Need advice:bass reflex not tuned in high power

[FLAVIO MARINS]

Hello to all.
After a long time preparing myself , buying measurement equipment and the materials I built a subwoofer for low frequency effects in home theater.

My front and surround speakers are Behringer 2031A which have a nice output from 35 Hz up. They are externaly equalized and delayed to have similar response in all seats.

The subwoffer is a selenium extreme tweve inches which had one of the spidders removed in order to reduce the ressonance from 40 Hz to 24Hz. VAS = 220 liters and qts=0.37 after the modifications. I t was installed in a 200liter bass reflex box with two four inches pvc tubes not flared tuned to 22Hz..

According to my mini dsp usb microphone and REW software the frequency response and distortion are better than I deserve🙂.

The subwoofer is feed from a behringer 3000 dsp, equalized with several deeps to reduce the room ressonances.

The only problem: Ican not reach THX sound pressure levels due to the voice coil hitting the magnetic structure in high intensity passages of movies. Measurements indicate the hitting occurs even at the ressonance frequency of the bass reflex in high power.

My first diagnostic is : the high turbulence of the air in the 4inches tubes is taking the bass reflex out of tuning. Am i correct? Do you have any ideas how tochange the project?

Thanks for your time and help.
Flavio

 

[chris661]

A pair of 4" ports for a 12" driver should be plenty.

A few things to check...
- are you sure you're causing the driver to bottom out? - the iNuke amps sound like crap when you hit clipping - you could be hearing that.
- are you sure the ports are tuned to 22Hz? Can you check?
- do you have a high-pass filter set to 20Hz to cut off the very low bass?

Chris

 

[wg_ski]

What is x-max on the woofers? I've got some old Eminence 12's with very similar T/S and an x-max of 8 mm. The models say they run out of gas at *80 watts*. As a woofer in a 3-way in a similar large low tuned cab, a 200 wpc amp will bottom them out with music. They certainly don't have the guts for HT sub duty. Yours might not either. There may have been a reason the original design was only intended to get into the 40's.

 

[Inductor]

Good comparison. The woofer is out of spec now. You can't manipulate all the specs to your desires...
What's the full target specs anyway?!

 

[tb46]

Hi FLAVIO MARINS,

Post #1: "...reduce the resonance from 40 Hz to 24Hz. VAS = 220 liters and qts=0.37 after the modifications. I t was installed in a 200liter bass reflex box with two four inches pvc tubes not flared tuned to 22Hz..."

Vas=220L seems too high. I'll attach an example BR using the TC Sounds Epic 12", that one has Fs=24Hz, and Qts=.4. The Vas is 91.27L. Are your values measured?

Either way, you need to use a steep low cut (high pass) filter below Fb, or your driver will bottom out at just about any high power level signal below resonance.

Your ports may be a little too small, that depends on how much power you use. Try to keep the port particle velocity below 15m/sec in your designs. That would be a reasonable value, 10m/sec would be better. 🙂

I'll attach a Hornresp example (which should be Vrc=100L [or less]), you can just enter your T/S parameters, and take a look around.

Regards,

 

[Inductor]

I gave a second look at your thread and changing from a 12" to a 15" should be fine.
In top the priority (this if you are in the Brasil controlled market):
Selenium 15WS600
Selenium 15WS600 15" 600W Woofer
http://www.jblpro.com/ProductAttachments/15WS600_SpecSheet.pdf
Selenium WPU1505
http://www.selenium.com.br/sitenovo/admin/Documentos/WPU1505_i.pdf
Selenium WPU1509
http://www.parts-express.com/pedocs/specs/264-345-selenium-specifications-45221.pdf
Selenium 15SW1P (large Xmax, Xlim 9.3mm and 25.0mm. You can use to spec 800 RMS with right align/tuning on this one, maybe smaller box)
http://www.selenium.com.br/sitenovo/admin/Documentos/15SW1P_p.pdf

The problem with the SELENIUM 15WS600, VB = 200.0 L, FB = 30.0 Hz is that (with most of the Seleniums) you can use only RMS ~80W for Xmax... You can take your cup of venom!!!
If you opt for one of this drivers post it for further development. Have fun.

