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Question for our experts - why aren't more amps designed for 2 ohm loads?

#82
Jazzdogg said:
I don't like compromising cabinets I can buy based upon the limitations of a bass amp.
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But don't we always have to do that? We don't buy 16ohm cabs if we think we "need all our watts" even though it's not unknown for higher impedance drivers to have slightly better sensitivity than lower impedance ones. If we are mixing cabs of different types then we have to take care that the power is appropriately balanced between all the drivers.
It's probably completely illogical, but bearing in mind the nominal nature of impedance calcs, a 2ohm rated amp into a nominal 2ohm cab setup would worry me more than a 4ohm rated amp into nominal 4 ohms.
 
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#83
JimChjones said:
But don't we always have to do that? We don't buy 16ohm cabs if we think we "need all our watts" even though it's not unknown for higher impedance drivers to have slightly better sensitivity than lower impedance ones. If we are mixing cabs of different types then we have to take care that the power is appropriately balanced between all the drivers.
It's probably completely illogical, but bearing in mind the nominal nature of impedance calcs, a 2ohm rated amp into a nominal 2ohm cab setup would worry me more than a 4ohm rated amp into nominal 4 ohms.
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Why should it, especially if the same design margins are used? For example, I use 1.5 ohms as the minimum impedance for a nominal 2 ohm design.
 
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#84
@agedhorse
I appreciate I can read you posts

As for mechanical properties: Eminence publishes cabinet designs and maximum power is limited by xmax, not thermal RMS. In first example RMS of speaker os 200W, but xmax limits power to 75W and maximum SPL for 41 Hz is ~99dB and for 100 it's 114. When one includes compression and frequency response chart it get more messy. I'b be happy to know how many dB I can get at 30, 40, 60, 80 and 100 Hz before speaker hits xmax, i.e. before it starts to distort.
https://cdn.shopify.com/s/files/1/0270/8665/1462/files/Legend_BP102_cab.pdf



As for group delay: I made (on purpose) a vented cab with speaker suitable to sealed cab only. QTS = 1.23. In vented it had audible latency in lows and since calculated GD was high, I took it as related. Perhaps other factors were more important I am not aware of.

As for manufacturing costs: in automotive business I had few examples of parts that were made for 1$ (excluding R&D) and sold to end customer for 20$. I guess volumes aren't even similar in amps business and it was kind of a stretch
 
#85
agedhorse said:
Why should it, especially if the same design margins are used? For example, I use 1.5 ohms as the minimum impedance for a nominal 2 ohm design.
Click to expand...

I share the perception that there are more problems with 2 ohm capable amps pushing the minimum load, VS 4 ohm capable amps pushing the minimum load.

Perhaps not every amp designer uses the same margin for 2 and 4 ohms designs.

The problem could also relate to design practices with cabs. Not every cab design meets EIA guidelines where minimum Z should not drop below 80% of nominal Z.
 
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#86
sokolasty said:
@agedhorse
I appreciate I can read you posts

As for mechanical properties: Eminence publishes cabinet designs and maximum power is limited by xmax, not thermal RMS. In first example RMS of speaker os 200W, but xmax limits power to 75W and maximum SPL for 41 Hz is ~99dB and for 100 it's 114. When one includes compression and frequency response chart it get more messy. I'b be happy to know how many dB I can get at 30, 40, 60, 80 and 100 Hz before speaker hits xmax, i.e. before it starts to distort.
https://cdn.shopify.com/s/files/1/0270/8665/1462/files/Legend_BP102_cab.pdf



As for group delay: I made (on purpose) a vented cab with speaker suitable to sealed cab only. QTS = 1.23. In vented it had audible latency in lows and since calculated GD was high, I took it as related. Perhaps other factors were more important I am not aware of.

As for manufacturing costs: in automotive business I had few examples of parts that were made for 1$ (excluding R&D) and sold to end customer for 20$. I guess volumes aren't even similar in amps business and it was kind of a stretch
Click to expand...

Your power handling example does not contradict my statement, though with the right choice of design parameters and driver design, it is possible to design speaker systems with mechanical power handling similar to thermal power handling.

Your example of a driver designed for sealed applications used in vented cabinet applications can sound terrible but it has nothing to do with group delay.

Costs are costs, how they are accounted for depends on each specific application, and if there are any external subsidies.

Wasnex said:
I share the perception that there are more problems with 2 ohm capable amps pushing the minimum load, VS 4 ohm capable amps pushing the minimum load.

Perhaps not every amp designer uses the same margin for 2 and 4 ohms designs.

The problem could also relate to design practices with cabs. Not every cab design meets EIA guidelines where minimum Z should not drop below 80% of nominal Z.
Click to expand...

If the designer is competent, there should be no difference in reliability. My own product’s metrics fully support my statement.

Designing reliable high powered, 2 ohm stable power amps takes some advanced techniques and more engineering experience/skill. I’ve been designing 2 ohm stable power amps for almost 40 years, reliability is not an issue for me, but I have seen many “designers” struggle, it’s not the technology but the engineering capabilities that determines the success.
 
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#87
agedhorse said:
it is possible to design speaker systems with mechanical power handling similar to thermal power handling.
Click to expand...

The cab designs for the Kappalite LF variants support this.

