Diy project, need your help!

[maxserg]

My K 145 were reconed vith the E-145 type suspension (M roll) I don't know the real parameters presently. I'd like to make a new enclosure versus the one I have (4,5 cu ft according to JBL plans) I could go around 7 cu ft in a bass reflex enclosure. What should I measure with for res freq with ohm meter and audio generator (that's what I have presently)?

This project is going to be a 3 way system mainly for music and occasionally video films or live music shows...

Components are: JBL K-145 reconed, AE TD-8 M, JBL 2420 with McCaully horn lens (9 inches)

I want to use these components even under their natural bandwidth. I will use the DCX 2496 3 way stereo electronic Xover with great flexibility, (delay, choice of different xover types, etc) Xover choice (not final) From bass to 300HZ, 300Hz to 2KHz for the AE TD8M, and 2kHz to end for the 2420.

I already have a a fully revamped Phase Linear 700B for bass, a Crown D-150 for lo-mid and I have to find an amp for the 2420... It is a project for the long run... I'm not in a rush.

And another question: Should-I use two separate enclosures, one for bass and the other for lo-mid to high speakers?

I want to make cabinets from Baltic Birch (I can get, even 4X8 sheet of any thickness) probably 3/4" and well braced for bass cabinet.

Any suggestions are wecome!

Sorry for my english

[Ian Mackenzie]

Okay

There are lots of ways to approach this but if you have no experience of the individual drivers you might be best to get the woofer enclosure right first

There is a degree of speculation on the E145 box tuning
The Jbl enclosure guide says 4 cu ft3 tuning at 40 hz (musical instrument)
Elsewhere the VAS publication is wrong , it should be 427L

Even in a larger enclosure you are not going to get deep bass. It will get down to the 40 hertz region and fall off quickly after that. It’s not going to sound like a 4 way 4343 with an extended bass woofer. It’s just won’t.

But it will be fast natural bass...
If you want deep bass add a sub woofer
In a hifi application as near as we can tell JBL did the Everest with 8 cu ft and carefully tuning with the added dcr of the woofer crossover coil to get a balanced bass

You are going active so you can EQ a bit to get the right balance

You need to understand the woofer and your expectation of bass?

Read this thread http://www.audioheritage.org/vbullet...se-of-JBL-E145

With the mid range driver it’s all about how the driver behaves on the baffle.
I would place it a bit off centre on a wide baffle to avoid bumps in an otherwise smooth driver

[maxserg]

Thanks for your comprehensive answer! This why I should maybe go with two or tree separate enclosures, making a smaller enclosure for the 8 inches maybe just what it needs for the lower part of the xover at 300hz hi pass, something like just enough to contain the speaker... with depth necessary for total volume requested...

[Ian Mackenzie]

Use a Sono tune or golden ratio for the mid box.

But make the baffle the width of the woofer box.
If you think you might swap out drivers you might decide to make the baffle a split baffle for the woofer and mid and the horn sets on top. That way you can adjust the crossover by moving the horn back and forth a little bit and if you want to change direction of the project you can simply put in. Anew baffle

I would leave it as flexibility as possible until you gave a fair degree of certainty with your drivers and design.

A lot of diy loudspeaker people have the belief that they should be able to complete a design on paper then build it exactly to the last detail.

In theory yes but in reality with acoustics and drivers there is always going to be something that needs changing to get it right. Even the most experienced loudspeaker engineers do this.

[maxserg]

Many thanks for your suggestions🙂

[Robh3606]

But it will be fast natural bass...
If you want deep bass add a sub woofer
In a hifi application as near as we can tell JBL did the Everest with 8 cu ft and carefully tuning with the added dcr of the woofer crossover coil to get a balanced bass

You are going active so you can EQ a bit to get the right balance

You need to understand the woofer and your expectation of bass?

With respect to E-145's you really do need to know what to expect. Even though they look like can EQ them it just doesn't work. There is no weight or real power in the first octave bass, it's there but its thin if that makes any sense compared to what you get with a subwoofer. I have B380's/2235s under mine as subs and that is actually a very nice match. You get the speed and the weight with the combined response.

Rob

[Ian Mackenzie]

Totally

The efficiency, box resonance and Xmax are laws of physics you can’t argue with

In the link below a white paper by John Eargle discusses the bass response of the Everest.

At 100 dB sensitivity it opens the window for life like dynamics.

Keep an open mind and let your ears be the judge.

[Ian Mackenzie]

Some accurate information here

http://www.audioheritage.org/html/pr...bl/everest.htm

http://www.audioheritage.org/vbullet...ll=1#post54019

http://www.cieri.net/Documenti/JBL/T....1,%20No.3.pdf

There are a number of subtle things as a diy builder you can do differently to the commercial build that will make it more flexible. The thing is Jbl had to market a stand alone design that would be acceptable to the market.

Ie you are not wedded to a full passive full range high sensitivity loudspeaker for the 5 Watt Triode Guys

You have your active crossover as an ace card and you can play with different enclosure volumes if you plan to incorporate a sub as Robert did.

As Robert said you still need to know what to expect out of the E145? You might be happy with the 8 ft3 tuning or you might decide to use the E145 as a mid bass woofer in a smaller box with a sub doing the 1st octave.

The best way is to make a test box (8 cu ft3), mess with the tuning until you get the best balance, stiffen with braces it as best you can and listen. You will gain a lot of experience and insights by doing that.

You can always make it smaller.

Here is an interesting discussion on the E145 and other choices
http://www.audioheritage.org/vbullet...-vs-2235/page2

There is always latitude for evolution of your sound. It’s does not need to be perfect on day.
one. You will actually have more fun messing around with option along the way than the end result.

At that point it made sense to build a clone of the 4 way 4345.

If you have not used a Jbl 4 way before you might say hey l like it on more most music l play and l will use a sub when l need it.

On the other hand if you are like me and have used a Jbl 4345 with a 2245 under the hood for years you might pitch straight for a sub and use a smaller enclosure for the E145.

But it’s your call.

[maxserg]

Thanks for the good reading!

[Ian Mackenzie]

I had this Bassbox software simulation saved and thought you might be interested.

In the first image the cyan curve-normalised amplitude response is the simulated maximally flat bass response. The recommendation is an 81L ported enclosure tuned to 51 hertz. The yellow curve is the simulated custom 225L ported enclosure tuned to 40 hertz.

What are the Magenta curves?
Magenta curves are the addition of a very modest room acoustic boundary effects as measured in my listening room. This give you an indication of the effect of a listening room below 100 hertz when evaluating bass reflex response simulations.

In relative terms the maximum boost of the bass tone control on a vintage integrated amplifier is typically +20 db below 100 hertz. The human ear is actually fairly sensitive to overall level changes in bass around 40 hertz referenced to mid band frequencies. The open low E on a bass guitar is 41 hertz. Also to be taken into consideration are the listening room room dimensions, loudspeaker room placement and listening position that can also impact on the smoothness of the bass response of the loudspeaker. So there are several things that can impact on your bass response but its nothing to loose sleep over.

Back to the Magenta curve the f3 (-3 db) in room response simulation is in fact 40 hertz with the 40 hertz tuning. The port output falls sharply below 40 hertz and the level is -6 dB down at 36 hertz.

So the thing is you need to know if you are going to be comfortable with a bass response down to 40 hertz? As JBL says in the Everest literature it was an acceptable compromise given the high sensitivity of the system (100 db).

You can see that the smaller 81L enclosure has very little bass extension and would be a less attractive option unless you definitely plan using a subwoofer below 50-60 hertz.

The other thing to appreciate with high sensitivity woofers like the E145 is the tradeoff of enclosure size versus bass extension.

For comparison purposes I did another Bassbox simulation (see second image-cyan curve normalised amplitude response) with a lower 34.6 hertz port tuning in a 225L enclosure just to see what would happen with the bass extension? There is no impact on bass extension but the midbass is about +1.5 db higher with the 40 hertz tuning (see magenta curve)

The simulation conditions were QL =7 and corrected Vas =427L per the other thread. Fibreglass lining of 25mm on 5 internal surfaces.

Empirical enclosure tuning
Its important to note that JBL tuned the ports in the Everest based on auditions in a typical listening environment(s). I would urge you to do the same in your environment (see the white paper).
JBL know that they are doing and have decades of experience in diverse applications with their drivers so its worth paying some attention to that before making saw dust.

You can vary the port tuning and workout what really gives the best result for you in your environment.

Do not get get bogged down with the simulations or pay too much attention to people who spend hours working on the perfect simulation without ever building an enclosure.
The simulation won't tell you what it sounds like in your environment. Just confirm the maximum enclosure size you can accomodate. If the desired bass response falls within that enclosure size you are in business.

Finished enclosure size
The exterior enclosure dimensions will also need to account for the side wall thickness and everything that will occupy space within the enclosure like the driver, ports, the mid range enclosure and bracing.

Future plans
Looking outside the square with a box that size you might at some stage want to consider a 2245H which in the 225 L 30 hz tuning has f3 of 33 hertz and double the displacement .
This is in fact the same size and tuning as the pro vintage JBL sub using the 2245H. That might be an evolutionary plan if you were keen on the 225L box for the E145 and in the end felt the the urge for deeper louder bass particularly as you plan to use the 2123H mid cone driver.

*The 2245H is 95 dB sensitivity and can be used in 8-10 cu ft enclosures up to 300 hertz with tuning 30-27 hertz respectively.