 

[Inductor]

iNUKE NU3000DSP pdf
8 Ω per channel, stereo 440 W
8 Ω 1520 W

 

[FLAVIO MARINS]

Chris,
-Tomorrow morning I will put the iNuke in bridge mode. I was using just on amp .
Loudspeaker impedance curve shows a sadle in 22Hz, while at low power levels- up to 50 Watts. after 50 watts the loudspeakes impedance changes
-I have just a first order 18 Hz High pass.

Thanks for the advice.
Flavio

A pair of 4" ports for a 12" driver should be plenty.

A few things to check...
- are you sure you're causing the driver to bottom out? - the iNuke amps sound like crap when you hit clipping - you could be hearing that.
- are you sure the ports are tuned to 22Hz? Can you check?
- do you have a high-pass filter set to 20Hz to cut off the very low bass?

Chris

 

[FLAVIO MARINS]

You have a point. I just looked up in internet for the Xmax, but the manufacturer Xmax specified is the linear Xmax (height of voice coil minus gap height) =14mm. I could not find the mechanical Xmax, and as you said, the original design was 40 Hz...
Thanks!

What is x-max on the woofers? I've got some old Eminence 12's with very similar T/S and an x-max of 8 mm. The models say they run out of gas at *80 watts*. As a woofer in a 3-way in a similar large low tuned cab, a 200 wpc amp will bottom them out with music. They certainly don't have the guts for HT sub duty. Yours might not either. There may have been a reason the original design was only intended to get into the 40's.

 

[FLAVIO MARINS]

the project target is "just" THX ultra 2 spec - 130dB @ 30Hz, 122dB @ 20Hz, 112dB @ 15Hz 1/8 space, 1m with less than 10 % distortion.

In order to Measure this I use a calibrated microphone, which clips at 118 dBSPL, so I measure at 4 meters in the garden ( open field).

Thanks,
Flavio

Good comparison. The woofer is out of spec now. You can't manipulate all the specs to your desires...
What's the full target specs anyway?!

 

[Inductor]

I meant the T/S specs (target) for the new driver. Can't you go with the 15"? The 12" looks to me like a lost case. You can't measure T/S and can't know best parameters for vol.net and tuning.

 

[FLAVIO MARINS]

Hello tb46

The Vas was measured using the added mass procedure, and :
HP8116a function generator
tek 2235 scope.
the voltage aplied to the speaker during measurement- 1 volt at 150Hz.

regarding the high pass filter... the sub-sonic effects which I have now, (like in thunders, crashes, hits) are adictive. Is it an acceptable procedure to reduce the bass reflex tune frequency in order to negate the need of a steep high pass at... let`s say 20 Hz? I would like to fell since 15 Hz, which, I know, it is not a easy task for a 12 inches woffer.


Please, which software do you use for speaker simulation?

Thanks for the comments.
Flavio

Hi FLAVIO MARINS,

Post #1: "...reduce the resonance from 40 Hz to 24Hz. VAS = 220 liters and qts=0.37 after the modifications. I t was installed in a 200liter bass reflex box with two four inches pvc tubes not flared tuned to 22Hz..."

Vas=220L seems too high. I'll attach an example BR using the TC Sounds Epic 12", that one has Fs=24Hz, and Qts=.4. The Vas is 91.27L. Are your values measured?

Either way, you need to use a steep low cut (high pass) filter below Fb, or your driver will bottom out at just about any high power level signal below resonance.

Your ports may be a little too small, that depends on how much power you use. Try to keep the port particle velocity below 15m/sec in your designs. That would be a reasonable value, 10m/sec would be better. 🙂

I'll attach a Hornresp example (which should be Vrc=100L [or less]), you can just enter your T/S parameters, and take a look around.

