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La Scalas - surprising SPL graphs


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I recently tried characterizing the performance of my 1986 La Scalas using a calibrated  UMIK-1 microphone and REW. The results surprised me so that I wanted to share them with the forum in the hope of eliciting some comments.

 

TLDR: The La Scala bass performance was much worse than expected. Why? How can that be addressed?

 

Results

 

I took measurements with REW at 3 listening positions (left chair, right chair and in between the chairs; see positioning diagram, below). The measurements were taken with the amplifier set to full range speakers with no signal being directed to LFE for subwoofers.

 

This graph (which uses 1/12 smoothing) shows that the low-end performance of my La Scala drops precipitously below about 200Hz and is pretty much non-existent below 100 Hz.

1421944219_25-20KHzLaScalaonlynosubsdBFS.png.993ed5d9ecab20604b7269b44c505dca.png

 

For interest, here is the same data for frequencies below 200 Hz (i.e., zoomed in):

2012144340_15-200HzLaScalaonlynosubs.png.04f062779085a6e5a36e2d16c16de056.png

Although these charts use a dBFS scale, the ones using an SPL scale are identical (see bottom of post).

 

Clearly. my La Scala speakers perform poorly for frequencies below about 165 Hz (i.e., the lowest 3 octaves): performance drops from around -50 dBFS to around -80 dBFS.

 

Do these results seem reasonable?

 

I expected the La Scala’s bass to be OK until about 50 Hz but I was surprised to see their performance plummet below about 200 Hz.

 

According to discussion on this forum, the La Scala stops acting as a horn below 104Hz (i.e., > 3.3m wavelength) and does not produce much bass below about 51 Hz (i.e., > 6.7m wavelength). However, my results show much poorer performance than that.

 

I am interested in comments from forum members about these results. 

 

My system

 

My 1986 La Scalas have new Crites AA networks and @Dave A's SMAHL tweeters and lenses. I laminated 3/8 Baltic Birch plywood to the exterior of the cabinet to improve rigidity. I’m driving the La Scalas with a Yamaha R-N803 100W/channel receiver.

 

Although I have a pair of subwoofers, I turned them off for the test so that I could get a base line with just the La Scalas. I configured the amplifier to use Full Range speakers without subwoofers. The distance to the speakers as per the Yamaha’s YPAO (Yamaha Parametric room Acoustic Optimizer) tool was the same as I measured with my tape measure (roughly 11' to one and 12' to the other). As per YPAO’s recommendation, the Right speaker level was set 1 dB higher than the Left.

 

Positioning

 

This diagram shows my listening room:

 Picture1.png.cb6933f300d8d4c97b488d9656ac0869.png

 

In the meantime

 

I’ve been trying to blend my 2 THTLP subwoofers with the system, using the DSP features of the SPA250DSP plate amplifiers that power them. I may share the results I’ve achieved (so far) in a separate post. TLDR: music sounds anemic and lacking in bass when I get a flat SPL chart (20 Hz – 20 kHz).

 

TIA for your comments and suggestions.

 

In case you're interested - same charts but with SPL scale

 

Here is the 20 Hz - 20k Hz chart using an SPL scale:

15-20K Hz La Scala only, no subs, SPL.png

 

Here is the 20 Hz - 200 Hz (i.e., zoomed in) chart using an SPL scale:

15-200 Hz La Scala only, no subs, SPL.png

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How does it sound? Does the bass seem to be OK when listening? If so I would contribute it to test problem. If no bass you will need to isolate the problem. Unhook the mids and tweeter and see if their is any sound coming from the woofers. Something is wrong with your test setup or if not probably going to be in the crossover networks. I see no way the bass can drop off that much as your graphs are showing unless there is something wrong. 

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That does look odd.  It doesn't look like a room null since it covers such a wide frequency range.

I've never measured my Heresys just my THTs.  I know by listening that in my seating position their bass drops off dramatically around 80Hz.

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45 minutes ago, henry4841 said:

How does it sound? Does the bass seem to be OK when listening? If so I would contribute it to test problem. If no bass you will need to isolate the problem. Unhook the mids and tweeter and see if their is any sound coming from the woofers. Something is wrong with your test setup or if not probably going to be in the crossover networks. I see no way the bass can drop off that much as your graphs are showing unless there is something wrong. 

