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#1798354 - 11/30/11 01:43 PM
Need Help with Speakers
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Junior Member
Registered: 11/30/11
Posts: 1
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I have a Technics Digital Piano, Model SX-PR250. Now, the speakers are gone bad and I wanted to replace them. P/N SASG16PL03-F. Now, these speakers are discontinued and I ordered replacement ones from PartStore. After 2 months they still didn't come in!
My question is now, that I want to replace the speakers with some other 6.5" 8 Ohm speakers but I don't know the frequency range.
Not being a musician (my wife plays) but with engineering skills, I looked up the frequencies of the 88 keys, which are 27.5 Hz to 4,186.01 Hz.
The Technics has some tweeters also which should cover the higher frequency range.
But I am having trouble locating suitable speakers which can go down to 27.5 Hz. Most I have seen being offered are 55 to 100 Hz.
Is my logic incorrect, do I miss something? Can somebody point me in the right direction? Thanks...
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#1798392 - 11/30/11 02:30 PM
Re: Need Help with Speakers
[Re: uweus]
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1000 Post Club Member
Registered: 04/16/07
Posts: 1685
Loc: Pennsylvania
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Human ears can't hear below 40 hz, so those last few don't matter much.
When a speaker says it goes down to 55hz, what it usually means is that it will go down to that frequency at a volume proportional to what the audio signal requires. But it will still generally produce sounds lower than that, just at a lower volume.
It seems unlikely that the original part had superior frequency response to the things you are looking at to replace it. Digital pianos seldom have premium speakers built in.
BTW if my onboard speakers went out, I'd probably use the line-out (I assume it has one) and connect it to some external speakers and subwoofer. That would get you the whole audio spectrum and be simpler than trying to replace the part internally.
Edited by gvfarns (11/30/11 02:31 PM)
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#1798401 - 11/30/11 02:46 PM
Re: Need Help with Speakers
[Re: uweus]
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Full Member
Registered: 09/14/11
Posts: 129
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Ears can hear down to about 20hz (individuals may vary).
For many, 20-30hz is mostly felt. You can easily hear (ime) 30-50hz pure sine waves.
Piano's have tons of harmonics. Even if you play the low A, and can't reproduce 27.5hz, you will still hear higher frequency harmonics plus all the simulated sympathetic tones.
Replacing speakers is way more involved then simply finding the right size. There are a handful of important parameters that also need to be match (ie, Re, Fs, QES, QMS etc etc). Oh, and the frequency response for any given speaker on the low end is HIGHLY dependent on the enclosure volume and if sealed/ported/leaky.
For raw drivers, if PartsExpress and do a lesser extent Madisound, have a huge selection.
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#1798408 - 11/30/11 03:00 PM
Re: Need Help with Speakers
[Re: uweus]
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1000 Post Club Member
Registered: 04/16/07
Posts: 1685
Loc: Pennsylvania
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Oops. You are totally right about 20 hz. Not sure why I was thinking 40. Thanks for the correction.
Edited by gvfarns (11/30/11 03:36 PM)
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#1798656 - 11/30/11 11:41 PM
Re: Need Help with Speakers
[Re: gvfarns]
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3000 Post Club Member
Registered: 12/28/08
Posts: 3768
Loc: Redondo Beach, California
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Oops. You are totally right about 20 hz. Not sure why I was thinking 40. Thanks for the correction.
Yes human hearing is often said to be 20Hz to 20Khz. But that is like saying humans can run a mile in four minutes. Yes, some can, most can't. For most people over 40 the high end is not more than 15K and the low end is well up from 20Hz. I think 30Hz is about the limit for most people. Testing with home equipment is very hard because you might have harmonics in the test signal. You'd need a measurement mic at the listening position to verify. All this is moot for pianos because they only have a range from 27Hz to just over 4KHz and I think the piano needs 18 foot long stings to make the 27Hz pitch so most pianos depend on harmonics If your piano speakers cover about 40Hz to 16KHz you will do fine and not "loose" anything. Totally different story for HiFi. In this case the sound is mixed and the range is never wide enough. I have a good argument for why you'd like to go into the ultra sonic range out to 30K for HiFi (even if you can only hear to 12K) Beat frequencies. Likely those ultrasonics had intermodulation products down in the audible range, we don't know - good research area
Edited by ChrisA (11/30/11 11:47 PM)
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#1798662 - 11/30/11 11:57 PM
Re: Need Help with Speakers
[Re: ChrisA]
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Full Member
Registered: 09/14/11
Posts: 129
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Oops. You are totally right about 20 hz. Not sure why I was thinking 40. Thanks for the correction.
Yes human hearing is often said to be 20Hz to 20Khz. But that is like saying humans can run a mile in four minutes. Yes, some can, most can't. For most people over 40 the high end is not more than 15K and the low end is well up from 20Hz. I think 30Hz is about the limit for most people. Testing with home equipment is very hard because you might have harmonics in the test signal. You'd need a measurement mic at the listening position to verify. All this is moot for pianos because they only have a range from 27Hz to just over 4KHz and I think the piano needs 18 foot long stings to make the 27Hz pitch so most pianos depend on harmonics If your piano speakers cover about 40Hz to 16KHz you will do fine and not "loose" anything. Totally different story for HiFi. In this case the sound is mixed and the range is never wide enough. I have a good argument for why you'd like to go into the ultra sonic range out to 30K for HiFi (even if you can only hear to 12K) Beat frequencies. Likely those ultrasonics had intermodulation products down in the audible range, we don't know - good research area Chris, you're a man after my own heart lol. heterodyne detection is basically the optical equivalent of what you just mentioned. Don't need to hear 20-30k to hear the effects of it  And you are close with 18ft. a 27hz wave is 42 ft and the halfwave is 21ft which is as short as you can go for the fundamental (assuming typical speed of sound in air).
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#1798810 - 12/01/11 08:58 AM
Re: Need Help with Speakers
[Re: uweus]
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Full Member
Registered: 08/23/11
Posts: 24
Loc: PA
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All good points. I would agree with gvfarns and would get some external speakers. No matter what direction you decide to go I am sure your wife will notice a difference in the sound.
The question is does she like the sound better or worse with the new external speakers? You can go to many music stores that have external speakers hooked up to keybords to sort of get an idea how it might sound.
If you simply buy a replacement speaker of the right size make sure you seal it around the edges so air does not get between the speaker and the mounting panel or you may lose some low frequency response.
Lots of engineering factors to consider including the room you have your keyboard set up in.
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