What's to chat about?

[Seth]

Here's the short answer.....if the amp is 2 ohm capable per channel, then it can be bridged to 4 ohms. If it is only listed at 4 ohms capable per channel, then you can't bridge it to 4 ohms.....just 8.

A good example of this is the QSC GX series...they are good amps, but not 2 ohm capable, so no bridging to 4.

Yes, that's the standard, one size fits all, conventional by-the-book answer.

In spite of that, suppose you DID bridge a GX series into 4 ohms, but limited the voltage so the peak power delivered was the same as if it were an 8 ohm load? What do you suppose would occur? Overload/overheat? Pops, bangs, smoke, and flames? Run just fine and just as reliable as usual? Something in-between?

I get that there might not be a one size fits all answer to the question. It's a conversation. Let it roll around a bit. Give it some thought.

Are ya getting what I'm get'n at? Pick'n up what I'm throwing down? Smelling what I'm stepping in?

Whacha think?

[Tom Smit]

The manufacturer doesn't want the amp to go past 7.9 amps per channel (250/channel at 4 ohm). If trying to go to 44 volts bridge, that would end up being 11.2 amps as you indicated. My thoughts are that it would thermal out, and would shorten the life of the amp.

[Bruce Weldy]

Here's the short answer.....if the amp is 2 ohm capable per channel, then it can be bridged to 4 ohms. If it is only listed at 4 ohms capable per channel, then you can't bridge it to 4 ohms.....just 8.

A good example of this is the QSC GX series...they are good amps, but not 2 ohm capable, so no bridging to 4.

Yes, that's the standard, one size fits all, conventional by-the-book answer.

In spite of that, suppose you DID bridge a GX series into 4 ohms, but limited the voltage so the peak power delivered was the same as if it were an 8 ohm load? What do you suppose would occur? Overload/overheat? Pops, bangs, smoke, and flames? Run just fine and just as reliable as usual? Something in-between?

I get that there might not be a one size fits all answer to the question. It's a conversation. Let it roll around a bit. Give it some thought.

Are ya getting what I'm get'n at? Pick'n up what I'm throwing down? Smelling what I'm stepping in?

Whacha think?

ahhhhh.......ok.....you are jumping into the world of "what ifs". You can certainly hang as many speakers as you want on any amp, but as Tom said - at some point it will crap out on you. Determining exactly where and when that would occur is beyond my knowledge. But, if I was hazarding a guess - I would think it could handle less voltage than the math would suggest.....you'd have to take in to account the quality of the components of the amp as to how much they could handle at the lower impedance. And that would probably vary from amp to amp - widely.

[Grant Bunter]

But, I really don't know all too much about amplifiers other than basic principals of operation.

Perhaps it could be said that an amplifier's simplest explanation would be a voltage multiplier. It takes an input signal, and multiplies it, to increase volume when connected to loudspeakers.
It depends on the amplifiers design (eg Class A, AB, D, H) as to how it does that, but , like anything that's made, it has design parameters, and shouldn't be used in any way outside those parameters without expecting a failure of the amplifier for any number of reasons (when, not if).

...conversation worthy. What do you think? What's your gut or logic tell you?

My gut and logic tell me different things.
Logic says the amp you're talking it about, IMHO, is perfect for the WH6's you're building, but not to run bridged beyond it's capabilities for a pair of subs.

My gut tells using gear towards it's limits is ultimately heading towards some form of failure.
Since that failure can only occur, for me, mid show, that's not going to happen if I can prevent it.

Logic tells me there might be another way to tell you why what you're thinking isn't such a great idea.
Take a look at the chart in the Eminence BP102 specs sheet, just as an example:
https://www.eminence.com/pdf/Legend_BP102.pdf

Look for the impedance plot. Look for the lowest impedance this nominal 8 ohm driver can have. I found 6.5 ohms(ish)
Halve that (because that's what you do with cabs in parallel right). 3.25ohms.
The amp you're discussing isn't capable of 4 ohms in bridged mode, let alone 3.25ohms.

