Truextent Diaphragms in JBL four-inch compression drivers

[originaltubino]

Compared to the others, the Truextent diaphragms do not appear to have any special FR extension in the 14K to 20K range.

The Yuichi and Edgar do not differ as much as I expected. This is all on-axis, right? Both are pretty well-behaved.

THANKS for doing this and sharing it!

[timc]

I'm surprised that there are acutually less HF extension with the Be diaphragm than with the original Ti's.

Any idea why?

[Zilch]

I'm surprised that there are acutually less HF extension with the Be diaphragm than with the original Ti's.

Any idea why?

Absence of the diamond surround, perhaps....

[timc]

Could be. Softer surround (higher compliance) should reduce HF extension. Good call Zilch.

[Ian Mackenzie]

Here is a link to Yuichi's own measurement.

http://www.geocities.jp/arai401204/H.../A290-S90.html

I dont have a 2445 / 2446 core to compare but my own measurements of the 4001 confirm the HF extension.

With a simple two stage passive EQ / impedance circuit per Tads design its quite easy to get a flat response and impedance from 600 hertz response to 18 khertz.

Controlling or should I say damping the impedance has a marked effect on sound quality.

I expect the Tad diaphgram surround and the 4001 phase plug play a big part on how it performs on paper. As to subjective impressions its a matter of taste.

[4313B]

Compared to the others, the Truextent diaphragms do not appear to have any special FR extension in the 14K to 20K range.

The Yuichi and Edgar do not differ as much as I expected. This is all on-axis, right? Both are pretty well-behaved.

THANKS for doing this and sharing it!

They are nice horns. Yes, this is all on-axis. I did a few off-axis shots just to see where the horns started dropping off. I was especially curious as to how tight a sweet spot the Edgar might have.

Here is a link to Yuichi's own measurement.

http://www.geocities.jp/arai401204/H.../A290-S90.html

I dont have a 2445 / 2446 core to compare but my own measurements of the 4001 confirm the HF extension.

With a simple two stage passive EQ / impedance circuit per Tads design its quite easy to get a flat response and impedance from 600 hertz response to 18 khertz.

Controlling or should I say damping the impedance has a marked effect on sound quality.

I expect the Tad diaphgram surround and the 4001 phase plug play a big part on how it performs on paper. As to subjective impressions its a matter of taste.

Thanks Ian. That link was helpful. I know nothing about these Yuichi horns. They look and measure nice. I'll have to hear a pair someday.

It looks like he got a bit more extension from his 2441 than I get from either of mine. I tried both on the Yuichi and determined that they were probably a wee bit low on flux density. That's why I pulled their diaphragms and put them in the 2445 core.

I'd like to see a schematic of the Tad circuit.

Softer surround (higher compliance) should reduce HF extension.

It does. The Truextent uses less beryllium as well as the soft surround (as compared to the 476Be diaphragm) with the result being reduced extension. The Truextent also has a bit higher distortion according to JBL's measurements.



The titanium and aluminum diaphragms can't really compete with the sound quality of the berylliums. The Tad and JBL four-inch beryllium compression drivers are very expensive (and in the case of the JBL, nearly impossible to get). These aftermarket beryllium diaphragms offer excellent cost/performance.

THANKS for doing this and sharing it!

You're welcome. I really don't enjoy handling other people's beryllium diaphragms and swapping them around in various cores. Everytime one is exposed I get real nervous.

When I ran the impedance curve on the second 2445 with the Truextent installed I didn't like the way it sounded. There were unwanted resonances. I opened it up, cleaned out the little bit of mold on the felt in the backcap and then cleaned the gap out (there were a few metal particles in the gap) and then reassembled it. That fixed the problem. I'll check the first 2445 (the one with the mold) today so Dan can get two fully functional drivers back. Don't use Arlene's glue in these back caps guys. I used the Moyen recone glue in my 2445J's and there weren't any issues.

[Ian Mackenzie]

I will try and find the schematic. Its a lot simpler then you might imagine.

Yuichi also has a 1.5 to 2 inch adapter for using 1.5 inch drivers (people with Tad 4003s are not complaining..except for the price)

What you have measured about these alternative Be diapgragms is consistant with what I have been advise by company that uses Truextent diaphragms in field coil compression drivers with a Tractrix horn, hence they use a Be super horn tweeter above 16 khertz. The tractrix horns are apparently subjectively better then the Tad 4001 horn but you need a super tweeter.

So don't throw out your 2405s yet.

I am inclined to think the 0476 with the bi radial is still the winner.

What this means is as usual there is no free lunch but you can have fun making it work.

The notion of a flat response to 20 khertz is more important on paper to the Japanese than it is subjectively anyways provided the diaphragm is not in breakup mode too early.

A gentle tappering off above 10 khertz can be a good thing in some situations

I think Greg has mentioned this before.

By the way I got some complaints from the local natives attempting to run a series external ground plane measurements with LMS. 2.83 volts at 110db sensitivity above 10 khertz is freakin loud if you are a dog I guess.

