Cube shaped speakers

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Hello!

I'm new here and I have few questions. I hope you can help me or explain what I have understood incorrectly.

I want to build a small full-range cube shaped speaker for wireless portable use to use in my garage or in my office room. The airport express, battery and amplification part will stay outside the speaker. I will use:

1. MarkAudio CHR-70 driver 4 inch
2. Outside measurements 18x18x18 cm high quality baltic birch plywood, 18mm thick. Volume of the box will be 3.0 litres. (This is the maximum size I want). The box has to be small! :)
3. The box will be sealed
4. I will use Chinese 2x50W TPA3116D2 mini amplifier
TPA3116 HIFI Class 2.0 Stereo Audio Digital Amplifier Advanced 2X50W Breeze Amp | eBay
5. Chinese 12000mAh 12v battery
6. Modified 1 generation Airport Express with 12v power input
7. The amp + airport express + battery will be standing separately and connected to the speaker via normal speaker cables/plugs
8. I will stream via AirPlay from Tidal HiFi from my iPhone.
9. Since my demand is small and portable then proper stereo image will not my goal - I will bridge to mono. Goal is to have one small portable box shaped speaker with good sound.
10. I chose a sealed enclosure because I am a beginner and I don't my first project to be a ported design which is more complicated to make it sound good and needs a bigger enclosure. There are no vented cube designs available for CHR-70. I also appreciate precise bass more than boomy bass.

First question: Amplifier specs read: 12V ------- 8 Ohm speaker / 12W (left channel) + 12W (right channel) - when bridged to mono will it be safe for CHR-70? I plan to listen only around 50% of volume, not very loudly.

Second question: I know 3 liters will be little bit small even if it's sealed, but with sealed enclosure will it affect the sound little bit or a lot? Strassacker: Lautsprecher - Boxen - Selbstbau recommended closed cabinet is 3,7 L volume
from 96/61 Hz (-3dB/-8dB)

Third question: I know cubed shaped enclosure is not the ideal solution, but design to me very important, I really like the idea of a full range speaker in a cube shaped enclosure. Why many high end manufacturers use full range driver+cube shaped design if it is not recommended by audiophiles?

Fourth question: I listen to lot of Motown classics, Dire Straits, Yacht Rock, Jazz, but also some modern well produced hip-hop/pop. So bass needs to be precise, but also not too weak. My question is how is good bass response achieved in high-end small sealed enclosures like this? 17x17x17 cm box enclosure, sealed, with 4 inch full range driver and goes down to 30hz. How is this possible? 4 inch models cost $12,000 pair... http://www.kubotek.com/haniwaaudio/image_1/toppage/1104/HSP1C.pdf


Fifth question: If I make the same enclosure vented (rear panel port) will it sound awful (even if I will not listen loudly) because its too small for vented CHR-70? Vented it should be 15 litres (Strassacker: Lautsprecher - Boxen - Selbstbau recommendation).

Sixth question: If in the end sealed enclosure will be too bass-light for me and I will let go of the cube shaped cabinet dream and find a new proper vented design for CHR-70 then how important is the port placement and shape? Most CHR-70 vented designs are with front ports - rectangular opening in the bottom of the speaker. If I will use round port tube in the lower back side instead will it change the sound dramatically if other cabinet design parameters are left the same? The reason for rear port tube is easier construction and most of all aesthetics, because with single full range element front port will ruin the otherwise clean design.

So lot of questions. I hope someone can answer even some of them :)

Thank you!
 
First question: Amplifier specs read: 12V ------- 8 Ohm speaker / 12W (left channel) + 12W (right channel) - when bridged to mono will it be safe for CHR-70? I plan to listen only around 50% of volume, not very loudly.

Yes, no issue in power terms. You're more likely to damage a driver through under than over-driving, and it's quite difficult to do either if common sense is applied.

Second question: I know 3 liters will be little bit small even if it's sealed, but with sealed enclosure will it affect the sound little bit or a lot? Strassacker: Lautsprecher - Boxen - Selbstbau recommended closed cabinet is 3,7 L volume
from 96/61 Hz (-3dB/-8dB)

I can't comment on the Strassacker alignment; it's smaller than I'd normally employ. Be that as it may, assuming a small amount of series R from wiring & connections, 3 litres is in the middling 0.8 regions with lagged walls, although in practice it will be a bit higher because the driver itself takes up some of the internal volume. Not optimal, but should be workable enough for your intended purposes.

Third question: I know cubed shaped enclosure is not the ideal solution, but design to me very important, I really like the idea of a full range speaker in a cube shaped enclosure. Why many high end manufacturers use full range driver+cube shaped design if it is not recommended by audiophiles?