For example, the 3015LF is rated for 450W RMS

upload_2024-2-11_16-48-6.png


upload_2024-2-11_16-48-31.png


upload_2024-2-11_16-49-17.png


Not every 3015LF design is thermally limited to 450W
upload_2024-2-11_16-49-59.png
 
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#88
My SWR 350 was rated to be stable at 2 ohms but when I used it with 2 4 ohm Acme B2s it would fart out at higher volumes. I suspect that the Acmes dip below 4 ohms at certain frequencies but if you are using 2 or more 4 ohm cabs you are better off using a 2 channel power amp to drive 4 ohm loads. Once I started using a 2 channel power amp I didn't have any problems with the Acmes.

Rick B.
 
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#89
RickBlair said:
My SWR 350 was rated to be stable at 2 ohms but when I used it with 2 4 ohm Acme B2s it would fart out at higher volumes. I suspect that the Acmes dip below 4 ohms at certain frequencies but if you are using 2 or more 4 ohm cabs you are better off using a 2 channel power amp to drive 4 ohm loads. Once I started using a 2 channel power amp I didn't have any problems with the Acmes.

Rick B.
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Perhaps the problem wasn’t the speakers, but the power amp not really being 2 ohm stable in spite of the claims? Maybe the combination of both issues?
 
#90
RickBlair said:
My SWR 350 was rated to be stable at 2 ohms but when I used it with 2 4 ohm Acme B2s it would fart out at higher volumes. I suspect that the Acmes dip below 4 ohms at certain frequencies but if you are using 2 or more 4 ohm cabs you are better off using a 2 channel power amp to drive 4 ohm loads. Once I started using a 2 channel power amp I didn't have any problems with the Acmes.

Rick B.
Click to expand...

You have two things working against you.
1. Acmes are extremely inefficient.
2. Many SWR have extended LF reponse, which eats up a lot of power.

Most likely the Low B2 dips below 4 ohms...but min Z is typically less than nominal Z. Per the EIA standard, min Z should not drop below 80% of nominal Z. For two ohms that is 1.6 ohms. No idea what min Z is for the Low B2.
 
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#91
sokolasty said:
As for manufacturing costs: in automotive business I had few examples of parts that were made for 1$ (excluding R&D) and sold to end customer for 20$. I guess volumes aren't even similar in amps business and it was kind of a stretch
Click to expand...

Unfortunately I have seen this in the domestic electrical aftermarket parts business, try pricing something like a drain-pump in a dishwasher.
I have seen the same pump sell for RRP $7 up to RRP $120 by different brands of appliances, they are usually completely interchangeable and they look exactly the same.

I have seen refrigerators that cost $25,000 that uses the same parts as another brands $1,000 refrigerator.
Both brands were owned by the same main company but sold under different brands.

Those prices were the RRP for when the products were still under warranty, I worked for a short time as a domestic sparky doing mainly warranty repairs on domestic goods.
 
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#95
Pop C said:
Hmmm....Not sure? It has a 4ohm/2ohm switch on the rear panel. Could have been a speaker compatibility thing. I was using Hartke Hy Drive 1x 12 cabs. 2 set at 8ohms and 1 set at 4ohms. Do you think that was the problem?
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These cabs, right, with the selectable 4/8 Ohm impedance?

Regardless of the reliability of your amp at 2 Ohms (which, it seems, might be questionable), don't run two of those 112s at 8 Ohms apiece and the other at 4 Ohms. Doing so, you're stressing the 4 Ohm cab way more than the others (since it's getting twice the juice) and significantly limiting how loud your rig can go (since the 4 Ohm cab will hit its limit when the other two are halfway there).

Set all three cabs to 8 Ohms and your amp to 2 Ohms. You'll get more usable power from the rig (even if the amp will make a little less in theory, it'll make more - and more usefully distributed - before toasting a cab), present an easier load to the amp (2.7 vs. 2 Ohms), and your rig should sound better (at least fuller and more even) since all of the 12s will see equal power.

Now, a 212 + two 112s, the 212 should be 4 Ohms, but that's still equal power to each woofer.

Easy mistake to make, but trying to run at 2 Ohms vs. 2.7 isn't helping you in this case.

EDIT: With a solid state amp like this, setting it to "2 Ohms" means "2 Ohms minimum." It'll be fine (and have an easier time) running a 2.7 Ohm load.

Tassieviking said:
Unfortunately I have seen this in the domestic electrical aftermarket parts business, try pricing something like a drain-pump in a dishwasher.
I have seen the same pump sell for RRP $7 up to RRP $120 by different brands of appliances, they are usually completely interchangeable and they look exactly the same.

I have seen refrigerators that cost $25,000 that uses the same parts as another brands $1,000 refrigerator.
Both brands were owned by the same main company but sold under different brands.

Those prices were the RRP for when the products were still under warranty, I worked for a short time as a domestic sparky doing mainly warranty repairs on domestic goods.
Click to expand...

Having recently bought a fridge with my mom, I appreciate hearing this. We asked about how often the models we were looking at came in for service (and for what) and in the course of the conversation got a glimpse into some of what you're saying re. parts used (among other things).

Figured, with something like a fridge, it wouldn't hurt to know what the guy repairing them would get for his mom.

EDIT: No, not an Ampeg fridge - the kind with a compressor (one of the parts we asked about).

EDIT EDIT: No, not that kind of compressor...
 
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#97
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