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Project Lilscala


Guest David H

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Guest David H

No, I still have some bass concerns. I have no response below 80hz its 12 db down from 100hz. What I am going to do to correct the concern is extend the bass chamber up into the the upper horn section, this will take my bass chamber from 1.3 cf to 2.0 cf. (Speakerfritz came up with this idea.)

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What I am going to do to correct the concern is extend the bass chamber up into the the upper horn section, this will take my bass chamber from 1.3 cf to 2.0 cf. (Speakerfritz came up with this idea.)

This is the main way djk does the bass mod to a full size LaScala. Open the doghouse into the top and seal the back. With added ports the response is -3db at 31Hz.

Bruce

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Guest David H

How did you get the ramps in the top section? Just curious...

Bruce

I should have taken a pic of that, but it was far easier than installing the lower ramp, I simply slid the ramp in through the opening you see in the the pic you saw in the previous post. The ramp extends approx .25 inches past the opening in the pic. I then brad nailed it in place, applied wood glue from the back and caulk on the front side, and the finishing touch was installing a drywall screw at the end of each ramp....They're not gonna move....
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"This is the main way djk does the bass mod to a full size LaScala.
Open the doghouse into the top and seal the back. With added ports the
response is -3db at 31Hz."

I agree with the port idea. I'm not sure what the tuning target will be. The Heresy cab has an internal volume of over 2.5cf. In this senerio GotHover estimates his LiLscala with the top cut thru the bottom to connect the dog house will have a volume of 2.0cf. Can anyone run the numbers and make a recomendation for port (s) lenth and diameter?

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What I am
going to do to correct the concern is extend the bass chamber up into
the the upper horn section, this will take my bass chamber from 1.3 cf
to 2.0 cf. (Speakerfritz came up with this idea.)

This
is the main way djk does the bass mod to a full size LaScala. Open the
doghouse into the top and seal the back. With added ports the response
is -3db at 31Hz.

Bruce

Don't forget the
EQ either (peaking 2nd order highpass that takes advantage of the
reduced cone excursion at the tuning frequency). Without the EQ it's basically pointless, and with the EQ it's still only a bass-shelf (making the -3dB claim a bit misleading).

For what it's
worth, the reason you have no bass is because you simply cannot scale
down a horn for a smaller driver and expect the same results. In fact,
you should expect to use a larger horn with a smaller driver! (Unless
of course you can find a way to scale down the wavelengths of sound).
Also, the lascala bass bin was already undersized...so the issue is
just compounded.

In other words, making the rear chamber larger
isn't going to help. In fact, the volume of the rear chamber affects
the reactance anulling of the horn, which is a fancy way to describe
the frequency response changes that happen above the Fc of the horn.
The only way you can make the Fc lower is by making the pathlength
through the horn longer.

This is where hornresp comes in handy...so you can see what the horn 'should' do and compare against what it actually does. The correlation in my experience so far has been very consistent. Hornresp also models the porting of the horn (like the djk mod, not like Roy's version of porting into the throat) which could be used to predict the possible benefits of porting your current version. My gut feeling is that it won't help very much (since you're so undersized).

Btw, do you have any measuring equipment? Sometimes it can be extremely helpful to know what exactly is happening with the system, which makes tracking down problems much easier.

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I think trying to get a lower Fc with a 12 inch woofer in such a short horn is futile.

I know no calcluations were used for this project.....but there are some things you can get out of this in hindsight....to get an idea of what to expect for the lowend. Your project isn't trash by any means.

The three variables that will give you an idea is...throat size,,,horn length...and size of "physical mouth". Of course the woofer chamber has a role too...but this is getting complicated.

I may have aready said this....can't remember...but the Fc will probably be between 80-100Hz. Any thing lower than this.....EQing....could bring in distortion. Now a simple 3dB shelf....probably won't be of much harm.

I would put a limiter on it so that it doesn't play much under 90Hz or so....and try to get some "thwack" out of it.

Now....I'm no pro...just a hacker.

jc

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"The three variables that will give you an idea is...throat
size,,,horn length...and size of "physical mouth". Of course the
woofer chamber has a role too...but this is getting complicated."

So whats the ideal state? The biggest mouth possible? A high excursion woofer like the K-31?

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Guest David H

Btw, do you have any measuring equipment? Sometimes it can be extremely helpful to know what exactly is happening with the system, which makes tracking down problems much easier.

I have a calibrated mic, pink noise generator and a spectrum analyser, I also use a laptop with tone software. I almost forgot my nearly useless Rat Shack decible meter.

I also made an error in measuring the box internal volume ported into the top, because I was taking into consideration the displacement of the horns and xovers and I was not adding the cut-outs through the top of the box, it all adds up. Actual internal volume is 2.506cf ported through the top. I think this is more volume than the Heresy, but I havent made internal measurements on the Heresy as of yet.

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What is the volume taken up by the woofer, mid horn/driver and tweeter? You need to subtract that from the volume of the cabinet. A Tangent 400 has cabinet volume of around 3.38 cu ft, before subtracting the driver volume. You could make a pseudo belle cabinet with the ports on the front. It would still come out smaller than a full sized belle. And get way more bass.

Bruce

btw, those cabinets are beautiful looking. I am not wanting to take anything away from that...

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"This is the main way djk does the bass mod to a full size LaScala.
Open the doghouse into the top and seal the back. With added ports the
response is -3db at 31Hz."

I agree with the port idea. I'm not sure what the tuning target will be. The Heresy cab has an internal volume of over 2.5cf. In this senerio GotHover estimates his LiLscala with the top cut thru the bottom to connect the dog house will have a volume of 2.0cf. Can anyone run the numbers and make a recomendation for port (s) lenth and diameter?

I think I remember reading about the modified La Scala. Get's the bass down to -3d at 31Hz. I'll have to go dig out that thread to find out what the tradeoffs are to extend the response.

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Guest David H

I am pleased to report, that openeing the bass bin into the upper chamber solved my bass issue. I now have solid bass down to 50hz at -3db and -10db at 40hz, what an amazing change. Btw this also affected the box gain that I was getting, and I was able to drop the tweeter and mid down 3db on the autoformer.

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I am pleased to report, that openeing the bass bin into the upper chamber solved my bass issue. I now have solid bass down to 50hz at -3db and -10db at 40hz, what an amazing change. Btw this also affected the box gain that I was getting, and I was able to drop the tweeter and mid down 3db on the autoformer.

congrat's

I'm really happy to see this.

btw, what slot size did you use in front of the k-22?

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Don't forget the
EQ either (peaking 2nd order highpass that takes advantage of the
reduced cone excursion at the tuning frequency). Without the EQ it's basically pointless, and with the EQ it's still only a bass-shelf (making the -3dB claim a bit misleading).

On the LS it is still an improvement without the EQ. It is misleading in what way?

The mod causes a small loss in efficiency over the horn only cabinet.

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