Ian

[cooky1257]

That's a shed load of work for the benefit and enlightenment of us all.
Thank you.
Anyone tried a Yuichi 290 with a 3" Be driver?.....Doh! thanks Ian.

[Robh3606]

Hello 4313B

Thanks for measuring and posting all those measurements.

Rob

[cosmos]

Thanks 4313B for doing these measurements. As it turns out, I am even more glad as you uncovered and resolved a couple problems as well. I can't thank you enough for that!

If I am interpreting this correctly, the FR looks very similar to the stock Titanium diaphragms they are meant to replace. That is probably a good thing in some respects as it allows a similar compensation scheme and at the same time offers significantly improved quality of sound.

Ian, I am looking forward to seeing the schematic of the TAD compensation circuit. In addition, I'd really like to see any other adaptable compensation networks. Getting reasonably flat to 18KHz without a tweeter and with this quality sound would be a dream come true for me. I've heard these drivers with the TrueXtents and they sound great to me.. besides, I already own them..

476Be would very likely be a better driver, (I have never heard them) but these are reasonably priced and readily available.

Now, I really wonder how TAD TD-4001 would measure in the same setup.

In any case, Thank you again for your time and help!

[originaltubino]

476Be would very likely be a better driver, (I have never heard them) but these are reasonably priced and readily available.

Claude Rains(Louis):The waters? What waters? We're in the desert.
Humphrey Bogart (Rick): I was misinformed.

Now, I really wonder how TAD TD-4001 would measure in the same setup.

Me too, and with the compensation scheme Ian mentions.

That's the problem with generous competence. It only gets you more work requests!

[spkrman57]

First off I would like to point out that the 350hz Edgarhorns are mine and are the ones in my avatar.

I had tried some EV DH1A compression drivers on them in the past. Dan (Cosmos) also heard them when he visited me before. We both agreed the HF extension was decent enough(passive crossover @ 800hz using passive attenuation/EQ), but the "simbilance" or what I call the "titanium sound" was readily evident.

I plan to use a 4-Pi (Wayne Parham) 1.6khz crossover w/JBL 2226J's on the bottom end w/JBL 2446 compression driver equipped with Be diaphrams as soon as I can afford to make that happen!

I see with the 2446/Be/Edgarhorn plots that the 1.6 khz region looks to be fairly flat response wise. I don't know enough to extrapolate all the info here so I'm actually speculating!

Thanks a million for the help 4313B!!!

Regards, Ron

PS: Did my e-mail with the att/EQ chart help show what Wayne is trying to do with his crossovers?

[eso]

First off I would like to point out that the 350hz Edgarhorns are mine ..

I'm curious about where the Yuichi's came from. There's not many of those floating around and I just sold my old pair to a buyer in Ohio...

Do they look like this:





eso

[4313B]

If I am interpreting this correctly, the FR looks very similar to the stock Titanium diaphragms they are meant to replace. That is probably a good thing in some respects as it allows a similar compensation scheme and at the same time offers significantly improved quality of sound.

Yeah. I did measure the 2421B, 2441, 2445 with Truextent, and the 2446H (before I started swapping diaphragms and cores) with the stock 4344/4345 network last Sunday and none of the 4-inch drivers are a bolt-in without tweaking the network (or using EQ like Bo does).

As far as compensation schemes, I was thinking about trying to put together one of Wayne Parham's real quick as per Ron's email to everyone. I'm not sure I will get to it today though.

First off I would like to point out that the 350hz Edgarhorns are mine and are the ones in my avatar.

I plan to use a 4-Pi (Wayne Parham) 1.6khz crossover w/JBL 2226J's on the bottom end w/JBL 2446 compression driver equipped with Be diaphrams as soon as I can afford to make that happen!

Send me some values so I can see what I have around and I'll measure the results if possible before all this has to be returned.

I see with the 2446/Be/Edgarhorn plots that the 1.6 khz region looks to be fairly flat response wise.

I'd have to look at the raw data again to confirm that. These are half octave plots without all the warts. They're good for trend analysis. We'd have to look at the rough stuff while actually building any networks.

PS: Did my e-mail with the att/EQ chart help show what Wayne is trying to do with his crossovers?

Yes. But give me some values for your application. I don't want to have to figure anything out right now. Just toss me some values.

[spkrman57]

Using my chart on the e-mail I sent out:

R2 20 ohms
R1 60 ohms
C1 .2 ufd

This is for approx 15 db attenuation/EQ on a 1.6 khz crossover which is the closest I can find for the difference between the JBL 2226 @ 97.4 db/watt and the JBL 2446 @ 112 db/watt if I have the information correct.

The crossover I plan to use is the one I sent you the schematic of. I adjusted the values to reflect the 16 ohm LF and HF drivers I'm using (ie: 2 x coil/resistor values and .5 x cap values).

My application is for passive crossover vs the active bi-amping that Rick, Brad and Dan are going to use.

Thanks again 4313B!

Regards, Ron