Advice on replacing LE15A 'bottom end'

[scorpio]

Hi all,
I perused the archives in this site, but I am a little confused, in part because there is too much to read!

I currently use a 2 way system, based on a LE15A in a 5.5 cuft box as per JBL guidelines, this is crossed to LE85 at 800Hz. The problem is that the LE15A are showing signs of aging, and have strange impedance curves (both have lost their impedance peak at resonance frequency...). The system sounds good to my ears (I can't compare it with anything close to where I live), but it bothers me a lot.

To adress this, and also because I like woodworking as much as hifi, I would like to design a new 'bottom end' to my system, with some limitations:


No less than at least 97 db efficient (I use a 2A3 triode amp, and that one is definitely not going!)
Max volume if possible inthe 6-7 cuft range (I have a small room)
Could be based on single or double woofers, 12 or 15", I have no preference
lower frequency as low as possible (30 Hz or lower? would like to avoid subwoof - again problem of a small room that needs to keep some empty volume for me and the rest of my stuff!)
I read a lot about 2235's, but they would be borderline to what I want (higher box volume for housing a pair to have the right efficiency).

Any other suggestions to make?

Thanks a lot for the help, I realize I still have a lot to learn, but then, I only started this way 2 yrs ago!

Cheers,

[Zilch]

Do we know the relative efficiencies of LE15A and 2235H?

Consider merely swapping 2235H into your present setup, perhaps....

[Mr. Widget]

Do we know the relative efficiencies of LE15A and 2235H?


LE15A 94dB
2235H 93dB

[Robh3606]

"The problem is that the LE15A are showing signs of aging, and have strange impedance curves (both have lost their impedance peak at resonance frequency...)."

What surrounds?? If they are the original Lansalloy and they are stiffening up that could explain the curves and the low end.

Rob:)

[John]

Off the top of my head I kind of thought there was more than a 1db. spread between those woofers:hmm:

[Mr. Widget]

That is the JBL spec. I just double checked and my foggy brain was correct.

Numbers like that don't really tell the whole story though... just an indicator.

Scorpio,

If a 97dB efficiency rating is of paramount importance and you need bass below 50Hz, I'd suggest you use 2242s with the high efficiency mid bass driver of your choice above. You could pack these into a 7 cu ft box.


Widget

[scorpio]

mmmh,
The 97dB comes from the data I had showing the LE15A clocking at 96.7 dB, and the dynamic I get being perfect for my amp set up - I'll have a closer look at these specs, I did not realise the 2235 could be so close to the LE15A.

I would like to avoid as much as possible going to 3 ways, I am in favour of keeping things simple if possible, even if it is not based on any good theory!

Thanks for the feedbacks, I'll check the 2235 again, around here when you can find them they seem to be cheaper as well (not much!)

Cheers

:bouncy:

[Robh3606]

Take a look at a 2234 while your at it. You get another 3 dB so for at 96dB and the lowend isn't all that bad. Use 2 if you can fit think 4435.


Rob:)

[Zilch]

I would like to avoid as much as possible going to 3 ways, I am in favour of keeping things simple if possible, even if it is not based on any good theory!Not hardly. :)

The theory is quite sound:

http://www.audioheritage.org/html/profiles/jbl/4430-35.htm

What horns are you running your LE85's on? Are they still 16 Ohms?

If so, find some 2344A horns and build NL200t3-16 crossovers for them.

Explore the possibilities!

Here, today, with LE14A:

[John B]

1 or 3 db difference in efficiency depends on whether you are measuring at 1 watt or 2.83 volts. 2235 are 8 ohm, LE15 are 16 ohm. Specs per BB6

[Mr. Widget]

That makes sense... I wonder where JBL got their 94 dB rating?

The whole deal is rather arbitrary anyway as unit to unit variation will be greater than a dB or two and the impedance below 100Hz will rise quite dramatically for either of these woofers based on the cabinet loading.


Widget

[Zilch]

Does 2A3 triode amp deliver more power into lower impedance?

2234H per BB6P:

[scorpio]

Even if it does, it's not going to be big, it's only 3.5 W to start with, but those are very good Watts (as someone else was saying, if the 1st W sucks, why have 200?).

Thanks all for the data, I think it begins to make more sense to me, I did not realize the 1W vs 2.83V would give different data, somehow thought it was the same measurement.

Any 12" you'd recommend beyond LE14A's? Just checking as this could give an opportunity for a slender cabinet.

[scorpio]

Zilch, you asked

What horns are you running your LE85's on? Are they still 16 Ohms?


The LE85 are original, still with the wax seals - but I think they are numerous threads around this site pointing out that they are all rally 8 Ohms.

I am using them on home made 400Hz round horns based on JM Le Cleach' s hypex expansion scheme, and using the original crossover from the LE200b the driver was salvaged from. I am currently rebuilding the Xover with new, higher specs components, keeping in there the HF equalisation (thanks to your comments from a previous thread)

Cheers,

[Zilch]

All of the ring radiators are really the same impedance, no matter what the foilcal says, but your original LE85's are actually 16 Ohms, nominal. Same for 2420's, the pro version.

8-Ohm diaphragms to fit them became available with the introduction of the 4430, I believe.

There's better Heritage historians than me here, if I've got it wrong. :p

2.8284 Volts across 8 Ohms yields 1 Watt of power; the specs are the same only if the impedance is 8 Ohms.

I forgot that, too.... :blink: