Simplex port tuning frequencies?

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tvent
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Location: Helena, AR

Simplex port tuning frequencies?

#1 Post by tvent » Sat Oct 13, 2018 7:36 pm

I'd like to set my (lower-end) high-pass to the f3 dB down point on my Simplex 12's and (in process) Simplex Tilt-back.
What are the ports tuned to in those cabinets and what is the f3 dB down point if using 3012LF's as low-frequency drivers?

Thanks,
Tim
Built:
4 x WH10 melded
4 x WH8 melded
2 x Jack15 melded
2 x Simplex 12 w/BGH-25 for Bass
1 x Simplex Tiltback (powered PPA800DSP) for Keys
2 x SLA Pro
Bought:
6 x T39 20" 3012LF loaded

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Bill Fitzmaurice
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Re: Simplex port tuning frequencies?

#2 Post by Bill Fitzmaurice » Sat Oct 13, 2018 8:53 pm

They're tuned to 45Hz and 50Hz respectively. F3 is moot, it doesn't affect excursion, which is at a minimum at the tuning frequency no matter what driver is used.

tvent
Posts: 88
Joined: Sun Sep 26, 2010 4:29 pm
Location: Helena, AR

Re: Simplex port tuning frequencies?

#3 Post by tvent » Mon Oct 15, 2018 5:58 pm

Bill Fitzmaurice wrote:
Sat Oct 13, 2018 8:53 pm
They're tuned to 45Hz and 50Hz respectively. F3 is moot, it doesn't affect excursion, which is at a minimum at the tuning frequency no matter what driver is used.
Bill, thanks for all the responses to all my recent questions. I really appreciate the personal attention to detail you provide both in the plans and here on the forums.

I guess I was thinking back to my old car stereo days. Seems I remember we would high-pass at (I thought) F3 to increase efficiency, reduce port chuff, and generally not send energy to the cabinet that couldn't generally be reproduced by it anyway. I remember it seemed to really let us squeeze out the last little bit of performance on small, ported, low-power systems. Now that I think about it, that was over 20 years ago though so my memory may be a bit suspect. ;)

Is that worth worrying about in the Simplex designs or no?
Built:
4 x WH10 melded
4 x WH8 melded
2 x Jack15 melded
2 x Simplex 12 w/BGH-25 for Bass
1 x Simplex Tiltback (powered PPA800DSP) for Keys
2 x SLA Pro
Bought:
6 x T39 20" 3012LF loaded

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Bill Fitzmaurice
Site Admin
Posts: 26936
Joined: Tue May 02, 2006 5:59 pm

Re: Simplex port tuning frequencies?

#4 Post by Bill Fitzmaurice » Mon Oct 15, 2018 9:26 pm

High passing at Fb isn't a bad idea, not only to prevent driver over-excursion but also to keep the sound on stage from being too muddy.

ACUA
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Joined: Sun Sep 25, 2016 6:21 pm

Re: Simplex port tuning frequencies?

#5 Post by ACUA » Wed Oct 17, 2018 10:58 am

When I build my own bass reflex cabinets I use bass box pro, I usually model a few drivers and I play with making the cabinet as large as possible to get lowest frequency extension I can while balancing the driver excursion to be just under peak at full power right to the edge of the high pass filter. Or that lets me know where I must filter at. I have to manipulate the vent tuning as I go to optimize and I am not a wizard so it’s some trial and error. With that program I can graph predicted excursion while making enclosure changes and it’s pretty easy to land the point that I would consider optomization. That point is prediction via the program but I have had success. I won’t be selling plans any time soon if you know what I mean.
Advanced concepts underground audio

EduBH1978
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Re: Simplex port tuning frequencies?

#6 Post by EduBH1978 » Fri Oct 19, 2018 12:57 pm

Bill Fitzmaurice wrote:
Mon Oct 15, 2018 9:26 pm
High passing at Fb isn't a bad idea, not only to prevent driver over-excursion but also to keep the sound on stage from being too muddy.
Sorry if I'm being too nooby but.. I'll start the construction of a Simplexx 112 with tweeter (deltalite II 2512 + BGH25-8). I've purchased the pre-built crossover at Speakerhardware.

Isn't the speaker protected against over-excursion at low frequency (below 45hz)? I mean, I believe it's ok if I use one box, 8ohm, and my 150w amp.. but let's say, if I make another 112 (plans for the future), stack them at 4ohm and play a 5 string bass with a 500w amp, may I burn the driver?

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Bill Fitzmaurice
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Re: Simplex port tuning frequencies?

#7 Post by Bill Fitzmaurice » Fri Oct 19, 2018 3:41 pm

Harmonics, harmonics, harmonics. When you play a low B that's what makes up around 75% of the signal, not 31Hz.

EduBH1978
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Joined: Tue Sep 04, 2018 3:12 pm

Re: Simplex port tuning frequencies?

#8 Post by EduBH1978 » Sat Oct 20, 2018 12:47 am

Bill Fitzmaurice wrote:
Fri Oct 19, 2018 3:41 pm
Harmonics, harmonics, harmonics. When you play a low B that's what makes up around 75% of the signal, not 31Hz.
Ok, but, sorry again, this is my first build... you said before that the HPF isn`t a bad idea (not just for the over-excursion, I understand) so... are these 25% of the fundamentals a real risk if I use more power?

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Bill Fitzmaurice
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Re: Simplex port tuning frequencies?

#9 Post by Bill Fitzmaurice » Sat Oct 20, 2018 7:59 am

More power means more power at all frequencies, not just the fundamentals. Unless you do something really silly, like cranking a 32Hz EQ slider all the way up, you'll never have an excursion problem with the B string. The main benefit to a high pass is reducing string thump noise.

EduBH1978
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Re: Simplex port tuning frequencies?

#10 Post by EduBH1978 » Sat Oct 20, 2018 9:45 am

Bill Fitzmaurice wrote:
Sat Oct 20, 2018 7:59 am
More power means more power at all frequencies, not just the fundamentals. Unless you do something really silly, like cranking a 32Hz EQ slider all the way up, you'll never have an excursion problem with the B string. The main benefit to a high pass is reducing string thump noise.
Ok, now I understand! Thank you very much!!!

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