DEEPER BASS: D. B. KEELE/E-V's STEP-DOWN MODE

[Ian Mackenzie]

The DD67000 port assembly is cast aluminium

I have seen a 15 inch port on a 2225 system many years ago.

In Alex Bradminoff and Don Davis red loudspeaker book they make reference to vent area equalling cone area

A port can be constructed out of timber and baced where one enclosure wall forms one side of the port

Perhaps a point to consider is pipe organ resonance with long ports and volume occupied by large ports

A port should be ideally at least one diameter from any enclosure wall
If you consider enclosure construction then the practicality of large port area becomes a limiting factor

I think the associated concerns of power compression points to the use of multiple subs where the total power is divided across 2 or more subwoofers. For example 1000 Watts into a voice coil is on the spectrum when a large portion of that is lost in heat. Stacking of subs then becomes a reality.

Others claim tapped horns are more effective at high power levels

I once heard Steve Schells bass horn
On just a tiny digital amp it was dynamite. Deeper, faster and more dynamic than any bass reflex system
I would not mind hearing the OMA bass horn with a 21 inch driver

[RMC]

RE POST # 105

The suggestion definitely has merit in the absence of a best or second-best thing. Here's why in my view, as I like to know the reasons for choosing between different options.

Having dealt with some 8" of those a while ago, I'm not sure though its thick enough to avoid resonating at the very high powers involved... I don't remember their thickness, but I seem to remember (right or wrong) its a bit flimsy not very sturdy? I'll need to check that next time I go to Home Depot. On the other hand, in the world of vents using larger dia. often means longer port tube (e.g. post # 26, 12 cu.ft. 2245 box, 9" dia. vent, Lv 20" and 30"!! with "Duct screwed into bottom and side of Enclosure". First time I ever see that, seems contrary to some vent advice, but anyhow). Longer vents are more prone to resonance. Yet, I still don't discard the idea.

However, this was not exactly the type of vent I had in mind when I wrote my post. What I had in mind, and should have been more precise about this I guess, is the type of vent mentioned a little higher in my article and used in the JBL 4897/A or something similar, or with the same virtues. I know that's a damn big order, this is why I wrote at the end "...unless one is lucky to find the appropriate ready-made device, which may not happen."

I did check in the 4897/A Technical Manuals specifications beforehand as pretty often vents of JBL made boxes have a part number, though besides that it usually says NOT FOR SALE... I did the same verification for 4897 vent just in case to see if there's a part number for that, hoping (a dream) that MAYBE such could be available ? Not a chance! I couldn't see a part number for the clever device and it appears to be part of the cabinet. Strike out # 1

Failing which, large round flared vent(s) certainly come to mind as second best. But in this case one should read the Salvatti, Devantier & Button article on ports, at least for the parts understandable by non-Engineers, to avoid wasting money on "unfit" flared vents or to increase the chances of getting something worthwhile for the dollars spent. Again, at the very high powers involved here, one doesn't need nor want a donkey...

After looking into that paper, one may wonder if the commercially available flared vents sold left and right have the required Engineering built in/can really do a nice job or is it partly hype? The concept is certainly good, no doubt about this (as shown by Salvatti & al.) but the execution of that, mass-produced in China in "all shapes and sizes" (!) for the majority?? Most of the time there's very little, if any, technical info given on these, other than dimensions and type (flanged or flared). BTW one well-known retailer of these, I'm looking at now, sure doesn't know his knee from his elbow, as it wrongly describes many of both types in product descriptions, with no tech data... Its gonna be a long way! Strike out # 2

Bottom line: for most people its either your idea/or equivalent (i.e. multiple smaller vents) or taking a chance with some round flared vent(s) of unknown properties/specs. Personnaly, at this point I'd probably go with the former instead of the latter...

Richard

[Ian Mackenzie]

Hi Richard

Else where you have posted that QL losses are largely enclosure leaks and not attributed to losses from other sources.

(Regardless of small or large signal analysis any port noise, port power compression that can
be actually measured compared to the theoretical ideal must be a loss.)

That being the case your most recent blog on ports seems to be a contradiction of your earlier writing?

