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RCF dBu SPL measurement

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djmihaigabriel View Drop Down
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    Posted: 10 January 2023 at 7:57pm
Hi everyone, I was looking recently on some datasheets from RCF, for example the following for TTL 6a

https://www.rcf.it/en/products/product-detail/ttl-6-a?p_p_id=it_dvel_rcf_products_frontend_web_portlet_ProductDownloadsPortlet&p_p_lifecycle=2&p_p_state=normal&p_p_mode=view&p_p_resource_id=downloadProductFileEntry&p_p_cacheability=cacheLevelPage&_it_dvel_rcf_products_frontend_web_portlet_ProductDownloadsPortlet_productCode=STP0105&_it_dvel_rcf_products_frontend_web_portlet_ProductDownloadsPortlet_profileId=239127

There is a SPL measurement for -20dBu/2m and there is no voltage or resistance specified. I know that dBu is related to voltage and voltage to resistance and I can't figure out how to calculate SPL 1 W/1 m. I'm sure their max SPL is fiction, so what would be max dBu or max SPL calculated ? Do they do this dBu measurement intentionally so it's more confusing? 

Big thanks


Edited by djmihaigabriel - 11 January 2023 at 1:53pm
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madboffin View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote madboffin Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2023 at 9:35pm
dBu is a measurement of voltage relative to 0.775V (same voltage as for dBm, but with the impedance unspecified). So -20dBu is 77.5 mV.

I coudn't get your link to work, but the TTL6A is an active speaker, so the sensitivity will be specified for a signal voltage into the processor, rather than power into the actual speakers.




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djmihaigabriel View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djmihaigabriel Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2023 at 11:02pm
Thanks for explanation madboffin

I think I fixed the link. The datasheet is the official one for RCF TTL 6a from rcf.it website.

https://www.rcf.it/en/products/product-detail/ttl-6-a

What would be the max dBu ? 

Based on this dBu measurement is there any way to figure out the db SPL for 1W at 1m or 2m distance ? 

Is there any way to compare it with other datasheets that provide db SPL at 1W/1m measurements?

Thank you!


Edited by djmihaigabriel - 11 January 2023 at 2:03pm
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djmihaigabriel View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djmihaigabriel Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2023 at 11:10pm

I've uploaded some images of the datasheet

https://ibb.co/B4yqSHC -

https://ibb.co/3FyqSHx -

https://ibb.co/M8nnZMW -

https://ibb.co/Fg66NJT -

https://ibb.co/mFshYDC -




Edited by djmihaigabriel - 10 January 2023 at 11:10pm
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djmihaigabriel View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djmihaigabriel Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2023 at 1:35pm
Without nominal and maximum dBu levels specified, does this RCF charts make any sense to you? What is max dBu level for full power +4 or +8 or +10 ? Am I missing something, how this charts help us in any way in choosing a pa system, what is the real db spl at full power? No impedance specified, but they specified max spl 139db and the source for this measurement is 'trust me bro'

Please take a look at the following chart from FBT (another italian brand) for Himaxx 60a speaker. They mention the db spl and full space, that's it. Is this for 1w at 1 meter or full power at 100 meters or what, should I guess this? Also they don't mention if this is with any dsp preset or smoothing and many manufacturers do this. 

I think that either I'm too stupid to understand this datasheets, either these brands are intentionally hiding some details and come up with a good looking max spl number and charts to fool people.

I know there are many smart people around here so what do you think?

https://ibb.co/f12YzkC -





Edited by djmihaigabriel - 11 January 2023 at 3:17pm
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FOO View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FOO Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2023 at 3:51pm
Can't help you with the numbers, but I can tell you that these boxes are L.O.U.D....
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djmihaigabriel View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djmihaigabriel Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2023 at 4:41pm
Thanks FOO for your opinion.

I believe they are loud, but I have no interest in this speakers in particular.

I was wondering what's up with these datasheets and if they are part of the marketing trend to push as many W and Max SPL as main sell point since we all seen lately many respectable brands pushing low cost products to compete with Behringer, Tbox etc.

An almost good datasheet I found recently that I can share is the following one from Seeburg Acoustics. For the active version of the X8 speaker they provide 
- a chart for Sensitivity 1 W @ 1 m + Impedance - without any preset
- another chart for Frequency Response with Presets

Based on the max RMS power they specify for the amp module, the spl of the speaker can be calculated very easily.

But this is still not perfect for me because they don't mention if the measurement is for full space or not, so I have to assume that it is.

https://ibb.co/Xb8Qk1q -













Edited by djmihaigabriel - 11 January 2023 at 4:51pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2023 at 4:48pm
The problem with Max SPL numbers is that there's no standard way of measuring them.
It's completely common for manufacturers to use a test method that yields the highest possible figure even if there's no real chance of achieving that in ordinary use. The 139dB quoted here is certainly plausible, if we look at the peak power available to the HF and the likely maximum sensitivity of the driver. A good 3" coil, 1.4" exit driver will have a sensitivity of 110-112dB over at least part of its range; apply 800W peak at just that frequency and there you are: 139-141dB. Obviously, that could only happen for a very short time, but happen it could.

So, they're not lying with that figure - just choosing to find a way of getting the biggest possible number.

For a more real world figure, download the gll file and view it in EaseGllViewer.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djmihaigabriel Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2023 at 4:58pm
Thanks DMorison, I will take a look!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djmihaigabriel Quote  Post ReplyReply Direct Link To This Post Posted: 11 January 2023 at 9:19pm
Just tried the GLL Viewer software for a speaker that I have - FBT Mitus 206L (passive speaker).

This speaker have nominal impedance 16 ohm LF, 16 ohm HF.

The software gives a sensitivity of 100.6 dB SPL at 2.83Vrms/1m which, if it's for 16 ohm, would mean 103.6 dB SPL at 1W/1m.

There is no way this is correct. There are 2 x 6.5" speakers in a ported enclosure.

The whole chart from 80hz and up is around 100 dB.

Maybe the 100.6 dB sensitivity is for 8 ohm even if the speaker impedance is 16 ohm? In this case it would mean 97.6 dB at 16 ohm. Which still does not make sense because this mean 100.6 dB at 1W/1m and does not match the 97 dB at 1W/1m declared by the manufacturer in the datasheet.

To match the declared sensitivity the software should show 94 dB at 2.83V/1m (16ohm)

Any explanation for this?




Edited by djmihaigabriel - 12 January 2023 at 3:22am
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