades ago.

B.
*and can play all kinds of recordings. Alas, some sources or music intended for the bubble-gum crowd - including male announcers on some radio stations - might be doubly horrible on a good system.
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Last edited by bentoronto; 19th July 2018 at 06:25 PM.
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Old 19th July 2018, 06:13 PM   #153
bentoronto is offline bentoronto  Canada
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Vintage JBL for subwofer
Quote:
Originally Posted by academia50 View Post
With these "temporary subwofers" in phase or counter phase with respect to the main ones, no difference is perceived from the listening point.
Yes, weird how you can do all kinds of "wrong" things with polarity and phase and come out better. REW does provide trustworthy guidance on that matter (by comparing single speakers with speakers playing in pairs). And the "wrong" connection may measure better for your purposes.

Gross time offsets can be fixed with a DSP. But the benefits, esp with a the nicely ambient system you are sketching may be minor. Conversely, those of us who favour bi-pole sound and more purist acoustic recordings, wouldn't know where to begin.

BTW, as REW will quickly illuminate, you may have put your chair in a poor location for bass room modes, at least for systems with conventional front woofers.

Start playing with REW. Takes a while to master some aspects (DAMHIK).

B.
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Old 19th July 2018, 08:21 PM   #154
bentoronto is offline bentoronto  Canada
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Vintage JBL for subwofer
As an academic, I am sure you will be delighted to see actual measurements from my room... with my chair near the centre of the modest-sized room. The plot has no EQ or crossover. It shows (1) my 5 cu ft sub as measured at about 2 inches and then (2) one spot (randomly set) at my chair about 10 feet or so (I added 22 dB as my best guess at comparison).*

Anybody need help guessing which curve is which? Anybody want tp pick a good spot for crossing-over?

But the real question for all of us is: what is the best way to work with a sim, slide-rule, crystal ball, or prior-measurements to anticipate the chair FR?

Nice output below 20 Hz.

B.
*my subs are driven by my swell 1980 JVC receiver I bought at the Salvation Army for can$20
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File Type: jpg Sub close vs at chair.jpg (82.7 KB, 77 views)
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Last edited by bentoronto; 19th July 2018 at 08:27 PM.
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Old 19th July 2018, 08:33 PM   #155
bentoronto is offline bentoronto  Canada
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Vintage JBL for subwofer
And here's sealed box distortion up-close. An astonishing curve below 1% for most of the sub passband albeit at rather low volume. The at-chair curve is of course identical although REW necessarily de-rates it due to noise.

(I don't know about that bump in distortion. Maybe it is the FR bump and/or the accelerometer I glued to the dust cap.)

B.
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File Type: jpg Brutus dist.jpg (84.9 KB, 70 views)
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Old 20th July 2018, 03:20 PM   #156
academia50 is offline academia50  Argentina
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Quote:
Originally Posted by bentoronto View Post
As an academic, I am sure you will be delighted to see actual measurements from my room... with my chair near the centre of the modest-sized room. The plot has no EQ or crossover. It shows (1) my 5 cu ft sub as measured at about 2 inches and then (2) one spot (randomly set) at my chair about 10 feet or so (I added 22 dB as my best guess at comparison).*

Anybody need help guessing which curve is which? Anybody want tp pick a good spot for crossing-over?

But the real question for all of us is: what is the best way to work with a sim, slide-rule, crystal ball, or prior-measurements to anticipate the chair FR?

Nice output below 20 Hz.

B.
*my subs are driven by my swell 1980 JVC receiver I bought at the Salvation Army for can$20

Well, I think your room is the blue curve, the one that does not have so many peaks and valleys.

I understand what is your point, you say that before buying the horse carriage
you have to know if it pulled a racehorse (thoroughbred) or a percheron (draft horse) ...
Well, I already have the car and the horse, just need the rider to adapt more and more to it. I do not know if the example is valid, but it's the same .....

So I appreciate your good intentions, but I'll do the baffles first and if I decide to use REW the room will be conditioned later. If I noticed it necessary.

I would buy MiniDSP + Umik -1 + REW, I have been advised in this thread a long time ago, but this is learning with obstacles. It is not the same to live in Toronto as in Buenos Aires ... there are very big logistical and monetary problems here! Keep in mind that I bought Delta Pro 18 A because there were not many other options for a good subwoofer speaker.

Also, as I mentioned, my room behaves acceptably well, the irregular dimensions help the stationary waves to extinguish quite quickly.
There are also many books, armchairs, wooden furniture, carpets, etc. Everything helps to function as bass traps. Nor should there be too much, because it would kill the upper spectrum, even the dynamic range. I have a lot of accumulated experience in this regard. There has to be a balance "in disorder" between the objects, I'm sure you understand ..
Well, now I have to define the material to use for the boxes, calculate the exact dimensions of the cuts, the screws to use, etc, etc.
There will be no dowels for a craft work this time.

