This blog post focuses on the maximum SPL of various speakers.
Why measure SPL?
Measuring Distortion Limited SPL helps you determine what speakers you'll need for your desired listening level (volume level) without introducing excessive distortion. These tests were carried out in a 100 cubic meter room, which represents a large living room or domestic living space.
A "Distortion Limited" SPL measurement is a type of measurement that looks at the maximum SPL a speaker can reproduce before a certain distortion threshold is met. Different thresholds can be selected but for this test I am limiting distortion to 1%. Distortion Limited SPL measurements are an important metric in a speaker system design.
I will test 6 different speaker configurations starting with the lowest SPL rating. This will help give some reference to some common speaker sizes contrasted against a horn speaker. Hopefully this test will shed some light on the very different performance levels that can be achieved outside of simply looking at a frequency response graph. Frequency response won't mean much if your distortion levels are hovering around the 1% mark.
The speakers under test are:
- Signet SL-16 Bookshelf speaker (2-way bookshelf with 6.5" woofer)
- Yamaha NS-690 Speaker (Mid Size 3-way with 3" dome midrange)
- E-250 Double Planar Front Horn (with and without rear chamber)
- E-250 with Quad Thiel/Scanspeak 10F midrange drivers (with and without rear chamber)
Signet SL-16 2-way Bookshelf Speaker
I begin my testing by measuring the Signet 2-way bookshelf speaker. I set my mic at 1 meter distance. The amplifier used is a 200watt class A/B. I am using REW measurement software with a calibrated mic. This means SPL measurements are accurate as indicated in the frequency response graphs.
Below is the frequency response of the Signet speaker at 5dB increment increases until distortion reaches the 1% threshold.
Below are the distortion measurements for the corresponding five measurements shown in the above frequency response measurements. As you can see from the below distortion plots the distortion actually never goes below 1% in the lower midrange (below 1kHz). This really surprised me. Realistically the speaker's maximum SPL is only 95 dB at 1 meter before sever distortion sets in. This is mainly limited by the woofer's distortion (6.5" woofer).
Yamaha NS-690 3-way Speaker
I then setup the Yamaha NS-690 speaker for testing. Below is the measured frequency response at various SPL levels.
Below are the distortion plots for each respective frequency response show above. As you can see the distortion in the lower midrange is much lower than the Signet Bookshelf. If using a distortion threshold of 1% then the Yamaha NS-690's maximum SPL is around 105dB.
E-250 Front Horn with Dual BG Neo8 Planar Transducers
I then measured the distortion/SPL for the E-250 Double Planar front Horn with no rear chamber
Below is the corresponding distortion plots for the above frequency response measurements. Distortion steadily rises to 1% which corresponds to 105dB SPL. This is the same as the Yamaha NS-690 which also share approximately the same physical size. Please note the E-250 measurements are with no crossover or EQ.
E-250 Dual Planar (Neo8) with rear Chamber
Next I add a rear chamber onto the E-250 Horn and retested under the same conditions.
Below are the corresponding distortion measurements for the above frequency response measurements. Adding the rear chamber helps increase the maximum SPL from 105dB to 109dB. At 100dB SPL the rear chamber lowers distortion from 0.5% down to 0.20% in the lower midrange.
E-250 with Quad Thiel/ScanSpeak 10F/8424G02
Next I tested the E-250 Horn with Quad ScanSpeak 10F/8424G02 10cm midrange drivers. Below are the frequency response measurements taken at various SPL levels.
Below are the corresponding distortion measurements for the frequency response measurements shown above. This configuration is able to produce 115dB SPL through the midrange (250Hz - 2kHz) based on a 1% distortion threshold.
For interests sake, with the same input power the Yamaha only achieves 95dB SPL.
E-250 with Quad Thiel/ScanSpeak 10F/8424G02 with Rear Chamber
Below are the frequency response measurements with the rear chamber at various SPL levels. As you can see 122dB SPL is achieved through the midrange. This horn could easily be crossed over to a 1" compression driver at 2kHz for example. Otherwise distortion remains low even in the upper treble. So all that is required is to EQ the frequency response either actively or with a passive crossover. After EQ you could expect 110dB SPL from 250Hz - 17kHz. If using as a midrange only then you can expect the full 122dB SPL output.
Below are the resulting distortion plot measurements for the above frequency response measurements. Notice that if listening at lower listening levels distortion drops to very low levels.
Conclusion
Below is a summary of the maximum SPL each speaker was able to achieve.
Signet: 95dB SPL
Yamaha: 105dB SPL
E-250 Dual Planar (no Chamber): 105dB SPL
E-250 Dual Planar (With Chamber): 107dB SPL
E-250 Quad 10F (no Chamber): 115dB SPL (Midrange Only), 103dB (Midrange + Treble)
E-250 Quad 10F (With Chamber): 122dB SPL (Midrange Only), 109dB (Midrange + Treble)
All of my measurements were taken at 1 meter distance. To figure out what this means in terms of SPL at the listening chair, just subtract 6.5dB from the above figures. This assumes a stereo setup with a 3 meter listening distance from the speakers. For example the E-250 Quad 10F used fullrange is 109dB at 1 meter, or 102.5dB at the listening chair. By contrast the Signet is 95dB at 1 meter, and 88.5dB at the listening chair. For reference the THX standard for home theaters is 105dB SPL at the listening chair. So the only speaker in this comparison that meets the THX standard would be the E-250 Quad 10F used as a midrange only. You would need to supplement with a 1" compression driver crossed over at 2kHz. Alternatively if your goal is strictly sound quality as is the case with an Audiophile setup, then the lowest distortion comes from the E-250 Dual Planar with the rear cover. It achieves 0.30% THD% from 250Hz-10kHz at 93.5dB at the listening chair. When comparing to the Signet 2-way bookshelf, the 6.5" woofer distorts badly at 2% when attempting the same SPL level.