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La Scalas - surprising SPL graphs

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On 3/7/2022 at 10:38 AM, Dave MacKay said:

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?




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.



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


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.




This diagram shows my listening room:



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

Dave , what kind of woofers are you using  ....... the stock  K-33-E  round magnet ? 

have you re-sealed the bottom woofer panel  with gaskets  ?  have you checked that the screws on the woofers are tight

is this an original stock LS   ?  or ,  are you using an open  lower bass extension  under the speakers

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To the OP I know you posted about trying to figure out why the bass is poor on your La Scalas but imho there was a reason I moved from la scalas to belles and wasn’t happy till I settled on K402 with direct radiating lowers.  The large horn with a direct radiating woofer (heresy, Cornwall, cornscala, ect) has way more bass.  I think it boils down to the type of sound you like. And it sounds like (pun intended) that you may want to try out a Cornwall.  I think you may find it has more of the sound character you are looking for.

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In my basement, and my LaScalas pushed into the corners, I was flat solid to 43Hz. With no real room gain, he should still be relatively flat to 50Hz.


So, either there is a weird issue with that room, placement, problem with the measuring set up, or a problem with the speaker(s). The Captain suggested using a different amp, which isn't a bad idea either -- just to rule it out.


I always start with the speakers. We've seen everything around here over the years, including woofers being chewed up by mice.


Rudy gives a lot of good advice, but I would start with Henry's suggestion of disconnecting the squawker, tweeter and just measuring the bass. 


Get the microphone on a tripod, drop it down to about three feet, and three feet back.


I'm pretty sure anything coming off that back wall is going to mess with your bass response, but it shouldn't just be disappearing on you like that.


Also, AL, AL-2, or some other network?

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REW has a room simulator module that's pretty accurate.  Click on the room-sim button on the top right and enter your dimensions, speaker locations, and listening position.  It will tell you where the room hot spots and nulls are below 200hz.

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I’d like to thank the members of the forum (@henry4841, @yamahaSHO, @wuzzzer, @billybob, @captainbeefheart, @hanksjim1, @Shakeydeal, @Crankysoldermeister, @babadono, @Rudy81, @garyrc, @Rolox, @NBPK402, @RandyH, @pbphoto, and @Kalifornian) who contributed to this thread.


The suggestions tended to deal with EQ, phase, speaker placement, and room treatment.

·         Given the layout and furnishings of the listening room, my options for placement are rather constrained.

·         Certainly, the room does need some acoustic treatment. In time, that will be addressed.

·         I’ve verified that the polarity of the AA networks and all of the drivers , including the woofers, is correct.

·         I’ve stopped using the EQ capabilities of my receiver and am now operating in Pure Direct mode (which bypasses all EQ and tone controls).


My goal was to “dial in” my La Scalas before adding (and EQing) my two THTLP subwoofers. For the purposes of this exercise, I configured the amp for stereo only (no subwoofer).


Initially, I used only a small set of the YPAO (Yamaha Parametric room Acoustic Optimizer) capabilities of my Yamaha R-N803 receiver. I thought that all I was doing was setting the distances and levels from the speakers to the listening position. I referred to this configuration as “YPAO neutral”.


When I followed up on suggestions from @wuzzzer and others, I found that the YPAO was altering the signal quite a bit: it boosted the low-mids and high frequencies, but diminished the bass substantially.

·         the low-end performance of the La Scala dropped precipitously below about 200Hz and was pretty much non-existent below 100 Hz

·         frequencies above 1 kHz were boosted by about 5 dBFS

·         frequencies between 200 Hz and 500 Hz were also boosted


I then turned the YPAO off and re-ran the tests.


Finally, I put the receiver in Pure Direct mode so that the receiver bypasses all signal processing and routes the input signal directly to the amp. The YPAO and all tone controls are completely bypassed.


This graph shows the results of the tests. For clarity, I averaged the results from each of the 3 microphone positions for each test and applied 1/6 smoothing.

·         The red line shows the results from the first (YPAO neutral) tests

·         The blue line shows the results from the YPAO off tests

·         the green line shows the results from the Pure Direct tests



There appears to be little discernible difference between the YPAO off and Pure Direct amplifier settings. Both are a significant improvement over the results when the YPAO system was enabled.


With my Yamaha R-N803 receiver configured in either YPAO off or Pure Direct mode, my La Scalas perform +/- 5dB from 64Hz to 18.5 kHz. I’m pretty satisfied with that.


My next challenge will be to blend my two THTLP subwoofers with the speakers. Fortunately, that may not be as hard as I feared since, according to Yamaha, in Pure Direct mode the receiver still sends 100 Hz and lower to the subwoofer output.


Since it’s clear that my room presents challenges at low frequencies, I expect I’ll need to make use of the EQ available from the SPA250DSP plate amps that power each subwoofer.


Thanks to all for your help.

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If you are interested, you can search for opinions on the various computer algorithms like Audyssey etc.  I found, once I was objective, that those pieces of software don't work as well as the manufacturers pretend they do.  You are way better off without all that stuff.


