AN Std 8 + SI Super T-Amp = Weak Bass? - diyAudio
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Old 11th February 2008, 06:22 PM   #1
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Default AN Std 8 + SI Super T-Amp = Weak Bass?

Hi, first post!

I'm a DIY audio newbie. About a year ago, I read that TNT review of the Sonic Impact T-Amp, and had to have one. My goal was to use my computer as the source (lossless, CD-quality FLAC), and have the best sound possible at a reasonable price.

I received the Super version of the T-Amp as a gift. Also based on a review on the TNT audio site, I ended up buying the Audio Nirvana Standard 8" Full Range speakers. I built the "1.3" cabinet with plans from the CommonSense Audio website.

For reference, I've never really had any "hi-fi" or "audiophile" quality equipment. FWIW, I've got Paradigm Monitor 5's powered by a Pioneer Elite stereo amp as my "reference" system (also using computer FLAC as source).

Anyway, I've been running the Super T-Amp amp and Audio Nirvana speakers about 30 hours now. They sound great, except that the bass seems rather weak. The bass doesn't sound bad, just not nearly as prominent as the highs and mids. For example, as a guitar player, I think the guitar sounds really well-defined, very realistic. But the bass just isn't there. Example: I played Metallica's "One"---there's that intense double kick-drum breakdown in the middle of the song---the effect was kind of lost.

I've been doing some Internet research, and from what I've gleaned, neither the Sonic Impact nor the Audio Nirvana speakers are strong on bass. So as a combo, I probably should have expected this.

So I'm basically looking for suggestions as to what I could do to get some more bass out of this setup without spending a lot of money. I'd rather not use a sub, as I don't have the room---the "1.3" cabinets are really already too big! Likewise, I've seen lots of suggestions for the "BIB" (bigger is better) cabinets. Again, in my little apartment, that's just not practical.

So I'm wondering if there's a better (but not bigger!) cabinet I can build for the AN drivers? Or perhaps use a different amp? One idea is to pair the T-Amp with those Insignia NS-B2111 speakers from Best Buy, and get something like the Panasonic XR55S for my Audio Nirvana speakers. Just random ideas from the random information I've been reading!

Any thoughts or suggestions would be much appreciated!

Thanks,
Matt
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Old 11th February 2008, 07:11 PM   #2
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Hi Matt,

I'm afraid you have a problem mate, because we can't break the laws of physics. The amp is fine, no problems there. The Super T doesn't have the LF issues the el-cheapo version suffers from. Your major problem is / are the drivers. The AN units are low Q drivers, of limited excursion. That means that they have a very powerful motor, and don't move very far. They're basically over-damped in the bass, and they need a big box (and preferably a horn, whatever it claims on the commonsenseaudio site) to generate any bass heft -bigger than the 1.3. If you can let me know what the vent dimensions are, I can run a model in MathCAD on what exactly it's doing.

As is, you could stick a fairly large resistor on them, which will bring the LF up a bit, but the amp will probably run out of steam. Try a 3ohm resistor in the + lead to the driver. That will probably help a bit.

Another separate issue is baffle-step. You'll have a ~3db loss below about 450Hz; correcting for this with a simple compensation circuit will help make the speaker better balanced.

Best
Scott
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Old 11th February 2008, 08:07 PM   #3
Jeb-D. is offline Jeb-D.  United States
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Quote:
Another separate issue is baffle-step. You'll have a ~3db loss below about 450Hz; correcting for this with a simple compensation circuit will help make the speaker better balanced.
Agreed.


By looking at the spec sheet it appears that the driver runs hot in the mid and highs on top of the natural acoustic baffle step. You may end up needing 10dB to get it sounding balanced. But let your ears are the judge, do what sounds best. As-is, it appears the speaker puts out 100-110dB from 1.5k to 15kHz. Where as 100-500Hz is 90-92ish dB @1W. The compensation will bring the upper frequencies down to the level of the midbass. When all is said and done your speaker will probably be about 90-91dB efficient, but much more balanced. If your worried about the loss in efficiency start with 6dB of compensation rather than 10.