(Btw why have you not posted a link to where someone can read or buy the paper? Your take on the document may not be the same as an experiment loudspeaker builder?)

Perhaps you forgot what you previously said or you think a port is not a good port unless you understand the paper above?

Before you fly into another blog you might be well advised to leave out your own “ judgments “ and let the findings in these references be available for those interested to draw their own conclusions.

[RMC]

RE POST # 108

Thanks again for clicking on the thread and dropping in consistently we are flattered, as it shows your personal attachment to the thread. We know its getting more and more difficult for you to fake its a lousy thread considering the 5,500+ views. Plus you just can't beat, nor match it with LE8T/4311 stuff...

Looking at your posts one can hardly find any meat, other than the usual go around, dubious claims and beating around the bush.

As for a post regarding QL losses you sure didn't have the guts to show the full original post, like you didn't with what Keele said either, which anyone would normally do to at least try to support what he claims. Not you though, as it may not have served your purpose here by not saying what you pretend... Perhaps it was more "convenient" to make your own "romanced" interpretation of post?

BTW had there been a millimeter of "contradiction", and there isn't, it would have been quite easily and logically explained and understood by anyone, but by your own writings its evident you haven't figured it out yet, or just trying to create the regular controversy that doesn't exist.

In fact, the only contradiction that does exist is the one with your post # 101: "If nothing else it’s a strong reason for closure of this thread. Done and dusted." And you're still here! Definitely, the thread IS quite attractive!

Cheap way to use others as bait or pretext in trying to get, in reality, an easy free copy of the paper for yourself. Its available, coordinates too, but you're just too busy with the fake news to find it. Since you won't really read it, as is evident from you're "reading" of Keele's paper, you might not really need this one. Those who genuinely need or want the paper have probably found it by now. The sudden "circumstantial interest" about the paper is quite revealing about the intent.

As many know already, I don't have a habit of copyrighted material infrigement and violation of author rights, as some others do left and right. "Who cares" will be your answer to that too? Up until such time where there will be no more quality writings available... Quoting from a text for illustration and/or explanation purposes IS permitted as long as reference is mentioned, as I do.

"...experiment loudspeaker builder?)" My understanding on this is that you're talking about others, not yourself, right? Considering many probably have found it already, but not you.

"...you might be well advised to leave out your own “ judgments..." Sounds pretty much like the Emperor is back again, doesn't it? He who's own posts are filled with unsubstantiated judgments and claims! Does that mean you'll follow your own rule or is it good only for others ?

RE Post # 106

"In Alex Bradminoff and Don Davis red loudspeaker book they make reference to vent area equalling cone area"

Though initially this may have some merit, there's more to it in real life that was not mentioned here...

If you knew the book a little more, first it seems you would have noted that "Bradminoff" is in fact Alexis Badmaieff, second the "red" book is called "How to Build Speaker Enclosures", third and best of all is it was published in 1966 (books.Google.com and Amazon.in) or 1967 (Amazon.com) for hardcover. Paperback version 1970?

Not exactly a contemporary reference or a more recent and preferred vented-box Loudspeaker Engineering book or article. Also, issued before R.H. Small's monumental vented-box work was published in JAES in 1973 or so, followed by many other more current articles/books by various people with varying scopes and magnitudes...

"I have seen a 15 inch port on a 2225 system many years ago."

It sure looks impressive when said, but while mentioning 15" port use one should check, also inform, about the feasibility of this practically speaking. Knowing that is even nicer. Since you don't show having done the verification, its a good thing that JBL did cover this issue many years ago:

"... the largest practical port should be used. Computer listings of port choices calculated to limit air velocity inside the port duct will list duct sizes which are normally impractical. A 380 mm (15 in) diameter port is not an unreasonable choice for a 380 mm bass driver, however the necessary length would dictate that such a port might itself have a volume of many cubic feet, sometimes equal to or larger than the original enclosure." (JBL, The most commonly asked questions about building enclosures, from Q. 11, P. 4 of 10. Document not dated, but I've had this since July 25, 2001, date printed; Drew Daniels of JBL may well be the author of this as he wrote a paper with the same title, mentioned in the present one, the latter would appear to be subsequent).

