Ascend Acoustic Ribbon Towers

[William Lemmerhirt]

Hey @Pogre. Can you try and explain RLO offset if you don’t mind? I have mine set to 0 . What would changing it to -10 do?

It changes the point at which DEQ is engaged.
So at rlo at zero, when the MV gets to zero, Deq will being doing nothing. At -10 it will have applied some boost, at -20 or -30 much more boost.
RLO changes the amount of boost applied for a given MV level.
Here’s what DEQ looks like on paper.
As you can see once you get above MV-0 it starts to reduce boost.
I can’t remember the algorithm, but it’s something to the effect of, for every 6db MV setting below zero, Deq applies 3db of boost(bass range). Once you get to MV zero, no boost.

 

[TLS Guy]

I hope someone like @PENG can correct me if I am wrong, but ultimately, whether you bi-amp or not, you are asking the amps to drive the speakers the same way (assuming the system is properly balanced and the SPL is the same). So the amount of energy required would be the same. There may be a little more energy attributed to having the extra two amps energized during quiet spots (it take more energy for four amps to "do nothing" than two); however, I would expect the fact that you are distributing that same load over four sets of heat sinks to result in an overall lower temperature. If you are anywhere near working the amps, I would rather have the load (and heat) spread out more than concentrated.

You are correct. To make sense of the issue you need to know impedance curves, phase angles and sensitivity of the speakers. As we all know what a manufacturer of a speakers says the impedance is, is totally useless information.

 

[Swerd]

You are correct. To make sense of the issue you need to know impedance curves, phase angles and sensitivity of the speakers. As we all know what a manufacturer of a speakers says the impedance is, is totally useless information.

Fortunately, Ascend Acoustics provides very good information on its speakers. See their measurements of the Sierra Tower here:
http://www.ascendacoustics.com/pages/products/speakers/SRT/srtmeas.html

Edit: This is the wrong link. See post #214 below for the correct link. Sorry for the confusion.

Here is the impedance magnitude and phase plots. I don't recall what the crossover frequencies are for this 3-way speaker.

 

[Verdinut]

Fortunately, Ascend Acoustics provides very good information on its speakers. See their measurements of the Sierra Tower here:
http://www.ascendacoustics.com/pages/products/speakers/SRT/srtmeas.html

Here is the impedance magnitude and phase plots. I don't recall what the crossover frequencies are for this 3-way speaker.
View attachment 36962

IMO, both the impedance and the phase angle curves are good. That is a 4 ohm system and there are no serious dips in the impedance.

@TLS Guy, several days ago while perusing those curves, I thought that the woofers were operating in a sealed box but Pogre told me they were ported. There is only one impedance peak around 70 Hz. You have more experience with speaker enclosures than I do. Would the little bump around 27 Hz represent the lower impedance peak? And the box would be tuned to around 40 Hz I presume.

 

[TLS Guy]

Fortunately, Ascend Acoustics provides very good information on its speakers. See their measurements of the Sierra Tower here:
http://www.ascendacoustics.com/pages/products/speakers/SRT/srtmeas.html

Here is the impedance magnitude and phase plots. I don't recall what the crossover frequencies are for this 3-way speaker.
View attachment 36962

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.

 

[ryanosaur]

That's it, @Pogre ...
You are hereby obligated to pop your woofs and take pictures of the internals!




Pleeeeeeeeeaaaaassssssse?

 

[Trebdp83]

No! He can’t even put the grilles on properly and you want him to remove a speaker?! The next pic with be of a screw driver sticking out of the speaker surround.

 

[lovinthehd]

Or worse, get a pic after Danzilla's done....

 

[ryanosaur]

Or worse, get a pic after Danzilla's done....

Oh...
That's just...
Dirty.
SMDH

...

Ah hell, I can't even keep a straight face typing that!

 

[shadyJ]

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.

I think you are just missing the lower ridge of the saddle which looks like that small bump at around 25 Hz. Yes, in an optimally tuned ported design, those saddle ridges would be of equal height, but if the port was on the small side, the lower ridge would be short. I think that some tower speaker manufacturers do this to have a sloped bass response rather than a flat response down to port tuning, in order to prevent room gain from bloating the bass.

 

[Pogre]

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.

That's the FR with the NrT tweeter. It's not a world of difference, but they're not quite the same. This chart shows both.

 

[Pogre]

That's it, @Pogre ...
You are hereby obligated to pop your woofs and take pictures of the internals!




Pleeeeeeeeeaaaaassssssse?

I might do it... I might...

 

[Verdinut]

I think you are just missing the lower ridge of the saddle which looks like that small bump at around 25 Hz. Yes, in an optimally tuned ported design, those saddle ridges would be of equal height, but if the port was on the small side, the lower ridge would be short. I think that some tower speaker manufacturers do this to have a sloped bass response rather than a flat response down to port tuning, in order to prevent room gain from bloating the bass.