Cubes are not popular among high end manufacturers as far as I know. Some exist; not many. Technically speaking a cube per se is a very poor shape for a loudspeaker enclosure from the POV of external diffraction, and powerful internal standing waves concentrated at a specific frequency due to the equal distance of all the walls. Now, having said all that, a couple of caveats apply. Firstly, the fact that a box might externally happen to be cubic does not necessarily mean that it is internally; it may have internal panels and / or shaping that alters this significantly. And secondly, these issues are typically reduced with smaller box sizes as the standing waves are at a comparatively high frequency, & the higher the frequency, the shorter the wavelegnths of the unwanted standing waves, and the more easily absorbed they become. In outright performance terms, a cube is still best avoided, but for very small boxes, it's therefore less of an issue, particularly when the design goals accept a potentially modest performance compromise in order to achieve other objects.

Fourth question: I listen to lot of Motown classics, Dire Straits, Yacht Rock, Jazz, but also some modern well produced hip-hop/pop. So bass needs to be precise, but also not too weak. My question is how is good bass response achieved in high-end small sealed enclosures like this? 17x17x17 cm box enclosure, sealed, with 4 inch full range driver and goes down to 30hz. How is this possible? 4 inch models cost $12,000 pair... http://www.kubotek.com/haniwaaudio/image_1/toppage/1104/HSP1C.pdf

EQ. Note that this will result in restricted dynamic range & excursion increases. For small spaces & modest SPLs though, this can be effective.

Fifth question: If I make the same enclosure vented (rear panel port) will it sound awful (even if I will not listen loudly) because its too small for vented CHR-70?

Depends what you're tuning to, but it's not something I would consider / recommend. There are no good alignments with this volume.

Sixth question: If in the end sealed enclosure will be too bass-light for me and I will let go of the cube shaped cabinet dream and find a new proper vented design for CHR-70 then how important is the port placement and shape?

It depends on the details of the cabinet so there isn't any one answer to that. Nominally location isn't overly significant assuming there are no (or very little) in the way of internal standing waves. In many there are so it isn't quite so simple, but within reason, there is some flexibility. WRT shape, providing the aspect ratio doesn't become excessive, which results in high friction & potentially vent noise in some cases, again there is some leeway.

Most CHR-70 vented designs are with front ports - rectangular opening in the bottom of the speaker. If I will use round port tube in the lower back side instead will it change the sound dramatically if other cabinet design parameters are left the same? The reason for rear port tube is easier construction and most of all aesthetics, because with single full range element front port will ruin the otherwise clean design.

Providing the vent CSA and length are not changed, it should not cause any significant change in itself, although depending on where the box is positioned it may couple differently to the room.
 
frugal-phile™
Joined 2001
Paid Member
Brock,

CHR-70 version 1, 2 or 3? 2 or 3 will work OK in this volume, Series 1 would really like a bit bigger box. F10 is going to be near 60 Hz. About as good as you’ll get (in a really big box) with the CHR is something like 40-50 Hz.

With 12mm panels:

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dave
 

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What you are describing is the classic Auratone 5C, which is useful in the recording studio for getting the midrange right, mono compatibility, and to avoid issues with time delay with mutiple drivers in the pre-DSP Era

Auratone 5C Super Sound Cube |

I built a clone from a knockdown box from diyrecordingequipment, but used a much better driver than traditionally used:

Tone Cube Assembly Guide – DIY Recording Equipment

You can also buy other clones these days, both active and passive monitors:

Avantone Pro Active MixCube 5.25" Powered Studio Monitor - Retro Cream (each) | Sweetwater

I never regretted building my clones, which are actually very respectable speakers. Go for it.
 
Little progress, I attached a photo. I decided to make a pair, so I could test them and run them in with my home system. I will sand them to 320 grit, then use two layers of Osmo Polyx oil wax (3075 dark brown, which better matches champagne colored drivers than bare birch) and then sand to 600 grit for ultimate smoothness :)
An externally hosted image should be here but it was not working when we last tested it.
 
One more question - should I use polyfill stuffing for such small enclosures? Or only for some of the walls - rear and sides?
You should get his wonderful book
Loudspeaker Design Cookbook 7th Edition Book
which has all kinds of information. My recollection is "polyfill" (i.e. pillow stuffing type) is pretty worthless. This
Acousta-Stuf Polyfill Speaker Cabinet Sound Damping Material 1 lb. Bag
was much better IIRC. There are also tests in combination of foams, probably too thick for your small enclosure.