Regards,

 

[bjorno]

Hi All,

If the Driver is a Selenium Extreme-12SW5: There is no chance to retune this Driver to a Qts of 0.37,Vas= 220 liter and fs=24Hz without altering the Mass of the Cone, even if the Spiders are dried out making the Qts= 0.4.

b🙂

 

[FLAVIO MARINS]

Bjorno,

I do not have the background to understand in a pass of eyes the page you sent. 🙂 I will print it and download to my mobile, in order to study and learn.

Other thing I will do: repeat the measurement of the speaker with great attention to the details in order to get accurate results.

Bjorno, thanks for the time you spent in the analysis, and the oportunity you gave me to learn more🙂

Hi All,

If the Driver is a Selenium Extreme-12SW5: There is no chance to retune this Driver to a Qts of 0.37,Vas= 220 liter and fs=24Hz without altering the Mass of the Cone, even if the Spiders are dried out making the Qts= 0.4.

b🙂

 

[richie00boy]

The spider is necessary to keep the cone alignment at high excursion, it is not optional! Even more a problem if you try to run the sub at high levels.

120dB+ at 20Hz from a single 12 inch driver in a garden is just not going to happen, not even close.

 

[bjorno]

Hi All,

FYI: A Simulation depicting a 200L BR using a Selenium Extreme 12 SW5 with altered Parameters:

b🙂

 

[tb46]

Simulation Software, here: Hornresp

Hi FLAVIO MARINS,

Post #12: "...which software do you use for speaker simulation?"

The example I attached to Post #5 was done in Hornresp. Post #5: "...attach a Hornresp example..."

Hornresp is the name of the software, you can download David McBean's Hornresp for free:

Hornresp

It does have a Help file, and there are tutorials on the web:

Hornresp for Dum... hmm... Everyone 😉 - Home Theater Forum and Systems - HomeTheaterShack.com

Simple Tapped Horn Tutorial using Hornresp - AVS Forum | Home Theater Discussions And Reviews

It is well worth the effort to learn. One of the features is a Filter Wizard that lets you modify the input filter, and observe the impact on e.g.: SPL and displacement.

Regards,

 

[FLAVIO MARINS]

Uopsss ... this speaker has 2 spiders originaly. Just one is enough to keep the alignement. So far not a problem the operation with only one spider.

The spider is necessary to keep the cone alignment at high excursion, it is not optional! Even more a problem if you try to run the sub at high levels.

120dB+ at 20Hz from a single 12 inch driver in a garden is just not going to happen, not even close.

 

[FLAVIO MARINS]

Regarding the 120dB SPL at 1 meter in a open enviroment I agree that it is not feasible with a 12 inches, but this is the final target for in the room, where I will have some reinforcement from the room itself.

By the way, I am already thinking how to change the wife acceptance factor in order to have a second sub in the room.

Thanks,
Flávio

The spider is necessary to keep the cone alignment at high excursion, it is not optional! Even more a problem if you try to run the sub at high levels.

120dB+ at 20Hz from a single 12 inch driver in a garden is just not going to happen, not even close.

 

[FLAVIO MARINS]

A pair of 4" ports for a 12" driver should be plenty.

A few things to check...
- are you sure you're causing the driver to bottom out? - the iNuke amps sound like crap when you hit clipping - you could be hearing that.
- are you sure the ports are tuned to 22Hz? Can you check?
- do you have a high-pass filter set to 20Hz to cut off the very low bass?

Chris

Chris,

you were correct about the Inuke clipping... using sweeps from 10Hz to 200 Hz I got some very nice problems, as you can see in the picture attached.
Not sure if it is just clipping or a protection circuit being engaged due to the HIGH inductance of the speaker.
The sweep should be like in the tek0001 picutre, but the sound produced when playing the sweep in lower volume produced the voltage showed in tek0003, and it really sounds like a ehnnn let`s say loud Shot or speaker bottoning..

Thanks for the tip.
Flavio