Hello Ivica
The 2235's have a BX-63A to extend their response the E-145's are more or less mid-bass drivers so no LF assist. They are crossed at about 80hz or so. The boxes would just naturally roll off. They actually don't sound bad but are missing the first octave defiantly a 40Hz system with no subs in those 5 cubic ft boxes.
Rob
"I could be arguing in my spare time"
Hi Ivica, Ian, Rob (and Robert)
In Yamaha's Sound Reinforcement Handbook, 2nd Ed., 1989, P. 229 they show the Effect of Boundary Conditions (how spl increases due to boundary effect) and the effect indicated is even further, than what I wrote in post # 66, from Ivica's/Ian's 6, 12 and 18 db increases: from free field to half-space + 3 db, from half-space to quarter-space another + 3 db and from quarter-space to eighth-space another + 3 db, for a total of 9 db (half of your totals!) from Yamaha. On the first boundary (full to half-space), Yamaha's number (+ 3 db) is not in accordance with John Eargle's 4 Pi to 2 Pi 6 db step mentioned in his Loudspeaker Handbook P. 104, but for the other boundaries at + 3 db each that is in agreement with the Electro-Voice's data sheet I quoted from in my post # 66 (BTW their data sheets are usually quite informative on system positioning (speaker placement) , mutual coupling, vent tuning, etc. even more so than JBL's).
By simple logic, which is not science and could be wrong, the 6/3/3 db room gain per boundary seems to make sense considering the first boundary is from sphere (full space) divided into half-sphere (half-space) for 6 db gain because it results from division of a larger surface (full to half). Then the smaller + 3 db for other boundary added would be because it's from dividing a smaller quantity (half of half-space = quarter-space) ?
I did also think of the mutual coupling analogy (like Ivica) when writing my post # 66 but it didn't seem to make sense in my mind, so I tossed it...
RE Ivica's post # 67 mentioning Mutual coupling as a model ( analogy?) for LF room gain, which also refers to one of your previous post dated 12-04-2016 in a Dual drivers Thread. In that latter post you reproduced, among others, "Figure 7-6 Details of mutual coupling", directly from JBL's Sound System Design Reference Manual (SSDRM), page 7-8 with no mention of source ("bad boy") to support your position here.
However, since I'm in that JBL document right now, I might as well mention that your theory (or the one you report about is obscure or esoteric on the origin of the second 3 db increase re mutual coupling) and is NOT suppported in JBL's SSDRM you "borrowed" from: "In addition to the double power handling capability afforded by the two units (possible + 3 db), the dotted curve shows a 3 db increase in transmission coefficient at low frequencies. This is due basically to the tendency for the two drivers to behave has a single unit with a larger cone diameter, and hence higher efficiency."(P. 7-8). Authors of SSDRM: George Augspurger and John Eargle...
Same explanation as I've always seen before, and I've quoted extensively before from John Eargle and E-V. Nothing new here, and more important nothing obscure or esoteric on the origin of each of the two 3db increases: one for doubled power handling (if used) and one for doubled efficiency. Enough said i guess, I'll stick to my stated sources/references regarding mutual coupling, as I'm quite comfortable with them and still willing to believe in Eargle's, JBL's and E-V's words on that issue for the time being, as in my post # 66.
To Ivica, again in your post # 72 your Pdf file titled "Driver step response" is partial only info, also taken from someone else with no mention of the source (MH-Audio.nl, Gound-plane Measurement) nor explanation...
To Ian, gone through my Bullock and Dickason (5th ed.) copies again and found no trace of LF room gain numbers (6/12/18 db) you mentioned in your post # 62. Not much on this from these two in the Hi-Fi side, so from the Sound Reinforcement side I quoted E-V's info in my post # 66, and John Eargle's plus Yamaha's such numbers in the present post.
To Rob, re post 74, the words of wisdom, from the sage man, as usual. Thanks for that enlighting statement. I can only hope/wish to reach that status some day, even though Audio has been my thing for 40+ years...
Regards,
Richard
Hello RichardTo Rob, re post 74, the words of wisdom, from the sage man, as usual. Thanks for that enlighting statement. I can only hope/wish to reach that status some day, even though Audio has been my thing for 40+ years...
Hey I am no sage we are both into this for about the same amount of time. Not for nothing but with all the Hocus Pocus in this hobby there is no substitute for a willingness to read and educate yourself and then just use some common sense which you seem to be doing. I have no doubt that whatever you decide will workout just fine. Please keep us posted on how things go.
