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ClaudeJ1

Quarter Pie Bass Horn: Measured FR, How2Build, and Hornresp

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The front QPs are currently 50- 400 HZ. I should have REW up and running soon and that could change.

IM distortion drops significantly at high output levels when you do the high pass section of the filter at 60Hz. Although, at 50 Hz. it's still lower than so many other bass sections in the world that use a single 15" driver.

Edited by ClaudeJ1

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Which way did you turn the THT? Like this?

 

 

 

 

No, both THTs aim towards me and they are in parallel. I also use separete amp for each THT with 0-180 phase adjustment. In practice I measured low frequency response in my listening position and made it as flat as possible correcting phase.

post-60882-0-71340000-1464683622_thumb.j

Edited by Mariusz_
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Which way did you turn the THT? Like this?

 

 

 

 

No, both THTs aim towards me and they are in parallel. I also use separete amp for each THT with 0-180 phase adjustment. In practice I measured low frequency response in my listening position and made it as flat as possible correcting phase.

 

With the overhang of the Qpie, and the coupling of the walls and floor, you are extending the horn length to 13.6' and lowering the tuning frequency to 20.7Hz and increasing the mouth size of the THT with a flare like a BFM T-30. 

 

Tell me how it sounds.

Edited by mustang guy

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Lowering the response was not my intention. By the setup I made I did extend the length and increased the mouth size but at the same time I put a special woofer into THT. By “special” I mean more musical than HT-assigned one. It is Beyma SM-115K with qts=0.25, fs=29Hz and moving mass of 121g, when recommended Dayton has qts=0.43, fs=19.5Hz and moving mass of 306g. And I got fast impulse response matching seamlessly my QPs. And it is still reasonably low player starting to sound good at 23-24Hz (when I use a single frequency generator and evaluate quality be hearing) or even from 20 Hz (when I sweep low tones and measure them with microphone).

Well, and eventually it is very powerful subwoofer, so I one likes high volume levels, my THTs can make one's hair moving when listening :-).

Edited by Mariusz_

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Interesting. I had some time on my hands, so I modeled both drivers in the THT with the added 12" wide flare:

 

B1SfJzJ.png

 

I really think this looks great. I wish I had the knowhow to model Claude's bass bin with it. 

Edited by mustang guy

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I modeled it too and it helped me to choose Beyma. Look at my simulation and the real response measured outside.

 

 

post-60882-0-45060000-1464712188_thumb.j

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Speaking of a horn sub for QP. Some time ago I tried to model a sub based on QP profile. It is not too difficult to "put" a long truncated horn inside QP. At least on paper :-). I never built it because I am happy with my current system, but if anyone is interested...

 

To simulate it in Hornresp enter 

s1=100

s2=500

s3=1250

s4=2250

 

Lenghts (conical)

100

330

60

post-60882-0-19700000-1464712639_thumb.j

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Speaking of a horn sub for QP. Some time ago I tried to model a sub based on QP profile. It is not too difficult to "put" a long truncated horn inside QP. At least on paper :-). I never built it because I am happy with my current system, but if anyone is interested...

 

To simulate it in Hornresp enter 

s1=100

s2=500

s3=1250

s4=2250

 

Lenghts (conical)

100

330

60

Your Qpiesub has a horn length 107cm longer than the THT.  That has a tune of about 18Hz if you ever wanted to squeeze another 2.5 Hz out of your corner sub. :)

 

About my hornresp graph. Mine doesn't look like yours. Mine peaks at 32-33Hz for both drivers. I must be off on a measurement... I guess I have to go relearn that program...

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Lowering the response was not my intention. By the setup I made I did extend the length and increased the mouth size but at the same time I put a special woofer into THT. By “special” I mean more musical than HT-assigned one. It is Beyma SM-115K with qts=0.25, fs=29Hz and moving mass of 121g, when recommended Dayton has qts=0.43, fs=19.5Hz and moving mass of 306g. And I got fast impulse response matching seamlessly my QPs. And it is still reasonably low player starting to sound good at 23-24Hz (when I use a single frequency generator and evaluate quality be hearing) or even from 20 Hz (when I sweep low tones and measure them with microphone).

Well, and eventually it is very powerful subwoofer, so I one likes high volume levels, my THTs can make one's hair moving when listening :-).