@james,

I noticed that but my first impression was that it was a sealed design. Over the years, I have seen a lot of bass reflex impedance curves and the port would have to be really small to show a rather low bump in one of the tuning impedance peaks, and I've never read or heard of that phenomenon.

To tell you frankly, I have trouble agreeing with you on this. Show us an actual impedance curve of an enclosure from another manufacturer than Ascend or Axiom where one of the impedance peaks is that minimal.

 

[Swerd]

@TLS Guy, @Verdinut, @shadyJ, @Pogre, and all others

I goofed when I posted the previous link. That was for the Sierra Tower with the NrT dome tweeter.

This link is for the Sierra Ribbon Tower. There are lots of graphs that compare the dome tweeter version to the ribbon tweeter version.
http://www.ascendacoustics.com/pages/products/speakers/SRT/Ascend Sierra Ribbon Tower.pdf

Here is a frequency response curve comparing the Sierra Tower (yellow) with the Sierra Ribbon Tower (green). Below 1000 Hz they look identical.

The impedance magnitude and impedance phase curves look similar in the lower frequencies.

The description of this tower, and a photo, describe a ported reflex bass alignment, but the impedance curve does not look like a typical reflex speaker. I can find no explanation for this. Otherwise, the impedance curves look quite good.

Look on page 7 at the Impulse Response curves for the ribbon and NrT versions. The start and stop times for the ribbon tweeter are significantly quicker than for the NrT tweeter. I would expect that, but it's nice to see the comparison.

 

[Beave]

Edit: Several posts came in while I was typing this!

The earlier posts showed the frequency response of the NrT towers, not the RAAL towers.

The plot shared by Pogre shows the response of both tower versions, but it doesn't include the bass.

My guess would be that they are the same in the bass region, but that can't be determined from the plot showing the response of both speakers, because that plot doesn't include the bass.

You can look at the impedance plots and compare between the two models and see that they're very similar* in the bass, implying that the bass is likely the same for both speaker models.

*The impedance plot of the RAAL tower has a kink around 180Hz in the phase measurement that isn't there for the NrT tower. I've always wondered about that. Usually such kinks imply some sort of resonance in the cabinet, the woofers, or in the port output. But there's no kink in the corresponding magnitude plot. So I'm not sure what to make of it. It might be a measurement anomaly. DaveF might be able to explain.

 

[Beave]

In this link you can see impedance measurements for the Thiel TT1. It has some similarities to the Ascend Towers in that it has a midrange driver in a sealed compartment with no electrical highpass filter on the midrange; and it also has two woofers in another compartment that is ported.

You can see from the measurements that it too has one large peak and one very small peak in the bass impedance magnitude, although for this speaker the higher peak is the one lower in frequency.

You can also see that the port output has a broad hump instead of the more common higher-Q peak. I wonder if the Sierra Tower's port output is also broad like this.

https://www.stereophile.com/content/thiel-audio-tt1-loudspeaker-measurements

 

[Pogre]

To whet the appetite...

The bass drivers are definitely ported. The mid is in a sealed enclosure.

 

[TLS Guy]

I think you are just missing the lower ridge of the saddle which looks like that small bump at around 25 Hz. Yes, in an optimally tuned ported design, those saddle ridges would be of equal height, but if the port was on the small side, the lower ridge would be short. I think that some tower speaker manufacturers do this to have a sloped bass response rather than a flat response down to port tuning, in order to prevent room gain from bloating the bass.

That is exactly what some of the early Dynaudio speakers were. There was resistance in the port to cause this effect. They called it their Variovent system and had plans for DIY enthusiasts. I never built one, but I did seriously consider it. And yes, the issue was room gain. However with the T/S parameters of the Dynaudio drivers at that time, I thought that actually making a sealed design was the better option.

My surround speakers are from that era and are sealed. F3 is 52 Hz. So they are only 15 db down at 25 Hz with a smaller cabinet as a bonus. The way I calculated it, I had more low bass with a fully sealed design. That was an era when computer assisted design was in its infancy. I was an early adopter and bought floppy discs off Bullock and White.

So those speakers I have for my surrounds, are among the earliest speakers to use computer assistance for box and crossover design. That is 36 years ago now. How time flies?

I built them for location monitoring my outside broadcasts. Musicians would crowd my control room afterwards to hear some of the playback. They were always very complimentary of the sound. They still match the sound of the other speakers in the studio very well indeed.

 

[TLS Guy]

To whet the appetite...

The bass drivers are definitely ported. The mid is in a sealed enclosure.

View attachment 36975View attachment 36976

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.

 

[Beave]

There is nothing at the port origin to block airflow. The cabinet is wide open where the port is. The port does seem unusually short to me, however. At about 5" in total length, it's shorter than the ports on any of the other speakers I own. It appears to be flared on both ends.