I'd always thought that the bass was present, albeit fairly anemic. That's what drove me to get the THTLP subwoofers.

 

I'll disconnect everything except the woofers to verify that the woofers are actually producing sound. 

 

How might I check the crossover networks? They're new; I got them from Crites in the summer.

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Just now, wuzzzer said:

Do you have everything disabled in your receiver such as Audyssey, dynamic EQ, or anything else that would be messing with the signal?

My receiver has what's called YPAO (Yamaha Parametric room Acoustic Optimizer), not Audyssey. I mistakenly called it Audyssey because that's what my Denon home theatre receiver uses. I'll edit my original post to correct that.

 

Nevertheless, I don't think that there is any unusual signal processing happening within the receiver. YPAO did set some parameters such as speaker distance (11' and 12') and levels (0 dB and +1 dB). 

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2 minutes ago, captainbeefheart said:

A valid test would have to have zero acoustic processing enabled and use a power amplifier with a low output impedance and flat frequency response.

 

 

If this is an issue of processing why on earth would it attenuate the bass this much?

Typically, main are set to small which transfers most of bass to subs.

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15 minutes ago, billybob said:

Yes, you need to go stereo direct to bypass processor settings...

I think that's what I did, but I'll do it again just to be sure.

 

But, even if the receiver was messing with the signal, with the speakers set to Full Range and no subwoofer configured, it would't make sense for the receiver to throw away frequencies below 200 Hz --- unless there is something wrong (or misconfigured) with the receiver.

 

I wonder if the fall off from 200 Hz matches a typical slope, such as 24 dB/octave? My La Scalas drop from around -50 dBFS at 200 Hz to -80 dBFS at around 90 Hz, which seems pretty close to 24 dB/octave. It seems like a long shot, but perhaps the receiver is fouling up the signal.

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1 minute ago, Dave MacKay said:

I think that's what I did, but I'll do it again just to be sure.

 

But, even if the receiver was messing with the signal, with the speakers set to Full Range and no subwoofer configured, it would't make sense for the receiver to throw away frequencies below 200 Hz --- unless there is something wrong (or misconfigured) with the receiver.

 

I wonder if the fall off from 200 Hz matches a typical slope, such as 24 dB/octave? My La Scalas drop from around -50 dBFS at 200 Hz to -80 dBFS at around 90 Hz, which seems pretty close to 30 dB/octave. It seems like a long shot, but perhaps the receiver is fouling up the signal.

Could be wrong but, if configured for HT, you need to do direct stereo mode to LaScalas. Please refer to your users manual.

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2 minutes ago, billybob said:

Typically, main are set to small which transfers most of bass to subs.

 

I understand that when in home theater settings but he had it configured to full range speakers and no subwoofer.

 

I should have been more specific with the question. Where he has the the receiver in full range and no subwoofer setting that doesn't mean the processing is off, it's just in a different mode. I can't think of any situation besides home theater mode where the programming would cut bass this drastically, especially when we have found that loudness controls are popular and typically at lower volumes the bass is boosted. Basically I am wondering if there is something actually defective with the receiver.

 

If at all possible try the same test with a different amplifier.

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Just now, billybob said:

Could be wrong but, if configured for HT, you need to do direct stereo mode to LaScalas. Please refer to your users manual.

My receiver is stereo only. It doesn't support HT, just 2.1 (i.e., stereo plus subwoofer). 

 

I can confirm that the speakers were set to Full Range on the receiver.

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Just now, Dave MacKay said:

My receiver is stereo only. It doesn't support HT, just 2.1 (i.e., stereo plus subwoofer). 

 

I can confirm that the speakers were set to Full Range on the receiver.

Oh, was wondering why ypao.

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8 minutes ago, hanksjim1 said:

woofers out of phase?

Visually, the speaker wiring from the amp to the networks, and from the networks to the drivers is correct. I can double check everything (except the network to woofer wiring) with a multimeter.

 

I'd prefer to avoid having to flip the La Scalas upside down and remove the access panel to check the woofers until I've ruled out other possibilities. I could run the test with just one speaker to see if I still see the bass drop when testing the speakers one at a time. Would that be worthwhile?

 

The YPAO on the receiver gives an out of phase error, but that's apparently pretty common. Since the wiring is correct, I figured the "out of phase" warning had to be due to reflections from hard surfaces in the room.

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