Amplifiers capable of dual woofers?

[Dr.db]

I would like to build a passive diy-speaker using 2 lowfreq. woofers.

Unfortunatelly almost all JBL´s like the 2235, LE14h, 1500FE, 2216nd are 8ohms... Using 2 woofers per box sums up to 4ohms nominal impedance. But I expect the minimum impedance to be as low as 2-3ohms...

Most amplifiers are 4ohm stable.
I´m talking integrated amps, not seperate amps.
What happens when I run dual woofers as described which could have a minimum impedance even below these 4ohms?

Looking at the JBL DD67000 Everest it claims 8ohm nominal impedance.
Resulting in 8ohms total the dual 1501al woofers should be 16ohms each I guess... That should be easy to drive for amplifiers...
But the older 4435 had 4ohms nominal impedance with the dual 2234 being 8ohms each...
Same with the Westlake Audio BBSM-15 with dual JBL 2235 woofers... Westlake claims 4ohms nominal and 2ohms (!!!!!) minimal impedance.
Now that should be much harder to find a capable integrated amp?

Best regards,
Olaf

[RMC]

Hi Olaf,

RE "But I expect the minimum impedance to be as low as 2-3ohms... (...) I´m talking integrated amps, not seperate amps. (...) Now that should be much harder to find a capable integrated amp?"

If you have an impedance curve for the driver you plan to use this would help you be sure about minimum impedance presented to amp or choose speaker model accordingly.

In any case the following is about my older NAD integrated amplifier.

First pic from owner manual and second pic from amp tech sheet. I assume more recent models might have kept that two-ohm driving capability? Regards,

Richard

8754787548

[Dr.db]

Hi Richard,

thanks for the specs on the NAD amps.
These should work....

I had a look at models like the Accuphase E-480 or Yamaha A-S3000. They state the usual 4-16ohms impedance requirement for the connected speakers. No additional infos...
Looking at the big Parasound separate amps they state 4ohms impedance too, but impedance dips to 1,5ohms possible.
The informations you can find are very incosistent between different brands.

I mean nearly every loudspeaker on the market with a nominal rated 4ohms impedance will have impedance dips below that. So a laymen should think an amplifier that is rated 4-8ohms should work with a speaker rated at 4ohms nominal impedance, right?

[Mr. Widget]

I would make a short list of amps that appeal to you and then I would send emails to the manufacturers and ask if they feel their amps will be stable under your conditions. They will know for sure if their amp is stable at sub 4 ohm impedances.


Widget

[BMWCCA]

I realize you specifically mentioned "integrated" amps but why limit yourself if you're buying anyway?

Every Crown amp I've ever owned has been good to 2-ohm load. I think that's still their claim.

I don't recall seeing a budget but a vintage Crown PS-series amp is one tough amp, hard to kill and fairly cheap to buy. :dont-know:

I still own everything from Soundcraftsmen, Carver, JBL/Urei, to Adcom and always seem to come back to the Crowns.

[Dr.db]

@widget:
That´s a good idea, for shure. Right now I´m not looking to buy a specific amp, I`m rather trying to figure out if such a project makes any sense.
If I would know that most amps wouldn´t work with dual 2235 etc. I would try to come up with a different speaker layout....

@BMWCCA:
I would like to use a single device for amplification and keep it simple.
I don´t want a huge pile of equipment in my rack...

[Mr. Widget]

If the plan is for a system with dual 2235Hs, I doubt you'll have too much trouble. Years ago on my 4355 clones I used a Hafler 9505 and a handful of other amps on the woofers with no issues.


Widget

[RMC]

Hi Olaf,

RE "I would like to use a single device for amplification and keep it simple. I don´t want a huge pile of equipment in my rack..."

I've had a few integrated amps over the years and the only one i kept for a long time, about 20 years now, is the NAD. Haven't kept a lot of hi-fi stuff, the NAD, turntable/cartridges, pairs of speakers & phones that's about it, all the rest is pro gear. The reason i hold-on to the NAD is its intelligent and useful features in one package, not often seen. The 2 ohm capability is only a part of the story.