Last edited by academia50; 20th July 2018 at 03:27 PM.
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Old 20th July 2018, 03:51 PM   #157
bentoronto is offline bentoronto  Canada
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Vintage JBL for subwofer
The smooth, lovely, sim-like curve is the up-close miking. The awful curve (with the swell lower bass) is the REALITY.* Ummmmm.

If any other reader made the same noobie mistake, take it as a "learning moment".

You seem to have a conceptual understanding of room furnishings. At least until you actually test and discover the reality. Of course even poor rooms become your norm once you are used to them (AKA your current "adaptation level" in psychology).

My point is that it is misplaced effort (and perhaps conceptually wrong) to follow sim slavishly, like some people who drive into lakes by following their GPS.

Get ready to sort-out your system after it is operational in your room.

B.
*the room curve looks awful; while any other haphazardly chosen single ear location would look awful too, it isn't the same as hearing perception.
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Last edited by bentoronto; 20th July 2018 at 04:12 PM.
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Old 20th July 2018, 05:06 PM   #158
academia50 is offline academia50  Argentina
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I respectfully believe that you have a need to be right above all things.
Pretty common in human beings, by the way.
If you listen according to that awful curve, it is because your ears have adapted to it, as you yourself say.
If you like it, go ahead, I can not question the tastes.
But, IMHO, I think that then it has not been very useful to use room optimization programs ....
The question is to listen as flat as possible.
Arriving at this point is the goal.
Now, if your ears do not capture exactly that technical acoustic ideal achieved, that is another problem, which we are not discussing here. I suffer from mild tinnitus and I know people who are absolutely deaf in one ear and enjoy music....
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Old 24th July 2018, 07:33 PM   #159
jjccoutcher is offline jjccoutcher  United States
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One thing to remember in the end the only one you need to impress is yourself. As far as our listening rooms they all suck just some more than others. As an example I spent about 20K and hundred hours of labor building my audio room. I used staggered 2x4s to reduce sound transfer to outside. In the end it is a great sounding room but there are still areas that could be better.


B, Looking at your frequency responses, I would find the reason for the peak. Our ears can hear a peak much better than a dip. Start with a near field response of the speakers, to help remove the room from the equation. If it is the speaker the location of the peak looks like either cabinet movement or lack of stuffing.


My system has been together for a year now and is very listenable but am always trying to make it better.
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Old 25th July 2018, 04:54 PM   #160
academia50 is offline academia50  Argentina
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I agree to set up a room. And I consider it essential if it is exclusively destined to listen to music.
Have you been visiting a home for sale / rent empty? You can not put a sound system there and just go to enjoy
But you can do it in the garden, is not it? And you do not need any conditioning .... then, DSP is to improve what the normal environments of homes spoil. I have used DSP in my room, (5.1 system Yamaha) and personally I do not plan to invest more hours than I already spent trying to adjust time delays, balances between speakers with pink noise, etc.
My ears have not noticed differences in favor of this technique.
And thank God I still have a good hearing, except for that buzzing ... luckily you only realize when you think about it! Imagine the hum of the tube amplifiers, you only noticed when it was completely silent ...

Also, I think that no adjustment is final, when you change the sound source, (and the volume of hearing) all the ideal settings will no longer be. Because there are not two identical recording rooms, nor do they all use the same studio monitors, nor do all sound engineers use the same criteria for mixing, and none listen exactly like the others.
Does anyone remember the EQ Soundcraftsmen ?

Soundcraftsmen - Wikipedia

I have used it for a few years with SS equipment, and (I do not want to enter into technical discussions here) I do not think there is much difference with DSP
(Yes, I know, some modify the group delay, others the gain level in the different frequencies, and the parametric is not the same as the graph, etc. etc.
My current solution, with respect to the fidelity of the bass, because I am very satisfied in the rest of the spectrum:
When I perceive that they are too many or too few, I adjust the gain and / or crossover frequency on the subwoofer amplifier, but not "to my liking". I adjust according to what I consider how a particular instrument should sound live in my own room.
You just close your eyes and think.
Is Charlie Haden in front of me right now, then, how should the double bass sound? And then I adjust to get closer to that sense of reality. Very simple and effective, for me.
But ...... I can not place a symphony orchestra in my room!, And recreating that sound will always be an impossible mission for any system, for obvious reasons!
Sound reproduction systems are machines of illusions, utopias, it is good to want to get closer to those nirvanas, I do it, but I am aware of the limits.

And my monetary limitations too.....

Remember all, i do not speak english, then, I use GT .

Last edited by academia50; 25th July 2018 at 04:59 PM.
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