As for bass, bass volume requires moving air. This simply cannot happen significantly from small drivers and small boxes, though some designs can give a nice illusion, and close-field (i.e. desktop) of course gives much higher sound pressure. So something like what you are making can sound very nice, however I hope you're not a long-pipe organ music fan. ;)

Tiny boxes don't allow significant sized ports to tune very low, so I'm not really a fan of that. I recall a college friend complaining the heartbeat in Dark Side Of The Moon made his speakers sound funny. The woofers were bottoming out, as the energy was below the tuning frequency of the small port in the small box. Plugging the ports improved things tremendously, and made the speakers less tubby sounding to boot.
 
frugal-phile™
Joined 2001
Paid Member
One more question - should I use polyfill stuffing for such small enclosures? Or only for some of the walls - rear and sides?

Yes. Up to a point it acts to decrease the total Q of the system. Most sources suggest between 20-30% increase.

It will also work to damp out the single big internal resonance caused by the 1:1:1 box ratio. As Norman alludes to.

What generation CHR70 do you have? So i can pick the right set of sealed sims so that you can get an idea of what your bass rolloff should look like.

dave
 
Oh by the way if you want mono you cannot just bridge the amp. That amplifies the DIFFERENCE and it will sound weird. You need to sum to mono first, and you need to make a summing network not just some cables shorted together.

Also I would not believe the power output specs of that amp since there are no measuring conditions or distortion spec provided. It may be a fine little amp, but from a 12V supply and bridged, you can get maybe 15 watts maximum continuous in to 4 ohms before clipping, it becomes like a car audio amp.

Meanwhile, following @Scottmoose comment, "Head_Unit’s Rules Of Protection" are:
1) If when things start to sound distorted or odd you TURN IT DOWN, you are unlikely to ever break anything.
2) If you constantly "turn it up to 11" you will break something.
NOTE: the size and power ratings of the speakers and amp do not affect rules 1 and 2. (In any case, specs for amps are often not thorough and for speakers pretty meaningless).

Oh, as for the cube, you could just position some angled skinny (but stiff!) blocking panels inside the cube as well as stuffing. Somehow both top-bottom and side-side. Drive with sine waves to listen for big peaks...but this should be outdoors in an open space, so peaks are not due to echo effects, and so your neighbors can hate you ;-)
 
If I take - from left channel and + from right channel and connect them to one speaker it will sound weird? I've done it before and it sounded fine, maybe I was just lucky? :) I plan to listen at low to medium volume, I won't turn it up to eleven, so I hope I will be safe :)
In that case you are probably not bridging the amp. Most likely, the ground is common, and both negative terminals are electrically the same. So what you heard was probably just the right channel. Connect the speaker to + and +: then you hear just the out-of-phase parts, and it should sound weird. True bridging requires the amp to be set up for it, reversing the phase of one channel internally.
 
So I finished the speakers. Been running them in at low volumes and with classical recordings. After few days they already sound way better, revealing more details every day. I used online calculators to understand how low does the CHR-70.3 play in 3 litre sealed enclosure and I got 89 Hz, is that correct? My woodworking skills are left to be desired, so next time I will let professional paint my enclosures properly - my friend works at premium car paint shop.

After days of online searching I've finally found a speaker that I wanted in the first place. So maybe my next project will be this. Can anyone please comment is this idea totally out of touch or can I expect good results?

Idea I got from this: SUGS-23 - 4” PR design enclosure, active sub-woofer suggestion - TB SPEAKER CO., LTD.

* The 4” active driver W4-2089 and 1 passive radiators (we called PR15-A bundle) combine
* Cabinet Volume : 3L
* RESONANCE FREQUENCY:40 Hz
* CABINET SIZE:185*230*190 mm (WxDxH)

1. So my idea is to use exactly the same design and CHR-70.3 driver that I used with current cube, maybe increase the cabinet volume by 0.1 litres to accommodate the passive radiator
2. I will add small 3 cm furniture "legs" to the cabinet and install the passive radiator to the bottom of the speaker. Not to the side like Tang Band design. Passive radiator in the bottom plate will keep the design clean.
3. I will need to find similar passive radiator, because Tang Band doesn't sell theirs separately. Does anyone have any suggestions, is there similar product on sales with sensible price?
4. Tang Band 4 inch woofer included in this bundle goes way down to 40 Hz, I know it is unrealistic to expect this from CHR-70.3 but what kind of frequency response would I expect?
5. Is there anything I have not considered that might make this idea unrealistic in practice?

Thank you!

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IMG_20842.jpg
 
Last edited:
frugal-phile™
Joined 2001
Paid Member
how low does the CHR-70.3 play in 3 litre sealed enclosure and I got 89 Hz

F3 has been shown to be a meaningless number. Look at the F6 or F10 (~70, mid 50s). F3 is only of interest if you are using it as an XO.

A PR is a vent substitute. At least for the CHR you need to start with a bigger box.

We built a woofer with one of the small TB “subs” and it was underwhelming.

dave
 
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