Some other examples. The amp/preamp sections can be used together or separately as pre out/amp in with the use of two "U" shape metal jumpers plugged in or left out, very simple. The impedance selector switch mentioned in my last post is useful, but the user activated soft clipping switch is also quite interesting in a "single device" setup as you mention. A too ambitious user with a single amp may get into clipping trouble faster than in a bi/tri-amp setup. Soft clipping here reduces the risk of damaging tweeters for example ("gently limits the output waveform").

The bass EQ, separate from tone and loudness controls, provides a switchable +6db@40hz then a LF filter rolls-off sharply (rings a bell with you?) That may be used with certain speakers and is similar to boost/cut filter in a LF B6 aligment (I also have two EQs that can do this, one more extensively than the other since it has variable 20-200hz low-cut filters). The NAD also has a separate and switchable infrasonic filter -3db@15hz/24 db per oct. so gone is the LP garbage. Finally, that integrated amp requires 1V for rated power, pretty standard, but the preamp output is rated 12V/600 ohms, meaning it can drive about anything. Regards,

Richard

[Dr.db]

@widget:
Very insightful, thanks for sharing your experience.
The LE14H-3 should behave similar to the 2235h as they use the same motor and voicecoils, shouldn´t they?

I had a look at the Array 1400 spec-sheet.
It claims 8ohms nominal impedance, but 5ohms minimum impedance. If I would run dual LE14H-3´s in parallel that should result in 2,5ohm minimum impedance? That seems pretty risky for an amp, doesn`t it?



@rmc:
I liike NAD amps as well. In fact, I own the C165 and C275 units... But these are used in a different system. The C375 would deliver the same result as an integrated.
And for dual woofers I would like a little more power output than 150w...

[Mr. Widget]

I am not sure about the impedance load of the LE14H-3, but I do not think that is a good pairing from an audio perspective. If you want to use this size driver, the LE14H-4 would be a much better choice. I just don't think you will ever achieve a smooth extended response with a pair of LE14H-3 woofers in parallel or in a helper woofer model.


Widget

[Dr.db]

Could you please explain your thoughts?

Why shouldn´t dual LE14H-3 work if dual 2235 work?
I would use these below 300hz...

[Mr. Widget]

I didn’t know you were planning on using them below 300Hz, but I suppose it has to do with your intended purpose, crossover frequency, and performance expectations. Assuming a normal crossover frequency above 500 Hz or so, neither the 2235H or the LE14H-3 will work well. If you follow the model of the 4435 design with the 2234H woofers in the augmented bass fashion then the crossover can be much higher and the performance is quite good. I suggested the LE14H-4 with this in mind.

Getting back to the limitations of the LE14H-3, it won’t give you as deep of bass response as the 2235H. It is an awesome woofer when used in a moderately sized system, but when you use two of them you are no longer working with a moderately sized system and I just feel that there are better options. Two of these woofers brings the sensitivity up a bit and the power handling up a bit, but for the size enclosure required for the pair there are many other woofers out there that can match this level of performance.


Widget

[Dr.db]

I get your idea of an augmented bass similar to the 4435 or everest models. You´re absolutly right, for that purpose the LE14H-4 should be the choice.

I´m looking for woofers that are smaller in size than 15" woofers, as I would like to build a similar frontbaffle like the westlake audio 4-ways... But using 15" woofers the enclosure just gets too wide. So either 12" or 14" woofers with their square baskets. Hence I came up with the LE14´s...

I always thought of the LE14H-1 and LE14H-3 to be some kind of smaller 2235H. Similar in frequency response and sound, but a little less output.
Actually I´m a little bit surprised you´re saying the LE14H-3 won´t go as deep as a 2235H :blink:
I´ve read many people reporting the JBL 250ti to have a stellar bass performance. Very deep yet punchy.
The LE14H-3 has been reported to be a drop-in replacement for the LE14H-1, so I thought it should deliver deep punchy bass as well.

[Mr. Widget]

My only experience with the LE14H-3 is in a 1400 Array system. The bass is good, extremely listenable and enjoyable, but not in ultimate territory. My opinions are probably biased towards that goal. For the past few years I’ve mostly been chasing holy grail performance.

I’m sure a very enjoyable system could be built around a pair of these fine woofers especially if you cross them over between 200-300 Hz.