Tell us what the result would be for the actual drivers used in your T39's.

Amplifiers don't care what load is presented to them, as long as that load is within the design parameters. Stay in the parameters.

[Seth]

...Logic tells me there might be another way to tell you why what you're thinking isn't such a great idea.
Take a look at the chart in the Eminence BP102 specs sheet, just as an example:
https://www.eminence.com/pdf/Legend_BP102.pdf

Look for the impedance plot. Look for the lowest impedance this nominal 8 ohm driver can have. I found 6.5 ohms(ish)
Halve that (because that's what you do with cabs in parallel right). 3.25ohms.
The amp you're discussing isn't capable of 4 ohms in bridged mode, let alone 3.25ohms.

Tell us what the result would be for the actual drivers used in your T39's.

Amplifiers don't care what load is presented to them, as long as that load is within the design parameters. Stay in the parameters.

I'm glad you brought that up Grant. I was thinking about that too.

Here's an actual plot of my 16" T39 with a 3012LF

The same cab with an S2012


However, I do not have a plot for the wider T39's yet. Still have to assemble those.

Anyway, there doesn't seem to be anything too interesting there. But, take a look at this one.



That's 2 16ohm 2x6 SLA Pro's in parallel. 8 ohm load, right? But, what about that 2 ohm dip? Do you suppose, that's going to cause an issue if hooked up to an amp that's not rated for 2 ohm loads?

[Grant Bunter]

^ there's to little information about the measuring process to know if your results are significant, or not.
But if they are accurate plots, then, on the face of it, hell yes, you need either a 2 ohm capable amp for parallel cabs, or, a pair of identical amps that won't care about 16ohms per channel as that is well above the minimum specified impedance load.

That though is a different scenario to your discussion re running a 8 ohm bridge load capable amp a 4 ohms.
A little further to the discussion about amplifiers I made earlier, in bridge mode, one amp channel essentially becomes +, the other channel -.
In the case of your amp in question, 4+4 bridged, not surprise is 8 (as Bruce also mentioned earlier). Even though it doesn't say specifically it can't be a 4 ohm bridged load (regardless of limiting voltage), I'll tell you straight up, it can't be a 4 ohm bridged load!

[Bruce Weldy]

Anyway, there doesn't seem to be anything too interesting there. But, take a look at this one.

I'm not an expert in impedance charts, but I think there's something really wrong with that one. I've never seen a dip like that at that high a frequency. Typically, impedance rises along the frequency....at least that's my understanding. That said, I don't think an amp would have any problem with that impedance at that frequency.....Although, it would probably sound really bad if all that additional power went to 5k....not to mention blow up the tweeters.

Then again, maybe I don't understand the impedance/frequency/power implications that well.....

[Seth]

That dip is the 4ohm series resistor, inline with the piezo tweeters within the crossover described in the SLA Pro plans. Apparently, piezo tweeters present a capacitive/reactive load to the amp and sometimes can read almost 0 ohms... instead of the typical inductive load a voice coil presents. From what Bill has said in the past, the resistor is there to keep some amplifiers from producing unwanted audible oscillations... or something like that.

The traces were created with Ashly Protea DSP software on PC in conjunction with the Protea processor in the amplifier I was using.

[Seth]

Anyway, some thoughts I have on the query;

I'm pretty sure most Class D amplifiers are roughly between 80-90% efficient. Meaning if they draw 100 watts out of the wall, 10-20 watts is converted and lost to heat in the amplifier, 80-90 watts make it out to the speaker. If a speaker is 5% efficient, 76-86 watts are converted to heat in the voice coil, leaving only 4-4.5 watts getting converted into sound.

Looking at an amplifier from the perspective of thermal efficiency and thermal management, it seems that as long as the lower load doesn't effect the efficiency too much, that the amp should handle it just fine. Again... from a thermal management point of view... the amps ability to cool itself.

[Seth]

Bill,
Thanks for the screen name change.

