Pro Woofer Question - Power Handling Versus XMax

[scottsehlin]

Re: Pro Woofer Question - Power Handling Versus XMax

I've been doing some similar investigation as I have a pair of 10" Eminence woofers that can be tuned for an F3 into the low 50's with the right vented cabinet, but they will hit xmax with something like 50W in a 50L box. On the positive side, they will be playing at 110 dB at 1m, so if you have them in a home environment there is no issue. If they are fed their voice coil rated 250W, they will produce 118 dB at 1m, but will have excursion problems at or below 140 Hz. If one needed the extra dB, the answer would be to run them with a high pass filter.

I actually use that approach sometimes at home with my Hafnium project. They have a 5 1/4" sub playing down to 30 Hz in a 10L box. Needless to say, they can't do that very loud. I have occasionally had them firing out a bedroom window into the back yard for parties. This is not their preferred application, but I am powering them with a big 70's era receiver that has a 30 Hz high pass filter switch. When I use the high pass, I can get them as loud as the neighbors will tolerate.

[badman]

Re: Pro Woofer Question - Power Handling Versus XMax

All drivers run out of Xmax down low with SOME amount of power. Pro drivers are designed to take a beating- they're assumed to be overdriven at times, and often have progressive suspensions and large clearances so that the driver isn't wrecked when pushed hard, lower.

The limited Xmax is a concession to high efficiency, and the high power handling is important when playing at sustained high levels. A 12" is a mid in the prosound world for the most part, and will be high pass filtered to manage excursion, but the long timescale of high output in prosound means that they need to dissipate far more energy than home woofers. Run 25V at 200Hz for 10 minutes through some home "200W" 6.5"s and see how they fare (on second hand, don't, unless you're angry at the midwoofers). You'll likely let the smoke out in a hurry. Consider how hot a 100W lightbulb gets, and that's the sort of heat you're asking a driver to manage continually at these type of drive levels, for prolonged periods. Efficiency helps mitigate the power input level for a given SPL, and power handling via big coils and venting (shorting paths are helpful as heatsinks too) allows reliability.

So basically, they're optimized for efficiency, which means that the flux must be focused in a tight gap, and limited overhang is possible to maintain that efficiency. That type of construction allows the pro drivers to deal with things that would make even equivalent sized home/high Xmax drivers squeal. For sustained midwoofer duty;, I'll take a JBL 2206h over a Dayton RSS 12" sub, all day long- takes 1/10th(ish) the power, which matters on longer-term high output in things like concerts or DJ work.

[hongrn]

Re: Pro Woofer Question - Power Handling Versus XMax

Thank you Scott and Jeff for your detailed explanations. Much appreciated.

Hong

[Pete Basel]

Re: Pro Woofer Question - Power Handling Versus XMax

Also, the compression/distortion past Xmax is a gradual soft distortion so we tolerate
it well. If you look at a guitar driver with 1mm Xmax the top plate is often 6mm and
the VC can move 3mm more at which point half of the coil is out of the gap, so the
strength is only cut in half. My point is you don't hit zero as soon as you exceed
Xmax. Usually in a woofer Xmax50 as I call it is still usable but a bit dirty sounding.
But certainly pro woofers designed for bass usually have 5mm or more Xmax.

http://www.parts-express.com/dayton-audio-pa380-8-15-pro-woofer--295-034?utm_source=google&utm_medium=cpc&utm_campaign=pla

[badman]

Re: Pro Woofer Question - Power Handling Versus XMax

One thing I forgot to mention- when vented, some of these woofers can produce prodigious SPL at tuning, the limiting factors being vent size and power handling- you can give yourself a fair bit of extra oomph beyond what would be Xmax limited in a sealed system- just get your steep highpass right.

[Brian Steele]

Re: Pro Woofer Question - Power Handling Versus XMax

Beau,

That's the Tymphany 12" I was referring to, because I was looking at spending just $60 per driver. I got the Dayton H6512 waveguides on sale the other day, so I was thinking about doing something with them. By the way, did you see the xmax on that Audax?

That driver has an Fs of 61Hz and a Qts of 0.4. I wouldn't use that driver in a design with an Fb of 48Hz.

Have a look at the PA310 that was suggested in a previous message. 5mm Xmax and a lower Fs. I use one in a 40Hz TH that sound fine driven off a 300W amp, even though Sims saw it runs out of excursion around just under 100W.

[hongrn]

Re: Pro Woofer Question - Power Handling Versus XMax

Which WG and which tweeter did you use with the PA310? Thanks Brian.

[Brian Steele]

Re: Pro Woofer Question - Power Handling Versus XMax

Which WG and which tweeter did you use with the PA310? Thanks Brian.

The TH is a subwoofer design so there's no WG or tweeter. The Econowave design suggested by another poster looks good, but the cross over looks a bit complex for pa duty. I'd be tempted to try a BFM piezo array type solution for the high end and fix any FR issue with a basic xover and EQ.

[1100xxben]

Re: Pro Woofer Question - Power Handling Versus XMax

I'm a little late to the party on this one, but I can provide some insight on power ratings as I've done a considerable amount of testing for thermal capability using the ANSI/CEA-426-B test method.

First off, as a side-note: there is no such thing as RMS power, it is average power. What manufacturers call RMS power is a calculated number based on an RMS drive voltage and impedance.

As several have mentioned, the power rating is a thermal number, which has absolutely nothing to do with excursion. Excursion will be heavily dependent on the box style/alignment at low frequency, and the targeted frequency range that the driver will be used. The maximum average power rating is found by driving the speaker with a noise signal continuously for 8 hours. The noise signal is similar to pink noise, but shaped and compressed with an emphasis on the signal below 1 kHz. Since it is a wide-band noise signal, the driver should not reach maximum excursion levels, but the thermal capability of the voice-coil will be found.

[badman]

Re: Pro Woofer Question - Power Handling Versus XMax

I'm a little late to the party on this one, but I can provide some insight on power ratings as I've done a considerable amount of testing for thermal capability using the ANSI/CEA-426-B test method.

First off, as a side-note: there is no such thing as RMS power, it is average power. What manufacturers call RMS power is a calculated number based on an RMS drive voltage and impedance.

As several have mentioned, the power rating is a thermal number, which has absolutely nothing to do with excursion. Excursion will be heavily dependent on the box style/alignment at low frequency, and the targeted frequency range that the driver will be used. The maximum average power rating is found by driving the speaker with a noise signal continuously for 8 hours. The noise signal is similar to pink noise, but shaped and compressed with an emphasis on the signal below 1 kHz. Since it is a wide-band noise signal, the driver should not reach maximum excursion levels, but the thermal capability of the voice-coil will be found.

Have you done any work with dynamic power compression? That is to say, replication of short impulses, or music-like content? It's a tough topic to track but is argued as one of the big advantages of higher efficiency speakers, particularly those with larger-format voice coils and their associated high power handling.

[1100xxben]

Re: Pro Woofer Question - Power Handling Versus XMax

Have you done any work with dynamic power compression? That is to say, replication of short impulses, or music-like content? It's a tough topic to track but is argued as one of the big advantages of higher efficiency speakers, particularly those with larger-format voice coils and their associated high power handling.

I have not done any work in that subject. My main concern has been thermal limits of transducers and expected life.