Here is a helpfull spreadsheet.
http://www.quarter-wave.com/General/BSC_Calculator.xls
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Old 13th February 2008, 02:44 AM   #4
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Quote:
Originally posted by Scottmoose
If you can let me know what the vent dimensions are, I can run a model in MathCAD on what exactly it's doing.
What exactly is the vent? (Sorry, I'm still learning the terminology!)

Thanks again!
Matt
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Old 13th February 2008, 10:33 AM   #5
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The port (i.e. the hole in the box). Basically, how wide is it and how long is it?
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Old 13th February 2008, 03:38 PM   #6
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Quote:
Originally posted by Scottmoose
The port (i.e. the hole in the box). Basically, how wide is it and how long is it?

It's three inches in diameter. There is no tube---so the "length" is about 3/4", i.e. the width of the wood I used.

Thank you!
Matt
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Old 13th February 2008, 03:47 PM   #7
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OK, well, that puts box tuning to ~65Hz -it's working more like a small MLTL. See attached. Moderately well balanced, apart from the peak at cut-off, which isn't ideal, but extension isn't great.
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Old 13th February 2008, 04:03 PM   #8
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To improve LF extension, you could increase the vent length to 3.5in (there are plenty of pipes / ports available you should be able to utilise). You'll loose a bit of LF gain, but gain about 17Hz of extension, with a box tuning of about 48Hz, which is pretty reasonable for this driver in a relatively small / short cabinet.

I suspect baffle-step loss is probably causing you some problems too, especially in conjunction with the driver's naturally rising response. I suggest you put a 3ohm resistor in parallel with a 1mH inductor in the + lead to the driver. That should help flatten things out nicely. In conjunction with the increased vent length, it should give an anechoic LF response similar to the attached. To adjust the level of correction, increase or decrease the value of the resistor. Unfortunately, no voice-coil inductance figure is published for the driver, so setting a zobel value is tricky. FWIW, I'd probably try a 3uf cap in series with a 9ohm resistor across the + & - terminals. That should help a bit too. Overall, you should find the sound better balanced, with improved extension.

Hope that helps
Scott
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File Type: gif an mod.gif (5.7 KB, 480 views)
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Old 16th February 2008, 06:02 PM   #9
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Scottmoose & Jeb-D: thank you very much for all your help and suggestions! I'm definitely going to continue to hack on these speakers/enclosures a bit.

In the meantime, I have one more question: I've heard about listener fatigue, but don't believe I've ever experienced it... until last night.

I finally got a chance to listen to this setup for more than 30 minutes or so. I was listening to FLAC audio files (i.e. lossless CD quality). I also upgraded my computer's soundcard to an M-Audio Audiophile 2496. I never had the Super T-Amp above 9:00 o'clock on the volume control.

After about two hours of listening, I thought my ears kind of hurt. It wasn't really pain, it was just that my ears felt really sensitive, and sounds made me feel uncomfortable. Turning the volume down relieved the discomfort. I kept turning the volume down, until it was below typical speaking volume. I honestly don't think I had the music up too loud at all prior to this. And the sensation was different than I've experienced from being around music that's too loud for long periods of time (e.g. such as at a concert).

From what I've heard, listening fatigue is more likely when there are too many high frequencies in the sound. I don't know if this is accurate or not, but it fits with the behavior of these speakers as we've discussed thus far (i.e. too much emphasis on the high notes).

Anyway, just looking for thoughts or ideas... does my description sound like listening fatigue? And if so, would the mods you've suggested help alleviate this (as it flattens the frequency curve on the high side)?

Thanks again!
Matt
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Old 16th February 2008, 07:05 PM   #10
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It depends on the design as a number of things can cause discomfort in the long term, but I suspect in your case it's primarily caused by the rising response of the driver, compounded with additional LF losses. A compensation circuit should help greatly & you can tailor things by adjusting the value of the resistor.
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