The La Scala is a great speaker and with modern manufacturing methods, the drivers are not the problem.  The cabinet is not the problem. Our rooms are the problem.  We all have to deal with the rooms we have.  Once you focus on that, you will be able to spend your time improving things wisely.  


As I mentioned, take your speaker outside of the room confinement and run a sweep.  You will be able to 'see' that most problems are caused by our rooms.  True for every speaker made.

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When I got my Yamaha RX-A2060 receiver in 2016, the bass response seemed to be weaker than it had been with the previous unit, an RX-V750.  I checked a couple of things, but wound up calling Yamaha for advice, which solved the problem.


The first thing to do is check the impedance switch on your receiver, if it has one.  It should be set at 8 ohms, regardless of the speakers you have connected to it.  The switch is intended to protect the receiver from overheating if it has no ventilation at all and is being used at high volume with low-impedance speakers.  For normal use, it should always be switched to 8 ohms.  If it isn't, it limits the rail voltage, which reduces the bass energy produced.  Be sure to turn the receiver Off before moving the switch.


If you run YPAO, you'll find that it sets the bass response lower than you may like.  I think it's always done this, so don't be shy to bump it up to taste.


Next, there are some odd items in the Setup menu.  In one place, you have to enable Extra Bass to get the subs working properly.  At another location in the menu, you have to enable Extra Bass to get anything near flat bass response.  I didn't find those out by myself.  They were news to me.  I called Yamaha Technical Service, and the service rep was very helpful.  There was nothing wrong with my receiver, it just has a quirky Setup menu.  I wound up bumping the Bass up 3 dB and the Treble down 3 dB to get a flat response.  Even set like that, The Flaming Lips CDs still sound bass light, but when you have to dig into a menu to find the tone controls, instead of having a pair or more of plain ordinary tone control knobs, I just leave it as is. That was six years ago, and the receiver has made me happy ever since the Yamaha service rep helped me sort it out.

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8 hours ago, RandyH said:

Dave , what kind of woofers are you using  ....... the stock  K-33-E  round magnet ? 

have you re-sealed the bottom woofer panel  with gaskets  ?  have you checked that the screws on the woofers are tight

is this an original stock LS   ?  or ,  are you using an open  lower bass extension  under the speakers

The woofers are the original (1986) K-33-E.


The screws on the access panel are tight.


I will be replacing the gasket (which is original and is squished as thin as a playing card) with some 1 1/4" wide x 3/8" thick closed cell gasket tape when I veneer and refinish the speakers this spring.

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1 hour ago, Dave MacKay said:


I will be replacing the gasket

you can use  an elastomeric   membrane  between the cabinet and the access panel   , it's clean , re-usable and makes for an excellent seal

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I have an older Yamaha AVR and I've noticed that YPAO is sensitive to where the mic is placed.  My old AVR only has a single mic placement to determine YPAO corrections.  If I run it with the mic in the middle of the room (bass null), the bass gets set way too high during movies.  The opposite is true if I run it with the mic close to the back wall (bass peak).  I have to find the sweet spot and then YPAO works very well.


I last ran REW on my stock LS2's over a year ago - by themselves, the sub alone, and then blended.  This is without the Yamaha AVR in the path - strictly 2-channel.  You can see I have a bass null in my room around 50hz and a peak around 30hz.


RED = stock LS2's alone

GREEN = sub alone

BLUE = blended


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I’d only use actual  test tones , and I would check  them with a spl meter at 4 ft or so , never mind the room response for now , and make sure that your in phase .I never let the avr’s black box set anything, cause who knows what adjustments will be made , set up all bass management manually for best results. I guess the Lascala’s horn unloads at 104 hz , but you would never know  it , because it continues to operate as a direct radiator at much lower frequencys   , and does this very effectively ,so much for the theory that direct radiator bass is incapable of  blending with horn sound 🤷My Lascala’s start rolling off significantly around 60 hz.

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My two cents

I would black box diagnose.


I don't know if your measurement system is integral to the receiver or stand alone.

The results are so far off LaScala specs and observed and measured parameters, the LS are the least likely source of the problem. If the woofers had failed completely, or somehow disconnected from the crossovers, signal would drop off a cliff at 400Hz.


Was the bass good before changing to the crites crossovers ?


Possible points of failure:


Measuring device aka pc

Measurement software bad batch or config


Receiver config

cables reversed

test tone generator defective


I would put the mic 1-2 meters directly in front of one LS, disconnect the other speaker, push the direct and large speakers config, and measure. My guess is the receiver is the problem. If you can hear the bass but it doesn't measure as present, then look to the mic and PC


My guess is that the receiver is not configured correctly, and or the documentation is wrong or poor. It wants to send everything below freq X to the subs


If you have a stereo amp or old stereo receiver, connect the single speaker to it and play some music using the tone controls and see if your base has returned. You can set to flat and measure again.


If no change, the Mic swap it out, if no change then look at the pc and software.


Don't swap everything at once, one at a time in mono with only one speaker connected.


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