Rob
"I could be arguing in my spare time"
Hi Rob,
Thanks for your good words. Your "bottom line" type conclusion in post # 74 and remedy for it could not have been said better by me: "I see some concern about baffle step but I would not worry all that much as between the choice of the crossover point, placement/boundary reinforcement and potential mutual coupling between drivers through the crossover it gets a bit complicated. If you are running active you can stagger the levels on the drivers as well to give an added measure of response tailoring not to mention slopes, delay and EQ in the digital domain"
As for the "Hocus Pocus in this hobby", well I kind of find it difficult to swallow (i.e. annoying) when members don't take the time to verify their info before posting it on a public forum, seen by many who may think all is true here, or don't show respect for author's rights and work by copying publications right and left with no mention of sources. To acknowledge the expert who wrote the stuff is elementary courtesy it seems. And may improve the quality of info shared vs hearsay. I try to. Regards,
Richard
Originally Posted by RMC
Hi Richard,
Many thanks for Your suggestion about my posts here on the Forum. I have usually put the sources of some of the explanations when I thought that are not so well known, but I have to say that You are right that the other authors have to be referenced.
But if You read MY explanation with some care, You will note:
"..Generally speaking if we have TWO sources of sound (working together) very near each other, and producing the sound in the same frequency region, but independent each other (example each producing noise) we can expect the +3dB rise in the sound level, but if they are reproducing the same sound source (correlated sound) then the rise would be +6dB. Such behavior can be seen in the:
http://www.zainea.com/mutualcoupling.htm
http://www.audioheritage.org/vbullet...l=1#post399606
so if the distance between the sources is LESS then 0.5 Lambda (Lambda=345/f), or better to say LESS then 0.25*Lambda we can expect the rise in the response of MORE THEN +3dB, but not more then +6dB.
We can assume flat surface near the sound source as ideal reflecting surface (as a sound mirror), and that the sound source is not-directional (Omnidirectional) and IF THE DISTANCE BETWEEN THE SOURCE AND THE SURFACE IS LESS THEN 0.25*Lambda (or better 0.15*Lambda) then we can expect almost +6dB in rise in the sound level, because in such circumstances such sound source and the surface behave as TWO correlated sound source that are near (twice the distance the sound source from the surface) each other.
..."
So the frequency where F/R the rise +6dB depends of the distance of the source from the large surface.
If talking about te EFFICIENCY when dealing with the operations of the two drivers, do not forget that their combined impedance is reduced to the half of the single driver impednace, so they take twice larger current from the amp then a single driver operating on the same amp voltage output so only +3dB can be get, as shown on the JBL data documet You have mentioned in Your #77 post here.
Regards
ivica
Okay
To get to this l read Dons comments in the Library regards the final Everest design and l looked at 4313 post about the low Q drivers and the Vas error.
I then thought about Everest schematic and increased the Qts from 0.25 to 0.28 allowing for dcr of the chokes which seemed reasonable.
Plug that in to Bassbox and 3 minutes later you have an indicator of the tuning for a single E145
I would imagine +-2 Hz tuning would give you something quite acceptable either with a passive network or active.
I then added the Martin Colloms room gain curve that for anyone who can follow this so far knows it requires no explanation.
These are educated assumptions based on a working design
The box details below are with the above assumptions (Everest design)
When trying to figure out how JBL make a JBL woofer work I always look at what they did before screwing around with a diy design from scatch. There nothing in it really
8 cu ft
Normal fill
Fb 35.3Hz
F3 2pi 66.5 Hz
F3 in room 32 Hz with Colloms curve per the illustrated curve QTS=0.280
Raw driver box details (QTS 0.25, no room gain)
8 cu ft
Normal fill
Fb 34.6 Hz
F3 2pi 91 Hz per the illustrated curve (no Colloms rom gain, QTS=0.250)
-6 Db 2pi 38 Hz
The 2 ports are 4 inch 2.36 inches long
One E145
The tuning is really about the room and getting the best Xmax out of those woofers
You could do what Rob did in a smaller box with a sub but I sense you want to have a go at using the E145 like JBL did with a large horn
An 8 cu ft box is scalable for your horn
2 E145 per channel seems excessive unless you are going to use it in a large room.
Of course using the Drive rack makes most of this moot. Just eq out the response below 150Hz
Jbl did opt for the B460 sub for the Everest
In the Everest network Greg incorporated a network in the woofer to compensate for corner placement (see the manual)
A very useful link below if you wish to understand what a 2pi loudspeaker load is all about.
As I mentioned earlier if you look closely not all JBL system tech sheets are 2 pi response measurements. Some are also ground plane and some are a cut and paste of both as hand written notes advise probably by GT.
https://trueaudio.com/st_spcs1.htm
If you understand that then it is obvious that designing a bass reflex box to a maximally flat butterworth QB3 bass response in a 2 pi load on a similator will result in an overly excessive bass response that has the potential to hump up below 100 hertz depending on where you put the enclosure.
