MF 1000

Sub bass & bass Speakers with 18" Volt RV4564 drivers

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Had some more time late this afternoon to tweak the dsp/eq settings even more ....and I soon hit a sweet spot 😁

56D1E0D0-7608-4552-B674-0CA8D0D7AD5A.thumb.jpeg.572dfecbede28edcfd4b68374cea18c6.jpeg

The Red line is the new settings ....nice and flat 😁😁😁😁 the blue was yesterday’s setup and the green was the previous setup with the KEFs.

Of course measurements aren’t everything ...lol so it was a quick listen to a couple of Yello tracks and Money Can’t Buy It by Annie Lennox .....a step change with the punchy bass lines equalled by detail & weight in the midrange.  More listening to do now 

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On 18/10/2020 at 08:39, MF 1000 said:

Hi Frank

https://www.merseymdfplasandply.co.uk/cutting-and-edging-service/
 

they are on the border of aintree/bootle, supply & cut all thickness of mdf.  Not the cheapest but good quality and quote a 0.1mm accuracy.

Thanks very much Keith.

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1EDA488E-1894-4EA4-BF3D-09FABABA146A.jpeg.0bc4dd7896f7816c9c2ca726165d1d10.jpeg

a bit more tweaking with REW today whilst Jane was out (the sweep tones driver her nuts) 

and I’ve managed to somewhat level out the 2-400Hz area (Blue Curve is the modified eq one) and lift the > 1KHz area too ....still more to come I think and even now learning more about REW and eq levels 😀

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Super Dealer

Why is the output so low above 800Hz?

The ‘norm’ usually is a 10dB drop from 20-20kHz.

Keith

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27 minutes ago, PuritéAudio said:

Why is the output so low above 800Hz?

The ‘norm’ usually is a 10dB drop from 20-20kHz.

Keith

Look at the title on the graph - this is just his mid-bass.

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Super Dealer

Sorry, could you post a full system/ FR plot?

Keith

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EB2418F7-29E8-45EC-B497-1F3571D64F78.thumb.jpeg.75b08cdbe2a2bbfaa011c52703be557b.jpegI’ve fitted some temp bowls behind the mid range soft dome driver (Janes missing a couple of plastic Xmas pudding dishes 😁) and done some further analysis/tweaking on the DCX units 

Blue curve is the latest iteration ...addressed some of the drop off after 1KHz and a good lift over 5KHz too, still more to find  - the dip at 1KHz is at a cover point......but sound wise it’s now really motoring.

I turned the wick up on track 7 of Tron this morning .....and the 18” volt driver in the new bass cab actually started to hit its end stops !!!  - this driver has 44mm of travel so to have it use all of that - wow.  A quick 2dB reduction in gain on the bass amps and we stepped back from the edge.

Edited by MF 1000
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Had some time again late afternoon to tweak the eq settings 

0F71A7E2-22FD-4C7F-BE5B-CAE071B909F2.thumb.jpeg.a10314d83a349877428c1f74417a99c3.jpeg

Blue trace is the revised eq ....managed to lift the top end and infill some if the dip at 1KHz 

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Whilst I was away last week I was thinking of what was the driver behind the HF drop off in the system, given that if I increased the gain on the SMTL amps driving the tweeters & supertweeters it did not seem to have much of an effect.

As I still have the two Behringer A500 amps I wondered if a big amp/psu might be able to provide a solution.

After my 5 hr drive home early on Sat morning I set about quickly rigging up a A500 to feed just the Scanspeak tweeters in the monitors and leave the Fostex supertweeters turned off.

A carefull power up ....the A500 can deliver 300 wpc (easily frying a £125 tweeter) and slowly increasing the gain whilst listening to a Yello CD.  To my ears the top end was now a great deal brighter but to alleviate any ‘bias’ on Sunday morning I ran a REW sweep ....

2CA8DCC3-341D-4843-887B-1BB3C448852B.jpeg.2dc285a6b0049c2f9089bbdc0d133639.jpeg

The green line is with the A500 driving just the tweeters in the monitors, the red line was with both sets of tweeters driven by the SMTL amps.

