ICG: I completely agree with you. I'm not trying to get useful output at 16Hz. My goal is 25Hz to 20khz from each tower, at 103-105dB 1m.
Weltersys: Thanks for the suggestion, I get your point i think. You're suggesting that I might have run out of headroom somewhere between my source and my driver. That's fair enough. I haven't directly tested this. I think in order to do a real comparison pre/post eq with same excursion, I'll need to use a different amplifier. Currently for these tests I've been using the Dayton APA150, bridged, driving the impedance shown in an above post.
At 17Hz from earlier, with max LineOUT from my interface (0dBFS), and max volume setting on the APA150 amplifer, I was not able to produce any noise, while having the EQ in the chain. However at other frequencies there's more Boost (25Hz max boost), so this is worth a look. But if I disable the eq, I'll need to increase the level somewhere else to makeup for the 13.5dB loss. So I think that points to grabbing a bigger amplifier, right? I think I have a 1000W crown somewhere in my lab.
I've been of the same mindset lately. I am either ignorant to some or several phenomena regarding fluid dynamics, loudspeaker dynamics, or I've missed something along the way that I've taken for granted. So, I think the low hanging fruit right now is to certify my test system / amplifier / DSP is without blame. Then I can move onto the more complex topics. Thanks for your advice.
Yes.
150 watts at 8 ohms is only 34volts.
At 25Hz, your series speaker impedance is ~40 ohms, ~29 watts from the amp.
Even without running a simulation, fairly sure 29 watts won't drive a pair of 500 watt speakers to 14mm excursion 😉 .
3-4mm sounds about like where that Dayton APA150 would run out of steam.
And I bet it makes any speaker sound like blat when it clips.
If your Crown can deliver 1000 watts at 8 ohms, that's ~89volts, 200 watts into 40 ohms, probably close to what's required to reach Xmax at the impedance peak without clipping.
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Uhm... YES YES YES! I just strapped a 1kW across that thing, and there's absolutely no issue anymore. My house is SHAKING. Gracias. It was for sure the amplifier saturation. I feel simultaneously stupid and excited at the same time. Thanks again.
It's always best to remember that "power amplifiers" are actually voltage amplifiers.
Brandon, could you check what voltage is required to reach 28mm peak to peak at the 50 ohm 17Hz impedance peak?
Art
Depending on the spl, even 20Hz is very ambitious..you cannot expect fat home cinema rumbling noises from a dipole/ripole at ht levels.
That's not correct. Your estimate is perfectly reasonable for BR subs but for a ripole practically free air conditions apply..The maximum power capacity does not in the least say anything about the excursion. In horns it's not uncommon the maximum power is exceeded far below the xmax. On dipole, ripole etc it's the opposite, the acoustical impedance is very low. That means, the membrane swings almost free and can reach the xmax at ridiculous low power, no matter what the electrical power capability may be. 29W sounds about right for unhinged excursion, to get higher spl, a low cut at ~30Hz is mandatory. Without any lowcut you will not get more than low 90s spl, even if the drivers are capable of ~125dB in a br single enclosure!
The solution is a low cut. If that's not enough, put more subs. If that's not enough either, use an enclosure type that can provide more spl.
I have some amplifier questions. After just a little investigation with my Fluke 179, strapped across the Crown XLS2500 amplifier terminals, I see I'm only reading 2.4VAC rms, on max/hold, sine wave 50Hz, dual 15's in parallel creating this 2.13 Ohm load:
I increased the amplifier / LineOUT level until I smelled the voice coil, and the output level was 103dB at the listening position (roughly 3 m away).
So, I'm a little confused and I feel I'm once again missing something obvious. Most of my acoustic experience has been designing microphones and signal processing. I'm clearly new to the world of large power amplifiers and big subwoofers. So I would appreciate some guidance if you can 🙂.
Previous amplifier: Dayton APA150, bridged, 150W rated into 8ohm. Saturated with the 8ohm load I presented it (dual 15's in series), and never fully reached the output level I wanted.
