Anyone build a bigger la scala with/for the 15pr400

[Bas Horneman]

I want to build a bass horn a la scala. But with the 15pr400 like Volti audio.

It (15pr400) mostly needs a bigger doghouse. So I was thinking 20 percent bigger la scala all round. Perhaps also with a bass reflex mod as well. As is now 'standard' on the AL6 model.

I guess I have to learn to use hornresp?

 

[Bas Horneman]

Alright — let’s calculate the new horn mouth area, throat area, and cutoff frequency when scaling up the La Scala by 20%.

📐 1. Assumptions about the original La Scala​

• Horn path length ≈ 2.6 m (102″)
• Mouth area ≈ 0.4 m² (4.3 ft² ≈ 24″×24″)
• Throat area ≈ 0.02 m² (about 3 in²)
• Cutoff frequency ≈ 104 Hz (theoretical)
  (This is derived from the mouth area.)

We scale everything by a factor of:

s = 1.20

---

📐 2. New horn path length​

Already calculated:

2.6 \, m \times 1.20 = 3.12 \, m

---

📐 3. New mouth area​

Area scales with the square of the linear scale:

A_\text{new} = A_\text{original} \times s^2

So:

0.4 \, m² \times (1.20)^2 ≈ 0.4 \times 1.44 ≈ 0.576 m²

≈ 0.576 m² ≈ 6.2 ft²
That’s about 30″ × 30″.

---

📐 4. New throat area​

Similarly:

0.02 \, m² \times (1.20)^2 ≈ 0.0288 m²

≈ 0.0288 m² ≈ 44.7 cm² ≈ 6.9 in²

---

📐 5. New cutoff frequency​

Horn cutoff frequency depends inversely on the mouth size.
The approximate formula is:

f_c ≈ \frac{c}{2\pi} \sqrt{\frac{\pi}{A_\text{mouth}}}

where (speed of sound).
If you scale the mouth area by , the cutoff scales as:

f_{c,\text{new}} = \frac{f_c}{s}

So:

104 Hz / 1.20 ≈ 87 Hz

---

📋 Final Results:​

Parameter	Original	Scaled ×1.2
Horn path length	2.6 m (102″)	3.12 m (122.4″)
Mouth area	0.4 m²	0.576 m² (6.2 ft²)
Throat area	0.02 m²	0.0288 m²
Cutoff frequency	~104 Hz	~87 Hz

---

✅ After scaling up the La Scala by 20%, you get:

• ~22″ longer path
• ~44% larger mouth and throat areas
• ~17 Hz lower cutoff frequency (~87 Hz instead of ~104 Hz)

If you’d like, I can also help you draft a table of new dimensions (height, width, depth) or even draw a scaled plan. Let me know!
ChatGPT...

 

[Bas Horneman]

 

[phase_accurate]

How in all the world do you come to a horn path length of 2.6m in a La Scala ?
It is much less than half of that actually.
If this were correct the following would happen:
2.6m combined with your throat and mouth area would give a horn-constant based cutoff frequency of 31 Hz for the original and 27 Hz for the enlarged one. Since the throat area would be much too small for that the frequency response would be very irrgular.

But since your path lengts are way off this will not happen that way.

Regards

Charles

 

[Bas Horneman]

Chatgpt came up with those number...it summed left and right. So I asked it and now says it's around 1.70cm

 

[pelanj]

Peavey FH-1 is very similar to what you need.

 

[Azrael]

I strongly recommend that you only use AI for topics that you know enough about so that you can check for yourself whether what the AI claims is true. AIs are otherwise all kinds of things, but they are not reliable sources of information.

 

[Bas Horneman]

True. And I'm aware of that. I catch many mistakes. But last night I thought I'd just throw it in the forum. I do think it is useful still...despite the mistakes it often makes.

 

[Cask05]

I think it's basically already been done...31 Hz F3 (eighth space loading):

(anechoic response - full space)

Be careful of the dimensions at the back of the bin--near the 180 turn (point "C" in the AES paper). This seems to be the place where errors in DIY drawings were made in the past.