Clearly the SMTL amps didn’t have enough ‘grunt’ to drive the tweeters to the levels need, a 10dB lift at 10 KHz with the A500 is significantly better 😀

I need to rearrange my amp rack now to remove the SMTL amps and fit in a single A500......my plan now being to fit the next level of ring radiator Scanspeak tweeters and move on the Fostex units - reverting back to a ‘simple’ 4 way active system .....:rofl:

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Further tweakery on the DCX today and I’ve arrived at the curve below

819C48D8-3500-4FCA-9043-611AF2CB4989.jpeg.d3da680592883329f8de49950229a888.jpeg

25Hz to 12.5KHz across a 10dB spread 😁

as a comparison to the first steps with the A500 amp on the tweeters

69BC75CC-1D9C-44FE-BEA9-275EFA9E95C4.jpeg.91fccf8430e398c9f4d86d69b5a0c570.jpeg

with the blue line the curve prior to today’s tweaks....the new curve is a bit smoother over 3 KHz with a slight increase in response above 10 KHz 

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On 27/03/2019 at 08:18, MF 1000 said:

After acquiring a pair of bass speakers fitted with Volt RV4564 drivers from eBay, the challenge now is to make them more aesthetically pleasing, if I make new cabinets - not to go too big, tune the existing cabinets to try to achieve sub 20Hz frequencies and eliminate any cabinet flexing/vibration.

As posted in the bits & bobs thread here is a pic of the speakers 'as collected' 

IMG_0045.JPG.e63b680119d49e56c81ec167805e028f.JPG

not pretty in any ones eyes.

A quick bit about the Volt drivers....

18" dia, weighing in at 17Kg each, they are the ones used in the top end PMC speakers and numerous studio monitors or high end home cinema subs.  With a vMax of +/- 12.5mm and a 8" dia magnet they are more or less bullet proof, so I doubt my MF A370 is ever going to over drive them.

Ill do some analysis with REW this weekend using the same dcx settings I've driven my transmission lines with and use this as a base line.

The front facing port is 150mm dia (good job we haven't a cat .....I could see them being an attraction as a 'home' 🙈.  The cabinet is nominally 167 litres ( 45 x 54 x 69 cm) and the current port length is 10 cm, which gives a tuning frequency of 56 Hz ☹️ - not very low for such a big driver.

A quick call of various port length/tuning frequency combinations for a 167 litre cabinet gives the following options:

51 cm port length - 25 Hz

80 cm port length - 20 Hz

98 cm port length - 18 Hz

124 cm port length 16 Hz 

The challenge now is 'snaking' a >80 cm long 15 cm dial pipe inside the cabinet to achieve a low tuning frequency.....possible but challenging 😁.

My usual approach to isolating cabinet stiffness will be applied using internal ribs and cross dowelling to support the walls and reduce potential colourations.

Visually it might be easier to simply wrap the cabinet in a new layer if mdf or ply prior to veneering etc, this would also aid reducing cabinet flexing as well.

I will try to remember to take pics of each change etc and measure it if I can with REW.

👍

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Was doing some testing this morning on the monitors and thought that I’d never done a LHS to RHS comparison sweep from my listening position .....LHS being the original cab in its extra layer carcass and the RHS being the new design/build cab

0AD87E5D-525A-44BC-8679-C60C7CCBB7D6.jpeg.53938e79f9829c3a3538a706d61e73bc.jpeg

I knew the bass was better overall ....but the RHS (purple curve) really highlights the benefits of my design ideas and build +15 dB at 15 Hz 😁 and a much smoother curve approaching the xover point at 180 Hz ....ill look at the 5 dB dip rapt 200 Hz next I think.

Running the averaging function on REW gave the curve below is red

1E6F1343-3059-4F78-9D9A-395EF8DD1217.jpeg.b4b7e76b06714d269f335db38674c180.jpeg

The green curve is my std test with both LHS & RHS running measured at ear height from my listening position .....to me this validates my std measuring approach.

I must order the next batch of 300mm mdf so I can collect it after England is hopefully unlocked on the 2nd Dec and build the LHS cab .....I’ve a feeling that thunderous bass will be available when I have identical cabs - not that it’s poor at the bottom end at the mo ! 

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Looking good Keith.

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Played around with REW this afternoon and the Room analysis side ...recommended a 11ms delay on the subs so I dialled it in and also tried a phase inversion on the mid bass.  A few simple tweaks and a balance out of the midrange/tweeters against the sub/bass/mid bass and I’ve got the curve below (physco acoustic smoothed) 

B809CD62-7E56-4DA3-AB58-B8773FD8F6DA.jpeg.94ceafb90c80d15ead5575e599a828c9.jpeg

really pleased with it now - nicely set within a 10dB band, 25Hz to 13KHz but with almost 20Hz at 5dB lower too 😁

Cant wait for the chance to build the second cabinet and in sure 20Hz at -10 dB is achievable 

Edited by MF 1000
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