Hence my previous mention of Harman Engineers indicating : "... the largest port area allowable by a given design should be employed..." (Salvatti & al, p.43).

The JBL recommended min./max. box volume for the 2225H is 3-10 cu.ft.(cf), and a box tuning of 40 hz is suggested in two of their papers (see 1). So I modeled in Winspeakerz (QL 7, Half-space) what would be the effect on vent length (Lv) with a constant 15" dia. (176.7 sq. in.) port and tuning frequency of 40 hz, while varying box volume from 3 to 10 cubic feet.

Results I get: 3 cf Lv 88.65"; 4 cf Lv 63.75"; 5 cf Lv 48.81"; 6 cf Lv 38.85"; 7 cf Lv 31.73"; 8 cf Lv 26.4"; 9 cf Lv 22.25" and 10 cf Lv 18.93".

So the shortest vent length would be 19 in. long, that in a 10 cu.ft. box, in which JBL doesn't normally use/suggest the 2225. Instead: 4 cf in Enclosure Guide, 5 cf in model 4507 and 4 cf in the second reference below. The cabinets larger than the preceding are usually specified for other single woofer, e.g. 2240 (6 cf); 2240/2245 (8 cf, as in model 4518); 2241, 2242 and 2245 (10 cf).

Practically speaking, in the type of box volumes the 2225 is typically used, the vent length for a 15" dia. port would need to be at least 4 feet long. Stretching it to 6 cf the vent is still one meter long or so. We have not even mentioned the resonances issue here.

Obviously there's other material that my faithful fan probably doesn't know about, so I will continue my work with another informative post (including some vent stuff!). This way he can keep coming back, though right after someone else came just before him, as he does, to add his own two cents...

1) JBL Pro Enclosure Guide p.1; JBL, Vented Loudspeaker Enclosure Construction and Operation, P. 4.

[grumpy]

Perhaps more DIY and less GFY.

[Lee in Montreal]

RE POST # 108

Thanks again for clicking on the thread and dropping in consistently we are flattered, as it shows your personal attachment to the thread. We know its getting more and more difficult for you to fake its a lousy thread considering the 5,500+ views.

We ?

[Ian Mackenzie]

Nothing l post is ever taken seriously to the point of going “Off Beam.”

At any rate it’s a public forum and anything is open for discussion or debate on any thread.

The forums are NOT a democracy.

Of more amusing tone if l was attempting to collate numerous papers wall papered around the house because l ran out of desk space l would probably fuck up writing about “what he said she said “ more often then not so it’s fun to call out continuity bleeps when they surface.

[RMC]

Hi Grumpy,

Thanks for visiting us. More DIY is certainly a possibility. Especially in consumer speakers, manufacturers seem to prefer showing 3 smaller vents than a larger one for example. Big hole in a box doesn't look good and is less practical configuration wise. Marketing is king as some say.

However, DIY or otherwhise the issue with extra long vent remains when the port diameter is "excessive". Unless one uses a pretty large box of say 10 cu.ft net in the present case. But then this large Vb for a 2225 presents another issue with the driver: getting a proper alignment, with an acceptable response curve.

Since I modeled 8 boxes one after the other for purposes of seeing Lv changes only, not for nice alignment or frequency response appropriateness, I didn't spend time on that aspect, though I did look quickly at each curve generated just to see, but I don't remember exactly each one for each Vb used.

I do remember seeing, in the frequency responses, some where the woofer was not really "at ease" in the box, showing sign of being "overstretched", i.e. getting further away from a somewhat optimal or a reasonably flat LF alignment.

If some folks like it this way, good for them, since its their money and gear. I've seen on this site a number of months ago a fellow using a box tuned lower than normal (as in step-down mode) with no boost/cut filter. Though there are good reasons, mentioned, for not doing this, he liked it this way, although the system may not be performing as it should or could (room gain was not in the picture). Fine then.

