Already have a prebought sub/box/amp can I mod it for deeper bass?

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Hi Guys

I recently picked up a set of accusound speakers which I have been pretty happy with. Unfortunately the Sub only goes down to 35 which isn't cutting it for home theatre. Before I take the drastic measures of buying a completely new sub/box/amp I was wondering if it would be possible to reuse the existing box and amp and just replace the driver? I have very little understanding when it comes to this kind of stuff but do know that sub drivers are very dependent upon the box and amp but I figured I'd ask anyway.

The specs of the sub can be found here (the reference 8 set)

Frequency Range 35Hz-150Hz
Power Handling (Watts RMS) 150 (built in 240V amplifier)
Bass Drivers 1 x 250mm Woofer
Dimensions (mm)
H 460
W 311
D 432
Weight (kgs per speaker) 24.2

The box also has two ports firing downwards.

Please let me know if you need any more details.

Look forward to your replies
Since it's a small vented sub tuned quite high, there's not much you can do with it to get more extension and output. The driver probably doesn't have the capability to get down any lower with authority, so they tuned it fairly high. I'd say sell it and get what you can, then spend a bit more and you will get something FAR better. Put a decent 12" driver in a decent sized box and you can easily get down to 20 Hz. For about AU $700 you can do a pretty decent sub.
Hi Guys

Thanks for your advice it's appreciated.

One thing I forgot to mention is I really like the small size of this box it fits nicely in my room. All the DIY options appear to need a much larger box :(

Also $700 is pretty close to what I spent on the entire speaker setup so it would hurt putting that into a sub that I'd use quite rarely. I use the system most of the time for hdtv playback, music and xbox gaming none if which seem to use the sub a whole lot I do watch some dvd's but have to keep the volume relatively low or the family will show me the door :/

Does not needing a whole lot of volume help amp wise at all? I guess if I could find a design with a similar sized box I would look into it.

As for sealing one of the ports what am I risking by doing that? could I pop the driver?

thanks again
You probably won't do any harm by plugging one of the holes but I am curious as to how you have the frequency cut off set and what the gain and phase are set at. Have you fooled around with those to see if you can get it to sound better? The reason I'm asking is a couple of occaisions I've heard people say what you are, only to find out they had not optimized their system to the room. They had taken the woofer out of the box and not bothered with any controls other than the gain on the plate amp. All I had to do was to lower the frequency and add some gain. 35 Hz is really low. 35Hz is below my hearing range. Many times I've heard people talk about a 20 Hz signal knowing very well that we were dealing with harmonics, not the original signal. In fact one of the better HT set ups I've heard used an 18" PA driver for the low end with a cut off of about 40Hz. This set up darn near crushed your chest.

I currently use a 10" woofer in my HT in a 250 sq ft room with no concerns at all.

You don't risk anything by closing one port at lower volume levels. Then, slowly bring the volume higher and higher on a heavy bass track.

If the subwoofer is starting to make awful or bizzare noises, then you can't go higher. If that volume level is enough for you, great. If it's not as loud as you like, then you'll need to upgrade my friend if you want more low bass.

Good luck!

(Btw, yes your box is quite small, but it's possible to stay small, with drivers like AE speakers)
Hi Guys

Thanks again for your input it is really appreciated. Adjustment wise I'm basically running it all from my receiver (denon avr2805) I've run the auto setup with microphone, I have the xover set to 80hz on the Denon and turned up all the way on the subs amp. The actual volume dial is only at about 1/3 on the sub but I was more concerned with frequencies below 35hz as I quick ran some test tones and couldn't hear or feel much coming from the sub.

I will try blocking one of the ports if I can find something to fit in the port, May I ask why would the designer put two ports in if it may have better low down response with only the single port?
BassAwdyO said:
I can hear down to 24hz

I would be interested in knowing how you know. If you generated a 24Hz noise and heard it, did you also have a pick up mic there recording what was actually coming out of your system, to ensure you weren't hearing the harmonics? So many have fallen into that trap. That is the point I was making.

This is not intended to challenge your word, I would simply like to know how you know you can "hear" 24Hz and not just feel it.


Edit: Were you using headphones?
dcourtney said:
I will try blocking one of the ports if I can find something to fit in the port, May I ask why would the designer put two ports in if it may have better low down response with only the single port?

To block the port, a good temporary solution is to use one or two heavily compressed socks, dirty or clean depending on your preference.

The designer put two ports to make the enclosure louder instead of deeper. You'll get more output around 30 Hz but you'll lose some output maybe (heavy guessing) around ~60 Hz. Making a subwoofer is always making some compromises.
Blocking one port will tune it lower, but you need to make the box bigger or you will get a lot of rolloff. Subjectively it will probably have less authority and it's only likely to be an improvement if the box is deliberately designed with a bit of a bass hump or if room acoustics is giving you some midbass boom.

