Sierra Ribbon Towers and Safe SPL

[Pogre]

4 ohm's is minimum Impedance for the Towers. If you look at the graphs, the impedance is higher than that as you get above 20 hz. I wouldn't assume 4 ohms whilst doing your power calculations.

http://www.ascendacoustics.com/pages...T/srtmeas.html

That chart actually raises another question. It measures like a sealed enclosure, at least that's what I was told. To quote:

That is very interesting. It is described as a ported reflex enclosure, but it is not.

Lets add the FR

Notice there is only one peak of impedance and a very small one at that, and not two as there would be with reflex tuning. The nadir between the twin peaks would tell you Fb. So there is no Fb.

If you look there is a slight rise in output centered on 80 Hz, and then the roll off below that is 12 db per octave, not 24 until 30 Hz and then it rolls off 24 db per octave.

So this is not any of the reflex alignments. So that port has an unusual function, and seems to be behaving much more like the old Variovents on some Dynaudio designs from years ago.

The speaker does not have the characteristics of a typical ported enclosure though and it looks to me as if there is something at the origin of that port giving resistance.

I think their has to be some resistance to airflow, or deliberate miss tuning to give those results. That is not a typical tuned Qb4 box by a long shot.

[John Galt]

Mine look just like that on some tracks when pushed hard. I'd still like to know if this is normal or potentially harmful.

My old B&W 683 S2s never had this much excursion, but also don't sound as good...not that that means anything.

[Pogre]

Mine look just like that on some tracks when pushed hard. I'd still like to know if this is normal or potentially harmful.

My old B&W 683 S2s never had this much excursion, but also don't sound as good...not that that means anything.

That's where I'm at. I've never had speakers exhibit that much extension before. The 6" mids on my Ultras barely move at all in comparison. Kinda apples n oranges tho, since the Ultras also have a pair of 8s in each cabinet too.

I'm with you, I just want to know if this excursion potentially harmful or just the way they're designed.

[Beave]

The SVS Ultra's mids don't play down nearly as low as the mid on the Sierra Tower does.

Even though you have the crossover set at 80Hz, it's not a brickwall (as you know), so there's still substantial output coming from the speakers in the 40-80Hz region. What's more, there's probably quite a bit of cone excursion for the 80-120Hz range too.

If you could see a plot of cone excursion vs frequency, cone excursion is very low, then it starts going up as you go down in frequency, ramping up from 150Hz down to about 100Hz or 80Hz, then it drops significantly around the port frequency (40 to 60Hz, roughly), then it goes WAY up once you're below port tuning frequency (below about 40Hz).

With the 80Hz crossover, you're eliminating a lot of the dramatic, out of control movement that occurs below port tuning, but you're still getting nearly all of the movement that occurs above port tuning.

So it's less likely to be catastrophic, but it's still a little risky to the drivers.

As I said on that other forum, I've never played my towers anywhere near loud enough to see driver movement like that. My neighbors above would have me evicted.

[Pogre]

Thanks Beave.

Yeah, the bass frequencies are passed off to the 8" drivers in the Ultras at 180 hz so the mids wouldn't move as much. I'm just going to dial back my max volume about 3 - 5 dB. I mean, that's still pretty frickin' loud, lol. I'll rearrange a little so I'm closer to the front stage. I sit too damned far from my TV anyway... I'll post back here when I get a reply from Dave or whoever at Ascend replies to the email to give you guys an update.

4 ohm's is minimum Impedance for the Towers. If you look at the graphs, the impedance is higher than that as you get above 20 hz. I wouldn't assume 4 ohms whilst doing your power calculations.

http://www.ascendacoustics.com/pages...T/srtmeas.html

You mentioned impedance to me before, I wasn't blowing you off, lol. They're more 5 ohm nominal with a dip to 4 ohm is what I believe you said? Very friendly phase angles too. My amp runs cooler with the Sierras than with the Ultras and they're s'posed to be 8 ohm speakers.

[mikesiskav]

I remember this topic coming up in the past. Dave said he crosses over the mid-range to the woofers at a lower frequency than what some other speakers use so that the midrange driver covers as much of the vocal range as possible. This is why the towers sound so good with vocals.

[Beave]

I should add for clarity: My explanation of woofer excursion is for ported designs. So it applies to the tower woofers. But the tower midrange isn't ported. I think it's in its own sealed enclosure. I'm not sure whether it has an electrical high pass filter or if it just uses the enclosure for 'natural' rolloff. In any case that means the midrange excursion plot vs frequency is different from the woofer excursion plot.

I wonder if upping your crossover frequency to something like 120Hz or 150Hz will make a dramatic reduction in driver excursion. You could try it, at the same levels you're playing on the videos, just for curiosity, to see if the excursion is reduced by a lot.

But yea, the real solution is probably just to back off the volume a little! :-)

[Beave]

Thanks Beave.

Yeah, the bass frequencies are passed off to the 8" drivers in the Ultras at 180 hz so the mids wouldn't move as much.

That's probably a similar frequency for the Sierra Tower woofer-to-mid crossover, but I bet the crossover slopes on the SVS speaker are steeper than the slopes on the Sierra Tower.

