Why can’t I hear my THTLPs?

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DaveMacKay
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Why can’t I hear my THTLPs?

#1 Post by DaveMacKay »

I have two minimum-size (15"x18"x72" with 12” RSS315HF-4 driver) THTLPs in my listening room. They are upright with the mouths firing towards the ceiling.

I have the THTLPs connected to my stereo and use them for listening to music. I typically listen at levels of 75 to 85 dB.

I know that they are working:
  • With REW, I can see how they perform in my room (see attached graph).
  • If I turn them off, the music seems hollow.
But I can’t hear them making any sound. Even when I put my ear right against the THTLP (near where the driver is located) I can’t discern them making any sound.

Is that how they should be performing? Do they only become more pronounced at higher volumes? Or might I have a problem that needs investigating?
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THTLPs.jpg
Last edited by DaveMacKay on Wed Dec 21, 2022 12:14 pm, edited 3 times in total.

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J_Dunavin
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Re: Why can’t I hear my THTLPs?

#2 Post by J_Dunavin »

Try unplugging just one.
Make sure they are not playing out of phase with each other
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Bill Fitzmaurice
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Re: Why can’t I hear my THTLPs?

#3 Post by Bill Fitzmaurice »

The reasons are equal loudness and localization. It takes a 100dB tone at 60Hz to sound as loud as an 85dB tone at 600Hz. Even with the subs at a relatively high level the sound will seem to be coming from the mains, because of the distance between your ears. When that's relatively long compared to the wavelengths being heard you can directionally located where they're coming from. When that's very short compared to the wavelengths being heard you can't. A 60Hz wavelength is 18.75 feet. Even elephants don't hear very low frequencies, which they use to communicate over very long distances. They sense them with their feet via ground conduction.

DaveMacKay
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Re: Why can’t I hear my THTLPs?

#4 Post by DaveMacKay »

Deleted message. Taking new measurements.
Last edited by DaveMacKay on Wed Dec 21, 2022 5:00 pm, edited 2 times in total.

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Bill Fitzmaurice
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Re: Why can’t I hear my THTLPs?

#5 Post by Bill Fitzmaurice »

Do it again with two different mic positions. That should give two different results. If not something is amiss. The peaks and valleys are caused by boundary reflections. They should shift with the mic placement.

DaveMacKay
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Re: Why can’t I hear my THTLPs?

#6 Post by DaveMacKay »

J_Dunavin wrote: Wed Dec 21, 2022 12:00 pm Try unplugging just one.
Make sure they are not playing out of phase with each other
Thanks for the suggestions. In pursuing them, I've taken some measurements with REW and created charts showing the results.

This shows how my two subwoofers perform together, orchestrated by a MiniDSP 2x4HD:
both on.jpg

This shows how each subwoofer measures individually when the other subwoofer is muted:
individual.jpg

This shows the affect that changing the phase has on each individual subwoofer:
one at a time.jpg
To take these measurements, I set 1 subwoofer at 0 degrees phase and set the other to 180, then switched them vice versa.

This shows the affect that setting the phase to 0 or 180 on both speakers has:
both 0 or 180.jpg

Based on that data, I have changed my subwoofer configuration so that the LF sub is inverted (i.e., phase at 180 degrees) and the RR subwoofer is as 0 degrees.
new config.jpg

So .. I know that the subwoofers are working and --- thanks to your suggestion --- I've improved my configuration. Thank-you.

However, it still seems odd that I don't hear sound emanating from the subwoofers.

DaveMacKay
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Joined: Tue Aug 03, 2021 3:10 pm

Re: Why can’t I hear my THTLPs?

#7 Post by DaveMacKay »

Bill Fitzmaurice wrote: Wed Dec 21, 2022 12:31 pm The reasons are equal loudness and localization. It takes a 100dB tone at 60Hz to sound as loud as an 85dB tone at 600Hz. Even with the subs at a relatively high level the sound will seem to be coming from the mains, because of the distance between your ears. When that's relatively long compared to the wavelengths being heard you can directionally located where they're coming from. When that's very short compared to the wavelengths being heard you can't. A 60Hz wavelength is 18.75 feet.
Thanks Bill.

I do hear satisfying sound at the low end, it just doesn't sound like it comes from the subwoofers. Your explanation has taught me why that's the case.

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