You can make this bass bin single-height (12" woofer) or double height (two 12" woofers)--like my bass bins. I recommend the flat "shelf-type" stiffeners instead of the original "struts" used on the first bass bins (like the ones I own). The shelf stiffeners locate the other pieces (like a jig) much better and significantly decrease assembly time.

Chris

 

[Bas Horneman]

Thank you! Nice to have as an option. Whole different level of skill needed for this build. But doable ofcourse. I suppose this could also scale to my 15pr400. Will need a box under that to increase the volume. What 12 inch drivers did you use?

 

[Cask05]

Klipsch K31s:

https://community.klipsch.com/topic/181896-k-31-e/
Is there a replacement driver for the K31K woofer?

I've got a lot more pictures of the build of this bass bin (the two-12" woofer version)...if you want them. I can post them on Google Drive account and access you to them if it's necessary/desirable.

Chris

 

[Bas Horneman]

I'd love to see pics.

 

[Bas Horneman]

The Jubilee is not scaled easily for 15 inch. And K31 is unobtainium in Europe. Shipping from the US has also become too expensive. Looks like scaling up or just extending the dog box with more volume including bass reflex is still the best option I have.

 

[Fuling]

I've never been in the same room as a pair of La Scalas but I have some experience of short horns with ported back chambers (i.e feeding the landfill with ugly one note bass-wonders made of unpainted chipboard). Somewhere around the fourth iteration I had learned enough to build a pair that actually sounds good.
The latest pair is wedged to get as far into the corners as possible, without corner loading they sound lite transistor radios. The bass reflex part also has an unusually high tuning frequency to maximize its efficiency in order to get a smooth transition between horn loading and BR loading.
Together with a little crossover voodoo I managed to get a reasonably flat response down to 55Hz or so.

 

[Cask05]

I understand you don't wish to use the KPT-KHJ-LF bass bin design--for your own reasons, but...

I believe that I posted a link to a thread where a Ciare HW321 was identified as a replacement woofer. That's why I posted that link. There are apparently other woofers available that can be used, too.

The KPT-KHJ-LF bass bin (the one in the AES article posted above) was specifically designed to avoid having to use a 15" woofer (using two 12" woofers instead) in order to keep the two side-by-side mouths closer together in order to avoid lobing at frequencies above 200 Hz. That was a design objective for that bass bin. The older Klipschorn bass bin with its 15" woofer has a wider central doghouse, resulting in lobing issues and a lower effective high pass frequency than the present bass bin design.

Using bass reflex ports increases the phase growth at lower frequencies. Recommend the KPT-KHJ-LF design approach instead.

JMTC.

Chris

 

[freddi]

Here's one of my FH1 out in my hillside yard ~110Hz horn or so - well braced cabinet - kinda "boring"... (I've only run stock woofers)

 

[Cask05]

Of course, if you are willing to accommodate a "nose" on the exit plane of the dual-mouth "W" section horn--like the La Scala design--the problem of lobing polars at higher frequencies (near the high pass crossover frequency) is mitigated. But that design approach, i.e., fully rejoining the two side-by-side bass bin mouths with a gradual central taper nose, also results in a less convenient overall footprint to fit the bass bin into the room, especially into corners, etc. with toe-in, which in my experience is an important factor:

Chris

 

[TG]

The bigger (but actually good sounding) version of La Scala is called Peavey FH-1.
I can see it's been recomended already, so just my two cents:

Plans are available on the net, and the build is relatively easy.

There's YouTube channel called Audioplile room where you can find lots of sound demos for FH-1 with the JBL 2226G, which isn't that far off from 15PR400 in terms of parameters.

As for rear chamber calculations, remember that the resonance frequency of the horn loaded driver is substantialy lower than it's Fs (due to added air mass).
Usually the rear chamber volume is adjusted to put the resonance frequency exactly on the horn cutoff frequency - that makes for flattest response. The chamber volume is relatively small in this case (~30-60 liters)
And yes, hornresp is your friend here.