For your use I'd suggest what you have is probably not going to be improved without an upgrade.

If you want to go deeper in a small box it's going to cost more!
Cal, I was playing the tone over my stereo (adire Tumult subwoofer in a 6ft^3 enclosure tuned to ~16hz) Using a PC as the source and running the frequency generator in WinISD. I've looked at the waveform using a computer scope and it seems that it's a pretty pure sine(no harmonics) but there is some sound card noise.

The tone is... VERY deep! It does rattle everything quite well and you can feel it in your body.

how have you tested your hearing cal?
lynchingacers said:
would doing the same kind of test except on some goodm headphones give betteer results? cause thered be no harmonics far as i can tell causse theres no room just a smal chamber and ur ear ?

You are confusing harmonics and room modes, two very different things! Headphones won't have "room modes" but that's irrelevant to this discussion.

I have noticed that when using computer to generate sine waves with various applications that it is far from being a pure tone. In fact there is surprising energy either side of the intended tone. It's actually quite annoying. I know this occurs since I have a RTA in line.
Hear Hear

I usually read these threads and chuckle. THis one I fell compelled to comment on. THe advice is good.

The opinions on how low you can hear are nothing short of ludicrous.

Cal get yourself to a pipe organ concert. Or find yourself a good disc and discover all the sections that are to quiet, but have drivers maddly flapping. These are below the bottom end of your current setup. You will be astounded at how low you can really hear when the source is loud enough and above all clean enough. I've been to many. And can attest to hearing all the way down to 16hz. You can count the wave fronts on some notes. An open C on a 32 ft rank is roughly 16hz. Freeky!

Most people have never been next to a system or an instrument that can reproduce these frequencies with enough clarity and authority to have ever heard them. To them they don't exist. I believe you fall into the latter group. Because if you have heard the nether reaches of music you will never forget it!

Mark, so kind of you to stoop to enlighten us mere mortals! :angel:

Unless you have measurements, you don't really know what you are hearing!

I have no conclusion as to how low I can hear, but it's a bit hard to draw a line, since there is no line except those we choose to draw. I have no had the chance to hear a pure tone with only 20 Hz content or below. Even if the signal was pure, any subwoofer will produce some harmonic distortion.
Nothing to do with being a mere mortal

YOu are excused for being a mere mortal!

Seriously I don't mean to be talking down to any one person. But hear the stuff and then talk about it.

As for measurements I do have a decent lab. SPL Meter and spectrum analyser. As for know how I was a decent anateuer musician versed in the requirements and sounds of most if not all of the instruments in an orchestra. And yes I have played a pipe organ! I have the sheet music to most of the stuff that I like and know what was written. I have designed and built custom audio since 1989. Some of those systems could reproduce bass down to 16 hz at concert levels. My own system when hooked up again produces 16 hz at 118 db ( 8 x 15" 11mm X-max ) without taking room gain into account. Granted it's very difficult to measure low frequencies in an acoustically small room. But to hear the stuff you need to move a lot of air. Four liters of diaphram stroke will get you in the ball park.

Some of the people on this forum are more than armchair quarterbacks with opinions! I've got the experience to show what I do and do not know. Check out previous posts and see what I mean. So that all being said I think I can speak with a little authority on the subject of low notes in audio.

Mark, I don't question your experience, or even necessarily disagree with your opinions on this issue. On this issue, I'm interested in facts that can be proven and measured. But how exactly do you prove that you are hearing a pure tone at 16 Hz and not harmonics?

To be able to prove it, first the signal must measure as pure. Secondly, the speaker must not add anything to the pure tone by ways of audible harmonic distortion. As there will always be some harmonic distortion, you would not only have to demonstrate its level, you would also have to demonstrate that the level of distortion is not of a nature that would make the results misleading. This second part may be more difficult to establish than the first.

As a musician you may argue that the pipe organ live goes down to 16 Hz, however have you measured to determine if there are harmonics that are audible?

I think we are all relying on opinions here. It would certainly not surprise me, however, if human hearing does extend a little below 20 Hz, but at this point the "sound" becomes more of an intangible annoyance, a feeling of pressure on your ears. Does it matter if we hear it as well as feel it? It's a fairly artificial thing to try to prove or argue, since we never really hear pure tones in nature anyway!

I have a RTA in my system permanently, and it often surprises me to see the amount of deep bass that is present in any audio signal. There is always signal content down as low as 20 Hz, even if its acoustic bass where the fundamental is near 40 Hz. My system has close to 5L of displacement and yes its nice to have it go flat down to 20 Hz.

Some peoples minds are like concrete. All mixed up and permanently set.

Very true!
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