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Mini Bookshelf/Desktop using 3" Fullrange

Wharfedale EVO4.4 Speaker

aashish351

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Hi,

Building a simple mini speaker using a 3" single full range driver for desktop use. The driver is Peerless India S07NI (Peerless Fabrikkerne (I) Ltd - 3" Full Range - S07NE)

Since I don't have any T/S measuring tools, I have used those listed on the link above. Listed below as well:

Fs: 100.87 Hz
Qts: 0.51
Vas: 1.27 Ltr
Sd: 31.17 sq. cm
Freq. Resp.: 100-10000 Hz
Impedance: 4 ohm
SPL: 88.5 dB

Calculated volume of the bass reflex box is 2.8 litres and port tuning is 77 Hz. I have used 15mm ply since I had that lying around. The external box dimensions are 5" (width), 11" (Height), 7" (Depth). Slot port is 0.50" wide and 6" deep. Box is stuffed up to 40% volume using polyfill.

First impression: "Is that really a 3" single driver!?" Ok, that was slightly exaggerated. But, I am pleasantly surprised with the midbass response. Must be going down to 65-70Hz (I think I should invest in acoustic measurement if I am to continue to waste my money in this). Of course, I am testing these with Exposure 3010 which gives me the confidence that it is being tested to its capability (keeping care not to send the cone flying into space). In its final application, it will be powered by a much smaller amplifier. But, somehow I am not getting worried! This little driver is taking almost the same amount of volume (8-10 o'clock position) that I use with the much bigger 100W rated Focals. Power rating of the driver is not listed so I actually don't know its capability.

Second impression: Midrange and vocal are obvisouly the strengths compared to the bass for this speaker and I am not disappointed. Treble is of course rolled off. There is not enough of the highest details available in the treble. But let's keep in mind, it is going to compete with a low-mid budget active multimedia speakers or mid-sized docking/bluetooth speakers. And compared to those, I am already happy with what it is doing. While designing, I suspected that a baffle step compensation may be required as suggested by a previous experience with similar drivers. However, although there may be a bit more vocal/upper midrange energy than ideal, it's actually not bad. It is rather enjoyable. Something often missed in 'safe' souding commercial gear.

NOW, to the advice I need from experts:

I decided to put a 1st order high pass filter on it to avoid pushing the driver beyond its capability and avoiding cone breakup and distortions. So as per calculations, a 440 uF capacitor was ordered to get 6dB roll off down from 90Hz. The thing is, for the first two days, I did not install it. So all the above mentioned observations were without any passive components. The problem is when I finally connected the caps, I got a mixed result with a net negative effect sonically. The relative full bodied-ness of the mid bass gave away to lean/thin character. Now I was not liking the high energy of midrange as much. It is not a big change, but very clearly noticed. On the positive side, maybe, just a very little bit improvement in the clean-ness of sound. A tad less grainy. But on the whole, I prefer the crossover-less sound.

So I can just throw the cap out of the picture, right? Or do I risk breaking the driver in the long run?

Oh! Forgot a few pictures.



 
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aashish351

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Not at all. Just a simple slot port box. But I just checked tabaq. Coincidence that it looks same. Now I'm thinking why I didn't do that!!
 

keith_correa

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Why would the highs be rolled off. The FR graph suggests otherwise. You should be getting strident highs.
 

doors666

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its a 6db crossover at 90hz, it will start rolling off the bass much earlier. aim for a lower crossover point, try something like 50-60hz
 

aashish351

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Doesn't the graph also show steeply falling response after 9 KHz? -3db at 10KHz and almost -15db at 15Khz.

But like I said, there is enough for me to enjoy music casually.

I have compared both again several times now on different tracks and the conclusion is the same - less enjoyable sound with filter in place. The suggestion of crossing lower could work, but I am not inclined to try that, as in principle I am not in favour of adding more passive components. I will need to add a third 220 microfarad cap (taking the total to 660uF) in parallel to cross at 60 Hz.

So, I am going to try a software filter (foobar dsp xover or others) and see what happens. The result I want to achieve is to get the one improvement with the caps - cleaner sound, and avoid the negatives - thin/sharp sound.
 
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Sumanta

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Ashish,
Just an idea from me - put a baffle in the middle (or two third from front) of your cabinet, parallel to the front baffle. lower part of that baffle should end on top of the horizontal baffle that is making your 6" deep port. Seal gaps. You will have a TL speaker.

I think you will get better bass. I do not think you need any cross overs any more.
 

aashish351

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Unfortunately, I can't open the box anymore! It's sealed off. But thanks for the suggestion.
 

aashish351

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While the high pass filter or no filter is still an open point, I want to get some advice on the finishing options. Because this is a very simple, frugal build, no veneer or glossy PU paint is an option. I have decided to simply follow this:

Sanding -> Wood putty (may repeat a coat if needed) -> Sanding -> Enamel paint (may repeat a coat if needed).