Hi Ivica,
RE Ivica Post # 80
"But if You read MY explanation with some care, You will note:"
"..Generally speaking if we have TWO sources of sound (working together) very near each other, and producing the sound in the same frequency region, but independent each other (example each producing noise) we can expect the +3dB rise in the sound level, but if they are reproducing the same sound source (correlated sound) then the rise would be +6dB. Such behavior can be seen in the: " (...)
"If talking about te EFFICIENCY when dealing with the operations of the two drivers, do not forget that their combined impedance is reduced to the half of the single driver impednace, so they take twice larger current from the amp then a single driver operating on the same amp voltage output so only +3dB can be get, as shown on the JBL data documet You have mentioned in Your #77 post here."
I did read many times YOUR explanation and it still doesn't look more convincing to me, hence my "obscure or esoteric" qualification for that theory in a previous post. Without going into small details, first there's a contradiction between "working together" and "but independant of each other". Second, "producing noise" or "reproducing the same sound source (correlated sound)" doesn't really make a difference to me, sound is sound, and NONE of the experts I consulted (Dickason, Eargle, JBL, E-V) make that difference in real life... Maybe they do at the University of Southampton, UK in the article you referred to. But that would be at a quite different level of sophistication than others ... Hence my "esoteric" qualification.
As for the "efficiency" aspect you describe for drivers in parallel, Eargle explains that with more details (but with same results) than the quote I made in post # 77, regarding mutual coupling, from JBL's Sound System Design Reference Manual, 1999.
"It is common in many applications to mount two or more LF drivers adjacent to each other on the same baffle, normally driving them electrically in parallel. At the same time, the drivers are acting acoustically in parallel. (...) Note that the response of the dual driver system is 3 db greater than the single unit, both with the same electrical power input. This increase is caused by the fact that the two closely coupled drivers behave essentially like a single "new" driver with twice the cone area, ... The doubling of cone area will result in a doubling of efficiency, ... The term "mutual coupling" is often used to describe this effect. It is further obvious that the dual driver system can handle twice the electrical input power than the single unit. Therefore, there is a net 6 db greater output capability with the dual unit as opposed to the single unit." John Eargle, Loudspeaker Handbook, Chapman & Hall, 1997, P. 79-80, in the Parallel Operation sub-section of the Transducers in Acoustical Series and in Parallel section. 3 db re coupling, and 3 db re power handling, if used.
As everyone can see, no magic, no obscure science, no BS, no "esoteric" theory, just simple principles well explained by one of the Masters in the field, long associated with JBL, which has/had one of the most advanced speaker lab on the planet and some of the most talented Speaker Engineers on the planet he had full access to every day the sun shined... AMEN, as they say.
As for impedance and voltage, Dickason mentions "The advantage of multiple driver combinations is more obvious at higher power levels. [doesn't that sound/look like or refer to the higher power handling issue?] (...) The voltage input to get this SPL is 12.68 V for a single driver and 6.35 V for the two-and four-driver combinations." The voltage is the same for four as for two drivers because as he says: "... but putting two parallel sets of woofers in series decreases gain by - 3 db, for a net change of zero when compared to the output of the two-woofer box." In other words, he used parallel/series connections in the four-woofer box instead of four parallel. (Vance Dickason, The Loudspeaker Design Cookbook, 5th Ed., 1995, P. 30-1, in the Multiple Woofer Formats section, Standard Configuration). This is from the closed-box LF Systems chapter because in the Vented box chapter, Dual Woofer Formats section, he says to refer to the former: "Everything discussed in the closed-box section applies when you are using a vented enclosure."(p.61).
Since I'm a fair player, and because it MAY (?) help your cause/theory, Eargle does mention about mutual coupling, in his other book I have, "The above equation assumes that the LF units are located as closely together as possible, and this is an important requirement in getting the most out of mutual coupling." (John Eargle, Handbook of Sound System Design, ELAR, 1989, P. 115). The nominal spacing between drivers is considered in the equation he mentions. But at NO time in his books, same for Dickason, JBL and E-V, do they go to the sophistication level mentioned by you.
Again, enough said on this matter for me and I'm paraphrasing myself from post # 77: Nothing new here, and more important nothing obscure or esoteric on the origin of each of the two 3db increases: one for doubled power handling (if used) and one for doubled efficiency. I'll stick to my stated sources/references regarding mutual coupling, as I'm quite comfortable with them and still willing to believe in Eargle's, Dickason's, JBL's and E-V's words on that issue for the time being. Regards,
Richard
Hi Richard,
It would be very difficult to understand each other (because MY English is very bad, as not my native language), but if You are not aware the differences between correlated and uncorrelated sources, the rest of the explanations can not be logical. May be some of the AH forum member can help.
