Vintage JBL for subwofer

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here's your 137 liter box sealed with capacitor and vented with typical active EQ which peaks around tuning and rolls off below cutoff, both in 0.5 pi

when using the filter wizard of hornresp, I first set the highpass filter at 20Hz/2nd order then applied the peaking to get the composite response


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Very thanks freddi ! :)

The conventional blue line looks very good (very similar to WinIsd, that's good for me, it gives me peace of mind) I do not like the red line with capacitor, because it levels the response from 50 to 100 hertz, and DtqwtII already has a lot of weight there . Troels designed a passive divider that gives a lot of weight to the second and third octaves. The Dayton plate amplifier that I will use for now has a subsonic filter at 20 hertz 12 / db per octave, which is fixed, not switchable ... So I look for a soft roll off between 40 and 20 hertz.

I think that people who are fond of HT systems will think that this project is a waste, two huge cabinets with 18 inch drivers and are limited below 20 hertz ?

Well, this is to listen to music, again. I'm not interested in a subwofer that moves the furniture in its place, nor for the windows to vibrate when there are earthquakes in the movies....

Tocatta and Fuga de Bach (original work conceived for pipe organs) has a musical note that is a "natural Do" of organ that corresponds to 25 hertz. I'll be fine there. I will miss notes of 16 hertz? (see post number 14) Well, I think you can not have everything in life, you live better accepting this ...
 
" Every choice of a transducer / box is always a commitment ..."

Could not been more easy ? :rolleyes:


Next step :
External dimensions of the box calculating the cushioning material ....

(just to be sure ...:D)



Speaker Box Volume Calculator / Designer Help
 

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bjorno:

As I mentioned before, the graphics provided by you are excellent but I have to admit that they surpass me in knowledge.

In the attached graphic I see two of my simulations with WinIsd.
One is from a sealed cabinet and the other from a ventilated cabinet.

A red line with the square root symbol on it, which means? That sign replaces a cross, that is, not viable, crossed out ? :confused:

And the OK in green, to which of the two systems does it refer?

I think your answer will be for me the strawberry that is missing the dessert, please allow me to enjoy it properly....:)

Thank you !
 

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I have a new concern for everyone:

The calculations for a cabinet are made trying to be as accurate as possible, because we want to achieve the best sound.
If we already have the exact volume of the cabinet, but then we add buffer material inside it, the virtual volume will increase, as freddi pointed out earlier.

But, there are no exact formulas here, how much will it increase? 10%? 15 % ? And this percentage will also vary depending on the type of material used. :confused:
The bracing and the volume occupied by the tuning tube will be easy to add to the overall volume, but not the influence of the absorbent material.
In short, is it worth taking risks using material in my particular case, with large drivers and boxes?

I leave a study here:


Data-Bass

What do you think ?
 
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Hello

I've been reading a lot and the conclusions I've reached are:
I go for sealed by the undoubted advantage of better transients in the low frequencies of work that I look for.
It will not be necessary to place any type of absorbent material inside the cabinet, because in fact it does not have the least effect on the quality of the sound, again, in the first two octaves.
There would only be an increase in virtual volume and that is unnecessary if we do not have space problems in the room, as my case fortunately.
But if the virtual volume changed the magic number Qtc = 0.707. Has no sense....:D

New readings that I have made with respect to the group delay seem to show that the high pass filter to protect the speaker at very low frequencies,
it can be counterproductive in the low frequency spectrum ...:eek:
(since it is permanently incorporated - it can not be switched ON OFF - on the Dayton SPA250 plate amplifier ...)

I think these high pass filters are important if we use ventilated cabinets, due to the "hanging effect" of these systems below the frequency of tuning (Fb), but this does not happen in the sealed ones, so it would be unnecessary and also counterproductive. .
But I must investigate more deeply about this...;)

Ps: The final choice is the boxes will be sealed.
It remains to define if there will be two, with a speaker in each one, or if it will be one with two speakers, which interests me again by saving material and work, only the excessive weight of the creature scares me ....:D
 

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But if the virtual volume changed the magic number Qtc = 0.707. Has no sense....:D....It remains to define if there will be two, with a speaker in each one, or if it will be one with two speakers, which interests me again by saving material and work, only the excessive weight of the creature scares me ....:D
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.

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.
 
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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 ?


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.

:cool: 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" :rolleyes: 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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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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With these "temporary subwofers" :rolleyes: 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.
 
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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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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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.
 
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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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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 ...:confused:.
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....:D;)
 
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.
 
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.....:D

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