Is that fine? Please note that this is a multi-layer 15mm plywood.
 

Hari Iyer

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As suggested by FM Sumanta a TL would have been better, but looking at tour box I think it can easily be an aperiodic loading. Try to balance the harmonics by using passive components and u should not require a crossover imo.
 

aashish351

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As suggested by FM Sumanta a TL would have been better, but looking at tour box I think it can easily be an aperiodic loading. Try to balance the harmonics by using passive components and u should not require a crossover imo.

Hari, can you explain a bit more? What is aperiodic loading?

By balancing harmonics, do you mean using a Zobel/BSC/Notch etc. type of filters?
 

Hari Iyer

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Aperiodic loading will not have a tubing type port but just a small opening like the one in your box. Add stuffing around 400gms of low density. This willvdamp all freq till around 150Hz, below that it will escape from the opening allowing good and tight bass below that freq. Its impedance at resonance is lower than sealed enclosure and tuning is for the cutoff freq of ur box based on its dimension.


Uou can use all of them for balancing the harmonics, but its difficult to predict without measurements and simulation. If you do not have the resources to do so, then trail and error is the only way out.

All the best.
 

aashish351

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Aperiodic loading will not have a tubing type port but just a small opening like the one in your box. Add stuffing around 400gms of low density. This willvdamp all freq till around 150Hz, below that it will escape from the opening allowing good and tight bass below that freq. Its impedance at resonance is lower than sealed enclosure and tuning is for the cutoff freq of ur box based on its dimension.


Uou can use all of them for balancing the harmonics, but its difficult to predict without measurements and simulation. If you do not have the resources to do so, then trail and error is the only way out.

All the best.
Thanks for explaining it nicely. I think, very close to what you have said, might have happened in my build by sheer luck in the first attempt itself. I'm quite happy with the outcome.

And, I agree there is definitely scope for improvement in balancing the harmonics in the mid and upper octaves. But I'm mindful that too much trial and error with passive components might be out of the scope of this project.
 

philipreji

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It should be worthwhile to try 1000 microF and 2200 microF capacitors instead of the 440 microF. Of course this will bring down the cut-off from 90 Hz, but the lost dynamics will come back. The other option is a 4th order L-R filter designed for 50 Hz or so, but higher order filters are not everybody's choice because they affect the dynamics of the music.
 

aashish351

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It should be worthwhile to try 1000 microF and 2200 microF capacitors instead of the 440 microF. Of course this will bring down the cut-off from 90 Hz, but the lost dynamics will come back. The other option is a 4th order L-R filter designed for 50 Hz or so, but higher order filters are not everybody's choice because they affect the dynamics of the music.
Thanks for that suggestion. I am just trying to get my head around this - so if the driver's Fs is 100 Hz and the box tuning is 77 Hz, how exactly does a filter much below that frequency work in terms of: a) protecting the driver from over excursion and b) improving dynamics. Pardon my lack of technical knowledge in this! :)
 

aashish351

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In the meantime...







Horrible paint job. But very good considering it is my office electrician's first attempt!
 

keith_correa

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While the high pass filter or no filter is still an open point, I want to get some advice on the finishing options. Because this is a very simple, frugal build, no veneer or glossy PU paint is an option. I have decided to simply follow this:

Sanding -> Wood putty (may repeat a coat if needed) -> Sanding -> Enamel paint (may repeat a coat if needed).

Is that fine? Please note that this is a multi-layer 15mm plywood.
Try enamel & wet sand it to finish.
 

philipreji

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Hi Ashish,

Thanks for that suggestion. I am just trying to get my head around this - so if the driver's Fs is 100 Hz and the box tuning is 77 Hz, how exactly does a filter much below that frequency work in terms of: a) protecting the driver from over excursion and b) improving dynamics. Pardon my lack of technical knowledge in this! :)

Thanks for the pics; I didn't quite realize earlier that you are using subwoofers. Then you shouldn't have a problem: your crossover frequency of 94.7 Hz should work well and together the subwoofer and fullrange drivers should sing well..any chance the cap you used is faulty/of a wrong value? A long shot of course, but electrolytics are notorious for this..

What follows is redundant now but for the sake of completion: Lower cut-off does not protect the driver from over excursion. But assuming you did not have the subwoofer, the dynamics would have certainly improved by lowering the cut-off. Reason is the following: your current first order filter has a slow 6 dB/octave slope, and it will diminish frequencies above the 94.7 Hz cut-off also to some extent (as pointed out by FM doors666). The solution is to cut low, while ensuring that it is not too low.

cheers,
Reji
 
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aashish351

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Re: Mini Bookshelf/Desktop using 3" Fullrange

Oh! Those are not subwoofers! I'm not using subwoofers. Those are the Boston Hi-Q build. There is a need for improvement in those as well, but that is another thread.

I'm using Nichicon two 220 microF 35 V caps to reach the 440 value required since a single one for 440 was not available. Could that be the problem? I read that you can do that.
 
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