Sometimes (also seen recently here) some fellow trying to get deeper bass type of performance from a less capable or inappropriate woofer, just by increasing box size and being confident this would do the trick (bigger being better in their mind), with no step-down mode involved. Even if there's more to it than just that, but this is another matter.

I sure would not use a 2225 in a 8-10 cu.ft. enclosure for example, whereas others may. Folks can certainly build whatever they want or like since its their own thing. In my view the most important issue is, as long as they have the relevant info on a situation, at least they can make an informed choice, optimal or not, and know why...

Regards,

Richard

[RMC]

RE Post # 112

No new technical matters there, as usual. But he remains the thread's most faithful fan and supporter regardless of his go around...

"Nothing l post is ever taken seriously..." This is certainly the most interesting statement from the poster, along with "...l would probably fuck up writing..." Quite conscious revelations! "Off Beam" or not, and straight from the horse's mouth!

The above statements sound pretty much like the poster is telling us viewers around here consider him more like an entertainer, a comedian role playing, or an actor trying to get attention with stuff not to be taken seriously.

Then, poster should look at himself about the credibility issue HE raises and the why of not being taken earnestly. Often people build their reputation themselves, with their own acts. Could be a message the viewers are sending.

"At any rate it’s a public forum and anything is open for discussion or debate on any thread."
Anything, anywhere, being good enough just to create fictitious debate in threads, regardless of facts? Is that the mission statement?

"The forums are NOT a democracy." Well, he sure added quite a few "votes" here. With numerous options to choose from on the "ballot", and consistently choosing this one freely, one can't avoid seeing this as real democratic support on his part. Can't get anymore democratic than that, since in totalitarian regimes there's only one name to choose from...

Sure quotes from knowledgeable sources in audio bug him a lot, particularly when stories told don't match with reality and audio engineering. When a bleep really surfaces or rather when he THINKS he sees a bleep because he doesn't understand, or fakes the imaginary one for convenience?

Nice try, but even more amusing is the fact he still hasn't shown any alleged "contradiction", nor any LE8T/4311 stuff btw, that HE said people want to know about! As he won't deliver on these, he could still be debating the stuff with himself and show his skills while doing it. No wonder he's not being taken seriously...

[RMC]

F1A) CONSTRUCTION DETAILS

The fellows wanting to clone boxes mentioned in the Kramer/timbers article regarding assisted designs or not should look closer at the construction details and box volumes given in that paper as some of that stuff doesn't seem to make sense in real life. I don't know if someone here has raised these concerns in the past, but here are my issues.

There are basically three cabinets identified in the article: 4.5 cu.ft./2235H (equivalent to B 380 subwoofer), 8 cu.ft./2245H (equivalent to B 460 LF speaker) and 12 cu.ft./2245H box in two versions, the difference between the latter two being the duct length. The boost/cut filter used in some isn't a box physical issue covered here, but rather an electronic equalization matter. The box plan in post # 26 gives more details on the 12 cu.ft. cabinet than in the article.

In the construction details given on page 5 of the article for the 8 cu.ft. cabinet, one-inch thick particleboard is recommended, 50-pound density or more, "for the requisite acoustical deadness". The panels should be braced with 2 X 4s. There is no front to back brace used in the plan, e.g. from the baffle brace to the back panel brace, I assume since it would not be centered because of the woofer. Still a rigid box considering the 1" material and the 2X4s.

The construction details of the 4.5 cu.ft. box are the same, except vent, 3/4" thick material use and "For the smaller panel sizes of this enclosure, 1 X 3-inch braces are sufficient." P. 7

Things are getting more "slippery" for the 12 cu.ft. one, when compared to the above two boxes... Even though at least 3/4" material is indicated, the plan was in fact made with that material thickness, and no mention of Baltic Birch use for example. As for the panel braces, they're all 1 X 3 inch pine mentioned on the plan. A 50% larger box (12 cf) gets thinner panels and bracing than an 8 cf enclosure with the same driver!