Widget

[Robh3606]

Something to consider this is from a Stereophile article about how speakers stress amplifiers. Phase angle can be as important as minimum impedance. This is the Array 1400 so this is an Le-14-3 and as you can see the actual load can be lower than you think.



Let's look at specifics, beginning with the JBL 1400 Array. Its minimum modulus of 4.9 ohms occurs at 92Hz. Its minimum EPDR is 1.9 ohms and occurs at 70Hz, where the impedance modulus is 6.1 ohms—almost 25% above minimum—but the phase angle is a high –52°.


https://www.stereophile.com/reference/707heavy/index.html


Rob:)

[RMC]

RE "but the phase angle is a high –52°."

Stereophile unduly picky? Another viewpoint on this...

With regards to Recording Monitor Loudspeakers, which is a demanding application, Eargle talks about their impedance, then adds "... and the phase angle should not exceed + or - 60°." (John Eargle, Loudspeaker Handbook, 2nd Edition, P. 246).

The 1400 Array is still within that margin. If the 60° is good for monitor loudspeakers why it wouldn't be acceptable for a home speaker is somewhat beyond me.

Richard

[Robh3606]

The 1400 Array is still within that margin. If the 60° is good for monitor loudspeakers why it wouldn't be acceptable for a home speaker is somewhat beyond me.

You are missing the point it's the combination of impedance and phase angle. Looking at the impedance curve the worst case is not at the expected low point of 4.9@ 92Hz. So looking at just the impedance curve WRT actual load seen by the amp is useless without the phase curve. In a reflex box the tuning determines the curve.

Going back to the OP's question if you wanted to use a pair of these there is a real possibility of ending up with a worst case of close to or under 1 ohm.

Not many amps like 1 ohm loads. That is a general statement and does not address the combination of the two.

Rob:)

[Dr.db]

@ widget:
I think I know what you mean. You have owned the Everest 66000 if Im correct and I believe those AL1501 woofers are a little bit more precise than the LE14H-3´s... Not mentioning the output capabilities...
As you have allready mentioned, the most limiting factor on the LE14h-3 should be the midrange and higher crossover frequencies.
I suppose running them below 300hz minimizes the disadvantages in soundqualitiy when compared to more modern woofers.

@rob:
I´ve never heard of that EPDR-number, thanks for bringing that up.
Actually that EPDR of 1,9ohms :eek: for a single LE14h-3 looks pretty scary.

[Mr. Widget]

I suppose running them below 300hz minimizes the disadvantages in soundqualitiy when compared to more modern woofers.
Absolutely.
They will likely satisfy, but based on the info Rob posted, you may want to use them with a stereo amp per side. Meaning a dedicated amp channel per woofer.


Widget

[Dr.db]

Yes, a stereo-amp per side would be on the safe side for shure. Allthough I get the impression it might not work with a single amp, I would be happier using less electronics.

[RMC]

RE posts # 16 and 17

Somewhat late reply, been quite busy, however they say its better late than never...

Sorry for cutting short the quote from Eargle. This gave the impression that phase angle alone was the important matter (the impedance part having been skipped). MY BAD. Eargle certainly didn't put aside the impedance issue, along with phase angle, as outlined in this corrected quote of the whole paragraph (subject is a list of attributes that recording monitor speakers should have):

"7. Well behaved impedance characteristic. The dc resistance of the system should not drop below 80% of the nominal impedance value, and the phase angle should not exceed +/- 60°." Btw he does admit that his list is a tall order: "This is an imposing list, and few monitor loudspeakers earn outstanding marks in all areas. In many cases, the optimization of one attribute may work against another." (Loudspeaker Handbook, 2nd ed., p. 246)

The above corrects the error and should put me back "in phase"...

Did a quick search for one ohm rated amplifiers but what i saw was pretty much car audio amps... (assuming they are really 1 ohm capable).

Aside from the above, Dickason mentions in his Loudspeaker Design Cookbook, 5th ed., that "Phase is, however, generally not well understood, and the following explanation may be helpful." (p. 138). This explanation along with others should follow shortly.

Richard

[Dr.db]

Thanks a lot for this additional info`s!

[RMC]

Hi Olaf,
i'll post in my BGW thread the phase stuff promised, this way it won't highjack yours.
Richard

[Dr.db]

Thanks ;)