[Seth]

So, a new year is upon us. I'm back home from family holiday vacation stuff and ready to get some things rolling. Gotta button up and finish the two Wedgehorn 6's I started a month or two ago. They're so close, but so far away from completion. Really, all I have to do is put in the SpeakOn jacks and top hats, glue the horn into the outer enclosure, make a flange for the access door, then fill/flush/round/sand/paint. Shouldn't take too much time to polish that project off. OH! The piezo array's too.

I'm putting together an order for the remaining parts I'll need to start and complete a 4x ultralight DR200 build. Would like to get those completed in April, May at the latest. Also have/want to get the 4x 30" T39's assembled and finished around that time too.

I have a feeling that when the COVID restrictions start to lift, there will be a demand for live entertainment systems. Wanna be ready to capitalize on that if/when it becomes a reality.

Also, I received a Kala U-Bass (Ukulele Bass) as a Christmas Gift and have had a good time learning to play bass. It's an acoustic/electric, but without amplification it's pretty much only good for practicing. Which isn't really a bad thing at all. Tiny little thing. Surprised it plays all the same frequencies/notes as a full size 4 string. Small, compact, light, easy to tote and stow, and unique... Right up my alley. I like it! I picked up a secondhand 10" bass combo (Line 6 Lowdown Studio 110) to practice with. Sounds good enough for the purpose. I also plugged directly into the rehearsal PA (1 2x6 SLAP shorty and one 16" 3012LF T39) and did a little playing simple tunes with Dad for a little bit. He was very surprised at how good it sounds. Me too, to be honest. From what I saw on YouTube, a lot of times these bass uke's have rubber strings and sound like an upright bass. The one I received came with round wounds. I'm quite happy with it as is. Although, I'm not a life long bass player like some of you. I probably wouldn't notice the nuances in sound qualities without having someone point them out. In any case, I'm enjoying learning the instrument and look forward to playing live, if/when that ever becomes a thing.


What about you guys? Any plans, relative to what we do around here, for the new year?

[Tom Smit]

Seth, I'll respond to your uke-bass. I listened to one with rubber strings while my son played it at Long and McQuade (similar to Guitar Center). I was actually impressed with that little thing, so much so that I might get one once I have almost too much money.

[Seth]

Seth, I'll respond to your uke-bass. I listened to one with rubber strings while my son played it at Long and McQuade (similar to Guitar Center). I was actually impressed with that little thing, so much so that I might get one once I have almost too much money.

Tom, do you play bass already? If so, how long have you been playing? And, how long would you say it took you to become fairly proficient?

I heard a joke on one of the YouTube instructions/lessons I was watching the other day and thought it was cute. New to me, but apparently an old joke, so forgive me if you guys have heard it a million times already...

Prospective bass player starts taking lessons.
First lesson, learns the first note.
Second lesson, learns the tonic and the dominant.
Doesn't show up to the third lesson. Why not?
They've got a gig.

[Bruce Weldy]

Prospective bass player starts taking lessons.
First lesson, learns the first note.
Second lesson, learns the tonic and the dominant.
Doesn't show up to the third lesson. Why not?
They've got a gig.

Yep, that's the old joke. And as much as I like giving bass players grief - they can make or break a band. A good bass player makes the band sound good.....a great bass player makes the band play good.


I've had the good fortune to play with a few good bass players over the years, but Earl was special - you didn't realize how good he was until you went back and listened to the performance. I wrote and recorded this tribute to him. Was able to play it for him the weekend before he died.

https://soundcloud.com/bruceweldy/earls-gone

[AntonZ]

What about you guys? Any plans, relative to what we do around here, for the new year?

I miss having a horn loaded sub in the living room. I might build a TTLS to fix that. I already have a T18 but the cube shape doesn't fit. TTLS can be tucked away vertically in a corner. And it goes quite a bit lower, should be nice for movies. Painted in just about the same color as the walls I think that should be the path of least resistance past the war office.