The 12 cu.ft. box has an Fb of 20 hz in the assisted version (thermally limited down to 18 hz!, except for a 1 db or so restriction on a 10hz portion, as mentioned before; all this subject to my earlier mention of halfway done step-down data). This is 5-6 hz lower Fb than the other boxes mentioned here. Now, if one compares box sizes involved (4.5, 8 and 12 cu.ft) with the construction details given above and the lower frequencies to be reproduced, the latter one's material/bracing is quite questionable. Someone dropped the ball at JBL?

3/4" and 1 X 3" might make sense for the 4.5 cf enclosure. Yet It wasn't good enough for the 8 cf box, but its presented as if it is sufficient for the larger 12 cf cab, both using the same 2245H. Since larger panels are more at risk of vibration than smaller ones, it seems logical to me and technically sound to indicate the use of 1" material and 2X4s first and foremost for the 12 cf box, instead of the 8 cf box, or for both of these. The "requisite acoustical deadness" certainly applies, even more so, to the largest of the boxes...

Cloning enclosures looks nice and easier considering the ready-made recipe. However, one should still use judgment in the making, as some recipes would likely require nuance or fine tuning.

More to come.

Richard

[Lee in Montreal]

Dear Richard. You do not realize how annoying you are with your self pumping ego as all you do is copying articles off the net. Have you developed anything? Did you reach a breakthrough? What did you build? Effing nothing is the answer. Is there any point to your latest rambling or is that your ego feeling hurt? Come on. Stop being pompous. You're ultra annoying. Oh, and people don't contradict you simply perhaps because most people don't even care. Did you realize that?

[Ian Mackenzie]

http://www.audioheritage.org/vbullet...OWN-MODE/page2

Hi Lee can l suggest the ignore button. As long as “it” pontificates here in this thread and stays away from populated public places no one will ever care:

The above link states at least 3/4 inch particle board or void free plywood.

At “least” being the point.

I do agree with your comments.

The reality is RMC has come to these forums with no familiarity of Jbl product or heritage.
The critical and rather judgmental postings have no real substance or plausible merit.

If anyone, a “ normal “ person identified real mistakes or short commings in an article they would first seek validation by their peers. They would then make an effort to contact the authors for comment and feedback. He does not do this because there’s no real basis for the criticism. It’s just slanderous negativity.

The inflammatory nature of the postings is such that when l did post feedback from DB Keele Jnr with approval of the administrator on how the step down tuning works he launched into a personal attack and vendetta.

The official feedback was Really?

He just being a little prick because he enjoys it.

[Ian Mackenzie]

For those interested in this topic l contacted the author of the paper below requesting clarity on the EV step down implementation.

The author kindly responded with the explanation below.

There are 3 steps:

Step 1
You just tune your vented box with two identical ports which tunes the box to a conventional 4th-order HP Butterworth alignment.

Step 2
You then cover one of the ports which drops box tuning down about one-half octave ( x 0.707 fB).

Step 3
You then EQ the response with a second-order HP filter with a Q of 2 (boost of +6 dB) at the lowered resonance. This changes the tuning to a 6th-order HP with the lowered f3 about one-half octave below the original fB.
The paper explains all this. See Figs. 2, 3, and 4.


http://www.xlrtechs.com/dbkeele.com/...Alignments.pdf

For those interested the facts above and most useful post in this thread

[DES-1]

can l suggest the ignore button.

AH, that's where the ignore button is

[Ian Mackenzie]

In reference to comments made concerning baffle panel thickness and bracing dimensions my suggestion is as follows.

Follow the article holistically. Read the text with the plans and study the notes on the plans carefully. The article gives recommendations for construction and offers latitude for a choice of enclosure options. Minimum material requirements are given.

http://www.lansingheritage.org/html/.../1983-subs.htm

On Interpretation of the different plans one needs to appreciate the mass (weight) and practicality of moving a 12 cu ft enclosure using using thicker panels and bracing than the minimum specified. Note the bracing has been scaled to the panel thickness it is fastened to. There is absolutely no point making something you can’t move! (Ref post 26)

Those of us with real practical experience who have been down the path of large enclosure construction can guide anyone interested in these types of enclosures on the forums.

The JBL Library has some great references for enclosure construction.

http://www.lansingheritage.org/html/.../jbl-plans.htm