New amplifier: Crown XLS2500, not bridged, single channel, rated 1200W into 2 Ohm load (Dual 15's in parallel). Nowhere near amp saturation, but only delivering 2.4V RMS into the load (2 Ohms) (4.2 W?) and the loudspeaker is as loud as I could ever want it.
In the final implementation of this 4-way speaker design, I want to use one of the HYPEX Fusion amp plates, either the FA253 or FA503. Based on what I'm measuring, and the THD plots at 2Ohms for the HYPEX amp, I see no reason to want for the 503, since I'm currently delivering only 4.2 Watts and this thing is loud AF.
So what am I missing? Why does the APA150 crap out and the crownXLS deliver only 4-5 watts and I'm blown back with my house shaking? Is the Crown amp just presenting a lower output impedance? Higher current reserves? Am I measuring the amp incorrectly?
I increased the amplifier / LineOUT level until I smelled the voice coil, and the output level was 103dB at the listening position (roughly 3 m away).
So, I'm a little confused and I feel I'm once again missing something obvious. Most of my acoustic experience has been designing microphones and signal processing. I'm clearly new to the world of large power amplifiers and big subwoofers. So I would appreciate some guidance if you can 🙂.
Previous amplifier: Dayton APA150, bridged, 150W rated into 8ohm. Saturated with the 8ohm load I presented it (dual 15's in series), and never fully reached the output level I wanted.
New amplifier: Crown XLS2500, not bridged, single channel, rated 1200W into 2 Ohm load (Dual 15's in parallel). Nowhere near amp saturation, but only delivering 2.4V RMS into the load (2 Ohms) (4.2 W?) and the loudspeaker is as loud as I could ever want it.
In the final implementation of this 4-way speaker design, I want to use one of the HYPEX Fusion amp plates, either the FA253 or FA503. Based on what I'm measuring, and the THD plots at 2Ohms for the HYPEX amp, I see no reason to want for the 503, since I'm currently delivering only 4.2 Watts and this thing is loud AF.
So what am I missing? Why does the APA150 crap out and the crownXLS deliver only 4-5 watts and I'm blown back with my house shaking? Is the Crown amp just presenting a lower output impedance? Higher current reserves? Am I measuring the amp incorrectly?
Like I already said, such a boost will limit the max spl by a lot. If you have the normal sub power at 20W, a 15dB increase means you're looking at 632W! Even with 2 of these Dayton 15" drivers, that's WAY above their capabilities.
If you want that level, you need approximately 4 of these ripole subs to have some headroom left.
ICG, I'm not sure you understand what I've done. I'm at 104dB SPL, 50Hz (which already includes the 13dB boost) and the amplifier is only outputting 2.4V AC. I've already reached my target. I DONT NEED 15dB More than I already have.
My question right now is about the Fusion amps from Hypex. If the crown XLS2500 is measuring 2.4VAC RMS (consistently with sine wave) and this level is MORE THAN ENOUGH for my listening, should I expect the FA253 amplifier plate will be able to provide similar results?
There is no need to use the hold function with a sine wave.
Check an AC outlet (60 Hz 120v nominal in the USA), it should read between 110V (old 220 volt transformers) to near 120 volts (the more usual 240v single phase transformers) between the hot (smaller blade) and neutral (larger blade).
If it reads ~12volts, you know you have made an error in your reading.
Fresh voice coil epoxy doesn't take a huge amount of power to stink, but it shouldn't stink at all with ~one watt per driver.
Yes, but you will find it.
"Saturated" is a term usually reserved for rather benign distortions such as those from overdriving tape or an audio transformer. Your APA150 was either voltage limiting (usually doesn't sound bad) or clipping (chopping the tops off) the audio waves to make the distortion you heard.
The more extreme the clipping, the closer a sine wave is to a square wave.
A square wave sounds very harsh, and contains twice the power of a sine wave of equal voltage.
This has led to the misconception that clipping burns voice coils, when it is too much average power that burns them.