[davef]

There are basically two ways woofers produce sound, wavelengths that are within the piston range of the woofer, and wavelengths that are out of the piston range (shorter wavelengths). Within the piston range of a woofer, in order for the woofer to reproduce this - the cone most move forward and back no different than a piston. For shorter wavelengths - the woofer cone itself resonates (out of the piston range). When a typical transducer (a woofer, for example) produces soundwaves that are out of the piston range - these wavelengths become extremely directional (also known as beaming).

One of the major design goals of the Sierra Tower was to come as close as mechanically possible to matching the exceptionally wide and linear off-axis response of the 70-20xram ribbon tweeter, which is designed to easily handle a low crossover point (which we take advantage of). In order to achieve this goal, we used smaller diameter woofers with very high excursion and crossover points optimized to keep the woofers operating within their piston range.

The pro's to this are obvious, very wide and linear horizontal dispersion which is clearly visible in the horizontal polar response (no blooming, wide dispersion etc.). This is a key performance attribute.

The con's to this is that the woofers can exhibit a lot of excursion depending on the source material, especially at very loud volume levels. Is this harmful or will it shorten the longevity of a woofer - no, not in the least provided you are not bottoming the woofers. In fact, that movement is what helps keep the voice coils cool.

You will absolutely know when you bottom a woofer as you will hear a noticeable "bang" and these woofers are built for extreme excursion. Again, woofers are designed to operate like a piston, sometimes you will see a lot of movement depending on the source and volume level.

Pogre, from your video - everything looks completely normal to me - but this is obviously at a very loud volume level.

That said, if you are exceeding your amplifier's power specifications - and the amp is starting to clip - the distortion produced by this will produce transverse waves. (this may or may not be audible) These wavelengths are problematic for any speaker as they will cause excess movement - this is what destroys dome tweeters, tears up ribbon diaphragms and burns woofer voice coils.

With your amplifier, which is rated at 200 watts and considering your 15 foot listening distance, do not try and exceed 100dB from 1 speaker at your listening distance. 103dB from both speakers combined.

I have a hunch with that video, you are well over 100dB from that one speaker.

What device are you using to measure spl?

Also, Dolby Reference level is really just an arbitrary number and has no application for music. It was originally designed for movie theater volume levels - to attempt to achieve 85dB average listening volume at every seat in a theater and for this to become a standard at every theater. In this way, mastering engineers are able to set channel levels appropriately so that dialogue and effects are appropriately "leveled" on the mix so that the mix tracks well from one theater to another etc. It works very well for theaters but as Curtis mentioned, is not really appropriate for movies mixed for home theaters. Sometimes movies are re-mixed specifically for home environments, sometimes they are not.

Ever wonder why in some mixes for the home, dialogue is impossible to hear - or effects are much too loud? The intention was good, and it has worked very well for theaters, but it's been a disaster IMO for home theater.

I wish a new standard was developed for home theater mixes as most consumers unknowingly blame the speakers when they watch a movie and can't hear dialogue, or effects are so loud forcing someone to constantly adjust volume levels. They think something is wrong with the speakers...

To repeat, Dolby Reference level is 85dB average listening SPL from one speaker at the listening position. Dolby Digital mixes allow for a massive 20dB of headroom, this is where that 105dB "peak" reference level comes from. It has no bearing for music. Some music sources have as little as 3-6dB headroom (thanks to the damn loudness wars) - even a well recorded CD will never come close 20dB of headroom.

All that said, in a home environment - I would considering anything above 97dB to be too loud and potentially damaging to your hearing.

Hope this makes sense!

[davef]

That's probably a similar frequency for the Sierra Tower woofer-to-mid crossover, but I bet the crossover slopes on the SVS speaker are steeper than the slopes on the Sierra Tower.

Yep - we use a shallow slope on the mid crossed to the woofers, and a steep slope on the woofers crossed to this mid. Plus that SVS Ultra tower has (2) mids, that automatically cuts the excursion requirements in half, plus they are larger woofers which increases efficiency - further reducing excursion requirements at the same volume levels.

Pogre, you really can't compare one speaker to another with regard to excursion, unless it is a subwoofer with the same size woofer and similar tuning, similar filtering and EQ. It gets complicated. Our Towers were not designed as SPL beasts but I have run ours in our demo room at 110dB for hours at a time, at a listening distance of about - 9 feet in a very well damped room. We have had customers turn up the volume to insane levels at times, often prompting me in the factory area to knock on the door and ask them to turn it down a bit. We have had these same towers in our demo room, which have been seriously abused and with many thousands of hours of listening time on them for close to ten years now. We have yet to have to swap out a woofer or the RAAL 70-20xr. In fact, I believe in an early demo of the towers - I believe Curtis and some other people accidentally bottomed the hell out of the woofers when Mike (I believe it might have been Mike but I could be wrong) played an insane Linkin Park track, full range at about 110dB.

Even more reassuring to you - in many thousands of ribbon towers sold, we have only had (2) customers damage the RAAL 70-20xram. One because the tower got knocked over and landed square on the face, basically shattering the tweeter - and another who used the towers outdoors at his own party, threw an insane amount of power into them and burned up every component, including melting the inductors and resistors in the crossover. That was an interesting situation, as the customer attempted to blame the speaker and fought with us over the warranty -- that was until his some dropped the speaker off at our facility, met Dina and Joe - felt bad and told us the truth as to what really happened