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Discussion Starter · #1 · (Edited)
Hi,

How can I adjust settings to test my subwoofer at higher db with a macbook. When I run "check levels" before taking a measurement I can get clipping if I try and set it around 90db.

I'm hoping running a sweep at a higher level will give me a better idea of response of between 18-20hz.
I built a diy subwoofer cabinet that is 7.5 ~ cuft at 18.5hz tuning, according to the specs on avsforum.com and I wanted to be able to see the tuning results in the rew graphs.

The subwoofer is an stereo integrity ht18d4 being driven by an inuke3000dsp amp, in a very large cabinet.

I'll post some graphs after I take a couple sweeps around my listening position.

Thanks.

Also as I understand:

-Turn Audyssey and any other processing off from avr
-run sweep
-analyze measurements, plug filters into peq
-run sweep
-turn audyssey back on

Thanks

IMG_20150824_100648.jpg
 

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I'm hoping running a sweep at a higher level will give me a better idea of response of between 18-20hz.
It won’t get you any better results that you could get with a measurement in the 75 dB range. Measurements at 75 dB and 90 dB will look identical. The only difference is that the latter would be higher on the graph.

Regards,
Wayne
 

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Just adding to Wayne Post - I was typing this:
It's possible to recalibrate using lower input gain on the mic (either USB or XLR types) to allow for more headroom in measurements so getting higher SPL before overload is possible. For an XLR mic just reduce audio interface input gain and then recalibrate the REW SPL meter. The available headroom is reported during the process.

There are really 2 subjects here; the speaker response, and the LP response.
1. Measuring the speaker response to 18Hz in a room accurately is very difficult.
> You could take it outside and follow procedures available for that situation.
> You could measure the woofer with the mic right in front 1" or so from the driver dust cap and also measure with the mic 0-1" from the center of one of the ports. The 2 responses can them be spliced together to get a maybe reasonable idea of the speaker response. There are guidelines someplace on exactly how to do that.
75 dB is fine for either of those methods. High levels don't change SPL response measurements until capacity limitations occur. You will not have any capacity limitations with your SW. The TS predictions are very accurate so if the design and construction was reasonably done the measurements will be close. If model vs measurements differ significantly, I would suspect the measurement setup first. Then design/construction errors.
> You could also get an indirect SPL result by measuring the SW impedance to determine if you achieved the targeted box tuning frequency. If that is reasonably close the speaker SPL response will follow accord to the model.

2. The LP response has very little to do with the speaker SPL response at low frequency. The room is a far bigger influence. As long as there is SPL capacity of the SW any SPL raggedness of the speaker response becomes moot. It takes a large design error to impact the SPL significantly. EQ is needed anyway to smooth the response below 200Hz. Before and after EQ charts are all over the web so examples of the magnitude of room impact can be easily seen no matter the cost/quality/response of the SW. There is nothing than can be done for room nulls other than move the SW, but other peaks and dips can be EQed to a reasonable extent.
 
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