This is a great example of combining theoretical behavior, measurement and LISTENING to arrive at a practical solution............all in the name of musical detail and the grand ILLUSION of 2 channel audio, which we all seek!

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Speaking of a horn sub for QP. Some time ago I tried to model a sub based on QP profile. It is not too difficult to "put" a long truncated horn inside QP. At least on paper :-). I never built it because I am happy with my current system, but if anyone is interested...

 

To simulate it in Hornresp enter 

s1=100

s2=500

s3=1250

s4=2250

 

Lenghts (conical)

100

330

60

Thanks for coming back with this sketch and info. I will model a few drivers and see if I can build one. It looks like a great option, although I have, literally a TON of subwoofers right now, but this may change after another move.

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...but this may change after another move.
You seem to be moving every couple of years... are you trying to avoid an ex? ;)

 

Bruce

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...but this may change after another move.
You seem to be moving every couple of years... are you trying to avoid an ex? ;)

 

Bruce

 

Not at all, jobs related mostly (contract), downsizing, but I finally met a great lady who like music and movies........so.......who knows......you do the math.

Edited by ClaudeJ1

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Hi Claude

 

Well I've just got my new minidsp and mic so I was able to measure the quarter pie. I don't think it looks too bad for an in room reading, a few big room dips and peaks to sort out. This reading was taken in room at my listening location, no filters or crossover. 

 

I'm thinking about the eq for this now, as most of the lower issues are room created I think I'll leave this and just give it a bit of lift after 250hz, sound about right?

 

Cross over point? It behaves well almost to 1khz so would i t be ok to 650-700hz? My mid horn is 340hz and they say it should be crossed 1 octave higher than this.

 

Your thoughts please.

 

Many thanks Dave 

post-62431-0-59900000-1466486662_thumb.j

Edited by nzlowie
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Cross over point?

 

Both drivers need to be 6dB down at the crossover point.    I wouldn't apply any significant boost to achieve this.

 

 

... perhaps serendipitously.... the -6dB point for the QP is right around approximately 340Hz.

 

 

should be crossed 1 octave higher than this

 

This advice is especially critical if you using a crossover with a shallow slope....  less so if the slope is steeper.      It's hard to generalise, but if you have your -6dB point at ~340hz for your midhorn, then that should be ok.

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Cross over point? It behaves well almost to 1khz so would i t be ok to 650-700hz? My mid horn is 340hz and they say it should be crossed 1 octave higher than this.   Your thoughts please.   Many thanks Dave 

 

With a 4th order Linkwitz-Riley digital xover, you can cross anywhere from 350 to 500. I'm confident you will prefer the sound at a lower xover point. but it's up to your ears and your measurements. 

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Your thoughts please.

 

Which woofer are you using? 

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I'm using the kappa 15c. I had tried a few different cross over points but 450 was the lowest I went and yes it did sound better than say 600. This build has forced me to look at a whole new bunch of areas... I'd never really had to look into cross over design as the other speakers I've made have always been fully designed. The other area I'm having to learn about is room eq, in the past I've just put some corner traps in place and the rooms sounded good.

Now I can see the room response I know what I have to work on. Also finding about house curves, which explained why my flat response sounded bad!

So, as frustrating as this can be, I'm learning a lot so thanks again to everyone who help people like myself. I believe in the old saying, no such thing as a stupid question, just stupid mistake. Much appreciated.

Cheers Dave

Sent from my D5833 using Tapatalk

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I'm using the kappa 15c. I had tried a few different cross over points but 450 was the lowest I went and yes it did sound better than say 600

 

This underscores the need to measure AND listen. Are you finding that you have tight, well defined, authoritative bass with or without EQ? 

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which explained why my flat response sounded bad!

 

Indeed.  Once you have got the speaker working with a flat response - meaning the drivers are all level and flat relative to each other, and their phases match through the crossover regions.

 

... then, the final step, is to turn on your "house curve".      If I'm using a miniDSP (for example), I keep the "house curve" on the input channel.     I keep it off, while in "design" (and my "target" = flat) ..... but then as soon as I want to listen, I turn the input channel EQ on.

 

 

 

Roughly, mine would be 6dB to 10dB rise between 20 to 60 Hz (depending on content/genre) .... and a 3dB to 6dB fall between 1khz and 20khz .....  but there's a lot of "it depends" about that, with personal preference being a large factor.

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