As well as your voltage reading, your math is off.
Power in watts= voltage squared divided by ohms.
2.4v X 2.4v=5.76/2.13 ohms = 2.7 watts.
Many obvious mistakes preclude jumping to conclusions about your power amp requirements.
Look at your four ohm driver sensitivity:
2.83 volts into a 4 ohm load =2 watt
2.83 volts into 2 ohms =4 watt
Doubling drivers (2xSd) adds +3dB sensitivity, which would bring the pair up to 91.2 dB/1w/1m best case- which a ripole is not regarding sensitivity. You read more than 10dB higher at three times that distance with what would only be 2.7watts if your voltage read correct !
As you should remember from microphone design, each doubling of the distance of the sound source to the diaphragm reduces SPL by -6dB.
Loudspeakers behave exactly the same in a free field, though in small rooms the low frequency may only drop around -3dB doubling distance.
Obviously, you measured incorrectly.
Most likely the voltage was off by an order of magnitude.
24 volts would be 288 watts into 2 ohms.
The XLS 2500 should do around 49 volts at 2 ohms for 1200 watts, but current limits.
Limit your high power sine wave speaker testing time to a few seconds at a crack to avoid the stink.
Still curious to find what voltage is required to reach 28mm peak to peak at the series 50 ohm 17Hz impedance peak (series) connection or parallel 10 ohm impedance peak once you sort out your voltmeter operation.
Art
How did you measure the 2,4V AC? I hope not by a multi-meter. Anyway, that doesn't really matter. In a ripole it's absolutely impossible to get 104dB/1W/1m, even with dual 15". realistically, you're at 90, at most 93dB. Your drivers are 4 Ohm, so with two of them you're already at already 8W! That means you already reach the max power below your target 105dB @ 3m. And there's still no headroom in it!
Absolutely right!
I might be wrong but I doubt the meter is able to measure anything the common 50/60Hz power grid frequency.
Yes, you are wrong about that.
Brandon's Fluke 179 is a particularly good true RMS multimeter, can read any AC or DC source one would be likely to encounter, and can also read the frequency:
That said, it has enough functions that it could easily confuse someone like Brandon, yourself or myself unfamiliar with a specific type of measurement.
Any common AC volt meter can measure the voltage of 50/60Hz grid power, I do it before plugging an amplifier into an unknown outlet.
I also check mains voltage before testing an amplifier's output, they can't reach rated power when the voltage drops.
I also have made plenty of measurement mistakes, especially with auto-ranging meters 😉
Art
Something is wrong with your voltage measurement - check the settings on the Fluke. Maybe you had it showing min voltage rather than max?
That Crown will deliver its rated power. Were you lighting up the -20dB or -10dB indicators?
Actually, it's not. It's voltage capped. It's not current capped either at all, it's the protection triggering. Disabling the protection, it works fine down to 1,6 Ohm.
Quite right, the leads weren't reliable. I am getting much more "correct" answers now. I noticed a 120V reading when I plugged it into the outlet, until I wiggled the lead a bit, then it was reading between 4-10V. So, I replaced the leads with new ones, and now I'm getting reliable, consistent readings...even with my shaky hands...lol.
20VAC at the output of amp gives me 96dB SPL, 34 Hz sine, 2m. That's somewhere around 150W at 2.6 or 2.7 Ohms. This seems to be in line with expectations. Whew! Hopefully the math is mathing now 😳 (sometimes my ADHD brain grabs values from another problem, like 3V instead of 2.4 yesterday). Lovely varnish smell too 🙂.
Okay At 2m, 17 Hz (impedance peak 10.4 Ohm)
16.5VAC 87dB ~26W
20.8VAC 89dB ~42W
26VAC 91dB ~65W
Based on the air chuffing, I'm hesitant to push further at that frequency, also because of the energy exposure. I'd rather not speculate on their actual excursion, but it's further than I'd ever push them, just aerodynamically. I'll be applying a HPF at 25Hz in the end.