Receive My Best Regards
Ivica
Hi Ivica,
It seems I'm not the only one in that situation since Dickason, Eargle, JBL, E-V don't mention that issue re mutual coupling. Or they felt that it was not of importance or not worth mentioning in their writings... If this had been critical I guess they would have covered it. Regards,
Richard
Hi Richard,
You are right. I believe that they did not want to deal with small frequency region.
If center of the driver is about 1m away from the surface then real influence (+6dB) would be for the frequencies LESS then 52Hz, and for the higher frequencies (say over 60Hz) almost +3dB can be assumed.
regards
ivica
Okay you experts
Here is a trick question
When you double the cone area with two identical woofers for the same output spl what is the difference in the cone excursion of the drivers? (assuming close proximity)
Is it the same, half or quarter?
Now don't go and look up a reference and quote it like you read it out of a book
Think about it and type in the answer
So I installed the woofers today and played a bit. I found a sine wave sweep that I could adjust so I played it through the speakers from 30Hz to 55 Hz. At a low volume level the woofers would stop vibrating from 47Hz to 50Hz. When I blocked one vent it would drop approximately 9 Hz and the woofer vibration would stop for a period of 2Hz instead of three. I laid the speakers on their backs and put a popcorn kernel on the cone so I could tell when they stopped vibrating.
Does this mean the enclosure is tuned to 47Hz, 50Hz or somewhere in between?
I ordered six speaker port tubes with flanged ends, they are four inches long and they should slide right in to my 4" plumbing pipe ports. From what I have read they should be slightly longer than the 1.25" that I have right now to lower the frequency. My target was 45Hz.
This is what I ordered.
Hi Robert,
Good news, you are in fact tuned in the 47-50hz range. Pretty close. This need not be precise to 1 hz close. You can still try though. Also use a finger very lightly touching the cone near the surround to get the feeling for yourself, though the popcorn is clever. To get a bit lower to 45 hz you'll need little longer vents, not much. But better to have little too much which can be cut than not enough... Trial and error tuning, but real life measurements, not theory ! Once your tests are done you'll have only one vent thick right? Regards,
Richard
Hi Ian,
Re your sept 8 post # 86 with a tricky question about excursion when doubling cone area. I see nobody replied to you 4 days later... For myself I didn't reply since I had already seen part of the answer, and may be told I cheated.
However, If you look at my post # 82 dated sept 4 (4 days before yours) you can see I quoted from Dickason's Cookbook, 5th ed., p. 30-1. On those same Dickason pages I read 4-5 days before your question, a partial or incomplete answer to your question appears. So no real contest. Read below for more.
However again, I'm NOT satisfied with his explanation of driver coupling effect on sensitivity, doesn't seem to make sense, looks like a contradiction or typo made its way in his text. This is why in my sept 4 # 82 post I quoted John Eargle instead for the coupling effect on sensitivity issue, and Dickason on the voltage/impedance issue.
That speaker experts seem to disagree on science (!) is surprising, but does exist. Look at Bullock's book on p. 62 bottom right column where he says + 6 db for two woofers in parallel, and on p. 66 left column from the middle and on where he repeats that, as opposed to Eargle's clear explanation of + 3db for coupling and another possible + 3 db for power handling I quoted in post # 82 (Handbook of Sound System Design, p. 114, and Loudspeaker Handbook, p. 79). Then have a look at Dickason's, 5th ed., p.30 for a confusing or confused explanation of 3 vs 6 db in 1, 2, and 4 woofer formats ...
I tend to give more credibility to Eargle since his manuscript was reviewed before publication by W. J. J. Hoge, another well-known Speaker Engineer (CTS, JBL, etc.), who would normally have picked-up a gross error... JBL's own Sound System Design Reference Manual says the same as Eargle (Authors: Augspurger and Eargle).
Same power input to identical single and double-woofer (in parallel and closely mounted) boxes, gives a 3 db sensitivity advantage to the double-woofer box and cone excursion would be half that of a single woofer box. Dickason stops here, the rest is mine.
This makes sense because a larger cone area can move more air or "take a bigger "bite" at it" and need not go as far (excursion) to reproduce the same sound. If I remember correctly the good old days, the E-V 30" woofer and the Hartley 21" woofer didn't have nor needed a lot of Xmax considering their huge cone area that moved lots of air more efficiently.
But since you mention specifically "for the same output spl" then that would imply a half reduction in input power to the double-woofer box (to get - 3 db) for spl to be equal to that of single woofer box. Logically, lower input also means less excursion and distortion, therefore the answer would be "quarter", if its already half the cone travel at + 3 db as mentioned by Dickason for double-woofer compared to single. Regards,
Richard
1/4 excursion is correct
You are correct distortion is lower at 1/4 the excursion.
The trade off is double the enclosure size.
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